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diff --git a/14986.txt b/14986.txt new file mode 100644 index 0000000..04bf483 --- /dev/null +++ b/14986.txt @@ -0,0 +1,23916 @@ +The Project Gutenberg eBook, Experimental Researches in Electricity, +Volume 1, by Michael Faraday + + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + + + + +Title: Experimental Researches in Electricity, Volume 1 + +Author: Michael Faraday + +Release Date: February 9, 2005 [eBook #14986] +[Date last updated: November 5, 2005] + +Language: English + +Character set encoding: ASCII + + +***START OF THE PROJECT GUTENBERG EBOOK EXPERIMENTAL RESEARCHES IN +ELECTRICITY, VOLUME 1*** + + +E-text prepared by Paul Murray, Richard Prairie, and the Project Gutenberg +Online Distributed Proofreading Team from images generously made available +by the Bibliotheque nationale de France (BnF/Gallica) at +http://gallica.bnf.fr. + + + +EXPERIMENTAL RESEARCHES IN ELECTRICITY + +by + +MICHAEL FARADAY, D.C.L. F.R.S. + +Fullerian Profesor of Chemistry in the Royal Institution. +Corresponding Member, etc. of the Royal and Imperial Academies of +Science of Paris, Petersburgh, Florence, Copenhagen, Berlin, +Gottingen, Modena, Stockholm, Palermo, etc. etc. + +In Two Volumes + +VOL. I. + +Second Edition + +Reprinted from the PHILOSOPHICAL TRANSACTIONS of 1831-1838. + +London: +Richard and John Edward Taylor, +Printers and Publishers to the University of London, +Red Lion Court, Fleet Street + +1849 + + + + + + + +PREFACE + + +I have been induced by various circumstances to collect in One Volume the +Fourteen Series of Experimental Researches in Electricity, which have +appeared in the Philosophical Transactions during the last seven years: the +chief reason has been the desire to supply at a moderate price the whole of +these papers, with an Index, to those who may desire to have them. + +The readers of the volume will, I hope, do me the justice to remember that +it was not written as a _whole_, but in parts; the earlier portions rarely +having any known relation at the time to those which might follow. If I had +rewritten the work, I perhaps might have considerably varied the form, but +should not have altered much of the real matter: it would not, however, +then have been considered a faithful reprint or statement of the course and +results of the whole investigation, which only I desired to supply. + +I may be allowed to express my great satisfaction at finding, that the +different parts, written at intervals during seven years, harmonize so well +as they do. There would have been nothing particular in this, if the parts +had related only to matters well-ascertained before any of them were +written:--but as each professes to contain something of original discovery, +or of correction of received views, it does surprise even my partiality, +that they should have the degree of consistency and apparent general +accuracy which they seem to me to present. + +I have made some alterations in the text, but they have been altogether of +a typographical or grammatical character; and even where greatest, have +been intended to explain the sense, not to alter it. I have often added +Notes at the bottom of the page, as to paragraphs 59, 360, 439, 521, 552, +555, 598, 657, 883, for the correction of errors, and also the purpose of +illustration: but these are all distinguished from the Original Notes of +the Researches by the date of _Dec. 1838_. + +The date of a scientific paper containing any pretensions to discovery is +frequently a matter of serious importance, and it is a great misfortune +that there are many most valuable communications, essential to the history +and progress of science, with respect to which this point cannot now be +ascertained. This arises from the circumstance of the papers having no +dates attached to them individually, and of the journals in which they +appear having such as are inaccurate, i.e. dates of a period earlier than +that of publication. I may refer to the note at the end of the First +Series, as an illustration of the kind of confusion thus produced. These +circumstances have induced me to affix a date at the top of every other +page, and I have thought myself justified in using that placed by the +Secretary of the Royal Society on each paper as it was received. An author +has no right, perhaps, to claim an earlier one, unless it has received +confirmation by some public act or officer. + +Before concluding these lines I would beg leave to make a reference or two; +first, to my own Papers on Electro-magnetic Rotations in the Quarterly +Journal of Science, 1822. xii. 74. 186. 283. 416, and also to my Letter on +Magneto-electric Induction in the Annales de Chimie, li. p. 404. These +might, as to the matter, very properly have appeared in this volume, but +they would have interfered with it as a simple reprint of the "Experimental +Researches" of the Philosophical Transactions. + +Then I wish to refer, in relation to the Fourth Series on a new law of +Electric Conduction, to Franklin's experiments on the non-conduction of +ice, which have been very properly separated and set forth by Professor +Bache (Journal of the Franklin Institute, 1836. xvii. 183.). These, which I +did not at all remember as to the extent of the effect, though they in no +way anticipate the expression of the law I state as to the general effect +of liquefaction on electrolytes, still should never be forgotten when +speaking of that law as applicable to the case of water. + +There are two papers which I am anxious to refer to, as corrections or +criticisms of parts of the Experimental Researches. The first of these is +one by Jacobi (Philosophical Magazine, 1838. xiii. 401.), relative to the +possible production of a spark on completing the junction of the two metals +of a single pair of plates (915.). It is an excellent paper, and though I +have not repeated the experiments, the description of them convinces me +that I must have been in error. The second is by that excellent +philosopher, Marianini (Memoria della Societa Italiana di Modena, xxi. +205), and is a critical and experimental examination of Series viii, and of +the question whether metallic contact is or is not _productive_ of a part +of the electricity of the voltaic pile. I see no reason as yet to alter the +opinion I have given; but the paper is so very valuable, comes to the +question so directly, and the point itself is of such great importance, +that I intend at the first opportunity renewing the inquiry, and, if I can, +rendering the proofs either on the one side or the other undeniable to all. + +Other parts of these researches have received the honour of critical +attention from various philosophers, to all of whom I am obliged, and some +of whose corrections I have acknowledged in the foot notes. There are, no +doubt, occasions on which I have not felt the force of the remarks, but +time and the progress of science will best settle such cases; and, although +I cannot honestly say that I _wish_ to be found in error, yet I do +fervently hope that the progress of science in the hands of its many +zealous present cultivators will be such, as by giving us new and other +developments, and laws more and more general in their applications, will +even make me think that what is written and illustrated in these +experimental researches, belongs to the by-gone parts of science. + +MICHAEL FARADAY. + +Royal Institution, +March, 1839. + + + +CONTENTS. + + Par. +Series I. S. 1. Induction of electric currents 6 + S. 2. Evolution of electricity from magnetism 27 + S. 3. New electrical state or condition of matter 60 + S. 4. Explication of Arago's magnetic phenomena 81 +Series II. S. 5. Terrestrial magneto-electric induction 140 + S. 6. Force and direction of magneto-electric + induction generally 193 +Series III. S. 7. Identity of electricities from different + sources 265 + ---- ---- i Voltaic electricity 268 + ---- ---- ii Ordinary electricity 284 + ---- ---- iii Magneto-electricity 343 + ---- ---- iv Thermo-electricity 349 + ---- ---- v Animal electricity 351 + S. 8. Relation by measure of common and voltaic + electricity 361 + ---- Note respecting Ampere's inductive results + after 379 +Series IV. S. 9. New law of electric conduction 380 + S. 10. On conducting power generally 418 +Series V. S. 11. Electro-chemical decomposition 450 + ---- P 1. New conditions of electro-chemical + decomposition 453 + ---- P 2. Influence of water in such decomposition 472 + ---- P 3. Theory of electro-chemical decomposition 477 +Series VI. S. 12. Power of platina, &c. to induce combination 564 +Series VII. S. 11.* Electro-chemical decomposition continued + (nomenclature) 661 + ---- P 4. Some general conditions of + Electro-chemical decomposition 669 + ---- P 5. Volta-electrometer 704 + ---- P 6. Primary and secondary results 742 + ---- P 7. Definite nature and extent of + electro-chemical forces 783 + ---- ---- Electro-chemical equivalents 822 + S. 13. Absolute quantity of Electricity in the + molecules of matter 852 +Series VIII. S. 14. Electricity of the voltaic pile 875 + ---- P 1. Simple voltaic circles 875 + ---- P 2. Electrolytic intensity 966 + ---- P 3. Associated voltaic circles; or battery 989 + ---- P 4. Resistance of an electrolyte to + decomposition 1007 + ---- P 5. General remarks on the active battery 1034 +Series IX. S. 15. Induction of a current on itself 1048 + ---- Inductive action of currents generally 1101 +Series X. S. 16. Improved voltaic battery 1119 + S. 17. Practical results with the voltaic battery 1136 +Series XI. S. 18. On static induction 1161 + ---- P 1. Induction an action of contiguous + particles 1161 + ---- P 2. Absolute charge of matter 1169 + ---- P 3. Electrometer and inductive apparatus 1179 + ---- P 4. Induction in curved lines 1215 + ---- ---- Conduction by glass, lac, sulphur, &c. 1283 + ---- P 5. Specific inductive capacity 1252 + ---- P 6. General results as to the nature of + induction 1295 + ---- ---- Differential inductometer 1307 +Series XII. ---- P 7. Conduction or conductive discharge 1320 + ---- P 8. Electrolytic discharge 1343 + ---- P 9. Disruptive discharge 1359 + ---- ---- ---- Insulation 1362 + ---- ---- ---- as spark 1406 + ---- ---- ---- as brush 1425 + ---- ---- ---- positive and negative 1465 +Series XIII. ---- ---- ---- as glow 1526 + ---- ---- ---- dark 1544 + ---- P 10. Convection; or carrying discharge 1562 + ---- P 11. Relation of a vacuum to electrical + phenomena 1613 + S. 19. Nature of the electric current 1617 + ---- ---- its transverse forces 1653 +Series XIV. S. 20. Nature of the electric force or forces 1667 + S. 21. Relation of the electric and magnetic + forces 1709 + S. 22. Note on electrical excitation 1737 +Index +Notes + + + + +EXPERIMENTAL RESEARCHES +IN +ELECTRICITY. + + + + +FIRST SERIES. + +S 1. _On the Induction of Electric Currents._ S 2. _On the Evolution of +Electricity from Magnetism._ S 3. _On a new Electrical Condition of +Matter._ S 4. _On_ Arago's _Magnetic Phenomena._ + +[Read November 24, 1831.] + + +1. The power which electricity of tension possesses of causing an opposite +electrical state in its vicinity has been expressed by the general term +Induction; which, as it has been received into scientific language, may +also, with propriety, be used in the same general sense to express the +power which electrical currents may possess of inducing any particular +state upon matter in their immediate neighbourhood, otherwise indifferent. +It is with this meaning that I purpose using it in the present paper. + +2. Certain effects of the induction of electrical currents have already +been recognised and described: as those of magnetization; Ampere's +experiments of bringing a copper disc near to a flat spiral; his repetition +with electro-magnets of Arago's extraordinary experiments, and perhaps a +few others. Still it appeared unlikely that these could be all the effects +which induction by currents could produce; especially as, upon dispensing +with iron, almost the whole of them disappear, whilst yet an infinity of +bodies, exhibiting definite phenomena of induction with electricity of +tension, still remain to be acted upon by the induction of electricity in +motion. + +3. Further: Whether Ampere's beautiful theory were adopted, or any other, +or whatever reservation were mentally made, still it appeared very +extraordinary, that as every electric current was accompanied by a +corresponding intensity of magnetic action at right angles to the current, +good conductors of electricity, when placed within the sphere of this +action, should not have any current induced through them, or some sensible +effect produced equivalent in force to such a current. + +4. These considerations, with their consequence, the hope of obtaining +electricity from ordinary magnetism, have stimulated me at various times to +investigate experimentally the inductive effect of electric currents. I +lately arrived at positive results; and not only had my hopes fulfilled, +but obtained a key which appeared to me to open out a full explanation of +Arago's magnetic phenomena, and also to discover a new state, which may +probably have great influence in some of the most important effects of +electric currents. + +5. These results I purpose describing, not as they were obtained, but in +such a manner as to give the most concise view of the whole. + + +S 1. _Induction of Electric Currents._ + + +6. About twenty-six feet of copper wire one twentieth of an inch in +diameter were wound round a cylinder of wood as a helix, the different +spires of which were prevented from touching by a thin interposed twine. +This helix was covered with calico, and then a second wire applied in the +same manner. In this way twelve helices were superposed, each containing an +average length of wire of twenty-seven feet, and all in the same direction. +The first, third, fifth, seventh, ninth, and eleventh of these helices were +connected at their extremities end to end, so as to form one helix; the +others were connected in a similar manner; and thus two principal helices +were produced, closely interposed, having the same direction, not touching +anywhere, and each containing one hundred and fifty-five feet in length of +wire. + +7. One of these helices was connected with a galvanometer, the other with a +voltaic battery of ten pairs of plates four inches square, with double +coppers and well charged; yet not the slightest sensible reflection of the +galvanometer-needle could be observed. + +8. A similar compound helix, consisting of six lengths of copper and six of +soft iron wire, was constructed. The resulting iron helix contained two +hundred and fourteen feet of wire, the resulting copper helix two hundred +and eight feet; but whether the current from the trough was passed through +the copper or the iron helix, no effect upon the other could be perceived +at the galvanometer. + +9. In these and many similar experiments no difference in action of any +kind appeared between iron and other metals. + +10. Two hundred and three feet of copper wire in one length were coiled +round a large block of wood; other two hundred and three feet of similar +wire were interposed as a spiral between the turns of the first coil, and +metallic contact everywhere prevented by twine. One of these helices was +connected with a galvanometer, and the other with a battery of one hundred +pairs of plates four inches square, with double coppers, and well charged. +When the contact was made, there was a sudden and very slight effect at the +galvanometer, and there was also a similar slight effect when the contact +with the battery was broken. But whilst the voltaic current was continuing +to pass through the one helix, no galvanometrical appearances nor any +effect like induction upon the other helix could be perceived, although the +active power of the battery was proved to be great, by its heating the +whole of its own helix, and by the brilliancy of the discharge when made +through charcoal. + +11. Repetition of the experiments with a battery of one hundred and twenty +pairs of plates produced no other effects; but it was ascertained, both at +this and the former time, that the slight deflection of the needle +occurring at the moment of completing the connexion, was always in one +direction, and that the equally slight deflection produced when the contact +was broken, was in the other direction; and also, that these effects +occurred when the first helices were used (6. 8.). + +12. The results which I had by this time obtained with magnets led me to +believe that the battery current through one wire, did, in reality, induce +a similar current through the other wire, but that it continued for an +instant only, and partook more of the nature of the electrical wave passed +through from the shock of a common Leyden jar than of the current from a +voltaic battery, and therefore might magnetise a steel needle, although it +scarcely affected the galvanometer. + +13. This expectation was confirmed; for on substituting a small hollow +helix, formed round a glass tube, for the galvanometer, introducing a steel +needle, making contact as before between the battery and the inducing wire +(7. 10.), and then removing the needle before the battery contact was +broken, it was found magnetised. + +14. When the battery contact was first made, then an unmagnetised needle +introduced into the small indicating helix (13.), and lastly the battery +contact broken, the needle was found magnetised to an equal degree +apparently as before; but the poles were of the contrary kind. + +15. The same effects took place on using the large compound helices first +described (6. 8.). + +16. When the unmagnetised needle was put into the indicating helix, before +contact of the inducing wire with the battery, and remained there until the +contact was broken, it exhibited little or no magnetism; the first effect +having been nearly neutralised by the second (13. 14.). The force of the +induced current upon making contact was found always to exceed that of the +induced current at breaking of contact; and if therefore the contact was +made and broken many times in succession, whilst the needle remained in the +indicating helix, it at last came out not unmagnetised, but a needle +magnetised as if the induced current upon making contact had acted alone on +it. This effect may be due to the accumulation (as it is called) at the +poles of the unconnected pile, rendering the current upon first making +contact more powerful than what it is afterwards, at the moment of breaking +contact. + +17. If the circuit between the helix or wire under induction and the +galvanometer or indicating spiral was not rendered complete _before_ the +connexion between the battery and the inducing wire was completed or +broken, then no effects were perceived at the galvanometer. Thus, if the +battery communications were first made, and then the wire under induction +connected with the indicating helix, no magnetising power was there +exhibited. But still retaining the latter communications, when those with +the battery were broken, a magnet was formed in the helix, but of the +second kind (14.), i.e. with poles indicating a current in the same +direction to that belonging to the battery current, or to that always +induced by that current at its cessation. + +18. In the preceding experiments the wires were placed near to each other, +and the contact of the inducing one with the buttery made when the +inductive effect was required; but as the particular action might be +supposed to be exerted only at the moments of making and breaking contact, +the induction was produced in another way. Several feet of copper wire were +stretched in wide zigzag forms, representing the letter W, on one surface +of a broad board; a second wire was stretched in precisely similar forms on +a second board, so that when brought near the first, the wires should +everywhere touch, except that a sheet of thick paper was interposed. One of +these wires was connected with the galvanometer, and the other with a +voltaic battery. The first wire was then moved towards the second, and as +it approached, the needle was deflected. Being then removed, the needle was +deflected in the opposite direction. By first making the wires approach and +then recede, simultaneously with the vibrations of the needle, the latter +soon became very extensive; but when the wires ceased to move from or +towards each other, the galvanometer-needle soon came to its usual +position. + +19. As the wires approximated, the induced current was in the _contrary_ +direction to the inducing current. As the wires receded, the induced +current was in the _same_ direction as the inducing current. When the wires +remained stationary, there was no induced current (54.). + +20. When a small voltaic arrangement was introduced into the circuit +between the galvanometer (10.) and its helix or wire, so as to cause a +permanent deflection of 30 deg. or 40 deg., and then the battery of one hundred +pairs of plates connected with the inducing wire, there was an +instantaneous action as before (11.); but the galvanometer-needle +immediately resumed and retained its place unaltered, notwithstanding the +continued contact of the inducing wire with the trough: such was the case +in whichever way the contacts were made (33.). + +21. Hence it would appear that collateral currents, either in the same or +in opposite directions, exert no permanent inducing power on each other, +affecting their quantity or tension. + +22. I could obtain no evidence by the tongue, by spark, or by heating fine +wire or charcoal, of the electricity passing through the wire under +induction; neither could I obtain any chemical effects, though the contacts +with metallic and other solutions were made and broken alternately with +those of the battery, so that the second effect of induction should not +oppose or neutralise the first (13. 16.). + +23. This deficiency of effect is not because the induced current of +electricity cannot pass fluids, but probably because of its brief duration +and feeble intensity; for on introducing two large copper plates into the +circuit on the induced side (20.), the plates being immersed in brine, but +prevented from touching each other by an interposed cloth, the effect at +the indicating galvanometer, or helix, occurred as before. The induced +electricity could also pass through a voltaic trough (20.). When, however, +the quantity of interposed fluid was reduced to a drop, the galvanometer +gave no indication. + +24. Attempts to obtain similar effects by the use of wires conveying +ordinary electricity were doubtful in the results. A compound helix similar +to that already described, containing eight elementary helices (6.), was +used. Four of the helices had their similar ends bound together by wire, +and the two general terminations thus produced connected with the small +magnetising helix containing an unmagnetised needle (13.). The other four +helices were similarly arranged, but their ends connected with a Leyden +jar. On passing the discharge, the needle was found to be a magnet; but it +appeared probable that a part of the electricity of the jar had passed off +to the small helix, and so magnetised the needle. There was indeed no +reason to expect that the electricity of a jar possessing as it does great +tension, would not diffuse itself through all the metallic matter +interposed between the coatings. + +25. Still it does not follow that the discharge of ordinary electricity +through a wire does not produce analogous phenomena to those arising from +voltaic electricity; but as it appears impossible to separate the effects +produced at the moment when the discharge begins to pass, from the equal +and contrary effects produced when it ceases to pass (16.), inasmuch as +with ordinary electricity these periods are simultaneous, so there can be +scarcely any hope that in this form of the experiment they can be +perceived. + +26. Hence it is evident that currents of voltaic electricity present +phenomena of induction somewhat analogous to those produced by electricity +of tension, although, as will be seen hereafter, many differences exist +between them. The result is the production of other currents, (but which +are only momentary,) parallel, or tending to parallelism, with the inducing +current. By reference to the poles of the needle formed in the indicating +helix (13. 14.) and to the deflections of the galvanometer-needle (11.), it +was found in all cases that the induced current, produced by the first +action of the inducing current, was in the contrary direction to the +latter, but that the current produced by the cessation of the inducing +current was in the same direction (19.). For the purpose of avoiding +periphrasis, I propose to call this action of the current from the voltaic +battery, _volta-electric induction_. The properties of the second wire, +after induction has developed the first current, and whilst the electricity +from the battery continues to flow through its inducing neighbour (10. +18.), constitute a peculiar electric condition, the consideration of which +will be resumed hereafter (60.). All these results have been obtained with +a voltaic apparatus consisting of a single pair of plates. + + +S 2. _Evolution of Electricity from Magnetism._ + + +27. A welded ring was made of soft round bar-iron, the metal being +seven-eighths of an inch in thickness, and the ring six inches in external +diameter. Three helices were put round one part of this ring, each +containing about twenty-four feet of copper wire one twentieth of an inch +thick; they were insulated from the iron and each other, and superposed in +the manner before described (6.), occupying about nine inches in length +upon the ring. They could be used separately or conjointly; the group may +be distinguished by the letter A (Pl. I. fig. 1.). On the other part of the +ring about sixty feet of similar copper wire in two pieces were applied in +the same manner, forming a helix B, which had the same common direction +with the helices of A, but being separated from it at each extremity by +about half an inch of the uncovered iron. + +28. The helix B was connected by copper wires with a galvanometer three +feet from the ring. The helices of A were connected end to end so as to +form one common helix, the extremities of which were connected with a +battery of ten pairs of plates four inches square. The galvanometer was +immediately affected, and to a degree far beyond what has been described +when with a battery of tenfold power helices _without iron_ were used +(10.); but though the contact was continued, the effect was not permanent, +for the needle soon came to rest in its natural position, as if quite +indifferent to the attached electro-magnetic arrangement. Upon breaking the +contact with the batterry, the needle was again powerfully deflected, but +in the contrary direction to that induced in the first instance. + +29. Upon arranging the apparatus so that B should be out of use, the +galvanometer be connected with one of the three wires of A (27.), and the +other two made into a helix through which the current from the trough (28.) +was passed, similar but rather more powerful effects were produced. + +30. When the battery contact was made in one direction, the +galvanometer-needle was deflected on the one side; if made in the other +direction, the deflection was on the other side. The deflection on breaking +the battery contact was always the reverse of that produced by completing +it. The deflection on making a battery contact always indicated an induced +current in the opposite direction to that from the battery; but on breaking +the contact the deflection indicated an induced current in the same +direction as that of the battery. No making or breaking of the contact at B +side, or in any part of the galvanometer circuit, produced any effect at +the galvanometer. No continuance of the battery current caused any +deflection of the galvanometer-needle. As the above results are common to +all these experiments, and to similar ones with ordinary magnets to be +hereafter detailed, they need not be again particularly described. + +31. Upon using the power of one hundred pairs of plates (10.) with this +ring, the impulse at the galvanometer, when contact was completed or +broken, was so great as to make the needle spin round rapidly four or five +times, before the air and terrestrial magnetism could reduce its motion to +mere oscillation. + +32. By using charcoal at the ends of the B helix, a minute _spark_ could be +perceived when the contact of the battery with A was completed. This spark +could not be due to any diversion of a part of the current of the battery +through the iron to the helix B; for when the battery contact was +continued, the galvanometer still resumed its perfectly indifferent state +(28.). The spark was rarely seen on breaking contact. A small platina wire +could not be ignited by this induced current; but there seems every reason +to believe that the effect would be obtained by using a stronger original +current or a more powerful arrangement of helices. + +33. A feeble voltaic current was sent through the helix B and the +galvanometer, so as to deflect the needle of the latter 30 deg. or 40 deg., and +then the battery of one hundred pairs of plates connected with A; but after +the first effect was over, the galvanometer-needle resumed exactly the +position due to the feeble current transmitted by its own wire. This took +place in whichever way the battery contacts were made, and shows that here +again (20.) no permanent influence of the currents upon each other, as to +their quantity and tension, exists. + +34. Another arrangement was then employed connecting the former experiments +on volta-electric induction (6-26.) with the present. A combination of +helices like that already described (6.) was constructed upon a hollow +cylinder of pasteboard: there were eight lengths of copper wire, containing +altogether 220 feet; four of these helices were connected end to end, and +then with the galvanometer (7.); the other intervening four were also +connected end to end, and the battery of one hundred pairs discharged +through them. In this form the effect on the galvanometer was hardly +sensible (11.), though magnets could be made by the induced current (13.). +But when a soft iron cylinder seven eighths of an inch thick, and twelve +inches long, was introduced into the pasteboard tube, surrounded by the +helices, then the induced current affected the galvanometer powerfully and +with all the phenomena just described (30.). It possessed also the power of +making magnets with more energy, apparently, than when no iron cylinder was +present. + +35. When the iron cylinder was replaced by an equal cylinder of copper, no +effect beyond that of the helices alone was produced. The iron cylinder +arrangement was not so powerful as the ring arrangement already described +(27.). + +36. Similar effects were then produced by _ordinary magnets_: thus the +hollow helix just described (34.) had all its elementary helices connected +with the galvanometer by two copper wires, each five feet in length; the +soft iron cylinder was introduced into its axis; a couple of bar magnets, +each twenty-four inches long, were arranged with their opposite poles at +one end in contact, so as to resemble a horse-shoe magnet, and then contact +made between the other poles and the ends of the iron cylinder, so as to +convert it for the time into a magnet (fig. 2.): by breaking the magnetic +contacts, or reversing them, the magnetism of the iron cylinder could be +destroyed or reversed at pleasure. + +37. Upon making magnetic contact, the needle was deflected; continuing the +contact, the needle became indifferent, and resumed its first position; on +breaking the contact, it was again deflected, but in the opposite direction +to the first effect, and then it again became indifferent. When the +magnetic contacts were reversed the deflections were reversed. + +38. When the magnetic contact was made, the deflection was such as to +indicate an induced current of electricity in the opposite direction to +that fitted to form a magnet, having the same polarity as that really +produced by contact with the bar magnets. Thus when the marked and unmarked +poles were placed as in fig. 3, the current in the helix was in the +direction represented, P being supposed to be the end of the wire going to +the positive pole of the battery, or that end towards which the zinc plates +face, and N the negative wire. Such a current would have converted the +cylinder into a magnet of the opposite kind to that formed by contact with +the poles A and B; and such a current moves in the opposite direction to +the currents which in M. Ampere's beautiful theory are considered as +constituting a magnet in the position figured[A]. + + [A] The relative position of an electric current and a magnet is by + most persons found very difficult to remember, and three or four helps + to the memory have been devised by M. Ampere and others. I venture to + suggest the following as a very simple and effectual assistance in + these and similar latitudes. Let the experimenter think he is looking + down upon a dipping needle, or upon the pole of the north, and then + let him think upon the direction of the motion of the hands of a + watch, or of a screw moving direct; currents in that direction round a + needle would make it into such a magnet as the dipping needle, or + would themselves constitute an electro-magnet of similar qualities; or + if brought near a magnet would tend to make it take that direction; or + would themselves be moved into that position by a magnet so placed; or + in M. Ampere's theory are considered as moving in that direction in + the magnet. These two points of the position of the dipping-needle and + the motion of the watch hands being remembered, any other relation of + the current and magnet can be at once deduced from it. + +39. But as it might be supposed that in all the preceding experiments of +this section, it was by some peculiar effect taking place during the +formation of the magnet, and not by its mere virtual approximation, that +the momentary induced current was excited, the following experiment was +made. All the similar ends of the compound hollow helix (34.) were bound +together by copper wire, forming two general terminations, and these were +connected with the galvanometer. The soft iron cylinder (34.) was removed, +and a cylindrical magnet, three quarters of an inch in diameter and eight +inches and a half in length, used instead. One end of this magnet was +introduced into the axis of the helix (fig. 4.), and then, the +galvanometer-needle being stationary, the magnet was suddenly thrust in; +immediately the needle was deflected in the same direction as if the magnet +had been formed by either of the two preceding processes (34. 36.). Being +left in, the needle resumed its first position, and then the magnet being +withdrawn the needle was deflected in the opposite direction. These effects +were not great; but by introducing and withdrawing the magnet, so that the +impulse each time should be added to those previously communicated to the +needle, the latter could be made to vibrate through an arc of 180 deg. or more. + +40. In this experiment the magnet must not be passed entirely through the +helix, for then a second action occurs. When the magnet is introduced, the +needle at the galvanometer is deflected in a certain direction; but being +in, whether it be pushed quite through or withdrawn, the needle is +deflected in a direction the reverse of that previously produced. When the +magnet is passed in and through at one continuous motion, the needle moves +one way, is then suddenly stopped, and finally moves the other way. + +41. If such a hollow helix as that described (34.) be laid east and west +(or in any other constant position), and a magnet be retained east and +west, its marked pole always being one way; then whichever end of the helix +the magnet goes in at, and consequently whichever pole of the magnet enters +first, still the needle is deflected the same way: on the other hand, +whichever direction is followed in withdrawing the magnet, the deflection +is constant, but contrary to that due to its entrance. + +42. These effects are simple consequences of the _law_ hereafter to be +described (114). + +43. When the eight elementary helices were made one long helix, the effect +was not so great as in the arrangement described. When only one of the +eight helices was used, the effect was also much diminished. All care was +taken to guard against tiny direct action of the inducing magnet upon the +galvanometer, and it was found that by moving the magnet in the same +direction, and to the same degree on the outside of the helix, no effect on +the needle was produced. + +44. The Royal Society are in possession of a large compound magnet formerly +belonging to Dr. Gowin Knight, which, by permission of the President and +Council, I was allowed to use in the prosecution of these experiments: it +is at present in the charge of Mr. Christie, at his house at Woolwich, +where, by Mr. Christie's kindness, I was at liberty to work; and I have to +acknowledge my obligations to him for his assistance in all the experiments +and observations made with it. This magnet is composed of about 450 bar +magnets, each fifteen inches long, one inch wide, and half an inch thick, +arranged in a box so as to present at one of its extremities two external +poles (fig. 5.). These poles projected horizontally six inches from the +box, were each twelve inches high and three inches wide. They were nine +inches apart; and when a soft iron cylinder, three quarters of an inch in +diameter and twelve inches long, was put across from one to the other, it +required a force of nearly one hundred pounds to break the contact. The +pole to the left in the figure is the marked pole[A]. + + [A] To avoid any confusion as to the poles of the magnet, I shall + designate the pole pointing to the north as the marked pole; I may + occasionally speak of the north and south ends of the needle, but do + not mean thereby north and south poles. That is by many considered the + true north pole of a needle which points to the south; but in this + country it in often called the south pole. + +45. The indicating galvanometer, in all experiments made with this magnet, +was about eight feet from it, not directly in front of the poles, but about +16 deg. or 17 deg. on one side. It was found that on making or breaking the +connexion of the poles by soft iron, the instrument was slightly affected; +but all error of observation arising from this cause was easily and +carefully avoided. + +46. The electrical effects exhibited by this magnet were very striking. +When a soft iron cylinder thirteen inches long was put through the compound +hollow helix, with its ends arranged as two general terminations (39.), +these connected with the galvanometer, and the iron cylinder brought in +contact with the two poles of the magnet (fig. 5.), so powerful a rush of +electricity took place that the needle whirled round many times in +succession[A]. + + [A] A soft iron bar in the form of a lifter to a horse-shoe magnet, + when supplied with a coil of this kind round the middle of it, + becomes, by juxta-position with a magnet, a ready source of a brief + but determinate current of electricity. + +47. Notwithstanding this great power, if the contact was continued, the +needle resumed its natural position, being entirely uninfluenced by the +position of the helix (30.). But on breaking the magnetic contact, the +needle was whirled round in the opposite direction with a force equal to +the former. + +48. A piece of copper plate wrapped _once_ round the iron cylinder like a +socket, but with interposed paper to prevent contact, had its edges +connected with the wires of the galvanometer. When the iron was brought in +contact with the poles the galvanometer was strongly affected. + +49. Dismissing the helices and sockets, the galvanometer wire was passed +over, and consequently only half round the iron cylinder (fig. 6.); but +even then a strong effect upon the needle was exhibited, when the magnetic +contact was made or broken. + +50. As the helix with its iron cylinder was brought towards the magnetic +poles, but _without making contact_, still powerful effects were produced. +When the helix, without the iron cylinder, and consequently containing no +metal but copper, was approached to, or placed between the poles (44.), the +needle was thrown 80 deg., 90 deg., or more, from its natural position. The +inductive force was of course greater, the nearer the helix, either with or +without its iron cylinder, was brought to the poles; but otherwise the same +effects were produced, whether the helix, &c. was or was not brought into +contact with the magnet; i.e. no permanent effect on the galvanometer was +produced; and the effects of approximation and removal were the reverse of +each other (30.). + +51. When a bolt of copper corresponding to the iron cylinder was +introduced, no greater effect was produced by the helix than without it. +But when a thick iron wire was substituted, the magneto-electric induction +was rendered sensibly greater. + +52. The direction of the electric current produced in all these experiments +with the helix, was the same as that already described (38.) as obtained +with the weaker bar magnets. + +53. A spiral containing fourteen feet of copper wire, being connected with +the galvanometer, and approximated directly towards the marked pole in the +line of its axis, affected the instrument strongly; the current induced in +it was in the reverse direction to the current theoretically considered by +M. Ampere as existing in the magnet (38.), or as the current in an +electro-magnet of similar polarity. As the spiral was withdrawn, the +induced current was reversed. + +54. A similar spiral had the current of eighty pairs of 4-inch plates sent +through it so as to form an electro-magnet, and then the other spiral +connected with the galvanometer (58.) approximated to it; the needle +vibrated, indicating a current in the galvanometer spiral the reverse of +that in the battery spiral (18. 26.). On withdrawing the latter spiral, the +needle passed in the opposite direction. + +55. Single wires, approximated in certain directions towards the magnetic +pole, had currents induced in them. On their removal, the currents were +inverted. In such experiments the wires should not be removed in directions +different to those in which they were approximated; for then occasionally +complicated and irregular effects are produced, the causes of which will be +very evident in the fourth part of this paper. + +56. All attempts to obtain chemical effects by the induced current of +electricity failed, though the precautions before described (22.), and all +others that could be thought of, were employed. Neither was any sensation +on the tongue, or any convulsive effect upon the limbs of a frog, produced. +Nor could charcoal or fine wire be ignited (133.). But upon repeating the +experiments more at leisure at the Royal Institution, with an armed +loadstone belonging to Professor Daniell and capable of lifting about +thirty pounds, a frog was very _powerfully convulsed_ each time magnetic +contact was made. At first the convulsions could not be obtained on +breaking magnetic contact; but conceiving the deficiency of effect was +because of the comparative slowness of separation, the latter act was +effected by a blow, and then the frog was convulsed strongly. The more +instantaneous the union or disunion is effected, the more powerful the +convulsion. I thought also I could perceive the _sensation_ upon the tongue +and the _flash_ before the eyes; but I could obtain no evidence of chemical +decomposition. + +57. The various experiments of this section prove, I think, most completely +the production of electricity from ordinary magnetism. That its intensity +should be very feeble and quantity small, cannot be considered wonderful, +when it is remembered that like thermo-electricity it is evolved entirely +within the substance of metals retaining all their conducting power. But an +agent which is conducted along metallic wires in the manner described; +which whilst so passing possesses the peculiar magnetic actions and force +of a current of electricity; which can agitate and convulse the limbs of a +frog; and which, finally, can produce a spark[A] by its discharge through +charcoal (32.), can only be electricity. As all the effects can be produced +by ferruginous electro-magnets (34.), there is no doubt that arrangements +like the magnets of Professors Moll, Henry, Ten Eyke, and others, in which +as many as two thousand pounds have been lifted, may be used for these +experiments; in which case not only a brighter spark may be obtained, but +wires also ignited, and, as the current can pass liquids (23.), chemical +action be produced. These effects are still more likely to be obtained when +the magneto-electric arrangements to be explained in the fourth section are +excited by the powers of such apparatus. + + [A] For a mode of obtaining the spark from the common magnet which I + have found effectual, see the Philosophical Magazine for June 1832, p. + 5. In the same Journal for November 1834, vol. v. p. 349, will be + found a method of obtaining the magneto-electric spark, still simpler + in its principle, the use of soft iron being dispensed with + altogether.--_Dec. 1838._ + +58. The similarity of action, almost amounting to identity, between common +magnets and either electro-magnets or volta-electric currents, is +strikingly in accordance with and confirmatory of M. Ampere's theory, and +furnishes powerful reasons for believing that the action is the same in +both cases; but, as a distinction in language is still necessary, I propose +to call the agency thus exerted by ordinary magnets, _magneto-electric_ or +_magnelectric_ induction (26). + +59. The only difference which powerfully strikes the attention as existing +between volta-electric and magneto-electric induction, is the suddenness of +the former, and the sensible time required by the latter; but even in this +early state of investigation there are circumstances which seem to +indicate, that upon further inquiry this difference will, as a +philosophical distinction, disappear (68).[A] + + [A] For important additional phenomena and developments of the + induction of electrical currents, see now the ninth series, + 1048-1118.--_Dec. 1838._ + + +S 3. _New Electrical State or Condition of Matter._[A] + + [A] This section having been read at the Royal Society and reported + upon, and having also, in consequence of a letter from myself to M. + Hachette, been noticed at the French Institute, I feel bound to let it + stand as part of the paper; but later investigations (intimated 73. + 76. 77.) of the laws governing those phenomena, induce me to think + that the latter can be fully explained without admitting the + electro-tonic state. My views on this point will appear in the second + series of these researches.--M.F. + + +60. Whilst the wire is subject to either volta-electric or magneto-electric +induction, it appears to be in a peculiar state; for it resists the +formation of an electrical current in it, whereas, if in its common +condition, such a current would be produced; and when left uninfluenced it +has the power of originating a current, a power which the wire does not +possess under common circumstances. This electrical condition of matter has +not hitherto been recognised, but it probably exerts a very important +influence in many if not most of the phenomena produced by currents of +electricity. For reasons which will immediately appear (71.), I have, after +advising with several learned friends, ventured to designate it as the +_electro-ionic_ state. + +61. This peculiar condition shows no known electrical effects whilst it +continues; nor have I yet been able to discover any peculiar powers +exerted, or properties possessed, by matter whilst retained in this state. + +62. It shows no reaction by attractive or repulsive powers. The various +experiments which have been made with powerful magnets upon such metals, as +copper, silver, and generally those substances not magnetic, prove this +point; for the substances experimented upon, if electrical conductors, must +have acquired this state; and yet no evidence of attractive or repulsive +powers has been observed. I have placed copper and silver discs, very +delicately suspended on torsion balances in vacuo near to the poles of very +powerful magnets, yet have not been able to observe the least attractive or +repulsive force. + +63. I have also arranged a fine slip of gold-leaf very near to a bar of +copper, the two being in metallic contact by mercury at their extremities. +These have been placed in vacuo, so that metal rods connected with the +extremities of the arrangement should pass through the sides of the vessel +into the air. I have then moved powerful magnetic poles, about this +arrangement, in various directions, the metallic circuit on the outside +being sometimes completed by wires, and sometimes broken. But I never could +obtain any sensible motion of the gold-leaf, either directed to the magnet +or towards the collateral bar of copper, which must have been, as far as +induction was concerned, in a similar state to itself. + +64. In some cases it has been supposed that, under such circumstances, +attractive and repulsive forces have been exhibited, i.e. that such bodies +have become slightly magnetic. But the phenomena now described, in +conjunction with the confidence we may reasonably repose in M. Ampere's +theory of magnetism, tend to throw doubt on such cases; for if magnetism +depend upon the attraction of electrical currents, and if the powerful +currents at first excited, both by volta-electric and magneto-electric +induction, instantly and naturally cease (12. 28. 47.), causing at the same +time an entire cessation of magnetic effects at the galvanometer needle, +then there can be little or no expectation that any substances not +partaking of the peculiar relation in which iron, nickel, and one or two +other bodies, stand, should exhibit magneto-attractive powers. It seems far +more probable, that the extremely feeble permanent effects observed have +been due to traces of iron, or perhaps some other unrecognised cause not +magnetic. + +65. This peculiar condition exerts no retarding or accelerating power upon +electrical currents passing through metal thus circumstanced (20. 33.). +Neither could any such power upon the inducing current itself be detected; +for when masses of metal, wires, helices, &c. were arranged in all possible +ways by the side of a wire or helix, carrying a current measured by the +galvanometer (20.), not the slightest permanent change in the indication of +the instrument could be perceived. Metal in the supposed peculiar state, +therefore, conducts electricity in all directions with its ordinary +facility, or, in other words, its conducting power is not sensibly altered +by it. + +66. All metals take on the peculiar state. This is proved in the preceding +experiments with copper and iron (9.), and with gold, silver, tin, lead, +zinc, antimony, bismuth, mercury, &c. by experiments to be described in the +fourth part (132.), admitting of easy application. With regard to iron, the +experiments prove the thorough and remarkable independence of these +phenomena of induction, and the ordinary magnetical appearances of that +metal. + +67. This state is altogether the effect of the induction exerted, and +ceases as soon as the inductive force is removed. It is the same state, +whether produced by the collateral passage of voltaic currents (26.), or +the formation of a magnet (34. 36.), or the mere approximation of a magnet +(39. 50.); and is a strong proof in addition to those advanced by M. +Ampere, of the identity of the agents concerned in these several +operations. It probably occurs, momentarily, during the passage of the +common electric spark (24.), and may perhaps be obtained hereafter in bad +conductors by weak electrical currents or other means (74. 76). + +68. The state appears to be instantly assumed (12.), requiring hardly a +sensible portion of time for that purpose. The _difference_ of time between +volta-electric and magneto-electric induction, rendered evident by the +galvanometer (59.), may probably be thus explained. When a voltaic current +is sent through one of two parallel wires, as those of the hollow helix +(34.), a current is produced in the other wire, as brief in its continuance +as the time required for a single action of this kind, and which, by +experiment, is found to be inappreciably small. The action will seem still +more instantaneous, because, as there is an accumulation of power in the +poles of the battery before contact, the first rush of electricity in the +wire of communication is greater than that sustained after the contact is +completed; the wire of induction becomes at the moment electro-tonic to an +equivalent degree, which the moment after sinks to the state in which the +continuous current can sustain it, but in sinking, causes an opposite +induced current to that at first produced. The consequence is, that the +first induced wave of electricity more resembles that from the discharge of +an electric jar, than it otherwise would do. + +69. But when the iron cylinder is put into the same helix (31.), previous +to the connexion being made with the battery, then the current from the +latter may be considered as active in inducing innumerable currents of a +similar kind to itself in the iron, rendering it a magnet. This is known by +experiment to occupy time; for a magnet so formed, even of soft iron, does +not rise to its fullest intensity in an instant, and it may be because the +currents within the iron are successive in their formation or arrangement. +But as the magnet can induce, as well as the battery current, the combined +action of the two continues to evolve induced electricity, until their +joint effect is at a maximum, and thus the existence of the deflecting +force is prolonged sufficiently to overcome the inertia of the galvanometer +needle. + +70. In all those cases where the helices or wires are advanced towards or +taken from the magnet (50. 55.), the direct or inverted current of induced +electricity continues for the time occupied in the advance or recession; +for the electro-tonic state is rising to a higher or falling to a lower +degree during that time, and the change is accompanied by its corresponding +evolution of electricity; but these form no objections to the opinion that +the electro-tonic state is instantly assumed. + +71. This peculiar state appears to be a state of tension, and may be +considered as _equivalent_ to a current of electricity, at least equal to +that produced either when the condition is induced or destroyed. The +current evolved, however, first or last, is not to be considered a measure +of the degree of tension to which the electro-tonic state has risen; for as +the metal retains its conducting powers unimpaired (65.), and as the +electricity evolved is but for a moment, (the peculiar state being +instantly assumed and lost (68.),) the electricity which may be led away by +long wire conductors, offering obstruction in their substance proportionate +to their small lateral and extensive linear dimensions, can be but a very +small portion of that really evolved within the mass at the moment it +assumes this condition. Insulated helices and portions of metal instantly +assumed the state; and no traces of electricity could be discovered in +them, however quickly the contact with the electrometer was made, after +they were put under induction, either by the current from the battery or +the magnet. A single drop of water or a small piece of moistened paper (23. +56.) was obstacle sufficient to stop the current through the conductors, +the electricity evolved returning to a state of equilibrium through the +metal itself, and consequently in an unobserved manner. + +72. The tension of this state may therefore be comparatively very great. +But whether great or small, it is hardly conceivable that it should exist +without exerting a reaction upon the original inducing current, and +producing equilibrium of some kind. It might be anticipated that this would +give rise to a retardation of the original current; but I have not been +able to ascertain that this is the case. Neither have I in any other way as +yet been able to distinguish effects attributable to such a reaction. + +73. All the results favour the notion that the electro-tonic state relates +to the particles, and not to the mass, of the wire or substance under +induction, being in that respect different to the induction exerted by +electricity of tension. If so, the state may be assumed in liquids when no +electrical current is sensible, and even in non-conductors; the current +itself, when it occurs, being as it were a contingency due to the existence +of conducting power, and the momentary propulsive force exerted by the +particles during their arrangement. Even when conducting power is equal, +the currents of electricity, which as yet are the only indicators of this +state, may be unequal, because of differences as to numbers, size, +electrical condition, &c. &c. in the particles themselves. It will only be +after the laws which govern this new state are ascertained, that we shall +be able to predict what is the true condition of, and what are the +electrical results obtainable from, any particular substance. + +74. The current of electricity which induces the electro-tonic state in a +neighbouring wire, probably induces that state also in its own wire; for +when by a current in one wire a collateral wire is made electro-tonic, the +latter state is not rendered any way incompatible or interfering with a +current of electricity passing through it (62.). If, therefore, the current +were sent through the second wire instead of the first, it does not seem +probable that its inducing action upon the second would be less, but on the +contrary more, because the distance between the agent and the matter acted +upon would be very greatly diminished. A copper bolt had its extremities +connected with a galvanometer, and then the poles of a battery of one +hundred pairs of plates connected with the bolt, so as to send the current +through it; the voltaic circuit was then suddenly broken, and the +galvanometer observed for any indications of a return current through the +copper bolt due to the discharge of its supposed electro-tonic state. No +effect of the kind was obtained, nor indeed, for two reasons, ought it to +be expected; for first, as the cessation of induction and the discharge of +the electro-tonic condition are simultaneous, and not successive, the +return current would only be equivalent to the neutralization of the last +portion of the inducing current, and would not therefore show any +alteration of direction; or assuming that time did intervene, and that the +latter current was really distinct from the former, its short, sudden +character (12. 26.) would prevent it from being thus recognised. + +75. No difficulty arises, I think, in considering the wire thus rendered +electro-tonic by its own current more than by any external current, +especially when the apparent non-interference of that state with currents +is considered (62. 71.). The simultaneous existence of the conducting and +electro-tonic states finds an analogy in the manner in which electrical +currents can be passed through magnets, where it is found that both the +currents passed, and those of the magnets, preserve all their properties +distinct from each other, and exert their mutual actions. + +76. The reason given with regard to metals extends also to fluids and all +other conductors, and leads to the conclusion that when electric currents +are passed through them they also assume the electro-tonic state. Should +that prove to be the case, its influence in voltaic decomposition, and the +transference of the elements to the poles, can hardly be doubted. In the +electro-tonic state the homogeneous particles of matter appear to have +assumed a regular but forced electrical arrangement in the direction of the +current, which if the matter be undecomposable, produces, when relieved, a +return current; but in decomposable matter this forced state may be +sufficient to make an elementary particle leave its companion, with which +it is in a constrained condition, and associate with the neighbouring +similar particle, in relation to which it is in a more natural condition, +the forced electrical arrangement being itself discharged or relieved, at +the same time, as effectually as if it had been freed from induction. But +as the original voltaic current is continued, the electro-tonic state may +be instantly renewed, producing the forced arrangement of the compound +particles, to be as instantly discharged by a transference of the +elementary particles of the opposite kind in opposite directions, but +parallel to the current. Even the differences between common and voltaic +electricity, when applied to effect chemical decomposition, which Dr. +Wollaston has pointed out[A], seem explicable by the circumstances +connected with the induction of electricity from these two sources (25.). +But as I have reserved this branch of the inquiry, that I might follow out +the investigations contained in the present paper, I refrain (though much +tempted) from offering further speculations. + + [A] Philosophical Transactions, 1801, p. 247. + +77. Marianini has discovered and described a peculiar affection of the +surfaces of metallic discs, when, being in contact with humid conductors, a +current of electricity is passed through them; they are then capable of +producing a reverse current of electricity, and Marianini has well applied +the effect in explanation of the phenomena of Ritter's piles[A]. M.A. de la +Rive has described a peculiar property acquired by metallic conductors, +when being immersed in a liquid as poles, they have completed, for some +time, the voltaic circuit, in consequence of which, when separated from the +battery and plunged into the same fluid, they by themselves produce an +electric current[B]. M.A. Van Beek has detailed cases in which the +electrical relation of one metal in contact with another has been preserved +after separation, and accompanied by its corresponding chemical effects[C]. +These states and results appear to differ from the electro-tonic state and +its phenomena; but the true relation of the former to the latter can only +be decided when our knowledge of all these phenomena has been enlarged. + + [A] Annales de Chimie, xxxviii. 5. + + [B] Ibid. xxviii. 190. + + [C] Ibid. xxxviii. 49. + +78. I had occasion in the commencement of this paper (2.) to refer to an +experiment by Ampere, as one of those dependent upon the electrical +induction of currents made prior to the present investigation, and have +arrived at conclusions which seem to imply doubts of the accuracy of the +experiment (62. &c.); it is therefore due to M. Ampere that I should attend +to it more distinctly. When a disc of copper (says M. Ampere) was suspended +by a silk thread and surrounded by a helix or spiral, and when the charge +of a powerful voltaic battery was sent through the spiral, a strong magnet +at the same time being presented to the copper disc, the latter turned at +the moment to take a position of equilibrium, exactly as the spiral itself +would have turned had it been free to move. I have not been able to obtain +this effect, nor indeed any motion; but the cause of my failure in the +_latter_ point may be due to the momentary existence of the current not +allowing time for the inertia of the plate to be overcome (11. 12.). M. +Ampere has perhaps succeeded in obtaining motion from the superior delicacy +and power of his electro-magnetical apparatus, or he may have obtained only +the motion due to cessation of action. But all my results tend to invert +the sense of the proposition stated by M. Ampere, "that a current of +electricity tends to put the electricity of conductors near which it passes +in motion in the same direction," for they indicate an opposite direction +for the produced current (26. 53.); and they show that the effect is +momentary, and that it is also produced by magnetic induction, and that +certain other extraordinary effects follow thereupon. + +79. The momentary existence of the phenomena of induction now described is +sufficient to furnish abundant reasons for the uncertainty or failure of +the experiments, hitherto made to obtain electricity from magnets, or to +effect chemical decomposition or arrangement by their means[A]. + + [A] The Lycee, No. 36, for January 1st, has a long and rather + premature article, in which it endeavours to show anticipations by + French philosophers of my researches. It however mistakes the + erroneous results of MM. Fresnel and Ampere for true ones, and then + imagines my true results are like those erroneous ones. I notice it + here, however, for the purpose of doing honour to Fresnel in a much + higher degree than would have been merited by a feeble anticipation of + the present investigations. That great philosopher, at the same time + with myself and fifty other persons, made experiments which the + present paper proves could give no expected result. He was deceived + for the moment, and published his imaginary success; but on more + carefully repeating his trials, he could find no proof of their + accuracy; and, in the high and pure philosophic desire to remove error + as well as discover truth, he recanted his first statement. The + example of Berzelius regarding the first Thorina is another instance + of this fine feeling; and as occasions are not rare, it would be to + the dignity of science if such examples were more frequently + followed.--February 10th, 1832. + +80. It also appears capable of explaining fully the remarkable phenomena +observed by M. Arago between metals and magnets when neither are moving +(120.), as well as most of the results obtained by Sir John Herschel, +Messrs. Babbage, Harris, and others, in repeating his experiments; +accounting at the same time perfectly for what at first appeared +inexplicable; namely, the non-action of the same metals and magnets when at +rest. These results, which also afford the readiest means of obtaining +electricity from magnetism, I shall now proceed to describe. + + +S 4. _Explication of Arago's Magnetic Phenomena._ + + +81. If a plate of copper be revolved close to a magnetic needle, or magnet, +suspended in such a way that the latter may rotate in a plane parallel to +that of the former, the magnet tends to follow the motion of the plate; or +if the magnet be revolved, the plate tends to follow its motion; and the +effect is so powerful, that magnets or plates of many pounds weight may be +thus carried round. If the magnet and plate be at rest relative to each +other, not the slightest effect, attractive or repulsive, or of any kind, +can be observed between them (62.). This is the phenomenon discovered by M. +Arago; and he states that the effect takes place not only with all metals, +but with solids, liquids, and even gases, i.e. with all substances (130.). + +82. Mr. Babbage and Sir John Herschel, on conjointly repeating the +experiments in this country[A], could obtain the effects only with the +metals, and with carbon in a peculiar state (from gas retorts), i.e. only +with excellent conductors of electricity. They refer the effect to +magnetism induced in the plate by the magnet; the pole of the latter +causing an opposite pole in the nearest part of the plate, and round this a +more diffuse polarity of its own kind (120.). The essential circumstance in +producing the rotation of the suspended magnet is, that the substance +revolving below it shall acquire and lose its magnetism in sensible time, +and not instantly (124.). This theory refers the effect to an attractive +force, and is not agreed to by the discoverer, M. Arago, nor by M. Ampere, +who quote against it the absence of all attraction when the magnet and +metal are at rest (62. 126.), although the induced magnetism should still +remain; and who, from experiments made with a long dipping needle, conceive +the action to be always repulsive (125.). + + [A] Philosophical Transactions, 1825, p. 467. + +83. Upon obtaining electricity from magnets by the means already described +(36 46.), I hoped to make the experiment of M. Arago a new source of +electricity; and did not despair, by reference to terrestrial +magneto-electric induction, of being able to construct a new electrical +machine. Thus stimulated, numerous experiments were made with the magnet of +the Royal Society at Mr. Christie's house, in all of which I had the +advantage of his assistance. As many of these were in the course of the +superseded by more perfect arrangements, I shall consider myself at liberty +investigation to rearrange them in a manner calculated to convey most +readily what appears to me to be a correct view of the nature of the +phenomena. + +84. The magnet has been already described (44.). To concentrate the poles, +and bring them nearer to each other, two iron or steel bars, each about six +or seven inches long, one inch wide, and half an inch thick, were put +across the poles as in fig. 7, and being supported by twine from slipping, +could be placed as near to or far from each other as was required. +Occasionally two bars of soft iron were employed, so bent that when +applied, one to each pole, the two smaller resulting poles were vertically +over each other, either being uppermost at pleasure. + +85. A disc of copper, twelve inches in diameter, and about one fifth of an +inch in thickness, fixed upon a brass axis, was mounted in frames so as to +allow of revolution either vertically or horizontally, its edge being at +the same time introduced more or less between the magnetic poles (fig. 7.). +The edge of the plate was well amalgamated for the purpose of obtaining a +good but moveable contact, and a part round the axis was also prepared in a +similar manner. + +86. Conductors or electric collectors of copper and lead were constructed +so as to come in contact with the edge of the copper disc (85.), or with +other forms of plates hereafter to be described (101.). These conductors +were about four inches long, one third of an inch wide, and one fifth of an +inch thick; one end of each was slightly grooved, to allow of more exact +adaptation to the somewhat convex edge of the plates, and then amalgamated. +Copper wires, one sixteenth of an inch in thickness, attached, in the +ordinary manner, by convolutions to the other ends of these conductors, +passed away to the galvanometer. + +87. The galvanometer was roughly made, yet sufficiently delicate in its +indications. The wire was of copper covered with silk, and made sixteen or +eighteen convolutions. Two sewing-needles were magnetized and fixed on to a +stem of dried grass parallel to each other, but in opposite directions, and +about half an inch apart; this system was suspended by a fibre of unspun +silk, so that the lower needle should be between the convolutions of the +multiplier, and the upper above them. The latter was by much the most +powerful magnet, and gave terrestrial direction to the whole; fig. 8. +represents the direction of the wire and of the needles when the instrument +was placed in the magnetic meridian: the ends of the wires are marked A and +B for convenient reference hereafter. The letters S and N designate the +south and north ends of the needle when affected merely by terrestrial +magnetism; the end N is therefore the marked pole (44.). The whole +instrument was protected by a glass jar, and stood, as to position and +distance relative to the large magnet, under the same circumstances as +before (45.). + +88. All these arrangements being made, the copper disc was adjusted as in +fig. 7, the small magnetic poles being about half an inch apart, and the +edge of the plate inserted about half their width between them. One of the +galvanometer wires was passed twice or thrice loosely round the brass axis +of the plate, and the other attached to a conductor (86.), which itself was +retained by the hand in contact with the amalgamated edge of the disc at +the part immediately between the magnetic poles. Under these circumstances +all was quiescent, and the galvanometer exhibited no effect. But the +instant the plate moved, the galvanometer was influenced, and by revolving +the plate quickly the needle could be deflected 90 deg. or more. + +89. It was difficult under the circumstances to make the contact between +the conductor and the edge of the revolving disc uniformly good and +extensive; it was also difficult in the first experiments to obtain a +regular velocity of rotation: both these causes tended to retain the needle +in a continual state of vibration; but no difficulty existed in +ascertaining to which side it was deflected, or generally, about what line +it vibrated. Afterwards, when the experiments were made more carefully, a +permanent deflection of the needle of nearly 45 deg. could be sustained. + +90. Here therefore was demonstrated the production of a permanent current +of electricity by ordinary magnets (57.). + +91. When the motion of the disc was reversed, every other circumstance +remaining the same, the galvanometer needle was deflected with equal power +as before; but the deflection was on the opposite side, and the current of +electricity evolved, therefore, the reverse of the former. + +92. When the conductor was placed on the edge of the disc a little to the +right or left, as in the dotted positions fig. 9, the current of +electricity was still evolved, and in the same direction as at first (88. +91.). This occurred to a considerable distance, i.e. 50 deg. or 60 deg. on each +side of the place of the magnetic poles. The current gathered by the +conductor and conveyed to the galvanometer was of the same kind on both +sides of the place of greatest intensity, but gradually diminished in force +from that place. It appeared to be equally powerful at equal distances from +the place of the magnetic poles, not being affected in that respect by the +direction of the rotation. When the rotation of the disc was reversed, the +direction of the current of electricity was reversed also; but the other +circumstances were not affected. + +93. On raising the plate, so that the magnetic poles were entirely hidden +from each other by its intervention, (a. fig. 10,) the same effects were +produced in the same order, and with equal intensity as before. On raising +it still higher, so as to bring the place of the poles to c, still the +effects were produced, and apparently with as much power as at first. + +94. When the conductor was held against the edge as if fixed to it, and +with it moved between the poles, even though but for a few degrees, the +galvanometer needle moved and indicated a current of electricity, the same +as that which would have been produced if the wheel had revolved in the +same direction, the conductor remaining stationary. + +95. When the galvanometer connexion with the axis was broken, and its wires +made fast to two conductors, both applied to the edge of the copper disc, +then currents of electricity were produced, presenting more complicated +appearances, but in perfect harmony with the above results. Thus, if +applied as in fig. 11, a current of electricity through the galvanometer +was produced; but if their place was a little shifted, as in fig. 12, a +current in the contrary direction resulted; the fact being, that in the +first instance the galvanometer indicated the difference between a strong +current through A and a weak one through B, and in the second, of a weak +current through A and a strong one through B (92.), and therefore produced +opposite deflections. + +96. So also when the two conductors were equidistant from the magnetic +poles, as in fig. 13, no current at the galvanometer was perceived, +whichever way the disc was rotated, beyond what was momentarily produced by +irregularity of contact; because equal currents in the same direction +tended to pass into both. But when the two conductors were connected with +one wire, and the axis with the other wire, (fig. 14,) then the +galvanometer showed a current according with the direction of rotation +(91.); both conductors now acting consentaneously, and as a single +conductor did before (88.). + +97. All these effects could be obtained when only one of the poles of the +magnet was brought near to the plate; they were of the same kind as to +direction, &c., but by no means so powerful. + +98. All care was taken to render these results independent of the earth's +magnetism, or of the mutual magnetism of the magnet and galvanometer +needles. The contacts were made in the magnetic equator of the plate, and +at other parts; the plate was placed horizontally, and the poles +vertically; and other precautions were taken. But the absence of any +interference of the kind referred to, was readily shown by the want of all +effect when the disc was removed from the poles, or the poles from the +disc; every other circumstance remaining the same. + +99. The _relation of the current_ of electricity produced, to the magnetic +pole, to the direction of rotation of the plate, &c. &c., may be expressed +by saying, that when the unmarked pole (44. 84.) is beneath the edge of the +plate, and the latter revolves horizontally, screw-fashion, the electricity +which can be collected at the edge of the plate nearest to the pole is +positive. As the pole of the earth may mentally be considered the unmarked +pole, this relation of the rotation, the pole, and the electricity evolved, +is not difficult to remember. Or if, in fig. 15, the circle represent the +copper disc revolving in the direction of the arrows, and _a_ the outline +of the unmarked pole placed beneath the plate, then the electricity +collected at _b_ and the neighbouring parts is positive, whilst that +collected at the centre _c_ and other parts is negative (88.). The currents +in the plate are therefore from the centre by the magnetic poles towards +the circumference. + +100. If the marked pole be placed above, all other things remaining the +same, the electricity at _b_, fig. 15, is still positive. If the marked +pole be placed below, or the unmarked pole above, the electricity is +reversed. If the direction of revolution in any case is reversed, the +electricity is also reversed. + +101. It is now evident that the rotating plate is merely another form of +the simpler experiment of passing a piece of metal between the magnetic +poles in a rectilinear direction, and that in such cases currents of +electricity are produced at right angles to the direction of the motion, +and crossing it at the place of the magnetic pole or poles. This was +sufficiently shown by the following simple experiment: A piece of copper +plate one fifth of an inch thick, one inch and a half wide, and twelve +inches long, being amalgamated at the edges, was placed between the +magnetic poles, whilst the two conductors from the galvanometer were held +in contact with its edges; it was then drawn through between the poles of +the conductors in the direction of the arrow, fig. 16; immediately the +galvanometer needle was deflected, its north or marked end passed eastward, +indicating that the wire A received negative and the wire B positive +electricity; and as the marked pole was above, the result is in perfect +accordance with the effect obtained by the rotatory plate (99.). + +102. On reversing the motion of the plate, the needle at the galvanometer +was deflected in the opposite direction, showing an opposite current. + +103. To render evident the character of the electrical current existing in +various parts of the moving copper plate, differing in their relation to +the inducing poles, one collector (86.) only was applied at the part to be +examined near to the pole, the other being connected with the end of the +plate as the most neutral place: the results are given at fig. 17-20, the +marked pole being above the plate. In fig. 17, B received positive +electricity; but the plate moving in the same direction, it received on the +opposite side, fig. 18, negative electricity: reversing the motion of the +latter, as in fig. 20, B received positive electricity; or reversing the +motion of the first arrangement, that of fig. 17 to fig. 19, B received +negative electricity. + +104. When the plates were previously removed sideways from between the +magnets, as in fig. 21, so as to be quite out of the polar axis, still the +same effects were produced, though not so strongly. + +105. When the magnetic poles were in contact, and the copper plate was +drawn between the conductors near to the place, there was but very little +effect produced. When the poles were opened by the width of a card, the +effect was somewhat more, but still very small. + +106. When an amalgamated copper wire, one eighth of an inch thick, was +drawn through between the conductors and poles (101.), it produced a very +considerable effect, though not so much as the plates. + +107. If the conductors were held permanently against any particular parts +of the copper plates, and carried between the magnetic poles with them, +effects the same as those described were produced, in accordance with the +results obtained with the revolving disc (94.). + +108. On the conductors being held against the ends of the plates, and the +latter then passed between the magnetic poles, in a direction transverse to +their length, the same effects were produced (fig. 22.). The parts of the +plates towards the end may be considered either as mere conductors, or as +portions of metal in which the electrical current is excited, according to +their distance and the strength of the magnet; but the results were in +perfect harmony with those before obtained. The effect was as strong as +when the conductors were held against the sides of the plate (101.). + +109. When a mere wire, connected with the galvanometer so as to form a +complete circuit, was passed through between the poles, the galvanometer +was affected; and upon moving the wire to and fro, so as to make the +alternate impulses produced correspond with the vibrations of the needle, +the latter could be increased to 20 deg. or 30 deg. on each side the magnetic +meridian. + +110. Upon connecting the ends of a plate of metal with the galvanometer +wires, and then carrying it between the poles from end to end (as in fig. +23.), in either direction, no effect whatever was produced upon the +galvanometer. But the moment the motion became transverse, the needle was +deflected. + +111. These effects were also obtained from _electro-magnetic poles_, +resulting from the use of copper helices or spirals, either alone or with +iron cores (34. 54.). The directions of the motions were precisely the +same; but the action was much greater when the iron cores were used, than +without. + +112. When a flat spiral was passed through edgewise between the poles, a +curious action at the galvanometer resulted; the needle first went strongly +one way, but then suddenly stopped, as if it struck against some solid +obstacle, and immediately returned. If the spiral were passed through from +above downwards, or from below upwards, still the motion of the needle was +in the same direction, then suddenly stopped, and then was reversed. But on +turning the spiral half-way round, i.e. edge for edge, then the directions +of the motions were reversed, but still were suddenly interrupted and +inverted as before. This double action depends upon the halves of the +spiral (divided by a line passing through its centre perpendicular to the +direction of its motion) acting in opposite directions; and the reason why +the needle went to the same side, whether the spiral passed by the poles in +the one or the other direction, was the circumstance, that upon changing +the motion, the direction of the wires in the approaching half of the +spiral was changed also. The effects, curious as they appear when +witnessed, are immediately referable to the action of single wires (40. +109.). + +113. Although the experiments with the revolving plate, wires, and plates +of metal, were first successfully made with the large magnet belonging to +the Royal Society, yet they were all ultimately repeated with a couple of +bar magnets two feet long, one inch and a half wide, and half an inch +thick; and, by rendering the galvanometer (87.) a little more delicate, +with the most striking results. Ferro-electro-magnets, as those of Moll, +Henry, &c. (57.), are very powerful. It is very essential, when making +experiments on different substances, that thermo-electric effects (produced +by contact of the fingers, &c.) be avoided, or at least appreciated and +accounted for; they are easily distinguished by their permanency, and their +independence of the magnets, or of the direction of the motion. + +114. The relation which holds between the magnetic pole, the moving wire or +metal, and the direction of the current evolved, i.e. _the law_ which +governs the evolution of electricity by magneto-electric induction, is very +simple, although rather difficult to express. If in fig. 24, PN represent a +horizontal wire passing by a marked magnetic pole, so that the direction of +its motion shall coincide with the curved line proceeding from below +upwards; or if its motion parallel to itself be in a line tangential to the +curved line, but in the general direction of the arrows; or if it pass the +pole in other directions, but so as to cut the magnetic curves[A] in the +same general direction, or on the same side as they would be cut by the +wire if moving along the dotted curved line;--then the current of +electricity in the wire is from P to N. If it be carried in the reverse +directions, the electric current will be from N to P. Or if the wire be in +the vertical position, figured P' N', and it be carried in similar +directions, coinciding with the dotted horizontal curve so far, as to cut +the magnetic curves on the same side with it, the current will be from P' +to N'. If the wire be considered a tangent to the curved surface of the +cylindrical magnet, and it be carried round that surface into any other +position, or if the magnet itself be revolved on its axis, so as to bring +any part opposite to the tangential wire,--still, if afterwards the wire be +moved in the directions indicated, the current of electricity will be from +P to N; or if it be moved in the opposite direction, from N to P; so that +as regards the motions of the wire past the pole, they may be reduced to +two, directly opposite to each other, one of which produces a current from +P to N, and the other from N to P. + + [A] By magnetic curves, I mean the lines of magnetic forces, however + modified by the juxtaposition of poles, which would be depicted by + iron filings; or those to which a very small magnetic needle would + form a tangent. + +115. The same holds true of the unmarked pole of the magnet, except that if +it be substituted for the one in the figure, then, as the wires are moved +in the direction of the arrows, the current of electricity would be from N +to P, and when they move in the reverse direction, from P to N. + +116. Hence the current of electricity which is excited in metal when moving +in the neighbourhood of a magnet, depends for its direction altogether upon +the relation of the metal to the resultant of magnetic action, or to the +magnetic curves, and may be expressed in a popular way thus; Let AB (fig. +25.) represent a cylinder magnet, A being the marked pole, and B the +unmarked pole; let PN be a silver knife-blade, resting across the magnet +with its edge upward, and with its marked or notched side towards the pole +A; then in whatever direction or position this knife be moved edge +foremost, either about the marked or the unmarked pole, the current of +electricity produced will be from P to N, provided the intersected curves +proceeding from A abut upon the notched surface of the knife, and those +from B upon the unnotched side. Or if the knife be moved with its back +foremost, the current will be from N to P in every possible position and +direction, provided the intersected curves abut on the same surfaces as +before. A little model is easily constructed, by using a cylinder of wood +for a magnet, a flat piece for the blade, and a piece of thread connecting +one end of the cylinder with the other, and passing through a hole in the +blade, for the magnetic curves: this readily gives the result of any +possible direction. + +117. When the wire under induction is passing by an electromagnetic pole, +as for instance one end of a copper helix traversed by the electric current +(34.), the direction of the current in the approaching wire is the same +with that of the current in the parts or sides of the spirals nearest to +it, and in the receding wire the reverse of that in the parts nearest to +it. + +118. All these results show that the power of inducing electric currents is +circumferentially exerted by a magnetic resultant or axis of power, just as +circumferential magnetism is dependent upon and is exhibited by an electric +current. + +119. The experiments described combine to prove that when a piece of metal +(and the same may be true of all conducting matter (213.) ) is passed +either before a single pole, or between the opposite poles of a magnet, or +near electro-magnetic poles, whether ferruginous or not, electrical +currents are produced across the metal transverse to the direction of +motion; and which therefore, in Arago's experiments, will approximate +towards the direction of radii. If a single wire be moved like the spoke of +a wheel near a magnetic pole, a current of electricity is determined +through it from one end towards the other. If a wheel be imagined, +constructed of a great number of these radii, and this revolved near the +pole, in the manner of the copper disc (85.), each radius will have a +current produced in it as it passes by the pole. If the radii be supposed +to be in contact laterally, a copper disc results, in which the directions +of the currents will be generally the same, being modified only by the +coaction which can take place between the particles, now that they are in +metallic contact. + +120. Now that the existence of these currents is known, Arago's phenomena +may be accounted for without considering them as due to the formation in +the copper, of a pole of the opposite kind to that approximated, surrounded +by a diffuse polarity of the same kind (82.); neither is it essential that +the plate should acquire and lose its state in a finite time; nor on the +other hand does it seem necessary that any repulsive force should be +admitted as the cause of the rotation (82.). + +121. The effect is precisely of the same kind as the electromagnetic +rotations which I had the good fortune to discover some years ago[A]. +According to the experiments then made which have since been abundantly +confirmed, if a wire (PN fig. 26.) be connected with the positive and +negative ends of a voltaic buttery, so that the positive electricity shall +pass from P to N, and a marked magnetic pole N be placed near the wire +between it and the spectator, the pole will move in a direction tangential +to the wire, i.e. towards the right, and the wire will move tangentially +towards the left, according to the directions of the arrows. This is +exactly what takes place in the rotation of a plate beneath a magnetic +pole; for let N (fig. 27.) be a marked pole above the circular plate, the +latter being rotated in the direction of the arrow: immediately currents of +positive electricity set from the central parts in the general direction of +the radii by the pole to the parts of the circumference _a_ on the other +side of that pole (99. 119.), and are therefore exactly in the same +relation to it as the current in the wire (PN, fig. 26.), and therefore the +pole in the same manner moves to the right hand. + + [A] Quarterly Journal of Science, vol. xii. pp. 74. 186. 416. 283. + +122. If the rotation of the disc be reversed, the electric currents are +reversed (91.), and the pole therefore moves to the left hand. If the +contrary pole be employed, the effects are the same, i.e. in the same +direction, because currents of electricity, the reverse of those described, +are produced, and by reversing both poles and currents, the visible effects +remain unchanged. In whatever position the axis of the magnet be placed, +provided the same pole be applied to the same side of the plate, the +electric current produced is in the same direction, in consistency with the +law already stated (114, &c.); and thus every circumstance regarding the +direction of the motion may be explained. + +123. These currents are _discharged or return_ in the parts of the plate on +each side of and more distant from the place of the pole, where, of course, +the magnetic induction is weaker; and when the collectors are applied, and +a current of electricity is carried away to the galvanometer (88.), the +deflection there is merely a repetition, by the same current or part of it, +of the effect of rotation in the magnet over the plate itself. + +124. It is under the point of view just put forth that I have ventured to +say it is not necessary that the plate should acquire and lose its state in +a finite time (120.); for if it were possible for the current to be fully +developed the instant _before_ it arrived at its state of nearest +approximation to the vertical pole of the magnet, instead of opposite to or +a little beyond it, still the relative motion of the pole and plate would +be the same, the resulting force being in fact tangential instead of +direct. + +125. But it is possible (though not necessary for the rotation) that _time_ +may be required for the development of the maximum current in the plate, in +which case the resultant of all the forces would be in advance of the +magnet when the plate is rotated, or in the rear of the magnet when the +latter is rotated, and many of the effects with pure electro-magnetic poles +tend to prove this is the case. Then, the tangential force may be resolved +into two others, one parallel to the plane of rotation, and the other +perpendicular to it; the former would be the force exerted in making the +plate revolve with the magnet, or the magnet with the plate; the latter +would be a repulsive force, and is probably that, the effects of which M. +Arago has also discovered (82.). + +126. The extraordinary circumstance accompanying this action, which has +seemed so inexplicable, namely, the cessation of all phenomena when the +magnet and metal are brought to rest, now receives a full explanation +(82.); for then the electrical currents which cause the motion cease +altogether. + +127. All the effects of solution of metallic continuity, and the consequent +diminution of power described by Messrs. Babbage and Herschel[A], now +receive their natural explanation, as well also as the resumption of power +when the cuts were filled up by metallic substances, which, though +conductors of electricity, were themselves very deficient in the power of +influencing magnets. And new modes of cutting the plate may be devised, +which shall almost entirely destroy its power. Thus, if a copper plate +(81.) be cut through at about a fifth or sixth of its diameter from the +edge, so as to separate a ring from it, and this ring be again fastened on, +but with a thickness of paper intervening (fig. 29.), and if Arago's +experiment be made with this compound plate so adjusted that the section +shall continually travel opposite the pole, it is evident that the magnetic +currents will be greatly interfered with, and the plate probably lose much +of its effect[B]. + + [A] Philosophical Transactions, 1825, p. 481. + + [B] This experiment has actually been made by Mr. Christie, with the + results here described, and is recorded in the Philosophical + Transactions for 1827, p. 82. + +An elementary result of this kind was obtained by using two pieces of thick +copper, shaped as in fig. 28. When the two neighbouring edges were +amalgamated and put together, and the arrangement passed between the poles +of the magnet, in the direction parallel to these edges, a current was +urged through the wires attached to the outer angles, and the galvanometer +became strongly affected; but when a single film of paper was interposed, +and the experiment repeated, no sensible effect could be produced. + +128. A section of this kind could not interfere much with the induction of +magnetism, supposed to be of the nature ordinarily received by iron. + +129. The effect of rotation or deflection of the needle, which M. Arago +obtained by ordinary magnets, M. Ampere succeeded in procuring by +electro-magnets. This is perfectly in harmony with the results relative to +volta-electric and magneto-electric induction described in this paper. And +by using flat spirals of copper wire, through which electric currents were +sent, in place of ordinary magnetic poles (Ill.), sometimes applying a +single one to one side of the rotating plate, and sometimes two to opposite +sides, I obtained the induced currents of electricity from the plate +itself, and could lead them away to, and ascertain their existence by, the +galvanometer. + +130. The cause which has now been assigned for the rotation in Arago's +experiment, namely, the production of electrical currents, seems abundantly +sufficient in all cases where the metals, or perhaps even other conductors, +are concerned; but with regard to such bodies as glass, resins, and, above +all, gases, it seems impossible that currents of electricity, capable of +producing these effects, should be generated in them. Yet Arago found that +the effects in question were produced by these and by all bodies tried +(81.). Messrs. Babbage and Herschel, it is true, did not observe them with +any substance not metallic, except carbon, in a highly conducting state +(82.). Mr. Harris has ascertained their occurrence with wood, marble, +freestone and annealed glass, but obtained no effect with sulphuric acid +and saturated solution of sulphate of iron, although these are better +conductors of electricity than the former substances. + +131. Future investigations will no doubt explain these difficulties, and +decide the point whether the retarding or dragging action spoken of is +always simultaneous with electric currents.[A] The existence of the action +in metals, only whilst the currents exist, i.e. whilst motion is given (82. +88.), and the explication of the repulsive action observed by M. Arago (82. +125.), are powerful reasons for referring it to this cause; but it may be +combined with others which occasionally act alone. + + [A] Experiments which I have since made convince me that this + particular action is always due to the electrical currents formed; and + they supply a test by which it may be distinguished from the action of + ordinary magnetism, or any other cause, including those which are + mechanical or irregular, producing similar effects (254.) + +132. Copper, iron, tin, zinc, lead, mercury, and all the metals tried, +produced electrical currents when passed between the magnetic poles: the +mercury was put into a glass tube for the purpose. The dense carbon +deposited in coal gas retorts, also produced the current, but ordinary +charcoal did not. Neither could I obtain any sensible effects with brine, +sulphuric acid, saline solutions, &c., whether rotated in basins, or +inclosed in tubes and passed between the poles. + +133. I have never been able to produce any sensation upon the tongue by the +wires connected with the conductors applied to the edges of the revolving +plate (88.) or slips of metal (101.). Nor have I been able to heat a fine +platina wire, or produce a spark, or convulse the limbs of a frog. I have +failed also to produce any chemical effects by electricity thus evolved +(22. 56). + +134. As the electric current in the revolving copper plate occupies but a +small space, proceeding by the poles and being discharged right and left at +very small distances comparatively (123.); and as it exists in a thick mass +of metal possessing almost the highest conducting power of any, and +consequently offering extraordinary facility for its production and +discharge; and as, notwithstanding this, considerable currents may be drawn +off which can pass through narrow wires, forty, fifty, sixty, or even one +hundred feet long; it is evident that the current existing in the plate +itself must be a very powerful one, when the rotation is rapid and the +magnet strong. This is also abundantly proved by the obedience and +readiness with which a magnet ten or twelve pounds in weight follows the +motion of the plate and will strongly twist up the cord by which it is +suspended. + +135. Two rough trials were made with the intention of constructing +_magneto-electric machines_. In one, a ring one inch and a half broad and +twelve inches external diameter, cut from a thick copper plate, was mounted +so as to revolve between the poles of the magnet and represent a plate +similar to those formerly used (101.), but of interminable length; the +inner and outer edges were amalgamated, and the conductors applied one to +each edge, at the place of the magnetic poles. The current of electricity +evolved did not appear by the galvanometer to be stronger, if so strong, as +that from the circular plate (88.). + +136. In the other, small thick discs of copper or other metal, half an inch +in diameter, were revolved rapidly near to the poles, but with the axis of +rotation out of the polar axis; the electricity evolved was collected by +conductors applied as before to the edges (86.). Currents were procured, +but of strength much inferior to that produced by the circular plate. + +137. The latter experiment is analogous to those made by Mr. Barlow with a +rotating iron shell, subject to the influence of the earth[A]. The effects +obtained by him have been referred by Messrs. Babbage and Herschel to the +same cause as that considered as influential in Arago's experiment[B]; but +it would be interesting to know how far the electric current which might be +produced in the experiment would account for the deflexion of the needle. +The mere inversion of a copper wire six or seven times near the poles of +the magnet, and isochronously with the vibrations of the galvanometer +needle connected with it, was sufficient to make the needle vibrate through +an arc of 60 deg. or 70 deg.. The rotation of a copper shell would perhaps decide +the point, and might even throw light upon the more permanent, though +somewhat analogous effects obtained by Mr. Christie. + + [A] Philosophical Transactions, 1825. p. 317. + + [B] Ibid. 1825. p. 485. + +138. The remark which has already been made respecting iron (66.), and the +independence of the ordinary magnetical phenomena of that substance and the +phenomena now described of magneto-electric induction in that and other +metals, was fully confirmed by many results of the kind detailed in this +section. When an iron plate similar to the copper one formerly described +(101.) was passed between the magnetic poles, it gave a current of +electricity like the copper plate, but decidedly of less power; and in the +experiments upon the induction of electric currents (9.), no difference in +the kind of action between iron and other metals could be perceived. The +power therefore of an iron plate to drag a magnet after it, or to intercept +magnetic action, should be carefully distinguished from the similar power +of such metals as silver, copper, &c. &c., inasmuch as in the iron by far +the greater part of the effect is due to what may be called ordinary +magnetic action. There can be no doubt that the cause assigned by Messrs. +Babbage and Herschel in explication of Arago's phenomena is the true one, +when iron is the metal used. + +139. The very feeble powers which were found by those philosophers to +belong to bismuth and antimony, when moving, of affecting the suspended +magnet, and which has been confirmed by Mr. Harris, seem at first +disproportionate to their conducting powers; whether it be so or not must +be decided by future experiment (73.)[A]. These metals are highly +crystalline, and probably conduct electricity with different degrees of +facility in different directions; and it is not unlikely that where a mass +is made up of a number of crystals heterogeneously associated, an effect +approaching to that of actual division may occur (127.); or the currents of +electricity may become more suddenly deflected at the confines of similar +crystalline arrangements, and so be more readily and completely discharged +within the mass. + + [A] I have since been able to explain these differences, and prove, + with several metals, that the effect is in the order of the conducting + power; for I have been able to obtain, by magneto-electric induction, + currents of electricity which are proportionate in strength to the + conducting power of the bodies experimented with (211.). + +S. _Royal Institution, November 1831._ + +_Note._--In consequence of the long period which has intervened between the +reading and printing of the foregoing paper, accounts of the experiments +have been dispersed, and, through a letter of my own to M. Hachette, have +reached France and Italy. That letter was translated (with some errors), +and read to the Academy of Sciences at Paris, 26th December, 1831. A copy +of it in _Le Temps_ of the 28th December quickly reached Signor Nobili, +who, with Signor Antinori, immediately experimented upon the subject, and +obtained many of the results mentioned in my letter; others they could not +obtain or understand, because of the brevity of my account. These results +by Signori Nobili and Antinori have been embodied in a paper dated 31st +January 1832, and printed and published in the number of the _Antologia_ +dated November 1831 (according at least to the copy of the paper kindly +sent me by Signor Nobili). It is evident the work could not have been then +printed; and though Signor Nobili, in his paper, has inserted my letter as +the text of his experiments, yet the circumstance of back date has caused +many here, who have heard of Nobili's experiments by report only, to +imagine his results were anterior to, instead of being dependent upon, +mine. + +I may be allowed under these circumstances to remark, that I experimented +on this subject several years ago, and have published results. (See +Quarterly Journal of Science for July 1825, p. 338.) The following also is +an extract from my note-book, dated November 28, 1825: "Experiments on +induction by connecting wire of voltaic battery:--a battery of four +troughs, ten pairs of plates, each arranged side by side--the poles +connected by a wire about four feet long, parallel to which was another +similar wire separated from it only by two thicknesses of paper, the ends +of the latter were attached to a galvanometer:--exhibited no action, &c. +&c. &c.--Could not in any way render any induction evident from the +connecting wire." The cause of failure at that time is now evident +(79.).--M.F. April, 1832. + + + + +SECOND SERIES. + +THE BAKERIAN LECTURE. + + +S 5. _Terrestrial Magneto-electric Induction._ S 6. _Force and Direction of +Magneto-electric Induction generally._ + +Read January 12, 1832. + + +S 5. _Terrestrial Magneto-electric Induction._ + +140. When the general facts described in the former paper were discovered, +and the _law_ of magneto-electric induction relative to direction was +ascertained (114.), it was not difficult to perceive that the earth would +produce the same effect as a magnet, and to an extent that would, perhaps, +render it available in the construction of new electrical machines. The +following are some of the results obtained in pursuance of this view. + +141. The hollow helix already described (6.) was connected with a +galvanometer by wires eight feet long; and the soft iron cylinder (34.) +after being heated red-hot and slowly cooled, to remove all traces of +magnetism, was put into the helix so as to project equally at both ends, +and fixed there. The combined helix and bar were held in the magnetic +direction or line of dip, and (the galvanometer needle being motionless) +were then inverted, so that the lower end should become the upper, but the +whole still correspond to the magnetic direction; the needle was +immediately deflected. As the latter returned to its first position, the +helix and bar were again inverted; and by doing this two or three times, +making the inversions and vibrations to coincide, the needle swung through +an arc of 150 deg. or 160 deg.. + +142. When one end of the helix, which may be called A, was uppermost at +first (B end consequently being below), then it mattered not in which +direction it proceeded during the inversion, whether to the right hand or +left hand, or through any other course; still the galvanometer needle +passed in the same direction. Again, when B end was uppermost, the +inversion of the helix and bar in any direction always caused the needle to +be deflected one way; that way being the opposite to the course of the +deflection in the former case. + +143. When the helix with its iron core in any given position was inverted, +the effect was as if a magnet with its marked pole downwards had been +introduced from above into the inverted helix. Thus, if the end B were +upwards, such a magnet introduced from above would make the marked end of +the galvanometer needle pass west. Or the end B being downwards, and the +soft iron in its place, inversion of the whole produced the same effect. + +144. When the soft iron bar was taken out of the helix and inverted in +various directions within four feet of the galvanometer, not the slightest +effect upon it was produced. + +145. These phenomena are the necessary consequence of the inductive +magnetic power of the earth, rendering the soft iron cylinder a magnet with +its marked pole downwards. The experiment is analogous to that in which two +bar magnets were used to magnetize the same cylinder in the same helix +(36.), and the inversion of position in the present experiment is +equivalent to a change of the poles in that arrangement. But the result is +not less an instance of the evolution of electricity by means of the +magnetism of the globe. + +146. The helix alone was then held permanently in the magnetic direction, +and the soft iron cylinder afterwards introduced; the galvanometer needle +was instantly deflected; by withdrawing the cylinder as the needle +returned, and continuing the two actions simultaneously, the vibrations +soon extended through an arc of 180 deg.. The effect was precisely the same as +that obtained by using a cylinder magnet with its marked pole downwards; +and the direction of motion, &c. was perfectly in accordance with the +results of former experiments obtained with such a magnet (39.). A magnet +in that position being used, gave the same deflections, but stronger. When +the helix was put at right angles to the magnetic direction or dip, then +the introduction or removal of the soft iron cylinder produced no effect at +the needle. Any inclination to the dip gave results of the same kind as +those already described, but increasing in strength as the helix +approximated to the direction of the dip. + +147. A cylinder magnet, although it has great power of affecting the +galvanometer when moving into or out of the helix, has no power of +continuing the deflection (39.); and therefore, though left in, still the +magnetic needle comes to its usual place of rest. But upon repeating (with +the magnet) the experiment of inversion in the direction of the dip (141), +the needle was affected as powerfully as before; the disturbance of the +magnetism in the steel magnet, by the earth's inductive force upon it, +being thus shown to be nearly, if not quite, equal in amount and rapidity +to that occurring in soft iron. It is probable that in this way +magneto-electrical arrangements may become very useful in indicating the +disturbance of magnetic forces, where other means will not apply; for it is +not the whole magnetic power which produces the visible effect, but only +the difference due to the disturbing causes. + +148. These favourable results led me to hope that the direct +magneto-electric induction of the earth might be rendered sensible; and I +ultimately succeeded in obtaining the effect in several ways. When the +helix just referred to (141. 6.) was placed in the magnetic dip, but +without any cylinder of iron or steel, and was then inverted, a feeble +action at the needle was observed. Inverting the helix ten or twelve times, +and at such periods that the deflecting forces exerted by the currents of +electricity produced in it should be added to the momentum of the needle +(39.), the latter was soon made to vibrate through an arc of 80 deg. or 90 deg.. +Here, therefore, currents of electricity were produced by the direct +inductive power of the earth's magnetism, without the use of any +ferruginous matter, and upon a metal not capable of exhibiting any of the +ordinary magnetic phenomena. The experiment in everything represents the +effects produced by bringing the same helix to one or both poles of any +powerful magnet (50.). + +149. Guided by the law already expressed (114.), I expected that all the +electric phenomena of the revolving metal plate could now be produced +without any other magnet than the earth. The plate so often referred to +(85.) was therefore fixed so as to rotate in a horizontal plane. The +magnetic curves of the earth (114. _note_), i.e. the dip, passes through +this plane at angles of about 70 deg., which it was expected would be an +approximation to perpendicularity, quite enough to allow of +magneto-electric induction sufficiently powerful to produce a current of +electricity. + +150. Upon rotation of the plate, the currents ought, according to the law +(114. 121.), to tend to pass in the direction of the radii, through _all_ +parts of the plate, either from the centre to the circumference, or from +the circumference to the centre, as the direction of the rotation of the +plate was one way or the other. One of the wires of the galvanometer was +therefore brought in contact with the axis of the plate, and the other +attached to a leaden collector or conductor (86.), which itself was placed +against the amalgamated edge of the disc. On rotating the plate there was a +distinct effect at the galvanometer needle; on reversing the rotation, the +needle went in the opposite direction; and by making the action of the +plate coincide with the vibrations of the needle, the arc through which the +latter passed soon extended to half a circle. + +151. Whatever part of the edge of the plate was touched by the conductor, +the electricity was the same, provided the direction of rotation continued +unaltered. + +152. When the plate revolved _screw-fashion_, or as the hands of a watch, +the current of electricity (150.) was from the centre to the circumference; +when the direction of rotation was _unscrew_, the current was from the +circumference to the centre. These directions are the same with those +obtained when the unmarked pole of a magnet was placed beneath the +revolving plate (99.). + +153. When the plate was in the magnetic meridian, or in any other plane +_coinciding_ with the magnetic dip, then its rotation produced no effect +upon the galvanometer. When inclined to the dip but a few degrees, +electricity began to appear upon rotation. Thus when standing upright in a +plane perpendicular to the magnetic meridian, and when consequently its own +plane was inclined only about 20 deg. to the dip, revolution of the plate +evolved electricity. As the inclination was increased, the electricity +became more powerful until the angle formed by the plane of the plate with +the dip was 90 deg., when the electricity for a given velocity of the plate was +a maximum. + +154. It is a striking thing to observe the revolving copper plate become +thus a _new electrical machine_; and curious results arise on comparing it +with the common machine. In the one, the plate is of the best +non-conducting substance that can be applied; in the other, it is the most +perfect conductor: in the one, insulation is essential; in the other, it is +fatal. In comparison of the quantities of electricity produced, the metal +machine does not at all fall below the glass one; for it can produce a +constant current capable of deflecting the galvanometer needle, whereas the +latter cannot. It is quite true that the force of the current thus evolved +has not as yet been increased so as to render it available in any of our +ordinary applications of this power; but there appears every reasonable +expectation that this may hereafter be effected; and probably by several +arrangements. Weak as the current may seem to be, it is as strong as, if +not stronger than, any thermo-electric current; for it can pass fluids +(23.), agitate the animal system, and in the case of an electro-magnet has +produced sparks (32.). + +155. A disc of copper, one fifth of an inch thick and only one inch and a +half in diameter, was amalgamated at the edge; a square piece of sheet lead +(copper would have been better) of equal thickness had a circular hole cut +in it, into which the disc loosely fitted; a little mercury completed the +metallic communication of the disc and its surrounding ring; the latter was +attached to one of the galvanometer wires, and the other wire dipped into a +little metallic cup containing mercury, fixed upon the top of the copper +axis of the small disc. Upon rotating the disc in a horizontal plane, the +galvanometer needle could be affected, although the earth was the only +magnet employed, and the radius of the disc but three quarters of an inch; +in which space only the current was excited. + +156. On putting the pole of a magnet under the revolving disc, the +galvanometer needle could be permanently deflected. + +157. On using copper wires one sixth of an inch in thickness instead of the +smaller wires (86.) hitherto constantly employed, far more powerful effects +were obtained. Perhaps if the galvanometer had consisted of fewer turns of +thick wire instead of many convolutions of thinner, more striking effects +would have been produced. + +158. One form of apparatus which I purpose having arranged, is to have +several discs superposed; the discs are to be metallically connected, +alternately at the edges and at the centres, by means of mercury; and are +then to be revolved alternately in opposite directions, i.e. the first, +third, fifth, &c. to the right hand, and the second, fourth, sixth, &c. to +the left hand; the whole being placed so that the discs are perpendicular +to the dip, or intersect most directly the magnetic curves of powerful +magnets. The electricity will be from the centre to the circumference in +one set of discs, and from the circumference to the centre in those on each +side of them; thus the action of the whole will conjoin to produce one +combined and more powerful current. + +159. I have rather, however, been desirous of discovering new facts and new +relations dependent on magneto-electric induction, than of exalting the +force of those already obtained; being assured that the latter would find +their full development hereafter. + + * * * * * + +160. I referred in my former paper to the probable influence of terrestrial +magneto-electric induction (137.) in producing, either altogether or in +part, the phenomena observed by Messrs. Christie and Barlow[A], whilst +revolving ferruginous bodies; and especially those observed by the latter +when rapidly rotating an iron shell, which were by that philosopher +referred to a change in the ordinary disposition of the magnetism of the +ball. I suggested also that the rotation of a copper globe would probably +insulate the effects due to electric currents from those due to mere +derangement of magnetism, and throw light upon the true nature of the +phenomena. + + [A] Christie, Phil. Trans. 1825, pp. 58, 347, &c. Barlow, Phil. Trans. + 1825, p. 317. + +161. Upon considering the law already referred to (114.), it appeared +impossible that a metallic globe could revolve under natural circumstances, +without having electric currents produced within it, circulating round the +revolving globe in a plane at right angles to the plane of revolution, +provided its axis of rotation did not coincide with the dip; and it +appeared that the current would be most powerful when the axis of +revolution was perpendicular to the dip of the needle: for then all those +parts of the ball below a plane passing through its centre and +perpendicular to the dip, would in moving cut the magnetic curves in one +direction, whilst all those parts above that plane would intersect them in +the other direction: currents therefore would exist in these moving parts, +proceeding from one pole of rotation to the other; but the currents above +would be in the reverse direction to those below, and in conjunction with +them would produce a continued circulation of electricity. + +162. As the electric currents are nowhere interrupted in the ball, powerful +effects were expected, and I endeavoured to obtain them with simple +apparatus. The ball I used was of brass; it had belonged to an old +electrical machine, was hollow, thin (too thin), and four inches in +diameter; a brass wire was screwed into it, and the ball either turned in +the hand by the wire, or sometimes, to render it more steady, supported by +its wire in a notched piece of wood, and motion again given by the hand. +The ball gave no signs of magnetism when at rest. + +163. A compound magnetic needle was used to detect the currents. It was +arranged thus: a sewing-needle had the head and point broken off, and was +then magnetised; being broken in halves, the two magnets thus produced were +fixed on a stem of dried grass, so as to be perpendicular to it, and about +four inches asunder; they were both in one plane, but their similar poles +in contrary directions. The grass was attached to a piece of unspun silk +about six inches long, the latter to a stick passing through a cork in the +mouth of a cylindrical jar; and thus a compound arrangement was obtained, +perfectly sheltered from the motion of the air, but little influenced by +the magnetism of the earth, and yet highly sensible to magnetic and +electric forces, when the latter were brought into the vicinity of the one +or the other needle. + +164. Upon adjusting the needles to the plane of the magnetic meridian; +arranging the ball on the outside of the glass jar to the west of the +needles, and at such a height that its centre should correspond +horizontally with the upper needle, whilst its axis was in the plane of the +magnetic meridian, but perpendicular to the dip; and then rotating the +ball, the needle was immediately affected. Upon inverting the direction of +rotation, the needle was again affected, but in the opposite direction. +When the ball revolved from east over to west, the marked pole went +eastward; when the ball revolved in the opposite direction, the marked pole +went westward or towards the ball. Upon placing the ball to the east of the +needles, still the needle was deflected in the same way; i.e. when the ball +revolved from east over to west, the marked pole wont eastward (or towards +the ball); when the rotation was in the opposite direction, the marked pole +went westward. + +165. By twisting the silk of the needles, the latter were brought into a +position perpendicular to the plane of the magnetic meridian; the ball was +again revolved, with its axis parallel to the needles; the upper was +affected as before, and the deflection was such as to show that both here +and in the former case the needle was influenced solely by currents of +electricity existing in the brass globe. + +166. If the upper part of the revolving ball be considered as a wire moving +from east to west, over the unmarked pole of the earth, the current of +electricity in it should be from north to south (99. 114. 150.); if the +under part be considered as a similar wire, moving from west to east over +the same pole, the electric current should be from south to north; and the +circulation of electricity should therefore be from north above to south, +and below back to north, in a metal ball revolving from east above to west +in these latitudes. Now these currents are exactly those required to give +the directions of the needle in the experiments just described; so that the +coincidence of the theory from which the experiments were deduced with the +experiments themselves, is perfect. + +167. Upon inclining the axis of rotation considerably, the revolving ball +was still found to affect the magnetic needle; and it was not until the +angle which it formed with the magnetic dip was rendered small, that its +effects, even upon this apparatus, were lost (153.). When revolving with +its axis parallel to the dip, it is evident that the globe becomes +analogous to the copper plate; electricity of one kind might be collected +at its equator, and of the other kind at its poles. + +168. A current in the ball, such as that described above (161.), although +it ought to deflect a needle the same way whether it be to the right or the +left of the ball and of the axis of rotation, ought to deflect it the +contrary way when above or below the ball; for then the needle is, or ought +to be, acted upon in a contrary direction by the current. This expectation +was fulfilled by revolving the ball beneath the magnetic needle, the latter +being still inclosed in its jar. When the ball was revolved from east over +to west, the marked pole of the needle, instead of passing eastward, went +westward; and when revolved from west over to east, the marked pole went +eastward. + +169. The deflections of the magnetic needle thus obtained with a brass ball +are exactly in the same direction as those observed by Mr. Barlow in the +revolution of the iron shell; and from the manner in which iron exhibits +the phenomena of magneto-electric induction like any other metal, and +distinct from its peculiar magnetic phenomena (132.), it is impossible but +that electric currents must have been excited, and become active in those +experiments. What proportion of the whole effect obtained is due to this +cause, must be decided by a more elaborate investigation of all the +phenomena. + +170. These results, in conjunction with the general law before stated +(114.), suggested an experiment of extreme simplicity, which yet, on trial, +was found to answer perfectly. The exclusion of all extraneous +circumstances and complexity of arrangement, and the distinct character of +the indications afforded, render this single experiment an epitome of +nearly all the facts of magneto-electric induction. + +171. A piece of common copper wire, about eight feet long and one twentieth +of an inch in thickness, had one of its ends fastened to one of the +terminations of the galvanometer wire, and the other end to the other +termination; thus it formed an endless continuation of the galvanometer +wire: it was then roughly adjusted into the shape of a rectangle, or rather +of a loop, the upper part of which could be carried to and fro over the +galvanometer, whilst the lower part, and the galvanometer attached to it, +remained steady (Plate II. fig. 30.). Upon moving this loop over the +galvanometer from right to left, the magnetic needle was immediately +deflected; upon passing the loop back again, the needle passed in the +contrary direction to what it did before; upon repeating these motions of +the loop in accordance with the vibrations of the needle (39.), the latter +soon swung through 90 deg. or more. + +172. The relation of the current of electricity produced in the wire, to +its motion, may be understood by supposing the convolutions at the +galvanometer away, and the wire arranged as a rectangle, with its lower +edge horizontal and in the plane of the magnetic meridian, and a magnetic +needle suspended above and over the middle part of this edge, and directed +by the earth (fig. 30.). On passing the upper part of the rectangle from +west to east into the position represented by the dotted line, the marked +pole of the magnetic needle went west; the electric current was therefore +from north to south in the part of the wire passing under the needle, and +from south to north in the moving or upper part of the parallelogram. On +passing the upper part of the rectangle from east to west over the +galvanometer, the marked pole of the needle went east, and the current of +electricity was therefore the reverse of the former. + +173. When the rectangle was arranged in a plane east and west, and the +magnetic needle made parallel to it, either by the torsion of its +suspension thread or the action of a magnet, still the general effects were +the same. On moving the upper part of the rectangle from north to south, +the marked pole of the needle went north; when the wire was moved in the +opposite direction, the marked pole went south. The same effect took place +when the motion of the wire was in any other azimuth of the line of dip; +the direction of the current always being conformable to the law formerly +expressed (114.), and also to the directions obtained with the rotating +ball (101.). + +174. In these experiments it is not necessary to move the galvanometer or +needle from its first position. It is quite sufficient if the wire of the +rectangle is distorted where it leaves the instrument, and bent so as to +allow the moving upper part to travel in the desired direction. + +175. The moveable part of the wire was then arranged _below_ the +galvanometer, but so as to be carried across the dip. It affected the +instrument as before, and in the same direction; i.e. when carried from +west to east under the instrument, the marked end of the needle went west, +as before. This should, of course, be the case; for when the wire is +cutting the magnetic dip in a certain direction, an electric current also +in a certain direction should be induced in it. + +176. If in fig. 31 _dp_ be parallel to the dip, and BA be considered as the +upper part of the rectangle (171.), with an arrow _c_ attached to it, both +these being retained in a plane perpendicular to the dip,--then, however BA +with its attached arrow is moved upon _dp_ as an axis, if it afterwards +proceed in the direction of the arrow, a current of electricity will move +along it from B towards A. + +177. When the moving part of the wire was carried up or down parallel to +the dip, no effect was produced on the galvanometer. When the direction of +motion was a little inclined to the dip, electricity manifested itself; and +was at a maximum when the motion was perpendicular to the magnetic +direction. + +178. When the wire was bent into other forms and moved, equally strong +effects were obtained, especially when instead of a rectangle a double +catenarian curve was formed of it on one side of the galvanometer, and the +two single curves or halves were swung in opposite directions at the same +time; their action then combined to affect the galvanometer: but all the +results were reducible to those above described. + +179. The longer the extent of the moving wire, and the greater the space +through which it moves, the greater is the effect upon the galvanometer. + +180. The facility with which electric currents are produced in metals when +moving under the influence of magnets, suggests that henceforth precautions +should always be taken, in experiments upon metals and magnets, to guard +against such effects. Considering the universality of the magnetic +influence of the earth, it is a consequence which appears very +extraordinary to the mind, that scarcely any piece of metal can be moved in +contact with others, either at rest, or in motion with different velocities +or in varying directions, without an electric current existing within them. +It is probable that amongst arrangements of steam-engines and metal +machinery, some curious accidental magneto-electric combinations may be +found, producing effects which have never been observed, or, if noticed, +have never as yet been understood. + + * * * * * + +181. Upon considering the effects of terrestrial magneto-electric induction +which have now been described, it is almost impossible to resist the +impression that similar effects, but infinitely greater in force, may be +produced by the action of the globe, as a magnet, upon its own mass, in +consequence of its diurnal rotation. It would seem that if a bar of metal +be laid in these latitudes on the surface of the earth parallel to the +magnetic meridian, a current of electricity tends to pass through it from +south to north, in consequence of the travelling of the bar from west to +east (172.), by the rotation of the earth; that if another bar in the same +direction be connected with the first by wires, it cannot discharge the +current of the first, because it has an equal tendency to have a current in +the same direction induced within itself: but that if the latter be carried +from east to west, which is equivalent to a diminution of the motion +communicated to it from the earth (172.), then the electric current from +south to north is rendered evident in the first bar, in consequence of its +discharge, at the same time, by means of the second. + +182. Upon the supposition that the rotation of the earth tended, by +magneto-electric induction, to cause currents in its own mass, these would, +according to the law (114.) and the experiments, be, upon the surface at +least, from the parts in the neighbourhood of or towards the plane of the +equator, in opposite directions to the poles; and if collectors could be +applied at the equator and at the poles of the globe, as has been done with +the revolving copper plate (150.), and also with magnets (220.), then +negative electricity would be collected at the equator, and positive +electricity at both poles (222.). But without the conductors, or something +equivalent to them, it is evident these currents could not exist, as they +could not be discharged. + +183. I did not think it impossible that some natural difference might occur +between bodies, relative to the intensity of the current produced or +tending to be produced in them by magneto-electric induction, which might +be shown by opposing them to each other; especially as Messrs. Arago, +Babbage, Herschel, and Harris, have all found great differences, not only +between the metals and other substances, but between the metals themselves, +in their power of receiving motion from or giving it to a magnet in trials +by revolution (130.). I therefore took two wires, each one hundred and +twenty feet long, one of iron and the other of copper. These were connected +with each other at their ends, and then extended in the direction of the +magnetic meridian, so as to form two nearly parallel lines, nowhere in +contact except at the extremities. The copper wire was then divided in the +middle, and examined by a delicate galvanometer, but no evidence of an +electrical current was obtained. + +184. By favour of His Royal Highness the President of the Society, I +obtained the permission of His Majesty to make experiments at the lake in +the gardens of Kensington-palace, for the purpose of comparing, in a +similar manner, water and metal. The basin of this lake is artificial; the +water is supplied by the Chelsea Company; no springs run into it, and it +presented what I required, namely, a uniform mass of still pure water, with +banks ranging nearly from east to west, and from north to south. + +185. Two perfectly clean bright copper plates, each exposing four square +feet of surface, were soldered to the extremities of a copper wire; the +plates were immersed in the water, north and south of each other, the wire +which connected them being arranged upon the grass of the bank. The plates +were about four hundred and eighty feet from each other, in a right line; +the wire was probably six hundred feet long. This wire was then divided in +the middle, and connected by two cups of mercury with a delicate +galvanometer. + +186. At first, indications of electric currents were obtained; but when +these were tested by inverting the direction of contact, and in other ways, +they were found to be due to other causes than the one sought for. A little +difference in temperature; a minute portion of the nitrate of mercury used +to amalgamate the wires, entering into the water employed to reduce the two +cups of mercury to the same temperature; was sufficient to produce currents +of electricity, which affected the galvanometer, notwithstanding they had +to pass through nearly five hundred feet of water. When these and other +interfering causes were guarded against, no effect was obtained; and it +appeared that even such dissimilar substances as water and copper, when +cutting the magnetic curves of the earth with equal velocity, perfectly +neutralized each other's action. + +187. Mr. Fox of Falmouth has obtained some highly important results +respecting the electricity of metalliferous veins in the mines of Cornwall, +which have been published in the Philosophical Transactions[A]. I have +examined the paper with a view to ascertain whether any of the effects were +probably referable to magneto-electric induction; but, though unable to +form a very strong opinion, believe they are not. When parallel veins +running east and west were compared, the general tendency of the +electricity _in the wires_ was from north to south; when the comparison was +made between parts towards the surface and at some depth, the current of +electricity in the wires was from above downwards. If there should be any +natural difference in the force of the electric currents produced by +magneto-electric induction in different substances, or substances in +different positions moving with the earth, and which might be rendered +evident by increasing the masses acted upon, then the wires and veins +experimented with by Mr. Fox might perhaps have acted as dischargers to the +electricity of the mass of strata included between them, and the directions +of the currents would agree with those observed as above. + + [A] 1830. p. 399. + +188. Although the electricity obtained by magneto-electric induction in a +few feet of wire is of but small intensity, and has not yet been observed +except in metals, and carbon in a particular state, still it has power to +pass through brine (23.); and, as increased length in the substance acted +upon produces increase of intensity, I hoped to obtain effects from +extensive moving masses of water, though quiescent water gave none. I made +experiments therefore (by favour) at Waterloo Bridge, extending a copper +wire nine hundred and sixty feet in length upon the parapet of the bridge, +and dropping from its extremities other wires with extensive plates of +metal attached to them to complete contact with the water. Thus the wire +and the water made one conducting circuit; and as the water ebbed or flowed +with the tide, I hoped to obtain currents analogous to those of the brass +ball (161.). + +189. I constantly obtained deflections at the galvanometer, but they were +very irregular, and were, in succession, referred to other causes than that +sought for. The different condition of the water as to purity on the two +sides of the river; the difference in temperature; slight differences in +the plates, in the solder used, in the more or less perfect contact made by +twisting or otherwise; all produced effects in turn: and though I +experimented on the water passing through the middle arches only; used +platina plates instead of copper; and took every other precaution, I could +not after three days obtain any satisfactory results. + +190. Theoretically, it seems a necessary consequence, that where water is +flowing, there electric currents should be formed; thus, if a line be +imagined passing from Dover to Calais through the sea, and returning +through the land beneath the water to Dover, it traces out a circuit of +conducting matter, one part of which, when the water moves up or down the +channel, is cutting the magnetic curves of the earth, whilst the other is +relatively at rest. This is a repetition of the wire experiment (171.), but +with worse conductors. Still there is every reason to believe that electric +currents do run in the general direction of the circuit described, either +one way or the other, according as the passage of the waters is up or down +the channel. Where the lateral extent of the moving water is enormously +increased, it does not seem improbable that the effect should become +sensible; and the gulf stream may thus, perhaps, from electric currents +moving across it, by magneto-electric induction from the earth, exert a +sensible influence upon the forms of the lines of magnetic variation[A]. + + [A] Theoretically, even a ship or a boat when passing on the surface + of the water, in northern or southern latitudes, should have currents + of electricity running through it directly across the line of her + motion; or if the water is flowing past the ship at anchor, similar + currents should occur. + +191. Though positive results have not yet been obtained by the action of +the earth upon water and aqueous fluids, yet, as the experiments are very +limited in their extent, and as such fluids do yield the current by +artificial magnets (23.), (for transference of the current is proof that it +may be produced (213.),) the supposition made, that the earth produces +these induced currents within itself (181.) in consequence of its diurnal +rotation, is still highly probable (222, 223.); and when it is considered +that the moving masses extend for thousands of miles across the magnetic +curves, cutting them in various directions within its mass, as well as at +the surface, it is possible the electricity may rise to considerable +intensity. + +192. I hardly dare venture, even in the most hypothetical form, to ask +whether the Aurora Borealis and Australia may not be the discharge of +electricity, thus urged towards the poles of the earth, from whence it is +endeavouring to return by natural and appointed means above the earth to +the equatorial regions. The non-occurrence of it in very high latitudes is +not at all against the supposition; and it is remarkable that Mr. Fox, who +observed the deflections of the magnetic needle at Falmouth, by the Aurora +Borealis, gives that direction of it which perfectly agrees with the +present view. He states that all the variations at night were towards the +east[A], and this is what would happen if electric currents were setting +from south to north in the earth under the needle, or from north to south +in space above it. + + [A] Philosophical Transactions, 1831, p. 202. + + +S 6. _General remarks and illustrations of the Force and Direction of +Magneto-electric Induction._ + + +193. In the repetition and variation of Arago's experiment by Messrs. +Babbage, Herschel, and Harris, these philosophers directed their attention +to the differences of force observed amongst the metals and other +substances in their action on the magnet. These differences were very +great[A], and led me to hope that by mechanical combinations of various +metals important results might be obtained (183.). The following +experiments were therefore made, with a view to obtain, if possible, any +such difference of the action of two metals, + + [B] Philosophical Transactions, 1825, p. 472; 1831, p.78. + +194. A piece of soft iron bonnet-wire covered with cotton was laid bare and +cleaned at one extremity, and there fastened by metallic contact with the +clean end of a copper wire. Both wires were then twisted together like the +strands of a rope, for eighteen or twenty inches; and the remaining parts +being made to diverge, their extremities were connected with the wires of +the galvanometer. The iron wire was about two feet long, the continuation +to the galvanometer being copper. + +195. The twisted copper and iron (touching each other nowhere but at the +extremity) were then passed between the poles of a powerful magnet arranged +horse-shoe fashion (fig. 32.); but not the slightest effect was observed at +the galvanometer, although the arrangement seemed fitted to show any +electrical difference between the two metals relative to the action of the +magnet, + +196. A soft iron cylinder was then covered with paper at the middle part, +and the twisted portion of the above compound wire coiled as a spiral +around it, the connexion with the galvanometer still being made at the ends +A and B. The iron cylinder was then brought in contact with the poles of a +powerful magnet capable of raising thirty pounds; yet no signs of +electricity appeared at the galvanometer. Every precaution was applied in +making and breaking contact to accumulate effect, but no indications of a +current could be obtained. + +197. Copper and tin, copper and zinc, tin and zinc, tin and iron, and zinc +and iron, were tried against each other in a similar manner (194), but not +the slightest sign of electric currents could be procured. + +198. Two flat spirals, one of copper and the other of iron, containing each +eighteen inches of wire, were connected with each other and with the +galvanometer, and then put face to face so as to be in contrary directions. +When brought up to the magnetic pole (53.). No electrical indications at +the galvanometer were observed. When one was turned round so that both were +in the same direction, the effect at the galvanometer was very powerful. + +199. The compound helix of copper and iron wire formerly described (8.) was +arranged as a double helix, one of the helices being all iron and +containing two hundred and fourteen feet, the other all copper and +continuing two hundred and eight feet. The two similar ends AA of the +copper and iron helix were connected together, and the other ends BB of +each helix connected with the galvanometer; so that when a magnet was +introduced into the centre of the arrangement, the induced currents in the +iron and copper would tend to proceed in contrary directions. Yet when a +magnet was inserted, or a soft iron bar within made a magnet by contact +with poles, no effect at the needle was produced. + +200. A glass tube about fourteen inches long was filled with strong +sulphuric acid. Twelve inches of the end of a clean copper wire were bent +up into a bundle and inserted into the tube, so as to make good superficial +contact with the acid, and the rest of the wire passed along the outside of +the tube and away to the galvanometer. A wire similarly bent up at the +extremity was immersed in the other end of the sulphuric acid, and also +connected with the galvanometer, so that the acid and copper wire were in +the same parallel relation to each other in this experiment as iron and +copper were in the first (194). When this arrangement was passed in a +similar manner between the poles of the magnet, not the slightest effect at +the galvanometer could be perceived. + +201. From these experiments it would appear, that when metals of different +kinds connected in one circuit are equally subject in every circumstance to +magneto-electric induction, they exhibit exactly equal powers with respect +to the currents which either are formed, or tend to form, in them. The same +even appears to be the case with regard to fluids, and probably all other +substances. + +202. Still it seemed impossible that these results could indicate the +relative inductive power of the magnet upon the different metals; for that +the effect should be in some relation to the conducting power seemed a +necessary consequence (139.), and the influence of rotating plates upon +magnets had been found to bear a general relation to the conducting power +of the substance used. + +203. In the experiments of rotation (81.), the electric current is excited +and discharged in the same substance, be it a good or bad conductor; but in +the experiments just described the current excited in iron could not be +transmitted but through the copper, and that excited in copper had to pass +through iron: i.e. supposing currents of dissimilar strength to be formed +in the metals proportionate to their conducting power, the stronger current +had to pass through the worst conductor, and the weaker current through the +best. + +204. Experiments were therefore made in which different metals insulated +from each other were passed between the poles of the magnet, their opposite +ends being connected with the same end of the galvanometer wire, so that +the currents formed and led away to the galvanometer should oppose each +other; and when considerable lengths of different wires were used, feeble +deflections were obtained. + +205. To obtain perfectly satisfactory results a new galvanometer was +constructed, consisting of two independent coils, each containing eighteen +feet of silked copper wire. These coils were exactly alike in shape and +number of turns, and were fixed side by side with a small interval between +them, in which a double needle could be hung by a fibre of silk exactly as +in the former instrument (87.). The coils may be distinguished by the +letters KL, and when electrical currents were sent through them in the same +direction, acted upon the needle with the sum of their powers; when in +opposite directions, with the difference of their powers. + +206. The compound helix (199. 8.) was now connected, the ends A and B of +the iron with A and B ends of galvanometer coil K, and the ends A and B of +the copper with B and A ends of galvanometer coil L, so that the currents +excited in the two helices should pass in opposite directions through the +coils K and L. On introducing a small cylinder magnet within the helices, +the galvanometer needle was powerfully deflected. On disuniting the iron +helix, the magnet caused with the copper helix alone still stronger +deflection in the same direction. On reuniting the iron helix, and +unconnecting the copper helix, the magnet caused a moderate deflection in +the contrary direction. Thus it was evident that the electric current +induced by a magnet in a copper wire was far more powerful than the current +induced by the same magnet in an equal iron wire. + +207. To prevent any error that might arise from the greater influence, from +vicinity or other circumstances, of one coil on the needle beyond that of +the other, the iron and copper terminations were changed relative to the +galvanometer coils KL, so that the one which before carried the current +from the copper now conveyed that from the iron, and vice versa. But the +same striking superiority of the copper was manifested as before. This +precaution was taken in the rest of the experiments with other metals to be +described. + +208. I then had wires of iron, zinc, copper, tin, and lead, drawn to the +same diameter (very nearly one twentieth of an inch), and I compared +exactly equal lengths, namely sixteen feet, of each in pairs in the +following manner: The ends of the copper wire were connected with the ends +A and B of galvanometer coil K, and the ends of the zinc wire with the +terminations A and B of the galvanometer coil L. The middle part of each +wire was then coiled six times round a cylinder of soft iron covered with +paper, long enough to connect the poles of Daniell's horse-shoe magnet +(56.) (fig. 33.), so that similar helices of copper and zinc, each of six +turns, surrounded the bar at two places equidistant from each other and +from the poles of the magnet; but these helices were purposely arranged so +as to be in contrary directions, and therefore send contrary currents +through the galvanometer coils K and L, + +209. On making and breaking contact between the soft iron bar and the poles +of the magnet, the galvanometer was strongly affected; on detaching the +zinc it was still more strongly affected in the same direction. On taking +all the precautions before alluded to (207.), with others, it was +abundantly proved that the current induced by the magnet in copper was far +more powerful than in zinc. + +210. The copper was then compared in a similar manner with tin, lead, and +iron, and surpassed them all, even more than it did zinc. The zinc was then +compared experimentally with the tin, lead, and iron, and found to produce +a more powerful current than any of them. Iron in the same manner proved +superior to tin and lead. Tin came next, and lead the last. + +211. Thus the order of these metals is copper, zinc, iron, tin, and lead. +It is exactly their order with respect to conducting power for electricity, +and, with the exception of iron, is the order presented by the +magneto-rotation experiments of Messrs. Babbage, Herschel, Harris, &c. The +iron has additional power in the latter kind of experiments, because of its +ordinary magnetic relations, and its place relative to magneto-electric +action of the kind now under investigation cannot be ascertained by such +trials. In the manner above described it may be correctly ascertained[A]. + + [A] Mr. Christie, who being appointed reporter upon this paper, had it + in his hands before it was complete, felt the difficulty (202.); and + to satisfy his mind, made experiments upon iron and copper with the + large magnet(44.), and came to the same conclusions as I have arrived + at. The two sets of experiments were perfectly independent of each + other, neither of us being aware of the other's proceedings. + +212. It must still be observed that in these experiments the whole effect +between different metals is not obtained; for of the thirty-four feet of +wire included in each circuit, eighteen feet are copper in both, being the +wire of the galvanometer coils; and as the whole circuit is concerned in +the resulting force of the current, tin's circumstance must tend to +diminish the difference which would appear between the metals if the +circuits were of the same substances throughout. In the present case the +difference obtained is probably not more than a half of that which would be +given if the whole of each circuit were of one metal. + +213. These results tend to prove that the currents produced by +magneto-electric induction in bodies is proportional to their conducting +power. That they are _exactly_ proportional to and altogether dependent +upon the conducting power, is, I think, proved by the perfect neutrality +displayed when two metals or other substances, as acid, water, &c. &c. +(201. 186.), are opposed to each other in their action. The feeble current +which tends to be produced in the worse conductor, has its transmission +favoured in the better conductor, and the stronger current which tends to +form in the latter has its intensity diminished by the obstruction of the +former; and the forces of generation and obstruction are so perfectly +neutralize each other exactly. Now as the obstruction is inversely as the +balanced as to conducting power, the tendency to generate a current must +be directly as that power to produce this perfect equilibrium. + +214. The cause of the equality of action under the various circumstances +described, where great extent of wire (183.) or wire and water (181.) were +connected together, which yet produced such different effects upon the +magnet, is now evident and simple. + +215. The effects of a rotating substance upon a needle or magnet ought, +where ordinary magnetism has no influence, to be directly as the conducting +power of the substance; and I venture now to predict that such will be +found to be the case; and that in all those instances where non-conductors +have been supposed to exhibit this peculiar influence, the motion has been +due to some interfering cause of an ordinary kind; as mechanical +communication of motion through the parts of the apparatus, or otherwise +(as in the case Mr. Harris has pointed out[A]); or else to ordinary +magnetic attractions. To distinguish the effects of the latter from those +of the induced electric currents, I have been able to devise a most perfect +test, which shall be almost immediately described (243.). + + [A] Philosophical Transactions, 1831. p. 68. + +216. There is every reason to believe that the magnet or magnetic needle +will become an excellent measurer of the conducting power of substances +rotated near it; for I have found by careful experiment, that when a +constant current of electricity was sent successively through a series of +wires of copper, platina, zinc, silver, lead, and tin, drawn to the same +diameter; the deflection of the needle was exactly equal by them all. It +must be remembered that when bodies are rotated in a horizontal plane, the +magnetism of the earth is active upon them. As the effect is general to the +whole of the plate, it may not interfere in these cases; but in some +experiments and calculations may be of important consequence. + +217. Another point which I endeavoured to ascertain, was, whether it was +essential or not that the moving part of the wire should, in cutting the +magnetic curves, pass into positions of greater or lesser magnetic force; +or whether, always intersecting curves of equal magnetic intensity, the +mere motion was sufficient for the production of the current. That the +latter is true, has been proved already in several of the experiments on +terrestrial magneto-electric induction. Thus the electricity evolved from +the copper plate (149.), the currents produced in the rotating globe (161, +&c.), and those passing through the moving wire (171.), are all produced +under circumstances in which the magnetic force could not but be the same +during the whole experiments. + +218. To prove the point with an ordinary magnet, a copper disc was cemented +upon the end of a cylinder magnet, with paper intervening; the magnet and +disc were rotated together, and collectors (attached to the galvanometer) +brought in contact with the circumference and the central part of the +copper plate. The galvanometer needle moved as in former cases, and the +_direction_ of motion was the _same_ as that which would have resulted, if +the copper only had revolved, and the magnet been fixed. Neither was there +any apparent difference in the quantity of deflection. Hence, rotating the +magnet causes no difference in the results; for a rotatory and a stationary +magnet produce the same effect upon the moving copper. + +219. A copper cylinder, closed at one extremity, was then put over the +magnet, one half of which it inclosed like a cap; it was firmly fixed, and +prevented from touching the magnet anywhere by interposed paper. The +arrangement was then floated in a narrow jar of mercury, so that the lower +edge of the copper cylinder touched the fluid metal; one wire of the +galvanometer dipped into this mercury, and the other into a little cavity +in the centre of the end of the copper cap. Upon rotating the magnet and +its attached cylinder, abundance of electricity passed through the +galvanometer, and in the same direction as if the cylinder had rotated +only, the magnet being still. The results therefore were the same as those +with the disc (218.). + +220. That the metal of the magnet itself might be substituted for the +moving cylinder, disc, or wire, seemed an inevitable consequence, and yet +one which would exhibit the effects of magneto-electric induction in a +striking form. A cylinder magnet had therefore a little hole made in the +centre of each end to receive a drop of mercury, and was then floated pole +upwards in the same metal contained in a narrow jar. One wire from the +galvanometer dipped into the mercury of the jar, and the other into the +drop contained in the hole at the upper extremity of the axis. The magnet +was then revolved by a piece of string passed round it, and the +galvanometer-needle immediately indicated a powerful current of +electricity. On reversing the order of rotation, the electrical current was +reversed. The direction of the electricity was the same as if the copper +cylinder (219.) or a copper wire had revolved round the fixed magnet in the +same direction as that which the magnet itself had followed. Thus a +_singular independence_ of the magnetism and the bar in which it resides is +rendered evident. + +221. In the above experiment the mercury reached about halfway up the +magnet; but when its quantity was increased until within one eighth of an +inch of the top, or diminished until equally near the bottom, still the +same effects and the _same direction_ of electrical current was obtained. +But in those extreme proportions the effects did not appear so strong as +when the surface of the mercury was about the middle, or between that and +an inch from each end. The magnet was eight inches and a half long, and +three quarters of an inch in diameter. + +222. Upon inversion of the magnet, and causing rotation in the same +direction, i.e. always screw or always unscrew, then a contrary current of +electricity was produced. But when the motion of the magnet was continued +in a direction constant in relation to its _own axis_, then electricity of +the same kind was collected at both poles, and the opposite electricity at +the equator, or in its neighbourhood, or in the parts corresponding to it. +If the magnet be held parallel to the axis of the earth, with its unmarked +pole directed to the pole star, and then rotated so that the parts at its +southern side pass from west to east in conformity to the motion of the +earth; then positive electricity may be collected at the extremities of the +magnet, and negative electricity at or about the middle of its mass. + +223. When the galvanometer was very sensible, the mere spinning of the +magnet in the air, whilst one of the galvanometer wires touched the +extremity, and the other the equatorial parts, was sufficient to evolve a +current of electricity and deflect the needle. + +224. Experiments were then made with a similar magnet, for the purpose of +ascertaining whether any return of the electric current could occur at the +central or axial parts, they having the same angular velocity of rotation +as the other parts (259.) the belief being that it could not. + +225. A cylinder magnet, seven inches in length, and three quarters of an +inch in diameter, had a hole pierced in the direction of its axis from one +extremity, a quarter of an inch in diameter, and three inches deep. A +copper cylinder, surrounded by paper and amalgamated at both extremities, +was introduced so as to be in metallic contact at the bottom of the hole, +by a little mercury, with the middle of the magnet; insulated at the sides +by the paper; and projecting about a quarter of an inch above the end of +the steel. A quill was put over the copper rod, which reached to the paper, +and formed a cup to receive mercury for the completion of the circuit. A +high paper edge was also raised round that end of the magnet and mercury +put within it, which however had no metallic connexion with that in the +quill, except through the magnet itself and the copper rod (fig. 34.). The +wires A and B from the galvanometer were dipped into these two portions of +mercury; any current through them could, therefore, only pass down the +magnet towards its equatorial parts, and then up the copper rod; or vice +versa. + +226. When thus arranged and rotated screw fashion, the marked end of the +galvanometer needle went west, indicating that there was a current through +the instrument from A to B and consequently from B through the magnet and +copper rod to A (fig. 34.). + +227. The magnet was then put into a jar of mercury (fig. 35.) as before +(219.); the wire A left in contact with the copper axis, but the wire B +dipped in the mercury of the jar, and therefore in metallic communication +with the equatorial parts of the magnet instead of its polar extremity. On +revolving the magnet screw fashion, the galvanometer needle was deflected +in the same direction as before, but far more powerfully. Yet it is evident +that the parts of the magnet from the equator to the pole were out of the +electric circuit. + +228. Then the wire A was connected with the mercury on the extremity of the +magnet, the wire B still remaining in contact with that in the jar (fig. +36.), so that the copper axis was altogether out of the circuit. The magnet +was again revolved screw fashion, and again caused the same deflection of +the needle, the current being as strong as it was in the last trial (227.), +and much stronger than at first (226.). + +229. Hence it is evident that there is no discharge of the current at the +centre of the magnet, for the current, now freely evolved, is up through +the magnet; but in the first experiment (226.) it was down. In fact, at +that time, it was only the part of the moving metal equal to a little disc +extending from the end of the wire B in the mercury to the wire A that was +efficient, i.e. moving with a different angular velocity to the rest of the +circuit (258.); and for that portion the direction of the current is +consistent with the other results. + +230. In the two after experiments, the _lateral_ parts of the magnet or of +the copper rod are those which move relative to the other parts of the +circuit, i.e. the galvanometer wires; and being more extensive, +intersecting more curves, or moving with more velocity, produce the greater +effect. For the discal part, the direction of the induced electric current +is the same in all, namely, from the circumference towards the centre. + + * * * * * + +231. The law under which the induced electric current excited in bodies +moving relatively to magnets, is made dependent on the intersection of the +magnetic curves by the metal (114.) being thus rendered more precise and +definite (217. 220. 224.), seem now even to apply to the cause in the first +section of the former paper (26.); and by rendering a perfect reason for +the effects produced, take away any for supposing that peculiar condition, +which I ventured to call the electro-tonic state (60.). + +232. When an electrical current is passed through a wire, that wire is +surrounded at every part by magnetic curves, diminishing in intensity +according to their distance from the wire, and which in idea may be likened +to rings situated in planes perpendicular to the wire or rather to the +electric current within it. These curves, although different in form, are +perfectly analogous to those existing between two contrary magnetic poles +opposed to each other; and when a second wire, parallel to that which +carries the current, is made to approach the latter (18.), it passes +through magnetic curves exactly of the same kind as those it would +intersect when carried between opposite magnetic poles (109.) in one +direction; and as it recedes from the inducing wire, it cuts the curves +around it in the same manner that it would do those between the same poles +if moved in the other direction. + +233. If the wire NP (fig. 40.) have an electric current passed through it +in the direction from P to N, then the dotted ring may represent a magnetic +curve round it, and it is in such a direction that if small magnetic +needles lie placed as tangents to it, they will become arranged as in the +figure, _n_ and _s_ indicating north and south ends (14. _note_.). + +234. But if the current of electricity were made to cease for a while, and +magnetic poles were used instead to give direction to the needles, and make +them take the same position as when under the influence of the current, +then they must be arranged as at fig. 41; the marked and unmarked poles +_ab_ above the wire, being in opposite directions to those _a'b'_ below. In +such a position therefore the magnetic curves between the poles _ab_ and +_a'b'_ have the same general direction with the corresponding parts of the +ring magnetic curve surrounding the wire NP carrying an electric current. + +235. If the second wire _pn_ (fig. 40.) be now brought towards the +principal wire, carrying a current, it will cut an infinity of magnetic +curves, similar in direction to that figured, and consequently similar in +direction to those between the poles _ab_ of the magnets (fig. 41.), and it +will intersect these current curves in the same manner as it would the +magnet curves, if it passed from above between the poles downwards. Now, +such an intersection would, with the magnets, induce an electric current in +the wire from _p_ to _n_ (114.); and therefore as the curves are alike in +arrangement, the same effect ought to result from the intersection of the +magnetic curves dependent on the current in the wire NP; and such is the +case, for on approximation the induced current is in the opposite direction +to the principal current (19.). + +236. If the wire _p'n'_ be carried up from below, it will pass in the +opposite direction between the magnetic poles; but then also the magnetic +poles themselves are reversed (fig. 41.), and the induced current is +therefore (114.) still in the same direction as before. It is also, for +equally sufficient and evident reasons, in the same direction, if produced +by the influence of the curves dependent upon the wire. + +237. When the second wire is retained at rest in the vicinity the principal +wire, no current is induced through it, for it is intersecting no magnetic +curves. When it is removed from the principal wire, it intersects the +curves in the opposite direction to what it did before (235.); and a +current in the opposite direction is induced, which therefore corresponds +with the direction of the principal current (19.). The same effect would +take place if by inverting the direction of motion of the wire in passing +between either set of poles (fig. 41.), it were made to intersect the +curves there existing in the opposite direction to what it did before. + +238. In the first experiments (10. 13.), the inducing wire and that under +induction were arranged at a fixed distance from each other, and then an +electric current sent through the former. In such cases the magnetic curves +themselves must be considered as moving (if I may use the expression) +across the wire under induction, from the moment at which they begin to be +developed until the magnetic force of the current is at its utmost; +expanding as it were from the wire outwards, and consequently being in the +same relation to the fixed wire under induction as if _it_ had moved in the +opposite direction across them, or towards the wire carrying the current. +Hence the first current induced in such cases was in the contrary direction +to the principal current (17. 235.). On breaking the battery contact, the +magnetic curves (which are mere expressions for arranged magnetic forces) +may be conceived as contracting upon and returning towards the failing +electrical current, and therefore move in the opposite direction across the +wire, and cause an opposite induced current to the first. + +239. When, in experiments with ordinary magnets, the latter, in place of +being moved past the wires, were actually made near them (27. 36.), then a +similar progressive development of the magnetic curves may be considered as +having taken place, producing the effects which would have occurred by +motion of the wires in one direction; the destruction of the magnetic power +corresponds to the motion of the wire in the opposite direction. + +240. If, instead of intersecting the magnetic curves of a straight wire +carrying a current, by approximating or removing a second wire (235.), a +revolving plate be used, being placed for that purpose near the wire, and, +as it were, amongst the magnetic curves, then it ought to have continuous +electric currents induced within it; and if a line joining the wire with +the centre of the plate were perpendicular to both, then the induced +current ought to be, according to the law (114.), directly across the +plate, from one side to the other, and at right angles to the direction of +the inducing current. + +241. A single metallic wire one twentieth of an inch in diameter had an +electric current passed through it, and a small copper disc one inch and a +half in diameter revolved near to and under, but not in actual contact with +it (fig. 39). Collectors were then applied at the opposite edges of the +disc, and wires from them connected with the galvanometer. As the disc +revolved in one direction, the needle was deflected on one side: and when +the direction of revolution was reversed, the needle was inclined on the +other side, in accordance with the results anticipated. + +242. Thus the reasons which induce me to suppose a particular state in the +wire (60.) have disappeared; and though it still seems to me unlikely that +a wire at rest in the neighbourhood of another carrying a powerful electric +current is entirely indifferent to it, yet I am not aware of any distinct +_facts_ which authorize the conclusion that it is in a particular state. + + * * * * * + +243. In considering the nature of the cause assigned in these papers to +account for the mutual influence of magnets and moving metals (120.), and +comparing it with that heretofore admitted, namely, the induction of a +feeble magnetism like that produced in iron, it occurred to me that a most +decisive experimental test of the two views could be applied (215.). + +244. No other known power has like direction with that exerted between an +electric current and a magnetic pole; it is tangential, while all other +forces, acting at a distance, are direct. Hence, if a magnetic pole on one +side of a revolving plate follow its course by reason of its obedience to +the tangential force exerted upon it by the very current of electricity +which it has itself caused, a similar pole on the opposite side of the +plate should immediately set it free from this force; for the currents +which tend to be formed by the action of the two poles are in opposite +directions; or rather no current tends to be formed, or no magnetic curves +are intersected (114.); and therefore the magnet should remain at rest. On +the contrary, if the action of a north magnetic pole were to produce a +southness in the nearest part of the copper plate, and a diffuse northness +elsewhere (82.), as is really the case with iron; then the use of another +north pole on the opposite side of the same part of the plate should double +the effect instead of destroying it, and double the tendency of the first +magnet to move with the plate. + +245. A thick copper plate (85.) was therefore fixed on a vertical axis, a +bar magnet was suspended by a plaited silk cord, so that its marked pole +hung over the edge of the plate, and a sheet of paper being interposed, the +plate was revolved; immediately the magnetic pole obeyed its motion and +passed off in the same direction. A second magnet of equal size and +strength was then attached to the first, so that its marked pole should +hang _beneath_ the edge of the copper plate in a corresponding position to +that above, and at an equal distance (fig. 37.). Then a paper sheath or +screen being interposed as before, and the plate revolved, the poles were +found entirely indifferent to its motion, although either of them alone +would have followed the course of rotation. + +246. On turning one magnet round, so that _opposite_ poles were on each +side of the plate, then the mutual action of the poles and the moving metal +was a maximum. + +247. On suspending one magnet so that its axis was level with the plate, +and either pole opposite its edge, the revolution of the plate caused no +motion of the magnet. The electrical currents dependent upon induction +would now tend to be produced in a vertical direction across the thickness +of the plate, but could not be so discharged, or at least only to so slight +a degree as to leave all effects insensible; but ordinary magnetic +induction, or that on an iron plate, would be equally if not more +powerfully developed in such a position (251.). + +248. Then, with regard to the production of electricity in these +cases:--whenever motion was communicated by the plate to the magnets, +currents existed; when it was not communicated, they ceased. A marked pole +of a large bar magnet was put under the edge of the plate; collectors (86.) +applied at the axis and edge of the plate as on former occasions (fig. +38.), and these connected with the galvanometer; when the plate was +revolved, abundance of electricity passed to the instrument. The unmarked +pole of a similar magnet was then put over the place of the former pole, so +that contrary poles were above and below; on revolving the plate, the +electricity was more powerful than before. The latter magnet was then +turned end for end, so that marked poles were both above and below the +plate, and then, upon revolving it, scarcely any electricity was procured. +By adjusting the distance of the poles so as to correspond with their +relative force, they at last were brought so perfectly to neutralize each +other's inductive action upon the plate, that no electricity could be +obtained with the most rapid motion. + +249. I now proceeded to compare the effect of similar and dissimilar poles +upon iron and copper, adopting for the purpose Mr. Sturgeon's very useful +form of Arago's experiment. This consists in a circular plate of metal +supported in a vertical plane by a horizontal axis, and weighted a little +at one edge or rendered excentric so as to vibrate like a pendulum. The +poles of the magnets are applied near the side and edges of these plates, +and then the number of vibrations, required to reduce the vibrating arc a +certain constant quantity, noted. In the first description of this +instrument[A] it is said that opposite poles produced the greatest +retarding effect, and similar poles none; and yet within a page of the +place the effect is considered as of the same kind with that produced in +iron. + + [A] Edin. Phil. Journal, 1825, p. 124. + +250. I had two such plates mounted, one of copper, one of iron. The copper +plate alone gave sixty vibrations, in the average of several experiments, +before the arc of vibration was reduced from one constant mark to another. +On placing opposite magnetic poles near to, and on each side of, the same +place, the vibrations were reduced to fifteen. On putting similar poles on +each side of it, they rose to fifty; and on placing two pieces of wood of +equal size with the poles equally near, they became fifty-two. So that, +when similar poles were used, the magnetic effect was little or none, (the +obstruction being due to the confinement of the air, rather,) whilst with +opposite poles it was the greatest possible. When a pole was presented to +the edge of the plate, no retardation occurred. + +251. The iron plate alone made thirty-two vibrations, whilst the arc of +vibration diminished a certain quantity. On presenting a magnetic pole to +the edge of the plate (247.), the vibrations were diminished to eleven; and +when the pole was about half an inch from the edge, to five. + +252. When the marked pole was put at the side of the iron plate at a +certain distance, the number of vibrations was only five. When the marked +pole of the second bar was put on the opposite side of the plate at the +same distance (250.), the vibrations were reduced to two. But when the +second pole was an unmarked one, yet occupying exactly the same position, +the vibrations rose to twenty-two. By removing the stronger of these two +opposite poles a little way from the plate, the vibrations increased to +thirty-one, or nearly the original number. But on removing it _altogether_, +they fell to between five and six. + +253. Nothing can be more clear, therefore, than that with iron, and bodies +admitting of ordinary magnetic induction, _opposite_ poles on opposite +sides of the edge of the plate neutralize each other's effect, whilst +_similar_ poles exalt the action; a single pole end on is also sufficient. +But with copper, and substances not sensible to ordinary magnetic +impressions, _similar_ poles on opposite sides of the plate neutralize each +other; _opposite_ poles exalt the action; and a single pole at the edge or +end on does nothing. + +254. Nothing can more completely show the thorough independence of the +effects obtained with the metals by Arago, and those due to ordinary +magnetic forces; and henceforth, therefore, the application of two poles to +various moving substances will, if they appear at all magnetically +affected, afford a proof of the nature of that affection. If opposite poles +produce a greater effect than one pole, the result will be due to electric +currents. If similar poles produce more effect than one, then the power is +_not_ electrical; it is not like that active in the metals and carbon when +they are moving, and in most cases will probably be found to be not even +magnetical, but the result of irregular causes not anticipated and +consequently not guarded against. + +255. The result of these investigations tends to show that there are really +but very few bodies that are magnetic in the manner of iron. I have often +sought for indications of this power in the common metals and other +substances; and once in illustration of Arago's objection (82.), and in +hopes of ascertaining the existence of currents in metals by the momentary +approach of a magnet, suspended a disc of copper by a single fibre of silk +in an excellent vacuum, and approximated powerful magnets on the outside of +the jar, making them approach and recede in unison with a pendulum that +vibrated as the disc would do: but no motion could be obtained; not merely, +no indication of ordinary magnetic powers, but none or _any electric +current_ occasioned in the metal by the approximation and recession of the +magnet. I therefore venture to arrange substances in three classes as +regards their relation to magnets; first, those which are affected when at +rest, like iron, nickel, &c., being such as possess ordinary magnetic +properties; then, those which are affected when in motion, being conductors +of electricity in which are produced electric currents by the inductive +force of the magnet; and, lastly, those which are perfectly indifferent to +the magnet, whether at rest or in motion. + +256. Although it will require further research, and probably close +investigation, both experimental and mathematical, before the exact mode of +action between a magnet and metal moving relatively to each other is +ascertained; yet many of the results appear sufficiently clear and simple +to allow of expression in a somewhat general manner.--If a terminated wire +move so as to cut a magnetic curve, a power is called into action which +tends to urge an electric current through it; but this current cannot be +brought into existence unless provision be made at the ends of the wire for +its discharge and renewal. + +257. If a second wire move in the same direction as the first, the same +power is exerted upon it, and it is therefore unable to alter the condition +of the first: for there appear to be no natural differences among +substances when connected in a series, by which, when moving under the same +circumstances relative to the magnet, one tends to produce a more powerful +electric current in the whole circuit than another (201. 214.). + +258. But if the second wire move with a different velocity, or in some +other direction, then variations in the force exerted take place; and if +connected at their extremities, an electric current passes through them. + +259. Taking, then, a mass of metal or an endless wire, and referring to the +pole of the magnet as a centre of action, (which though perhaps not +strictly correct may be allowed for facility of expression, at present,) if +all parts move in the same direction, and with the same angular velocity, +and through magnetic curves of constant intensity, then no electric +currents are produced. This point is easily observed with masses subject to +the earth's magnetism, and may be proved with regard to small magnets; by +rotating them, and leaving the metallic arrangements stationary, no current +is produced. + +260. If one part of the wire or metal cut the magnetic curves, whilst the +other is stationary, then currents are produced. All the results obtained +with the galvanometer are more or less of this nature, the galvanometer +extremity being the fixed part. Even those with the wire, galvanometer, and +earth (170.), may be considered so without any error in the result. + +261. If the motion of the metal be in the same direction, but the angular +velocity of its parts relative to the pole of the magnet different, then +currents are produced. This is the case in Arago's experiment, and also in +the wire subject to the earth's induction (172.), when it was moved from +west to east. + +262. If the magnet moves not directly to or from the arrangement, but +laterally, then the case is similar to the last. + +263. If different parts move in opposite directions across the magnetic +curves, then the effect is a maximum for equal velocities. + +264. All these in fact are variations of one simple condition, namely, that +all parts of the mass shall not move in the same direction across the +curves, and with the same angular velocity. But they are forms of +expression which, being retained in the mind, I have found useful when +comparing the consistency of particular phenomena with general results. + +_Royal Institution, +December 21, 1831._ + + + + +THIRD SERIES. + + +S 7. _Identity of Electricities derived from different sources._ S 8. +_Relation by measure of common and voltaic Electricity._ + +[Read January 10th and 17th, 1833.] + + +S 7. _Identity of Electricities derived from different sources._ + + +265. The progress of the electrical researches which I have had the honour +to present to the Royal Society, brought me to a point at which it was +essential for the further prosecution of my inquiries that no doubt should +remain of the identity or distinction of electricities excited by different +means. It is perfectly true that Cavendish[A], Wollaston[B], Colladon[C], +and others, have in succession removed some of the greatest objections to +the acknowledgement of the identity of common, animal and voltaic +electricity, and I believe that most philosophers consider these +electricities as really the same. But on the other hand it is also true, +that the accuracy of Wollaston's experiments has been denied[D]; and also +that one of them, which really is no proper proof of chemical decomposition +by common electricity (309. 327.), has been that selected by several +experimenters as the test of chemical action (336. 346.). It is a fact, +too, that many philosophers are still drawing distinctions between the +electricities from different sources; or at least doubting whether their +identity is proved. Sir Humphry Davy, for instance, in his paper on the +Torpedo[E], thought it probable that animal electricity would be found of a +peculiar kind; and referring to it, to common electricity, voltaic +electricity and magnetism, has said, "Distinctions might be established in +pursuing the various modifications or properties of electricity in those +different forms, &c." Indeed I need only refer to the last volume of the +Philosophical Transactions to show that the question is by no means +considered as settled[F]. + + [A] Phil. Trans. 1779, p. 196. + + [B] Ibid. 1801, p. 434. + + [C] Annnles de Chimie, 1826, p. 62, &c. + + [D] Phil. Trans. 1832, p. 282, note. + + [E] Phil. Trans. 1892, p. 17. + + "Common electricity is excited upon non-conductors, and is readily + carried off by conductors and imperfect conductors. Voltaic + electricity is excited upon combinations of perfect and imperfect + conductors, and is only transmitted by perfect conductors or imperfect + conductors of the best kind. Magnetism, if it be a form of + electricity, belongs only to perfect conductors; and, in its + modifications, to a peculiar class of them[1]. Animal electricity + resides only in the imperfect conductors forming the organs of living + animals, &c." + + [1] Dr. Ritchie has shown this is not the case. Phil. Trans. 1832, p. + 294. + + [F] Phil. Trans. 1832, p. 259. Dr. Davy, in making experiments on the + torpedo, obtains effects the same as those produced by common and + voltaic electricity, and says that in its magnetic and chemical power + it does not seem to be essentially peculiar,--p. 274; but he then + says, p. 275, there are other points of difference; and after + referring to them, adds, "How are these differences to be explained? + Do they admit of explanation similar to that advanced by Mr. Cavendish + in his theory of the torpedo; or may we suppose, according to the + analogy of the solar ray, that the electrical power, whether excited + by the common machine, or by the voltaic battery, or by the torpedo, + is not a simple power, but a combination of powers, which may occur + variously associated, and produce all the varieties of electricity + with which we are acquainted?" + +At p. 279 of the same volume of Transactions is Dr. Ritchie's paper, +from which the following are extracts: "Common electricity is diffused +over the surface of the metal;--voltaic electricity exists within the +metal. Free electricity is conducted over the surface of the thinnest +gold leaf as effectually as over a mass of metal having the same +surface;--voltaic electricity requires thickness of metal for its +conduction," p. 280: and again, "The supposed analogy between common and +voltaic electricity, which was so eagerly traced after the invention of +the pile, completely fails in this case, which was thought to afford the +most striking resemblance." p. 291. + +266. Notwithstanding, therefore, the general impression of the identity of +electricities, it is evident that the proofs have not been sufficiently +clear and distinct to obtain the assent of all those who were competent to +consider the subject; and the question seemed to me very much in the +condition of that which Sir H. Davy solved so beautifully,--namely, whether +voltaic electricity in all cases merely eliminated, or did not in some +actually produce, the acid and alkali found after its action upon water. +The same necessity that urged him to decide the doubtful point, which +interfered with the extension of his views, and destroyed the strictness of +his reasoning, has obliged me to ascertain the identity or difference of +common and voltaic electricity. I have satisfied myself that they are +identical, and I hope the experiments which I have to offer and the proofs +flowing from them, will be found worthy the attention of the Royal Society. + +267. The various phenomena exhibited by electricity may, for the purposes +of comparison, be arranged under two heads; namely, those connected with +electricity of tension, and those belonging to electricity in motion. This +distinction is taken at present not as philosophical, but merely as +convenient. The effect of electricity of tension, at rest, is either +attraction or repulsion at sensible distances. The effects of electricity +in motion or electrical currents may be considered as 1st, Evolution of +heat; 2nd, Magnetism; 3rd, Chemical decomposition; 4th, Physiological +phenomena; 5th, Spark. It will be my object to compare electricities from +different sources, and especially common and voltaic electricities, by +their power of producing these effects. + +I. _Voltaic Electricity._ + +268. _Tension._--When a voltaic battery of 100 pairs of plates has its +extremities examined by the ordinary electrometer, it is well known that +they are found positive and negative, the gold leaves at the same extremity +repelling each other, the gold leaves at different extremities attracting +each other, even when half an inch or more of air intervenes. + +269. That ordinary electricity is discharged by points with facility +through air; that it is readily transmitted through highly rarefied air; +and also through heated air, as for instance a flame; is due to its high +tension. I sought, therefore, for similar effects in the discharge of +voltaic electricity, using as a test of the passage of the electricity +either the galvanometer or chemical action produced by the arrangement +hereafter to be described (312. 316.). + +270. The voltaic battery I had at my disposal consisted of 140 pairs of +plates four inches square, with double coppers. It was insulated +throughout, and diverged a gold leaf electrometer about one third of an +inch. On endeavouring to discharge this battery by delicate points very +nicely arranged and approximated, either in the air or in an exhausted +receiver, I could obtain no indications of a current, either by magnetic or +chemical action. In this, however, was found no point of discordance +between voltaic and common electricity; for when a Leyden battery (291.) +was charged so as to deflect the gold leaf electrometer to the same degree, +the points were found equally unable to discharge it with such effect as to +produce either magnetic or chemical action. This was not because common +electricity could not produce both these effects (307. 310.); but because +when of such low intensity the quantity required to make the effects +visible (being enormously great (371. 375.),) could not be transmitted in +any reasonable time. In conjunction with the other proofs of identity +hereafter to be given, these effects of points also prove identity instead +of difference between voltaic and common electricity. + +271. As heated air discharges common electricity with far greater facility +than points, I hoped that voltaic electricity might in this way also be +discharged. An apparatus was therefore constructed (Plate III. fig. 46.), +in which AB is an insulated glass rod upon which two copper wires, C, D, +are fixed firmly; to these wires are soldered two pieces of fine platina +wire, the ends of which are brought very close to each other at _e_, but +without touching; the copper wire C was connected with the positive pole of +a voltaic battery, and the wire D with a decomposing apparatus (312. 316.), +from which the communication was completed to the negative pole of the +battery. In these experiments only two troughs, or twenty pairs of plates, +were used. + +272. Whilst in the state described, no decomposition took place at the +point _a_, but when the side of a spirit-lamp flame was applied to the two +platina extremities at _e_, so as to make them bright red-hot, +decomposition occurred; iodine soon appeared at the point _a_, and the +transference of electricity through the heated air was established. On +raising the temperature of the points _e_ by a blowpipe, the discharge was +rendered still more free, and decomposition took place instantly. On +removing the source of heat, the current immediately ceased. On putting the +ends of the wires very close by the side of and parallel to each other, but +not touching, the effects were perhaps more readily obtained than before. +On using a larger voltaic battery (270.), they were also more freely +obtained. + +273. On removing the decomposing apparatus and interposing a galvanometer +instead, heating the points _e_ as the needle would swing one way, and +removing the heat during the time of its return (302.), feeble deflections +were soon obtained: thus also proving the current through heated air; but +the instrument used was not so sensible under the circumstances as chemical +action. + +274. These effects, not hitherto known or expected under this form, are +only cases of the discharge which takes place through air between the +charcoal terminations of the poles of a powerful battery, when they are +gradually separated after contact. Then the passage is through heated air +exactly as with common electricity, and Sir H. Davy has recorded that with +the original battery of the Royal Institution this discharge passed through +a space of at least four inches[A]. In the exhausted receiver the +electricity would _strike_ through nearly half an inch of space, and the +combined effects of rarefaction and heat were such upon the inclosed air us +to enable it to conduct the electricity through a space of six or seven +inches. + + [A] Elements of Chemical Philosophy, p. 153 + +275. The instantaneous charge of a Leyden battery by the poles of a voltaic +apparatus is another proof of the tension, and also the quantity, of +electricity evolved by the latter. Sir H. Davy says[A], "When the two +conductors from the ends of the combination were connected with a Leyden +battery, one with the internal, the other with the external coating, the +battery instantly became charged; and on removing the wires and making the +proper connexions, either a shock or a _spark_ could be perceived: and the +least possible time of contact was sufficient to renew the charge to its +full intensity." + + [A] Elements of Chemical Philosophy, p. 154. + +276. _In motion:_ i. _Evolution of Heat._--The evolution of heat in wires +and fluids by the voltaic current is matter of general notoriety. + +277. ii. _Magnetism._--No fact is better known to philosophers than the +power of the voltaic current to deflect the magnetic needle, and to make +magnets according to _certain laws_; and no effect can be more distinctive +of an electrical current. + +278. iii. _Chemical decomposition._--The chemical powers of the voltaic +current, and their subjection to _certain laws_, are also perfectly well +known. + +279. iv. _Physiological effects._--The power of the voltaic current, when +strong, to shock and convulse the whole animal system, and when weak to +affect the tongue and the eyes, is very characteristic. + +280. v. _Spark_.--The brilliant star of light produced by the discharge of +a voltaic battery is known to all as the most beautiful light that man can +produce by art. + + * * * * * + +281. That these effects may be almost infinitely varied, some being exalted +whilst others are diminished, is universally acknowledged; and yet without +any doubt of the identity of character of the voltaic currents thus made to +differ in their effect. The beautiful explication of these variations +afforded by Cavendish's theory of quantity and intensity requires no +support at present, as it is not supposed to be doubted. + +282. In consequence of the comparisons that will hereafter arise between +wires carrying voltaic and ordinary electricities, and also because of +certain views of the condition of a wire or any other conducting substance +connecting the poles of a voltaic apparatus, it will be necessary to give +some definite expression of what is called the voltaic current, in +contradistinction to any supposed peculiar state of arrangement, not +progressive, which the wire or the electricity within it may be supposed to +assume. If two voltaic troughs PN, P'N', fig. 42, be symmetrically arranged +and insulated, and the ends NP' connected by a wire, over which a magnetic +needle is suspended, the wire will exert no effect over the needle; but +immediately that the ends PN' are connected by another wire, the needle +will be deflected, and will remain so as long as the circuit is complete. +Now if the troughs merely act by causing a peculiar arrangement in the wire +either of its particles or its electricity, that arrangement constituting +its electrical and magnetic state, then the wire NP' should be in a similar +state of arrangement _before_ P and N' were connected, to what it is +afterwards, and should have deflected the needle, although less powerfully, +perhaps to one half the extent which would result when the communication is +complete throughout. But if the magnetic effects depend upon a current, +then it is evident why they could not be produced in _any_ degree before +the circuit was complete; because prior to that no current could exist. + +283. By _current_, I mean anything progressive, whether it be a fluid of +electricity, or two fluids moving in opposite directions, or merely +vibrations, or, speaking still more generally, progressive forces. By +_arrangement_, I understand a local adjustment of particles, or fluids, or +forces, not progressive. Many other reasons might be urged in support of +the view of a _current_ rather than an _arrangement_, but I am anxious to +avoid stating unnecessarily what will occur to others at the moment. + +II. _Ordinary Electricity._ + +284. By ordinary electricity I understand that which can be obtained from +the common machine, or from the atmosphere, or by pressure, or cleavage of +crystals, or by a multitude of other operations; its distinctive character +being that of great intensity, and the exertion of attractive and repulsive +powers, not merely at sensible but at considerable distances. + +285. _Tension._ The attractions and repulsions at sensible distances, +caused by ordinary electricity, are well known to be so powerful in certain +cases, as to surpass, almost infinitely, the similar phenomena produced by +electricity, otherwise excited. But still those attractions and repulsions +are exactly of the same nature as those already referred to under the head +_Tension, Voltaic electricity_ (268.); and the difference in degree between +them is not greater than often occurs between cases of ordinary electricity +only. I think it will be unnecessary to enter minutely into the proofs of +the identity of this character in the two instances. They are abundant; are +generally admitted as good; and lie upon the surface of the subject: and +whenever in other parts of the comparison I am about to draw, a similar +case occurs, I shall content myself with a mere announcement of the +similarity, enlarging only upon those parts where the great question of +distinction or identity still exists. + +286. The discharge of common electricity through heated air is a well-known +fact. The parallel case of voltaic electricity has already been described +(272, &c.). + +287. _In motion._ i. _Evolution of heat._--The heating power of common +electricity, when passed through wires or other substances, is perfectly +well known. The accordance between it and voltaic electricity is in this +respect complete. Mr. Harris has constructed and described[A] a very +beautiful and sensible instrument on this principle, in which the heat +produced in a wire by the discharge of a small portion of common +electricity is readily shown, and to which I shall have occasion to refer +for experimental proof in a future part of this paper (344.). + + [A] Philosophical Transactions, 1827, p. 18. Edinburgh Transactions, + 1831. Harris on a New Electrometer, &c. &c. + +288. ii. _Magnetism._--Voltaic electricity has most extraordinary and +exalted magnetic powers. If common electricity be identical with it, it +ought to have the same powers. In rendering needles or bars magnetic, it is +found to agree with voltaic electricity, and the _direction_ of the +magnetism, in both cases, is the same; but in deflecting the magnetic +needle, common electricity has been found deficient, so that sometimes its +power has been denied altogether, and at other times distinctions have been +hypothetically assumed for the purpose of avoiding the difficulty[A]. + + [A] Demonferrand's Manuel d'Electricite dynamique, p. 121. + +289. M. Colladon, of Geneva, considered that the difference might be due to +the use of insufficient quantities of common electricity in all the +experiments before made on this head; and in a memoir read to the Academie +des Sciences in 1826[A], describes experiments, in which, by the use of a +battery, points, and a delicate galvanometer, he succeeded in obtaining +deflections, and thus establishing identity in that respect. MM. Arago, +Ampere, and Savary, are mentioned in the paper as having witnessed a +successful repetition of the experiments. But as no other one has come +forward in confirmation, MM. Arago, Ampere, and Savary, not having +themselves published (that I am aware of) their admission of the results, +and as some have not been able to obtain them, M. Colladon's conclusions +have been occasionally doubted or denied; and an important point with me +was to establish their accuracy, or remove them entirely from the body of +received experimental research. I am happy to say that my results fully +confirm those by M. Colladon, and I should have had no occasion to describe +them, but that they are essential as proofs of the accuracy of the final +and general conclusions I am enabled to draw respecting the magnetic and +chemical action of electricity (360. 366. 367. 377. &c.). + + [A] Annales de Chimie, xxxiii. p. 62. + +290. The plate electrical machine I have used is fifty inches in diameter; +it has two sets of rubbers; its prime conductor consists of two brass +cylinders connected by a third, the whole length being twelve feet, and the +surface in contact with air about 1422 square inches. When in good +excitation, one revolution of the plate will give ten or twelve sparks from +the conductors, each an inch in length. Sparks or flashes from ten to +fourteen inches in length may easily be drawn from the conductors. Each +turn of the machine, when worked moderately, occupies about 4/5ths of a +second. + +291. The electric battery consisted of fifteen equal jars. They are coated +eight inches upwards from the bottom, and are twenty-three inches in +circumference, so that each contains one hundred and eighty-four square +inches of glass, coated on both sides; this is independent of the bottoms, +which are of thicker glass, and contain each about fifty square inches. + +292. A good _discharging train_ was arranged by connecting metallically a +sufficiently thick wire with the metallic gas pipes of the house, with the +metallic gas pipes belonging to the public gas works of London; and also +with the metallic water pipes of London. It was so effectual in its office +as to carry off instantaneously electricity of the feeblest tension, even +that of a single voltaic trough, and was essential to many of the +experiments. + +293. The galvanometer was one or the other of those formerly described (87. +205.), but the glass jar covering it and supporting the needle was coated +inside and outside with tinfoil, and the upper part (left uncoated, that +the motions of the needle might be examined,) was covered with a frame of +wire-work, having numerous sharp points projecting from it. When this frame +and the two coatings were connected with the discharging train (292.), an +insulated point or ball, connected with the machine when most active, might +be brought within an inch of any part of the galvanometer, yet without +affecting the needle within by ordinary electrical attraction or repulsion. + +294. In connexion with these precautions, it may be necessary to state that +the needle of the galvanometer is very liable to have its magnetic power +deranged, diminished, or even inverted by the passage of a shock through +the instrument. If the needle be at all oblique, in the wrong direction, to +the coils of the galvanometer when the shock passes, effects of this kind +are sure to happen. + +295. It was to the retarding power of bad conductors, with the intention of +diminishing its _intensity_ without altering its _quantity_, that I first +looked with the hope of being able to make common electricity assume more +of the characters and power of voltaic electricity, than it is usually +supposed to have. + +296, The coating and armour of the galvanometer were first connected with +the discharging train (292.); the end B (87.) of the galvanometer wire was +connected with the outside coating of the battery, and then both these with +the discharging train; the end A of the galvanometer wire was connected +with a discharging rod by a wet thread four feet long; and finally, when +the battery (291.) had been positively charged by about forty turns of the +machine, it was discharged by the rod and the thread through the +galvanometer. The needle immediately moved. + +297. During the time that the needle completed its vibration in the first +direction and returned, the machine was worked, and the battery recharged; +and when the needle in vibrating resumed its first direction, the discharge +was again made through the galvanometer. By repeating this action a few +times, the vibrations soon extended to above 40 deg. on each side of the line +of rest. + +298. This effect could be obtained at pleasure. Nor was it varied, +apparently, either in direction or degree, by using a short thick string, +or even four short thick strings in place of the long fine thread. With a +more delicate galvanometer, an excellent swing of the needle could be +obtained by one discharge of the battery. + +299. On reversing the galvanometer communications so as to pass the +discharge through from B to A, the needle was equally well deflected, but +in the opposite direction. + +300. The deflections were in the same direction as if a voltaic current had +been passed through the galvanometer, i.e. the positively charged surface +of the electric battery coincided with the positive end of the voltaic +apparatus (268.) and the negative surface of the former with the negative +end of the latter. + +301. The battery was then thrown out of use, and the communications so +arranged that the current could be passed from the prime conductor, by the +discharging rod held against it, through the wet string, through the +galvanometer coil, and into the discharging train (292), by which it was +finally dispersed. This current could be stopped at any moment, by removing +the discharging rod, and either stopping the machine or connecting the +prime conductor by another rod with the discharging train; and could be as +instantly renewed. The needle was so adjusted, that whilst vibrating in +moderate and small arcs, it required time equal to twenty-five beats of a +watch to pass in one direction through the arc, and of course an equal time +to pass in the other direction. + +302. Thus arranged, and the needle being stationary, the current, direct +from the machine, was sent through the galvanometer for twenty-five beats, +then interrupted for other twenty-five beats, renewed for twenty-five beats +more, again interrupted for an equal time, and so on continually. The +needle soon began to vibrate visibly, and after several alternations of +this kind, the vibration increased to 40 deg. or more. + +303. On changing the direction of the current through the galvanometer, the +direction of the deflection of the needle was also changed. In all cases +the motion of the needle was in direction the same as that caused either by +the use of the electric battery or a voltaic trough (300). + +304. I now rejected the wet string, and substituted a copper wire, so that +the electricity of the machine passed at once into wires communicating +directly with the discharging train, the galvanometer coil being one of the +wires used for the discharge. The effects were exactly those obtained above +(302). + +305. Instead of passing the electricity through the system, by bringing the +discharging rod at the end of it into contact with the conductor, four +points were fixed on to the rod; when the current was to pass, they were +held about twelve inches from the conductor, and when it was not to pass, +they were turned away. Then operating as before (302.), except with this +variation, the needle was soon powerfully deflected, and in perfect +consistency with the former results. Points afforded the means by which +Colladon, in all cases, made his discharges. + +306. Finally, I passed the electricity first through an exhausted receiver, +so as to make it there resemble the aurora borealis, and then through the +galvanometer to the earth; and it was found still effective in deflecting +the needle, and apparently with the same force as before. + +307. From all these experiments, it appears that a current of common +electricity, whether transmitted through water or metal, or rarefied air, +or by means of points in common air, is still able to deflect the needle; +the only requisite being, apparently, to allow time for its action: that it +is, in fact, just as magnetic in every respect as a voltaic current, and +that in this character therefore no distinction exists. + +308. Imperfect conductors, as water, brine, acids, &c. &c. will be found +far more convenient for exhibiting these effects than other modes of +discharge, as by points or balls; for the former convert at once the charge +of a powerful battery into a feeble spark discharge, or rather continuous +current, and involve little or no risk of deranging the magnetism of the +needles (294.). + +309. iii. _Chemical decomposition._--The chemical action of voltaic +electricity is characteristic of that agent, but not more characteristic +than are the _laws_ under which the bodies evolved by decomposition arrange +themselves at the poles. Dr. Wollaston showed[A] that common electricity +resembled it in these effects, and "that they are both essentially the +same"; but he mingled with his proofs an experiment having a resemblance, +and nothing more, to a case of voltaic decomposition, which however he +himself partly distinguished; and this has been more frequently referred to +by some, on the one hand, to prove the occurrence of electro-chemical +decomposition, like that of the pile, and by others to throw doubt upon the +whole paper, than the more numerous and decisive experiments which he has +detailed. + + [A] Philosophical Transactions, 1801, pp. 427, 434. + +310. I take the liberty of describing briefly my results, and of thus +adding my testimony to that of Dr. Wollaston on the identity of voltaic and +common electricity as to chemical action, not only that I may facilitate +the repetition of the experiments, but also lead to some new consequences +respecting electrochemical decomposition (376. 377.). + +311. I first repeated Wollaston's fourth experiment[A], in which the ends +of coated silver wires are immersed in a drop of sulphate of copper. By +passing the electricity of the machine through such an arrangement, that +end in the drop which received the electricity became coated with metallic +copper. One hundred turns of the machine produced an evident effect; two +hundred turns a very sensible one. The decomposing action was however very +feeble. Very little copper was precipitated, and no sensible trace of +silver from the other pole appeared in the solution. + + [A] Philosophical Transactions, 1801, p. 429. + +312. A much more convenient and effectual arrangement for chemical +decompositions by common electricity, is the following. Upon a glass plate, +fig. 43, placed over, but raised above a piece of white paper, so that +shadows may not interfere, put two pieces of tinfoil _a, b_; connect one of +these by an insulated wire _c_, or wire and string (301.) with the machine, +and the other _g_, with the discharging train (292.) or the negative +conductor; provide two pieces of fine platina wire, bent as in fig. 44, so +that the part _d, f_ shall be nearly upright, whilst the whole is resting +on the three bearing points _p, e, f_ place these as in fig. 43; the points +_p, n_ then become the decomposing poles. In this way surfaces of contact, +as minute as possible, can be obtained at pleasure, and the connexion can +be broken or renewed in a moment, and the substances acted upon examined +with the utmost facility. + +313. A coarse line was made on the glass with solution of sulphate of +copper, and the terminations _p_ and _n_ put into it; the foil _a_ was +connected with the positive conductor of the machine by wire and wet +string, so that no sparks passed: twenty turns of the machine caused the +precipitation of so much copper on the end _n_, that it looked like copper +wire; no apparent change took place at _p_. + +314. A mixture of equal parts of muriatic acid and water was rendered deep +blue by sulphate of indigo, and a large drop put on the glass, fig. 43, so +that _p_ and _n_ were immersed at opposite sides: a single turn of the +machine showed bleaching effects round _p_, from evolved chlorine. After +twenty revolutions no effect of the kind was visible at _n_, but so much +chlorine had been set free at _p_, that when the drop was stirred the whole +became colourless. + +315. A drop of solution of iodide of potassium mingled with starch was put +into the same position at _p_ and _n_; on turning the machine, iodine was +evolved at _p_, but not at _n_. + +316. A still further improvement in this form of apparatus consists in +wetting a piece of filtering paper in the solution to be experimented on, +and placing that under the points _p_ and _n_, on the glass: the paper +retains the substance evolved at the point of evolution, by its whiteness +renders any change of colour visible, and allows of the point of contact +between it and the decomposing wires being contracted to the utmost degree. +A piece of paper moistened in the solution of iodide of potassium and +starch, or of the iodide alone, with certain precautions (322.), is a most +admirable test of electro-chemical action; and when thus placed and acted +upon by the electric current, will show iodine evolved at _p_ by only half +a turn of the machine. With these adjustments and the use of iodide of +potassium on paper, chemical action is sometimes a more delicate test of +electrical currents than the galvanometer (273.). Such cases occur when the +bodies traversed by the current are bad conductors, or when the quantity of +electricity evolved or transmitted in a given time is very small. + +317. A piece of litmus paper moistened in solution of common salt or +sulphate of soda, was quickly reddened at _p_. A similar piece moistened in +muriatic acid was very soon bleached at _p_. No effects of a similar kind +took place at _n_. + +318. A piece of turmeric paper moistened in solution of sulphate of soda +was reddened at _n_ by two or three turns of the machine, and in twenty or +thirty turns plenty of alkali was there evolved. On turning the paper +round, so that the spot came under _p_, and then working the machine, the +alkali soon disappeared, the place became yellow, and a brown alkaline spot +appeared in the new part under _n_. + +319. On combining a piece of litmus with a piece of turmeric paper, wetting +both with solution of sulphate of soda, and putting the paper on the glass, +so that _p_ was on the litmus and _n_ on the turmeric, a very few turns of +the machine sufficed to show the evolution of acid at the former and alkali +at the latter, exactly in the manner effected by a volta-electric current. + +320. All these decompositions took place equally well, whether the +electricity passed from the machine to the foil _a_, through water, or +through wire only; by _contact_ with the conductor, or by _sparks_ there; +provided the sparks were not so large as to cause the electricity to pass +in sparks from _p_ to _n_, or towards _n_; and I have seen no reason to +believe that in cases of true electro-chemical decomposition by the +machine, the electricity passed in sparks from the conductor, or at any +part of the current, is able to do more, because of its tension, than that +which is made to pass merely as a regular current. + +321. Finally, the experiment was extended into the following form, +supplying in this case the tidiest analogy between common and voltaic +electricity. Three compound pieces of litmus and turmeric paper (319.) were +moistened in solution of sulphate of soda, and arranged on a plate of glass +with platina wires, as in fig. 45. The wire _m_ was connected with the +prime conductor of the machine, the wire _t_ with the discharging train, +and the wires _r_ and _s_ entered into the course of the electrical current +by means of the pieces of moistened paper; they were so bent as to rest +each on three points, _n, r, p; n, s, p_, the points _r_ and _s_ being +supported by the glass, and the others by the papers; the three +terminations _p, p, p_ rested on the litmus, and the other three _n, n, n_ +on the turmeric paper. On working the machine for a short time only, acid +was evolved at _all_ the poles or terminations _p, p, p_, by which the +electricity entered the solution, and alkali at the other poles _n, n, n_, +by which the electricity left the solution. + +322. In all experiments of electro-chemical decomposition by the common +machine and moistened papers (316.), it is necessary to be aware of and to +avoid the following important source of error. If a spark passes over +moistened litmus and turmeric paper, the litmus paper (provided it be +delicate and not too alkaline,) is reddened by it; and if several sparks +are passed, it becomes powerfully reddened. If the electricity pass a +little way from the wire over the surface of the moistened paper, before it +finds mass and moisture enough to conduct it, then the reddening extends as +far as the ramifications. If similar ramifications occur at the termination +_n_, on the turmeric paper, they _prevent_ the occurrence of the red spot +due to the alkali, which would otherwise collect there: sparks or +ramifications from the points _n_ will also redden litmus paper. If paper +moistened by a solution of iodide of potassium (which is an admirably +delicate test of electro-chemical action,) be exposed to the sparks or +ramifications, or even a feeble stream of electricity through the air from +either the point _p_ or _n_, iodine will be immediately evolved. + +323. These effects must not be confounded with those due to the true +electro-chemical powers of common electricity, and must be carefully +avoided when the latter are to be observed. No sparks should be passed, +therefore, in any part of the current, nor any increase of intensity +allowed, by which the electricity may be induced to pass between the +platina wires and the moistened papers, otherwise than by conduction; for +if it burst through the air, the effect referred to above (322.) ensues. + +324. The effect itself is due to the formation of nitric acid by the +combination of the oxygen and nitrogen of the air, and is, in fact, only a +delicate repetition of Cavendish's beautiful experiment. The acid so +formed, though small in quantity, is in a high state of concentration as to +water, and produces the consequent effects of reddening the litmus paper; +or preventing the exhibition of alkali on the turmeric paper; or, by acting +on the iodide of potassium, evolving iodine. + +325. By moistening a very small slip of litmus paper in solution of caustic +potassa, and then passing the electric spark over its length in the air, I +gradually neutralized the alkali, and ultimately rendered the paper red; on +drying it, I found that nitrate of potassa had resulted from the operation, +and that the paper had become touch-paper. + +326. Either litmus paper or white paper, moistened in a strong solution of +iodide of potassium, offers therefore a very simple, beautiful, and ready +means of illustrating Cavendish's experiment of the formation of nitric +acid from the atmosphere. + +327. I have already had occasion to refer to an experiment (265. 309.) made +by Dr. Wollaston, which is insisted upon too much, both by those who oppose +and those who agree with the accuracy of his views respecting the identity +of voltaic and ordinary electricity. By covering fine wires with glass or +other insulating substances, and then removing only so much matter as to +expose the point, or a section of the wires, and by passing electricity +through two such wires, the guarded points of which were immersed in water, +Wollaston found that the water could be decomposed even by the current from +the machine, without sparks, and that two streams of gas arose from the +points, exactly resembling, in appearance, those produced by voltaic +electricity, and, like the latter, giving a mixture of oxygen and hydrogen +gases. But Dr. Wollaston himself points out that the effect is different +from that of the voltaic pile, inasmuch as both oxygen and hydrogen are +evolved from _each_ pole; he calls it "a very close _imitation_ of the +galvanic phenomena," but adds that "in fact the resemblance is not +complete," and does not trust to it to establish the principles correctly +laid down in his paper. + +328. This experiment is neither more nor less than a repetition, in a +refined manner, of that made by Dr. Pearson in 1797[A], and previously by +MM. Paets Van Troostwyk and Deiman in 1789 or earlier. That the experiment +should never be quoted as proving true electro-chemical decomposition, is +sufficiently evident from the circumstance, that the _law_ which regulates +the transference and final place of the evolved bodies (278. 309.) has no +influence here. The water is decomposed at both poles independently of each +other, and the oxygen and hydrogen evolved at the wires are the elements of +the water existing the instant before in those places. That the poles, or +rather points, have no mutual decomposing dependence, may be shown by +substituting a wire, or the finger, for one of them, a change which does +not at all interfere with the other, though it stops all action at the +changed pole. This fact may be observed by turning the machine for some +time; for though bubbles will rise from the point left unaltered, in +quantity sufficient to cover entirely the wire used for the other +communication, if they could be applied to it, yet not a single bubble will +appear on that wire. + + [A] Nicholson's Journal, 4to. vol. I. pp. 311, 299. 349. + +329. When electro-chemical decomposition takes place, there is great reason +to believe that the _quantity_ of matter decomposed is not proportionate to +the intensity, but to the quantity of electricity passed (320.). Of this I +shall be able to offer some proofs in a future part of this paper (375. +377.). But in the experiment under consideration, this is not the case. If, +with a constant pair of points, the electricity be passed from the machine +in sparks, a certain proportion of gas is evolved; but if the sparks be +rendered shorter, less gas is evolved; and if no sparks be passed, there is +scarcely a sensible portion of gases set free. On substituting solution of +sulphate of soda for water, scarcely a sensible quantity of gas could be +procured even with powerful sparks, and nearly none with the mere current; +yet the quantity of electricity in a given time was the same in all these +cases. + +330. I do not intend to deny that with such an apparatus common electricity +can decompose water in a manner analogous to that of the voltaic pile; I +believe at present that it can. But when what I consider the true effect +only was obtained, the quantity of gas given off was so small that I could +not ascertain whether it was, as it ought to be, oxygen at one wire and +hydrogen at the other. Of the two streams one seemed more copious than the +other, and on turning the apparatus round, still the same side in relation +to the machine; gave the largest stream. On substituting solution of +sulphate of soda for pure water (329.), these minute streams were still +observed. But the quantities were so small, that on working the machine for +half an hour I could not obtain at either pole a bubble of gas larger than +a small grain of sand. If the conclusion which I have drawn (377.) relating +to the amount of chemical action be correct, this ought to be the case. + +331. I have been the more anxious to assign the true value of this +experiment as a test of electro-chemical action, because I shall have +occasion to refer to it in cases of supposed chemical action by +magneto-electric and other electric currents (336. 346.) and elsewhere. +But, independent of it, there cannot be now a doubt that Dr. Wollaston was +right in his general conclusion; and that voltaic and common electricity +have powers of chemical decomposition, alike in their nature, and governed +by the same law of arrangement. + +332. iv. _Physiological effects._--The power of the common electric current +to shock and convulse the animal system, and when weak to affect the tongue +and the eyes, may be considered as the same with the similar power of +voltaic electricity, account being taken of the intensity of the one +electricity and duration of the other. When a wet thread was interposed in +the course of the current of common electricity from the battery (291.) +charged by eight or ten[A] revolutions of the machine in good action +(290.), and the discharge made by platina spatulas through the tongue or +the gums, the effect upon the tongue and eyes was exactly that of a +momentary feeble voltaic circuit. + + [A] Or even from thirty to forty. + +333. v. _Spark._--The beautiful flash of light attending the discharge of +common electricity is well known. It rivals in brilliancy, if it does not +even very much surpass, the light from the discharge of voltaic +electricity; but it endures for an instant only, and is attended by a sharp +noise like that of a small explosion. Still no difficulty can arise in +recognising it to be the same spark as that from the voltaic battery, +especially under certain circumstances. The eye cannot distinguish the +difference between a voltaic and a common electricity spark, if they be +taken between amalgamated surfaces of metal, at intervals only, and through +the same distance of air. + +334. When the Leyden battery (291.) was discharged through a wet string +placed in some part of the circuit away from the place where the spark was +to pass, the spark was yellowish, flamy, having a duration sensibly longer +than if the water had not been interposed, was about three-fourths of an +inch in length, was accompanied by little or no noise, and whilst losing +part of its usual character had approximated in some degree to the voltaic +spark. When the electricity retarded by water was discharged between pieces +of charcoal, it was exceedingly luminous and bright upon both surfaces of +the charcoal, resembling the brightness of the voltaic discharge on such +surfaces. When the discharge of the unretarded electricity was taken upon +charcoal, it was bright upon both the surfaces, (in that respect resembling +the voltaic spark,) but the noise was loud, sharp, and ringing. + +335. I have assumed, in accordance, I believe, with the opinion of every +other philosopher, that atmospheric electricity is of the same nature with +ordinary electricity (284.), and I might therefore refer to certain +published statements of chemical effects produced by the former as proofs +that the latter enjoys the power of decomposition in common with voltaic +electricity. But the comparison I am drawing is far too rigorous to allow +me to use these statements without being fully assured of their accuracy; +yet I have no right to suppress them, because, if accurate, they establish +what I am labouring to put on an undoubted foundation, and have priority to +my results. + +336. M. Bonijol of Geneva[A] is said to have constructed very delicate +apparatus for the decomposition of water by common electricity. By +connecting an insulated lightning rod with his apparatus, the decomposition +of the water proceeded in a continuous and rapid manner even when the +electricity of the atmosphere was not very powerful. The apparatus is not +described; but as the diameter of the wire is mentioned as very small, it +appears to have been similar in construction to that of Wollaston (327.); +and as that does not furnish a case of true polar electro-chemical +decomposition (328.), this result of M. Bonijol does not prove the identity +in chemical action of common and voltaic electricity. + + [A] Bibliotheque Universelle, 1830, tome xlv. p. 213. + +337. At the same page of the Bibliotheque Universelle, M. Bonijol is said +to have decomposed, _potash_, and also chloride of silver, by putting them +into very narrow tubes and passing electric sparks from an ordinary machine +over them. It is evident that these offer no analogy to cases of true +voltaic decomposition, where the electricity only decomposes when it is +_conducted_ by the body acted upon, and ceases to decompose, according to +its ordinary laws, when it passes in sparks. These effects are probably +partly analogous to that which takes place with water in Pearson's or +Wollaston's apparatus, and may be due to very high temperature acting on +minute portions of matter; or they may be connected with the results in air +(322.). As nitrogen can combine directly with oxygen under the influence of +the electric spark (324.), it is not impossible that it should even take it +from the potassium of the potash, especially as there would be plenty of +potassa in contact with the acting particles to combine with the nitric +acid formed. However distinct all these actions may be from true polar +electro-chemical decompositions, they are still highly important, and +well-worthy of investigation. + +338. The late Mr. Barry communicated a paper to the Royal Society[A] last +year, so distinct in the details, that it would seem at once to prove the +identity in chemical action of common and voltaic electricity; but, when +examined, considerable difficulty arises in reconciling certain of the +effects with the remainder. He used two tubes, each having a wire within it +passing through the closed end, as is usual for voltaic decompositions. The +tubes were filled with solution of sulphate of soda, coloured with syrup of +violets, and connected by a portion of the same solution, in the ordinary +manner; the wire in one tube was connected by a _gilt thread_ with the +string of an insulated electrical kite, and the wire in the other tube by a +similar _gilt thread_ with the ground. Hydrogen soon appeared in the tube +connected with the kite, and oxygen in the other, and in ten minutes the +liquid in the first tube was green from the alkali evolved, and that in the +other red from free acid produced. The only indication of the strength or +intensity of the atmospheric electricity is in the expression, "the usual +shocks were felt on touching the string." + + [A] Philosophical Transactions, 1831, p. 165. + +339. That the electricity in this case does not resemble that from any +ordinary source of common electricity, is shown by several circumstances. +Wollaston could not effect the decomposition of water by such an +arrangement, and obtain the gases in _separate_ vessels, using common +electricity; nor have any of the numerous philosophers, who have employed +such an apparatus, obtained any such decomposition, either of water or of a +neutral salt, by the use of the machine. I have lately tried the large +machine (290.) in full action for a quarter of an hour, during which time +seven hundred revolutions were made, without producing any sensible +effects, although the shocks that it would then give must have been far +more powerful and numerous than could have been taken, with any chance of +safety, from an electrical kite-string; and by reference to the comparison +hereafter to be made (371.), it will be seen that for common electricity to +have produced the effect, the quantity must have been awfully great, and +apparently far more than could have been conducted to the earth by a gilt +thread, and at the same time only have produced the "usual shocks." + +340. That the electricity was apparently not analogous to voltaic +electricity is evident, for the "usual shocks" only were produced, and +nothing like the terrible sensation due to a voltaic battery, even when it +has a tension so feeble as not to strike through the eighth of an inch of +air. + +341. It seems just possible that the air which was passing by the kite and +string, being in an electrical state sufficient to produce the "usual +shocks" only, could still, when the electricity was drawn off below, renew +the charge, and so continue the current. The string was 1500 feet long, and +contained two double threads. But when the enormous quantity which must +have been thus collected is considered (371. 376.), the explanation seems +very doubtful. I charged a voltaic battery of twenty pairs of plates four +inches square with double coppers very strongly, insulated it, connected +its positive extremity with the discharging train (292.), and its negative +pole with an apparatus like that of Mr. Barry, communicating by a wire +inserted three inches into the wet soil of the ground. This battery thus +arranged produced feeble decomposing effects, as nearly as I could judge +answering the description Mr. Barry has given. Its intensity was, of +course, far lower than the electricity of the kite-string, but the supply +of quantity from the discharging train was unlimited. It gave no shocks to +compare with the "usual shocks" of a kite-string. + +342. Mr. Barry's experiment is a very important one to repeat and verify. +If confirmed, it will be, as far as I am aware, the first recorded case of +true electro-chemical decomposition of water by common electricity, and it +will supply a form of electrical current, which, both in quantity and +intensity, is exactly intermediate with those of the common electrical +machine and the voltaic pile. + + * * * * * + +III. _Magneto-Electricity._ + +343. _Tension_.--The attractions and repulsions due to the tension of +ordinary electricity have been well observed with that evolved by +magneto-electric induction. M. Pixii, by using an apparatus, clever in its +construction and powerful in its action[A], was able to obtain great +divergence of the gold leaves of an electrometer[B]. + + [A] Annales de Chimie, l. p. 322. + + [B] Ibid. li. p 77. + +344. _In motion_: i. _Evolution of Heat._--The current produced by +magneto-electric induction can heat a wire in the manner of ordinary +electricity. At the British Association of Science at Oxford, in June of +the present year, I had the pleasure, in conjunction with Mr. Harris, +Professor Daniell, Mr. Duncan, and others, of making an experiment, for +which the great magnet in the museum, Mr. Harris's new electrometer (287.), +and the magneto-electric coil described in my first paper (34.), were put +in requisition. The latter had been modified in the manner I have elsewhere +described[A] so as to produce an electric spark when its contact with the +magnet was made or broken. The terminations of the spiral, adjusted so as +to have their contact with each other broken when the spark was to pass, +were connected with the wire in the electrometer, and it was found that +each time the magnetic contact was made and broken, expansion of the air +within the instrument occurred, indicating an increase, at the moment, of +the temperature of the wire. + + [A] Phil, Mag. and Annals, 1832, vol. xi. p. 405. + +315. ii. _Magnetism._--These currents were discovered by their magnetic +power. + +346. iii. _Chemical decomposition._--I have made many endeavours to effect +chemical decomposition by magneto-electricity, but unavailingly. In July +last I received an anonymous letter (which has since been published[A],) +describing a magneto-electric apparatus, by which the decomposition of +water was effected. As the term "guarded points" is used, I suppose the +apparatus to have been Wollaston's (327. &c.), in which case the results +did not indicate polar electro-chemical decomposition. Signor Botto has +recently published certain results which he has obtained[B]; but they are, +as at present described, inconclusive. The apparatus he used was apparently +that of Dr. Wollaston, which gives only fallacious indications (327. &c.). +As magneto-electricity can produce sparks, it would be able to show the +effects proper to this apparatus. The apparatus of M. Pixii already +referred to (343.) has however, in the hands of himself[C] and M. +Hachctte[D], given decisive chemical results, so as to complete this link +in the chain of evidence. Water was decomposed by it, and the oxygen and +hydrogen obtained in separate tubes according to the law governing +volta-electric and machine-electric decomposition. + + [A] Lond. and Edinb. Phil. Mag. and Journ., 1832, vol. i. p. 161. + + [B] Ibid. 1832. vol. i. p. 441. + + [C] Annales de Chimie, li, p. 77. + + [D] Ibid. li. p. 72 + +347. iv. _Physiological effects._--A frog was convulsed in the earliest +experiments on these currents (56.). The sensation upon the tongue, and the +flash before the eyes, which I at first obtained only in a feeble degree +(56.), have been since exalted by more powerful apparatus, so as to become +even disagreeable. + +348. v. _Spark._--The feeble spark which I first obtained with these +currents (32.), has been varied and strengthened by Signori Nobili and +Antinori, and others, so as to leave no doubt as to its identity with the +common electric spark. + + * * * * * + +IV. _Thermo-Electricity._ + +349. With regard to thermo-electricity, (that beautiful form of electricity +discovered by Seebeck,) the very conditions under which it is excited are +such as to give no ground for expecting that it can be raised like common +electricity to any high degree of tension; the effects, therefore, due to +that state are not to be expected. The sum of evidence respecting its +analogy to the electricities already described, is, I believe, as +follows:--_Tension._ The attractions and repulsions due to a certain degree +of tension have not been observed. _In currents_: i. _Evolution of Heat._ I +am not aware that its power of raising temperature has been observed. ii. +_Magnetism._ It was discovered, and is best recognised, by its magnetic +powers. iii. _Chemical decomposition_ has not been effected by it. iv. +_Physiological effects._ Nobili has shown[A] that these currents are able +to cause contractions in the limbs of a frog. v. _Spark._ The spark has not +yet been seen. + + [A] Bibliotheque Universelle, xxxvii. 15. + +350. Only those effects are weak or deficient which depend upon a certain +high degree of intensity; and if common electricity be reduced in that +quality to a similar degree with the thermo-electricity, it can produce no +effects beyond the latter. + + * * * * * + +V. _Animal Electricity._ + +351. After an examination of the experiments of Walsh[A] Ingenhousz[B], +Cavendish[C], Sir H. Davy[D], and Dr. Davy[E], no doubt remains on my mind +as to the identity of the electricity of the torpedo with common and +voltaic electricity; and I presume that so little will remain on the minds +of others as to justify my refraining from entering at length into the +philosophical proofs of that identity. The doubts raised by Sir H. Davy +have been removed by his brother Dr. Davy; the results of the latter being +the reverse of those of the former. At present the sum of evidence is as +follows:-- + + [A] Philosophical Transactions, 1773, p. 461. + + [B] Ibid. 1775, p. 1. + + [C] Ibid. 1776, p. 196. + + [D] Ibid. 1829, p. 15. + + [E] Ibid. 1832, p. 259. + +352. _Tension._--No sensible attractions or repulsions due to tension have +been observed. + +353. _In motion_: i. Evolution of Heat; not yet observed; I have little or +no doubt that Harris's electrometer would show it (287. 359.). + +354. ii. _Magnetism._--Perfectly distinct. According to Dr. Davy[A], the +current deflected the needle and made magnets under the same law, as to +direction, which governs currents of ordinary and voltaic electricity. + + [A] Philosophical Transactions, 1832, p. 260. + +355. iii. _Chemical decomposition._--Also distinct; and though Dr. Davy +used an apparatus of similar construction with that of Dr. Wollaston +(327.), still no error in the present case is involved, for the +decompositions were polar, and in their nature truly electro-chemical. By +the direction of the magnet it was found that the under surface of the fish +was negative, and the upper positive; and in the chemical decompositions, +silver and lead were precipitated on the wire connected with the under +surface, and not on the other; and when these wires were either steel or +silver, in solution of common salt, gas (hydrogen?) rose from the negative +wire, but none from the positive. + +356. Another reason for the decomposition being electrochemical is, that a +Wollaston's apparatus constructed with _wires_, coated by sealing-wax, +would most probably not have decomposed water, even in its own peculiar +way, unless the electricity had risen high enough in intensity to produce +sparks in some part of the circuit; whereas the torpedo was not able to +produce sensible sparks. A third reason is, that the purer the water in +Wollaston's apparatus, the more abundant is the decomposition; and I have +found that a machine and wire points which succeeded perfectly well with +distilled water, failed altogether when the water was rendered a good +conductor by sulphate of soda, common salt, or other saline bodies. But in +Dr. Davy's experiments with the torpedo, _strong_ solutions of salt, +nitrate of silver, and superacetate of lead were used successfully, and +there is no doubt with more success than weaker ones. + +357. iv. _Physiological effects._--These are so characteristic, that by +them the peculiar powers of the torpedo and gymnotus are principally +recognised. + +358. v. _Spark._--The electric spark has not yet been obtained, or at least +I think not; but perhaps I had better refer to the evidence on this point. +Humboldt, speaking of results obtained by M. Fahlberg, of Sweden, says, +"This philosopher has seen an electric spark, as Walsh and Ingenhousz had +done before him in London, by placing the gymnotus in the air, and +interrupting the conducting chain by two gold leaves pasted upon glass, and +a line distant from each other[A]." I cannot, however, find any record of +such an observation by either Walsh or Ingenhousz, and do not know where to +refer to that by M. Fahlberg. M. Humboldt could not himself perceive any +luminous effect. + + [A] Edinburgh Phil. Journal, ii. p. 249. + +Again, Sir John Leslie, in his dissertation on the progress of mathematical +and physical science, prefixed to the seventh edition of the Encyclopaedia +Britannica, Edinb. 1830, p. 622, says, "From a healthy specimen" of the +_Silurus electricus,_ meaning rather the _gymnotus_, "exhibited in London, +vivid sparks were drawn in a darkened room"; but he does not say he saw +them himself, nor state who did see them; nor can I find any account of +such a phenomenon; so that the statement is doubtful[A]. + + [A] Mr. Brayley, who referred me to those statements, and has + extensive knowledge of recorded facts, is unacquainted with any + further account relating to them. + +359. In concluding this summary of the powers of torpedinal electricity, I +cannot refrain from pointing out the enormous absolute quantity of +electricity which the animal must put in circulation at each effort. It is +doubtful whether any common electrical machine has as yet been able to +supply electricity sufficient in a reasonable time to cause true +electro-chemical decomposition of water (330. 339.), yet the current from +the torpedo has done it. The same high proportion is shown by the magnetic +effects (296. 371.). These circumstances indicate that the torpedo has +power (in the way probably that Cavendish describes,) to continue the +evolution for a sensible time, so that its successive discharges rather +resemble those of a voltaic arrangement, intermitting in its action, than +those of a Leyden apparatus, charged and discharged many times in +succession. In reality, however, there is _no philosophical difference_ +between these two cases. + +360. The _general conclusion_ which must, I think, be drawn from this +collection of facts is, that _electricity, whatever may be its source, is +identical in its nature_. The phenomena in the five kinds or species +quoted, differ, not in their character but only in degree; and in that +respect vary in proportion to the variable circumstances of _quantity_ and +_intensity_[A] which can at pleasure be made to change in almost any one of +the kinds of electricity, as much as it does between one kind and another. + + [A] The term _quantity_ in electricity is perhaps sufficiently definite +as to sense; the term _intensity_ is more difficult to define strictly. +I am using the terms in their ordinary and accepted meaning. + +Table of the experimental Effects common to the Electricities derived from +different Sources[A]. + +Table headings + +A: Physiological Effects +B: Magnetic Deflection. +C: Magnets made. +D: Spark. +E: Heating Power. +F: True chemical Action. +G: Attraction and Repulsion. +H: Discharge by Hot Air. + _________________________________________________________ +| | | | | | | | | | +| | A | B | C | D | E | F | G | H | +|_________________________|___|___|___|___|___|___|___|___| +| | | | | | | | | | +| 1. Voltaic electricity | X | X | X | X | X | X | X | X | +|_________________________|___|___|___|___|___|___|___|___| +| | | | | | | | | | +| 2. Common electricity | X | X | X | X | X | X | X | X | +|_________________________|___|___|___|___|___|___|___|___| +| | | | | | | | | | +| 3. Magneto-Electricity | X | X | X | X | X | X | X | | +|_________________________|___|___|___|___|___|___|___|___| +| | | | | | | | | | +| 4. Thermo-Electricity | X | X | + | + | + | + | | | +|_________________________|___|___|___|___|___|___|___|___| +| | | | | | | | | | +| 5. Animal Electricity | X | X | X | + | + | X | | | +|_________________________|___|___|___|___|___|___|___|___| + + [A] Many of the spaces in this table originally left blank may now be + filled. Thus with _thermo-electricity_, Botto made magnets and + obtained polar chemical decomposition: Antinori produced the spark; + and if it has not been done before, Mr. Watkins has recently heated a + wire in Harris's thermo-electrometer. In respect to _animal + electricity_, Matteucci and Linari have obtained the spark from the + torpedo, and I have recently procured it from the gymnotus: Dr. Davy + has observed the heating power of the current from the torpedo. I have + therefore filled up these spaces with crosses, in a different position + to the others originally in the table. There remain but five spaces + unmarked, two under _attraction_ and _repulsion_, and three under + _discharge by hot air_; and though these effects have not yet been + obtained, it is a necessary conclusion that they must be possible, + since the _spark_ corresponding to them has been procured. For when a + discharge across cold air can occur, that intensity which is the only + essential additional requisite for the other effects must be + present.--_Dec. 13 1838._ + + +S 8. _Relation by Measure of common and voltaic Electricity._[A] + + [A] In further illustration of this subject see 855-873 in Series + VII.--_Dec. 1838._ + + +361. Believing the point of identity to be satisfactorily established, I +next endeavoured to obtain a common measure, or a known relation as to +quantity, of the electricity excited by a machine, and that from a voltaic +pile; for the purpose not only of confirming their identity (378.), but +also of demonstrating certain general principles (366, 377, &c.), and +creating an extension of the means of investigating and applying the +chemical powers of this wonderful and subtile agent. + +362. The first point to be determined was, whether the same absolute +quantity of ordinary electricity, sent through a galvanometer, under +different circumstances, would cause the same deflection of the needle. An +arbitrary scale was therefore attached to the galvanometer, each division +of which was equal to about 4 deg., and the instrument arranged as in former +experiments (296.). The machine (290.), battery (291.), and other parts of +the apparatus were brought into good order, and retained for the time as +nearly as possible in the same condition. The experiments were alternated +so as to indicate any change in the condition of the apparatus and supply +the necessary corrections. + +363. Seven of the battery jars were removed, and eight retained for present +use. It was found that about forty turns would fully charge the eight jars. +They were then charged by thirty turns of the machine, and discharged +through the galvanometer, a thick wet string, about ten inches long, being +included in the circuit. The needle was immediately deflected five +divisions and a half, on the one side of the zero, and in vibrating passed +as nearly as possible through five divisions and a half on the other side. + +364. The other seven jars were then added to the eight, and the whole +fifteen charged by thirty turns of the machine. The Henley's electrometer +stood not quite half as high as before; but when the discharge was made +through the galvanometer, previously at rest, the needle immediately +vibrated, passing _exactly_ to the same division as in the former instance. +These experiments with eight and with fifteen jars were repeated several +times alternately with the same results. + +365. Other experiments were then made, in which all the battery was used, +and its charge (being fifty turns of the machine,) sent through the +galvanometer: but it was modified by being passed sometimes through a mere +wet thread, sometimes through thirty-eight inches of thin string wetted by +distilled water, and sometimes through a string of twelve times the +thickness, only twelve inches in length, and soaked in dilute acid (298.). +With the thick string the charge passed at once; with the thin string it +occupied a sensible time, and with the thread it required two or three +seconds before the electrometer fell entirely down. The current therefore +must have varied extremely in intensity in these different cases, and yet +the deflection of the needle was sensibly the same in all of them. If any +difference occurred, it was that the thin string and thread caused greatest +deflection; and if there is any lateral transmission, as M. Colladon says, +through the silk in the galvanometer coil, it ought to have been so, +because then the intensity is lower and the lateral transmission less. + +366. Hence it would appear that _if the same absolute quantity of +electricity pass through the galvanometer, whatever may be its intensity, +the dejecting force upon the magnetic needle is the same._ + +367. The battery of fifteen jars was then charged by sixty revolutions of +the machine, and discharged, as before, through the galvanometer. The +deflection of the needle was now as nearly as possible to the eleventh +division, but the graduation was not accurate enough for me to assert that +the arc was exactly double the former arc; to the eye it appeared to be so. +The probability is, that _the deflecting force of an electric current is +directly proportional to the absolute quantity of electricity passed_, at +whatever intensity that electricity may be[A]. + + [A] The great and general value of the galvanometer, as an actual + measure of the electricity passing through it, either continuously or + interruptedly, must be evident from a consideration of these two + conclusions. As constructed by Professor Ritchie with glass threads + (see Philosophical Transactions, 1830, p. 218, and Quarterly Journal + of Science, New Series, vol. i. p.29.), it apparently seems to leave + nothing unsupplied in its own department. + +368. Dr. Ritchie has shown that in a case where the intensity of the +electricity remained the same, the deflection of the magnetic needle was +directly as the quantity of electricity passed through the galvanometer[A]. +Mr. Harris has shown that the _heating_ power of common electricity on +metallic wires is the same for the same quantity of electricity whatever +its intensity might have previously been[B]. + + [A] Quarterly Journal of Science, New Series, vol. i. p. 33. + + [B] Plymouth Transactions, page 22. + +369. The next point was to obtain a _voltaic_ arrangement producing an +effect equal to that just described (367.). A platina and a zinc wire were +passed through the same hole of a draw-plate, being then one eighteenth of +an inch in diameter; these were fastened to a support, so that their lower +ends projected, were parallel, and five sixteenths of an inch apart. The +upper ends were well-connected with the galvanometer wires. Some acid was +diluted, and, after various preliminary experiments, that adopted as a +standard which consisted of one drop strong sulphuric acid in four ounces +distilled water. Finally, the time was noted which the needle required in +swinging either from right to left or left to right: it was equal to +seventeen beats of my watch, the latter giving one hundred and fifty in a +minute. The object of these preparations was to arrange a voltaic +apparatus, which, by immersion in a given acid for a given time, much less +than that required by the needle to swing in one direction, should give +equal deflection to the instrument with the discharge of ordinary +electricity from the battery (363. 364.); and a new part of the zinc wire +having been brought into position with the platina, the comparative +experiments were made. + +370. On plunging the zinc and platina wires five eighths of an inch deep +into the acid, and retaining them there for eight beats of the watch, +(after which they were quickly withdrawn,) the needle was deflected, and +continued to advance in the same direction some time after the voltaic +apparatus had been removed from the acid. It attained the five-and-a-half +division, and then returned swinging an equal distance on the other side. +This experiment was repeated many times, and always with the same result. + +371. Hence, as an approximation, and judging from _magnetic force_ only at +present (376.), it would appear that two wires, one of platina and one of +zinc, each one eighteenth of an inch in diameter, placed five sixteenths of +an inch apart and immersed to the depth of five eighths of an inch in acid, +consisting of one drop oil of vitriol and four ounces distilled water, at a +temperature about 60 deg., and connected at the other extremities by a copper +wire eighteen feet long and one eighteenth of an inch thick (being the wire +of the galvanometer coils), yield as much electricity in eight beats of my +watch, or in 8/150ths of a minute, as the electrical battery charged by +thirty turns of the large machine, in excellent order (363. 364.). +Notwithstanding this apparently enormous disproportion, the results are +perfectly in harmony with those effects which are known to be produced by +variations in the intensity and quantity of the electric fluid. + +372. In order to procure a reference to _chemical action_, the wires were +now retained immersed in the acid to the depth of five eighths of an inch, +and the needle, when stationary, observed; it stood, as nearly as the +unassisted eye could decide, at 5-1/3 division. Hence a permanent +deflection to that extent might be considered as indicating a constant +voltaic current, which in eight beats of my watch (369.) could supply as +much electricity as the electrical battery charged by thirty turns of the +machine. + +373. The following arrangements and results are selected from many that +were made and obtained relative to chemical action. A platina wire one +twelfth of an inch in diameter, weighing two hundred and sixty grains, had +the extremity rendered plain, so as to offer a definite surface equal to a +circle of the same diameter as the wire; it was then connected in turn with +the conductor of the machine, or with the voltaic apparatus (369.), so as +always to form the positive pole, and at the same time retain a +perpendicular position, that it might rest, with its whole weight, upon the +test paper to be employed. The test paper itself was supported upon a +platina spatula, connected either with the discharging train (292.), or +with the negative wire of the voltaic apparatus, and it consisted of four +thicknesses, moistened at all times to an equal degree in a standard +solution of hydriodate of potassa (316.). + +374. When the platina wire was connected with the prime conductor of the +machine, and the spatula with the discharging train, ten turns of the +machine had such decomposing power as to produce a pale round spot of +iodine of the diameter of the wire; twenty turns made a much darker mark, +and thirty turns made a dark brown spot penetrating to the second thickness +of the paper. The difference in effect produced by two or three turns, more +or less, could be distinguished with facility. + +375. The wire and spatula were then connected with the voltaic apparatus +(369.), the galvanometer being also included in the arrangement; and, a +stronger acid having been prepared, consisting of nitric acid and water, +the voltaic apparatus was immersed so far as to give a permanent deflection +of the needle to the 5-1/3 division (372.), the fourfold moistened paper +intervening as before[A]. Then by shifting the end of the wire from place +to place upon the test paper, the effect of the current for five, six, +seven, or any number of the beats of the watch (369.) was observed, and +compared with that of the machine. After alternating and repeating the +experiments of comparison many times, it was constantly found that this +standard current of voltaic electricity, continued for eight beats of the +watch, was equal, in chemical effect, to thirty turns of the machine; +twenty-eight revolutions of the machine were sensibly too few. + + [A] Of course the heightened power of the voltaic battery was + necessary to compensate for the bad conductor now interposed. + +376. Hence it results that both in _magnetic deflection_ (371.) and in +_chemical force_, the current of electricity of the standard voltaic +battery for eight beats of the watch was equal to that of the machine +evolved by thirty revolutions. + +377. It also follows that for this case of electro-chemical decomposition, +and it is probable for all cases, that the _chemical power, like the +magnetic force_ (36.), _is in direct proportion to the absolute quantity +of electricity_ which passes. + +378. Hence arises still further confirmation, if any were required, of the +identity of common and voltaic electricity, and that the differences of +intensity and quantity are quite sufficient to account for what were +supposed to be their distinctive qualities. + +379. The extension which the present investigations have enabled me to make +of the facts and views constituting the theory of electro-chemical +decomposition, will, with some other points of electrical doctrine, be +almost immediately submitted to the Royal Society in another series of +these Researches. + +_Royal Institution, +15th Dec. 1832._ + +Note.--I am anxious, and am permitted, to add to this paper a correction of +an error which I have attributed to M. Ampere the first series of these +Experimental Researches. In referring to his experiment on the induction of +electrical currents (78.), I have called that a disc which I should have +called a circle or a ring. M. Ampere used a ring, or a very short cylinder +made of a narrow plate of copper bent into a circle, and he tells me that +by such an arrangement the motion is very readily obtained. I have not +doubted that M. Ampere obtained the motion he described; but merely mistook +the kind of mobile conductor used, and so far I described his _experiment_ +erroneously. + +In the same paragraph I have stated that M. Ampere says the disc turned "to +take a position of equilibrium exactly as the spiral itself would have +turned had it been free to move"; and further on I have said that my +results tended to invert the sense of the proposition "stated by M. Ampere, +_that a current of electricity tends to put the electricity of conductors +near which it passes in motion in the same direction._" M. Ampere tells me +in a letter which I have just received from him, that he carefully avoided, +when describing the experiment, any reference to the direction of the +induced current; and on looking at the passages he quotes to me, I find +that to be the case. I have therefore done him injustice in the above +statements, and am anxious to correct my error. + +But that it may not be supposed I lightly wrote those passages, I will +briefly refer to my reasons for understanding them in the sense I did. At +first the experiment failed. When re-made successfully about a year +afterwards, it was at Geneva in company with M.A. De la Rive: the latter +philosopher described the results[A], and says that the plate of copper +bent into a circle which was used as the mobile conductor "sometimes +advanced between the two branches of the (horse-shoe) magnet, and sometimes +was repelled, _according_ to the direction of the current in the +surrounding conductors." + + [A] Bibliotheque Universelle, xxi. p. 48. + +I have been in the habit of referring to Demonferrand's _Manuel +d'Electricite Dynamique_, as a book of authority in France; containing the +general results and laws of this branch of science, up to the time of its +publication, in a well arranged form. At p. 173, the author, when +describing this experiment, says, "The mobile circle turns to take a +position of equilibrium as a conductor would do in which the current moved +in the _same direction_ as in the spiral;" and in the same paragraph he +adds, "It is therefore proved _that a current of electricity tends to put +the electricity of conductors, near which it passes, in motion in the same +direction._" These are the words I quoted in my paper (78.). + +Le Lycee of 1st of January, 1832, No. 36, in an article written after the +receipt of my first unfortunate letter to M. Hachette, and before my papers +were printed, reasons upon the direction of the induced currents, and says, +that there ought to be "an elementary current produced in the same +direction as the corresponding portion of the producing current." A little +further on it says, "therefore we ought to obtain currents, moving in the +_same direction_, produced upon a metallic wire, either by a magnet or a +current. M. Ampere _was so thouroughly persuaded that such ought to be the +direction of the currents by influence_, that he neglected to assure +himself of it in his experiment at Geneva." + +It was the precise statements in Demonferrand's Manuel, agreeing as they +did with the expression in M. De la Rive's paper, (which, however, I now +understand as only meaning that when the inducing current was changed, the +motion of the mobile circle changed also,) and not in discordance with +anything expressed by M. Ampere himself where he speaks of the experiment, +which made me conclude, when I wrote the paper, that what I wrote was +really his avowed opinion; and when the Number of the Lycee referred to +appeared, which was before my paper was printed, it could excite no +suspicion that I was in error. + +Hence the mistake into which I unwittingly fell. I am proud to correct it +and do full justice to the acuteness and accuracy which, as far as I can +understand the subjects, M. Ampere carries into all the branches of +philosophy which he investigates. + +Finally, my note to (79.) says that the Lycee, No. 36. "mistakes the +erroneous results of MM. Fresnel and Ampere for true ones," &c. &c. In +calling M. Ampere's results erroneous, I spoke of the results described in, +and referred to by the Lycee itself; but _now_ that the expression of the +direction of the induced current is to be separated, the term _erroneous_ +ought no longer to be attached to them. + +April 29, 1833. +M.F.] + + + + +FOURTH SERIES. + + +S 9. _On a new Law of Electric Conduction._ S 10. _On Conducting Power +generally._ + +Received April 24,--Read May 23, 1833. + + +S 9. _On a new Law of Electric Conduction._[A] + + [A] In reference to this law see further considerations at 910. 1358. + 1705.--_Dec. 1838._ + + +380. It was during the progress of investigations relating to +electro-chemical decomposition, which I still have to submit to the Royal +Society, that I encountered effects due to a very _general law_ of electric +conduction not hitherto recognised; and though they prevented me from +obtaining the condition I sought for, they afforded abundant compensation +for the momentary disappointment, by the new and important interest which +they gave to an extensive part of electrical science. + +381. I was working with ice, and the solids resulting from the freezing of +solutions, arranged either as barriers across a substance to be decomposed, +or as the actual poles of a voltaic battery, that I might trace and catch +certain elements in their transit, when I was suddenly stopped in my +progress by finding that ice was in such circumstances a non-conductor of +electricity; and that as soon as a thin film of it was interposed, in the +circuit of a very powerful voltaic battery, the transmission of electricity +was prevented, and all decomposition ceased. + +382. At first the experiments were made with common ice, during the cold +freezing weather of the latter end of January 1833; but the results were +fallacious, from the imperfection of the arrangements, and the following +more unexceptionable form of experiment was adopted. + +383. Tin vessels were formed, five inches deep, one inch and a quarter wide +in one direction, of different widths from three eighths to five eighths of +an inch in the other, and open at one extremity. Into these were fixed by +corks, plates of platina, so that the latter should not touch the tin +cases; and copper wires having previously been soldered to the plate, these +were easily connected, when required, with a voltaic pile. Then distilled +water, previously boiled for three hours, was poured into the vessels, and +frozen by a mixture of salt and snow, so that pure transparent solid ice +intervened between the platina and tin; and finally these metals were +connected with the opposite extremities of the voltaic apparatus, a +galvanometer being at the same time included in the circuit. + +384. In the first experiment, the platina pole was three inches and a half +long, and seven eighths of an inch wide; it was wholly immersed in the +water or ice, and as the vessel was four eighths of an inch in width, the +average thickness of the intervening ice was only a quarter of an inch, +whilst the surface of contact with it at both poles was nearly fourteen +square inches. After the water was frozen, the vessel was still retained in +the frigorific mixture, whilst contact between the tin and platina +respectively was made with the extremities of a well-charged voltaic +battery, consisting of twenty pairs of four-inch plates, each with double +coppers. Not the slightest deflection of the galvanometer needle occurred. + +385. On taking the frozen arrangement out of the cold mixture, and applying +warmth to the bottom of the tin case, so as to melt part of the ice, the +connexion with the battery being in the mean time retained, the needle did +not at first move; and it was only when the thawing process had extended so +far as to liquefy part of the ice touching the platina pole, that +conduction took place; but then it occurred effectually, and the +galvanometer needle was permanently deflected nearly 70 deg.. + +386. In another experiment, a platina spatula, five inches in length and +seven eighths of an inch in width, had four inches fixed in the ice, and +the latter was only three sixteenths of an inch thick between one metallic +surface and the other; yet this arrangement insulated as perfectly as the +former. + +387. Upon pouring a little water in at the top of this vessel on the ice, +still the arrangement did not conduct; yet fluid water was evidently there. +This result was the consequence of the cold metals having frozen the water +where they touched it, and thus insulating the fluid part; and it well +illustrates the non-conducting power of ice, by showing how thin a film +could prevent the transmission of the battery current. Upon thawing parts +of this thin film, at _both_ metals, conduction occurred. + +388. Upon warming the tin case and removing the piece of ice, it was found +that a cork having slipped, one of the edges of the platina had been all +but in contact with the inner surface of the tin vessel; yet, +notwithstanding the extreme thinness of the interfering ice in this place, +no sensible portion of electricity had passed. + +389. These experiments were repeated many times with the same results. At +last a battery of fifteen troughs, or one hundred and fifty pairs of +four-inch plates, powerfully charged, was used; yet even here no sensible +quantity of electricity passed the thin barrier of ice. + +390. It seemed at first as if occasional departures from these effects +occurred; but they could always be traced to some interfering +circumstances. The water should in every instance be well-frozen; for +though it is not necessary that the ice should reach from pole to pole, +since a barrier of it about one pole would be quite sufficient to prevent +conduction, yet, if part remain fluid, the mere necessary exposure of the +apparatus to the air or the approximation of the hands, is sufficient to +produce, at the _upper surface_ of the water and ice, a film of fluid, +extending from the platina to the tin; and then conduction occurs. Again, +if the corks used to block the platina in its place are damp or wet within, +it is necessary that the cold be sufficiently well applied to freeze the +water in them, or else when the surfaces of their contact with the tin +become slightly warm by handling, that part will conduct, and the interior +being ready to conduct also, the current will pass. The water should be +pure, not only that unembarrassed results may be obtained, but also that, +as the freezing proceeds, a minute portion of concentrated saline solution +may not be formed, which remaining fluid, and being interposed in the ice, +or passing into cracks resulting from contraction, may exhibit conducting +powers independent of the ice itself. + +391. On one occasion I was surprised to find that after thawing much of the +ice the conducting power had not been restored; but I found that a cork +which held the wire just where it joined the platina, dipped so far into +the ice, that with the ice itself it protected the platina from contact +with the melted part long after that contact was expected. + +392. This insulating power of ice is not effective with electricity of +exalted intensity. On touching a diverged gold-leaf electrometer with a +wire connected with the platina, whilst the tin case was touched by the +hand or another wire, the electrometer was instantly discharged (419.). + +393. But though electricity of an intensity so low that it cannot diverge +the electrometer, can still pass (though in very limited quantities +(419.),) through ice; the comparative relation of water and ice to the +electricity of the voltaic apparatus is not less extraordinary on that +account, Or less important in its consequences. + +394. As it did not seem likely that this _law of the assumption of +conducting power during liquefaction, and loss of it during congelation_, +would be peculiar to water, I immediately proceeded to ascertain its +influence in other cases, and found it to be very general. For this purpose +bodies were chosen which were solid at common temperatures, but readily +fusible; and of such composition as, for other reasons connected with +electrochemical action, led to the conclusion that they would be able when +fused to replace water as conductors. A voltaic battery of two troughs, or +twenty pairs of four-inch plates (384.), was used as the source of +electricity, and a galvanometer introduced into the circuit to indicate the +presence or absence of a current. + +395. On fusing a little chloride of lead by a spirit lamp on a fragment of +a Florence flask, and introducing two platina wires connected with the +poles of the battery, there was instantly powerful action, the galvanometer +was most violently affected, and the chloride rapidly decomposed. On +removing the lamp, the instant the chloride solidified all current and +consequent effects ceased, though the platina wires remained inclosed in +the chloride not more than the one-sixteenth of an inch from each other. On +renewing the heat, as soon as the fusion had proceeded far enough to allow +liquid matter to connect the poles, the electrical current instantly +passed. + +396. On fusing the chloride, with one wire introduced, and then touching +the liquid with the other, the latter being cold, caused a little knob to +concrete on its extremity, and no current passed; it was only when the wire +became so hot as to be able to admit or allow of contact with the liquid +matter, that conduction took place, and then it was very powerful. + +397. When chloride of silver and chlorate of potassa were experimented +with, in a similar manner, exactly the same results occurred. + +398. Whenever the current passed in these cases, there was decomposition of +the substances; but the electro-chemical part of this subject I purpose +connecting with more general views in a future paper[A]. + + [A] In 1801, Sir H. Davy knew that "dry nitre, caustic potash, and + soda are conductors of galvanism when rendered fluid by a high degree + of heat," (Journals of the Royal Institution, 1802, p. 53,) but was + not aware of the general law which I have been engaged in developing. + It is remarkable, that eleven years after that, he should say, "There + are no fluids known except such as contain water, which are capable of + being made the medium of connexion between the metal or metals of the + voltaic apparatus."--Elements of Chemical Philosophy, p. 169. + +399. Other substances, which could not be melted on glass, were fused by +the lamp and blowpipe on platina connected with one pole of the battery, +and then a wire, connected with the other, dipped into them. In this way +chloride of sodium, sulphate of soda, protoxide of lead, mixed carbonates +of potash and soda, &c. &c., exhibited exactly the same phenomena as those +already described: whilst liquid, they conducted and were decomposed; +whilst solid, though very hot, they insulated the battery current even when +four troughs were used. + +400. Occasionally the substances were contained in small bent tubes of +green glass, and when fused, the platina poles introduced, one on each +side. In such cases the same general results as those already described +were procured; but a further advantage was obtained, namely, that whilst +the substance was conducting and suffering decomposition, the final +arrangement of the elements could be observed. Thus, iodides of potassium +and lead gave iodine at the positive pole, and potassium or lead at the +negative pole. Chlorides of lead and silver gave chlorine at the positive, +and metals at the negative pole. Nitre and chlorate; of potassa gave +oxygen, &c., at the positive, and alkali, or even potassium, at the +negative pole. + +[Illustration] + +401. A fourth arrangement was used for substances requiring very high +temperatures for their fusion. A platina wire was connected with one pole +of the battery; its extremity bent into a small ring, in the manner +described by Berzelius, for blowpipe experiments; a little of the salt, +glass, or other substance, was melted on this ring by the ordinary +blowpipe, or even in some cases by the oxy-hydrogen blowpipe, and when the +drop, retained in its place by the ring, was thoroughly hot and fluid, a +platina wire from the opposite pole of the battery was made to touch it, +and the effects observed. + +402. The following are various substances, taken from very different +classes chemically considered, which are subject to this law. The list +might, no doubt, be enormously extended; but I have not had time to do more +than confirm the law by a sufficient number of instances. + +First, _water_. + +Amongst _oxides_;--potassa, protoxide of lead, glass of antimony, protoxide +of antimony, oxide of bismuth. + +_Chlorides_ of potassium, sodium, barium, strontium, calcium, magnesium, +manganese, zinc, copper (proto-), lead, tin (proto-), antimony, silver. + +_Iodides_ of potassium, zinc and lead, protiodide of tin, periodide of +mercury; _fluoride_ of potassium; _cyanide_ of potassium; _sulpho-cyanide_ +of potassium. + +_Salts._ Chlorate of potassa; nitrates of potassa, soda, baryta, strontia, +lead, copper, and silver; sulphates of soda and lead, proto-sulphate of +mercury; phosphates of potassa, soda, lead, copper, phosphoric glass or +acid phosphate of lime; carbonates of potassa and soda, mingled and +separate; borax, borate of lead, per-borate of tin; chromate of potassa, +bi-chromate of potassa, chromate of lead; acetate of potassa. + +_Sulphurets._ Sulphuret of antimony, sulphuret of potassium made by +reducing sulphate of potassa by hydrogen; ordinary sulphuret of potassa. + +Silicated potassa; chameleon mineral. + +403. It is highly interesting in the instances of those substances which +soften before they liquefy, to observe at what period the conducting power +is acquired, and to what degree it is exalted by perfect fluidity. Thus, +with the borate of lead, when heated by the lamp upon glass, it becomes as +soft as treacle, but it did not conduct, and it was only when urged by the +blowpipe and brought to a fair red heat, that it conducted. When rendered +quite liquid, it conducted with extreme facility. + +404. I do not mean to deny that part of the increased conducting power in +these cases of softening was probably due to the elevation of temperature +(432. 445.); but I have no doubt that by far the greater part was due to +the influence of the general law already demonstrated, and which in these +instances came gradually, instead of suddenly, into operation. + +405. The following are bodies which acquired no conducting power upon +assuming the liquid state:-- + +Sulphur, phosphorus; iodide of sulphur, per-iodide of tin; orpiment, +realgar; glacial acetic acid, mixed margaric and oleic acids, artificial +camphor; caffeine, sugar, adipocire, stearine of cocoa-nut oil, spermaceti, +camphor, naphthaline, resin, gum sandarach, shell lac. + +406. Perchloride of tin, chloride of arsenic, and the hydrated chloride of +arsenic, being liquids, had no sensible conducting power indicated by the +galvanometer, nor were they decomposed. + +407. Some of the above substances are sufficiently remarkable as exceptions +to the general law governing the former cases. These are orpiment, realgar, +acetic acid, artificial camphor, per-iodide of tin, and the chlorides of +tin and arsenic. I shall have occasion to refer to these cases in the paper +on Electro-chemical Decomposition. + +408. Boracic acid was raised to the highest possible temperature by an +oxy-hydrogen flame (401.), yet it gained no conducting powers sufficient to +affect the galvanometer, and underwent no apparent voltaic decomposition. +It seemed to be quite as bad a conductor as air. Green bottle-glass, heated +in the same manner, did not gain conducting power sensible to the +galvanometer. Flint glass, when highly heated, did conduct a little and +decompose; and as the proportion of potash or oxide of lead was increased +in the glass, the effects were more powerful. Those glasses, consisting of +boracic acid on the one hand, and oxide of lead or potassa on the other, +show the assumption of conducting power upon fusion and the accompanying +decomposition very well. + +409. I was very anxious to try the general experiment with sulphuric acid, +of about specific gravity 1.783, containing that proportion of water which +gives it the power of crystallizing at 40 deg. Fahr.; but I found it impossible +to obtain it so that I could be sure the whole would congeal even at 0 deg. +Fahr. A ten-thousandth part of water, more or less than necessary, would, +upon cooling the whole, cause a portion of uncongealable liquid to +separate, and that remaining in the interstices of the solid mass, and +moistening the planes of division, would prevent the correct observation of +the phenomena due to entire solidification and subsequent liquefaction. + +410. With regard to the substances on which conducting power is thus +conferred by liquidity, the degree of power so given is generally very +great. Water is that body in which this acquired power is feeblest. In the +various oxides, chlorides, salts, &c. &c., it is given in a much higher +degree. I have not had time to measure the conducting power in these cases, +but it is apparently some hundred times that of pure water. The increased +conducting power known to be given to water by the addition of salts, would +seem to be in a great degree dependent upon the high conducting power of +these bodies when in the liquid state, that state being given them for the +time, not by heat but solution in the water[A]. + + [A] See a doubt on this point at 1356.--_Dec. 1838._ + +411. Whether the conducting power of these liquefied bodies is a +consequence of their decomposition or not (413.), or whether the two +actions of conduction and decomposition are essentially connected or not, +would introduce no difference affecting the probable accuracy of the +preceding statement. + +412. This _general assumption of conducting power_ by bodies as soon as +they pass from the solid to the liquid state, offers a new and +extraordinary character, the existence of which, as far as I know, has not +before been suspected; and it seems importantly connected with some +properties and relations of the particles of matter which I may now briefly +point out. + +413. In almost all the instances, as yet observed, which are governed by +this law, the substances experimented with have been those which were not +only compound bodies, but such as contain elements known to arrange +themselves at the opposite poles; and were also such as could be +_decomposed_ by the electrical current. When conduction took place, +decomposition occurred; when decomposition ceased, conduction ceased also; +and it becomes a fair and an important question, Whether the conduction +itself may not, wherever the law holds good, be a consequence not merely of +the capability, but of the act of decomposition? And that question may be +accompanied by another, namely, Whether solidification does not prevent +conduction, merely by chaining the particles to their places, under the +influence of aggregation, and preventing their final separation in the +manner necessary for decomposition? + +414. But, on the other hand, there is one substance (and others may occur), +the _per-iodide of mercury_, which, being experimented with like the others +(400.), was found to insulate when solid, and to acquire conducting power +when fluid; yet it did not seem to undergo decomposition in the latter +case. + +415. Again, there are many substances which contain elements such as would +be expected to arrange themselves at the opposite poles of the pile, and +therefore in that respect fitted for decomposition, which yet do not +conduct. Amongst these are the iodide of sulphur, per-iodide of zinc, +per-chloride of tin, chloride of arsenic, hydrated chloride of arsenic, +acetic acid, orpiment, realgar, artificial camphor, &c.; and from these it +might perhaps be assumed that decomposition is dependent upon conducting +power, and not the latter upon the former. The true relation, however, of +conduction and decomposition in those bodies governed by the general law +which it is the object of this paper to establish, can only be +satisfactorily made out from a far more extensive series of observations +than those I have yet been able to supply[A]. + + [A] See 673, &c. &c.--_Dec. 1838._ + +416. The relation, under this law, of the conducting power for electricity +to that for heat, is very remarkable, and seems to imply a natural +dependence of the two. As the solid becomes a fluid, it loses almost +entirely the power of conduction for heat, but gains in a high degree that +for electricity; but as it reverts hack to the solid state, it gains the +power of conducting heat, and loses that of conducting electricity. If, +therefore, the properties are not incompatible, still they are most +strongly contrasted, one being lost as the other is gained. We may hope, +perhaps, hereafter to understand the physical reason of this very +extraordinary relation of the two conducting powers, both of which appear +to be directly connected with the corpuscular condition of the substances +concerned. + +417. The assumption of conducting power and a decomposable condition by +liquefaction, promises new opportunities of, and great facilities in, +voltaic decomposition. Thus, such bodies as the oxides, chlorides, +cyanides, sulpho-cyanides, fluorides, certain vitreous mixtures, &c. &c., +may be submitted to the action of the voltaic battery under new +circumstances; and indeed I have already been able, with ten pairs of +plates, to decompose common salt, chloride of magnesium, borax, &c. &c., +and to obtain sodium, magnesium, boron, &c., in their separate states. + + +S 10. _On Conducting Power generally._[A] + + [A] In reference to this S refer to 983 in series viii., and the + results connected with it.--_Dec. 1838._ + + +418. It is not my intention here to enter into an examination of all the +circumstances connected with conducting power, but to record certain facts +and observations which have arisen during recent inquiries, as additions to +the general stock of knowledge relating to this point of electrical +science. + +419. I was anxious, in the first place, to obtain some idea of the +conducting power of ice and solid salts for electricity of high tension +(392.), that a comparison might be made between it and the large accession +of the same power gained upon liquefaction. For this purpose the large +electrical machine (290.) was brought into excellent action, its conductor +connected with a delicate gold-leaf electrometer, and also with the platina +inclosed in the ice (383.), whilst the tin case was connected with the +discharging train (292.). On working the machine moderately, the gold +leaves barely separated; on working it rapidly, they could be opened nearly +two inches. In this instance the tin case was five-eighths of an inch in +width; and as, after the experiment, the platina plate was found very +nearly in the middle of the ice, the average thickness of the latter had +been five-sixteenths of an inch, and the extent of surface of contact with +tin and platina fourteen square inches (384.). Yet, under these +circumstances, it was but just able to conduct the small quantity of +electricity which this machine could evolve (371.), even when of a tension +competent to open the leaves two inches; no wonder, therefore, that it +could not conduct any sensible portion of the electricity of the troughs +(384.), which, though almost infinitely surpassing that of the machine in +quantity, had a tension so low as not to be sensible to an electrometer. + +420. In another experiment, the tin case was only four-eighths of an inch +in width, and it was found afterwards that the platina had been not quite +one-eighth of an inch distant in the ice from one side of the tin vessel. +When this was introduced into the course of the electricity from the +machine (419.), the gold leaves could be opened, but not more than half an +inch; the thinness of the ice favouring the conduction of the electricity, +and permitting the same quantity to pass in the same time, though of a much +lower tension. + +421. Iodide of potassium which had been fused and cooled was introduced +into the course of the electricity from the machine. There were two pieces, +each about a quarter of an inch in thickness, and exposing a surface on +each side equal to about half a square inch; these were placed upon platina +plates, one connected with the machine and electrometer (419.), and the +other with the discharging train, whilst a fine platina wire connected the +two pieces, resting upon them by its two points. On working the electrical +machine, it was possible to open the electrometer leaves about two-thirds +of an inch. + +422. As the platina wire touched only by points, the facts show that this +salt is a far better conductor than ice; but as the leaves of the +electrometer opened, it is also evident with what difficulty conduction, +even of the small portion of electricity produced by the machine, is +effected by this body in the solid state, when compared to the facility +with which enormous quantities at very low tensions are transmitted by it +when in the fluid state. + +423. In order to confirm these results by others, obtained from the voltaic +apparatus, a battery of one hundred and fifty plates, four inches square, +was well-charged: its action was good; the shock from it strong; the +discharge would _continue_ from copper to copper through four-tenths of an +inch of air, and the gold-leaf electrometer before used could be opened +nearly a quarter of an inch. + +424. The ice vessel employed (420.) was half an inch in width; as the +extent of contact of the ice with the tin and platina was nearly fourteen +square inches, the whole was equivalent to a plate of ice having a surface +of seven square inches, of perfect contact at each side, and only one +fourth of an inch thick. It was retained in a freezing mixture during the +experiment. + +425. The order of arrangement in the course of the electric current was as +follows. The positive pole of the battery was connected by a wire with the +platina plate in the ice; the plate was in contact with the ice, the ice +with the tin jacket, the jacket with a wire, which communicated with a +piece of tin foil, on which rested one end of a bent platina wire (312.), +the other or decomposing end being supported on paper moistened with +solution of iodide of potassium (316.): the paper was laid flat on a +platina spatula connected with the negative end of the battery. All that +part of the arrangement between the ice vessel and the decomposing wire +point, including both these, was insulated, so that no electricity might +pass through the latter which had not traversed the former also. + +426. Under these circumstances, it was found that, a pale brown spot of +iodine was slowly formed under the decomposing platina point, thus +indicating that ice could conduct a little of the electricity evolved by a +voltaic battery charged up to the degree of intensity indicated by the +electrometer. But it is quite evident that notwithstanding the enormous +quantity of electricity which the battery could furnish, it was, under +present circumstances, a very inferior instrument to the ordinary machine; +for the latter could send as much through the ice as it could carry, being +of a far higher intensity, i.e. able to open the electrometer leaves half +an inch or more (419. 420.). + +427. The decomposing wire and solution of iodide of potassium were then +removed, and replaced by a very delicate galvanometer (205.); it was so +nearly astatic, that it vibrated to and fro in about sixty-three beats of a +watch giving one hundred and fifty beats in a minute. The same feebleness +of current as before was still indicated; the galvanometer needle was +deflected, but it required to break and make contact three or four times +(297.), before the effect was decided. + +428. The galvanometer being removed, two platina plates were connected with +the extremities of the wires, and the tongue placed between them, so that +the whole charge of the battery, so far as the ice would let it pass, was +free to go through the tongue. Whilst standing on the stone floor, there +was shock, &c., but when insulated, I could feel no sensation. I think a +frog would have been scarcely, if at all, affected. + +429. The ice was now removed, and experiments made with other solid bodies, +for which purpose they were placed under the end of the decomposing wire +instead of the solution of iodide of potassium (125.). For instance, a +piece of dry iodide of potassium was placed on the spatula connected with +the negative pole of the battery, and the point of the decomposing wire +placed upon it, whilst the positive end of the battery communicated with +the latter. A brown spot of iodine very slowly appeared, indicating the +passage of a little electricity, and agreeing in that respect with the +results obtained by the use of the electrical machine (421.). When the +galvanometer was introduced into the circuit at the same time with the +iodide, it was with difficulty that the action of the current on it could +be rendered sensible. + +430. A piece of common salt previously fused and solidified being +introduced into the circuit was sufficient almost entirely to destroy the +action on the galvanometer. Fused and cooled chloride of lead produced the +same effect. The conducting power of these bodies, _when fluid_, is very +great (395. 402.). + +431. These effects, produced by using the common machine and the voltaic +battery, agree therefore with each other, and with the law laid down in +this paper (394.); and also with the opinion I have supported, in the Third +Series of these Researches, of the identity of electricity derived from +different sources (360.). + +432. The effect of heat in increasing the conducting power of many +substances, especially for electricity of high tension, is well known. I +have lately met with an extraordinary case of this kind, for electricity of +low tension, or that of the voltaic pile, and which is in direct contrast +with the influence of heat upon metallic bodies, as observed and described +by Sir Humphry Davy[A]. + + [A] Philosophical Transactions, 1821, p. 131. + +433. The substance presenting this effect is sulphuret of silver. It was +made by fusing a mixture of precipitated silver and sublimed sulphur, +removing the film of silver by a file from the exterior of the fused mass, +pulverizing the sulphuret, mingling it with more sulphur, and fusing it +again in a green glass tube, so that no air should obtain access during the +process. The surface of the sulphuret being again removed by a file or +knife, it was considered quite free from uncombined silver. + +434. When a piece of this sulphuret, half an inch in thickness, was put +between surfaces of platina, terminating the poles of a voltaic battery of +twenty pairs of four-inch plates, a galvanometer being also included in the +circuit, the needle was slightly deflected, indicating a feeble conducting +power. On pressing the platina poles and sulphuret together with the +fingers, the conducting power increased as the whole became warm. On +applying a lamp under the sulphuret between the poles, the conducting power +rose rapidly with the heat, and at last-the galvanometer needle jumped into +a fixed position, and the sulphuret was found conducting in the manner of a +metal. On removing the lamp and allowing the heat to fall, the effects were +reversed, the needle at first began to vibrate a little, then gradually +left its transverse direction, and at last returned to a position very +nearly that which it would take when no current was passing through the +galvanometer. + +435. Occasionally, when the contact of the sulphuret with the platina poles +was good, the battery freshly charged, and the commencing temperature not +too low, the mere current of electricity from the battery was sufficient to +raise the temperature of the sulphuret; and then, without any application +of extraneous heat, it went on increasing conjointly in temperature and +conducting power, until the cooling influence of the air limited the +effects. In such cases it was generally necessary to cool the whole +purposely, to show the returning series of phenomena. + +436. Occasionally, also, the effects would sink of themselves, and could +not be renewed until a fresh surface of the sulphuret had been applied to +the positive pole. This was in consequence of peculiar results of +decomposition, to which I shall have occasion to revert in the section on +Electro-chemical Decomposition, and was conveniently avoided by inserting +the ends of two pieces of platina wire into the opposite extremities of a +portion of sulphuret fused in a glass tube, and placing this arrangement +between the poles of the battery. + +437. The hot sulphuret of silver conducts sufficiently well to give a +bright spark with charcoal, &c. &c., in the manner of a metal. + +438. The native grey sulphuret of silver, and the ruby silver ore, both +presented the same phenomena. The native malleable sulphuret of silver +presented precisely the same appearances as the artificial sulphuret. + +439. There is no other body with which I am acquainted, that, like +sulphuret of silver, can compare with metals in conducting power for +electricity of low tension when hot, but which, unlike them, during +cooling, loses in power, whilst they, on the contrary, gain. Probably, +however, many others may, when sought for, be found[A]. + + [A] See now on this subject, 1340, 1341.--_Dec. 1838._ + +440. The proto-sulphuret of iron, the native per-sulphuret of iron, +arsenical sulphuret of iron, native yellow sulphuret of copper and iron, +grey artificial sulphuret of copper, artificial sulphuret of bismuth, and +artificial grey sulphuret of tin, all conduct the voltaic battery current +when cold, more or less, some giving sparks like the metals, others not +being sufficient for that high effect. They did not seem to conduct better +when heated, than before; but I had not time to enter accurately into the +investigation of this point. Almost all of them became much heated by the +transmission of the current, and present some very interesting phenomena in +that respect. The sulphuret of antimony does not conduct the same current +sensibly either hot or cold, but is amongst those bodies acquiring +conducting power when fused (402.). The sulphuret of silver and perhaps +some others decompose whilst in the solid state; but the phenomena of this +decomposition will be reserved for its proper place in the next series of +these Researches. + +441. Notwithstanding the extreme dissimilarity between sulphuret of silver +and gases or vapours, I cannot help suspecting the action of heat upon them +to be the same, bringing them all into the same class as conductors of +electricity, although with those great differences in degree, which are +found to exist under common circumstances. When gases are heated, they +increase in conducting power, both for common and voltaic electricity +(271.); and it is probable that if we could compress and condense them at +the same time, we should still further increase their conducting power. +Cagniard de la Tour has shown that a substance, for instance water, may be +so expanded by heat whilst in the liquid state, or condensed whilst in the +vaporous state, that the two states shall coincide at one point, and the +transition from one to the other be so gradual that no line of demarcation +can be pointed out[A]; that, in fact, the two states shall become +one;--which one state presents us at different times with differences in +degree as to certain properties and relations; and which differences are, +under ordinary circumstances, so great as to be equivalent to two different +states. + + [A] Annales de Chimie, xxi. pp. 127, 178. + +442. I cannot but suppose at present that at that point where the liquid +and the gaseous state coincide, the conducting properties are the same for +both; but that they diminish as the expansion of the matter into a rarer +form takes place by the removal of the necessary pressure; still, however, +retaining, as might be expected, the capability of having what feeble +conducting power remains, increased by the action of heat. + +443. I venture to give the following summary of the conditions of electric +conduction in bodies, not however without fearing that I may have omitted +some important points[A]. + + [A] See now in relation to this subject, 1320--1242.--_Dec. 1838._ + +444. All bodies conduct electricity in the same manner from metals to lac +and gases, but in very different degrees. + +445. Conducting power is in some bodies powerfully increased by heat, and +in others diminished, yet without our perceiving any accompanying essential +electrical difference, either in the bodies or in the changes occasioned by +the electricity conducted. + +446. A numerous class of bodies, insulating electricity of low intensity, +when solid, conduct it very freely when fluid, and are then decomposed by +it. + +447. But there are many fluid bodies which do not sensibly conduct +electricity of this low intensity; there are some which conduct it and are +not decomposed; nor is fluidity essential to decomposition[A]. + + [A] See the next series of these Experimental Researches. + +448. There is but one body yet discovered[A] which, insulating a voltaic +current when solid, and conducting it when fluid, is not decomposed in the +latter case (414.). + + [A] It is just possible that this case may, by more delicate + experiment, hereafter disappear. (See now, 1340, 1341, in relation to + this note.--_Dec. 1838._) + +449. There is no strict electrical distinction of conduction which can, as +yet, be drawn between bodies supposed to be elementary, and those known to +be compounds. + +_Royal Institution, +April 15, 1833_. + + + + +FIFTH SERIES. + + +S 11. _On Electro-chemical Decomposition._ P i. _New conditions of +Electro-chemical Decomposition._ P ii. _Influence of Water in +Electro-chemical Decomposition._ P iii. _Theory of Electro-chemical +Decomposition._ + +Received June 18,--Read June 20, 1833. + + +S 11. _On Electro-chemical Decomposition._[A] + + [A] Refer to the note after 1047, Series viii.--_Dec. 1838._ + + +450. I have in a recent series of these Researches (265.) proved (to my own +satisfaction, at least,) the identity of electricities derived from +different sources, and have especially dwelt upon the proofs of the +sameness of those obtained by the use of the common electrical machine and +the voltaic battery. + +451. The great distinction of the electricities obtained from these two +sources is the very high tension to which the small quantity obtained by +aid of the machine may be raised, and the enormous quantity (371. 376.) in +which that of comparatively low tension, supplied by the voltaic battery, +may be procured; but as their actions, whether magnetical, chemical, or of +any other nature, are essentially the same (360.), it appeared evident that +we might reason from the former as to the manner of action of the latter; +and it was, to me, a probable consequence, that the use of electricity of +such intensity as that afforded by the machine, would, when applied to +effect and elucidate electro-chemical decomposition, show some new +conditions of that action, evolve new views of the internal arrangements +and changes of the substances under decomposition, and perhaps give +efficient powers over matter as yet undecomposed. + +452. For the purpose of rendering the bearings of the different parts of +this series of researches more distinct, I shall divide it into several +heads. + + +P i. _New conditions of Electro-chemical Decomposition._ + +453. The tension of machine electricity causes it, however small in +quantity, to pass through any length of water, solutions, or other +substances classing with these as conductors, as fast as it can be +produced, and therefore, in relation to quantity, as fast as it could have +passed through much shorter portions of the same conducting substance. With +the voltaic battery the case is very different, and the passing current of +electricity supplied by it suffers serious diminution in any substance, by +considerable extension of its length, but especially in such bodies as +those mentioned above. + +454. I endeavoured to apply this facility of transmitting the current of +electricity through any length of a conductor, to an investigation of the +transfer of the elements in a decomposing body, in contrary directions, +towards the poles. The general form of apparatus used in these experiments +has been already described (312. 316); and also a particular experiment +(319.), in which, when a piece of litmus paper and a piece of turmeric +paper were combined and moistened in solution of sulphate of soda, the +point of the wire from the machine (representing the positive pole) put +upon the litmus paper, and the receiving point from the discharging train +(292. 316.), representing the negative pole, upon the turmeric paper, a +very few turns of the machine sufficed to show the evolution of acid at the +former, and alkali at the latter, exactly in the manner effected by a +volta-electric current. + +455. The pieces of litmus and turmeric paper were _now_ placed each upon a +separate plate of glass, and connected by an insulated string four feet +long, moistened in the same solution of sulphate of soda: the terminal +decomposing wire points were placed upon the papers as before. On working +the machine, the same evolution of acid and alkali appeared as in the +former instance, and with equal readiness, notwithstanding that the places +of their appearance were four feet apart from each other. Finally, a piece +of string, seventy feet long, was used. It was insulated in the air by +suspenders of silk, so that the electricity passed through its entire +length: decomposition took place exactly as in former cases, alkali and +acid appearing at the two extremities in their proper places. + +456. Experiments were then made both with sulphate of soda and iodide of +potassium, to ascertain if any diminution of decomposing effect was +produced by such great extension as those just described of the moist +conductor or body under decomposition; but whether the contact of the +decomposing point connected with the discharging train was made with +turmeric paper touching the prime conductor, or with other turmeric paper +connected with it through the seventy feet of string, the spot of alkali +for an equal number of turns of the machine had equal intensity of colour. +The same results occurred at the other decomposing wire, whether the salt +or the iodide were used; and it was fully proved that this great extension +of the distance between the poles produced no effect whatever on the amount +of decomposition, provided the same _quantity_ of electricity were passed +in both cases (377.). + +457. The negative point of the discharging train, the turmeric paper, and +the string were then removed; the positive point was left resting upon the +litmus paper, and the latter touched by a piece of moistened string held in +the hand. A few turns of the machine evolved acid at the positive point as +freely as before. + +458. The end of the moistened string, instead of being held in the hand, +was suspended by glass in the air. On working the machine the electricity +proceeded from the conductor through the wire point to the litmus paper, +and thence away by the intervention of the string to the air, so that there +was (as in the last experiment) but one metallic pole; still acid was +evolved there as freely as in any former case. + +459. When any of these experiments were repeated with electricity from the +negative conductor, corresponding effects were produced whether one or two +decomposing wires were used. The results were always constant, considered +in relation to the _direction_ of the electric current. + +460. These experiments were varied so as to include the action of only one +metallic pole, but that not the pole connected with the machine. Turmeric +paper was moistened in solution of sulphate of soda, placed upon glass, and +connected with the discharging train (292.) by a decomposing wire (312.); a +piece of wet string was hung from it, the lower extremity of which was +brought opposite a point connected with the positive prime conductor of the +machine. The machine was then worked for a few turns, and alkali +immediately appeared at the point of the discharging train which rested on +the turmeric paper. Corresponding effects took place at the negative +conductor of a machine. + +461. These cases are abundantly sufficient to show that electrochemical +decomposition does not depend upon the simultaneous action of two metallic +poles, since a single pole might be used, decomposition ensue, and one or +other of the elements liberated, pass to the pole, according as it was +positive or negative. In considering the course taken by, and the final +arrangement of, the other element, I had little doubt that I should find it +had receded towards the other extremity, and that the air itself had acted +as a pole, an expectation which was fully confirmed in the following +manner. + +462. A piece of turmeric paper, not more than 0.4 of an inch in length and +0.5 of an inch in width, was moistened with sulphate of soda and placed +upon the edge of a glass plate opposite to, and about two inches from, a +point connected with the discharging train (Plate IV. fig. 47.); a piece of +tinfoil, resting upon the same glass plate, was connected with the machine, +and also with the turmeric paper, by a decomposing wire _a_ (312.). The +machine was then worked, the positive electricity passing into the turmeric +paper at the point _p_, and out at the extremity _n_. After forty or fifty +turns of the machine, the extremity _n_ was examined, and the two points or +angles found deeply coloured by the presence of free alkali (fig. 48.). + +463. A similar piece of litmus paper, dipped in solution of sulphate of +soda _n_, fig. 49, was now supported upon the end of the discharging train +_a_, and its extremity brought opposite to a point _p_, connected with the +conductor of the machine. After working the machine for a short time, acid +was developed at both the corners towards the point, i.e. at both the +corners receiving the electricities from the air. Every precaution was +taken to prevent this acid from being formed by sparks or brushes passing +through the air (322.); and these, with the accompanying general facts, are +sufficient to show that the acid was really the result of electro-chemical +decomposition (466.). + +464. Then a long piece of turmeric paper, large at one end and pointed at +the other, was moistened in the saline solution, and immediately connected +with the conductor of the machine, so that its pointed extremity was +opposite a point upon the discharging train. When the machine was worked, +alkali was evolved at that point; and even when the discharging train was +removed, and the electricity left to be diffused and carried off altogether +by the air, still alkali was evolved where the electricity left the +turmeric paper. + +465. Arrangements were then made in which no metallic communication with +the decomposing matter was allowed, but both poles (if they might now be +called by that name) formed of air only. A piece of turmeric paper _a_ fig. +50, and a piece of litmus paper _b_, were dipped in solution of sulphate of +soda, put together so as to form one moist pointed conductor, and supported +on wax between two needle points, one, _p_, connected by a wire with the +conductor of the machine, and the other, _n_, with the discharging train. +The interval in each case between the points was about half an inch; the +positive point _p_ was opposite the litmus paper; the negative point _n_ +opposite the turmeric. The machine was then worked for a time, upon which +evidence of decomposition quickly appeared, for the point of the litmus _b_ +became reddened from acid evolved there, and the point of the turmeric _a_ +red from a similar and simultaneous evolution of alkali. + +466. Upon turning the paper conductor round, so that the litmus point +should now give off the positive electricity, and the turmeric point +receive it, and working the machine for a short time, both the red spots +disappeared, and as on continuing the action of the machine no red spot was +re-formed at the litmus extremity, it proved that in the first instance +(463.) the effect was not due to the action of brushes or mere electric +discharges causing the formation of nitric acid from the air (322.). + +467. If the combined litmus and turmeric paper in this experiment be +considered as constituting a conductor independent of the machine or the +discharging train, and the final places of the elements evolved be +considered in relation to this conductor, then it will be found that the +acid collects at the _negative_ or receiving end or pole of the +arrangement, and the alkali at the _positive_ or delivering extremity. + +468. Similar litmus and turmeric paper points were now placed upon glass +plates, and connected by a string six feet long, both string and paper +being moistened in solution of sulphate of soda; a needle point connected +with the machine was brought opposite the litmus paper point, and another +needle point connected with the discharging train brought opposite the +turmeric paper. On working the machine, acid appeared on the litmus, and +alkali on the turmeric paper; but the latter was not so abundant as in +former cases, for much of the electricity passed off from the string into +the air, and diminished the quantity discharged at the turmeric point. + +469. Finally, a series of four small compound conductors, consisting of +litmus and turmeric paper (fig. 51.) moistened in solution of sulphate of +soda, were supported on glass rods, in a line at a little distance from +each other, between the points _p_ and _n_ of the machine and discharging +train, so that the electricity might pass in succession through them, +entering in at the litmus points _b, b_, and passing out at the turmeric +points _a, a_. On working the machine carefully, so as to avoid sparks and +brushes (322.), I soon obtained evidence of decomposition in each of the +moist conductors, for all the litmus points exhibited free acid, and the +turmeric points equally showed free alkali. + +470. On using solutions of iodide of potassium, acetate of lead, &c., +similar effects were obtained; but as they were all consistent with the +results above described, I refrain from describing the appearances +minutely. + +471. These cases of electro-chemical decomposition are in their nature +exactly of the same kind as those affected under ordinary circumstances by +the voltaic battery, notwithstanding the great differences as to the +presence or absence, or at least as to the nature of the parts usually +called poles; and also of the final situation of the elements eliminated at +the electrified boundary surfaces (467.). They indicate at once an internal +action of the parts suffering decomposition, and appear to show that the +power which is effectual in separating the elements is exerted there, and +not at the poles. But I shall defer the consideration of this point for a +short time (493. 518.), that I may previously consider another supposed +condition of electro-chemical decomposition[A]. + + [A] I find (since making and describing these results,) from a note to + Sir Humphry Davy's paper in the Philosophical Transactions, 1807, p. + 31, that that philosopher, in repeating Wollaston's experiment of the + decomposition of water by common electricity (327. 330.) used an + arrangement somewhat like some of those I have described. He immersed + a guarded platina point connected with the machine in distilled water, + and dissipated the electricity from the water into the air by + moistened filaments of cotton. In this way he states that he obtained + oxygen and hydrogen _separately_ from each other. This experiment, had + I known of it, ought to have been quoted in an earlier series of these + Researches (342.); but it does not remove any of the objections I have + made to the use of Wollaston's apparatus as a test of true chemical + action (331.). + + +P ii. _Influence of Water in Electro-chemical Decomposition._ + +472. It is the opinion of several philosophers, that the presence of water +is essential in electro-chemical decomposition, and also for the evolution +of electricity in the voltaic battery itself. As the decomposing cell is +merely one of the cells of the battery, into which particular substances +are introduced for the purpose of experiment, it is probable that what is +an essential condition in the one case is more or less so in the other. The +opinion, therefore, that water is necessary to decomposition, may have been +founded on the statement made by Sir Humphry Davy, that "there are no +fluids known, except such as contain water, which are capable of being made +the medium of connexion between the metals or metal of the voltaic +apparatus[A]:" and again, "when any substance rendered fluid by heat, +consisting of _water_, oxygen, and inflammable or metallic matter, is +exposed to those wires, similar phenomena (of decomposition) occur[B]." + + [A] Elements of Chemical Philosophy, p. 160, &c. + + [B] Ibid. pp. 144, 145. + +473. This opinion has, I think, been shown by other philosophers not to be +accurate, though I do not know where to refer for a contradiction of it. +Sir Humphry Davy himself said in 1801[A], that dry nitre, caustic potash +and soda are conductors of galvanism when rendered fluid by a high degree +of heat, but he must have considered them, or the nitre at least, as not +suffering decomposition, for the statements above were made by him eleven +years subsequently. In 1826 he also pointed out, that bodies not containing +water, as _fused litharge_ and _chlorate of potassa_, were sufficient to +form, with platina and zinc, powerful electromotive circles[B]; but he is +here speaking of the _production_ of electricity in the pile, and not of +its effects when evolved; nor do his words at all imply that any correction +of his former distinct statements relative to _decomposition_ was required. + + [A] Journal of the Royal Institution, 1802, p. 53. + + [B] Philosophical Transactions, 1826, p. 406. + +474. I may refer to the last series of these Experimental Researches (380. +402.) as setting the matter at rest, by proving that there are hundreds of +bodies equally influential with water in this respect; that amongst binary +compounds, oxides, chlorides, iodides, and even sulphurets (402.) were +effective; and that amongst more complicated compounds, cyanides and salts, +of equal efficacy, occurred in great numbers (402.). + +475. Water, therefore, is in this respect merely one of a very numerous +class of substances, instead of being the _only one_ and _essential_; and +it is of that class one of the _worst_ as to its capability of facilitating +conduction and suffering decomposition. The reasons why it obtained for a +time an exclusive character which it so little deserved are evident, and +consist, in the general necessity of a fluid condition (394.); in its being +the _only one_ of this class of bodies existing in the fluid state at +common temperatures; its abundant supply as the great natural solvent; and +its constant use in that character in philosophical investigations, because +of its having a smaller interfering, injurious, or complicating action upon +the bodies, either dissolved or evolved, than any other substance. + +476. The analogy of the decomposing or experimental cell to the other cells +of the voltaic battery renders it nearly certain that any of those +substances which are decomposable when fluid, as described in my last paper +(402.), would, if they could be introduced between the metallic plates of +the pile, be equally effectual with water, if not more so. Sir Humphry Davy +found that litharge and chlorate of potassa were thus effectual[A]. I have +constructed various voltaic arrangements, and found the above conclusion to +hold good. When any of the following substances in a fused state were +interposed between copper and platina, voltaic action more or less powerful +was produced. Nitre; chlorate of potassa; carbonate of potassa; sulphate of +soda; chloride of lead, of sodium, of bismuth, of calcium; iodide of lead; +oxide of bismuth; oxide of lead: the electric current was in the same +direction as if acids had acted upon the metals. When any of the same +substances, or phosphate of soda, were made to act on platina and iron, +still more powerful voltaic combinations of the same kind were produced. +When either nitrate of silver or chloride of silver was the fluid substance +interposed, there was voltaic action, but the electric current was in the +reverse direction. + + [A] Philosophical Transactions, 1826, p. 406. + +iii. _Theory of Electro-chemical Decomposition._ + +477. The extreme beauty and value of electro-chemical decompositions have +given to that power which the voltaic pile possesses of causing their +occurrence an interest surpassing that of any other of its properties; for +the power is not only intimately connected with the continuance, if not +with the production, of the electrical phenomena, but it has furnished us +with the most beautiful demonstrations of the nature of many compound +bodies; has in the hands of Becquerel been employed in compounding +substances; has given us several new combinations, and sustains us with the +hope that when thoroughly understood it will produce many more. + +478. What may be considered as the general facts of electrochemical +decomposition are agreed to by nearly all who have written on the subject. +They consist in the separation of the decomposable substance acted upon +into its proximate or sometimes ultimate principles, whenever both poles of +the pile are in contact with that substance in a proper condition; in the +evolution of these principles at distant points, i.e. at the poles of the +pile, where they are either finally set free or enter into union with the +substance of the poles; and in the constant determination of the evolved +elements or principles to particular poles according to certain +well-ascertained laws. + +479. But the views of men of science vary much as to the nature of the +action by which these effects are produced; and as it is certain that we +shall be better able to apply the power when we really understand the +manner in which it operates, this difference of opinion is a strong +inducement to further inquiry. I have been led to hope that the following +investigations might be considered, not as an increase of that which is +doubtful, but a real addition to this branch of knowledge. + +480. It will be needful that I briefly state the views of electro-chemical +decomposition already put forth, that their present contradictory and +unsatisfactory state may be seen before I give that which seems to me more +accurately to agree with facts; and I have ventured to discuss them freely, +trusting that I should give no offence to their high-minded authors; for I +felt convinced that if I were right, they would be pleased that their views +should serve as stepping-stones for the advance of science; and that if I +were wrong, they would excuse the zeal which misled me, since it was +exerted for the service of that great cause whose prosperity and progress +they have desired. + +481. Grotthuss, in the year 1805, wrote expressly on the decomposition of +liquids by voltaic electricity[A]. He considers the pile as an electric +magnet, i.e. as an attractive and repulsive agent; the poles having +_attractive_ and _repelling_ powers. The pole from whence resinous +electricity issues attracts hydrogen and repels oxygen, whilst that from +which vitreous electricity proceeds attracts oxygen and repels hydrogen; so +that each of the elements of a particle of water, for instance, is subject +to an attractive and a repulsive force, acting in contrary directions, the +centres of action of which are reciprocally opposed. The action of each +force in relation to a molecule of water situated in the course of the +electric current is in the inverse ratio of the square of the distance at +which it is exerted, thus giving (it is stated) for such a molecule a +_constant force_[B]. He explains the appearance of the elements at a +distance from each other by referring to a succession of decompositions and +recompositions occurring amongst the intervening particles[C], and he +thinks it probable that those which are about to separate at the poles +unite to the two electricities there, and in consequence become gases[D]. + + [A] Annales de Chimie, 1806, tom, lviii. p. 64. + + [B] Ibid. pp. 66, 67, also tom. lxiii. p. 20. + + [C] Ibid. tom. lviii. p. 68, tom, lxiii. p. 20. + + [D] Ibid. tom. lxiii. p. 34. + +482. Sir Humphry Davy's celebrated Bakerian Lecture on some chemical +agencies of electricity was read in November 1806, and is almost entirely +occupied in the consideration of _electro-chemical decompositions_. The +facts are of the utmost value, and, with the general points established, +are universally known. The _mode of action_ by which the effects take place +is stated very generally, so generally, indeed, that probably a dozen +precise schemes of electro-chemical action might be drawn up, differing +essentially from each other, yet all agreeing with the statement there +given. + +483. When Sir Humphry Davy uses more particular expressions, he seems to +refer the decomposing effects to the attractions of the poles. This is the +case in the "general expression of facts" given at pp. 28 and 29 of the +Philosophical Transactions for 1807, also at p. 30. Again at p. 160 of the +Elements of Chemical Philosophy, he speaks of the great attracting powers +of the surfaces of the poles. He mentions the probability of a succession +of decompositions and recompositions throughout the fluid,--agreeing in +that respect with Grotthuss[A]; and supposes that the attractive and +repellent agencies may be communicated from the metallic surfaces +throughout the whole of the menstruum[B], being communicated from _one +particle to another particle of the same kind_[C], and diminishing in +strength from the place of the poles to the middle point, which is +necessarily neutral[D]. In reference to this diminution of power at +increased distances from the poles, he states that in a circuit of ten +inches of water, solution of sulphate of potassa placed four inches from +the positive pole, did not decompose; whereas when only two inches from +that pole, it did render up its elements[E]. + + [A] Philosophical Transactions, 1807, pp. 29, 30. + + [B] Ibid. p. 39. + + [C] Ibid. p. 29. + + [D] Ibid. p. 42. + + [E] Ibid. p. 42. + +484. When in 1826 Sir Humphry Davy wrote again on this subject, he stated +that he found nothing to alter in the fundamental theory laid down in the +original communication[A], and uses the terms attraction and repulsion +apparently in the same sense as before[B]. + + [A] Philosophical Transactions, 1826, p. 383. + + [B] Ibid. pp. 389, 407, 115. + +485. Messrs. Riffault and Chompre experimented on this subject in 1807. +They came to the conclusion that the voltaic current caused decompositions +throughout its whole course in the humid conductor, not merely as +preliminary to the recompositions spoken of by Grotthuss and Davy, but +producing final separation of the elements in the _course_ of the current, +and elsewhere than at the poles. They considered the _negative_ current as +collecting and carrying the acids, &c. to the _positive_ pole, and the +_positive_ current as doing the same duty with the bases, and collecting +them at the _negative_ pole. They likewise consider the currents as _more +powerful_ the nearer they are to their respective poles, and state that the +positive current is _superior_ in power to the negative current[A]. + + [A] Annales de Chimie, 1807, tom. lxiii. p. 83, &c. + +486. M. Biot is very cautious in expressing an opinion as to the cause of +the separation of the elements of a compound body[A]. But as far as the +effects can be understood, he refers them to the opposite electrical states +of the portions of the decomposing substance in the neighbourhood of the +two poles. The fluid is most positive at the positive pole; that state +gradually diminishes to the middle distance, where the fluid is neutral or +not electrical; but from thence to the negative pole it becomes more and +more negative[B]. When a particle of salt is decomposed at the negative +pole, the acid particle is considered as acquiring a negative electrical +state from the pole, stronger than that of the surrounding _undecomposed_ +particles, and is therefore repelled from amongst them, and from out of +that portion of the liquid towards the positive pole, towards which also it +is drawn by the attraction of the pole itself and the particles of positive +_undecomposed_ fluid around it[C]. + + [A] Precis Elementaire de Physique, 3me edition, 1824, tom. i. p. 641. + + [B] Ibid. p. 637. + + [C] Ibid. pp. 641, 642. + +487. M. Biot does not appear to admit the successive decompositions and +recompositions spoken of by Grotthuss, Davy, &c. &c.; but seems to consider +the substance whilst in transit as combined with, or rather attached to, +the electricity for the time[A], and though it communicates this +electricity to the surrounding undecomposed matter with which it is in +contact, yet it retains during the transit a little superiority with +respect to that kind which it first received from the pole, and is, by +virtue of that difference, carried forward through the fluid to the +opposite pole[B]. + + [A] Precis Elementaire de Physique, 3me edition, 1824, tom. i. p. 636. + + [B] Ibid. p, 642. + +488. This theory implies that decomposition takes place at both poles upon +distinct portions of fluid, and not at all in the intervening parts. The +latter serve merely as imperfect conductors, which, assuming an electric +state, urge particles electrified more highly at the poles through them in +opposite directions, by virtue of a series of ordinary electrical +attractions and repulsions[A]. + + [A] Precis Elementaire de Physique, 3me edition, 1824, tom. i. pp. + 638, 642. + +489. M.A. de la Rive investigated this subject particularly, and published +a paper on it in 1825[A]. He thinks those who have referred the phenomena +to the attractive powers of the poles, rather express the general fact than +give any explication of it. He considers the results as due to an actual +combination of the elements, or rather of half of them, with the +electricities passing from the poles in consequence of a kind of play of +affinities between the matter and electricity[B]. The current from the +positive pole combining with the hydrogen, or the bases it finds there, +leaves the oxygen and acids at liberty, but carries the substances it is +united with across to the negative pole, where, because of the peculiar +character of the metal as a conductor[C], it is separated from them, +entering the metal and leaving the hydrogen or bases upon its surface. In +the same manner the electricity from the negative pole sets the hydrogen +and bases which it finds there, free, but combines with the oxygen and +acids, carries them across to the positive pole, and there deposits +them[D]. In this respect M. de la Rive's hypothesis accords in part with +that of MM. Riffault and Chompre (485.). + + [A] Annales de Chimie, tom, xxviii. p. 190. + + [B] Ibid. pp. 200, 202. + + [C] Ibid. p. 202. + + [D] Ibid. p. 201. + +490. M. de la Rive considers the portions of matter which are decomposed to +be those contiguous to _both_ poles[A]. He does not admit with others the +successive decompositions and recompositions in the whole course of the +electricity through the humid conductor[B], but thinks the middle parts are +in themselves unaltered, or at least serve only to conduct the two contrary +currents of electricity and matter which set off from the opposite +poles[C]. The decomposition, therefore, of a particle of water, or a +particle of salt, may take place at either pole, and when once effected, it +is final for the time, no recombination taking place, except the momentary +union of the transferred particle with the electricity be so considered. + + [A] Annales de Chimie, tom, xxviii. pp. 197, 198. + + [B] Ibid. pp. 192, 199. + + [C] Ibid. p. 200. + +491. The latest communication that I am aware of on the subject is by M. +Hachette: its date is October 1832[A]. It is incidental to the description +of the decomposition of water by the magneto-electric currents (346.). One +of the results of the experiment is, that "it is not necessary, as has been +supposed, that for the chemical decomposition of water, the action of the +two electricities, positive and negative, should be simultaneous." + + [A] Annales de Chimie, tom, xxviii. tom. li. p. 73. + +492. It is more than probable that many other views of electro-chemical +decomposition may have been published, and perhaps amongst them some which, +differing from those above, might, even in my own opinion, were I +acquainted with them, obviate the necessity for the publication of my +views. If such be the case, I have to regret my ignorance of them, and +apologize to the authors. + + * * * * * + +493. That electro-chemical decomposition does not depend upon any direct +attraction and repulsion of the poles (meaning thereby the metallic +terminations either of the voltaic battery, or ordinary electrical machine +arrangements (312.),) upon the elements in contact with or near to them, +appeared very evident from the experiments made in air (462, 465, &c.), +when the substances evolved did not collect about any poles, but, in +obedience to the direction of the current, were evolved, and I would say +ejected, at the extremities of the decomposing substance. But +notwithstanding the extreme dissimilarity in the character of air and +metals, and the almost total difference existing between them as to their +mode of conducting electricity, and becoming charged with it, it might +perhaps still be contended, although quite hypothetically, that the +bounding portions of air were now the surfaces or places of attraction, as +the metals had been supposed to be before. In illustration of this and +other points, I endeavoured to devise an arrangement by which I could +decompose a body against a surface of water, as well as against air or +metal, and succeeded in doing so unexceptionably in the following manner. +As the experiment for very natural reasons requires many precautions, to be +successful, and will be referred to hereafter in illustration of the views +I shall venture to give, I must describe it minutely. + +494. A glass basin (fig. 52.), four inches in diameter and four inches +deep, had a division of mica _a_, fixed across the upper part so as to +descend one inch and a half below the edge, and be perfectly water-tight at +the sides: a plate of platina _b_, three inches wide, was put into the +basin on one side of the division _a_, and retained there by a glass block +below, so that any gas produced by it in a future stage of the experiment +should not ascend beyond the mica, and cause currents in the liquid on that +side. A strong solution of sulphate of magnesia was carefully poured +without splashing into the basin, until it rose a little above the lower +edge of the mica division _a_, great care being taken that the glass or +mica on the unoccupied or _c_ side of the division in the figure, should +not be moistened by agitation of the solution above the level to which it +rose. A thin piece of clean cork, well-wetted in distilled water, was then +carefully and lightly placed on the solution at the _c_ side, and distilled +water poured gently on to it until a stratum the eighth of an inch in +thickness appeared over the sulphate of magnesia; all was then left for a +few minutes, that any solution adhering to the cork might sink away from +it, or be removed by the water on which it now floated; and then more +distilled water was added in a similar manner, until it reached nearly to +the top of the glass. In this way solution of the sulphate occupied the +lower part of the glass, and also the upper on the right-hand side of the +mica; but on the left-hand side of the division a stratum of water from _c_ +to _d_, one inch and a half in depth, reposed upon it, the two presenting, +when looked through horizontally, a comparatively definite plane of +contact. A second platina pole _e_, was arranged so as to be just under the +surface of the water, in a position nearly horizontal, a little inclination +being given to it, that gas evolved during decomposition might escape: the +part immersed was three inches and a half long by one inch wide, and about +seven-eighths of an inch of water intervened between it and the solution of +sulphate of magnesia. + +495. The latter pole _e_ was now connected with the negative end of a +voltaic battery, of forty pairs of plates four inches square, whilst the +former pole _b_ was connected with the positive end. There was action and +gas evolved at both poles; but from the intervention of the pure water, the +decomposition was very feeble compared to what the battery would have +effected in a uniform solution. After a little while (less than a minute,) +magnesia also appeared at the negative side: _it did not make its +appearance at the negative metallic pole, but in the water_, at the plane +where the solution and the water met; and on looking at it horizontally, it +could be there perceived lying in the water upon the solution, not rising +more than the fourth of an inch above the latter, whilst the water between +it and the negative pole was perfectly clear. On continuing the action, the +bubbles of hydrogen rising upwards from the negative pole impressed a +circulatory movement on the stratum of water, upwards in the middle, and +downwards at the side, which gradually gave an ascending form to the cloud +of magnesia in the part just under the pole, having an appearance as if it +were there attracted to it; but this was altogether an effect of the +currents, and did not occur until long after the phenomena looked for were +satisfactorily ascertained. + +496. After a little while the voltaic communication was broken, and the +platina poles removed with as little agitation as possible from the water +and solution, for the purpose of examining the liquid adhering to them. The +pole _c_, when touched by turmeric paper, gave no traces of alkali, nor +could anything but pure water be found upon it. The pole _b_, though drawn +through a much greater depth and quantity of fluid, was found so acid as to +give abundant evidence to litmus paper, the tongue, and other tests. Hence +there had been no interference of alkaline salts in any way, undergoing +first decomposition, and then causing the separation of the magnesia at a +distance from the pole by mere chemical agencies. This experiment was +repeated again and again, and always successfully. + +497. As, therefore, the substances evolved in cases of electrochemical +decomposition may be made to appear against air (465. 469.),--which, +according to common language, is not a conductor, nor is decomposed, or +against water (495.), which is a conductor, and can be decomposed,--as well +as against the metal poles, which are excellent conductors, but +undecomposable, there appears but little reason to consider the phenomena +generally, as due to the _attraction_ or attractive powers of the latter, +when used in the ordinary way, since similar attractions can hardly be +imagined in the former instances. + +498. It may be said that the surfaces of air or of water in these cases +become the poles, and exert attractive powers; but what proof is there of +that, except the fact that the matters evolved collect there, which is the +point to be explained, and cannot be justly quoted as its own explanation? +Or it may be said, that any section of the humid conductor, as that in the +present case, where the solution and the water meet, may be considered as +representing the pole. But such does not appear to me to be the view of +those who have written on the subject, certainly not of some of them, and +is inconsistent with the supposed laws which they have assumed, as +governing the diminution of power at increased distances from the poles. + +499. Grotthuss, for instance, describes the poles as centres of attractive +and repulsive forces (481.), these forces varying inversely as the squares +of the distances, and says, therefore, that a particle placed anywhere +between the poles will be acted upon by a constant force. But the compound +force, resulting from such a combination as he supposes, would be anything +but a constant force; it would evidently be a force greatest at the poles, +and diminishing to the middle distance. Grotthuss is right, however, _in +the fact_, according to my experiments (502. 505.), that the particles are +acted upon by equal force everywhere in the circuit, when the conditions of +the experiment are the simplest possible; but the fact is against his +theory, and is also, I think, against all theories that place the +decomposing effect in the attractive power of the poles. + +500. Sir Humphry Davy, who also speaks of the _diminution_ of power with +increase of distance from the poles[A] (483.), supposes, that when both +poles are acting on substances to decompose them, still the power of +decomposition _diminishes_ to the middle distance. In this statement of +fact he is opposed to Grotthuss, and quotes an experiment in which sulphate +of potassa, placed at different distances from the poles in a humid +conductor of constant length, decomposed when near the pole, but not when +at a distance. Such a consequence would necessarily result theoretically +from considering the poles as centres of attraction and repulsion; but I +have not found the statement borne out by other experiments (505.); and in +the one quoted by him the effect was doubtless due to some of the many +interfering causes of variation which attend such investigations. + + [A] Philosophical Transactions, 1807, p. 42. + +501. A glass vessel had a platina plate fixed perpendicularly across it, so +as to divide it into two cells: a head of mica was fixed over it, so as to +collect the gas it might evolve during experiments; then each cell, and the +space beneath the mica, was filled with dilute sulphuric acid. Two poles +were provided, consisting each of a platina wire terminated by a plate of +the same metal; each was fixed into a tube passing through its upper end by +an air-tight joint, that it might be moveable, and yet that the gas evolved +at it might be collected. The tubes were filled with the acid, and one +immersed in each cell. Each platina pole was equal in surface to one side +of the dividing plate in the middle glass vessel, and the whole might be +considered as an arrangement between the poles of the battery of a humid +decomposable conductor divided in the middle by the interposed platina +diaphragm. It was easy, when required, to draw one of the poles further up +the tube, and then the platina diaphragm was no longer in the middle of the +humid conductor. But whether it were thus arranged at the middle, or +towards one side, it always evolved a quantity of oxygen and hydrogen equal +to that evolved by both the extreme plates[A]. + + [A] There are certain precautions, in this and such experiments, which + can only be understood and guarded against by a knowledge of the + phenomena to be described in the first part of the Sixth Series of + these Researches. + +502. If the wires of a galvanometer be terminated by plates, and these be +immersed in dilute acid, contained in a regularly formed rectangular glass +trough, connected at each end with a voltaic battery by poles equal to the +section of the fluid, a part of the electricity will pass through the +instrument and cause a certain deflection. And if the plates are always +retained at the _same distance from each other_ and from the sides of the +trough, are always parallel to each other, and uniformly placed relative to +the fluid, then, whether they are immersed near the middle of the +decomposing solution, or at one end, still the instrument will indicate the +same deflection, and consequently the same electric influence. + +503. It is very evident, that when the width of the decomposing conductor +varies, as is always the case when mere wires or plates, as poles, are +dipped into or are surrounded by solution, no constant expression can be +given as to the action upon a single particle placed in the course of the +current, nor any conclusion of use, relative to the supposed attractive or +repulsive force of the poles, be drawn. The force will vary as the distance +from the pole varies; as the particle is directly between the poles, or +more or less on one side; and even as it is nearer to or further from the +sides of the containing vessels, or as the shape of the vessel itself +varies; and, in fact, by making variations in the form of the arrangement, +the force upon any single particle may be made to increase, or diminish, or +remain constant, whilst the distance between the particle and the pole +shall remain the same; or the force may be made to increase, or diminish, +or remain constant, either as the distance increases or as it diminishes. + +504. From numerous experiments, I am led to believe the following general +expression to be correct; but I purpose examining it much further, and +would therefore wish not to be considered at present as pledged to its +accuracy. The _sum of chemical decomposition is constant_ for any section +taken across a decomposing conductor, uniform in its nature, at whatever +distance the poles may be from each other or from the section; or however +that section may intersect the currents, whether directly across them, or +so oblique as to reach almost from pole to pole, or whether it be plane, or +curved, or irregular in the utmost degree; provided the current of +electricity be retained constant in quantity (377.), and that the section +passes through every part of the current through the decomposing conductor. + +505. I have reason to believe that the statement might be made still more +general, and expressed thus: That _for a constant quantity of electricity, +whatever the decomposing conductor may be, whether water, saline solutions, +acids, fused bodies, &c., the amount of electro-chemical action is also a +constant quantity, i.e. would always be equivalent to a standard chemical +effect founded upon ordinary chemical affinity_. I have this investigation +in hand, with several others, and shall be prepared to give it in the next +series but one of these Researches. + +506. Many other arguments might be adduced against the hypotheses of the +attraction of the poles being the cause of electro-chemical decomposition; +but I would rather pass on to the view I have thought more consistent with +facts, with this single remark; that if decomposition by the voltaic +battery depended upon the attraction of the poles, or the parts about them, +being stronger than the mutual attraction of the particles separated, it +would follow that the weakest _electrical_ attraction was stronger than, if +not the strongest, yet very strong _chemical_ attraction, namely, such as +exists between oxygen and hydrogen, potassium and oxygen, chlorine and +sodium, acid and alkali, &c., a consequence which, although perhaps not +impossible, seems in the present state of the subject very unlikely. + +507. The view which M. de la Rive has taken (489.), and also MM. Riffault +and Chompre (485.), of the manner in which electro-chemical decomposition +is effected, is very different to that already considered, and is not +affected by either the arguments or facts urged against the latter. +Considering it as stated by the former philosopher, it appears to me to be +incompetent to account for the experiments of decomposition against +surfaces of air (462. 469.) and water (495.), which I have described; for +if the physical differences between metals and humid conductors, which M. +de la Rive supposes to account for the transmission of the compound of +matter and electricity in the latter, and the transmission of the +electricity only with the rejection of the matter in the former, be allowed +for a moment, still the analogy of air to metal is, electrically +considered, so small, that instead of the former replacing the latter +(462.), an effect the very reverse might have been expected. Or if even +that were allowed, the experiment with water (495.), at once sets the +matter at rest, the decomposing pole being now of a substance which is +admitted as competent to transmit the assumed compound of electricity and +matter. + +508. With regard to the views of MM. Riffault and Chompre (485.), the +occurrence of decomposition alone in the _course_ of the current is so +contrary to the well-known effects obtained in the forms of experiment +adopted up to this time, that it must be proved before the hypothesis +depending on it need be considered. + +509. The consideration of the various theories of electro-chemical +decomposition, whilst it has made me diffident, has also given me +confidence to add another to the number; for it is because the one I have +to propose appears, after the most attentive consideration, to explain and +agree with the immense collection of facts belonging to this branch of +science, and to remain uncontradicted by, or unopposed to, any of them, +that I have been encouraged to give it. + +510. Electro-chemical decomposition is well known to depend essentially +upon the _current_ of electricity. I have shown that in certain cases +(375.) the decomposition is proportionate to the quantity of electricity +passing, whatever may be its intensity or its source, and that the same is +probably true for all cases (377.), even when the utmost generality is +taken on the one hand, and great precision of expression on the other +(505.). + +511. In speaking of the current, I find myself obliged to be still more +particular than on a former occasion (283.), in consequence of the variety +of views taken by philosophers, all agreeing in the effect of the current +itself. Some philosophers, with Franklin, assume but one electric fluid; +and such must agree together in the general uniformity and character of the +electric current. Others assume two electric fluids; and here singular +differences have arisen. + +512. MM. Riffault and Chompre, for instance, consider the positive and +negative currents each as causing decomposition, and state that the +positive current is _more powerful_ than the negative current[A], the +nitrate of soda being, under similar circumstances, decomposed by the +former, but not by the latter. + + [A] Annales de Chimie, 1807, tom, lxiii. p. 84. + +513. M. Hachette states[A] that "it is not necessary, as has been believed, +that the action of the two electricities, positive and negative, should be +simultaneous for the decomposition of water." The passage implying, if I +have caught the meaning aright, that one electricity can be obtained, and +can be applied in effecting decompositions, independent of the other. + + [A] Annales de Chimie, 1832, tom. li. p. 73. + +514. The view of M. de la Rive to a certain extent agrees with that of M. +Hachette, for he considers that the two electricities decompose separate +portions of water (490.)[A]. In one passage he speaks of the two +electricities as two influences, wishing perhaps to avoid offering a +decided opinion upon the independent existence of electric fluids; but as +these influences are considered as combining with the elements set free as +by a species of chemical affinity, and for the time entirely masking their +character, great vagueness of idea is thus introduced, inasmuch as such a +species of combination can only be conceived to take place between things +having independent existences. The two elementary electric currents, moving +in opposite directions, from pole to pole, constitute the ordinary _voltaic +current._ + + [A] Annales de Chimie, 1825, tom, xxviii. pp. 197, 201. + +515. M. Grotthuss is inclined to believe that the elements of water, when +about to separate at the poles, combine with the electricities, and so +become gases. M. de la Rive's view is the exact reverse of this: whilst +passing through the fluid, they are, according to him, compounds with the +electricities; when evolved at the poles, they are de-electrified. + +516. I have sought amongst the various experiments quoted in support of +these views, or connected with electro-chemical decompositions or electric +currents, for any which might be considered as sustaining the theory of two +electricities rather than that of one, but have not been able to perceive a +single fact which could be brought forward for such a purpose: or, +admitting the hypothesis of two electricities, much less have I been able +to perceive the slightest grounds for believing that one electricity in a +current can be more powerful than the other, or that it can be present +without the other, or that one can be varied or in the slightest degree +affected, without a corresponding variation in the other[A]. If, upon the +supposition of two electricities, a current of one can be obtained without +the other, or the current of one be exalted or diminished more than the +other, we might surely expect some variation either of the chemical or +magnetical effects, or of both; but no such variations have been observed. +If a current be so directed that it may act chemically in one part of its +course, and magnetically in another, the two actions are always found to +take place together. A current has not, to my knowledge, been produced +which could act chemically and not magnetically, nor any which can act on +the magnet, and not _at the same time_ chemically[B]. + + [A] See now in relation to this subject, 1627-1645.--_Dec. 1838._ + + [B] Thermo-electric currents are of course no exception, because when + they fail to act chemically they also fail to be currents. + +517. _Judging from facts only_, there is not as yet the slightest reason +for considering the influence which is present in what we call the electric +current,--whether in metals or fused bodies or humid conductors, or even in +air, flame, and rarefied elastic media,--as a compound or complicated +influence. It has never been resolved into simpler or elementary +influences, and may perhaps best be conceived of as _an axis of power +having contrary forces, exactly equal in amount, in contrary directions_. + + * * * * * + +518. Passing to the consideration of electro-chemical decomposition, it +appears to me that the effect is produced by an _internal corpuscular +action_, exerted according to the direction of the electric current, and +that it is due to a force either _super to_, or _giving direction to the +ordinary chemical affinity_ of the bodies present. The body under +decomposition may be considered as a mass of acting particles, all those +which are included in the course of the electric current contributing to +the final effect; and it is because the ordinary chemical affinity is +relieved, weakened, or partly neutralized by the influence of the electric +current in one direction parallel to the course of the latter, and +strengthened or added to in the opposite direction, that the combining +particles have a tendency to pass in opposite courses. + +519. In this view the effect is considered as _essentially dependent_ upon +the _mutual chemical affinity_ of the particles of opposite kinds. +Particles _aa_, fig. 53, could not be transferred or travel from one pole N +towards the other P, unless they found particles of the opposite kind _bb_, +ready to pass in the contrary direction: for it is by virtue of their +increased affinity for those particles, combined with their diminished +affinity for such as are behind them in their course, that they are urged +forward: and when any one particle _a_, fig. 54, arrives at the pole, it is +excluded or set free, because the particle _b_ of the opposite kind, with +which it was the moment before in combination, has, under the superinducing +influence of the current, a greater attraction for the particle _a'_, which +is before it in its course, than for the particle _a_, towards which its +affinity has been weakened. + +520. As far as regards any single compound particle, the case may be +considered as analogous to one of ordinary decomposition, for in fig. 54, +_a_ may be conceived to be expelled from the compound _ab_ by the superior +attraction of _a'_ for _b_, that superior attraction belonging to it in +consequence of the relative position of _a'b_ and _a_ to the direction of +the axis of electric power (517.) superinduced by the current. But as all +the compound particles in the course of the current, except those actually +in contact with the poles, act conjointly, and consist of elementary +particles, which, whilst they are in one direction expelling, are in the +other being expelled, the case becomes more complicated, but not more +difficult of comprehension. + +521. It is not here assumed that the acting particles must be in a right +line between the poles. The lines of action which may be supposed to +represent the electric currents passing through a decomposing liquid, have +in many experiments very irregular forms; and even in the simplest case of +two wires or points immersed as poles in a drop or larger single portion of +fluid, these lines must diverge rapidly from the poles; and the direction +in which the chemical affinity between particles is most powerfully +modified (519. 520.) will vary with the direction of these lines, according +constantly with them. But even in reference to these lines or currents, it +is not supposed that the particles which mutually affect each other must of +necessity be parallel to them, but only that they shall accord generally +with their direction. Two particles, placed in a line perpendicular to the +electric current passing in any particular place, are not supposed to have +their ordinary chemical relations towards each other affected; but as the +line joining them is inclined one way to the current their mutual affinity +is increased; as it is inclined in the other direction it is diminished; +and the effect is a maximum, when that line is parallel to the current[A]. + + [A] In reference to this subject see now electrolytic induction and + discharge, Series XII. P viii. 1343-1351, &c.--_Dec. 1838._ + +522. That the actions, of whatever kind they may be, take place frequently +in oblique directions is evident from the circumstance of those particles +being included which in numerous cases are not in a line between the poles. +Thus, when wires are used as poles in a glass of solution, the +decompositions and recompositions occur to the right or left of the direct +line between the poles, and indeed in every part to which the currents +extend, as is proved by many experiments, and must therefore often occur +between particles obliquely placed as respects the current itself; and when +a metallic vessel containing the solution is made one pole, whilst a mere +point or wire is used for the other, the decompositions and recompositions +must frequently be still more oblique to the course of the currents. + +523. The theory which I have ventured to put forth (almost) requires an +admission, that in a compound body capable of electro-chemical +decomposition the elementary particles have a mutual relation to, and +influence upon each other, extending beyond those with which they are +immediately combined. Thus in water, a particle of hydrogen in combination +with oxygen is considered as not altogether indifferent to other particles +of oxygen, although they are combined with other particles of hydrogen; but +to have an affinity or attraction towards them, which, though it does not +at all approach in force, under ordinary circumstances, to that by which it +is combined with its own particle, can, under the electric influence, +exerted in a definite direction, be made even to surpass it. This general +relation of particles already in combination to other particles with which +they are not combined, is sufficiently distinct in numerous results of a +purely chemical character; especially in those where partial decompositions +only take place, and in Berthollet's experiments on the effects of quantity +upon affinity: and it probably has a direct relation to, and connexion +with, attraction of aggregation, both in solids and fluids. It is a +remarkable circumstance, that in gases and vapours, where the attraction of +aggregation ceases, there likewise the decomposing powers of electricity +apparently cease, and there also the chemical action of quantity is no +longer evident. It seems not unlikely, that the inability to suffer +decomposition in these cases may be dependent upon the absence of that +mutual attractive relation of the particles which is the cause of +aggregation. + +524. I hope I have now distinctly stated, although in general terms, the +view I entertain of the cause of electro-chemical decomposition, _as far as +that cause can at present be traced and understood_. I conceive the effects +to arise from forces which are _internal_, relative to the matter under +decomposition--and _not external_, as they might be considered, if directly +dependent upon the poles. I suppose that the effects are due to a +modification, by the electric current, of the chemical affinity of the +particles through or by which that current is passing, giving them the +power of acting more forcibly in one direction than in another, and +consequently making them travel by a series of successive decompositions +and recompositions in opposite directions, and finally causing their +expulsion or exclusion at the boundaries of the body under decomposition, +in the direction of the current, _and that_ in larger or smaller +quantities, according as the current is more or less powerful (377.). I +think, therefore, it would be more philosophical, and more directly +expressive of the facts, to speak of such a body, in relation to the +current passing through it, rather than to the poles, as they are usually +called, in contact with it; and say that whilst under decomposition, +oxygen, chlorine, iodine, acids, &c., are rendered at its negative +extremity, and combustibles, metals, alkalies, bases, &c., at its positive +extremity (467.), I do not believe that a substance can be transferred in +the electric current beyond the point where it ceases to find particles +with which it can combine; and I may refer to the experiments made in air +(465.) and in water (495.), already quoted, for facts illustrating these +views in the first instance; to which I will now add others. + +525. In order to show the dependence of the decomposition and transfer of +elements upon the chemical affinity of the substances present, experiments +were made upon sulphuric acid in the following manner. Dilute sulphuric +acid was prepared: its specific gravity was 1.0212. A solution of sulphate +of soda was also prepared, of such strength that a measure of it contained +exactly as much sulphuric acid as an equal measure of the diluted acid just +referred to. A solution of pure soda, and another of pure ammonia, were +likewise prepared, of such strengths that a measure of either should be +exactly neutralized by a measure of the prepared sulphuric acid. + +526. Four glass cups were then arranged, as in fig. 55; seventeen measures +of the free sulphuric acid (525.) were put into each of the vessels _a_ and +_b_, and seventeen measures of the solution of sulphate of soda into each +of the vessels A and B. Asbestus, which had been well-washed in acid, acted +upon by the voltaic pile, well-washed in water, and dried by pressure, was +used to connect _a_ with _b_ and A with B, the portions being as equal as +they could be made in quantity, and cut as short as was consistent with +their performing the part of effectual communications, _b_ and A were +connected by two platina plates or poles soldered to the extremities of one +wire, and the cups _a_ and B were by similar platina plates connected with +a voltaic battery of forty pairs of plates four inches square, that in _a_ +being connected with the negative, and that in B with the positive pole. +The battery, which was not powerfully charged, was retained in +communication above half an hour. In this manner it was certain that the +same electric current had passed through _a b_ and A B, and that in each +instance the same quantity and strength of acid had been submitted to its +action, but in one case merely dissolved in water, and in the other +dissolved and also combined with an alkali. + +527. On breaking the connexion with the battery, the portions of asbestus +were lifted out, and the drops hanging at the ends allowed to fall each +into its respective vessel. The acids in _a_ and _b_ were then first +compared, for which purpose two evaporating dishes were balanced, and the +acid from _a_ put into one, and that from _b_ into the other; but as one +was a little heavier than the other, a small drop was transferred from the +heavier to the lighter, and the two rendered equal in weight. Being +neutralized by the addition of the soda solution (525.), that from _a_, or +the negative vessel, required 15 parts of the soda solution, and that from +_b_, or the positive vessel, required 16.3 parts. That the sum of these is +not 34 parts is principally due to the acid removed with the asbestus; but +taking the mean of 15.65 parts, it would appear that a twenty-fourth part +of the acid originally in the vessel _a_ had passed, through the influence +of the electric current, from _a_ into _b_. + +528. In comparing the difference of acid in A and B, the necessary equality +of weight was considered as of no consequence, because the solution was at +first neutral, and would not, therefore, affect the test liquids, and all +the evolved acid would be in B, and the free alkali in A. The solution in A +required 3.2 measures of the prepared acid (525.) to neutralize it, and the +solution in B required also 3.2 measures of the soda solution (525.) to +neutralize it. As the asbestus must have removed a little acid and alkali +from the glasses, these quantities are by so much too small; and therefore +it would appear that about a tenth of the acid originally in the vessel A +had been transferred into B during the continuance of the electric action. + +529. In another similar experiment, whilst a thirty-fifth part of the acid +passed from _a_ to _b_; in the free acid vessels, between a tenth and an +eleventh passed from A to B in the combined acid vessels. Other experiments +of the same kind gave similar results. + +530. The variation of electro-chemical decomposition, the transfer of +elements and their accumulation at the poles, according as the substance +submitted to action consists of particles opposed more or less in their +chemical affinity, together with the consequent influence of the latter +circumstances, are sufficiently obvious in these cases, where sulphuric +acid is acted upon in the _same quantity_ by the _same_ electric current, +but in one case opposed to the comparatively weak affinity of water for it, +and in the other to the stronger one of soda. In the latter case the +quantity transferred is from two and a half to three times what it is in +the former; and it appears therefore very evident that the transfer is +greatly dependent upon the mutual action of the particles of the +decomposing bodies[A]. + + [A] See the note to (675.),--_Dec. 1838._ + +531. In some of the experiments the acid from the vessels _a_ and _b_ was +neutralized by ammonia, then evaporated to dryness, heated to redness, and +the residue examined for sulphates. In these cases more sulphate was always +obtained from _a_ than from _b_; showing that it had been impossible to +exclude saline bases (derived from the asbestus, the glass, or perhaps +impurities originally in the acid,) and that they had helped in +transferring the acid into _b_. But the quantity was small, and the acid +was principally transferred by relation to the water present. + +532. I endeavoured to arrange certain experiments by which saline solutions +should be decomposed against surfaces of water; and at first worked with +the electric machine upon a piece of bibulous paper, or asbestus moistened +in the solution, and in contact at its two extremities with pointed pieces +of paper moistened in pure water, which served to carry the electric +current to and from the solution in the middle piece. But I found numerous +interfering difficulties. Thus, the water and solutions in the pieces of +paper could not be prevented from mingling at the point where they touched. +Again, sufficient acid could be derived from the paper connected with the +discharging train, or it may be even from the air itself, under the +influence of electric action, to neutralize the alkali developed at the +positive extremity of the decomposing solution, and so not merely prevent +its appearance, but actually transfer it on to the metal termination: and, +in fact, when the paper points were not allowed to touch there, and the +machine was worked until alkali was evolved at the delivering or positive +end of the turmeric paper, containing the sulphate of soda solution, it was +merely necessary to place the opposite receiving point of the paper +connected with the discharging train, which had been moistened by distilled +water, upon the brown turmeric point and press them together, when the +alkaline effect immediately disappeared. + +533. The experiment with sulphate of magnesia already described (495.) is a +case in point, however, and shows most clearly that the sulphuric acid and +magnesia contributed to each other's transfer and final evolution, exactly +as the same acid and soda affected each other in the results just given +(527, &c.); and that so soon as the magnesia advanced beyond the reach of +the acid, and found no other substance with which it could combine, it +appeared in its proper character, and was no longer able to continue its +progress towards the negative pole. + + * * * * * + +534. The theory I have ventured to put forth appears to me to explain all +the prominent features of electro-chemical decomposition in a satisfactory +manner. + +535. In the first place, it explains why, in all ordinary cases, the +evolved substances _appear only at the poles_; for the poles are the +limiting surfaces of the decomposing substance, and except at them, every +particle finds other particles having a contrary tendency with which it can +combine. + +536. Then it explains why, in numerous cases, the elements or evolved +substances are not _retained_ by the poles; and this is no small difficulty +in those theories which refer the decomposing effect directly to the +attractive power of the poles. If, in accordance with the usual theory, a +piece of platina be supposed to have sufficient power to attract a particle +of hydrogen from the particle of oxygen with which it was the instant +before combined, there seems no sufficient reason, nor any fact, except +those to be explained, which show why it should not, according to analogy +with all ordinary attractive forces, as those of gravitation, magnetism, +cohesion, chemical affinity, &c. _retain_ that particle which it had just +before taken from a distance and from previous combination. Yet it does not +do so, but allows it to escape freely. Nor does this depend upon its +assuming the gaseous state, for acids and alkalies, &c. are left equally at +liberty to diffuse themselves through the fluid surrounding the pole, and +show no particular tendency to combine with or adhere to the latter. And +though there are plenty of cases where combination with the pole does take +place, they do not at all explain the instances of non-combination, and do +not therefore in their particular action reveal the general principle of +decomposition. + +537. But in the theory that I have just given, the effect appears to be a +natural consequence of the action: the evolved substances are _expelled_ +from the decomposing mass (518. 519.), not _drawn out by an attraction_ +which ceases to act on one particle without any assignable reason, while it +continues to act on another of the same kind: and whether the poles be +metal, water, or air, still the substances are evolved, and are sometimes +set free, whilst at others they unite to the matter of the poles, according +to the chemical nature of the latter, i.e. their chemical relation to those +particles which are leaving the substance under operation. + +538. The theory accounts for the _transfer of elements_ in a manner which +seems to me at present to leave nothing unexplained; and it was, indeed, +the phenomena of transfer in the numerous cases of decomposition of bodies +rendered fluid by heat (380. 402.), which, in conjunction with the +experiments in air, led to its construction. Such cases as the former where +binary compounds of easy decomposability are acted upon, are perhaps the +best to illustrate the theory. + +539. Chloride of lead, for instance, fused in a bent tube (400.), and +decomposed by platina wires, evolves lead, passing to what is usually +called the negative pole, and chlorine, which being evolved at the positive +pole, is in part set free, and in part combines with the platina. The +chloride of platina formed, being soluble in the chloride of lead, is +subject to decomposition, and the platina itself is gradually transferred +across the decomposing matter, and found with the lead at the negative +pole. + +540. Iodide of lead evolves abundance of lead at the negative pole, and +abundance of iodine at the positive pole. + +541. Chloride of silver furnishes a beautiful instance, especially when +decomposed by silver wire poles. Upon fusing a portion of it on a piece of +glass, and bringing the poles into contact with it, there is abundance of +silver evolved at the negative pole, and an equal abundance absorbed at the +positive pole, for no chlorine is set free: and by careful management, the +negative wire may be withdrawn from the fused globule as the silver is +reduced there, the latter serving as the continuation of the pole, until a +wire or thread of revived silver, five or six inches in length, is +produced; at the same time the silver at the positive pole is as rapidly +dissolved by the chlorine, which seizes upon it, so that the wire has to be +continually advanced as it is melted away. The whole experiment includes +the action of only two elements, silver and chlorine, and illustrates in a +beautiful manner their progress in opposite directions, parallel to the +electric current, which is for the time giving a uniform general direction +to their mutual affinities (524.). + +542. According to my theory, an element or a substance not decomposable +under the circumstances of the experiment, (as for instance, a dilute acid +or alkali,) should not be transferred, or pass from pole to pole, unless it +be in chemical relation to some other element or substance tending to pass +in the opposite direction, for the effect is considered as essentially due +to the mutual relation of such particles. But the theories attributing the +determination of the elements to the attractions and repulsions of the +poles require no such condition, i.e. there is no reason apparent why the +attraction of the positive pole, and the repulsion of the negative pole, +upon a particle of free acid, placed in water between them, should not +(with equal currents of electricity) be as strong as if that particle were +previously combined with alkali; but, on the contrary, as they have not a +powerful chemical affinity to overcome, there is every reason to suppose +they would be stronger, and would sooner bring the acid to rest at the +positive pole[A]. Yet such is not the case, as has been shown by the +experiments on free and combined acid (526. 528.). + + [A] Even Sir Humphry Davy considered the attraction of the pole as + being communicated from one particle to another of the _same_ kind + (483.). + +543. Neither does M. de la Rive's theory, as I understand it, _require_ +that the particles should be in combination: it does not even admit, where +there are two sets of particles capable of combining with and passing by +each other, that they do combine, but supposes that they travel as separate +compounds of matter and electricity. Yet in fact the free substance +_cannot_ travel, the combined one _can_. + +544. It is very difficult to find cases amongst solutions or fluids which +shall illustrate this point, because of the difficulty of finding two +fluids which shall conduct, shall not mingle, and in which an element +evolved from one shall not find a combinable element in the other. +_Solutions_ of acids or alkalies will not answer, because they exist by +virtue of an attraction; and increasing the solubility of a body in one +direction, and diminishing it in the opposite, is just as good a reason for +transfer, as modifying the affinity between the acids and alkalies +themselves[A]. Nevertheless the case of sulphate of magnesia is in point +(494. 495.), and shows that _one element or principle only_ has no power of +transference or of passing towards either pole. + + [A] See the note to (670.).--_Dec. 1838._ + +545. Many of the metals, however, in their solid state, offer very fair +instances of the kind required. Thus, if a plate of platina be used as the +positive pole in a solution of sulphuric acid, oxygen will pass towards it, +and so will acid; but these are not substances having such chemical +relation to the platina as, even under the favourable condition +superinduced by the current (518. 524.), to combine with it; the platina +therefore remains where it was first placed, and has no tendency to pass +towards the negative pole. But if a plate of iron, zinc or copper, be +substituted for the platina, then the oxygen and acid can combine with +these, and the metal immediately begins to travel (as an oxide) to the +opposite pole, and is finally deposited there. Or if, retaining the platina +pole, a fused chloride, as of lead, zinc, silver, &c., be substituted for +the sulphuric acid, then, as the platina finds an element it can combine +with, it enters into union, acts as other elements do in cases of voltaic +decomposition, is rapidly transferred across the melted matter, and +expelled at the negative pole. + +546. I can see but little reason in the theories referring the +electro-chemical decomposition to the attractions and repulsions of the +poles, and I can perceive none in M. de la Rive's theory, why the metal of +the positive pole should not be transferred across the intervening +conductor, and deposited at the negative pole, even when it cannot act +chemically upon the element of the fluid surrounding it. It cannot be +referred to the attraction of cohesion preventing such an effect; for if +the pole be made of the lightest spongy platina, the effect is the same. Or +if gold precipitated by sulphate of iron be diffused through the solution, +still accumulation of it at the negative pole will not take place; and yet +the attraction of cohesion is almost perfectly overcome, the particles are +in it so small as to remain for hours in suspension, and are perfectly free +to move by the slightest impulse towards either pole; and _if in relation_ +by chemical affinity to any substance present, are powerfully determined to +the negative pole[A]. + + [A] In making this experiment, care must be taken that no substance be + present that can act chemically on the gold. Although I used the metal + very carefully washed, and diffused through dilute sulphuric acid, yet + in the first instance I obtained gold at the negative pole, and the + effect was repeated when the platina poles were changed. But on + examining the clear liquor in the cell, after subsidence of the + metallic gold, I found a little of that metal in solution, and a + little chlorine was also present. I therefore well washed the gold + which had thus been subjected to voltaic action, diffused it through + other pure dilute sulphuric acid, and then found, that on subjecting + it to the action of the pile, not the slightest tendency to the + negative pole could be perceived. + +547. In support of these arguments, it may be observed, that as yet no +determination of a substance to a pole, or tendency to obey the electric +current, has been observed (that I am aware of,) in cases of mere mixture; +i.e. a substance diffused through a fluid, but having no sensible chemical +affinity with it, or with substances that may be evolved from it during the +action, does not in any case seem to be affected by the electric current. +Pulverised charcoal was diffused through dilute sulphuric acid, and +subjected with the solution to the action of a voltaic battery, terminated +by platina poles; but not the slightest tendency of the charcoal to the +negative pole could be observed, Sublimed sulphur was diffused through +similar acid, and submitted to the same action, a silver plate being used +as the negative pole; but the sulphur had no tendency to pass to that pole, +the silver was not tarnished, nor did any sulphuretted hydrogen appear. The +case of magnesia and water (495. 533.), with those of comminuted metals in +certain solutions (546.), are also of this kind; and, in fact, substances +which have the instant before been powerfully determined towards the pole, +as magnesia from sulphate of magnesia, become entirely _indifferent to it_ +the moment they assume their independent state, and pass away, diffusing +themselves through the surrounding fluid. + +548. There are, it is true, many instances of insoluble bodies being acted +upon, as glass, sulphate of baryta, marble, slate, basalt, &c., but they +form no exception; for the substances they give up are in direct and strong +relation as to chemical affinity with those which they find in the +surrounding solution, so that these decompositions enter into the class of +ordinary effects. + +549. It may be expressed as a general consequence, that the more directly +bodies are opposed to each other in chemical affinity, the more _ready_ is +their separation from each other in cases of electro-chemical +decomposition, i.e. provided other circumstances, as insolubility, +deficient conducting power, proportions, &c., do not interfere. This is +well known to be the case with water and saline solutions; and I have found +it to be equally true with _dry_ chlorides, iodides, salts, &c., rendered +subject to electro-chemical decomposition by fusion (402.). So that in +applying the voltaic battery for the purpose of decomposing bodies not yet +resolved into forms of matter simpler than their own, it must be +remembered, that success may depend not upon the weakness, or failure upon +the strength, of the affinity by which the elements sought for are held +together, but contrariwise; and then modes of application may be devised, +by which, in _association_ with ordinary chemical powers, and the +assistance of fusion (394. 417.), we may be able to penetrate much further +than at present into the constitution of our chemical elements. + +550. Some of the most beautiful and surprising cases of electro-chemical +decomposition and _transfer_ which Sir Humphry Davy described in his +celebrated paper[A], were those in which acids were passed through +alkalies, and alkalies or earths through acids[B]; and the way in which +substances having the most powerful attractions for each other were thus +prevented from combining, or, as it is said, had their natural affinity +destroyed or suspended throughout the whole of the circuit, excited the +utmost astonishment. But if I be right in the view I have taken of the +effects, it will appear, that that which made the _wonder_, is in fact the +_essential condition_ of transfer and decomposition, and that the more +alkali there is in the course of an acid, the more will the transfer of +that acid be facilitated from pole to pole; and perhaps a better +illustration of the difference between the theory I have ventured, and +those previously existing, cannot be offered than the views they +respectively give of such facts as these. + + [A] Philosophical Transactions, 1807, p. 1. + + [B] Ibid. p, 24, &c. + +551. The instances in which sulphuric acid could not be passed though +baryta, or baryta through sulphuric acid[A], because of the precipitation +of sulphate of baryta, enter within the pale of the law already described +(380. 412.), by which liquidity is so generally required for conduction and +decomposition. In assuming the solid state of sulphate of baryta, these +bodies became virtually non-conductors to electricity of so low a tension +as that of the voltaic battery, and the power of the latter over them was +almost infinitely diminished. + + [A] Philosophical Transactions, 1807, p. 25, &c. + +552. The theory I have advanced accords in a most satisfactory manner with +the fact of an element or substance finding its place of rest, or rather of +evolution, sometimes at one pole and sometimes at the other. Sulphur +illustrates this effect very well[A]. When sulphuric acid is decomposed by +the pile, sulphur is evolved at the negative pole; but when sulphuret of +silver is decomposed in a similar way (436.), then the sulphur appears at +the positive pole; and if a hot platina pole be used so as to vaporize the +sulphur evolved in the latter case, then the relation of that pole to the +sulphur is exactly the same as the relation of the same pole to oxygen upon +its immersion in water. In both cases the element evolved is liberated at +the pole, but not retained by it; but by virtue of its elastic, +uncombinable, and immiscible condition passes away into the surrounding +medium. The sulphur is evidently determined in these opposite directions by +its opposite chemical relations to oxygen and silver; and it is to such +relations generally that I have referred all electro-chemical phenomena. +Where they do not exist, no electro-chemical action can take place. Where +they are strongest, it is most powerful; where they are reversed, the +direction of transfer of the substance is reversed with them. + + [A] At 681 and 757 of Series VII, will be found corrections of the + statement here made respecting sulphur and sulphuric acid. At present + there is no well-ascertained fact which proves that the same body can + go directly to _either_ of the two poles at pleasure.--_Dec. 1838._ + +553. _Water_ may be considered as one of those substances which can be made +to pass to _either_ pole. When the poles are immersed in dilute sulphuric +acid (527.), acid passes towards the positive pole, and water towards the +negative pole; but when they are immersed in dilute alkali, the alkali +passes towards the negative pole, and water towards the positive pole. + +554. Nitrogen is another substance which is considered as determinable to +either pole; but in consequence of the numerous compounds which it forms, +some of which pass to one pole, and some to the other, I have not always +found it easy to determine the true circumstances of its appearance. A pure +strong solution of ammonia is so bad a conductor of electricity that it is +scarcely more decomposable than pure water; but if sulphate of ammonia be +dissolved in it, then decomposition takes place very well; nitrogen almost +pure, and in some cases quite, is evolved at the positive pole, and +hydrogen at the negative pole. + +555. On the other hand, if a strong solution of nitrate of ammonia be +decomposed, oxygen appears at the positive pole, and hydrogen, with +sometimes nitrogen, at the negative pole. If fused nitrate of ammonia be +employed, hydrogen appears at the negative pole, mingled with a little +nitrogen. Strong nitric acid yields plenty of oxygen at the positive pole, +but no gas (only nitrous acid) at the negative pole. Weak nitric acid +yields the oxygen and hydrogen of the water present, the acid apparently +remaining unchanged. Strong nitric acid with nitrate of ammonia dissolved +in it, yields a gas at the negative pole, of which the greater part is +hydrogen, but apparently a little nitrogen is present. I believe, that in +some of these cases a little nitrogen appeared at the negative pole. I +suspect, however, that in all these, and in all former cases, the +appearance of the nitrogen at the positive or negative pole is entirely a +secondary effect, and not an immediate consequence of the decomposing power +of the electric current[A]. + + [A] Refer for proof of the truth of this supposition to 748, 752, + &c.--_Dec. 1838._ + +556. A few observations on what are called the _poles_ of the voltaic +battery now seem necessary. The poles are merely the surfaces or doors by +which the electricity enters into or passes out of the substance suffering +decomposition. They limit the extent of that substance in the course of the +electric current, being its _terminations_ in that direction: Hence the +elements evolved pass so far and no further. + +557. Metals make admirable poles, in consequence of their high conducting +power, their immiscibility with the substances generally acted upon, their +solid form, and the opportunity afforded of selecting such as are not +chemically acted upon by ordinary substances. + +558. Water makes a pole of difficult application, except in a few cases +(494.), because of its small conducting power, its miscibility with most of +the substances acted upon, and its general relation to them in respect to +chemical affinity. It consists of elements, which in their electrical and +chemical relations are directly and powerfully opposed, yet combining to +produce a body more neutral in its character than any other. So that there +are but few substances which do not come into relation, by chemical +affinity, with water or one of its elements; and therefore either the water +or its elements are transferred and assist in transferring the infinite +variety of bodies which, in association with it, can be placed in the +course of the electric current. Hence the reason why it so rarely happens +that the evolved substances rest at the first surface of the water, and why +it therefore does not exhibit the ordinary action of a pole. + +559. Air, however, and some gases are free from the latter objection, and +may be used as poles in many cases (461, &c.); but, in consequence of the +extremely low degree of conducting power belonging to them, they cannot be +employed with the voltaic apparatus. This limits their use; for the voltaic +apparatus is the only one as yet discovered which supplies sufficient +quantity of electricity (371. 376.) to effect electro-chemical +decomposition with facility. + +560. When the poles are liable to the chemical action of the substances +evolved, either simply in consequence of their natural relation to them, or +of that relation aided by the influence of the current (518.), then they +suffer corrosion, and the parts dissolved are subject to transference, in +the same manner as the particles of the body originally under +decomposition. An immense series of phenomena of this kind might be quoted +in support of the view I have taken of the cause of electro-chemical +decomposition, and the transfer and evolution of the elements. Thus platina +being made the positive and negative poles in a solution of sulphate of +soda, has no affinity or attraction for the oxygen, hydrogen, acid, or +alkali evolved, and refuses to combine with or retain them. Zinc can +combine with the oxygen and acid; at the positive pole it does combine, and +immediately begins to travel as oxide towards the negative pole. Charcoal, +which cannot combine with the metals, if made the negative pole in a +metallic solution, refuses to unite to the bodies which are ejected from +the solution upon its surface; but if made the positive pole in a dilute +solution of sulphuric acid, it is capable of combining with the oxygen +evolved there, and consequently unites with it, producing both carbonic +acid and carbonic oxide in abundance. + +561. A great advantage is frequently supplied, by the opportunity afforded +amongst the metals of selecting a substance for the pole, which shall or +shall not be acted upon by the elements to be evolved. The consequent use +of platina is notorious. In the decomposition of sulphuret of silver and +other sulphurets, a positive silver pole is superior to a platina one, +because in the former case the sulphur evolved there combines with the +silver, and the decomposition of the original sulphuret is rendered +evident; whereas in the latter case it is dissipated, and the assurance of +its separation at the pole not easily obtained. + +562. The effects which take place when a succession of conducting +decomposable and undecomposable substances are placed in the electric +circuit, as, for instance, of wires and solutions, or of air and solutions +(465, 469.), are explained in the simplest possible manner by the +theoretical view I have given. In consequence of the reaction of the +constituents of each portion of decomposable matter, affected as they are +by the supervention of the electric current (524.), portions of the +proximate or ultimate elements proceed in the direction of the current as +far as they find matter of a contrary kind capable of effecting their +transfer, and being equally affected by them; and where they cease to find +such matter, they are evolved in their free state, i.e. upon the surfaces +of metal or air bounding the extent of decomposable matter in the direction +of the current. + +563. Having thus given my theory of the mode in which electro-chemical +decomposition is effected, I will refrain for the present from entering +upon the numerous general considerations which it suggests, wishing first +to submit it to the test of publication and discussion. + +_Royal Institution, +June 1833._ + + + + +SIXTH SERIES. + + +S 12. _On the power of Metals and other Solids to induce the Combination +of Gaseous Bodies._ + +Received November 30, 1833,--Read January 11, 1834. + + +564. The conclusion at which I have arrived in the present communication +may seem to render the whole of it unfit to form part of a series of +researches in electricity; since, remarkable as the phenomena are, the +power which produces them is not to be considered as of an electric origin, +otherwise than as all attraction of particles may have this subtile agent +for their common cause. But as the effects investigated arose out of +electrical researches, as they are directly connected with other effects +which are of an electric nature, and must of necessity be understood and +guarded against in a very extensive series of electro-chemical +decompositions (707.), I have felt myself fully justified in describing +them in this place. + +565. Believing that I had proved (by experiments hereafter to be described +(705.),) the constant and definite chemical action of a certain quantity of +electricity, whatever its intensity might be, or however the circumstances +of its transmission through either the body under decomposition or the more +perfect conductors were varied, I endeavoured upon that result to construct +a new measuring instrument, which from its use might be called, at least +provisionally, a _Volta-electrometer_ (739.)[A]. + + [A] Or Voltameter.--_Dec. 1838._ + +566. During the course of the experiments made to render the instrument +efficient, I was occasionally surprised at observing a deficiency of the +gases resulting from the decompositions of water, and at last an actual +disappearance of portions which had been evolved, collected, and measured. +The circumstances of the disappearance were these. A glass tube, about +twelve inches in length and 3/4ths of an inch in diameter, had two platina +poles fixed into its upper, hermetically sealed, extremity: the poles, +where they passed through the glass, were of wire; but terminated below in +plates, which were soldered to the wires with gold (Plate V. fig. 56.). The +tube was filled with dilute sulphuric acid, and inverted in a cup of the +same fluid; a voltaic battery was connected with the two wires, and +sufficient oxygen and hydrogen evolved to occupy 4/5ths of the tube, or by +the graduation, 116 parts. On separating the tube from the voltaic battery +the volume of gas immediately began to diminish, and in about five hours +only 13-1/2 parts remained, and these ultimately disappeared. + +567. It was found by various experiments, that this effect was not due to +the escape or solution of the gas, nor to recombination of the oxygen or +hydrogen in consequence of any peculiar condition _they_ might be supposed +to possess under the circumstances; but to be occasioned by the action of +one or both of the poles within the tube upon the gas around them. On +disuniting the poles from the pile after they had acted upon dilute +sulphuric acid, and introducing them into separate tubes containing mixed +oxygen and hydrogen, it was found that the _positive_ pole effected the +union of the gases, but the negative pole apparently not (588.). It was +ascertained also that no action of a sensible kind took place between the +positive pole with oxygen or hydrogen alone. + +568. These experiments reduced the phenomena to the consequence of a power +possessed by the platina, after it had been the positive pole of a voltaic +pile, of causing the combination of oxygen and hydrogen at common, or even +at low, temperatures. This effect is, as far as I am aware, altogether new, +and was immediately followed out to ascertain whether it was really of an +electric nature, and how far it would interfere with the determination of +the quantities evolved in the cases of electro-chemical decomposition +required in the fourteenth section of these Researches. + +569. Several platina plates were prepared (fig. 57.). They were nearly half +an inch wide, and two inches and a half long: some were 1/200dth of an +inch, others not more than 1/600dth, whilst some were as much as 1/70th of +an inch in thickness. Each had a piece of platina wire, about seven inches +long, soldered to it by pure gold. Then a number of glass tubes were +prepared: they were about nine or ten inches in length, 5/8ths of an inch +in internal diameter, were sealed hermetically at one extremity, and were +graduated. Into these tubes was put a mixture of two volumes of hydrogen +and one of oxygen, at the water pneumatic trough, and when one of the +plates described had been connected with the positive or negative pole of +the voltaic battery for a given time, or had been otherwise prepared, it +was introduced through the water into the gas within the tube; the whole +set aside in a test-glass (fig. 58.), and left for a longer or shorter +period, that the action might be observed. + +570. The following result may be given as an illustration of the phenomenon +to be investigated. Diluted sulphuric acid, of the specific gravity 1.336, +was put into a glass jar, in which was placed also a large platina plate, +connected with the negative end of a voltaic battery of forty pairs of +four-inch plates, with double coppers, and moderately charged. One of the +plates above described (569.) was then connected with the positive +extremity, and immersed in the same jar of acid for five minutes, after +which it was separated from the battery, washed in distilled water, and +introduced through the water of the pneumatic trough into a tube containing +the mixture of oxygen and hydrogen (569.). The volume of gases immediately +began to lessen, the diminution proceeding more and more rapidly until +about 3/4ths of the mixture had disappeared. The upper end of the tube +became quite warm, the plate itself so hot that the water boiled as it rose +over it; and in less than a minute a cubical inch and a half of the gases +were gone, having been combined by the power of the platina, and converted +into water. + +571. This extraordinary influence acquired by the platina at the positive +pole of the pile, is exerted far more readily and effectively on oxygen and +hydrogen than on any other mixture of gases that I have tried. One volume +of nitrous gas was mixed with a volume of hydrogen, and introduced into a +tube with a plate which had been made positive in the dilute sulphuric acid +for four minutes (570.). There was no sensible action in an hour: being +left for thirty-six hours, there was a diminution of about one-eighth of +the whole volume. Action had taken place, but it had been very feeble. + +572. A mixture of two volumes of nitrous oxide with one volume of hydrogen +was put with a plate similarly prepared into a tube (569. 570.). This also +showed no action immediately; but in thirty-six hours nearly a fourth of +the whole had disappeared, i.e. about half of a cubic inch. By comparison +with another tube containing the same mixture without a plate, it appeared +that a part of the diminution was due to solution, and the other part to +the power of the platina; but the action had been very slow and feeble. + +573. A mixture of one volume olefiant gas and three volumes oxygen was not +affected by such a platina plate, even though left together for several +days (640. 641.). + +574. A mixture of two volumes carbonic oxide and one volume oxygen was also +unaffected by the prepared platina plate in several days (645, &c.). + +575. A mixture of equal volumes of chlorine and hydrogen was used in +several experiments, with plates prepared in a similar manner (570.). +Diminution of bulk soon took place; but when after thirty-six hours the +experiments were examined, it was found that nearly all the chlorine had +disappeared, having been absorbed, principally by the water, and that the +original volume of hydrogen remained unchanged. No combination of the +gases, therefore, had here taken place. + +576. Reverting to the action of the prepared plates on mixtures of oxygen +and hydrogen (570.), I found that the power, though gradually diminishing +in all cases, could still be retained for a period, varying in its length +with circumstances. When tubes containing plates (569.) were supplied with +fresh portions of mixed oxygen and hydrogen as the previous portions were +condensed, the action was found to continue for above thirty hours, and in +some cases slow combination could be observed even after eighty hours; but +the continuance of the action greatly depended upon the purity of the gases +used (638.). + +577. Some plates (569.) were made positive for four minutes in dilute +sulphuric acid of specific gravity 1.336: they were rinsed in distilled +water, after which two were put into a small bottle and closed up, whilst +others were left exposed to the air. The plates preserved in the limited +portion of air were found to retain their power after eight days, but those +exposed to the atmosphere had lost their force almost entirely in twelve +hours, and in some situations, where currents existed, in a much shorter +time. + +578. Plates were made positive for five minutes in sulphuric acid, specific +gravity 1.336. One of these was retained in similar acid for eight minutes +after separation from the battery: it then acted on mixed oxygen and +hydrogen with apparently undiminished vigour. Others were left in similar +acid for forty hours, and some even for eight days, after the +electrization, and then acted as well in combining oxygen and hydrogen gas +as those which were used immediately after electrization. + +579. The effect of a solution of caustic potassa in preserving the platina +plates was tried in a similar manner. After being retained in such a +solution for forty hours, they acted exceedingly well on oxygen and +hydrogen, and one caused such rapid condensation of the gases, that the +plate became much heated, and I expected the temperature would have risen +to ignition. + +580. When similarly prepared plates (569.) had been put into distilled +water for forty hours, and then introduced into mixed oxygen and hydrogen, +they were found to act but very slowly and feebly as compared with those +which had been preserved in acid or alkali. When, however, the quantity of +water was but small, the power was very little impaired after three or four +days. As the water had been retained in a wooden vessel, portions of it +were redistilled in glass, and this was found to preserve prepared plates +for a great length of time. Prepared plates were put into tubes with this +water and closed up; some of them, taken out at the end of twenty-four +days, were found very active on mixed oxygen and hydrogen; others, which +were left in the water for fifty-three days, were still found to cause the +combination of the gases. The tubes had been closed only by corks. + +581. The act of combination always seemed to diminish, or apparently +exhaust, the power of the platina plate. It is true, that in most, if not +all instances, the combination of the gases, at first insensible, gradually +increased in rapidity, and sometimes reached to explosion; but when the +latter did not happen, the rapidity of combination diminished; and although +fresh portions of gas were introduced into the tubes, the combination went +on more and more slowly, and at last ceased altogether. The first effect of +an increase in the rapidity of combination depended in part upon the water +flowing off from the platina plate, and allowing a better contact with the +gas, and in part upon the heat evolved during the progress of the +combination (630.). But notwithstanding the effect of these causes, +diminution, and at last cessation of the power, always occurred. It must +not, however, be unnoticed, that the purer the gases subjected to the +action of the plate, the longer was its combining power retained. With the +mixture evolved at the poles of the voltaic pile, in pure dilute sulphuric +acid, it continued longest; and with oxygen and hydrogen, of perfect +purity, it probably would not be diminished at all. + +582. Different modes of treatment applied to the platina plate, after it +had ceased to be the positive pole of the pile, affected its power very +curiously. A plate which had been a positive pole in diluted sulphuric acid +of specific gravity 1.336 for four or five minutes, if rinsed in water and +put into mixed oxygen and hydrogen, would act very well, and condense +perhaps one cubic inch and a half of gas in six or seven minutes; but if +that same plate, instead of being merely rinsed, had been left in distilled +water for twelve or fifteen minutes, or more, it would rarely fail, when +put into the oxygen and hydrogen, of becoming, in the course of a minute or +two, ignited, and would generally explode the gases. Occasionally the time +occupied in bringing on the action extended to eight or nine minutes, and +sometimes even to forty minutes, and yet ignition and explosion would +result. This effect is due to the removal of a portion of acid which +otherwise adheres firmly to the plate [A]. + + [A] In proof that this is the case, refer to 1038.--_Dec. 1838._ + +583. Occasionally the platina plates (569.), after being made the positive +pole of the battery, were washed, wiped with filtering-paper or a cloth, +and washed and wiped again. Being then introduced into mixed oxygen and +hydrogen, they acted apparently as if they had been unaffected by the +treatment. Sometimes the tubes containing the gas were opened in the air +for an instant, and the plates put in dry; but no sensible difference in +action was perceived, except that it commenced sooner. + +584. The power of heat in altering the action of the prepared platina +plates was also tried (595.). Plates which had been rendered positive in +dilute sulphuric acid for four minutes were well-washed in water, and +heated to redness in the flame of a spirit-lamp: after this they acted very +well on mixed oxygen and hydrogen. Others, which had been heated more +powerfully by the blowpipe, acted afterwards on the gases, though not so +powerfully as the former. Hence it appears that heat does not take away the +power acquired by the platina at the positive pole of the pile: the +occasional diminution of force seemed always referable to other causes than +the mere heat. If, for instance, the plate had not been well-washed from +the acid, or if the flame used was carbonaceous, or was that of an alcohol +lamp trimmed with spirit containing a little acid, or having a wick on +which salt, or other extraneous matter, had been placed, then the power of +the plate was quickly and greatly diminished (634. 636.). + +585. This remarkable property was conferred upon platina when it was made +the positive pole in sulphuric acid of specific gravity 1.336, or when it +was considerably weaker, or when stronger, even up to the strength of oil +of vitriol. Strong and dilute nitric acid, dilute acetic acid, solutions of +tartaric, citric, and oxalic acids, were used with equal success. When +muriatic acid was used, the plates acquired the power of condensing the +oxygen and hydrogen, but in a much inferior degree. + +586. Plates which were made positive in solution of caustic potassa did not +show any sensible action upon the mixed oxygen and hydrogen. Other plates +made positive in solutions of carbonates of potassa and soda exhibited the +action, but only in a feeble degree. + +587. When a neutral solution of sulphate of soda, or of nitre, or of +chlorate of potassa, or of phosphate of potassa, or acetate of potassa, or +sulphate of copper, was used, the plates, rendered positive in them for +four minutes, and then washed in water, acted very readily and powerfully +on the mixed oxygen and hydrogen. + +588. It became a very important point, in reference to the _cause_ of this +action of the platina, to determine whether the _positive_ pole _only_ +could confer it (567.), or whether, notwithstanding the numerous contrary +cases, the _negative_ pole might not have the power when such circumstances +as could interfere with or prevent the action were avoided. Three plates +were therefore rendered negative, for four minutes in diluted sulphuric +acid of specific gravity 1.336, washed in distilled water, and put into +mixed oxygen and hydrogen. _All_ of them _acted_, though not so strongly as +they would have done if they had been rendered positive. Each combined +about a cubical inch and a quarter of the gases in twenty-five minutes. On +every repetition of the experiment the same result was obtained; and when +the plates were retained in distilled water for ten or twelve minutes, +before being introduced into the gas (582.), the action was very much +quickened. + +589. But when there was any metallic or other substance present in the +acid, which could be precipitated on the negative plate, then that plate +ceased to act upon the mixed oxygen and hydrogen. + +590. These experiments led to the expectation that the power of causing +oxygen and hydrogen to combine, which could be conferred upon any piece of +platina by making it the positive pole of a voltaic pile, was not +essentially dependent upon the action of the pile, or upon any structure or +arrangement of parts it might receive whilst in association with it, but +belonged to the platina _at all times_, and was _always effective_ when the +surface was _perfectly clean_. And though, when made the _positive_ pole of +the pile in acids, the circumstances might well be considered as those +which would cleanse the surface of the platina in the most effectual +manner, it did not seem impossible that ordinary operations should produce +the same result, although in a less eminent degree. + +591. Accordingly, a platina plate (569.) was cleaned by being rubbed with a +cork, a little water, and some coal-fire ashes upon a glass plate: being +washed, it was put into mixed oxygen and hydrogen, and was found to act at +first slowly, and then more rapidly. In an hour, a cubical inch and a half +had disappeared. + +592. Other plates were cleaned with ordinary sand-paper and water; others +with chalk and water; others with emery and water; others, again, with +black oxide of manganese and water; and others with a piece of charcoal and +water. All of these acted in tubes of oxygen and hydrogen, causing +combination of the gases. The action was by no means so powerful as that +produced by plates having been in communication with the battery; but from +one to two cubical inches of the gases disappeared, in periods extending +from twenty-five to eighty or ninety minutes. + +593. Upon cleaning the plates with a cork, ground emery, and dilute +sulphuric acid, they were found to act still better. In order to simplify +the conditions, the cork was dismissed, and a piece of platina foil used +instead; still the effect took place. Then the acid was dismissed, and a +solution of _potassa_ used, but the effect occurred as before. + +594. These results are abundantly sufficient to show that the mere +mechanical cleansing of the surface of the platina is sufficient to enable +it to exert its combining power over oxygen and hydrogen at common +temperatures. + +595. I now tried the effect of heat in conferring this property upon +platina (584.). Plates which had no action on the mixture of oxygen and +hydrogen were heated by the flame of a freshly trimmed spirit-lamp, urged +by a mouth blowpipe, and when cold were put into tubes of the mixed gases: +they acted slowly at first, but after two or three hours condensed nearly +all the gases. + +596. A plate of platina, which was about one inch wide and two and +three-quarters in length, and which had not been used in any of the +preceding experiments, was curved a little so as to enter a tube, and left +in a mixture of oxygen and hydrogen for thirteen hours: not the slightest +action or combination of the gases occurred. It was withdrawn at the +pneumatic trough from the gas through the water, heated red-hot by the +spirit-lamp and blowpipe, and then returned when cold into the _same_ +portion of gas. In the course of a few minutes diminution of the gases +could be observed, and in forty-five minutes about one cubical inch and a +quarter had disappeared. In many other experiments platina plates when +heated were found to acquire the power of combining oxygen and hydrogen. + +597. But it happened not infrequently that plates, after being heated, +showed no power of combining oxygen and hydrogen gases, though left +undisturbed in them for two hours. Sometimes also it would happen that a +plate which, having been heated to dull redness, acted feebly, upon being +heated to whiteness ceased to act; and at other times a plate which, having +been slightly heated, did not act, was rendered active by a more powerful +ignition. + +598. Though thus uncertain in its action, and though often diminishing the +power given to the plates at the positive pole of the pile (584.), still it +is evident that heat can render platina active, which before was inert +(595.). The cause of its occasional failure appears to be due to the +surface of the metal becoming soiled, either from something previously +adhering to it, which is made to adhere more closely by the action of the +heat, or from matter communicated from the flame of the lamp, or from the +air itself. It often happens that a polished plate of platina, when heated +by the spirit-lamp and a blowpipe, becomes dulled and clouded on its +surface by something either formed or deposited there; and this, and much +less than this, is sufficient to prevent it from exhibiting the curious +power now under consideration (634. 636.). Platina also has been said to +combine with carbon; and it is not at all unlikely that in processes of +heating, where carbon or its compounds are present, a film of such a +compound may be thus formed, and thus prevent the exhibition of the +properties belonging to _pure_ platina[A]. + + [A] When heat does confer the property it is only by the destruction + or dissipation of organic or other matter which had previously soiled + the plate (632. 633. 634.).--_Dec. 1838._ + +599. The action of alkalies and acids in giving platina this property was +now experimentally examined. Platina plates (569.) having no action on +mixed oxygen and hydrogen, being boiled in a solution of caustic potassa, +washed, and then put into the gases, were found occasionally to act pretty +well, but at other times to fail. In the latter case I concluded that the +impurity upon the surface of the platina was of a nature not to be removed +by the mere solvent action of the alkali, for when the plates were rubbed +with a little emery, and the same solution of alkali (592.), they became +active. + +600. The action of acids was far more constant and satisfactory. A platina +plate was boiled in dilute nitric acid: being washed and put into mixed +oxygen and hydrogen gases, it acted well. Other plates were boiled in +strong nitric acid for periods extending from half a minute to four +minutes, and then being washed in distilled water, were found to act very +well, condensing one cubic inch and a half of gas in the space of eight or +nine minutes, and rendering the tube warm (570.). + +601. Strong sulphuric acid was very effectual in rendering the platina +active. A plate (569.) was heated in it for a minute, then washed and put +into the mixed oxygen and hydrogen, upon which it acted as well as if it +had been made the positive pole of a voltaic pile (570.). + +602. Plates which, after being heated or electrized in alkali, or after +other treatment, were found inert, immediately received power by being +dipped for a minute or two, or even only for an instant, into hot oil of +vitriol, and then into water. + +603. When the plate was dipped into the oil of vitriol, taken out, and then +heated so as to drive off the acid, it did not act, in consequence of the +impurity left by the acid upon its surface. + +604. Vegetable acids, as acetic and tartaric, sometimes rendered inert +platina active, at other times not. This, I believe, depended upon the +character of the matter previously soiling the plates, and which may easily +be supposed to be sometimes of such a nature as to be removed by these +acids, and at other times not. Weak sulphuric acid showed the same +difference, but strong sulphuric acid (601.) never failed in its action. + +605. The most favourable treatment, except that of making the plate a +positive pole in strong acid, was as follows. The plate was held over a +spirit-lamp flame, and when hot, rubbed with a piece of potassa fusa +(caustic potash), which melting, covered the metal with a coat of very +strong alkali, and this was retained fused upon the surface for a second or +two[A]: it was then put into water for four or five minutes to wash off the +alkali, shaken, and immersed for about a minute in hot strong oil of +vitriol; from this it was removed into distilled water, where it was +allowed to remain ten or fifteen minutes to remove the last traces of acid +(582.). Being then put into a mixture of oxygen and hydrogen, combination +immediately began, and proceeded rapidly; the tube became warm, the platina +became red-hot, and the residue of the gases was inflamed. This effect +could be repeated at pleasure, and thus the maximum phenomenon could be +produced without the aid of the voltaic battery. + + [A] The heat need not be raised so much as to make the alkali tarnish + the platina, although if that effect does take place it does not + prevent the ultimate action. + +606. When a solution of tartaric or acetic acid was substituted, in this +mode of preparation, for the sulphuric acid, still the plate was found to +acquire the same power, and would often produce explosion in the mixed +gases; but the strong sulphuric acid was most certain and powerful. + +607. If borax, or a mixture of the carbonates of potash and soda, be fused +on the surface of a platina plate, and that plate be well-washed in water, +it will be found to have acquired the power of combining oxygen and +hydrogen, but only in a moderate degree; but if, after the fusion and +washing, it be dipped in the hot sulphuric acid (601.), it will become very +active. + +608. Other metals than platina were then experimented with. Gold and +palladium exhibited the power either when made the positive pole of the +voltaic battery (570.), or when acted on by hot oil of vitriol (601.). When +palladium is used, the action of the battery or acid should be moderated, +as that metal is soon acted upon under such circumstances. Silver and +copper could not be made to show any effect at common temperatures. + + * * * * * + +609. There can remain no doubt that the property of inducing combination, +which can thus be conferred upon masses of platina and other metals by +connecting them with the poles of the battery, or by cleansing processes +either of a mechanical or chemical nature, is the same as that which was +discovered by Doebereiner[A], in 1823, to belong in so eminent a degree to +spongy platina, and which was afterwards so well experimented upon and +illustrated by MM. Dulong and Thenard[B], in 1823. The latter philosophers +even quote experiments in which a very fine platina wire, which had been +coiled up and digested in nitric, sulphuric, or muriatic acid, became +ignited when put into a jet of hydrogen gas[C]. This effect I can now +produce at pleasure with either wires or plates by the processes described +(570. 601. 605.); and by using a smaller plate cut so that it shall rest +against the glass by a few points, and yet allow the water to flow off +(fig. 59.), the loss of heat is less, the metal is assimilated somewhat to +the spongy state, and the probability of failure almost entirely removed. + + [A] Annales de Chimie, tom. xxiv. p. 93. + + [B] Ibid. tom. xxiii. p. 440; tom. xxiv. p. 380. + + [C] Ibid. tom. xxiv. p. 383. + +610. M. Doebereiner refers the effect entirely to an electric action. He +considers the platina and hydrogen as forming a voltaic element of the +ordinary kind, in which the hydrogen, being very highly positive, +represents the zinc of the usual arrangement, and like it, therefore, +attracts oxygen and combines with it[A]. + + [A] tom. xxiv. pp. 94, 95. Also Bibliotheque Universelle, tom. xxiv. + p. 54. + +611. In the two excellent experimental papers by MM. Dulong and Thenard[A], +those philosophers show that elevation of temperature favours the action, +but does not alter its character; Sir Humphry Davy's incandescent platina +wire being the same phenomenon with Doebereiner's spongy platina. They show +that _all_ metals have this power in a greater or smaller degree, and that +it is even possessed by such bodies as charcoal, pumice, porcelain, glass, +rock crystal, &c., when their temperatures are raised; and that another of +Davy's effects, in which oxygen and hydrogen had combined slowly together +at a heat below ignition, was really dependent upon the property of the +heated glass, which it has in common with the bodies named above. They +state that liquids do not show this effect, at least that mercury, at or +below the boiling point, has not the power; that it is not due to porosity; +that the same body varies very much in its action, according to its state; +and that many other gaseous mixtures besides oxygen and hydrogen are +affected, and made to act chemically, when the temperature is raised. They +think it probable that spongy platina acquires its power from contact with +the acid evolved during its reduction, or from the heat itself to which it +is then submitted. + + [A] Annales de Chimie, tom. xxiii. p. 440; tom. xxiv. p, 380. + +612. MM. Dulong and Thenard express themselves with great caution on the +theory of this action; but, referring to the decomposing power of metals on +ammonia when heated to temperatures not sufficient alone to affect the +alkali, they remark that those metals which in this case are most +efficacious, are the least so in causing the combination of oxygen and +hydrogen; whilst platina, gold, &c., which have least power of decomposing +ammonia, have most power of combining the elements of water:--from which +they are led to believe, that amongst gases, some tend to _unite_ under the +influence of metals, whilst others tend to _separate_, and that this +property varies in opposite directions with the different metals. At the +close of their second paper they observe, that the action is of a kind that +cannot be connected with any known theory; and though it is very remarkable +that the effects are transient, like those of most electrical actions, yet +they state that the greater number of the results observed by them are +inexplicable, by supposing them to be of a purely electric origin. + +613. Dr. Fusinieri has also written on this subject, and given a theory +which he considers as sufficient to account for the phenomena[A]. He +expresses the immediate cause thus: "The platina determines upon its +surface a continual renovation of _concrete laminae_ of the combustible +substance of the gases or vapours, which flowing over it are burnt, pass +away, and are renewed: this combustion at the surface raises and sustains +the temperature of the metal." The combustible substance, thus reduced into +imperceptible laminae, of which the concrete parts are in contact with the +oxygen, is presumed to be in a state combinable with the oxygen at a much +lower temperature than when it is in the gaseous state, and more in analogy +with what is called the nascent condition. That combustible gases should +lose their elastic state, and become concrete, assuming the form of +exceedingly attenuated but solid strata, is considered as proved by facts, +some of which are quoted in the Giornale di Fisica for 1824[B]; and though +the theory requires that they should assume this state at high +temperatures, and though the _similar_ films of aqueous and other matter +are dissipated by the action of heat, still the facts are considered as +justifying the conclusion against all opposition of reasoning. + + [A] Giornale di Fisica, &c., 1825, tom. viii. p. 259. + + [B] pp. 138, 371. + +614. The power or force which makes combustible gas or vapour abandon its +elastic state in contact with a solid, that it may cover the latter with a +thin stratum of its own proper substance, is considered as being neither +attraction nor affinity. It is able also to extend liquids and solids in +concrete laminae over the surface of the acting solid body, and consists in +a _repulsion_, which is developed from the parts of the solid body by the +simple fact of attenuation, and is highest when the attenuation is most +complete. The force has a progressive development, and acts most +powerfully, or at first, in the direction in which the dimensions of the +attenuated mass decrease, and then in the direction of the angles or +corners which from any cause may exist on the surface. This force not only +causes spontaneous diffusion of gases and other substances over the +surface, but is considered as very elementary in its nature, and competent +to account for all the phenomena of capillarity, chemical affinity, +attraction of aggregation, rarefaction, ebullition, volatilization, +explosion, and other thermometric effects, as well as inflammation, +detonation, &c. &c. It is considered as a form of heat to which the term +_native calorie_ is given, and is still further viewed as the principle of +the two electricities and the two magnetisms. + +615. I have been the more anxious to give a correct abstract of Dr. +Fusinieri's view, both because I cannot form a distinct idea of the power +to which he refers the phenomena, and because of my imperfect knowledge of +the language in which the memoir is written. I would therefore beg to refer +those who pursue the subject to the memoir itself. + +616. Not feeling, however, that the problem has yet been solved, I venture +to give the view which seems to me sufficient, upon _known principles_, to +account for the effect. + +617. It may be observed of this action, that, with regard to platina, it +cannot be due to any peculiar, temporary condition, either of an electric +or of any other nature: the activity of plates rendered either positive or +negative by the pole, or cleaned with such different substances as acids, +alkalies, or water; charcoal, emery, ashes, or glass; or merely heated, is +sufficient to negative such an opinion. Neither does it depend upon the +spongy and porous, or upon the compact and burnished, or upon the massive +or the attenuated state of the metal, for in any of these states it may be +rendered effective, or its action may be taken away. The only essential +condition appears to be a _perfectly clean_ and _metallic surface_, for +whenever that is present the platina acts, whatever its form and condition +in other respects may be; and though variations in the latter points will +very much affect the rapidity, and therefore the visible appearances and +secondary effects, of the action, i.e. the ignition of the metal and the +inflammation of the gases, they, even in their most favourable state, +cannot produce any effect unless the condition of a clean, pure, metallic +surface be also fulfilled. + +618. The effect is evidently produced by most, if not all, solid bodies, +weakly perhaps by many of them, but rising to a high degree in platina. +Dulong and Thenard have very philosophically extended our knowledge of the +property to its possession by all the metals, and by earths, glass, stones, +&c. (611.); and every idea of its being a known and recognised electric +action is in this way removed. + +619. All the phenomena connected with this subject press upon my mind the +conviction that the effects in question are entirely incidental and of a +secondary nature; that they are dependent upon the _natural conditions_ of +gaseous elasticity, combined with the exertion of that attractive force +possessed by many bodies, especially those which are solid, in an eminent +degree, and probably belonging to all; by which they are drawn into +association more or less close, without at the same time undergoing +chemical combination, though often assuming the condition of adhesion; and +which occasionally leads, under very favourable circumstances, as in the +present instance, to the combination of bodies simultaneously subjected to +this attraction. I am prepared myself to admit (and probably many others +are of the same opinion), both with respect to the attraction of +aggregation and of chemical affinity, that the sphere of action of +particles extends beyond those other particles with which they are +immediately and evidently in union (523.), and in many cases produces +effects rising into considerable importance: and I think that this kind of +attraction is a determining cause of Doebereiner's effect, and of the many +others of a similar nature. + +620. Bodies which become wetted by fluids with which they do not combine +chemically, or in which they do not dissolve, are simple and well-known +instances of this kind of attraction. + +621. All those cases of bodies which being insoluble in water and not +combining with it are hygrometric, and condense its vapour around or upon +their surface, are stronger instances of the same power, and approach a +little nearer to the cases under investigation. If pulverized clay, +protoxide or peroxide of iron, oxide of manganese, charcoal, or even +metals, as spongy platina or precipitated silver, be put into an atmosphere +containing vapour of water, they soon become moist by virtue of an +attraction which is able to condense the vapour upon, although not to +combine it with, the substances; and if, as is well known, these bodies so +damped be put into a dry atmosphere, as, for instance, one confined over +sulphuric acid, or if they be heated, then they yield up this water again +almost entirely, it not being in direct or permanent combination[A]. + + [A] I met at Edinburgh with a case, remarkable as to its extent, of + hygrometric action, assisted a little perhaps by very slight solvent + power. Some turf had been well-dried by long exposure in a covered + place to the atmosphere, but being then submitted to the action of a + hydrostatic press, it yielded, _by the mere influence of the + pressure_, 54 per cent. of water. + +622. Still better instances of the power I refer to, because they are more +analogous to the cases to be explained, are furnished by the attraction +existing between glass and air, so well known to barometer and thermometer +makers, for here the adhesion or attraction is exerted between a solid and +gases, bodies having very different physical conditions, having no power of +combination with each other, and each retaining, during the time of action, +its physical state unchanged[A]. When mercury is poured into a barometer +tube, a film of air will remain between the metal and glass for months, or, +as far as is known, for years, for it has never been displaced except by +the action of means especially fitted for the purpose. These consist in +boiling the mercury, or in other words, of forming an abundance of vapour, +which coming in contact with every part of the glass and every portion of +surface of the mercury, gradually mingles with, dilutes, and carries off +the air attracted by, and adhering to, those surfaces, replacing it by +other vapour, subject to an equal or perhaps greater attraction, but which +when cooled condenses into the same liquid as that with which the tube is +filled. + + [A] Fusinieri and Bellani consider the air as forming solid concrete + films in these cases.--Giornale di Fisica, tom. viii, p. 262. 1825. + +623. Extraneous bodies, which, acting as nuclei in crystallizing or +depositing solutions, cause deposition of substances on them, when it does +not occur elsewhere in the liquid, seem to produce their effects by a power +of the same kind, i.e. a power of attraction extending to neighbouring +particles, and causing them to become attached to the nuclei, although it +is not strong enough to make them combine chemically with their substance. + +624. It would appear from many cases of nuclei in solutions, and from the +effects of bodies put into atmospheres containing the vapours of water, or +camphor, or iodine, &c., as if this attraction were in part elective, +partaking in its characters both of the attraction of aggregation and +chemical affinity: nor is this inconsistent with, but agreeable to, the +idea entertained, that it is the power of particles acting, not upon others +with which they can immediately and intimately combine, but upon such as +are either more distantly situated with respect to them, or which, from +previous condition, physical constitution, or feeble relation, are unable +to enter into decided union with them. + +625. Then, of all bodies, the gases are those which might be expected to +show some _mutual_ action whilst _jointly_ under the attractive influence +of the platina or other solid acting substance. Liquids, such as water, +alcohol, &c., are in so dense and comparatively incompressible a state, as +to favour no expectation that their particles should approach much closer +to each other by the attraction of the body to which they adhere, and yet +that attraction must (according to its effects) place their particles as +near to those of the solid wetted body as they are to each other, and in +many cases it is evident that the former attraction is the stronger. But +gases and vapours are bodies competent to suffer very great changes in the +relative distances of their particles by external agencies; and where they +are in immediate contact with the platina, the approximation of the +particles to those of the metal may be very great. In the case of the +hygrometric bodies referred to (621.), it is sufficient to reduce the +vapour to the fluid state, frequently from atmospheres so rare that without +this influence it would be needful to compress them by mechanical force +into a bulk not more than 1/10th or even 1/20th of their original volume +before the vapours would become liquids. + +626. Another most important consideration in relation to this action of +bodies, and which, as far as I am aware, has not hitherto been noticed, is +the condition of elasticity under which the gases are placed against the +acting surface. We have but very imperfect notions of the real and intimate +conditions of the particles of a body existing in the solid, the liquid, +and the gaseous state; but when we speak of the gaseous state as being due +to the mutual repulsions of the particles or of their atmospheres, although +we may err in imagining each particle to be a little nucleus to an +atmosphere of heat, or electricity, or any other agent, we are still not +likely to be in error in considering the elasticity as dependent on +_mutuality_ of action. Now this mutual relation fails altogether on the +side of the gaseous particles next to the platina, and we might be led to +expect _a priori_ a deficiency of elastic force there to at least one half; +for if, as Dalton has shown, the elastic force of the particles of one gas +cannot act against the elastic force of the particles of another, the two +being as vacua to each other, so is it far less likely that the particles +of the platina can exert any influence on those of the gas against it, such +as would be exerted by gaseous particles of its own kind. + +627. But the diminution of power to one-half on the side of the gaseous +body towards the metal is only a slight result of what seems to me to flow +as a necessary consequence of the known constitution of gases. An +atmosphere of one gas or vapour, however dense or compressed, is in effect +as a vacuum to another: thus, if a little water were put into a vessel +containing a dry gas, as air, of the pressure of one hundred atmospheres, +as much vapour of the water would _rise_ as if it were in a perfect vacuum. +Here the particles of watery vapour appear to have no difficulty in +approaching within any distance of the particles of air, being influenced +solely by relation to particles of their own kind; and if it be so with +respect to a body having the same elastic powers as itself, how much more +surely must it be so with particles, like those of the platina, or other +limiting body, which at the same time that they have not these elastic +powers, are also unlike it in nature! Hence it would seem to result that +the particles of hydrogen or any other gas or vapour which are next to the +platina, &c., must be in such contact with it as if they were in the liquid +state, and therefore almost infinitely closer to it than they are to each +other, even though the metal be supposed to exert no attractive influence +over them. + +628. A third and very important consideration in favour of the mutual +action of gases under these circumstances is their perfect miscibility. If +fluid bodies capable of combining together are also capable of mixture, +_they do combine_ when they are mingled, not waiting for any other +determining circumstance; but if two such gases as oxygen and hydrogen are +put together, though they are elements having such powerful affinity as to +unite naturally under a thousand different circumstances, they do not +combine by mere mixture. Still it is evident that, from their perfect +association, the particles are in the most favourable state possible for +combination upon the supervention of any determining cause, such either as +the negative action of the platina in suppressing or annihilating, as it +were, their elasticity on its side; or the positive action of the metal in +condensing them against its surface by an attractive force; or the +influence of both together. + +629. Although there are not many distinct cases of combination under the +influence of forces external to the combining particles, yet there are +sufficient to remove any difficulty which might arise on that ground. Sir +James Hull found carbonic acid and lime to remain combined under pressure +at temperatures at which they would not have remained combined if the +pressure had been removed; and I have had occasion to observe a case of +direct combination in chlorine[A], which being compressed at common +temperatures will combine with water, and form a definite crystalline +hydrate, incapable either of being formed or of existing if that pressure +be removed. + + [A] Philosophical Transactions, 1823, p. 161. + +630. The course of events when platina acts upon, and combines oxygen and +hydrogen, may be stated, according to these principles, as follows. From +the influence of the circumstances mentioned (619. &c.), i.e. the +deficiency of elastic power and the attraction of the metal for the gases, +the latter, when they are in association with the former, are so far +condensed as to be brought within the action of their mutual affinities at +the existing temperature; the deficiency of elastic power, not merely +subjecting them more closely to the attractive influence of the metal, but +also bringing them into a more favourable state for union, by abstracting a +part of that power (upon which depends their elasticity,) which elsewhere +in the mass of gases is opposing their combination. The consequence of +their combination is the production of the vapour of water and an elevation +of temperature. But as the attraction of the platina for the water formed +is not greater than for the gases, if so great, (for the metal is scarcely +hygrometric,) the vapour is quickly diffused through the remaining gases; +fresh portions of this latter, therefore, come into juxtaposition with the +metal, combine, and the fresh vapour formed is also diffused, allowing new +portions of gas to be acted upon. In this way the process advances, but is +accelerated by the evolution of heat, which is known by experiment to +facilitate the combination in proportion to its intensity, and the +temperature is thus gradually exalted until ignition results. + +631. The dissipation of the vapour produced at the surface of the platina, +and the contact of fresh oxygen and hydrogen with the metal, form no +difficulty in this explication. The platina is not considered as causing +the combination of any particles with itself, but only associating them +closely around it; and the compressed particles are as free to move from +the platina, being replaced by other particles, as a portion of dense air +upon the surface of the globe, or at the bottom of a deep mine, is free to +move by the slightest impulse, into the upper and rarer parts of the +atmosphere. + +632. It can hardly be necessary to give any reasons why platina does not +show this effect under ordinary circumstances. It is then not sufficiently +clean (617.), and the gases are prevented from touching it, and suffering +that degree of effect which is needful to commence their combination at +common temperatures, and which they can only experience at its surface. In +fact, the very power which causes the combination of oxygen and hydrogen, +is competent, under the usual casual exposure of platina, to condense +extraneous matters upon its surface, which soiling it, take away for the +time its power of combining oxygen and hydrogen, by preventing their +contact with it (598.). + +633. Clean platina, by which I mean such as has been made the positive pole +of a pile (570.), or has been treated with acid (605.), and has then been +put into distilled water for twelve or fifteen minutes, has a _peculiar +friction_ when one piece is rubbed against another. It wets freely with +pure water, even after it has been shaken and dried by the heat of a +spirit-lamp; and if made the pole of a voltaic pile in a dilute acid, it +evolves minute bubbles from every part of its surface. But platina in its +common state wants that peculiar friction: it will not wet freely with +water as the clean platina does; and when made the positive pole of a pile, +it for a time gives off large bubbles, which seem to cling or adhere to the +metal, and are evolved at distinct and separate points of the surface. +These appearances and effects, as well as its want of power on oxygen and +hydrogen, are the consequences, and the indications, of a soiled surface. + +634. I found also that platina plates which had been cleaned perfectly soon +became soiled by mere exposure to the air; for after twenty-four hours they +no longer moistened freely with water, but the fluid ran up into portions, +leaving part of the surface bare, whilst other plates which had been +retained in water for the same time, when they were dried (580.) did +moisten, and gave the other indications of a clean surface. + +635. Nor was this the case with platina or metals only, but also with +earthy bodies, Rock crystal and obsidian would not wet freely upon the +surface, but being moistened with strong oil of vitriol, then washed, and +left in distilled water to remove all the acid, they did freely become +moistened, whether they were previously dry or whether they were left wet; +but being dried and left exposed to the air for twenty-four hours, their +surface became so soiled that water would not then adhere freely to it, but +ran up into partial portions. Wiping with a cloth (even the cleanest) was +still worse than exposure to air; the surface either of the minerals or +metals immediately became as if it were slightly greasy. The floating upon +water of small particles of metals under ordinary circumstances is a +consequence of this kind of soiled surface. The extreme difficulty of +cleaning the surface of mercury when it has once been soiled or greased, is +due to the same cause. + +636. The same reasons explain why the power of the platina plates in some +circumstances soon disappear, and especially upon use: MM. Dulong and +Thenard have observed the same effect with the spongy metal[A], as indeed +have all those who have used Doebereiner's instantaneous light machines. If +left in the air, if put into ordinary distilled water, if made to act upon +ordinary oxygen and hydrogen, they can still find in all these cases _that_ +minute portion of impurity which, when once in contact with the surface of +the platina, is retained there, and is sufficient to prevent its full +action upon oxygen and hydrogen at common temperatures: a slight elevation +of temperature is again sufficient to compensate this effect, and cause +combination. + + [A] Annales de Chimie, tom. xxiv. p. 386. + +637. No state of a solid body can be conceived more favourable for the +production of the effect than that which is possessed by platina obtained +from the ammonio-muriate by heat. Its surface is most extensive and pure, +yet very accessible to the gases brought in contact with it: if placed in +impurity, the interior, as Thenard and Dulong have observed, is preserved +clean by the exterior; and as regards temperature, it is so bad a conductor +of heat, because of its divided condition, that almost all which is evolved +by the combination of the first portions of gas is retained within the +mass, exalting the tendency of the succeeding portions to combine. + + * * * * * + +638. I have now to notice some very extraordinary interferences with this +phenomenon, dependent, not upon the nature or condition of the metal or +other acting solid, but upon the presence of certain substances mingled +with the gases acted upon; and as I shall have occasion to speak frequently +of a mixture of oxygen and hydrogen, I wish it always to be understood that +I mean a mixture composed of one volume of oxygen to two volumes of +hydrogen, being the proportions that form water. Unless otherwise +expressed, the hydrogen was always that obtained by the action of dilute +sulphuric acid on pure zinc, and the oxygen that obtained by the action of +heat from the chlorate of potassa. + +639. Mixtures of oxygen and hydrogen with _air_, containing one-fourth, +one-half, and even two-thirds of the latter, being introduced with prepared +platina plates (570. 605.) into tubes, were acted upon almost as well as if +no air were present: the retardation was far less than might have been +expected from the mere dilution and consequent obstruction to the contact +of the gases with the plates. In two hours and a half nearly all the oxygen +and hydrogen introduced as mixture was gone. + +640. But when similar experiments were made with _olefiant gas_ (the +platina plates having been made the positive poles of a voltaic pile (570.) +in acid), very different results occurred. A mixture was made of 29.2 +volumes hydrogen and 14.6 volumes oxygen, being the proportions for water; +and to this was added another mixture of 3 volumes oxygen and one volume +olefiant gas, so that the olefiant gas formed but 1/40th part of the whole; +yet in this mixture the platina plate would not act in forty-five hours. +The failure was not for want of any power in the plate, for when after that +time it was taken out of this mixture and put into one of oxygen and +hydrogen, it immediately acted, and in seven minutes caused explosion of +the gas. This result was obtained several times, and when larger +proportions of olefiant gas were used, the action seemed still more +hopeless. + +641. A mixture of forty-nine volumes oxygen and hydrogen (638.) with one +volume of olefiant gas had a well-prepared platina plate introduced. The +diminution of gas was scarcely sensible at the end of two hours, during +which it was watched; but on examination twenty-four hours afterwards, the +tube was found blown to pieces. The action, therefore, though it had been +very much retarded, had occurred at last, and risen to a maximum. + +642. With a mixture of ninety-nine volumes of oxygen and hydrogen (638.) +with one of olefiant gas, a feeble action was evident at the end of fifty +minutes; it went on accelerating (630.) until the eighty-fifth minute, and +then became so intense that the gas exploded. Here also the retarding +effect of the olefiant gas was very beautifully illustrated. + +643. Plates prepared by alkali and acid (605.) produced effects +corresponding to those just described. + +644. It is perfectly clear from these experiments, that _olefiant gas_, +even in small quantities, has a very remarkable influence in preventing the +combination of oxygen and hydrogen under these circumstances, and yet +without at all injuring or affecting the power of the platina. + +645. Another striking illustration of similar interference may be shown in +_carbonic oxide_; especially if contrasted with _carbonic acid_. A mixture +of one volume oxygen and hydrogen (638.) with four volumes of carbonic acid +was affected at once by a platina plate prepared with acid, &c. (605.); and +in one hour and a quarter nearly all the oxygen and hydrogen was gone. +Mixtures containing less carbonic acid were still more readily affected. + +646. But when carbonic oxide was substituted for the carbonic acid, not the +slightest effect of combination was produced; and when the carbonic oxide +was only one-eighth of the whole volume, no action occurred in forty and +fifty hours. Yet the plates had not lost their power; for being taken out +and put into pure oxygen and hydrogen, they acted well and at once. + +647. Two volumes of carbonic oxide and one of oxygen were mingled with nine +volumes of oxygen and hydrogen (638.). This mixture was not affected by a +plate which had been made positive in acid, though it remained in it +fifteen hours. But when to the same volumes of carbonic oxide and oxygen +were added thirty-three volumes of oxygen and hydrogen, the carbonic oxide +being then only 1/18th part of the whole, the plate acted, slowly at first, +and at the end of forty-two minutes the gases exploded. + +648. These experiments were extended to various gases and vapours, the +general results of which may be given as follow. Oxygen, hydrogen, +nitrogen, and nitrous oxide, when used to dilute the mixture of oxygen and +hydrogen, did not prevent the action of the plates even when they made +four-fifths of the whole volume of gas acted upon. Nor was the retardation +so great in any case as might have been expected from the mere dilution of +the oxygen and hydrogen, and the consequent mechanical obstruction to its +contact with the platina. The order in which carbonic acid and these +substances seemed to stand was as follows, the first interfering least with +the action; _nitrous oxide, hydrogen, carbonic acid, nitrogen, oxygen_: but +it is possible the plates were not equally well prepared in all the cases, +and that other circumstances also were unequal; consequently more numerous +experiments would be required to establish the order accurately. + +649. As to cases of _retardation_, the powers of olefiant gas and carbonic +oxide have been already described. Mixtures of oxygen and hydrogen, +containing from 1/16th to 1/20th of sulphuretted hydrogen or phosphuretted +hydrogen, seemed to show a little action at first, but were not further +affected by the prepared plates, though in contact with them for seventy +hours. When the plates were removed they had lost all power over pure +oxygen and hydrogen, and the interference of these gases was therefore of a +different nature from that of the two former, having permanently affected +the plate. + +650. A small piece of cork was dipped in sulphuret of carbon and passed up +through water into a tube containing oxygen and hydrogen (638.), so as to +diffuse a portion of its vapour through the gases. A plate being introduced +appeared at first to act a little, but after sixty-one hours the diminution +was very small. Upon putting the same plate into a pure mixture of oxygen +and hydrogen, it acted at once and powerfully, having apparently suffered +no diminution of its force. + +651. A little vapour of ether being mixed with the oxygen and hydrogen +retarded the action of the plate, but did not prevent it altogether. A +little of the vapour of the condensed oil-gas liquor[A] retarded the action +still more, but not nearly so much as an equal volume of olefiant gas would +have done. In both these cases it was the original oxygen and hydrogen +which combined together, the ether and the oil-gas vapour remaining +unaffected, and in both cases the plates retained the power of acting on +fresh oxygen and hydrogen. + + [A] Philosophical Transactions, 1825, p.440. + +652. Spongy platina was then used in place of the plates, and jets of +hydrogen mingled with the different gases thrown against it in air. The +results were exactly of the same kind, although presented occasionally in a +more imposing form. Thus, mixtures of one volume of olefiant gas or +carbonic oxide with three of hydrogen could not heat the spongy platina +when the experiments were commenced at common temperatures; but a mixture +of equal volumes of nitrogen and hydrogen acted very well, causing +ignition. With carbonic acid the results were still more striking. A +mixture of three volumes of that gas with one of hydrogen caused _ignition_ +of the platina, yet that mixture would not continue to burn from the jet +when attempts were made to light it by a taper. A mixture even of _seven_ +volumes of carbonic acid and _one_ of hydrogen will thus cause the ignition +of cold spongy platina, and yet, as if to supply a contrast, than which +none can be greater, _it cannot burn at a taper_, but causes the extinction +of the latter. On the other hand, the mixtures of carbonic oxide or +olefiant gas, which can do nothing with the platina, are _inflamed_ by the +taper, burning well. + +653. Hydrogen mingled with the vapour of ether or oil-gas liquor causes the +ignition of the spongy platina. The mixture with oil-gas burns with a flame +far brighter than that of the mixture of hydrogen and olefiant gas already +referred to, so that it would appear that the retarding action of the +hydrocarbons is not at all in proportion merely to the quantity of carbon +present. + +654. In connexion with these interferences, I must state, that hydrogen +itself, prepared from steam passed over ignited iron, was found when +mingled with oxygen to resist the action of platina. It had stood over +water seven days, and had lost all fetid smell; but a jet of it would not +cause the ignition of spongy platina, commencing at common temperatures; +nor would it combine with oxygen in a tube either under the influence of a +prepared plate or of spongy platina. A mixture of one volume of this gas +with three of pure hydrogen, and the due proportion of oxygen, was not +affected by plates after fifty hours. I am inclined to refer the effect to +carbonic oxide present in the gas, but have not had time to verify the +suspicion. The power of the plates was not destroyed (640. 646.). + +655. Such are the general facts of these remarkable interferences. Whether +the effect produced by such small quantities of certain gases depends upon +any direct action which they may exert upon the particles of oxygen and +hydrogen, by which the latter are rendered less inclined to combine, or +whether it depends upon their modifying the action of the plate temporarily +(for they produce no real change on it), by investing it through the agency +of a stronger attraction than that of the hydrogen, or otherwise, remains +to be decided by more extended experiments. + + * * * * * + +656. The theory of action which I have given for the original phenomena +appears to me quite sufficient to account for all the effects by reference +to known properties, and dispenses with the assumption of any new power of +matter. I have pursued this subject at some length, as one of great +consequence, because I am convinced that the superficial actions of matter, +whether between two bodies, or of one piece of the same body, and the +actions of particles not directly or strongly in combination, are becoming +daily more and more important to our theories of chemical as well as +mechanical philosophy[A]. In all ordinary cases of combustion it is evident +that an action of the kind considered, occurring upon the surface of the +carbon in the fire, and also in the bright part of a flame, must have great +influence over the combinations there taking place. + + [A] As a curious illustration of the influence of mechanical forces + over chemical affinity, I will quote the refusal of certain substances + to effloresce when their surfaces are perfect, which yield immediately + upon the surface being broken, If crystals of carbonate of soda, or + phosphate of soda, or sulphate of soda, having no part of their + surfaces broken, be preserved from external violence, they will not + effloresce. I have thus retained crystals of carbonate of soda + perfectly transparent and unchanged from September 1827 to January + 1833; and crystals of sulphate of soda from May 1832 to the present + time, November 1833. If any part of the surface were scratched or + broken, then efflorescence began at that part, and covered the whole. + The crystals were merely placed in evaporating basins and covered with + paper. + +657. The condition of elasticity upon the exterior of the gaseous or +vaporous mass already referred to (626. 627.), must be connected directly +with the action of solid bodies, as nuclei, on vapours, causing +condensation upon them in preference to any condensation in the vapours +themselves; and in the well-known effect of nuclei on solutions a similar +condition may have existence (623.), for an analogy in condition exists +between the parts of a body in solution, and those of a body in the +vaporous or gaseous state. This thought leads us to the consideration of +what are the respective conditions at the surfaces of contact of two +portions of the same substance at the same temperature, one in the solid or +liquid, and the other in the vaporous state; as, for instance, steam and +water. It would seem that the particles of vapour next to the particles of +liquid are in a different relation to the latter to what they would be with +respect to any other liquid or solid substance; as, for instance, mercury +or platina, if they were made to replace the water, i.e. if the view of +independent action which I have taken (626. 627.) as a consequence of +Dalton's principles, be correct. It would also seem that the mutual +relation of similar particles, and the indifference of dissimilar particles +which Dalton has established as a matter of fact amongst gases and vapours, +extends to a certain degree amongst solids and fluids, that is, when they +are in relation by contact with vapours, either of their own substance or +of other bodies. But though I view these points as of great importance with +respect to the relations existing between different substances and their +physical constitution in the solid, liquid, or gaseous state, I have not +sufficiently considered them to venture any strong opinions or statements +here[A]. + + [A] In reference to this paragraph and also 626, see a correction by + Dr. C. Henry, in his valuable paper on this curious subject. + Philosophical Magazine, 1835. vol. vi. p. 305.--_Dec. 1838._ + +658. There are numerous well-known cases, in which substances, such as +oxygen and hydrogen, act readily in their _nascent_ state, and produce +chemical changes which they are not able to effect if once they have +assumed the gaseous condition. Such instances are very common at the poles +of the voltaic pile, and are, I think, easily accounted for, if it be +considered that at the moment of separation of any such particle it is +entirely surrounded by other particles of a _different_ kind with which it +is in close contact, and has not yet assumed those relations and conditions +which it has in its fully developed state, and which it can only assume by +association with other particles of its own kind. For, at the moment, its +elasticity is absent, and it is in the same relation to particles with +which it is in contact, and for which it has an affinity, as the particles +of oxygen and hydrogen are to each other on the surface of clean platina +(626. 627.). + +659. The singular effects of retardation produced by very small quantities +of some gases, and not by large quantities of others (640. 645. 652.), if +dependent upon any relation of the added gas to the surface of the solid, +will then probably be found immediately connected with the curious +phenomena which are presented by different gases when passing through +narrow tubes at low pressures, which I observed many years ago[A]; and this +action of surfaces must, I think, influence the highly interesting +phenomena of the diffusion of gases, at least in the form in which it has +been experimented upon by Mr. Graham in 1829 and 1831[B], and also by Dr. +Mitchell of Philadelphia[C] in 1830. It seems very probable that if such a +substance as spongy platina were used, another law for the diffusion of +gases under the circumstances would come out than that obtained by the use +of plaster of Paris. + + [A] Quarterly Journal of Science, 1819, vol. vii. p. 106. + + [B] Quarterly Journal of Science, vol. xxviii. p. 74, and Edinburgh + Transactions, 1831. + + [C] Journal of the Royal Institution for 1831, p. 101. + +660. I intended to have followed this section by one on the secondary piles +of Ritter, and the peculiar properties of the poles of the pile, or of +metals through which electricity has passed, which have been observed by +Ritter, Van Marum, Yelin, De la Rive, Marianini, Berzelius, and others. It +appears to me that all these phenomena bear a satisfactory explanation on +known principles, connected with the investigation just terminated, and do +not require the assumption of any new state or new property. But as the +experiments advanced, especially those of Marianini, require very careful +repetition and examination, the necessity of pursuing the subject of +electro-chemical decomposition obliges me for a time to defer the +researches to which I have just referred. + +_Royal Institution, +November 30, 1833._ + + + + +SEVENTH SERIES. + + +S 11. _On Electro-chemical Decomposition, continued._[A] P iv. _On some +general conditions of Electro-decomposition._ P v. _On a new Measurer of +Volta-electricity._ P vi. _On the primary or secondary character of bodies +evolved in Electro-decomposition._ P vii. _On the definite nature and +extent of Electro-chemical Decompositions._ S 13. _On the absolute quantity +of Electricity associated with the particles or atoms of Matter._ + + [A] Refer to the note after 1047, Series VIII.--_Dec. 1838._ + +Received January 9,--Read January 23, February 6 and 13, 1834. + +_Preliminary._ + + +661. The theory which I believe to be a true expression of the facts of +electro-chemical decomposition, and which I have therefore detailed in a +former series of these Researches, is so much at variance with those +previously advanced, that I find the greatest difficulty in stating +results, as I think, correctly, whilst limited to the use of terms which +are current with a certain accepted meaning. Of this kind is the term +_pole_, with its prefixes of positive and negative, and the attached ideas +of attraction and repulsion. The general phraseology is that the positive +pole _attracts_ oxygen, acids, &c., or more cautiously, that it +_determines_ their evolution upon its surface; and that the negative pole +acts in an equal manner upon hydrogen, combustibles, metals, and bases. +According to my view, the determining force is _not_ at the poles, but +_within_ the body under decomposition; and the oxygen and acids are +rendered at the _negative_ extremity of that body, whilst hydrogen, metals, +&c., are evolved at the _positive_ extremity (518. 524.). + +662. To avoid, therefore, confusion and circumlocution, and for the sake of +greater precision of expression than I can otherwise obtain, I have +deliberately considered the subject with two friends, and with their +assistance and concurrence in framing them, I purpose henceforward using +certain other terms, which I will now define. The _poles_, as they are +usually called, are only the doors or ways by which the electric current +passes into and out of the decomposing body (556.); and they of course, +when in contact with that body, are the limits of its extent in the +direction of the current. The term has been generally applied to the metal +surfaces in contact with the decomposing substance; but whether +philosophers generally would also apply it to the surfaces of air (465. +471.) and water (493.), against which I have effected electro-chemical +decomposition, is subject to doubt. In place of the term pole, I propose +using that of _Electrode_[A], and I mean thereby that substance, or rather +surface, whether of air, water, metal, or any other body, which bounds the +extent of the decomposing matter in the direction of the electric current. + + [A] [Greek: elektron], and [Greek: -odos] _a way_. + +663. The surfaces at which, according to common phraseology, the electric +current enters and leaves a decomposing body, are most important places of +action, and require to be distinguished apart from the poles, with which +they are mostly, and the electrodes, with which they are always, in +contact. Wishing for a natural standard of electric direction to which I +might refer these, expressive of their difference and at the same time free +from all theory, I have thought it might be found in the earth. If the +magnetism of the earth be due to electric currents passing round it, the +latter must be in a constant direction, which, according to present usage +of speech, would be from east to west, or, which will strengthen this help +to the memory, that in which the sun appears to move. If in any case of +electro-decomposition we consider the decomposing body as placed so that +the current passing through it shall be in the same direction, and parallel +to that supposed to exist in the earth, then the surfaces at which the +electricity is passing into and out of the substance would have an +invariable reference, and exhibit constantly the same relations of powers. +Upon this notion we purpose calling that towards the east the _anode_[A], +and that towards the west the _cathode_[B]; and whatever changes may take +place in our views of the nature of electricity and electrical action, as +they must affect the _natural standard_ referred to, in the same direction, +and to an equal amount with any decomposing substances to which these terms +may at any time be applied, there seems no reason to expect that they will +lead to confusion, or tend in any way to support false views. The _anode_ +is therefore that surface at which the electric current, according to our +present expression, enters: it is the _negative_ extremity of the +decomposing body; is where oxygen, chlorine, acids, &c., are evolved; and +is against or opposite the positive electrode. The _cathode_ is that +surface at which the current leaves the decomposing body, and is its +_positive_ extremity; the combustible bodies, metals, alkalies, and bases, +are evolved there, and it is in contact with the negative electrode. + + [A] [Greek: ano] _upwards_, and [Greek: -odos] _a way_; the way which +the sun rises. + + [B] [Greek: kata] _downwards_, and [Greek: -odos] _a way_; the way + which the sun sets. + +664. I shall have occasion in these Researches, also, to class bodies +together according to certain relations derived from their electrical +actions (822.); and wishing to express those relations without at the same +time involving the expression of any hypothetical views, I intend using the +following names and terms. Many bodies are decomposed directly by the +electric current, their elements being set free; these I propose to call +_electrolytes_.[A] Water, therefore, is an electrolyte. The bodies which, +like nitric or sulphuric acids, are decomposed in a secondary manner (752. +757.), are not included under this term. Then for _electro-chemically +decomposed_, I shall often use the term _electrolyzed_, derived in the same +way, and implying that the body spoken of is separated into its components +under the influence of electricity: it is analogous in its sense and sound +to _analyse_, which is derived in a similar manner. The term +_electrolytical_ will be understood at once: muriatic acid is +electrolytical, boracic acid is not. + + [A] [Greek: elektron], and [Greek: lyo], _soluo_. N. Electrolyte, V. + Electrolyze. + +665. Finally, I require a term to express those bodies which can pass to +the _electrodes_, or, as they are usually called, the poles. Substances are +frequently spoken of as being _electro-negative_, or _electro-positive_, +according as they go under the supposed influence of a direct attraction to +the positive or negative pole. But these terms are much too significant for +the use to which I should have to put them; for though the meanings are +perhaps right, they are only hypothetical, and may be wrong; and then, +through a very imperceptible, but still very dangerous, because continual, +influence, they do great injury to science, by contracting and limiting the +habitual views of those engaged in pursuing it. I propose to distinguish +such bodies by calling those _anions_[A] which go to the _anode_ of the +decomposing body; and those passing to the _cathode, cations_[B]; and when +I have occasion to speak of these together, I shall call them _ions_. Thus +the chloride of lead is an _electrolyte_, and when _electrolyzed_ evolves +the two _ions_, chlorine and lead, the former being an _anion_, and the +latter a _cation_. + + [A] [Greek: anion] _that which goes up._ (Neuter participle.) + + [B] [Greek: kation] _that which goes down._ + +666. These terms being once well-defined, will, I hope, in their use enable +me to avoid much periphrasis and ambiguity of expression. I do not mean to +press them into service more frequently than will be required, for I am +fully aware that names are one thing and science another. + +667. It will be well understood that I am giving no opinion respecting the +nature of the electric current now, beyond what I have done on former +occasions (283. 517.); and that though I speak of the current as proceeding +from the parts which are positive to those which are negative (663.), it is +merely in accordance with the conventional, though in some degree tacit, +agreement entered into by scientific men, that they may have a constant, +certain, and definite means of referring to the direction of the forces of +that current. + + [Since this paper was read, I have changed some of the terms which were +first proposed, that I might employ only such as were at the same time +simple in their nature, clear in their reference, and free from +hypothesis. + + +P iv. _On some general conditions of Electro-chemical Decomposition._ + +669. From the period when electro-chemical decomposition was first effected +to the present time, it has been a remark, that those elements which, in +the ordinary phenomena of chemical affinity, were the most directly opposed +to each other, and combined with the greatest attractive force, were those +which were the most readily evolved at the opposite extremities of the +decomposing bodies (549.). + +670. If this result was evident when water was supposed to be essential to, +and was present in, almost every case of such decomposition (472.), it is +far more evident now that it has been shown and proved that water is not +necessarily concerned in the phenomena (474.), and that other bodies much +surpass it in some of the effects supposed to be peculiar to that +substance. + +671. Water, from its constitution and the nature of its elements, and from +its frequent presence in cases of electrolytic action, has hitherto stood +foremost in this respect. Though a compound formed by very powerful +affinity, it yields up its elements under the influence of a very feeble +electric current; and it is doubtful whether a case of electrolyzation can +occur, where, being present, it is not resolved into its first principles. + +672. The various oxides, chlorides, iodides, and salts, which I have shown +are decomposable by the electric current when in the liquid state, under +the same general law with water (402.), illustrate in an equally striking +manner the activity, in such decompositions, of elements directly and +powerfully opposed to each other by their chemical relations. + +673. On the other hand, bodies dependent on weak affinities very rarely +give way. Take, for instance, glasses: many of those formed of silica, +lime, alkali, and oxide of lead, may be considered as little more than +solutions of substances one in another[A]. If bottle-glass be fused, and +subjected to the voltaic pile, it does not appear to be at all decomposed +(408.). If flint glass, which contains substances more directly opposed, be +operated upon, it suffers some decomposition; and if borate of lead glass, +which is a definite chemical compound, be experimented with, it readily +yields up its elements (408.). + + [A] Philosophical Transactions, 1830, p. 49. + +674. But the result which is found to be so striking in the instances +quoted is not at all borne out by reference to other cases where a similar +consequence might have been expected. It may be said, that my own theory of +electro-chemical decomposition would lead to the expectation that all +compound bodies should give way under the influence of the electric current +with a facility proportionate to the strength of the affinity by which +their elements, either proximate or ultimate, are combined. I am not sure +that that follows as a consequence of the theory; but if the objection is +supposed to be one presented by the facts, I have no doubt it will be +removed when we obtain a more intimate acquaintance with, and precise idea +of, the nature of chemical affinity and the mode of action of an electric +current over it (518. 524.): besides which, it is just as directly opposed +to any other theory of electro-chemical decomposition as the one I have +propounded; for if it be admitted, as is generally the case, that the more +directly bodies are opposed to each other in their attractive forces, the +more powerfully do they combine, then the objection applies with equal +force to any of the theories of electrolyzation which have been considered, +and is an addition to those which I have taken against them. + +675. Amongst powerful compounds which are not decomposed, boracic acids +stand prominent (408.). Then again, the iodide of sulphur, and the +chlorides of sulphur, phosphorus, and carbon, are not decomposable under +common circumstances, though their elements are of a nature which would +lead to a contrary expectation. Chloride of antimony (402. 690.), the +hydro-carbons, acetic acid, ammonia, and many other bodies undecomposable +by the voltaic pile, would seem to be formed by an affinity sufficiently +strong to indicate that the elements were so far contrasted in their nature +as to sanction the expectation that, the pile would separate them, +especially as in some cases of mere solution (530. 544.), where the +affinity must by comparison be very weak, separation takes place[A]. + + [A] With regard to solution, I have met with some reasons for + supposing that it will probably disappear as a cause of transference, + and intend resuming the consideration at a convenient opportunity. + +676. It must not be forgotten, however, that much of this difficulty, and +perhaps the whole, may depend upon the absence of conducting power, which, +preventing the transmission of the current, prevents of course the effects +due to it. All known compounds being non-conductors when solid, but +conductors when liquid, are decomposed, with _perhaps_ the single exception +at present known of periodide of mercury (679. 691.)[A]; and even water +itself, which so easily yields up its elements when the current passes, if +rendered quite pure, scarcely suffers change, because it then becomes a +very bad conductor. + + [A] See now, 1340, 1341.--_Dec. 1838._ + +677. If it should hereafter be proved that the want of decomposition in +those cases where, from chemical considerations, it might be so strongly +expected (669, 672. 674.), is due to the absence or deficiency of +conducting power, it would also at the same time be proved that +decomposition _depends_ upon conduction, and not the latter upon the former +(413.); and in water this seems to be very nearly decided. On the other +hand, the conclusion is almost irresistible, that in electrolytes the power +of transmitting the electricity across the substance is _dependent_ upon +their capability of suffering decomposition; taking place only whilst they +are decomposing, and being proportionate to the quantity of elements +separated (821.). I may not, however, stop to discuss this point +experimentally at present. + +678. When a compound contains such elements as are known to pass towards +the opposite extremities of the voltaic pile, still the proportions in +which they are present appear to be intimately connected with capability in +the compound of suffering or resisting decomposition. Thus, the +protochloride of tin readily conducts, and is decomposed (402.), but the +perchloride neither conducts nor is decomposed (406.). The protiodide of +tin is decomposed when fluid (402.); the periodide is not (405.). The +periodide of mercury when fused is not decomposed (691.), even though it +does conduct. I was unable to contrast it with the protiodide, the latter +being converted into mercury and periodide by heat. + +679. These important differences induced me to look more closely to certain +binary compounds, with a view of ascertaining whether a _law_ regulating +the _decomposability_ according to some _relation of the proportionals or +equivalents_ of the elements, could be discovered. The proto compounds +only, amongst those just referred to, were decomposable; and on referring +to the substances quoted to illustrate the force and generality of the law +of conduction and decomposition which I discovered (402.), it will be found +that all the oxides, chlorides, and iodides subject to it, except the +chloride of antimony and the periodide of mercury, (to which may now +perhaps be added corrosive sublimate,) are also decomposable, whilst many +per compounds of the same elements, not subject to the law, were not so +(405. 406.). + +680. The substances which appeared to form the strongest exceptions to this +general result were such bodies as the sulphuric, phosphoric, nitric, +arsenic, and other acids. + +681. On experimenting with sulphuric acid, I found no reason to believe +that it was by itself a conductor of, or decomposable by, electricity, +although I had previously been of that opinion (552.). When very strong it +is a much worse conductor than if diluted[A]. If then subjected to the +action of a powerful battery, oxygen appears at the _anode_, or positive +electrode, although much is absorbed (728.), and hydrogen and sulphur +appear at the _cathode_, or negative electrode. Now the hydrogen has with +me always been pure, not sulphuretted, and has been deficient in proportion +to the sulphur present, so that it is evident that when decomposition +occurred water must have been decomposed. I endeavoured to make the +experiment with anhydrous sulphuric acid; and it appeared to me that, when +fused, such acid was not a conductor, nor decomposed; but I had not enough +of the dry acid in my possession to allow me to decide the point +satisfactorily. My belief is, that when sulphur appears during the action +of the pile on sulphuric acid, it is the result of a secondary action, and +that the acid itself is not electrolyzable (757.). + + [A] De la Rive. + +682. Phosphoric acid is, I believe, also in the same condition; but I have +found it impossible to decide the point, because of the difficulty of +operating on fused anhydrous phosphoric acid. Phosphoric acid which has +once obtained water cannot be deprived of it by heat alone. When heated, +the hydrated acid volatilizes. Upon subjecting phosphoric acid, fused upon +the ring end of a wire (401.), to the action of the voltaic apparatus, it +conducted, and was decomposed; but gas, which I believe to be hydrogen, was +always evolved at the negative electrode, and the wire was not affected as +would have happened had phosphorus been separated. Gas was also evolved at +the positive electrode. From all the facts, I conclude it was the water and +not the acid which was decomposed. + +683. _Arsenic acid_. This substance conducted, and was decomposed; but it +contained water, and I was unable at the time to press the investigation so +as to ascertain whether a fusible anhydrous arsenic acid could be obtained. +It forms, therefore, at present no exception to the general result. + +684. Nitrous acid, obtained by distilling nitrate of lead, and keeping it +in contact with strong sulphuric acid, was found to conduct and decompose +slowly. But on examination there were strong reasons for believing that +water was present, and that the decomposition and conduction depended upon +it. I endeavoured to prepare a perfectly anhydrous portion, but could not +spare the time required to procure an unexceptionable result. + +685. Nitric acid is a substance which I believe is not decomposed directly +by the electric current. As I want the facts in illustration of the +distinction existing between primary and secondary decomposition, I will +merely refer to them in this place (752.). + +686. That these mineral acids should confer facility of conduction and +decomposition on water, is no proof that they are competent to favour and +suffer these actions in themselves. Boracic acid does the same thing, +though not decomposable. M. de la Rive has pointed out that chlorine has +this power also; but being to us an elementary substance, it cannot be due +to its capability of suffering decomposition. + +687. _Chloride of sulphur_ does not conduct, nor is it decomposed. It +consists of single proportionals of its elements, but is not on that +account an exception to the rule (679.), which does not affirm that _all_ +compounds of single proportionals of elements are decomposable, but that +such as are decomposable are so constituted. + +688. _Protochloride of phosphorus_ does not conduct nor become decomposed. + +689. _Protochloride of carbon_ does not conduct nor suffer decomposition. +In association with this substance, I submitted the _hydro-chloride of +carbon_ from olefiant gas and chlorine to the action of the electric +current; but it also refused to conduct or yield up its elements. + +600. With regard to the exceptions (679.), upon closer examination some of +them disappear. Chloride of antimony (a compound of one proportional of +antimony and one and a half of chlorine) of recent preparation was put into +a tube (fig. 68.) (789.), and submitted when fused to the action of the +current, the positive electrode being of plumbago. No electricity passed, +and no appearance of decomposition was visible at first; but when the +positive and negative electrodes were brought very near each other in the +chloride, then a feeble action occurred and a feeble current passed. The +effect altogether was so small (although quite amenable to the law before +given (394.)), and so unlike the decomposition and conduction occurring in +all the other cases, that I attribute it to the presence of a minute +quantity of water, (for which this and many other chlorides have strong +attractions, producing hydrated chlorides,) or perhaps of a true +protochloride consisting of single proportionals (695, 796.). + +691. _Periodide of mercury_ being examined in the same manner, was found +most distinctly to insulate whilst solid, but conduct when fluid, according +to the law of _liquido-conduction_ (402.); but there was no appearance of +decomposition. No iodine appeared at the _anode_, nor mercury or other +substance at the _cathode_. The case is, therefore, no exception to the +rule, that only compounds of single proportionals are decomposable; but it +is an exception, and I think the only one, to the statement, that all +bodies subject to the law of liquido-conduction are decomposable. I +incline, however, to believe, that a portion of protiodide of mercury is +retained dissolved in the periodide, and that to its slow decomposition the +feeble conducting power is due. Periodide would be formed, as a secondary +result, at the _anode_; and the mercury at the _cathode_ would also form, +as a secondary result, protiodide. Both these bodies would mingle with the +fluid mass, and thus no final separation appear, notwithstanding the +continued decomposition. + +692. When _perchloride of mercury_ was subjected to the voltaic current, it +did not conduct in the solid state, but it did conduct when fluid. I think, +also, that in the latter case it was decomposed; but there are many +interfering circumstances which require examination before a positive +conclusion can be drawn[A]. + + [A] With regard to perchloride and periodide of mercury, see now 1340, + 1341.--_Dec. 1838._ + +693. When the ordinary protoxide of antimony is subjected to the voltaic +current in a fused state, it also is decomposed, although the effect from +other causes soon ceases (402, 801.). This oxide consists of one +proportional of antimony and one and a half of oxygen, and is therefore an +exception to the general law assumed. But in working with this oxide and +the chloride, I observed facts which lead me to doubt whether the compounds +usually called the protoxide and the protochloride do not often contain +other compounds, consisting of single proportions, which are the true proto +compounds, and which, in the case of the oxide, might give rise to the +decomposition above described. + +694. The ordinary sulphuret of antimony its considered as being the +compound with the smallest quantity of sulphur, and analogous in its +proportions to the ordinary protoxide. But I find that if it be fused with +metallic antimony, a new sulphuret is formed, containing much more of the +metal than the former, and separating distinctly, when fused, both from the +pure metal on the one hand, and the ordinary gray sulphuret on the other. +In some rough experiments, the metal thus taken up by the ordinary +sulphuret of antimony was equal to half the proportion of that previously +in the sulphuret, in which case the new sulphuret would consist of _single_ +proportionals. + +695. When this new sulphuret was dissolved in muriatic acid, although a +little antimony separated, yet it appeared to me that a true protochloride, +consisting of _single_ proportionals, was formed, and from that by +alkalies, &c., a true protoxide, consisting also of _single_ proportionals, +was obtainable. But I could not stop to ascertain this matter strictly by +analysis. + +696. I believe, however, that there is such an oxide; that it is often +present in variable proportions in what is commonly called protoxide, +throwing uncertainty upon the results of its analysis, and causing the +electrolytic decomposition above described[A]. + + [A] In relation to this and the three preceding paragraphs, and also + 801, see Berzelius's correction of the nature of the supposed now + sulphuret and oxide, Phil. Mag. 1836, vol. viii. 476: and for the + probable explanation of the effects obtained with the protoxide, refer + to 1340, 1341.--_Dec. 1838._ + +697. Upon the whole, it appears probable that all those binary compounds of +elementary bodies which are capable of being electrolyzed when fluid, but +not whilst solid, according to the law of liquido-conduction (394.), +consist of single proportionals of their elementary principles; and it may +be because of their departure from this simplicity of composition, that +boracic acid, ammonia, perchlorides, periodides, and many other direct +compounds of elements, are indecomposable. + +698. With regard to salts and combinations of compound bodies, the same +simple relation does not appear to hold good. I could not decide this by +bisulphates of the alkalies, for as long as the second proportion of acid +remained, water was retained with it. The fused salts conducted, and were +decomposed; but hydrogen always appeared at the negative electrode. + +699. A biphosphate of soda was prepared by heating, and ultimately fusing, +the ammonia-phosphate of soda. In this case the fused bisalt conducted, and +was decomposed; but a little gas appeared at the negative electrode; and +though I believe the salt itself was electrolyzed, I am not quite satisfied +that water was entirely absent. + +700. Then a biborate of soda was prepared; and this, I think, is an +unobjectionable case. The salt, when fused, conducted, and was decomposed, +and gas appeared at both electrodes: even when the boracic acid was +increased to three proportionals, the same effect took place. + +701. Hence this class of compound combinations does not seem to be subject +to the same simple law as the former class of binary combinations. Whether +we may find reason to consider them as mere solutions of the compound of +single proportionals in the excess of acid, is a matter which, with some +apparent exceptions occurring amongst the sulphurets, must be left for +decision by future examination. + +702. In any investigation of these points, great care must be taken to +exclude water; for if present, secondary effects are so frequently produced +as often seemingly to indicate an electro-decomposition of substances, when +no true result of the kind has occurred (742, &c.). + +703. It is evident that all the cases in which decomposition _does not +occur, may_ depend upon the want of conduction (677. 413.); but that does +not at all lessen the interest excited by seeing the great difference of +effect due to a change, not in the nature of the elements, but merely in +their proportions; especially in any attempt which may be made to elucidate +and expound the beautiful theory put forth by Sir Humphry Davy[A], and +illustrated by Berzelius and other eminent philosophers, that ordinary +chemical affinity is a mere result of the electrical attractions of the +particles of matter. + + [A] Philosophical Transactions, 1807, pp. 32, 39; also 1826, pp. 387, + 389. + + +P v. _On a new measure of Volta-electricity._ + +704. I have already said, when engaged in reducing common and voltaic +electricity to one standard of measurement (377.), and again when +introducing my theory of electro-chemical decomposition (504. 505. 510.), +that the chemical decomposing action of a current _is constant for a +constant quantity of electricity_, notwithstanding the greatest variations +in its sources, in its intensity, in the size of the _electrodes_ used, in +the nature of the conductors (or non-conductors (307.)) through which it is +passed, or in other circumstances. The conclusive proofs of the truth of +these statements shall be given almost immediately (783, &c.). + +705. I endeavoured upon this law to construct an instrument which should +measure out the electricity passing through it, and which, being interposed +in the course of the current used in any particular experiment, should +serve at pleasure, either as a _comparative standard_ of effect, or as a +_positive measurer_ of this subtile agent. + +706. There is no substance better fitted, under ordinary circumstances, to +be the indicating body in such an instrument than water; for it is +decomposed with facility when rendered a better conductor by the addition +of acids or salts; its elements may in numerous cases be obtained and +collected without any embarrassment from secondary action, and, being +gaseous, they are in the best physical condition for separation and +measurement. Water, therefore, acidulated by sulphuric acid, is the +substance I shall generally refer to, although it may become expedient in +peculiar cases or forms of experiment to use other bodies (843.). + +707. The first precaution needful in the construction of the instrument was +to avoid the recombination of the evolved gases, an effect which the +positive electrode has been found so capable of producing (571.). For this +purpose various forms of decomposing apparatus were used. The first +consisted of straight tubes, each containing a plate and wire of platina +soldered together by gold, and fixed hermetically in the glass at the +closed extremity of the tube (Plate V. fig. 60.). The tubes were about +eight inches long, 0.7 of an inch in diameter, and graduated. The platina +plates were about an inch long, as wide as the tubes would permit, and +adjusted as near to the mouths of the tubes as was consistent with the safe +collection of the gases evolved. In certain cases, where it was required to +evolve the elements upon as small a surface as possible, the metallic +extremity, instead of being a plate, consisted of the wire bent into the +form of a ring (fig. 61.). When these tubes were used as measurers, they +were filled with the dilute sulphuric acid, inverted in a basin of the same +liquid (fig. 62.), and placed in an inclined position, with their mouths +near to each other, that as little decomposing matter should intervene as +possible; and also, in such a direction that the platina plates should be +in vertical planes (720). + +708. Another form of apparatus is that delineated (fig. 63.). The tube is +bent in the middle; one end is closed; in that end is fixed a wire and +plate, _a_, proceeding so far downwards, that, when in the position +figured, it shall be as near to the angle as possible, consistently with +the collection, at the closed extremity of the tube, of all the gas evolved +against it. The plane of this plate is also perpendicular (720.). The other +metallic termination, _b_, is introduced at the time decomposition is to be +effected, being brought as near the angle as possible, without causing any +gas to pass from it towards the closed end of the instrument. The gas +evolved against it is allowed to escape. + +709. The third form of apparatus contains both electrodes in the same tube; +the transmission, therefore, of the electricity, and the consequent +decomposition, is far more rapid than in the separate tubes. The resulting +gas is the sum of the portions evolved at the two electrodes, and the +instrument is better adapted than either of the former as a measurer of the +quantity of voltaic electricity transmitted in ordinary cases. It consists +of a straight tube (fig. 64.) closed at the upper extremity, and graduated, +through the sides of which pass platina wires (being fused into the glass), +which are connected with two plates within. The tube is fitted by grinding +into one mouth of a double-necked bottle. If the latter be one-half or +two-thirds full of the dilute sulphuric acid (706.), it will, upon +inclination of the whole, flow into the tube and fill it. When an electric +current is passed through the instrument, the gases evolved against the +plates collect in the upper portion of the tube, and are not subject to the +recombining power of the platina. + +710. Another form of the instrument is given at fig. 65. + +711. A fifth form is delineated (fig. 66.). This I have found exceedingly +useful in experiments continued in succession for days together, and where +large quantities of indicating gas were to be collected. It is fixed on a +weighted foot, and has the form of a small retort containing the two +electrodes: the neck is narrow, and sufficiently long to deliver gas +issuing from it into a jar placed in a small pneumatic trough. The +electrode chamber, sealed hermetically at the part held in the stand, is +five inches in length, and 0.6 of an inch in diameter; the neck about nine +inches in length, and 0.4 of an inch in diameter internally. The figure +will fully indicate the construction. + +712. It can hardly be requisite to remark, that in the arrangement of any +of these forms of apparatus, they, and the wires connecting them with the +substance, which is collaterally subjected to the action of the same +electric current, should be so far insulated as to ensure a certainty that +all the electricity which passes through the one shall also be transmitted +through the other. + + * * * * * + +713. Next to the precaution of collecting the gases, if mingled, out of +contact with the platinum, was the necessity of testing the law of a +_definite electrolytic_ action, upon water at least, under all varieties of +condition; that, with a conviction of its certainty, might also be obtained +a knowledge of those interfering circumstances which would require to be +practically guarded against. + +714. The first point investigated was the influence or indifference of +extensive variations in the size of the electrodes, for which purpose +instruments like those last described (709. 710. 711.) were used. One of +these had plates 0.7 of an inch wide, and nearly four inches long; another +had plates only 0.5 of an inch wide, and 0.8 of an inch long; a third had +wires 0.02 of an inch in diameter, and three inches long; and a fourth, +similar wires only half an inch in length. Yet when these were filled with +dilute sulphuric acid, and, being placed in succession, had one common +current of electricity passed through them, very nearly the same quantity +of gas was evolved in all. The difference was sometimes in favour of one +and sometimes on the side of another; but the general result was that the +largest quantity of gases was evolved at the smallest electrodes, namely, +those consisting merely of platina wires. + +715. Experiments of a similar kind were made with the single-plate, +straight tubes (707.), and also with the curved tubes (708.), with similar +consequences; and when these, with the former tubes, were arranged together +in various ways, the result, as to the equality of action of large and +small metallic surfaces when delivering and receiving the same current of +electricity, was constantly the same. As an illustration, the following +numbers are given. An instrument with two wires evolved 74.3 volumes of +mixed gases; another with plates 73.25 volumes; whilst the sum of the +oxygen and hydrogen in two separate tubes amounted to 73.65 volumes. In +another experiment the volumes were 55.3, 55.3, and 54.4. + +716. But it was observed in these experiments, that in single-plate tubes +(707.) more hydrogen was evolved at the negative electrode than was +proportionate to the oxygen at the positive electrode; and generally, also, +more than was proportionate to the oxygen and hydrogen in a double-plate +tube. Upon more minutely examining these effects, I was led to refer them, +and also the differences between wires and plates (714.), to the solubility +of the gases evolved, especially at the positive electrode. + +717. When the positive and negative electrodes are equal in surface, the +bubbles which rise from them in dilute sulphuric acid are always different +in character. Those from the positive plate are exceedingly small, and +separate instantly from every part of the surface of the metal, in +consequence of its perfect cleanliness (633.); whilst in the liquid they +give it a hazy appearance, from their number and minuteness; are easily +carried down by currents, and therefore not only present far greater +surface of contact with the liquid than larger bubbles would do, but are +retained a much longer time in mixture with it. But the bubbles at the +negative surface, though they constitute twice the volume of the gas at the +positive electrode, are nevertheless very inferior in number. They do not +rise so universally from every part of the surface, but seem to be evolved +at different parts; and though so much larger, they appear to cling to the +metal, separating with difficulty from it, and when separated, instantly +rising to the top of the liquid. If, therefore, oxygen and hydrogen had +equal solubility in, or powers of combining with, water under similar +circumstances, still under the present conditions the oxygen would be far +the most liable to solution; but when to these is added its well-known +power of forming a compound with water, it is no longer surprising that +such a compound should be produced in small quantities at the positive +electrode; and indeed the blenching power which some philosophers have +observed in a solution at this electrode, when chlorine and similar bodies +have been carefully excluded, is probably due to the formation there, in +this manner, of oxywater. + +718. That more gas was collected from the wires than from the plates, I +attribute to the circumstance, that as equal quantities were evolved in +equal times, the bubbles at the wires having been more rapidly produced, in +relation to any part of the surface, must have been much larger; have been +therefore in contact with the fluid by a much smaller surface, and for a +much shorter time than those at the plates; hence less solution and a +greater amount collected. + +719. There was also another effect produced, especially by the use of large +electrodes, which was both a consequence and a proof of the solution of +part of the gas evolved there. The collected gas, when examined, was found +to contain small portions of nitrogen. This I attribute to the presence of +air dissolved in the acid used for decomposition. It is a well-known fact, +that when bubbles of a gas but slightly soluble in water or solutions pass +through them, the portion of this gas which is dissolved displaces a +portion of that previously in union with the liquid: and so, in the +decompositions under consideration, as the oxygen dissolves, it displaces a +part of the air, or at least of the nitrogen, previously united to the +acid; and this effect takes place _most extensively_ with large plates, +because the gas evolved at them is in the most favourable condition for +solution, + +720. With the intention of avoiding this solubility of the gases as much as +possible, I arranged the decomposing plates in a vertical position (707. +708.), that the bubbles might quickly escape upwards, and that the downward +currents in the fluid should not meet ascending currents of gas. This +precaution I found to assist greatly in producing constant results, and +especially in experiments to be hereafter referred to, in which other +liquids than dilute sulphuric acid, as for instance solution of potash, +were used. + +721. The irregularities in the indications of the measurer proposed, +arising from the solubility just referred to, are but small, and may be +very nearly corrected by comparing the results of two or three experiments. +They may also be almost entirely avoided by selecting that solution which +is found to favour them in the least degree (728.); and still further by +collecting the hydrogen only, and using that as the indicating gas; for +being much less soluble than oxygen, being evolved with twice the rapidity +and in larger bubbles (717.), it can be collected more perfectly and in +greater purity. + +722. From the foregoing and many other experiments, it results that +_variation in the size of the electrodes causes no variation in the +chemical action of a given quantity of electricity upon water_. + +723. The next point in regard to which the principle of constant +electro-chemical action was tested, was _variation of intensity_. In the +first place, the preceding experiments were repeated, using batteries of an +_equal_ number of plates, _strongly_ and _weakly_ charged; but the results +were alike. They were then repeated, using batteries sometimes containing +forty, and at other times only five pairs of plates; but the results were +still the same. _Variations therefore in the intensity_, caused by +difference in the strength of charge, or in the number of alternations +used, _produced no difference as to the equal action of large and small +electrodes_. + +724. Still these results did not prove that variation in the intensity of +the current was not accompanied by a corresponding variation in the +electro-chemical effects, since the actions at _all_ the surfaces might +have increased or diminished together. The deficiency in the evidence is, +however, completely supplied by the former experiments on different-sized +electrodes; for with variation in the size of these, a variation in the +intensity must have occurred. The intensity of an electric current +traversing conductors alike in their nature, quality, and length, is +probably as the quantity of electricity passing through a given sectional +area perpendicular to the current, divided by the time (360. _note_); and +therefore when large plates were contrasted with wires separated by an +equal length of the same decomposing conductor (714.), whilst one current +of electricity passed through both arrangements, that electricity must have +been in a very different state, as to _tension_, between the plates and +between the wires; yet the chemical results were the same. + +725. The difference in intensity, under the circumstances described, may be +easily shown practically, by arranging two decomposing apparatus as in fig. +67, where the same fluid is subjected to the decomposing power of the same +current of electricity, passing in the vessel A. between large platina +plates, and in the vessel B. between small wires. If a third decomposing +apparatus, such as that delineated fig. 66. (711.), be connected with the +wires at _ab_, fig. 67, it will serve sufficiently well, by the degree of +decomposition occurring in it, to indicate the relative state of the two +plates as to intensity; and if it then be applied in the same way, as a +test of the state of the wires at _a'b'_, it will, by the increase of +decomposition within, show how much greater the intensity is there than at +the former points. The connexions of P and N with the voltaic battery are +of course to be continued during the whole time. + +726. A third form of experiment, in which difference of intensity was +obtained, for the purpose of testing the principle of equal chemical +action, was to arrange three volta-electrometers, so that after the +electric current had passed through one, it should divide into two parts, +each of which should traverse one of the remaining instruments, and should +then reunite. The sum of the decomposition in the two latter vessels was +always equal to the decomposition in the former vessel. But the _intensity_ +of the divided current could not be the same as that it had in its original +state; and therefore _variation of intensity has no influence on the +results if the quantity of electricity remain the same_. The experiment, in +fact, resolves itself simply into an increase in the size of the electrodes +(725.). + +727. The _third point_, in respect to which the principle of equal +electro-chemical action on water was tested, was _variation of the strength +of the solution used_. In order to render the water a conductor, sulphuric +acid had been added to it (707.); and it did not seem unlikely that this +substance, with many others, might render the water more subject to +decomposition, the electricity remaining the same in quantity. But such did +not prove to be the case. Diluted sulphuric acid, of different strengths, +was introduced into different decomposing apparatus, and submitted +simultaneously to the action of the same electric current (714.). Slight +differences occurred, as before, sometimes in one direction, sometimes in +another; but the final result was, that _exactly the same quantity of water +was decomposed in all the solutions by the same quantity of electricity_, +though the sulphuric acid in some was seventy-fold what it was in others. +The strengths used were of specific gravity 1.495, and downwards. + +728. When an acid having a specific gravity of about 1.336 was employed, +the results were most uniform, and the oxygen and hydrogen (716.) most +constantly in the right proportion to each other. Such an acid gave more +gas than one much weaker acted upon by the same current, apparently because +it had less solvent power. If the acid were very strong, then a remarkable +disappearance of oxygen took place; thus, one made by mixing two measures +of strong oil of vitriol with one of water, gave forty-two volumes of +hydrogen, but only twelve of oxygen. The hydrogen was very nearly the same +with that evolved from acid of the specific gravity 1.232. I have not yet +had time to examine minutely the circumstances attending the disappearance +of the oxygen in this case, but imagine it is due to the formation of +oxywater, which Thenard has shown is favoured by the presence of acid. + +729. Although not necessary for the practical use of the instrument I am +describing, yet as connected with the important point of constant +chemical action upon water, I now investigated the effects produced by an +electro-electric current passing through aqueous solutions of acids, salts, +and compounds, exceedingly different from each other in their nature, and +found them to yield astonishingly uniform results. But many of them which +are connected with a secondary action will be more usefully described +hereafter (778.). + +730. When solutions of caustic potassa or soda, or sulphate of magnesia, or +sulphate of soda, were acted upon by the electric current, just as much +oxygen and hydrogen was evolved from them as from the diluted sulphuric +acid, with which they were compared. When a solution of ammonia, rendered a +better conductor by sulphate of ammonia (554.), or a solution of +subcarbonate of potassa was experimented with, the _hydrogen_ evolved was +in the same quantity as that set free from the diluted sulphuric acid with +which they were compared. Hence _changes in the nature of the solution do +not alter the constancy of electrolytic action upon water_. + +731. I have already said, respecting large and small electrodes, that +change of order caused no change in the general effect (715.). The same was +the case with different solutions, or with different intensities; and +however the circumstances of an experiment might be varied, the results +came forth exceedingly consistent, and proved that the electro-chemical +action was still the same. + +732. I consider the foregoing investigation as sufficient to prove the very +extraordinary and important principle with respect to WATER, _that when +subjected to the influence of the electric current, a quantity of it is +decomposed exactly proportionate to the quantity of electricity which has +passed_, notwithstanding the thousand variations in the conditions and +circumstances under which it may at the time be placed; and further, that +when the interference of certain secondary effects (742. &c.), together +with the solution or recombination of the gas and the evolution of air, are +guarded against, _the products of the decomposition may be collected with +such accuracy, as to afford a very excellent and valuable measurer of the +electricity concerned in their evolution_. + +733. The forms of instrument which I have given, figg. 64, 65, 66. (709. +710. 711.), are probably those which will be found most useful, as they +indicate the quantity of electricity by the largest volume of gases, and +cause the least obstruction to the passage of the current. The fluid which +my present experience leads me to prefer, is a solution of sulphuric acid +of specific gravity about 1.336, or from that to 1.25; but it is very +essential that there should be no organic substance, nor any vegetable +acid, nor other body, which, by being liable to the action of the oxygen or +hydrogen evolved at the electrodes (773. &c.), shall diminish their +quantity, or add other gases to them. + +734. In many cases when the instrument is used as a _comparative standard_, +or even as _a measurer_, it may be desirable to collect the hydrogen only, +as being less liable to absorption or disappearance in other ways than the +oxygen; whilst at the same time its volume is so large, as to render it a +good and sensible indicator. In such cases the first and second form of +apparatus have been used, figg. 62, 63. (707. 708.). The indications +obtained were very constant, the variations being much smaller than in +those forms of apparatus collecting both gases; and they can also be +procured when solutions are used in comparative experiments, which, +yielding no oxygen or only secondary results of its action, can give no +indications if the educts at both electrodes be collected. Such is the case +when solutions of ammonia, muriatic acid, chlorides, iodides, acetates or +other vegetable salts, &c., are employed. + +735. In a few cases, as where solutions of metallic salts liable to +reduction at the negative electrode are acted upon, the oxygen may be +advantageously used as the measuring substance. This is the case, for +instance, with sulphate of copper. + +736. There are therefore two general forms of the instrument which I submit +as a measurer of electricity; one, in which both the gases of the water +decomposed are collected (709. 710. 711.); and the other, in which a single +gas, as the hydrogen only, is used (707. 708.). When referred to as a +_comparative instrument_, (a use I shall now make of it very extensively,) +it will not often require particular precaution in the observation; but +when used as an _absolute measurer_, it will be needful that the barometric +pressure and the temperature be taken into account, and that the graduation +of the instruments should be to one scale; the hundredths and smaller +divisions of a cubical inch are quite fit for this purpose, and the +hundredth may be very conveniently taken as indicating a DEGREE of +electricity. + +737. It can scarcely be needful to point out further than has been done how +this instrument is to be used. It is to be introduced into the course of +the electric current, the action of which is to be exerted anywhere else, +and if 60 deg. or 70 deg. of electricity are to be measured out, either in one or +several portions, the current, whether strong or weak, is to be continued +until the gas in the tube occupies that number of divisions or hundredths +of a cubical inch. Or if a quantity competent to produce a certain effect +is to be measured, the effect is to be obtained, and then the indication +read off. In exact experiments it is necessary to correct the volume of gas +for changes in temperature and pressure, and especially for moisture[A]. +For the latter object the volta-electrometer (fig. 66.) is most accurate, +as its gas can be measured over water, whilst the others retain it over +acid or saline solutions. + + [A] For a simple table of correction for moisture, I may take the + liberty of referring to my Chemical Manipulation, edition of 1830, + p. 376. + +738. I have not hesitated to apply the term _degree_ (736.), in analogy +with the use made of it with respect to another most important imponderable +agent, namely, heat; and as the definite expansion of air, water, mercury, +&c., is there made use of to measure heat, so the equally definite +evolution of gases is here turned to a similar use for electricity. + +739. The instrument offers the only _actual measurer_ of voltaic +electricity which we at present possess. For without being at all affected +by variations in time or intensity, or alterations in the current itself, +of any kind, or from any cause, or even of intermissions of action, it +takes note with accuracy of the quantity of electricity which has passed +through it, and reveals that quantity by inspection; I have therefore named +it a VOLTA-ELECTROMETER. + +740. Another mode of measuring volta-electricity may be adopted with +advantage in many cases, dependent on the quantities of metals or other +substances evolved either as primary or as secondary results; but I refrain +from enlarging on this use of the products, until the principles on which +their constancy depends have been fully established (791. 848.); + +741. By the aid of this instrument I have been able to establish the +definite character of electro-chemical action in its most general sense; +and I am persuaded it will become of the utmost use in the extensions of +the science which these views afford. I do not pretend to have made its +detail perfect, but to have demonstrated the truth of the principle, and +the utility of the application[A]. + + [A] As early as the year 1811, Messrs. Gay-Lussac and Thenard employed + chemical decomposition as a measure of the electricity of the voltaic + pile. See _Recherches Physico-chymiques_, p. 12. The principles and + precautions by which it becomes an exact measure were of course not + then known.--_Dec. 1838._ + + +P vi. _On the primary or secondary character of the bodies evolved at the +Electrodes._ + +742. Before the _volta-electrometer_ could be employed in determining, as a +_general law_, the constancy of electro-decomposition, it became necessary +to examine a distinction, already recognised among scientific men, relative +to the products of that action, namely, their primary or secondary +character; and, if possible, by some general rule or principle, to decide +when they were of the one or the other kind. It will appear hereafter that +great mistakes inspecting electro-chemical action and its consequences have +arisen from confounding these two classes of results together. + +743. When a substance under decomposition yields at the electrodes those +bodies uncombined and unaltered which the electric current has separated, +then they may be considered as primary results, even though themselves +compounds. Thus the oxygen and hydrogen from water are primary results; and +so also are the acid and alkali (themselves compound bodies) evolved from +sulphate of soda. But when the substances separated by the current are +changed at the electrodes before their appearance, then they give rise to +secondary results, although in many cases the bodies evolved are +elementary. + +744. These secondary results occur in two ways, being sometimes due to the +mutual action of the evolved substance and the matter of the electrode, and +sometimes to its action upon the substances contained in the body itself +under decomposition. Thus, when carbon is made the positive electrode in +dilute sulphuric acid, carbonic oxide and carbonic acid occasionally appear +there instead of oxygen; for the latter, acting upon the matter of the +electrode, produces these secondary results. Or if the positive electrode, +in a solution of nitrate or acetate of lead, be platina, then peroxide of +lead appears there, equally a secondary result with the former, but now +depending upon an action of the oxygen on a substance in the solution. +Again, when ammonia is decomposed by platina electrodes, nitrogen appears +at the _anode_[A]; but though an _elementary_ body, it is a _secondary_ +result in this case, being derived from the chemical action of the oxygen +electrically evolved there, upon the ammonia in the surrounding solution +(554.). In the same manner when aqueous solutions of metallic salts are +decomposed by the current, the metals evolved at the _cathode_, though +elements, are _always_ secondary results, and not immediate consequences of +the decomposing power of the electric current. + + [A] Annales de Chimie, 1801, tom. li. p. 167. + +745. Many of these secondary results are extremely valuable; for instance, +all the interesting compounds which M. Becquerel has obtained by feeble +electric currents are of this nature; but they are essentially chemical, +and must, in the theory of electrolytic action, be carefully distinguished +from those which are directly due to the action of the electric current. + +746. The nature of the substances evolved will often lead to a correct +judgement of their primary or secondary character, but is not sufficient +alone to establish that point. Thus, nitrogen is said to be attracted +sometimes by the positive and sometimes by the negative electrode, +according to the bodies with which it may be combined (554. 555.), and it +is on such occasions evidently viewed as a primary result[A]; but I think I +shall show, that, when it appears at the positive electrode, or rather at +the _anode_, it is a secondary result (748.). Thus, also, Sir Humphry +Davy[B], and with him the great body of chemical philosophers, (including +myself,) have given the appearance of copper, lead, tin, silver, gold, &c., +at the negative electrode, when their aqueous solutions were acted upon by +the voltaic current, as proofs that the metals, as a class, were attracted +to that surface; thus assuming the metal, in each case, to be a primary +result. These, however, I expect to prove, are all secondary results; the +mere consequence of chemical action, and no proofs either of the attraction +or of the law announced respecting their places[C]. + + [A] Annales de Chimie, 1804, tom. li. p. 172. + + [B] Elements of Chemical Philosophy, pp. 144. 161. + + [C] It is remarkable that up to 1804 it was the received opinion that + the metals were reduced by the nascent hydrogen. At that date the + general opinion was reversed by Hisinger and Berzelius (Annales de + Chimie, 1804, tom. li. p. 174,), who stated that the metals were + evolved directly by the electricity: in which opinion it appears, from + that time, Davy coincided (Philosophical Transactions, 1826, p. 388). + +747. But when we take to our assistance the law of _constant +electro-chemical action_ already proved with regard to water (732.), and +which I hope to extend satisfactorily to all bodies (821.), and consider +the _quantities_ as well as the _nature_ of the substances set free, a +generally accurate judgement of the primary or secondary character of the +results may be formed: and this important point, so essential to the theory +of electrolyzation, since it decides what are the particles directly under +the influence of the current, (distinguishing them from such as are not +affected,) and what are the results to be expected, may be established with +such degree of certainty as to remove innumerable ambiguities and doubtful +considerations from this branch of the science. + +748. Let us apply these principles to the case of ammonia, and the supposed +determination of nitrogen to one or the other _electrode_ (554. 555,). A +pure strong solution of ammonia is as bad a conductor, and therefore as +little liable to electrolyzation, as pure water; but when sulphate of +ammonia is dissolved in it, the whole becomes a conductor; nitrogen +_almost_ and occasionally _quite_ pure is evolved at the _anode_, and +hydrogen at the _cathode_; the ratio of the volume of the former to that of +the latter varying, but being as 1 to about 3 or 4. This result would seem +at first to imply that the electric current had decomposed ammonia, and +that the nitrogen had been determined towards the positive electrode. But +when the electricity used was measured out by the volta-electrometer (707. +736.), it was found that the hydrogen obtained was exactly in the +proportion which would have been supplied by decomposed water, whilst the +nitrogen had no certain or constant relation whatever. When, upon +multiplying experiments, it was found that, by using a stronger or weaker +solution, or a more or less powerful battery, the gas evolved at the +_anode_ was a mixture of oxygen and nitrogen, varying both in proportion +and absolute quantity, whilst the hydrogen at the _cathode_ remained +constant, no doubt could be entertained that the nitrogen at the _anode_ +was a secondary result, depending upon the chemical action of the nascent +oxygen, determined to that surface by the electric current, upon the +ammonia in solution. It was the water, therefore, which was electrolyzed, +not the ammonia. Further, the experiment gives no real indication of the +tendency of the element nitrogen to either one electrode or the other; nor +do I know of any experiment with nitric acid, or other compounds of +nitrogen, which shows the tendency of this element, under the influence of +the electric current, to pass in either direction along its course. + +749. As another illustration of secondary results, the effects on a +solution of acetate of potassa, may be quoted. When a very strong solution +was used, more gas was evolved at the _anode_ than at the _cathode_, in the +proportion of 4 to 3 nearly: that from the _anode_ was a mixture of +carbonic oxide and carbonic acid; that from the _cathode_ pure hydrogen. +When a much weaker solution was used, less gas was evolved at the _anode_ +than at the _cathode_; and it now contained carburetted hydrogen, as well +as carbonic oxide and carbonic acid. This result of carburetted hydrogen at +the positive electrode has a very anomalous appearance, if considered as an +immediate consequence of the decomposing power of the current. It, however, +as well as the carbonic oxide and acid, is only a _secondary result_; for +it is the water alone which suffers electro-decomposition, and it is the +oxygen eliminated at the _anode_ which, reacting on the acetic acid, in the +midst of which it is evolved, produces those substances that finally appear +there. This is fully proved by experiments with the volta-electrometer +(707.); for then the hydrogen evolved from the acetate at the _cathode_ is +always found to be definite, being exactly proportionate to the electricity +which has passed through the solution, and, in quantity, the same as the +hydrogen evolved in the volta-electrometer itself. The appearance of the +carbon in combination with the hydrogen at the positive electrode, and its +non-appearance at the negative electrode, are in curious contrast with the +results which might have been expected from the law usually accepted +respecting the final places of the elements. + +750. If the salt in solution be an acetate of lead, then the results at +both electrodes are secondary, and cannot be used to estimate or express +the amount of electro-chemical action, except by a circuitous process +(843.). In place of oxygen or even the gases already described (749.), +peroxide of lead now appears at the positive, and lead itself at the +negative electrode. When other metallic solutions are used, containing, for +instance, peroxides, as that of copper, combined with this or any other +decomposable acid, still more complicated results will be obtained; which, +viewed as direct results of the electro-chemical action, will, in their +proportions, present nothing but confusion, but will appear perfectly +harmonious and simple if they be considered as secondary results, and will +accord in their proportions with the oxygen and hydrogen evolved from water +by the action of a definite quantity of electricity. + +751. I have experimented upon many bodies, with a view to determine whether +the results were primary or secondary. I have been surprised to find how +many of them, in ordinary cases, are of the latter class, and how +frequently water is the only body electrolyzed in instances where other +substances have been supposed to give way. Some of these results I will +give in as few words as possible. + +752. _Nitric acid._--When very strong, it conducted well, and yielded +oxygen at the positive electrode. No gas appeared at the negative +electrode; but nitrous acid, and apparently nitric oxide, were formed +there, which, dissolving, rendered the acid yellow or red, and at last even +effervescent, from the spontaneous separation of nitric oxide. Upon +diluting the acid with its bulk or more of water, gas appeared at the +negative electrode. Its quantity could be varied by variations, either in +the strength of the acid or of the voltaic current: for that acid from +which no gas separated at the _cathode_, with a weak voltaic battery, did +evolve gas there with a stronger; and that battery which evolved no gas +there with a strong acid, did cause its evolution with an acid more dilute. +The gas at the _anode_ was always oxygen; that at the _cathode_ hydrogen. +When the quantity of products was examined by the volta-electrometer +(707.), the oxygen, whether from strong or weak acid, proved to be in the +same proportion as from water. When the acid was diluted to specific +gravity 1.24, or less, the hydrogen also proved to be the same in quantity +as from water. Hence I conclude that the nitric acid does not undergo +electrolyzation, but the water only; that the oxygen at the _anode_ is +always a primary result, but that the products at the _cathode_ are often +secondary, and due to the reaction of the hydrogen upon the nitric acid. + +753. _Nitre._--A solution of this salt yields very variable results, +according as one or other form of tube is used, or as the electrodes are +large or small. Sometimes the whole of the hydrogen of the water decomposed +may be obtained at the negative electrode; at other times, only a part of +it, because of the ready formation of secondary results. The solution is a +very excellent conductor of electricity. + +754. _Nitrate of ammonia_, in aqueous solution, gives rise to secondary +results very varied and uncertain in their proportions. + +755. _Sulphurous acid._--Pure liquid sulphurous acid does not conduct nor +suffer decomposition by the voltaic current[A], but, when dissolved in +water, the solution acquires conducting power, and is decomposed, yielding +oxygen at the _anode_, and hydrogen and sulphur at the _cathode_. + + [A] See also De la Rive, Bibliotheque Universelle, tom. xl. p. 205; or + Quarterly Journal of Science, vol. xxvii. p, 407. + +756. A solution containing sulphuric acid in addition to the sulphurous +acid, was a better conductor. It gave very little gas at either electrode: +that at the _anode_ was oxygen, that at the _cathode_ pure hydrogen. From +the _cathode_ also rose a white turbid stream, consisting of diffused +sulphur, which soon rendered the whole solution milky. The volumes of gases +were in no regular proportion to the quantities evolved from water in the +voltameter. I conclude that the sulphurous acid was not at all affected by +the electric current in any of these cases, and that the water present was +the only body electro-chemically decomposed; that, at the _anode_, the +oxygen from the water converted the sulphurous acid into sulphuric acid, +and, at the _cathode_, the hydrogen electrically evolved decomposed the +sulphurous acid, combining with its oxygen, and setting its sulphur free. I +conclude that the sulphur at the negative electrode was only a secondary +result; and, in fact, no part of it was found combined with the small +portion of hydrogen which escaped when weak solutions of sulphurous acid +were used. + +757. _Sulphuric acid._--I have already given my reasons for concluding that +sulphuric acid is not electrolyzable, i.e. not decomposable directly by the +electric current, but occasionally suffering by a secondary action at the +_cathode_ from the hydrogen evolved there (681.). In the year 1800, Davy +considered the sulphur from sulphuric acid as the result of the action of +the nascent hydrogen[A]. In 1804, Hisinger and Berzelius stated that it was +the direct result of the action of the voltaic pile[B], an opinion which +from that time Davy seems to have adopted, and which has since been +commonly received by all. The change of my own opinion requires that I +should correct what I have already said of the decomposition of sulphuric +acid in a former series of these Researches (552.): I do not now think that +the appearance of the sulphur at the negative electrode is an immediate +consequence of electrolytic action. + + [A] Nicholson's Quarterly Journal, vol. iv. pp. 280, 281. + + [B] Annales de Chimie, 1804, tom. li. p. 173. + +758. _Muriatic acid._--A strong solution gave hydrogen at the negative +electrode, and chlorine only at the positive electrode; of the latter, a +part acted on the platina and a part was dissolved. A minute bubble of gas +remained; it was not oxygen, but probably air previously held in solution. + +759. It was an important matter to determine whether the chlorine was a +primary result, or only a secondary product, due to the action of the +oxygen evolved from water at the _anode_ upon the muriatic acid; i.e. +whether the muriatic acid was electrolyzable, and if so, whether the +decomposition was _definite_. + +760. The muriatic acid was gradually diluted. One part with six of water +gave only chlorine at the _anode_. One part with eight of water gave only +chlorine; with nine of water, a little oxygen appeared with the chlorine; +but the occurrence or non-occurrence of oxygen at these strengths depended, +in part, on the strength of the voltaic battery used. With fifteen parts of +water, a little oxygen, with much chlorine, was evolved at the _anode_. As +the solution was now becoming a bad conductor of electricity, sulphuric +acid was added to it: this caused more ready decomposition, but did not +sensibly alter the proportion of chlorine and oxygen. + +761. The muriatic acid was now diluted with 100 times its volume of dilute +sulphuric acid. It still gave a large proportion of chlorine at the +_anode_, mingled with oxygen; and the result was the same, whether a +voltaic battery of 40 pairs of plates or one containing only 5 pairs were +used. With acid of this strength, the oxygen evolved at the _anode_ was to +the hydrogen at the _cathode_, in volume, as 17 is to 64; and therefore the +chlorine would have been 30 volumes, had it not been dissolved by the +fluid. + +762. Next with respect to the quantity of elements evolved. On using the +volta-electrometer, it was found that, whether the strongest or the weakest +muriatic acid were used, whether chlorine alone or chlorine mingled with +oxygen appeared at the _anode_, still the hydrogen evolved at the _cathode_ +was a constant quantity, i.e. exactly the same as the hydrogen which the +_same quantity of electricity_ could evolve from water. + +763. This constancy does not decide whether the muriatic acid is +electrolyzed or not, although it proves that if so, it must be in definite +proportions to the quantity of electricity used. Other considerations may, +however, be allowed to decide the point. The analogy between chlorine and +oxygen, in their relations to hydrogen, is so strong, as to lead almost to +the certainty, that, when combined with that element, they would perform +similar parts in the process of electro-decomposition. They both unite with +it in single proportional or equivalent quantities; and the number of +proportionals appearing to have an intimate and important relation to the +decomposability of a body (697.), those in muriatic acid, as well as in +water, are the most favourable, or those perhaps even necessary, to +decomposition. In other binary compounds of chlorine also, where nothing +equivocal depending on the simultaneous presence of it and oxygen is +involved, the chlorine is directly eliminated at the _anode_ by the +electric current. Such is the case with the chloride of lead (395.), which +may be justly compared with protoxide of lead (402.), and stands in the +same relation to it as muriatic acid to water. The chlorides of potassium, +sodium, barium, &c., are in the same relation to the protoxides of the same +metals and present the same results under the influence of the electric +current (402.). + +764. From all the experiments, combined with these considerations, I +conclude that muriatic acid is decomposed by the direct influence of the +electric current, and that the quantities evolved are, and therefore the +chemical action is, _definite for a definite quantity of electricity_. For +though I have not collected and measured the chlorine, in its separate +state, at the _anode_, there can exist no doubt as to its being +proportional to the hydrogen at the _cathode_; and the results are +therefore sufficient to establish the general law of _constant +electro-chemical action_ in the case of muriatic acid. + +765. In the dilute acid (761.), I conclude that a part of the water is +electro-chemically decomposed, giving origin to the oxygen, which appears +mingled with the chlorine at the _anode_. The oxygen _may_ be viewed as a +secondary result; but I incline to believe that it is not so; for, if it +were, it might be expected in largest proportion from the stronger acid, +whereas the reverse is the fact. This consideration, with others, also +leads me to conclude that muriatic acid is more easily decomposed by the +electric current than water; since, even when diluted with eight or nine +times its quantity of the latter fluid, it alone gives way, the water +remaining unaffected. + +766. _Chlorides._--On using solutions of chlorides in water,--for instance, +the chlorides of sodium or calcium,--there was evolution of chlorine only +at the positive electrode, and of hydrogen, with the oxide of the base, as +soda or lime, at the negative electrode. The process of decomposition may +be viewed as proceeding in two or three ways, all terminating in the same +results. Perhaps the simplest is to consider the chloride as the substance +electrolyzed, its chlorine being determined to and evolved at the _anode_, +and its metal passing to the _cathode_, where, finding no more chlorine, it +acts upon the water, producing hydrogen and an oxide as secondary results. +As the discussion would detain me from more important matter, and is not of +immediate consequence, I shall defer it for the present. It is, however, of +_great consequence_ to state, that, on using the volta-electrometer, the +hydrogen in both cases was definite; and if the results do not prove the +definite decomposition of chlorides, (which shall be proved +elsewhere,--789. 794. 814.,) they are not in the slightest degree opposed +to such a conclusion, and do support the _general law_. + +767. _Hydriodic acid._--A solution of hydriodic acid was affected exactly +in the same manner as muriatic acid. When strong, hydrogen was evolved at +the negative electrode, in definite proportion to the quantity of +electricity which had passed, i.e. in the same proportion as was evolved by +the same current from water; and iodine without any oxygen was evolved at +the positive electrode. But when diluted, small quantities of oxygen +appeared with the iodine at the _anode_, the proportion of hydrogen at the +_cathode_ remaining undisturbed. + +768. I believe the decomposition of the hydriodic acid in this case to be +direct, for the reasons already given respecting muriatic acid (763. 764.). + +769. _Iodides._--A solution of iodide of potassium being subjected to the +voltaic current, iodine appeared at the positive electrode (without any +oxygen), and hydrogen with free alkali at the negative electrode. The same +observations as to the mode of decomposition are applicable here as were +made in relation to the chlorides when in solution (766.). + +770. _Hydro-fluoric acid and fluorides._--Solution of hydrofluoric acid did +not appear to be decomposed under the influence of the electric current: it +was the water which gave way apparently. The fused fluorides were +electrolysed (417.); but having during these actions obtained _fluorine_ in +the separate state, I think it better to refer to a future series of these +Researches, in which I purpose giving a fuller account of the results than +would be consistent with propriety here[A]. + + [A] I have not obtained fluorine: my expectations, amounting to + conviction, passed away one by one when subjected to rigorous + examination; some very singular results were obtained; and to one of + these I refer at 1340.--_Dec. 1838._ + +771. _Hydro-cyanic acid_ in solution conducts very badly. The definite +proportion of hydrogen (equal to that from water) was set free at the +_cathode_, whilst at the _anode_ a small quantity of oxygen was evolved and +apparently a solution of cyanogen formed. The action altogether +corresponded with that on a dilute muriatic or hydriodic acid. When the +hydrocyanic acid was made a better conductor by sulphuric acid, the same +results occurred. + +_Cyanides._--With a solution of the cyanide of potassium, the result was +precisely the same as with a chloride or iodide. No oxygen was evolved at +the positive electrode, but a brown solution formed there. For the reasons +given when speaking of the chlorides (766.), and because a fused cyanide of +potassium evolves cyanogen at the positive electrode[A], I incline to +believe that the cyanide in solution is _directly_ decomposed. + + [A] It is a very remarkable thing to see carbon and nitrogen in this + case determined powerfully towards the positive surface of the voltaic + battery; but it is perfectly in harmony with the theory of + electro-chemical decomposition which I have advanced. + +772. _Ferro-cyanic acid_ and the _ferro-cyanides_, as also _sulpho-cyanic +acid_ and the _sulpho-cyanides_, presented results corresponding with those +just described (771.). + +773. _Acetic acid._--Glacial acetic acid, when fused (405.), is not +decomposed by, nor does it conduct, electricity. On adding a little water +to it, still there were no signs of action; on adding more water, it acted +slowly and about as pure water would do. Dilute sulphuric acid was added to +it in order to make it a better conductor; then the definite proportion of +hydrogen was evolved at the _cathode_, and a mixture of oxygen in very +deficient quantity, with carbonic acid, and a little carbonic oxide, at the +_anode_. Hence it appears that acetic acid is not electrolyzable, but that +a portion of it is decomposed by the oxygen evolved at the _anode_, +producing secondary results, varying with the strength of the acid, the +intensity of the current, and other circumstances. + +774. _Acetates._--One of these has been referred to already, as affording +only secondary results relative to the acetic acid (749.). With many of the +metallic acetates the results at both electrodes are secondary (746. 750.). + +Acetate of soda fused and anhydrous is directly decomposed, being, as I +believe, a true electrolyte, and evolving soda and acetic acid at the +_cathode_ and _anode_. These however have no sensible duration, but are +immediately resolved into other substances; charcoal, sodiuretted hydrogen, +&c., being set free at the former, and, as far as I could judge under the +circumstances, acetic acid mingled with carbonic oxide, carbonic acid, &c. +at the latter. + +775. _Tartaric acid._--Pure solution of tartaric acid is almost as bad a +conductor as pure water. On adding sulphuric acid, it conducted well, the +results at the positive electrode being primary or secondary in different +proportions, according to variations in the strength of the acid and the +power of the electric current (752.). Alkaline tartrates gave a large +proportion of secondary results at the positive electrode. The hydrogen at +the negative electrode remained constant unless certain triple metallic +salts were used. + +776. Solutions, of salts containing other vegetable acids, as the +benzoates; of sugar, gum, &c., dissolved in dilute sulphuric acid; of +resin, albumen, &c., dissolved in alkalies, were in turn submitted to the +electrolytic power of the voltaic current. In all these cases, secondary +results to a greater or smaller extent were produced at the positive +electrode. + +777. In concluding this division of these Researches, it cannot but occur +to the mind that the final result of the action of the electric current +upon substances, placed between the electrodes, instead of being simple may +be very complicated. There are two modes by which these substances may be +decomposed, either by the direct force of the electric current, or by the +action of bodies which that current may evolve. There are also two modes by +which new compounds may be formed, i.e. by combination of the evolving +substances whilst in their nascent state (658.), directly with the matter +of the electrode; or else their combination with those bodies, which being +contained in, or associated with, the body suffering decomposition, are +necessarily present at the _anode_ and _cathode_. The complexity is +rendered still greater by the circumstance that two or more of these +actions may occur simultaneously, and also in variable proportions to each +other. But it may in a great measure be resolved by attention to the +principles already laid down (747.). + +778. When _aqueous_ solutions of bodies are used, secondary results are +exceedingly frequent. Even when the water is not present in large quantity, +but is merely that of combination, still secondary results often ensue: for +instance, it is very possible that in Sir Humphry Davy's decomposition of +the hydrates of potassa and soda, a part of the potassium produced was the +result of a secondary action. Hence, also, a frequent cause for the +disappearance of the oxygen and hydrogen which would otherwise be evolved: +and when hydrogen does _not_ appear at the _cathode_ in an _aqueous +solution_, it perhaps always indicates that a secondary action has taken +place there. No exception to this rule has as yet occurred to my +observation. + +779. Secondary actions are _not confined to aqueous solutions_, or cases +where water is present. For instance, various chlorides acted upon, when +fused (402.), by platina electrodes, have the chlorine determined +electrically to the _anode_. In many cases, as with the chlorides of lead, +potassium, barium, &c., the chlorine acts on the platina and forms a +compound with it, which dissolves; but when protochloride of tin is used, +the chlorine at the _anode_ does not act upon the platina, but upon the +chloride already there, forming a perchloride which rises in vapour (790. +804.). These are, therefore, instances of secondary actions of both kinds, +produced in bodies containing no water. + +780. The production of boron from fused borax (402. 417.) is also a case of +secondary action; for boracic acid is not decomposable by electricity +(408.), and it was the sodium evolved at the _cathode_ which, re-acting on +the boracic acid around it, took oxygen from it and set boron free in the +experiments formerly described. + +781. Secondary actions have already, in the hands of M. Becquerel, produced +many interesting results in the formation of compounds; some of them new, +others imitations of those occurring naturally[A]. It is probable they may +prove equally interesting in an opposite direction, i.e. as affording cases +of analytic decomposition. Much information regarding the composition, and +perhaps even the arrangement, of the particles of such bodies as the +vegetable acids and alkalies, and organic compounds generally, will +probably be obtained by submitting them to the action of nascent oxygen, +hydrogen, chlorine, &c. at the electrodes; and the action seems the more +promising, because of the thorough command which we possess over attendant +circumstances, such as the strength of the current, the size of the +electrodes, the nature of the decomposing conductor, its strength, &c., all +of which may be expected to have their corresponding influence upon the +final result. + +782. It is to me a great satisfaction that the extreme variety of secondary +results has presented nothing opposed to the doctrine of a constant and +definite electro-chemical action, to the particular consideration of which +I shall now proceed. + + +P vii. _On the definite nature and extent of Electro-chemical +Decomposition._ + +783. In the third series of these Researches, after proving the identity of +electricities derived from different sources, and showing, by actual +measurement, the extraordinary quantity of electricity evolved by a very +feeble voltaic arrangement (371. 376.), I announced a law, derived from +experiment, which seemed to me of the utmost importance to the science of +electricity in general, and that branch of it denominated electro-chemistry +in particular. The law was expressed thus: _The chemical power of a current +of electricity is in direct proportion to the absolute quantity of +electricity which passes_ (377.). + + [A] Annales de Chimie, tom, xxxv. p. 113. + +784. In the further progress of the successive investigations, I have had +frequent occasion to refer to the same law, sometimes in circumstances +offering powerful corroboration of its truth (456. 504. 505.); and the +present series already supplies numerous new cases in which it holds good +(704. 722. 726. 732.). It is now my object to consider this great principle +more closely, and to develope some of the consequences to which it leads. +That the evidence for it may be the more distinct and applicable, I shall +quote cases of decomposition subject to as few interferences from secondary +results as possible, effected upon bodies very simple, yet very definite in +their nature. + +785. In the first place, I consider the law as so fully established with +respect to the decomposition of _water_, and under so many circumstances +which might be supposed, if anything could, to exert an influence over it, +that I may be excused entering into further detail respecting that +substance, or even summing up the results here (732.). I refer, therefore, +to the whole of the subdivision of this series of Researches which contains +the account of the _volta-electrometer_ (704. &c.). + +786. In the next place, I also consider the law as established with respect +to _muriatic acid_ by the experiments and reasoning already advanced, when +speaking of that substance, in the subdivision respecting primary and +secondary results (758. &c.). + +787. I consider the law as established also with regard to _hydriodic acid_ +by the experiments and considerations already advanced in the preceding +division of this series of Researches (767. 768.). + +788. Without speaking with the same confidence, yet from the experiments +described, and many others not described, relating to hydro-fluoric, +hydro-cyanic, ferro-cyanic, and sulpho-cyanic acids (770. 771. 772.), and +from the close analogy which holds between these bodies and the hydracids +of chlorine, iodine, bromine, &c., I consider these also as coming under +subjection to the law, and assisting to prove its truth. + +789. In the preceding cases, except the first, the water is believed to be +inactive; but to avoid any ambiguity arising from its presence, I sought +for substances from which it should be absent altogether; and, taking +advantage of the law of conduction already developed (380. &c.), I soon +found abundance, amongst which _protochloride of tin_ was first subjected +to decomposition in the following manner. A piece of platina wire had one +extremity coiled up into a small knob, and, having been carefully weighed, +was sealed hermetically into a piece of bottle-glass tube, so that the knob +should be at the bottom of the tube within (fig. 68.). The tube was +suspended by a piece of platina wire, so that the heat of a spirit-lamp +could be applied to it. Recently fused protochloride of tin was introduced +in sufficient quantity to occupy, when melted, about one-half of the tube; +the wire of the tube was connected with a volta-electrometer (711.), which +was itself connected with the negative end of a voltaic battery; and a +platina wire connected with the positive end of the same battery was dipped +into the fused chloride in the tube; being however so bent, that it could +not by any shake of the hand or apparatus touch the negative electrode at +the bottom of the vessel. The whole arrangement is delineated in fig. 69. + +790. Under these circumstances the chloride of tin was decomposed: the +chlorine evolved at the positive electrode formed bichloride of tin (779.), +which passed away in fumes, and the tin evolved at the negative electrode +combined with the platina, forming an alloy, fusible at the temperature to +which the tube was subjected, and therefore never occasioning metallic +communication through the decomposing chloride. When the experiment had +been continued so long as to yield a reasonable quantity of gas in the +volta-electrometer, the battery connexion was broken, the positive +electrode removed, and the tube and remaining chloride allowed to cool. +When cold, the tube was broken open, the rest of the chloride and the glass +being easily separable from the platina wire and its button of alloy. The +latter when washed was then reweighed, and the increase gave the weight of +the tin reduced. + +791. I will give the particular results of one experiment, in illustration +of the mode adopted in this and others, the results of which I shall have +occasion to quote. The negative electrode weighed at first 20 grains; after +the experiment, it, with its button of alloy, weighed 23.2 grains. The tin +evolved by the electric current at the _cathode_: weighed therefore 3.2 +grains. The quantity of oxygen and hydrogen collected in the +volta-electrometer = 3.85 cubic inches. As 100 cubic inches of oxygen and +hydrogen, in the proportions to form water, may be considered as weighing +12.92 grains, the 3.85 cubic inches would weigh 0.49742 of a grain; that +being, therefore, the weight of water decomposed by the same electric +current as was able to decompose such weight of protochloride of tin as +could yield 3.2 grains of metal. Now 0.49742 : 3.2 :: 9 the equivalent of +water is to 57.9, which should therefore be the equivalent of tin, if the +experiment had been made without error, and if the electro-chemical +decomposition _is in this case also definite_. In some chemical works 58 is +given as the chemical equivalent of tin, in others 57.9. Both are so near +to the result of the experiment, and the experiment itself is so subject to +slight causes of variation (as from the absorption of gas in the +volta-electrometer (716.), &c.), that the numbers leave little doubt of the +applicability of the _law of definite action_ in this and all similar cases +of electro-decomposition. + +792. It is not often I have obtained an accordance in numbers so near as +that I have just quoted. Four experiments were made on the protochloride of +tin, the quantities of gas evolved in the volta-electrometer being from +2.05 to 10.29 cubic inches. The average of the four experiments gave 58.53 +as the electro-chemical equivalent for tin. + +793. The chloride remaining after the experiment was pure protochloride of +tin; and no one can doubt for a moment that the equivalent of chlorine had +been evolved at the _anode_, and, having formed bichloride of tin as a +secondary result, had passed away. + +794. _Chloride of lead_ was experimented upon in a manner exactly similar, +except that a change was made in the nature of the positive electrode; for +as the chlorine evolved at the _anode_ forms no perchloride of lead, but +acts directly upon the platina, it produces, if that metal be used, a +solution of chloride of platina in the chloride of lead; in consequence of +which a portion of platina can pass to the _cathode_, and would then +produce a vitiated result. I therefore sought for, and found in plumbago, +another substance, which could be used safely as the positive electrode in +such bodies as chlorides, iodides, &c. + +The chlorine or iodine does not act upon it, but is evolved in the free +state; and the plumbago has no re-action, under the circumstances, upon the +fused chloride or iodide in which it is plunged. Even if a few particles of +plumbago should separate by the heat or the mechanical action of the +evolved gas, they can do no harm in the chloride. + +795. The mean of three experiments gave the number of 100.85 as the +equivalent for lead. The chemical equivalent is 103.5. The deficiency in my +experiments I attribute to the solution of part of the gas (716.) in the +volta-electrometer; but the results leave no doubt on my mind that both the +lead and the chlorine are, in this case, evolved in _definite quantities_ +by the action of a given quantity of electricity (814. &c.). + +796. _Chloride of antimony._--It was in endeavouring to obtain the +electro-chemical equivalent of antimony from the chloride, that I found +reasons for the statement I have made respecting the presence of water in +it in an earlier part of these Researches (690. 693. &c.). + +797. I endeavoured to experiment upon the _oxide of lead_ obtained by +fusion and ignition of the nitrate in a platina crucible, but found great +difficulty, from the high temperature required for perfect fusion, and the +powerful fluxing qualities of the substance. Green-glass tubes repeatedly +failed. I at last fused the oxide in a small porcelain crucible, heated +fully in a charcoal fire; and, as it is was essential that the evolution of +the lead at the _cathode_ should take place beneath the surface, the +negative electrode was guarded by a green-glass tube, fused around it in +such a _manner as to expose only the knob of platina_ at the lower end +(fig. 70.), so that it could be plunged beneath the surface, and thus +exclude contact of air or oxygen with the lead reduced there. A platina +wire was employed for the positive electrode, that metal not being subject +to any action from the oxygen evolved against it. The arrangement is given +in fig. 71. + +798. In an experiment of this kind the equivalent for the lead came out +93.17, which is very much too small. This, I believe, was because of the +small interval between the positive and negative electrodes in the oxide of +lead; so that it was not unlikely that some of the froth and bubbles formed +by the oxygen at the _anode_ should occasionally even touch the lead +reduced at the _cathode_, and re-oxidize it. When I endeavoured to correct +this by having more litharge, the greater heat required to keep it all +fluid caused a quicker action on the crucible, which was soon eaten +through, and the experiment stopped. + +799. In one experiment of this kind I used borate of lead (408. 673.). It +evolves lead, under the influence of the electric current, at the _anode_, +and oxygen at the _cathode_; and as the boracic acid is not either directly +(408.) or incidentally decomposed during the operation, I expected a result +dependent on the oxide of lead. The borate is not so violent a flux as the +oxide, but it requires a higher temperature to make it quite liquid; and if +not very hot, the bubbles of oxygen cling to the positive electrode, and +retard the transfer of electricity. The number for lead came out 101.29, +which is so near to 103.5 as to show that the action of the current had +been definite. + +800. _Oxide of bismuth._--I found this substance required too high a +temperature, and acted too powerfully as a flux, to allow of any experiment +being made on it, without the application of more time and care than I +could give at present. + +801. The ordinary _protoxide of antimony_, which consists of one +proportional of metal and one and a half of oxygen, was subjected to the +action of the electric current in a green-glass tube (789.), surrounded by +a jacket of platina foil, and heated in a charcoal fire. The decomposition +began and proceeded very well at first, apparently indicating, according to +the general law (679. 697.), that this substance was one containing such +elements and in such proportions as made it amenable to the power of the +electric current. This effect I have already given reasons for supposing +may be due to the presence of a true protoxide, consisting of single +proportionals (696. 693.). The action soon diminished, and finally ceased, +because of the formation of a higher oxide of the metal at the positive +electrode. This compound, which was probably the peroxide, being infusible +and insoluble in the protoxide, formed a crystalline crust around the +positive electrode; and thus insulating it, prevented the transmission of +the electricity. Whether, if it had been fusible and still immiscible, it +would have decomposed, is doubtful, because of its departure from the +required composition (697.). It was a very natural secondary product at the +positive electrode (779.). On opening the tube it was found that a little +antimony had been separated at the negative electrode; but the quantity was +too small to allow of any quantitative result being obtained[A]. + + [A] This paragraph is subject to the corrective note now appended to + paragraph 696.--_Dec. 1838._ + +802. _Iodide of lead._--This substance can be experimented with in tubes +heated by a spirit-lamp (789.); but I obtained no good results from it, +whether I used positive electrodes of platina or plumbago. In two +experiments the numbers for the lead came out only 75.46 and 73.45, instead +of 103.5. This I attribute to the formation of a periodide at the positive +electrode, which, dissolving in the mass of liquid iodide, came in contact +with the lead evolved at the negative electrode, and dissolved part of it, +becoming itself again protiodide. Such a periodide does exist; and it is +very rarely that the iodide of lead formed by precipitation, and +well-washed, can be fused without evolving much iodine, from the presence +of this percompound; nor does crystallization from its hot aqueous solution +free it from this substance. Even when a little of the protiodide and +iodine are merely rubbed together in a mortar, a portion of the periodide +is formed. And though it is decomposed by being fused and heated to dull +redness for a few minutes, and the whole reduced to protiodide, yet that is +not at all opposed to the possibility, that a little of that which is +formed in great excess of iodine at the _anode_, should be carried by the +rapid currents in the liquid into contact with the _cathode_. + +803. This view of the result was strengthened by a third experiment, where +the space between the electrodes was increased to one third of an inch; for +now the interfering effects were much diminished, and the number of the +lead came out 89.04; and it was fully confirmed by the results obtained in +the cases of _transfer_ to be immediately described (818.). + +The experiments on iodide of lead therefore offer no exception to the +_general law_ under consideration, but on the contrary may, from general +considerations, be admitted as included in it. + +804. _Protiodide of tin._--This substance, when fused (402.), conducts and +is decomposed by the electric current, tin is evolved at the _anode_, and +periodide of tin as a secondary result (779. 790.) at the _cathode_. The +temperature required for its fusion is too high to allow of the production +of any results fit for weighing. + +805. _Iodide of potassium_ was subjected to electrolytic action in a tube, +like that in fig. 68. (789.). The negative electrode was a globule of lead, +and I hoped in this way to retain the potassium, and obtain results that +could be weighed and compared with the volta-electrometer indication; but +the difficulties dependent upon the high temperature required, the action +upon the glass, the fusibility of the platina induced by the presence of +the lead, and other circumstances, prevented me from procuring such +results. The iodide was decomposed with the evolution of iodine at the +_anode_, and of potassium at the _cathode_, as in former cases. + +806. In some of these experiments several substances were placed in +succession, and decomposed simultaneously by the same electric current: +thus, protochloride of tin, chloride of lead, and water, were thus acted on +at once. It is needless to say that the results were comparable, the tin, +lead, chlorine, oxygen, and hydrogen evolved being _definite in quantity_ +and electro-chemical equivalents to each other. + + * * * * * + +807. Let us turn to another kind of proof of the _definite chemical action +of electricity_. If any circumstances could be supposed to exert an +influence over the quantity of the matters evolved during electrolytic +action, one would expect them to be present when electrodes of different +substances, and possessing very different chemical affinities for such +matters, were used. Platina has no power in dilute sulphuric acid of +combining with the oxygen at the _anode_, though the latter be evolved in +the nascent state against it. Copper, on the other hand, immediately unites +with the oxygen, as the electric current sets it free from the hydrogen; +and zinc is not only able to combine with it, but can, without any help +from the electricity, abstract it directly from the water, at the same time +setting torrents of hydrogen free. Yet in cases where these three +substances were used as the positive electrodes in three similar portions +of the same dilute sulphuric acid, specific gravity 1.336, precisely the +same quantity of water was decomposed by the electric current, and +precisely the same quantity of hydrogen set free at the _cathodes_ of the +three solutions. + +808. The experiment was made thus. Portions of the dilute sulphuric acid +were put into three basins. Three volta-electrometer tubes, of the form +figg. 60. 62. were filled with the same acid, and one inverted in each +basin (707.). A zinc plate, connected with the positive end of a voltaic +battery, was dipped into the first basin, forming the positive electrode +there, the hydrogen, which was abundantly evolved from it by the direct +action of the acid, being allowed to escape. A copper plate, which dipped +into the acid of the second basin, was connected with the negative +electrode of the _first_ basin; and a platina plate, which dipped into the +acid of the third basin, was connected with the negative electrode of the +_second_ basin. The negative electrode of the third basin was connected +with a volta-electrometer (711.), and that with the negative end of the +voltaic battery. + +809. Immediately that the circuit was complete, the _electro-chemical +action_ commenced in all the vessels. The hydrogen still rose in, +apparently, undiminished quantities from the positive zinc electrode in the +first basin. No oxygen was evolved at the positive copper electrode in the +second basin, but a sulphate of copper was formed there; whilst in the +third basin the positive platina electrode evolved pure oxygen gas, and was +itself unaffected. But in _all_ the basins the hydrogen liberated at the +_negative_ platina electrodes was the _same in quantity_, and the same with +the volume of hydrogen evolved in the volta-electrometer, showing that in +all the vessels the current had decomposed an equal quantity of water. In +this trying case, therefore, the _chemical action of electricity_ proved to +be _perfectly definite_. + +810. A similar experiment was made with muriatic acid diluted with its bulk +of water. The three positive electrodes were zinc, silver, and platina; the +first being able to separate and combine with the chlorine _without_ the +aid of the current; the second combining with the chlorine only after the +current had set it free; and the third rejecting almost the whole of it. +The three negative electrodes were, as before, platina plates fixed within +glass tubes. In this experiment, as in the former, the quantity of hydrogen +evolved at the _cathodes_ was the same for all, and the same as the +hydrogen evolved in the volta-electrometer. I have already given my reasons +for believing that in these experiments it is the muriatic acid which is +directly decomposed by the electricity (764.); and the results prove that +the quantities so decomposed are _perfectly definite_ and proportionate to +the quantity of electricity which has passed. + +811. In this experiment the chloride of silver formed in the second basin +retarded the passage of the current of electricity, by virtue of the law of +conduction before described (394.), so that it had to be cleaned off four +or five times during the course of the experiment; but this caused no +difference between the results of that vessel and the others. + +812. Charcoal was used as the positive electrode in both sulphuric and +muriatic acids (808. 810.); but this change produced no variation of the +results. A zinc positive electrode, in sulphate of soda or solution of +common salt, gave the same constancy of operation. + +813. Experiments of a similar kind were then made with bodies altogether in +a different state, i.e. with _fused_ chlorides, iodides, &c. I have already +described an experiment with fused chloride of silver, in which the +electrodes were of metallic silver, the one rendered negative becoming +increased and lengthened by the addition of metal, whilst the other was +dissolved and eaten away by its abstraction. This experiment was repeated, +two weighed pieces of silver wire being used as the electrodes, and a +volta-electrometer included in the circuit. Great care was taken to +withdraw the negative electrodes so regularly and steadily that the +crystals of reduced silver should not form a _metallic_ communication +beneath the surface of the fused chloride. On concluding the experiment the +positive electrode was re-weighed, and its loss ascertained. The mixture of +chloride of silver, and metal, withdrawn in successive portions at the +negative electrode, was digested in solution of ammonia, to remove the +chloride, and the metallic silver remaining also weighed: it was the +reduction at the _cathode_, and exactly equalled the solution at the +_anode_; and each portion was as nearly as possible the equivalent to the +water decomposed in the volta-electrometer. + +814. The infusible condition of the silver at the temperature used, and the +length and ramifying character of its crystals, render the above experiment +difficult to perform, and uncertain in its results. I therefore wrought +with chloride of lead, using a green-glass tube, formed as in fig. 72. A +weighed platina wire was fused into the bottom of a small tube, as before +described (789.). The tube was then bent to an angle, at about half an inch +distance from the closed end; and the part between the angle and the +extremity being softened, was forced upward, as in the figure, so as to +form a bridge, or rather separation, producing two little depressions or +basins _a, b_, within the tube. This arrangement was suspended by a platina +wire, as before, so that the heat of a spirit-lamp could be applied to it, +such inclination being given to it as would allow all air to escape during +the fusion of the chloride of lead. A positive electrode was then provided, +by bending up the end of a platina wire into a knot, and fusing about +twenty grains of metallic lead on to it, in a small closed tube of glass, +which was afterwards broken away. Being so furnished, the wire with its +lead was weighed, and the weight recorded. + +815. Chloride of lead was now introduced into the tube, and carefully +fused. The leaded electrode was also introduced; after which the metal, at +its extremity, soon melted. In this state of things the tube was filled up +to _c_ with melted chloride of lead; the end of the electrode to be +rendered negative was in the basin _b_, and the electrode of melted lead +was retained in the basin _a_, and, by connexion with the proper conducting +wire of a voltaic battery, was rendered positive. A volta-electrometer was +included in the circuit. + +816. Immediately upon the completion of the communication with the voltaic +battery, the current passed, and decomposition proceeded. No chlorine was +evolved at the positive electrode; but as the fused chloride was +transparent, a button of alloy could be observed gradually forming and +increasing in size at _b_, whilst the lead at _a_ could also be seen +gradually to diminish. After a time, the experiment was stopped; the tube +allowed to cool, and broken open; the wires, with their buttons, cleaned +and weighed; and their change in weight compared with the indication of the +volta-electrometer. + +817. In this experiment the positive electrode had lost just as much lead +as the negative one had gained (795.), and the loss and gain were very +nearly the equivalents of the water decomposed in the volta-electrometer, +giving for lead the number 101.5. It is therefore evident, in this +instance, that causing a _strong affinity_, or _no affinity_, for the +substance evolved at the _anode_, to be active during the experiment +(807.), produces no variation in the definite action of the electric +current. + +818. A similar experiment was then made with iodide of lead, and in this +manner all confusion from the formation of a periodide avoided (803.). No +iodine was evolved during the whole action, and finally the loss of lead at +the _anode_ was the same as the gain at the _cathode_, the equivalent +number, by comparison with the result in the volta-electrometer, being +103.5. + +819. Then protochloride of tin was subjected to the electric current in the +same manner, using of course, a tin positive electrode. No bichloride of +tin was now formed (779. 790.). On examining the two electrodes, the +positive had lost precisely as much as the negative had gained; and by +comparison with the volta-electrometer, the number for tin came out 59. + +820. It is quite necessary in these and similar experiments to examine the +interior of the bulbs of alloy at the ends of the conducting wires; for +occasionally, and especially with those which have been positive, they are +cavernous, and contain portions of the chloride or iodide used, which must +be removed before the final weight is ascertained. This is more usually the +case with lead than tin. + +821. All these facts combine into, I think, an irresistible mass of +evidence, proving the truth of the important proposition which I at first +laid down, namely, _that the chemical power of a current of electricity is +in direct proportion to the absolute quantity of electricity which passes_ +(377. 783.). They prove, too, that this is not merely true with one +substance, as water, but generally with all electrolytic bodies; and, +further, that the results obtained with any _one substance_ do not merely +agree amongst themselves, but also with those obtained from _other +substances_, the whole combining together into _one series of definite +electro-chemical actions_ (505.). I do not mean to say that no exceptions +will appear: perhaps some may arise, especially amongst substances existing +only by weak affinity; but I do not expect that any will seriously disturb +the result announced. If, in the well-considered, well-examined, and, I may +surely say, well-ascertained doctrines of the definite nature of ordinary +chemical affinity, such exceptions occur, as they do in abundance, yet, +without being allowed to disturb our minds as to the general conclusion, +they ought also to be allowed if they should present themselves at this, +the opening of a new view of electro-chemical action; not being held up as +obstructions to those who may be engaged in rendering that view more and +more perfect, but laid aside for a while, in hopes that their perfect and +consistent explanation will ultimately appear. + + * * * * * + +822. The doctrine of _definite electro-chemical action_ just laid down, +and, I believe, established, leads to some new views of the relations and +classifications of bodies associated with or subject to this action. Some +of these I shall proceed to consider. + +823. In the first place, compound bodies may be separated into two great +classes, namely, those which are decomposable by the electric current, and +those which are not: of the latter, some are conductors, others +non-conductors, of voltaic electricity[A]. The former do not depend for +their decomposability upon the nature of their elements only; for, of the +same two elements, bodies may be formed, of which one shall belong to one +class and another to the other class; but probably on the proportions also +(697.). It is further remarkable, that with very few, if any, exceptions +(414. 691.), these decomposable bodies are exactly those governed by the +remarkable law of conduction I have before described (694.); for that law +does not extend to the many compound fusible substances that are excluded +from this class. I propose to call bodies of this, the decomposable class, +_Electrolytes_ (664.). + + [A] I mean here by voltaic electricity, merely electricity from a most + abundant source, but having very small intensity. + +824. Then, again, the substances into which these divide, under the +influence of the electric current, form an exceedingly important general +class. They are combining bodies; are directly associated with the +fundamental parts of the doctrine of chemical affinity; and have each a +definite proportion, in which they are always evolved during electrolytic +action. I have proposed to call these bodies generally _ions_, or +particularly _anions_ and _cations_, according as they appear at the +_anode_ or _cathode_ (665.); and the numbers representing the proportions +in which they are evolved _electro-chemical equivalents_. Thus hydrogen, +oxygen, chlorine, iodine, lead, tin are _ions_; the three former are +_anions_, the two metals are _cations_, and 1, 8, 3, 125, 104, 58, are +their _electro-chemical equivalents_ nearly. + +825. A summary of certain points already ascertained respecting +_electrolytes, ions_, and _electro-chemical equivalents_, may be given in +the following general form of propositions, without, I hope, including any +serious error. + +826. i. A single _ion_, i.e. one not in combination with another, will have +no tendency to pass to either of the electrodes, and will be perfectly +indifferent to the passing current, unless it be itself a compound of more +elementary _ions_, and so subject to actual decomposition. Upon this fact +is founded much of the proof adduced in favour of the new theory of +electro-chemical decomposition, which I put forth in a former series of +these Researches (518. &c.). + +827. ii. If one _ion_ be combined in right proportions (697.) with another +strongly opposed to it in its ordinary chemical relations, i.e. if an +_anion_ be combined with a _cation_, then both will travel, the one to the +_anode_, the other to the _cathode_, of the decomposing body (530, 542. +547.). + +828. iii. If, therefore, an _ion_ pass towards one of the electrodes, +another _ion_ must also be passing simultaneously to the other electrode, +although, from secondary action, it may not make its appearance (743.). + +829. iv. A body decomposable directly by the electric current, i.e. an +_electrolyte_, must consist of two _ions_, and must also render them up +during the act of decomposition. + +830. v. There is but one _electrolyte_ composed of the same two elementary +_ions_; at least such appears to be the fact (697.), dependent upon a law, +that _only single electro-chemical equivalents of elementary ions can go to +the electrodes, and not multiples_. + +831. vi. A body not decomposable when alone, as boracic acid, is not +directly decomposable by the electric current when in combination (780.). +It may act as an _ion_ going wholly to the _anode_ or _cathode_, but does +not yield up its elements, except occasionally by a secondary action. +Perhaps it is superfluous for me to point out that this proposition has _no +relation_ to such cases as that of water, which, by the presence of other +bodies, is rendered a better conductor of electricity, and _therefore_ is +more freely decomposed. + +832. vii. The nature of the substance of which the electrode is formed, +provided it be a conductor, causes no difference in the +electro-decomposition, either in kind or degree (807. 813.): but it +seriously influences, by secondary action (714.), the state in which the +finally appear. Advantage may be taken of this principle in combining and +_ions_ collecting such _ions_ as, if evolved in their _free_ state, would +be unmanageable[A]. + + [A] It will often happen that the electrodes used may be of such a + nature as, with the fluid in which they are immersed, to produce an + electric current, either according with or opposing that of the + voltaic arrangement used, and in this way, or by direct chemical + action, may sadly disturb the results. Still, in the midst of all + these confusing effects, the electric current, which actually passes + in any direction through the body suffering decomposition, will + produce its own definite electrolytic action. + +833. viii. A substance which, being used as the electrode, can combine with +the _ion_ evolved against it, is also, I believe, an _ion_, and combines, +in such cases, in the quantity represented by its _electro-chemical +equivalent_. All the experiments I have made agree with this view; and it +seems to me, at present, to result as a necessary consequence. Whether, in +the secondary actions that take place, where the _ion_ acts, not upon the +matter of the electrode, but on that which is around it in the liquid +(744.), the same consequence follows, will require more extended +investigation to determine. + +834. ix. Compound _ions_ are not necessarily composed of electro-chemical +equivalents of simple _ions_. For instance, sulphuric acid, boracic acid, +phosphoric acid, are _ions_, but not _electrolytes_, i.e. not composed of +electro-chemical equivalents of simple _ions_. + +835. x. Electro-chemical equivalents are always consistent; i.e. the same +number which represents the equivalent of a substance A when it is +separating from a substance B, will also represent A when separating from a +third substance C. Thus, 8 is the electro-chemical equivalent of oxygen, +whether separating from hydrogen, or tin, or lead; and 103.5 is the +electrochemical equivalent of lead, whether separating from oxygen, or +chlorine, or iodine. + +836. xi. Electro-chemical equivalents coincide, and are the same, with +ordinary chemical equivalents. + +837. By means of experiment and the preceding propositions, a knowledge of +_ions_ and their electro-chemical equivalents may be obtained in various +ways. + +838. In the first place, they may be determined directly, as has been done +with hydrogen, oxygen, lead, and tin, in the numerous experiments already +quoted. + +839. In the next place, from propositions ii. and iii., may be deduced the +knowledge of many other _ions_, and also their equivalents. When chloride +of lead was decomposed, platina being used for both electrodes (395.), +there could remain no more doubt that chlorine was passing to the _anode_, +although it combined with the platina there, than when the positive +electrode, being of plumbago (794.), allowed its evolution in the free +state; neither could there, in either case, remain any doubt that for every +103.5 parts of lead evolved at the _cathode_, 36 parts of chlorine were +evolved at the _anode_, for the remaining chloride of lead was unchanged. +So also, when in a metallic solution one volume of oxygen, or a secondary +compound containing that proportion, appeared at the _anode_, no doubt +could arise that hydrogen, equivalent to two volumes, had been determined +to the _cathode_, although, by a secondary action, it had been employed in +reducing oxides of lead, copper, or other metals, to the metallic state. In +this manner, then, we learn from the experiments already described in these +Researches, that chlorine, iodine, bromine, fluorine, calcium, potassium, +strontium, magnesium, manganese, &c., are _ions_ and that their +_electro-chemical equivalents_ are the same as their _ordinary chemical +equivalents_. + +840. Propositions iv. and v. extend our means of gaining information. For +if a body of known chemical composition is found to be decomposable, and +the nature of the substance evolved as a primary or even a secondary result +(743. 777.) at one of the electrodes, be ascertained, the electro-chemical +equivalent of that body may be deduced from the known constant composition +of the substance evolved. Thus, when fused protiodide of tin is decomposed +by the voltaic current (804.), the conclusion may be drawn, that both the +iodine and tin are _ions_, and that the proportions in which they combine +in the fused compound express their electro-chemical equivalents. Again, +with respect to the fused iodide of potassium (805.), it is an electrolyte; +and the chemical equivalents will also be the electro-chemical equivalents. + +841. If proposition viii. sustain extensive experimental investigation, +then it will not only help to confirm the results obtained by the use of +the other propositions, but will give abundant original information of its +own. + +842. In many instances, the _secondary results_ obtained by the action of +the evolved _ion_ on the substances present in the surrounding liquid or +solution, will give the electro-chemical equivalent. Thus, in the solution +of acetate of lead, and, as far as I have gone, in other proto-salts +subjected to the reducing action of the nascent hydrogen at the _cathode_, +the metal precipitated has been in the same quantity as if it had been a +primary product, (provided no free hydrogen escaped there,) and therefore +gave accurately the number representing its electro-chemical equivalent. + +843. Upon this principle it is that secondary results may occasionally be +used as measurers of the volta-electric current (706. 740.); but there are +not many metallic solutions that answer this purpose well: for unless the +metal is easily precipitated, hydrogen will be evolved at the _cathode_ and +vitiate the result. If a soluble peroxide is formed at the _anode_, or if +the precipitated metal crystallize across the solution and touch the +positive electrode, similar vitiated results are obtained. I expect to find +in some salts, as the acetates of mercury and zinc, solutions favourable +for this use. + +844. After the first experimental investigations to establish the definite +chemical action of electricity, I have not hesitated to apply the more +strict results of chemical analysis to correct the numbers obtained as +electrolytic results. This, it is evident, may be done in a great number of +cases, without using too much liberty towards the due severity of +scientific research. The series of numbers representing electro-chemical +equivalents must, like those expressing the ordinary equivalents of +chemically acting bodies, remain subject to the continual correction of +experiment and sound reasoning. + +845. I give the following brief Table of _ions_ and their electro-chemical +equivalents, rather as a specimen of a first attempt than as anything that +can supply the want which must very quickly be felt, of a full and complete +tabular account of this class of bodies. Looking forward to such a table as +of extreme utility (if well-constructed) in developing the intimate +relation of ordinary chemical affinity to electrical actions, and +identifying the two, not to the imagination merely, but to the conviction +of the senses and a sound judgement, I may be allowed to express a hope, +that the endeavour will always be to make it a table of _real_, and not +_hypothetical_, electro-chemical equivalents; for we shall else overrun the +facts, and lose all sight and consciousness of the knowledge lying directly +in our path. + +846. The equivalent numbers do not profess to be exact, and are taken +almost entirely from the chemical results of other philosophers in whom I +could repose more confidence, as to these points, than in myself. + +847. TABLE OF IONS. + +_Anions_. + +Oxygen 8 +Chlorine 35.5 +Iodine 126 +Bromine 78.3 +Fluorine 18.7 +Cyanogen 26 +Sulphuric acid 40 +Selenic acid 64 +Nitric acid 54 +Chloric acid 75.5 +Phosphoric acid 35.7 +Carbonic acid 22 +Boracic acid 24 +Acetic acid 51 +Tartaric acid 66 +Citric acid 58 +Oxalic acid 36 +Sulphur (?) 16 +Selenium (?) +Salpho-cyanogen + +_Cations_. + +Hydrogen 1 +Potassium 39.2 +Sodium 23.3 +Lithium 10 +Barium 68.7 +Strontium 43.8 +Calcium 20.5 +Magnesium 12.7 +Manganese 27.7 +Zinc 32.5 +Tin 57.9 +Lead 103.5 +Iron 28 +Copper 31.6 +Cadmium 55.8 +Cerium 46 +Cobalt 29.5 +Nickel 29.5 +Antimony 61.67 +Bismuth 71 +Mercury 200 +Silver 108 +Platina 98.6? +Gold (?) + +Ammonia 17 +Potassa 47.2 +Soda 31.3 +Lithia 18 +Baryta 76.7 +Strontia 51.8 +Lime 28.5 +Magnesia 20.7 +Alumina. (?) +Protoxides generally. +Quinia 171.6 +Cinchona 160 +Morphia 290 +Vegeto-alkalies generally. + +848. This Table might be further arrange into groups of such substances as +either act with, or replace, each other. Thus, for instance, acids and +bases act in relation to each other; but they do not act in association +with oxygen, hydrogen, or elementary substances. There is indeed little or +no doubt that, when the electrical relations of the particles of matter +come to be closely examined, this division must be made. The simple +substances, with cyanogen, sulpho-cyanogen, and one or two other compound +bodies, will probably form the first group; and the acids and bases, with +such analogous compounds as may prove to be _ions_, the second group. +Whether these will include all _ions_, or whether a third class of more +complicated results will be required, must be decided by future +experiments. + +849. It is _probable_ that all our present elementary bodies are _ions_, +but that is not as yet certain. There are some, such as carbon, phosphorus, +nitrogen, silicon, boron, alumium, the right of which to the title of _ion_ +it is desirable to decide as soon as possible. There are also many compound +bodies, and amongst them alumina and silica, which it is desirable to class +immediately by unexceptionable experiments. It is also _possible_, that all +combinable bodies, compound as well as simple, may enter into the class of +_ions_; but at present it does not seem to me probable. Still the +experimental evidence I have is so small in proportion to what must +gradually accumulate around, and bear upon, this point, that I am afraid to +give a strong opinion upon it. + +850. I think I cannot deceive myself in considering the doctrine of +definite electro-chemical action as of the utmost importance. It touches by +its facts more directly and closely than any former fact, or set of facts, +have done, upon the beautiful idea, that ordinary chemical affinity is a +mere consequence of the electrical attractions of the particles of +different kinds of matter; and it will probably lead us to the means by +which we may enlighten that which is at present so obscure, and either +fully demonstrate the truth of the idea, or develope that which ought to +replace it. + +851. A very valuable use of electro-chemical equivalents will be to decide, +in cases of doubt, what is the true chemical equivalent, or definite +proportional, or atomic number of a body; for I have such conviction that +the power which governs electro-decomposition and ordinary chemical +attractions is the same; and such confidence in the overruling influence of +those natural laws which render the former definite, as to feel no +hesitation in believing that the latter must submit to them also. Such +being the case, I can have, no doubt that, assuming hydrogen as 1, and +dismissing small fractions for the simplicity of expression, the equivalent +number or atomic weight of oxygen is 8, of chlorine 36, of bromine 78.4, of +lead 103.5, of tin 59, &c., notwithstanding that a very high authority +doubles several of these numbers. + + +S 13. _On the absolute quantity of Electricity associated with the +particles or atoms of Matter._ + + +852. The theory of definite electrolytical or electro-chemical action +appears to me to touch immediately upon the _absolute quantity_ of +electricity or electric power belonging to different bodies. It is +impossible, perhaps, to speak on this point without committing oneself +beyond what present facts will sustain; and yet it is equally impossible, +and perhaps would be impolitic, not to reason upon the subject. Although we +know nothing of what an atom is, yet we cannot resist forming some idea of +a small particle, which represents it to the mind; and though we are in +equal, if not greater, ignorance of electricity, so as to be unable to say +whether it is a particular matter or matters, or mere motion of ordinary +matter, or some third kind of power or agent, yet there is an immensity of +facts which justify us in believing that the atoms of matter are in some +way endowed or associated with electrical powers, to which they owe their +most striking qualities, and amongst them their mutual chemical affinity. +As soon as we perceive, through the teaching of Dalton, that chemical +powers are, however varied the circumstances in which they are exerted, +definite for each body, we learn to estimate the relative degree of force +which resides in such bodies: and when upon that knowledge comes the fact, +that the electricity, which we appear to be capable of loosening from its +habitation for a while, and conveying from place to place, _whilst it +retains its chemical force_, can be measured out, and being so measured is +found to be _as definite in its action_ as any of _those portions_ which, +remaining associated with the particles of matter, give them their +_chemical relation_; we seem to have found the link which connects the +proportion of that we have evolved to the proportion of that belonging to +the particles in their natural state. + +853. Now it is wonderful to observe how small a quantity of a compound body +is decomposed by a certain portion of electricity. Let us, for instance, +consider this and a few other points in relation to water. _One grain_ of +water, acidulated to facilitate conduction, will require an electric +current to be continued for three minutes and three quarters of time to +effect its decomposition, which current must be powerful enough to retain a +platina wire 1/104 of an inch in thickness[A], red-hot, in the air during +the whole time; and if interrupted anywhere by charcoal points, will +produce a very brilliant and constant star of light. If attention be paid +to the instantaneous discharge of electricity of tension, as illustrated in +the beautiful experiments of Mr. Wheatstone[B], and to what I have said +elsewhere on the relation of common and voltaic electricity (371. 375.), it +will not be too much to say that this necessary quantity of electricity is +equal to a very powerful flash of lightning. Yet we have it under perfect +command; can evolve, direct, and employ it at pleasure; and when it has +performed its full work of electrolyzation, it has only separated the +elements of _a single grain of water_. + + [A] I have not stated the length of wire used, because I find by + experiment, as would be expected in theory, that it is indifferent. + The same quantity of electricity which, passed in a given time, can + heat an inch of platina wire of a certain diameter red-hot, can also + heat a hundred, a thousand, or any length of the same wire to the same + degree, provided the cooling circumstances are the same for every part + in all cases. This I have proved by the volta-electrometer. I found + that whether half an inch or eight inches were retained at one + constant temperature of dull redness, equal quantities of water were + decomposed in equal times. When the half-inch was used, only the + centre portion of wire was ignited. A fine wire may even be used as a + rough but ready regulator of a voltaic current; for if it be made part + of the circuit, and the larger wires communicating with it be shifted + nearer to or further apart, so as to keep the portion of wire in the + circuit sensibly at the same temperature, the current passing through + it will be nearly uniform. + + [B] Literary Gazette, 1833, March 1 and 8. Philosophical Magazine, + 1833, p. 201. L'Institut, 1833, p.261. + +854. On the other hand, the relation between the conduction of the +electricity and the decomposition of the water is so close, that one cannot +take place without the other. If the water is altered only in that small +degree which consists in its having the solid instead of the fluid state, +the conduction is stopped, and the decomposition is stopped with it. +Whether the conduction be considered as depending upon the decomposition, +or not (443. 703.), still the relation of the two functions is equally +intimate and inseparable. + +855. Considering this close and twofold relation, namely, that without +decomposition transmission of electricity does not occur; and, that for a +given definite quantity of electricity passed, an equally definite and +constant quantity of water or other matter is decomposed; considering also +that the agent, which is electricity, is simply employed in overcoming +electrical powers in the body subjected to its action; it seems a probable, +and almost a natural consequence, that the quantity which passes is the +_equivalent_ of, and therefore equal to, that of the particles separated; +i.e. that if the electrical power which holds the elements of a grain of +water in combination, or which makes a grain of oxygen and hydrogen in the +right proportions unite into water when they are made to combine, could be +thrown into the condition of _a current_, it would exactly equal the +current required for the separation of that grain of water into its +elements again. + +856. This view of the subject gives an almost overwhelming idea of the +extraordinary quantity or degree of electric power which naturally belongs +to the particles of matter; but it is not inconsistent in the slightest +degree with the facts which can be brought to bear on this point. To +illustrate this I must say a few words on the voltaic pile[A]. + + [A] By the term voltaic pile, I mean such apparatus or arrangement of + metals as up to this time have been called so, and which contain + water, brine, acids, or other aqueous solutions or decomposable + substances (476.), between their plates. Other kinds of electric + apparatus may be hereafter invented, and I hope to construct some not + belonging to the class of instruments discovered by Volta. + +857. Intending hereafter to apply the results given in this and the +preceding series of Researches to a close investigation of the source of +electricity in the voltaic instrument, I have refrained from forming any +decided opinion on the subject; and without at all meaning to dismiss +metallic contact, or the contact of dissimilar substances, being +conductors, but not metallic, as if they had nothing to do with the origin +of the current, + +I still am fully of opinion with Davy, that it is at least continued by +chemical action, and that the supply constituting the current is almost +entirely from that source. + +858. Those bodies which, being interposed between the metals of the voltaic +pile, render it active, _are all of them electrolytes_ (476.); and it +cannot but press upon the attention of every one engaged in considering +this subject, that in those bodies (so essential to the pile) decomposition +and the transmission of a current are so intimately connected, that one +cannot happen without the other. This I have shown abundantly in water, and +numerous other cases (402. 476.). If, then, a voltaic trough have its +extremities connected by a body capable of being decomposed, as water, we +shall have a continuous current through the apparatus; and whilst it +remains in this state we may look at the part where the acid is acting upon +the plates, and that where the current is acting upon the water, as the +reciprocals of each other. In both parts we have the two conditions +_inseparable in such bodies as these_, namely, the passing of a current, +and decomposition; and this is as true of the cells in the battery as of +the water cell; for no voltaic battery has as yet been constructed in which +the chemical action is only that of combination: _decomposition is always +included_, and is, I believe, an essential chemical part. + +859. But the difference in the two parts of the connected battery, that is, +the decomposition or experimental cell, and the acting cells, is simply +this. In the former we urge the current through, but it, apparently of +necessity, is accompanied by decomposition: in the latter we cause +decompositions by ordinary chemical actions, (which are, however, +themselves electrical,) and, as a consequence, have the electrical current; +and as the decomposition dependent upon the current is definite in the +former case, so is the current associated with the decomposition also +definite in the latter (862. &c.). + +860. Let us apply this in support of what I have surmised respecting the +enormous electric power of each particle or atom of matter (856.). I showed +in a former series of these Researches on the relation by measure of common +and voltaic electricity, that two wires, one of platina and one of zinc, +each one-eighteenth of an inch in diameter, placed five-sixteenths of an +inch apart, and immersed to the depth of five-eighths of an inch in acid, +consisting of one drop of oil of vitriol and four ounces of distilled water +at a temperature of about 60 deg. Fahr., and connected at the other extremities +by a copper wire eighteen feet long, and one-eighteenth of an inch in +thickness, yielded as much electricity in little more than three seconds of +time as a Leyden battery charged by thirty turns of a very large and +powerful plate electric machine in full action (371.). This quantity, +though sufficient if passed at once through the head of a rat or cat to +have killed it, as by a flash of lightning, was evolved by the mutual +action of so small a portion of the zinc wire and water in contact with it, +that the loss of weight sustained by either would be inappreciable by our +most delicate instruments; and as to the water which could be decomposed by +that current, it must have been insensible in quantity, for no trace of +hydrogen appeared upon the surface of the platina during those three +seconds. + +861. What an enormous quantity of electricity, therefore, is required for +the decomposition of a single grain of water! We have already seen that it +must be in quantity sufficient to sustain a platina wire 1/104 of an inch +in thickness, red-hot, in contact with the air, for three minutes and three +quarters (853.), a quantity which is almost infinitely greater than that +which could be evolved by the little standard voltaic arrangement to which +I have just referred (860. 871.). I have endeavoured to make a comparison +by the loss of weight of such a wire in a given time in such an acid, +according to a principle and experiment to be almost immediately described +(862.); but the proportion is so high that I am almost afraid to mention +it. It would appear that 800,000 such charges of the Leyden battery as I +have referred to above, would be necessary to supply electricity sufficient +to decompose a single grain of water; or, if I am right, to equal the +quantity of electricity which is naturally associated with the elements of +that grain of water, endowing them with their mutual chemical affinity. + +862. In further proof of this high electric condition of the particles of +matter, and the _identity as to quantity of that belonging to them with +that necessary for their separation_, I will describe an experiment of +great simplicity but extreme beauty, when viewed in relation to the +evolution of an electric current and its decomposing powers. + +863. A dilute sulphuric acid, made by adding about one part by measure of +oil of vitriol to thirty parts of water, will act energetically upon a +piece of zinc plate in its ordinary and simple state: but, as Mr. Sturgeon +has shown[A], not at all, or scarcely so, if the surface of the metal has +in the first instance been amalgamated; yet the amalgamated zinc will act +powerfully with platina as an electromotor, hydrogen being evolved on the +surface of the latter metal, as the zinc is oxidized and dissolved. The +amalgamation is best effected by sprinkling a few drops of mercury upon the +surface of the zinc, the latter being moistened with the dilute acid, and +rubbing with the fingers or two so as to extend the liquid metal over the +whole of the surface. Any mercury in excess, forming liquid drops upon the +zinc, should be wiped off[B]. + + [A] Recent Experimental Researches, &c., 1830, p.74, &c. + + [B] The experiment may be made with pure zinc, which, as chemists well + know, is but slightly acted upon by dilute sulphuric acid in + comparison with ordinary zinc, which during the action is subject to + an infinity of voltaic actions. See De la Rive on this subject, + Bibliotheque Universelle, 1830, p.391. + +864. Two plates of zinc thus amalgamated were dried and accurately weighed; +one, which we will call A, weighed 163.1 grains; the other, to be called B, +weighed 148.3 grains. They were about five inches long, and 0.4 of an inch +wide. An earthenware pneumatic trough was filled with dilute sulphuric +acid, of the strength just described (863.), and a gas jar, also filled +with the acid, inverted in it[A]. A plate of platina of nearly the same +length, but about three times as wide as the zinc plates, was put up into +this jar. The zinc plate A was also introduced into the jar, and brought in +contact with the platina, and at the same moment the plate B was put into +the acid of the trough, but out of contact with other metallic matter. + + [A] The acid was left during a night with a small piece of + unamalgamated zinc in it, for the purpose of evolving such air as + might be inclined to separate, and bringing the whole into a constant + state. + +865. Strong action immediately occurred in the jar upon the contact of the +zinc and platina plates. Hydrogen gas rose from the platina, and was +collected in the jar, but no hydrogen or other gas rose from _either_ zinc +plate. In about ten or twelve minutes, sufficient hydrogen having been +collected, the experiment was stopped; during its progress a few small +bubbles had appeared upon plate B, but none upon plate A. The plates were +washed in distilled water, dried, and reweighed. Plate B weighed 148.3 +grains, as before, having lost nothing by the direct chemical action of the +acid. Plate A weighed 154.65 grains, 8.45 grains of it having been oxidized +and dissolved during the experiment. + +866. The hydrogen gas was next transferred to a water-trough and measured; +it amounted to 12.5 cubic inches, the temperature being 52 deg., and the +barometer 29.2 inches. This quantity, corrected for temperature, pressure, +and moisture, becomes 12.15453 cubic inches of dry hydrogen at mean +temperature and pressure; which, increased by one half for the oxygen that +must have gone to the _anode_, i.e. to the zinc, gives 18.232 cubic inches +as the quantity of oxygen and hydrogen evolved from the water decomposed by +the electric current. According to the estimate of the weight of the mixed +gas before adopted (791.), this volume is equal to 2.3535544 grains, which +therefore is the weight of water decomposed; and this quantity is to 8.45, +the quantity of zinc oxidized, as 9 is to 32.31. Now taking 9 as the +equivalent number of water, the number 32.5 is given as the equivalent +number of zinc; a coincidence sufficiently near to show, what indeed could +not but happen, that for an equivalent of zinc oxidized an equivalent of +water must be decomposed[A]. + + [A] The experiment was repeated several times with the same results. + +867. But let us observe _how_ the water is decomposed. It is electrolyzed, +i.e. is decomposed voltaically, and not in the ordinary manner (as to +appearance) of chemical decompositions; for the oxygen appears at the +_anode_ and the hydrogen at the _cathode_ of the body under decomposition, +and these were in many parts of the experiment above an inch asunder. +Again, the ordinary chemical affinity was not enough under the +circumstances to effect the decomposition of the water, as was abundantly +proved by the inaction on plate B; the voltaic current was essential. And +to prevent any idea that the chemical affinity was almost sufficient to +decompose the water, and that a smaller current of electricity might, under +the circumstances, cause the hydrogen to pass to the _cathode_, I need only +refer to the results which I have given (807. 813.) to shew that the +chemical action at the electrodes has not the slightest influence over the +_quantities_ of water or other substances decomposed between them, but that +they are entirely dependent upon the quantity of electricity which passes. + +868. What, then, follows as a necessary consequence of the whole +experiment? Why, this: that the chemical action upon 32.31 parts, or one +equivalent of zinc, in this simple voltaic circle, was able to evolve such +quantity of electricity in the form of a current, as, passing through +water, should decompose 9 parts, or one equivalent of that substance: and +considering the definite relations of electricity as developed in the +preceding parts of the present paper, the results prove that the quantity +of electricity which, being naturally associated with the particles of +matter, gives them their combining power, is able, when thrown into a +current, to separate those particles from their state of combination; or, +in other words, that _the electricity which decomposes, and that which is +evolved by the decomposition of a certain quantity of matter, are alike._ + +869. The harmony which this theory of the definite evolution and the +equivalent definite action of electricity introduces into the associated +theories of definite proportions and electrochemical affinity, is very +great. According to it, the equivalent weights of bodies are simply those +quantities of them which contain equal quantities of electricity, or have +naturally equal electric powers; it being the ELECTRICITY which +_determines_ the equivalent number, _because_ it determines the combining +force. Or, if we adopt the atomic theory or phraseology, then the atoms of +bodies which are equivalents to each other in their ordinary chemical +action, have equal quantities of electricity naturally associated with +them. But I must confess I am jealous of the term _atom_; for though it is +very easy to talk of atoms, it is very difficult to form a clear idea of +their nature, especially when compound bodies are under consideration. + +870. I cannot refrain from recalling here the beautiful idea put forth, I +believe, by Berzelius (703.) in his development of his views of the +electro-chemical theory of affinity, that the heat and light evolved during +cases of powerful combination are the consequence of the electric discharge +which is at the moment taking place. The idea is in perfect accordance with +the view I have taken of the _quantity_ of electricity associated with the +particles of matter. + +871. In this exposition of the law of the definite action of electricity, +and its corresponding definite proportion in the particles of bodies, I do +not pretend to have brought, as yet, every case of chemical or +electro-chemical action under its dominion. There are numerous +considerations of a theoretical nature, especially respecting the compound +particles of matter and the resulting electrical forces which they ought to +possess, which I hope will gradually receive their development; and there +are numerous experimental cases, as, for instance, those of compounds +formed by weak affinities, the simultaneous decomposition of water and +salts, &c., which still require investigation. But whatever the results on +these and numerous other points may be, I do not believe that the facts +which I have advanced, or even the general laws deduced from them, will +suffer any serious change; and they are of sufficient importance to justify +their publication, though much may yet remain imperfect or undone. Indeed, +it is the great beauty of our science, CHEMISTRY, that advancement in it, +whether in a degree great or small, instead of exhausting the subjects of +research, opens the doors to further and more abundant knowledge, +overflowing with beauty and utility, to those who will be at the easy +personal pains of undertaking its experimental investigation. + +872. The definite production of electricity (868.) in association with its +definite action proves, I think, that the current of electricity in the +voltaic pile: is sustained by chemical decomposition, or rather by chemical +action, and not by contact only. But here, as elsewhere (857.), I beg to +reserve my opinion as to the real action of contact, not having yet been +able to make up my mind as to whether it is an exciting cause of the +current, or merely necessary to allow of the conduction of electricity, +otherwise generated, from one metal to the other. + +873. But admitting that chemical action is the source of electricity, what +an infinitely small fraction of that which is active do we obtain and +employ in our voltaic batteries! Zinc and platina wires, one-eighteenth of +an inch in diameter and about half an inch long, dipped into dilute +sulphuric acid, so weak that it is not sensibly sour to the tongue, or +scarcely to our most delicate test-papers, will evolve more electricity in +one-twentieth of a minute (860.) than any man would willingly allow to pass +through his body at once. The chemical action of a grain of water upon four +grains of zinc can evolve electricity equal in quantity to that of a +powerful thunder-storm (868. 861.). Nor is it merely true that the quantity +is active; it can be directed and made to perform its full equivalent duty +(867. &c.). Is there not, then, great reason to hope and believe that, by a +closer _experimental_ investigation of the principles which govern the +development and action of this subtile agent, we shall be able to increase +the power of our batteries, or invent new instruments which shall a +thousandfold surpass in energy those which we at present possess? + +874. Here for a while I must leave the consideration of the _definite +chemical action of electricity_. But before I dismiss this series of +experimental Researches, I would call to mind that, in a former series, I +showed the current of electricity was also _definite in its magnetic +action_ (216. 366. 367. 376. 377.); and, though this result was not pursued +to any extent, I have no doubt that the success which has attended the +development of the chemical effects is not more than would accompany an +investigation of the magnetic phenomena. + + +_Royal Institution, +December 31st, 1833._ + + + + +EIGHTH SERIES. + + +S14. _On the Electricity of the Voltaic Pile; its source, quantity, +intensity, and general characters._ P i. _On simple Voltaic Circles._ P ii. +_On the intensity necessary for Electrolyzation._ P iii. _On associated +Voltaic Circles, or the Voltaic Battery._ P iv. _On the resistance of an +Electrolyte to Electrolytic action._ P v. _General remarks on the active +Voltaic Battery._ + +Received April 7,--Read June 5, 1831. + + +P i. _On simple Voltaic Circles._ + + +875. The great question of the source of electricity, in the voltaic pile +has engaged the attention of so many eminent philosophers, that a man of +liberal mind and able to appreciate their powers would probably conclude, +although he might not have studied the question, that the truth was +somewhere revealed. But if in pursuance of this impression he were induced +to enter upon the work of collating results and conclusions, he would find +such contradictory evidence, such equilibrium of opinion, such variation +and combination of theory, as would leave him in complete doubt respecting +what he should accept as the true interpretation of nature: he would be +forced to take upon himself the labour of repeating and examining the +facts, and then use his own judgement on them in preference to that of +others. + +876. This state of the subject must, to those who have made up their minds +on the matter, be my apology for entering upon its investigation. The views +I have taken of the definite action of electricity in decomposing bodies +(783.), and the identity of the power so used with the power to be overcome +(855.), founded not on a mere opinion or general notion, but on facts +which, being altogether new, were to my mind precise and conclusive, gave +me, as I conceived, the power of examining the question with advantages not +before possessed by any, and which might compensate, on my part, for the +superior clearness and extent of intellect on theirs. Such are the +considerations which have induced me to suppose I might help in deciding +the question, and be able to render assistance in that great service of +removing _doubtful knowledge_. Such knowledge is the early morning light of +every advancing science, and is essential to its development; but the man +who is engaged in dispelling that which is deceptive in it, and revealing +more clearly that which is true, is as useful in his place, and as +necessary to the general progress of the science, as he who first broke +through the intellectual darkness, and opened a path into knowledge before +unknown to man. + +877. The identity of the force constituting the voltaic current or +electrolytic agent, with that which holds the elements of electrolytes +together (855.), or in other words with chemical affinity, seemed to +indicate that the electricity of the pile itself was merely a mode of +exertion, or exhibition, or existence of _true chemical action_, or rather +of its cause; and I have consequently already said that I agree with those +who believe that the _supply_ of electricity is due to chemical powers +(857.). + +878. But the great question of whether it is originally due to metallic +contact or to chemical action, i.e. whether it is the first or the second +which _originates_ and determines the current, was to me still doubtful; +and the beautiful and simple experiment with amalgamated zinc and platina, +which I have described minutely as to its results (863, &c.), did not +decide the point; for in that experiment the chemical action does not take +place without the contact of the metals, and the metallic contact is +inefficient without the chemical action. Hence either might be looked upon +as the _determining_ cause of the current. + +879. I thought it essential to decide this question by the simplest +possible forms of apparatus and experiment, that no fallacy might be +inadvertently admitted. The well-known difficulty of effecting +decomposition by a single pair of plates, except in the fluid exciting them +into action (863.), seemed to throw insurmountable obstruction in the way +of such experiments; but I remembered the easy decomposability of the +solution of iodide of potassium (316.), and seeing no theoretical reason, +if metallic contact was not _essential_, why true electro-decomposition +should not be obtained without it, even in a single circuit, I persevered +and succeeded. + +880. A plate of zinc, about eight inches long and half an inch wide, was +cleaned and bent in the middle to a right angle, fig. 73 _a_, Plate VI. A +plate of platina, about three inches long and half an inch wide, was +fastened to a platina wire, and the latter bent as in the figure, _b_. +These two pieces of metal were arranged together as delineated, but as yet +without the vessel _c_, and its contents, which consisted of dilute +sulphuric acid mingled with a little nitric acid. At _x_ a piece of folded +bibulous paper, moistened in a solution of iodide of potassium, was placed +on the zinc, and was pressed upon by the end of the platina wire. When +under these circumstances the plates were dipped into the acid of the +vessel _c_, there was an immediate effect at _x_, the iodide being +decomposed, and iodine appearing at the _anode_ (663.), i.e. against the +end of the platina wire. + +881. As long as the lower ends of the plates remained in the acid the +electric current continued, and the decomposition proceeded at _x_. On +removing the end of the wire from place to place on the paper, the effect +was evidently very powerful; and on placing a piece of turmeric paper +between the white paper and zinc, both papers being moistened with the +solution of iodide of potassium, alkali was evolved at the _cathode_ (663.) +against the zinc, in proportion to the evolution of iodine at the _anode_. +Hence the decomposition was perfectly polar, and decidedly dependent upon a +current of electricity passing from the zinc through the acid to the +platina in the vessel _c_, and back from the platina through the solution +to the zinc at the paper _x_. + +882. That the decomposition at _x_ was a true electrolytic action, due to a +current determined by the state of things in the vessel _c_, and not +dependent upon any mere direct chemical action of the zinc and platina on +the iodide, or even upon any _current_ which the solution of iodide might +by its action on those metals tend to form at _x_, was shown, in the first +place, by removing the vessel _c_ and its acid from the plates, when all +decomposition at _x_ ceased, and in the next by connecting the metals, +either in or out of the acid, together, when decomposition of the iodide at +_x_ occurred, but in a _reverse order_; for now alkali appeared against the +end of the platina wire, and the iodine passed to the zinc, the current +being the contrary of what it was in the former instance, and produced +directly by the difference of action of the solution in the paper on the +two metals. The iodine of course _combined_ with the zinc. + +883. When this experiment was made with pieces of zinc amalgamated over the +whole surface (863.), the results were obtained with equal facility and in +the same direction, even when only dilute sulphuric acid was contained in +the vessel _c_ (fig. 73.). Whichsoever end of the zinc was immersed in the +acid, still the effects were the same: so that if, for a moment, the +mercury might be supposed to supply the metallic contact, the inversion of +the amalgamated piece destroys that objection. The use of _unamalgamated +zinc_ (880.) removes all possibility of doubt[A]. + + [A] The following is a more striking mode of making the above + elementary experiment. Prepare a plate of zinc, ten or twelve inches + long and two inches wide, and clean it thoroughly: provide also two + discs of clean platina, about one inch and a half in diameter:--dip + three or four folds of bibulous paper into a strong solution of iodide + of potassium, place them on the clean zinc at one end of the plate, + and put on them one of the platina discs: finally dip similar folds of + paper or a piece of linen cloth into a mixture of equal parts nitric + acid and water, and place it at the other end of the zinc plate with + the second platina disc upon it. In this state of things no change at + the solution of the iodide will be perceptible; but if the two discs + be connected by a platina (or any other) wire for a second or two, and + then that over the iodide be raised, it will be found that the _whole_ + of the surface beneath is deeply stained with _evolved iodine_.--_Dec. + 1838._ + +884 When, in pursuance of other views (930.), the vessel _c_ was made to +contain a solution of caustic potash in place of acid, still the same +results occurred. Decomposition of the iodide was effected freely, though +there was no metallic contact of dissimilar metals, and the current of +electricity was in the _same direction_ as when acid was used at the place +of excitement. + +885. Even a solution of common salt in the glass _c_ could produce all +these effects. + +886. Having made a galvanometer with platina wires, and introduced it into +the course of the current between the platina plate and the place of +decomposition _x_, it was affected, giving indications of currents in the +same direction as those shown to exist by the chemical action. + +887. If we consider these results generally, they lead to very important +conclusions. In the first place, they prove, in the most decisive manner, +that _metallic contact is not necessary for the production of the voltaic +current._ In the next place, they show a most extraordinary mutual relation +of the chemical affinities of the fluid which _excites_ the current, and +the fluid which is _decomposed_ by it. + +888. For the purpose of simplifying the consideration, let us take the +experiment with amalgamated zinc. The metal so prepared exhibits no effect +until the current can pass: it at the same time introduces no new action, +but merely removes an influence which is extraneous to those belonging +either to the production or the effect of the electric current under +investigation (1000.); an influence also which, when present, tends only to +confuse the results. + +889. Let two plates, one of amalgamated zinc and the other of platina, be +placed parallel to each other (fig. 74.), and introduce a drop of dilute +sulphuric acid, _y_, between them at one end: there will be no sensible +chemical action at that spot unless the two plates are connected somewhere +else, as at PZ, by a body capable of conducting electricity. If that body +be a metal or certain forms of carbon, then the current passes, and, as it +circulates through the fluid at _y_, decomposition ensues. + +890. Then remove the acid from _y_, and introduce a drop of the solution of +iodide of potassium at _x_ (fig. 75.). Exactly the same set of effects +occur, except that when the metallic communication is made at PZ, the +electric current is in the opposite direction to what it was before, as is +indicated by the arrows, which show the courses of the currents (667.). + +891. Now _both_ the solutions used are conductors, but the conduction in +them is essentially connected with decomposition (858.) in a certain +constant order, and therefore the appearance of the elements in certain +places _shows_ in what direction a current has passed when the solutions +are thus employed. Moreover, we find that when they are used at opposite +ends of the plates, as in the last two experiments (889. 890.), metallic +contact being allowed at the other extremities, the currents are in +opposite directions. We have evidently, therefore, the power of opposing +the actions of the two fluids simultaneously to each other at the opposite +ends of the plates, using each one as a conductor for the discharge of the +current of electricity, which the other tends to generate; in fact, +substituting them for metallic contact, and combining both experiments into +one (fig. 76.). Under these circumstances, there is an opposition of +forces: the fluid, which brings into play the stronger set of chemical +affinities for the zinc, (being the dilute acid,) overcomes the force of +the other, and determines the formation and direction of the electric +current; not merely making that current pass through the weaker liquid, but +actually reversing the tendency which the elements of the latter have in +relation to the zinc and platina if not thus counteracted, and forcing them +in the contrary direction to that they are inclined to follow, that its own +current may have free course. If the dominant action at _y_ be removed by +making metallic contact there, then the liquid at _x_ resumes its power; or +if the metals be not brought into contact at _y_ but the affinities of the +solution there weakened, whilst those active _x_ are strengthened, then the +latter gains the ascendency, and the decompositions are produced in a +contrary order. + +892. Before drawing a _final_ conclusion from this mutual dependence and +state of the chemical affinities of two distant portions of acting fluids +(916.), I will proceed to examine more minutely the various circumstances +under which the re-action of the body suffering decomposition is rendered +evident upon the action of the body, also undergoing decomposition, which +produces the voltaic current. + +893. The use of _metallic contact_ in a single pair of plates, and the +cause of its great superiority above contact made by other kinds of matter, +become now very evident. When an amalgamated zinc plate is dipped into +dilute sulphuric acid, the force of chemical affinity exerted between the +metal and the fluid is not sufficiently powerful to cause sensible action +at the surfaces of contact, and occasion the decomposition of water by the +oxidation of the metal, although it _is_ sufficient to produce such a +condition of the electricity (or the power upon which chemical affinity +depends) as would produce a current if there were a path open for it (916. +956.); and that current would complete the conditions necessary, under the +circumstances, for the decomposition of the water. + +894. Now the presence of a piece of platina touching both the zinc and the +fluid to be decomposed, opens the path required for the electricity. Its +_direct communication_ with the zinc is effectual, far beyond any +communication made between it and that metal, (i.e. between the platina +and zinc,) by means of decomposable conducting bodies, or, in other words, +_electrolytes_, as in the experiment already described (891.); because, +when _they_ are used, the chemical affinities between them and the zinc +produce a contrary and opposing action to that which is influential in the +dilute sulphuric acid; or if that action be but small, still the affinity +of their component parts for each other has to be overcome, for they cannot +conduct without suffering decomposition; and this decomposition is found +_experimentally_ to re-act back upon the forces which in the acid tend to +produce the current (904. 910. &c.), and in numerous cases entirely to +neutralize them. Where direct contact of the zinc and platina occurs, these +obstructing forces are not brought into action, and therefore the +production and the circulation of the electric current and the concomitant +action of decomposition are then highly favoured. + +895. It is evident, however, that one of these opposing actions may be +dismissed, and yet an electrolyte be used for the purpose of completing the +circuit between the zinc and platina immersed separately into the dilute +acid; for if, in fig. 73, the platina wire be retained in metallic contact +with the zinc plate _a_, at _x_, and a division of the platina be made +elsewhere, as at _s_, then the solution of iodide placed there, being in +contact with platina at both surfaces, exerts no chemical affinities for +that metal; or if it does, they are equal on both sides. Its power, +therefore, of forming a current in opposition to that dependent upon the +action of the acid in the vessel _c_, is removed, and only its resistance +to decomposition remains as the obstacle to be overcome by the affinities +exerted in the dilute sulphuric acid. + +896. This becomes the condition of a single pair of active plates where +_metallic contact_ is allowed. In such cases, only one set of opposing +affinities are to be overcome by those which are dominant in the vessel +_c_; whereas, when metallic contact is not allowed, two sets of opposing +affinities must be conquered (894.). + +897. It has been considered a difficult, and by some an impossible thing, +to decompose bodies by the current from a single pair of plates, even when +it was so powerful as to heat bars of metal red-hot, as in the case of +Hare's calorimeter, arranged as a single voltaic circuit, or of Wollaston's +powerful single pair of metals. This difficulty has arisen altogether from +the antagonism of the chemical affinity engaged in producing the current +with the chemical affinity to be overcome, and depends entirely upon their +relative intensity; for when the sum of forces in one has a certain degree +of superiority over the sum of forces in the other, the former gain the +ascendency, determine the current, and overcome the latter so as to make +the substance exerting them yield up its elements in perfect accordance, +both as to direction and quantity, with the course of those which are +exerting the most intense and dominant action. + +898. Water has generally been the substance, the decomposition of which has +been sought for as a chemical test of the passage of an electric current. +But I now began to perceive a reason for its failure, and for a fact which +I had observed long before (315. 316.) with regard to the iodide of +potassium, namely, that bodies would differ in facility of decomposition by +a given electric current, according to the condition and intensity of their +ordinary chemical affinities. This reason appeared in their _re-action upon +the affinities_ tending to cause the current; and it appeared probable, +that many substances might be found which could be decomposed by the +current of a single pair of zinc and platina plates immersed in dilute +sulphuric acid, although water resisted its action. I soon found this to be +the case, and as the experiments offer new and beautiful proofs of the +direct relation and opposition of the chemical affinities concerned in +producing and in resisting the stream of electricity, I shall briefly +describe them. + +899. The arrangement of the apparatus was as in fig. 77. The vessel _v_ +contained dilute sulphuric acid; Z and P are the zinc and platina plates; +_a_, _b_, and _c_ are platina wires; the decompositions were effected at +_x_, and occasionally, indeed generally, a galvanometer was introduced into +the circuit at _g_: its place only is here given, the circle at _g_ having +no reference to the size of the instrument. Various arrangements were made +at _x_, according to the kind of decomposition to be effected. If a drop of +liquid was to be acted upon, the two ends were merely dipped into it; if a +solution contained in the pores of paper was to be decomposed, one of the +extremities was connected with a platina plate supporting the paper, whilst +the other extremity rested on the paper, _e_, fig. 81: or sometimes, as +with sulphate of soda, a plate of platina sustained two portions of paper, +one of the ends of the wires resting upon each piece, _c_, fig. 86. The +darts represent the direction of the electric current (667.). + +900. Solution of _iodide of potassium_, in moistened paper, being placed at +the interruption of the circuit at _x_, was readily decomposed. Iodine was +evolved at the _anode_, and alkali at the _cathode_, of the decomposing +body. + +901. _Protochloride of tin_, when fused and placed at _x_, was also readily +decomposed, yielding perchloride of tin at the _anode_ (779.), and tin at +the _cathode_. + +902. Fused chloride of silver, placed at _x_, was also easily decomposed; +chlorine was evolved at the _anode_, and brilliant metallic silver, either +in films upon the surface of the liquid, or in crystals beneath, evolved at +the _cathode_. + +903. Water acidulated with sulphuric acid, solution of muriatic acid, +solution of sulphate of soda, fused nitre, and the fused chloride and +iodide of lead were not decomposed by this single pair of plates, excited +only by dilute sulphuric acid. + +904. These experiments give abundant proofs that a single pair of plates +can electrolyze bodies and separate their elements. They also show in a +beautiful manner the direct relation and opposition of the chemical +affinities concerned at the two points of action. In those cases where the +sum of the opposing affinities at _x_ was sufficiently beneath the sum of +the acting affinities in _v_, decomposition took place; but in those cases +where they rose higher, decomposition was effectually resisted and the +current ceased to pass (891.). + +905. It is however, evident, that the sum of acting affinities in _v_ may +be increased by using other fluids than dilute sulphuric acid, in which +latter case, as I believe, it is merely the affinity of the zinc for the +oxygen already combined with hydrogen in the water that is exerted in +producing the electric current (919.): and when the affinities are so +increased, the view I am supporting leads to the conclusion, that bodies +which resisted in the preceding experiments would then be decomposed, +because of the increased difference between their affinities and the acting +affinities thus exalted. This expectation was fully confirmed in the +following manner. + +906. A little nitric acid was added to the liquid in the vessel _r_, so as +to make a mixture which I shall call diluted nitro-sulphuric acid. On +repeating the experiments with this mixture, all the substances before +decomposed again gave way, and much more readily. But, besides that, many +which before resisted electrolyzation, now yielded up their elements. Thus, +solution of sulphate of soda, acted upon in the interstices of litmus and +turmeric paper, yielded acid at the _anode_ and alkali at the _cathode_; +solution of muriatic acid tinged by indigo yielded chlorine at the _anode_ +and hydrogen at the _cathode_; solution of nitrate of silver yielded silver +at the _cathode_. Again, fused nitre and the fused iodide and chloride of +lead were decomposable by the current of this single pair of plates, though +they were not by the former (903.). + +907. A solution of acetate of lead was apparently not decomposed by this +pair, nor did water acidulated by sulphuric acid seem at first to give way +(973.). + +908. The increase of intensity or power of the current produced by a simple +voltaic circle, with the increase of the force of the chemical action at +the exciting place, is here sufficiently evident. But in order to place it +in a clearer point of view, and to show that the decomposing effect was not +at all dependent, in the latter cases, upon the mere capability of evolving +_more_ electricity, experiments were made in which the quantity evolved +could be increased without variation in the intensity of the exciting +cause. Thus the experiments in which dilute sulphuric acid was used (899.), +were repeated, using large plates of zinc and platina in the acid; but +still those bodies which resisted decomposition before, resisted it also +under these new circumstances. Then again, where nitro-sulphuric acid was +used (906.), mere wires of platina and zinc were immersed in the exciting +acid; yet, notwithstanding this change, those bodies were now decomposed +which resisted any current tending to be formed by the dilute sulphuric +acid. For instance, muriatic acid could not be decomposed by a single pair +of plates when immersed in dilute sulphuric acid; nor did making the +solution of sulphuric acid strong, nor enlarging the size of the zinc and +platina plates immersed in it, increase the power; but if to a weak +sulphuric acid a very little nitric acid was added, then the electricity +evolved had power to decompose the muriatic acid, evolving chlorine at the +_anode_ and hydrogen at the _cathode_, even when mere wires of metals were +used. This mode of increasing the intensity of the electric current, as it +excludes the effect dependent upon many pairs of plates, or even the effect +of making any one acid stronger or weaker, is at once referable to the +condition and force of the chemical affinities which are brought into +action, and may, both in principle and practice, be considered as perfectly +distinct from any other mode. + +909. The direct reference which is thus experimentally made in the simple +voltaic circle of the _intensity_ of the electric current to the +_intensity_ of the chemical action going on at the place where the +existence and direction of the current is determined, leads to the +conclusion that by using selected bodies, as fused chlorides, salts, +solutions of acids, &c., which may act upon the metals employed with +different degrees of chemical force; and using also metals in association +with platina, or with each other, which shall differ in the degree of +chemical action exerted between them and the exciting fluid or electrolyte, +we shall be able to obtain a series of comparatively constant effects due +to electric currents of different intensities, which will serve to assist +in the construction of a scale competent to supply the means of determining +relative degrees of intensity with accuracy in future researches[A]. + + [A] In relation to this difference and its probable cause, see + considerations on inductive polarization, 1354, &c.--_Dec. 1838._ + +910. I have already expressed the view which I take of the decomposition in +the experimental place, as being the direct consequence of the superior +exertion at some other spot of the same kind of power as that to be +overcome, and therefore as the result of an antagonism of forces of the +_same_ nature (891. 904.). Those at the place of decomposition have a +re-action upon, and a power over, the exerting or determining set +proportionate to what is needful to overcome their own power; and hence a +curious result of _resistance_ offered by decompositions to the original +determining force, and consequently to the current. This is well shown in +the cases where such bodies as chloride of lead, iodide of lead, and water +would not decompose with the current produced by a single pair of zinc and +platina plates in sulphuric acid (903.), although they would with a current +of higher intensity produced by stronger chemical powers. In such cases no +sensible portion of the current passes (967.); the action is stopped; and I +am now of opinion that in the case of the law of conduction which I +described in the Fourth Series of these Researches (413.), the bodies which +are electrolytes in the fluid state cease to be such in the solid form, +because the attractions of the particles by which they are retained in +combination and in their relative position, are then too powerful for the +electric current[A]. The particles retain their places; and as +decomposition is prevented, the transmission of the electricity is +prevented also; and although a battery of many plates may be used, yet if +it be of that perfect kind which allows of no extraneous or indirect action +(1000.), the whole of the affinities concerned in the activity of that +battery are at the same time also suspended and counteracted. + + [A] Refer onwards to 1705.--_Dec. 1838._ + +911. But referring to the _resistance_ of each single case of +decomposition, it would appear that as these differ in force according to +the affinities by which the elements in the substance tend to retain their +places, they also would supply cases constituting a series of degrees by +which to measure the initial intensities of simple voltaic or other +currents of electricity, and which, combined with the scale of intensities +determined by different degrees of _acting force_ (909.), would probably +include a sufficient set of differences to meet almost every important case +where a reference to intensity would be required. + +912. According to the experiments I have already had occasion to make, I +find that the following bodies are electrolytic in the order in which I +have placed them, those which are first being decomposed by the current of +lowest intensity. These currents were always from a single pair of plates, +and may be considered as elementary _voltaic forces_. + +Iodide of potassium (solution). +Chloride of silver (fused). +Protochloride of tin (fused). +Chloride of lead (fused). +Iodide of lead (fused). +Muriatic acid (solution). +Water, acidulated with sulphuric acid. + +913. It is essential that, in all endeavours to obtain the relative +electrolytic intensity necessary for the decomposition of different bodies, +attention should be paid to the nature of the electrodes and the other +bodies present which may favour secondary actions (986.). If in +electro-decomposition one of the elements separated has an affinity for the +electrode, or for bodies present in the surrounding fluid, then the +affinity resisting decomposition is in part balanced by such power, and the +true place of the electrolyte in a table of the above kind is not obtained: +thus, chlorine combines with a positive platina electrode freely, but +iodine scarcely at all, and therefore I believe it is that the fused +chlorides stand first in the preceding Table. Again, if in the +decomposition of water not merely sulphuric but also a little nitric acid +be present, then the water is more freely decomposed, for the hydrogen at +the _cathode_ is not ultimately expelled, but finds oxygen in the nitric +acid, with which it can combine to produce a secondary result; the +affinities opposing decomposition are in this way diminished, and the +elements of the water can then be separated by a current of lower +intensity. + +914. Advantage may be taken of this principle to interpolate more minute +degrees into the scale of initial intensities already referred to (909. +911.) than is there spoken of; for by combining the force of a current +_constant_ in its intensity, with the use of electrodes consisting of +matter, having more or less affinity for the elements evolved from the +decomposing electrolyte, various intermediate degrees may be obtained. + + * * * * * + +915. Returning to the consideration of the source of electricity (878. +&c.), there is another proof of the most perfect kind that metallic contact +has nothing to do with the _production_ of electricity in the voltaic +circuit, and further, that electricity is only another mode of the exertion +of chemical forces. It is, the production of the _electric spark_ before +any contact of metals is made, and by the exertion of _pure and unmixed +chemical forces_. The experiment, which will be described further on +(956.), consists in obtaining the spark upon making contact between a plate +of zinc and a plate of copper plunged into dilute sulphuric acid. In order +to make the arrangement as elementary as possible, mercurial surfaces were +dismissed, and the contact made by a copper wire connected with the copper +plate, and then brought to touch a clean part of the zinc plate. The +electric spark appeared, and it must of necessity have existed and passed +_before the zinc and the copper were in contact_. + +916. In order to render more distinct the principles which I have been +endeavouring to establish, I will restate them in their simplest form, +according to my present belief. The electricity of the voltaic pile (856. +note) is not dependent either in its origin or its continuance upon the +contact of the metals with each other (880. 915.). It is entirely due to +chemical action (882.), and is proportionate in its intensity to the +intensity of the affinities concerned in its production (908.); and in its +quantity to the quantity of matter which has been chemically active during +its evolution (869.). This definite production is again one of the +strongest proofs that the electricity is of chemical origin. + +917. As _volta-electro-generation_ is a case of mere chemical action, so +_volta-electro-decomposition_ is simply a case of the preponderance of one +set of chemical affinities more powerful in their nature, over another set +which are less powerful: and if the instance of two opposing sets of such +forces (891.) be considered, and their mutual relation and dependence borne +in mind, there appears no necessity for using, in respect to such cases, +any other term than chemical affinity, (though that of electricity may be +very convenient,) or supposing any new agent to be concerned in producing +the results; for we may consider that the powers at the two places of +action are in direct communion and balanced against each other through the +medium of the metals (891.), fig. 76, in a manner analogous to that in +which mechanical forces are balanced against each other by the intervention +of the lever (1031.). + +918. All the facts show us that that power commonly called chemical +affinity, can be communicated to a distance through the metals and certain +forms of carbon; that the electric current is only another form of the +forces of chemical affinity; that its power is in proportion to the +chemical affinities producing it; that when it is deficient in force it may +be helped by calling in chemical aid, the want in the former being made up +by an equivalent of the latter; that, in other words, _the forces termed +chemical affinity and electricity are one and the same._ + +919. When the circumstances connected with the production of electricity in +the ordinary voltaic circuit are examined and compared, it appears that the +source of that agent, always meaning the electricity which circulates and +completes the current in the voltaic apparatus, and gives that apparatus +power and character (947. 996.), exists in the chemical action which takes +place directly between the metal and the body with which it combines, and +not at all in the subsequent action of the substance so produced with the +acid present[A]. Thus, when zinc, platina, and dilute sulphuric acid are +used, it is the union of the zinc with the oxygen of the water which +determines the current; and though the acid is essential to the removal of +the oxide so formed, in order that another portion of zinc may act on +another portion of water, it does not, by combination with that oxide, +produce any sensible portion of the current of electricity which +circulates; for the quantity of electricity is dependent upon the quantity +of zinc oxidized, and in definite proportion to it: its intensity is in +proportion to the intensity of the chemical affinity of the zinc for the +oxygen under the circumstances, and is scarcely, if at all, affected by the +use of either strong or weak acid (908.). + + [A] Wollaston, Philosophical Transactions, 1801, p. 427. + +920. Again, if zinc, platina, and muriatic acid are used, the electricity +appears to be dependent upon the affinity of the zinc for the chlorine, and +to be circulated in exact proportion to the number of particles of zinc and +chlorine which unite, being in fact an equivalent to them. + +921. But in considering this oxidation, or other direct action upon the +METAL itself, as the cause and source of the electric current, it is of the +utmost importance to observe that the oxygen or other body must be in a +peculiar condition, namely, in the state of _combination_; and not only so, +but limited still further to such a state of combination and in such +proportions as will constitute an _electrolyte_ (823.). A pair of zinc and +platina plates cannot be so arranged in oxygen gas as to produce a current +of electricity, or act as a voltaic circle, even though the temperature may +be raised so high as to cause oxidation of the zinc far more rapidly than +if the pair of plates were plunged into dilute sulphuric acid; for the +oxygen is not part of an electrolyte, and cannot therefore conduct the +forces onwards by decomposition, or even as metals do by itself. Or if its +gaseous state embarrass the minds of some, then liquid chlorine may be +taken. It does not excite a current of electricity through the two plates +by combining with the zinc, for its particles cannot transfer the +electricity active at the point of combination across to the platina. It is +not a conductor of itself, like the metals; nor is it an electrolyte, so as +to be capable of conduction during decomposition, and hence there is simple +chemical action at the spot, and no electric current[A]. + + [A] I do not mean to affirm that no traces of electricity ever appear + in such cases. What I mean is, that no electricity is evolved in any + way, due or related to the causes which excite voltaic electricity, or + proportionate to them. That which does appear occasionally is the + smallest possible fraction of that which the acting matter could + produce if arranged so as to act voltaically, probably not the one + hundred thousandth, or even the millionth part, and is very probably + altogether different in its source. + +922. It might at first be supposed that a conducting body not electrolytic, +might answer as the third substance between the zinc and the platina; and +it is true that we have some such capable of exerting chemical action upon +the metals. They must, however, be chosen from the metals themselves, for +there are no bodies of this kind except those substances and charcoal. To +decide the matter by experiment, I made the following arrangement. Melted +tin was put into a glass tube bent into the form of the letter V, fig. 78, +so as to fill the half of each limb, and two pieces of thick platina wire, +_p_, _w_, inserted, so as to have their ends immersed some depth in the +tin: the whole was then allowed to cool, and the ends _p_ and _w_ connected +with a delicate galvanometer. The part of the tube at _x_ was now reheated, +whilst the portion _y_ was retained cool. The galvanometer was immediately +influenced by the thermo-electric current produced. The heat was steadily +increased at _x_, until at last the tin and platina combined there; an +effect which is known to take place with strong chemical action and high +ignition; but not the slightest additional effect occurred at the +galvanometer. No other deflection than that due to the thermo-electric +current was observable the whole time. Hence, though a conductor, and one +capable of exerting chemical action on the tin, was used, yet, not being an +_electrolyte_, not the slightest effect of an electrical current could be +observed (947.). + +923. From this it seems apparent that the peculiar character and condition +of an electrolyte is _essential_ in one part of the voltaic circuit; and +its nature being considered, good reasons appear why it and it alone should +be effectual. An electrolyte is always a compound body: it can conduct, but +only whilst decomposing. Its conduction depends upon its decomposition and +the _transmission of its particles_ in directions parallel to the current; +and so intimate is this connexion, that if their transition be stopped, the +current is stopped also; if their course be changed, its course and +direction change with them; if they proceed in one direction, it has no +power to proceed in any other than a direction invariably dependent on +them. The particles of an electrolytic body are all so mutually connected, +are in such relation with each other through their whole extent in the +direction of the current, that if the last is not disposed of, the first is +not at liberty to take up its place in the new combination which the +powerful affinity of the most active metal tends to produce; and then the +current itself is stopped; for the dependencies of the current and the +decomposition are so mutual, that whichsoever be originally determined, +i.e. the motion of the particles or the motion of the current, the other is +invariable in its concomitant production and its relation to it. + +924. Consider, then, water as an electrolyte and also as an oxidizing body. +The attraction of the zinc for the oxygen is greater, under the +circumstances, than that of the oxygen for the hydrogen; but in combining +with it, it tends to throw into circulation a current of electricity in a +certain direction. This direction is consistent (as is found by innumerable +experiments) with the transfer of the hydrogen from the zinc towards the +platina, and the transfer in the opposite direction of fresh oxygen from +the platina towards the zinc; so that the current _can pass_ in that one +line, and, whilst it passes, can consist with and favour the renewal of the +conditions upon the surface of the zinc, which at first determined both the +combination and circulation. Hence the continuance of the action there, and +the continuation of the current. It therefore appears quite as essential +that there should be an electrolyte in the circuit, in order that the +action may be transferred forward, in a _certain constant direction,_ as +that there should be an oxidizing or other body capable of acting directly +on the metal; and it also appears to be essential that these two should +merge into one, or that the principle directly active on the metal by +chemical action should be one of the _ions_ of the electrolyte used. +Whether the voltaic arrangement be excited by solution of acids, or +alkalies, or sulphurets, or by fused substances (476.), this principle has +always hitherto, as far as I am aware, been an _anion_ (943.); and I +anticipate, from a consideration of the principles of electric action, that +it must of necessity be one of that class of bodies. + +925. If the action of the sulphuric acid used in the voltaic circuit be +considered, it will be found incompetent to produce any sensible portion of +the electricity of the current by its combination with the oxide formed, +for this simple reason, it is deficient in a most essential condition: it +forms no part of an electrolyte, nor is it in relation with any other body +present in the solution which will permit of the mutual transfer of the +particles and the consequent transfer of the electricity. It is true, that +as the plane at which the acid is dissolving the oxide of zinc formed by +the action of the water, is in contact with the metal zinc, there seems no +difficulty in considering how the oxide there could communicate an +electrical state, proportionate to its own chemical action on the acid, to +the metal, which is a conductor without decomposition. But on the side of +the acid there is no substance to complete the circuit: the water, as +water, cannot conduct it, or at least only so small a proportion that it is +merely an incidental and almost inappreciable effect (970.); and it cannot +conduct it as an electrolyte, because an electrolyte conducts in +consequence of the _mutual_ relation and action of its particles; and +neither of the elements of the water, nor even the water itself, as far as +we can perceive, are _ions_ with respect to the sulphuric acid (848.)[A]. + + [A] It will be seen that I here agree with Sir Humphry Davy, who has + experimentally supported the opinion that acids and alkalies in + combining do not produce any current of electricity. Philosophical + Transactions, 1826, p. 398. + +926. This view of the secondary character of the sulphuric acid as an agent +in the production of the voltaic current, is further confirmed by the fact, +that the current generated and transmitted is directly and exactly +proportional to the quantity of water decomposed and the quantity of zinc +oxidized (868. 991.), and is the same as that required to decompose the +same quantity of water. As, therefore, the decomposition of the water shows +that the electricity has passed by its means, there remains no other +electricity to be accounted for or to be referred to any action other than +that of the zinc and the water on each other. + +927. The general case (for it includes the former one (924.),) of acids and +bases, may theoretically be stated in the following manner. Let _a_, fig. +79, be supposed to be a dry oxacid, and _b_ a dry base, in contact at _c_, +and in electric communication at their extremities by plates of platina +_pp_, and a platina wire _w_. If this acid and base were fluid, and +combination took place at _c_, with an affinity ever so vigorous, and +capable of originating an electric current, the current could not circulate +in any important degree; because, according to the experimental results, +neither _a_ nor _b_ could conduct without being decomposed, for they are +either electrolytes or else insulators, under all circumstances, except to +very feeble and unimportant currents (970. 986.). Now the affinities at _c_ +are not such as tend to cause the _elements_ either of _a_ or _b_ to +separate, but only such as would make the two bodies combine together as a +whole; the point of action is, therefore, insulated, the action itself +local (921. 947.), and no current can be formed. + +928. If the acid and base be dissolved in water, then it is possible that a +small portion of the electricity due to chemical action may be conducted by +the water without decomposition (966. 984.); but the quantity will be so +small as to be utterly disproportionate to that due to the equivalents of +chemical force; will be merely incidental; and, as it does not involve the +essential principles of the voltaic pile, it forms no part of the phenomena +at present under investigation[A]. + + [A] It will I trust be fully understood, that in these investigations + I am not professing to take an account of every small, incidental, or + barely possible effect, dependent upon slight disturbances of the + electric fluid during chemical action, but am seeking to distinguish + and identify those actions on which the power of the voltaic battery + essentially depends. + +929. If for the oxacid a hydracid be substituted (927.),--as one analogous +to the muriatic, for instance,--then the state of things changes +altogether, and a current due to the chemical action of the acid on the +base is possible. But now both the bodies act as electrolytes, for it is +only one principle of each which combine mutually,--as, for instance, the +chlorine with the metal,--and the hydrogen of the acid and the oxygen of +the base are ready to traverse with the chlorine of the acid and the metal +of the base in conformity with the current and according to the general +principles already so fully laid down. + +930. This view of the oxidation of the metal, or other _direct_ chemical +action upon it, being the sole cause of the production of the electric +current in the ordinary voltaic pile, is supported by the effects which +take place when alkaline or sulphuretted solutions (931. 943.) are used for +the electrolytic conductor instead of dilute sulphuric acid. It was in +elucidation of this point that the experiments without metallic contact, +and with solution of alkali as the exciting fluid, already referred to +(884.), were made. + +931. Advantage was then taken of the more favourable condition offered, +when metallic contact is allowed (895.), and the experiments upon the +decomposition of bodies by a single pair of plates (899.) were repeated, +solution of caustic potassa being employed in the vessel _v_, fig. 77. in +place of dilute sulphuric acid. All the effects occurred as before: the +galvanometer was deflected; the decompositions of the solutions of iodide +of potassium, nitrate of silver, muriatic acid, and sulphate of soda ensued +at _x_; and the places where the evolved principles appeared, as well as +the deflection of the galvanometer, indicated a current in the _same +direction_ as when acid was in the vessel _v_; i.e. from the zinc through +the solution to the platina, and back by the galvanometer and substance +suffering decomposition to the zinc. + +932. The similarity in the action of either dilute sulphuric acid or +potassa goes indeed far beyond this, even to the proof of identity in +_quantity_ as well as in _direction_ of the electricity produced. If a +plate of amalgamated zinc be put into a solution of potassa, it is not +sensibly acted upon; but if touched in the solution by a plate of platina, +hydrogen is evolved on the surface of the latter metal, and the zinc is +oxidized exactly as when immersed in dilute sulphuric acid (863.). I +accordingly repeated the experiment before described with weighed plates of +zinc (864. &c.), using however solution of potassa instead of dilute +sulphuric acid. Although the time required was much longer than when acid +was used, amounting to three hours for the oxidizement of 7.55 grains of +zinc, still I found that the hydrogen evolved at the platina plate was the +equivalent of the metal oxidized at the surface of the zinc. Hence the +whole of the reasoning which was applicable in the former instance applies +also here, the current being in the same direction, and its decomposing +effect in the same degree, as if acid instead of alkali had been used +(868.). + +933. The proof, therefore, appears to me complete, that the combination of +the acid with the oxide, in the former experiment, had nothing to do with +the production of the electric current; for the same current is here +produced when the action of the acid is absent, and the reverse action of +an alkali is present. I think it cannot be supposed for a moment, that the +alkali acted chemically as an acid to the oxide formed; on the contrary, +our general chemical knowledge leads to the conclusion, that the ordinary +metallic oxides act rather as acids to the alkalies; yet that kind of +action would tend to give a reverse current in the present case, if any +were due to the union of the oxide of the exciting metal with the body +which combines with it. But instead of any variation of this sort, the +direction of the electricity was constant, and its quantity also directly +proportional to the water decomposed, or the zinc oxidized. There are +reasons for believing that acids and alkalies, when in contact with metals +upon which they cannot act directly, still have a power of influencing +their attractions for oxygen (941.); but all the effects in these +experiments prove, I think, that it is the oxidation of the metal +necessarily dependent upon, and associated as it is with, the +electrolyzation of the water (921. 923.) that produces the current; and +that the acid or alkali merely acts as solvents, and by removing the +oxidized zinc, allows other portions to decompose fresh water, and so +continues the evolution or determination of the current. + +934. The experiments were then varied by using solution of ammonia instead +of solution of potassa; and as it, when pure, is like water, a bad +conductor (554.), it was occasionally improved in that power by adding +sulphate of ammonia to it. But in all the cases the results were the same +as before; decompositions of the same kind were effected, and the electric +current producing these was in the same direction as in the experiments +just described. + +935. In order to put the equal and similar action of acid and alkali to +stronger proof, arrangements were made as in fig. 80.; the glass vessel A +contained dilute sulphuric acid, the corresponding glass vessel B solution +of potassa, PP was a plate of platina dipping into both solutions, and ZZ +two plates of amalgamated zinc connected with a delicate galvanometer. When +these were plunged at the same time into the two vessels, there was +generally a first feeble effect, and that in favour of the alkali, i.e. the +electric current tended to pass through the vessels in the direction of the +arrow, being the reverse direction of that which the acid in A would have +produced alone: but the effect instantly ceased, and the action of the +plates in the vessels was so equal, that, being contrary because of the +contrary position of the plates, no permanent current resulted. + +936. Occasionally a zinc plate was substituted for the plate PP, and +platina plates for the plates ZZ; but this caused no difference in the +results: nor did a further change of the middle plate to copper produce any +alteration. + +937. As the opposition of electro-motive pairs of plates produces results +other than those due to the mere difference of their independent actions +(1011. 1045.), I devised another form of apparatus, in which the action of +acid and alkali might be more directly compared. A cylindrical glass cup, +about two inches deep within, an inch in internal diameter, and at least a +quarter of an inch in thickness, was cut down the middle into halves, fig. +81. A broad brass ring, larger in diameter than the cup, was supplied with +a screw at one side; so that when the two halves of the cup were within the +ring, and the screw was made to press tightly against the glass, the cup +held any fluid put into it. Bibulous paper of different degrees of +permeability was then cut into pieces of such a size as to be easily +introduced between the loosened halves of the cup, and served when the +latter were tightened again to form a porous division down the middle of +the cup, sufficient to keep any two fluids on opposite sides of the paper +from mingling, except very slowly, and yet allowing them to act freely as +one _electrolyte_. The two spaces thus produced I will call the cells A and +B, fig. 82. This instrument I have found of most general application in the +investigation of the relation of fluids and metals amongst themselves and +to each other. By combining its use with that of the galvanometer, it is +easy to ascertain the relation of one metal with two fluids, or of two +metals with one fluid, or of two metals and two fluids upon each other. + +938. Dilute sulphuric acid, sp. gr. 1.25, was put into the cell A, and a +strong solution of caustic potassa into the cell B; they mingled slowly +through the paper, and at last a thick crust of sulphate of potassa formed +on the side of the paper next to the alkali. A plate of clean platina was +put into each cell and connected with a delicate galvanometer, but no +electric current could be observed. Hence the _contact_ of acid with one +platina plate, and alkali with the other, was unable to produce a current; +nor was the combination of the acid with the alkali more effectual (925.). + +939. When one of the platina plates was removed and a zinc plate +substituted, either amalgamated or not, a strong electric current was +produced. But, whether the zinc were in the acid whilst the platina was in +the alkali, or whether the reverse order were chosen, the electric current +was always from the zinc through the electrolyte to the platina, and back +through the galvanometer to the zinc, the current seeming to be strongest +when the zinc was in the alkali and the platina in the acid. + +940. In these experiments, therefore, the acid seems to have no power over +the alkali, but to be rather inferior to it in force. Hence there is no +reason to suppose that the combination of the oxide formed with the acid +around it has any direct influence in producing the electricity evolved, +the whole of which appears to be due to the oxidation of the metal (919.). + +941. The alkali, in fact, is superior to the acid in bringing a metal into +what is called the positive state; for if plates of the same metal, as +zinc, tin, lead, or copper, be used both in the acid or alkali, the +electric current is from the alkali across the cell to the acid, and back +through the galvanometer to the alkali, as Sir Humphry Davy formerly stated +[A]. This current is so powerful, that if amalgamated zinc, or tin, or lead +be used, the metal in the acid evolves hydrogen the moment it is placed in +communication with that in the alkali, not from any direct action of the +acid upon it, for if the contact be broken the action ceases, but because +it is powerfully negative with regard to the metal in the alkali. + + [A] Elements of Chemical Philosophy, p. 149; or Philosophical + Transactions, 1826, p. 403. + +942. The superiority of alkali is further proved by this, that if zinc and +tin be used, or tin and lead, whichsoever metal is put into the alkali +becomes positive, that in the acid being negative. Whichsoever is in the +alkali is oxidized, whilst that in the acid remains in the metallic state, +as far as the electric current is concerned. + +943. When sulphuretted solutions are used (930.) in illustration of the +assertion, that it is the chemical action of the metal and one of the +_ions_ of the associated electrolyte that produces all the electricity of +the voltaic circuit, the proofs are still the same. Thus, as Sir Humphry +Davy[A] has shown, if iron and copper be plunged into dilute acid, the +current is from the iron through the liquid to the copper; in solution of +potassa it is in the same direction, but in solution of sulphuret of +potassa it is reversed. In the two first cases it is oxygen which combines +with the iron, in the latter sulphur which combines with the copper, that +produces the electric current; but both of these are _ions_, existing as +such in the electrolyte, which is at the same moment suffering +decomposition; and, what is more, both of these are _anions_, for they +leave the electrolytes at their _anodes_, and act just as chlorine, iodine, +or any other _anion_ would act which might have been previously chosen as +that which should be used to throw the voltaic circle into activity. + + [A] Elements of Chemical Philosophy, p. 148. + +944. The following experiments complete the series of proofs of the origin +of the electricity in the voltaic pile. A fluid amalgam of potassium, +containing not more than a hundredth of that metal, was put into pure +water, and connected, through the galvanometer with a plate of platina in +the same water. There was immediately an electric current from the amalgam +through the electrolyte to the platina. This must have been due to the +oxidation only of the metal, for there was neither acid nor alkali to +combine with, or in any way act on, the body produced. + +945. Again, a plate of clean lead and a plate of platina were put into +_pure_ water. There was immediately a powerful current produced from the +lead through the fluid to the platina: it was even intense enough to +decompose solution of the iodide of potassium when introduced into the +circuit in the form of apparatus already described (880.), fig. 73. Here no +action of acid or alkali on the oxide formed from the lead could supply the +electricity: it was due solely to the oxidation of the metal. + + * * * * * + +946. There is no point in electrical science which seems to me of more +importance than the state of the metals and the electrolytic conductor in a +simple voltaic circuit _before and at_ the moment when metallic contact is +first completed. If clearly understood, I feel no doubt it would supply us +with a direct key to the laws under which the great variety of voltaic +excitements, direct and incidental, occur, and open out new fields of +research for our investigation[A]. + + [A] In connexion with this part of the subject refer now to Series XI. + 1164, Series XII. 1343-1358, and Series XIII. 1621. &c.--_Dec. 1838._ + +947. We seem to have the power of deciding to a certain extent in numerous +cases of chemical affinity, (as of zinc with the oxygen of water, &c. &c.) +which of _two modes of action of the attractive power_ shall be exerted +(996.). In the one mode we can transfer the power onwards, and make it +produce elsewhere its equivalent of action (867. 917.); in the other, it is +not transferred, but exerted wholly at the spot. The first is the case of +volta-electric excitation, the other ordinary chemical affinity: but both +are chemical actions and due to one force or principle. + +948. The general circumstances of the former mode occur in all instances of +voltaic currents, but may be considered as in their perfect condition, and +then free from those of the second mode, in some only of the cases; as in +those of plates of zinc and platina in solution of potassa, or of +amalgamated zinc and platina in dilute sulphuric acid. + +949. Assuming it sufficiently proved, by the preceding experiments and +considerations, that the electro-motive action depends, when zinc, platina, +and dilute sulphuric acid are used, upon the mutual affinity of the metal +zinc and the oxygen of the water (921. 924.), it would appear that the +metal, when alone, has not power enough, under the circumstances, to take +the oxygen and expel the hydrogen from the water; for, in fact, no such +action takes place. But it would also appear that it has power so far to +act, by its attraction for the oxygen of the particles in contact with it, +as to place the similar forces already active between these and the other +particles of oxygen and the particles of hydrogen in the water, in a +peculiar state of tension or polarity, and probably also at the same time +to throw those of its own particles which are in contact with the water +into a similar but opposed state. Whilst this state is retained, no further +change occurs; but when it is relieved, by completion of the circuit, in +which case the forces determined in opposite directions, with respect to +the zinc and the electrolyte, are found exactly competent to neutralize +each other, then a series of decompositions and recompositions takes place +amongst the particles of oxygen and hydrogen constituting the water, +between the place of contact with the platina and the place where the zinc +is active; these intervening particles being evidently in close dependence +upon and relation to each other. The zinc forms a direct compound with +those particles of oxygen which were, previously, in divided relation to +both it and the hydrogen: the oxide is removed by the acid, and a fresh +surface of zinc is presented to the water, to renew and repeat the action. + +950. Practically, the state of tension is best relieved by dipping a metal +which has less attraction for oxygen than the zinc, into the dilute acid, +and making it also touch the zinc. The force of chemical affinity, which +has been influenced or polarized in the particles of the water by the +dominant attraction of the zinc for the oxygen, is then transferred, in a +most extraordinary manner, through the two metals, so as to re-enter upon +the circuit in the electrolytic conductor, which, unlike the metals in that +respect, cannot convey or transfer it without suffering decomposition; or +rather, probably, it is exactly balanced and neutralized by the force which +at the same moment completes the combination of the zinc with the oxygen of +the water. The forces, in fact, of the two particles which are acting +towards each other, and which are therefore in opposite directions, are the +origin of the two opposite forces, or directions of force, in the current. +They are of necessity equivalent to each other. Being transferred forward +in contrary directions, they produce what is called the voltaic current: +and it seems to me impossible to resist the idea that it must be preceded +by a _state of tension_ in the fluid, and between the fluid and the zinc; +the _first consequence_ of the affinity of the zinc for the oxygen of the +water. + +951. I have sought carefully for indications of a state of tension in the +electrolytic conductor; and conceiving that it might produce something like +structure, either before or during its discharge, I endeavoured to make +this evident by polarized light. A glass cell, seven inches long, one inch +and a half wide, and six inches deep, had two sets of platina electrodes +adapted to it, one set for the ends, and the other for the sides. Those for +the _sides_ were seven inches long by three inches high, and when in the +cell were separated by a little frame of wood covered with calico; so that +when made active by connexion with a battery upon any solution in the cell, +the bubbles of gas rising from them did not obscure the central parts of +the liquid. + +952. A saturated solution of sulphate of soda was put into the cell, and +the electrodes connected with a battery of 150 pairs of 4-inch plates: the +current of electricity was conducted across the cell so freely, that the +discharge was as good as if a wire had been used. A ray of polarized light +was then transmitted through this solution, directly across the course of +the electric current, and examined by an analysing plate; but though it +penetrated seven inches of solution thus subject to the action of the +electricity, and though contact was sometimes made, sometimes broken, and +occasionally reversed during the observations, not the slightest trace of +action on the ray could be perceived. + +953. The large electrodes were then removed, and others introduced which +fitted the _ends_ of the cell. In each a slit was cut, so as to allow the +light to pass. The course of the polarized ray was now parallel to the +current, or in the direction of its axis (517.); but still no effect, under +any circumstances of contact or disunion, could be perceived upon it. + +954. A strong solution of nitrate of lead was employed instead of the +sulphate of soda, but no effects could be detected. + +955. Thinking it possible that the discharge of the electric forces by the +successive decompositions and recompositions of the particles of the +electrolyte might neutralize and therefore destroy any effect which the +first state of tension could by possibility produce, I took a substance +which, being an excellent electrolyte when fluid, was a perfect insulator +when solid, namely, borate of lead, in the form of a glass plate, and +connecting the sides and the edges of this mass with the metallic plates, +sometimes in contact with the poles of a voltaic battery, and sometimes +even with the electric machine, for the advantage of the much higher +intensity then obtained, I passed a polarized ray across it in various +directions, as before, but could not obtain the slightest appearance of +action upon the light. Hence I conclude, that notwithstanding the new and +extraordinary state which must be assumed by an electrolyte, either during +decomposition (when a most enormous quantity of electricity must be +traversing it), or in the state of tension which is assumed as preceding +decomposition, and which might be supposed to be retained in the solid form +of the electrolyte, still it has no power of affecting a polarized ray of +light; for no kind of structure or tension can in this way be rendered +evident. + +956. There is, however, one beautiful experimental proof of a state of +tension acquired by the metals and the electrolyte before the electric +current is produced, and _before contact_ of the different metals is made +(915.); in fact, at that moment when chemical forces only are efficient as +a cause of action. I took a voltaic apparatus, consisting of a single pair +of large plates, namely, a cylinder of amalgamated zinc, and a double +cylinder of copper. These were put into a jar containing dilute sulphuric +acid[A], and could at pleasure be placed in metallic communication by a +copper wire adjusted so as to dip at the extremities into two cups of +mercury connected with the two plates. + + [A] When nitro-sulphuric acid is used, the spark is more powerful, but + local chemical action can then commence, and proceed without requiring + metallic contact. + +957. Being thus arranged, there was no chemical action whilst the plates +were not connected. On _making_ the connexion a spark was obtained[A], and +the solution was immediately decomposed. On breaking it, the usual spark +was obtained, and the decomposition ceased. In this case it is evident that +the first spark must have occurred before metallic contact was made, for it +passed through an interval of air; and also that it must have tended to +pass before the electrolytic action began; for the latter could not take +place until the current passed, and the current could not pass before the +spark appeared. Hence I think there is sufficient proof, that as it is the +zinc and water which by their mutual action produce the electricity of this +apparatus, so these, by their first contact with each other, were placed in +a state of powerful tension (951.), which, though it could not produce the +actual decomposition of the water, was able to make a spark of electricity +pass between the zinc and a fit discharger as soon as the interval was +rendered sufficiently small. The experiment demonstrates the direct +production of the electric spark from pure chemical forces. + + [A] It has been universally supposed that no spark is produced on + making the contact between a single pair of plates. I was led to + expect one from the considerations already advanced in this paper. The + wire of communication should be short; for with a long wire, + circumstances strongly affecting the spark are introduced. + +958. There are a few circumstances connected with the production of this +spark by a single pair of plates, which should be known, to ensure success +to the experiment[B]. When the amalgamated surfaces of contact are quite +clean and dry, the spark, on making contact, is quite as brilliant as on +breaking it, if not even more so. When a film of oxide or dirt was present +at either mercurial surface, then the first spark was often feeble, and +often failed, the breaking spark, however, continuing very constant and +bright. When a little water was put over the mercury, the spark was greatly +diminished in brilliancy, but very regular both on making and breaking +contact. When the contact was made between clean platina, the spark was +also very small, but regular both ways. The true electric spark is, in +fact, very small, and when surfaces of mercury are used, it is the +combustion of the metal which produces the greater part of the light. The +circumstances connected with the burning of the mercury are most favourable +on breaking contact; for the act of separation exposes clean surfaces of +metal, whereas, on making contact, a thin film of oxide, or soiling matter, +often interferes. Hence the origin of the general opinion that it is only +when the contact is broken that the spark passes. + + [B] See in relation to precautions respecting a spark, 1074.--_Dec. + 1838._ + +959. With reference to the other set of cases, namely, those of local +action (947.) in which chemical affinity being exerted causes no +transference of the power to a distance where no electric current is +produced, it is evident that forces of the most intense kind must be +active, and in some way balanced in their activity, during such +combinations; these forces being directed so immediately and exclusively +towards each other, that no signs of the powerful electric current they can +produce become apparent, although the same final state of things is +obtained as if that current had passed. It was Berzelius, I believe, who +considered the heat and light evolved in cases of combustion as the +consequences of this mode of exertion of the electric powers of the +combining particles. But it will require a much more exact and extensive +knowledge of the nature of electricity, and the manner in which it is +associated with the atoms of matter, before we can understand accurately +the action of this power in thus causing their union, or comprehend the +nature of the great difference which it presents in the two modes of action +just distinguished. We may imagine, but such imaginations must for the time +be classed with the great mass of _doubtful knowledge_ (876.) which we +ought rather to strive to diminish than to increase; for the very extensive +contradictions of this knowledge by itself shows that but a small portion +of it can ultimately prove true[A]. + + [A] Refer to 1738, &c. Series XIV.--_Dec. 1838._ + +960. Of the two modes of action in which chemical affinity is exerted, it +is important to remark, that that which produces the electric current is as +_definite_ as that which causes ordinary chemical combination; so that in +examining the _production_ or _evolution_ of electricity in cases of +combination or decomposition, it will be necessary, not merely to observe +certain effects dependent upon a current of electricity, but also their +_quantity_: and though it may often happen that the forces concerned in any +particular case of chemical action may be partly exerted in one mode and +partly in the other, it is only those which are efficient in producing the +current that have any relation to voltaic action. Thus, in the combination +of oxygen and hydrogen to produce water, electric powers to a most enormous +amount are for the time active (861. 873.); but any mode of examining the +flame which they form during energetic combination, which has as yet been +devised, has given but the feeblest traces. These therefore may not, +cannot, be taken as evidences of the nature of the action; but are merely +incidental results, incomparably small in relation to the forces concerned, +and supplying no information of the way in which the particles are active +on each other, or in which their forces are finally arranged. + +961. That such cases of chemical action produce no _current of +electricity_, is perfectly consistent with what we know of the voltaic +apparatus, in which it is essential that one of the combining elements +shall form part of, or be in direct relation with, an electrolytic +conductor (921. 923.). That such cases produce _no free electricity of +tension_, and that when they are converted into cases of voltaic action +they produce a current in which the opposite forces are so equal as to +neutralize each other, prove the equality of the forces in the opposed +acting particles of matter, and therefore the equality of electric power in +those quantities of matter which are called _electro-chemical equivalents_ +(824). Hence another proof of the definite nature of electro-chemical +action (783. &c.), and that chemical affinity and electricity are forms of +the same power (917. &c.). + +962. The direct reference of the effects produced by the voltaic pile at +the place of experimental decomposition to the chemical affinities active +at the place of excitation (891. 917.), gives a very simple and natural +view of the cause why the bodies (or _ions_) evolved pass in certain +directions; for it is only when they pass in those directions that their +forces can consist with and compensate (in direction at least) the superior +forces which are dominant at the place where the action of the whole is +determined. If, for instance, in a voltaic circuit, the activity of which +is determined, by the attraction of zinc for the oxygen of water, the zinc +move from right to left, then any other _cation_ included in the circuit, +being part of an electrolyte, or forming part of it at the moment, will +also move from right to left: and as the oxygen of the water, by its +natural affinity for the zinc, moves from left to right, so any other body +of the same class with it (i.e. any other _anion_), under its government +for the time, will move from left to right. + +963. This I may illustrate by reference to fig. 83, the double circle of +which may represent a complete voltaic circuit, the direction of its forces +being determined by supposing for a moment the zinc _b_ and the platina _c_ +as representing plates of those metals acting upon water, _d, e_, and other +substances, but having their energy exalted so as to effect several +decompositions by the use of a battery at _a_ (989.). This supposition may +be allowed, because the action in the battery will only consist of +repetitions of what would take place between _b_ and _c_, if they really +constituted but a single pair. The zinc _b_, and the oxygen _d_, by their +mutual affinity, tend to unite; but as the oxygen is already in association +with the hydrogen _e_, and has its inherent chemical or electric powers +neutralized for the time by those of the latter, the hydrogen _e_ must +leave the oxygen _d_, and advance in the direction of the arrow head, or +else the zinc _b_ cannot move in the same direction to unite to the oxygen +_d_, nor the oxygen _d_ move in the contrary direction to unite to the zinc +_b_, the relation of the _similar_ forces of _b_ and _c_, in contrary +directions, to the _opposite_ forces of _d_ being the preventive. As the +hydrogen _e_ advances, it, on coming against the platina _c, f_, which +forms a part of the circuit, communicates its electric or chemical forces +through it to the next electrolyte in the circuit, fused chloride of lead, +_g, h_, where the chlorine must move in conformity with the direction of +the oxygen at _d_, for it has to compensate the forces disturbed in its +part of the circuit by the superior influence of those between the oxygen +and zinc at _d, b_, aided as they are by those of the battery _a_; and for +a similar reason the lead must move in the direction pointed out by the +arrow head, that it may be in right relation to the first moving body of +its own class, namely, the zinc _b_. If copper intervene in the circuit +from _i_ to _k_, it acts as the platina did before; and if another +electrolyte, as the iodide of tin, occur at _l, m_, then the iodine _l_, +being an _anion_, must move in conformity with the exciting _anion_, +namely, the oxygen _d_, and the _cation_ tin _m_ move in correspondence +with the other _cations b, e_, and _h_, that the chemical forces may be in +equilibrium as to their direction and quantity throughout the circuit. +Should it so happen that the anions in their circulation can combine with +the metals at the _anodes_ of the respective electrolytes, as would be the +case at the platina _f_ and the copper _k_, then those bodies becoming +parts of electrolytes, under the influence of the current, immediately +travel; but considering their relation to the zinc _b_, it is evidently +impossible that they can travel in any other direction than what will +accord with its course, and therefore can never tend to pass otherwise than +_from_ the anode and _to_ the cathode. + +964. In such a circle as that delineated, therefore, all the known _anions_ +may be grouped within, and all the _cations_ without. If any number of them +enter as _ions_ into the constitution of _electrolytes_, and, forming one +circuit, are simultaneously subject to one common current, the anions must +move in accordance with each other in one direction, and the cations in the +other. Nay, more than that, equivalent portions of these bodies must so +advance in opposite directions: for the advance of every 32.5 parts of the +zinc _b_ must be accompanied by a motion in the opposite direction of 8 +parts of oxygen at _d_, of 36 parts of chlorine at _g_, of 126 parts of +iodine at _l_; and in the same direction by electro-chemical equivalents of +hydrogen, lead, copper and tin, at _e, h, k_. and _m_. + +965. If the present paper be accepted as a correct expression of facts, it +will still only prove a confirmation of certain general views put forth by +Sir Humphry Davy in his Bakerian Lecture for 1806[A], and revised and +re-stated by him in another Bakerian Lecture, on electrical and chemical +changes, for the year 1826[B]. His general statement is, that "_chemical +and electrical attractions were produced by the same cause, acting in one +case on particles, in the other on masses, of matter; and that the same +property, under different modifications, was the cause of all the phenomena +exhibited by different voltaic combinations_[C]." This statement I believe +to be true; but in admitting and supporting it, I must guard myself from +being supposed to assent to all that is associated with it in the two +papers referred to, or as admitting the experiments which are there quoted +as decided proofs of the truth of the principle. Had I thought them so, +there would have been no occasion for this investigation. It may be +supposed by some that I ought to go through these papers, distinguishing +what I admit from what I reject, and giving good experimental or +philosophical reasons for the judgment in both cases. But then I should be +equally bound to review, for the same purpose, all that has been written +both for and against the necessity of metallic contact,--for and against +the origin of voltaic electricity in chemical action,--a duty which I may +not undertake in the present paper[D]. + + [A] Philosophical Transactions, 1807. + + [B] Ibid. 1826, p. 383. + + [C] Ibid. 1826, p. 389. + + [D] I at one time intended to introduce here, in the form of a note, a + table of reference to the papers of the different philosophers who + have referred the origin of the electricity in the voltaic pile to + contact, or to chemical action, or to both; but on the publication of + the first volume of M. Becquerel's highly important and valuable + Traite de l'Electricite et du Magnetisme, I thought it far better to + refer to that work for these references, and the views held by the + authors quoted. See pages 86, 91, 104, 110, 112, 117, 118, 120, 151, + 152, 224, 227, 228, 232, 233, 252, 255, 257, 258, 290, &c.--July 3rd, + 1834. + + +P ii. _On the Intensity necessary for Electrolyzation._ + +966. It became requisite, for the comprehension of many of the conditions +attending voltaic action, to determine positively, if possible, whether +electrolytes could resist the action of an electric current when beneath a +certain intensity? whether the intensity at which the current ceased to act +would be the same for all bodies? and also whether the electrolytes thus +resisting decomposition would conduct the electric current as a metal does, +after they ceased to conduct as electrolytes, or would act as perfect +insulators? + +967. It was evident from the experiments described (904. 906.) that +different bodies were decomposed with very different facilities, and +apparently that they required for their decomposition currents of different +intensities, resisting some, but giving way to others. But it was needful, +by very careful and express experiments, to determine whether a current +could really pass through, and yet not decompose an electrolyte (910.). + +968. An arrangement (fig. 84.) was made, in which two glass vessels +contained the same dilute sulphuric acid, sp. gr. 1.25. The plate _z_ was +amalgamated zinc, in connexion, by a platina wire _a_, with the platina +plate _e_; _b_ was a platina wire connecting the two platina plates PP'; +_c_ was a platina wire connected with the platina plate P". On the plate +_e_ was placed a piece of paper moistened in solution of iodide of +potassium: the wire _c_ was so curved that its end could be made to rest at +pleasure on this paper, and show, by the evolution of iodine there, whether +a current was passing; or, being placed in the dotted position, it formed a +direct communication with the platina plate _e_, and the electricity could +pass without causing decomposition. The object was to produce a current by +the action of the acid on the amalgamated zinc in the first vessel A; to +pass it through the acid in the second vessel B by platina electrodes, that +its power of decomposing water might, if existing, be observed; and to +verify the existence of the current at pleasure, by decomposition at _e_, +without involving the continual obstruction to the current which would +arise from making the decomposition there constant. The experiment, being +arranged, was examined and the existence of a current ascertained by the +decomposition at _e_; the whole was then left with the end of the wire _c_ +resting on the plate _e_, so as to form a constant metallic communication +there. + +969. After several hours, the end of the wire _c_ was replaced on the +test-paper at _e_: decomposition occurred, and _the proof_ of a passing +current was therefore complete. The current was very feeble compared to +what it had been at the beginning of the experiment, because of a peculiar +state acquired by the metal surfaces in the second vessel, which caused +them to oppose the passing current by a force which they possess under +these circumstances (1040.). Still it was proved, by the decomposition, +that this state of the plates in the second vessel was not able entirely to +stop the current determined in the first, and that was all that was needful +to be ascertained in the present inquiry. + +970. This apparatus was examined from time to time, and an electric current +always found circulating through it, until twelve days had elapsed, during +which the water in the second vessel had been constantly subject to its +action. Notwithstanding this lengthened period, not the slightest +appearance of a bubble upon either of the plates in that vessel occurred. +From the results of the experiment, I conclude that a current _had_ passed, +but of so low an intensity as to fall beneath that degree at which the +elements of water, unaided by any secondary force resulting from the +capability of combination with the matter of the electrodes, or of the +liquid surrounding them, separated from each other. + +971. It may be supposed, that the oxygen and hydrogen had been evolved in +such small quantities as to have entirely dissolved in the water, and +finally to have escaped at the surface, or to have reunited into water. +That the hydrogen can be so dissolved was shown in the first vessel; for +after several days minute bubbles of gas gradually appeared upon a glass +rod, inserted to retain the zinc and platina apart, and also upon the +platina plate itself, and these were hydrogen. They resulted principally in +this way:--notwithstanding the amalgamation of the zinc, the acid exerted a +little direct action upon it, so that a small stream of hydrogen bubbles +was continually rising from its surface; a little of this hydrogen +gradually dissolved in the dilute acid, and was in part set free against +the surfaces of the rod and the plate, according to the well-known action +of such solid bodies in solutions of gases (623. &c.). + +972. But if the gases had been evolved in the second vessel by the +decomposition of water, and had tended to dissolve, still there would have +been every reason to expect that a few bubbles should have appeared on the +electrodes, especially on the negative one, if it were only because of its +action as a nucleus on the solution supposed to be formed; but none +appeared even after twelve days. + +973. When a few drops only of nitric acid were added to the vessel A, fig. +84, then the results were altogether different. In less than five minutes +bubbles of gas appeared on the plates P' and P" in the second vessel. To +prove that this was the effect of the electric current (which by trial at +_c_ was found at the same time to be passing,) the connexion at _c_ was +broken, the plates P'P" cleared from bubbles and left in the acid of the +vessel B, for fifteen minutes: during that time no bubbles appeared upon +them; but on restoring the communication at _c_, a minute did not elapse +before gas appeared in bubbles upon the plates. The proof, therefore, is +most full and complete, that the current excited by dilute sulphuric acid +with a little nitric acid in vessel A, has intensity enough to overcome the +chemical affinity exerted between the oxygen and hydrogen of the water in +the vessel B, whilst that excited by dilute sulphuric acid alone has _not_ +sufficient intensity. + +974. On using a strong solution of caustic potassa in the vessel A, to +excite the current, it was found by the decomposing effects at _e_, that +the current passed. But it had not intensity enough to decompose the water +in the vessel B; for though left for fourteen days, during the whole of +which time the current was found to be passing, still not the slightest +appearance of gas appeared on the plates P'P", nor any other signs of the +water having suffered decomposition. + +975. Sulphate of soda in solution was then experimented with, for the +purpose of ascertaining with respect to it, whether a certain electrolytic +intensity was also required for its decomposition in this state, in analogy +with the result established with regard to water (974). The apparatus was +arranged as in fig. 85; P and Z are the platina and zinc plates dipping +into a solution of common salt; _a_ and _b_ are platina plates connected by +wires of platina (except in the galvanometer _g_) with P and Z; _c_ is a +connecting wire of platina, the ends of which can be made to rest either on +the plates _a, b_, or on the papers moistened in solutions which are placed +upon them; so that the passage of the current without decomposition, or +with one or two decompositions, was under ready command, as far as +arrangement was concerned. In order to change the _anodes_ and _cathodes_ +at the places of decomposition, the form of apparatus fig. 86, was +occasionally adopted. Here only one platina plate, _c_, was used; both +pieces of paper on which decomposition was to be effected were placed upon +it, the wires from P and Z resting upon these pieces of paper, or upon the +plate _c_, according as the current with or without decomposition of the +solutions was required. + +976. On placing solution of iodide of potassium in paper at one of the +decomposing localities, and solution of sulphate of soda at the other, so +that the electric current should pass through both at once, the solution of +iodide was slowly decomposed, yielding iodine at the _anode_ and alkali at +the _cathode_; but the solution of sulphate of soda exhibited no signs of +decomposition, neither acid nor alkali being evolved from it. On placing +the wires so that the iodide alone was subject to the action of the current +(900.), it was quickly and powerfully decomposed; but on arranging them so +that the sulphate of soda alone was subject to action, it still refused to +yield up its elements. Finally, the apparatus was so arranged under a wet +bell-glass, that it could be left for twelve hours, the current passing +during the whole time through a solution of sulphate of soda, retained in +its place by only two thicknesses of bibulous litmus and turmeric paper. At +the end of that time it was ascertained by the decomposition of iodide of +potassium at the second place of action, that the current was passing and +had passed for the twelve hours, and yet no trace of acid or alkali from +the sulphate of soda appeared. + +977. From these experiments it may, I think, be concluded, that a solution +of sulphate of soda can conduct a current of electricity, which is unable +to decompose the neutral salt present; that this salt in the state of +solution, like water, requires a certain electrolytic intensity for its +decomposition; and that the necessary intensity is much higher for this +substance than for the iodide of potassium in a similar state of solution. + +978. I then experimented on bodies rendered decomposable by fusion, and +first on _chloride of lead_. The current was excited by dilute sulphuric +acid without any nitric acid between zinc and platina plates, fig. 87, and +was then made to traverse a little chloride of lead fused upon glass at +_a_, a paper moistened in solution of iodide of potassium at _b_, and a +galvanometer at _g_. The metallic terminations at _a_ and _b_ were of +platina. Being thus arranged, the decomposition at _b_ and the deflection +at _g_ showed that an electric current was passing, but there was no +appearance of decomposition at _a_, not even after a _metallic_ +communication at _b_ was established. The experiment was repeated several +times, and I am led to conclude that in this case the current has not +intensity sufficient to cause the decomposition of the chloride of lead; +and further, that, like water (974.), fused chloride of lead can conduct an +electric current having an intensity below that required to effect +decomposition. + +979. _Chloride of silver_ was then placed at _a_, fig. 87, instead of +chloride of lead. There was a very ready decomposition of the solution of +iodide of potassium at _b_, and when metallic contact was made there, very +considerable deflection of the galvanometer needle at _g_. Platina also +appeared to be dissolved at the anode of the fused chloride at _a_, and +there was every appearance of a decomposition having been effected there. + +980. A further proof of decomposition was obtained in the following manner. +The platina wires in the fused chloride at _a_ were brought very near +together (metallic contact having been established at _b_), and left so; +the deflection at the galvanometer indicated the passage of a current, +feeble in its force, but constant. After a minute or two, however, the +needle would suddenly be violently affected, and indicate a current as +strong as if metallic contact had taken place at _a_. This I actually found +to be the case, for the silver reduced by the action of the current +crystallized in long delicate spiculae, and these at last completed the +metallic communication; and at the same time that they transmitted a more +powerful current than the fused chloride, they proved that electro-chemical +decomposition of that chloride had been going on. Hence it appears, that +the current excited by dilute sulphuric acid between zinc and platina, has +an intensity above that required to electrolyze the fused chloride of +silver when placed between platina electrodes, although it has not +intensity enough to decompose chloride of lead under the same +circumstances. + +981. A drop of _water_ placed at _a_ instead of the fused chlorides, showed +as in the former case (970.), that it could conduct a current unable to +decompose it, for decomposition of the solution of iodide at _b_ occurred +after some time. But its conducting power was much below that of the fused +chloride of lead (978.). + +982. Fused _nitre_ at _a_ conducted much better than water: I was unable to +decide with certainty whether it was electrolyzed, but I incline to think +not, for there was no discoloration against the platina at the _cathode_. +If sulpho-nitric acid had been used in the exciting vessel, both the nitre +and the chloride of lead would have suffered decomposition like the water +(906.). + +983. The results thus obtained of conduction without decomposition, and the +necessity of a certain electrolytic intensity for the separation of the +_ions_ of different electrolytes, are immediately connected with the +experiments and results given in S 10. of the Fourth Series of these +Researches (418. 423. 444. 419.). But it will require a more exact +knowledge of the nature of intensity, both as regards the first origin of +the electric current, and also the manner in which it may be reduced, or +lowered by the intervention of longer or shorter portions of bad +conductors, whether decomposable or not, before their relation can be +minutely and fully understood. + +984. In the case of water, the experiments I have as yet made, appear to +show, that, when the electric current is reduced in intensity below the +point required for decomposition, then the degree of conduction is the same +whether sulphuric acid, or any other of the many bodies which can affect +its transferring power as an electrolyte, are present or not. Or, in other +words, that the necessary electrolytic intensity for water is the same +whether it be pure, or rendered a better conductor by the addition of these +substances; and that for currents of less intensity than this, the water, +whether pure or acidulated, has equal conducting power. An apparatus, fig. +84, was arranged with dilute sulphuric acid in the vessel A, and pure +distilled water in the vessel B. By the decomposition at _c_, it appeared +as if water was a _better_ conductor than dilute sulphuric acid for a +current of such low intensity as to cause no decomposition. I am inclined, +however, to attribute this apparent superiority of water to variations in +that peculiar condition of the platina electrodes which is referred to +further on in this Series (1040.), and which is assumed, as far as I can +judge, to a greater degree in dilute sulphuric acid than in pure water. The +power therefore, of acids, alkalies, salts, and other bodies in solution, +to increase conducting power, appears to hold good only in those cases +where the electrolyte subject to the current suffers decomposition, and +loses all influence when the current transmitted has too low an intensity +to affect chemical change. It is probable that the ordinary conducting +power of an electrolyte in the solid state (419.) is the same as that which +it possesses in the fluid state for currents, the tension of which is +beneath the due electrolytic intensity. + +985. Currents of electricity, produced by less than eight or ten series of +voltaic elements, can be reduced to that intensity at which water can +conduct them without suffering decomposition, by causing them to pass +through three or four vessels in which water shall be successively +interposed between platina surfaces. The principles of interference upon +which this effect depends, will be described hereafter (1009. 1018.), but +the effect may be useful in obtaining currents of standard intensity, and +is probably applicable to batteries of any number of pairs of plates. + +986. As there appears every reason to expect that all electrolytes will be +found subject to the law which requires an electric current of a certain +intensity for their decomposition, but that they will differ from each +other in the degree of intensity required, it will be desirable hereafter +to arrange them in a table, in the order of their electrolytic intensities. +Investigations on this point must, however, be very much extended, and +include many more bodies than have been here mentioned before such a table +can be constructed. It will be especially needful in such experiments, to +describe the nature of the electrodes used, or, if possible, to select such +as, like platina or plumbago in certain cases, shall have no power of +assisting the separation of the _ions_ to be evolved (913). + +987. Of the two modes in which bodies can transmit the electric forces, +namely, that which is so characteristically exhibited by the metals, and +usually called conduction, and that in which it is accompanied by +decomposition, the first appears common to all bodies, although it occurs +with almost infinite degrees of difference; the second is at present +distinctive of the electrolytes. It is, however, just possible that it may +hereafter be extended to the metals; for their power of conducting without +decomposition may, perhaps justly, be ascribed to their requiring a very +high electrolytic intensity for their decomposition. + +987-1/2. The establishment of the principle that a certain electrolytic +intensity is necessary before decomposition can be effected, is of great +importance to all those considerations which arise regarding the probable +effects of weak currents, such for instance as those produced by natural +thermo-electricity, or natural voltaic arrangements in the earth. For to +produce an effect of decomposition or of combination, a current must not +only exist, but have a certain intensity before it can overcome the +quiescent affinities opposed to it, otherwise it will be conducted, +producing no permanent chemical effects. On the other hand, the principles +are also now evident by which an opposing action can be so weakened by the +juxtaposition of bodies not having quite affinity enough to cause direct +action between them (913.), that a very weak current shall be able to raise +the sum of actions sufficiently high, and cause chemical changes to occur. + +988. In concluding this division _on the intensity necessary for +electrolyzation_, I cannot resist pointing out the following remarkable +conclusion in relation to intensity generally. It would appear that when a +voltaic current is produced, having a certain intensity, dependent upon the +strength of the chemical affinities by which that current is excited +(916.), it can decompose a particular electrolyte without relation to the +quantity of electricity passed, the _intensity_ deciding whether the +electrolyte shall give way or not. If that conclusion be confirmed, then we +may arrange circumstances so that the _same quantity_ of electricity may +pass in the _same time_, in at the _same surface_, into the _same +decomposing body in the same state_, and yet, differing in intensity, will +_decompose in one case and in the other not_:--for taking a source of too +low an intensity to decompose, and ascertaining the quantity passed in a +given time, it is easy to take another source having a sufficient +intensity, and reducing the quantity of electricity from it by the +intervention of bad conductors to the same proportion as the former +current, and then all the conditions will be fulfilled which are required +to produce the result described. + + +P iii. _On associated Voltaic Circles, or the Voltaic Battery._ + +989. Passing from the consideration of single circles (875. &c.) to their +association in the voltaic battery, it is a very evident consequence, that +if matters are so arranged that two sets of affinities, in place of being +opposed to each other as in figg. 73. 76. (880. 891.), are made to act in +conformity, then, instead of either interfering with the other, it will +rather assist it. This is simply the case of two voltaic pairs of metals +arranged so as to form one circuit. In such arrangements the activity of +the whole is known to be increased, and when ten, or a hundred, or any +larger number of such alternations are placed in conformable association +with each other, the power of the whole becomes proportionally exalted, and +we obtain that magnificent instrument of philosophic research, the _voltaic +battery_. + +990. But it is evident from the principles of definite action already laid +down, that the _quantity_ of electricity in the current cannot be increased +with the increase of the _quantity of metal_ oxidized and dissolved at each +new place of chemical action. A single pair of zinc and platina plates +throws as much electricity into the form of a current, by the oxidation of +32.5 grains of the zinc (868.) as would be circulated by the same +alteration of a thousand times that quantity, or nearly five pounds of +metal oxidized at the surface of the zinc plates of a thousand pairs placed +in regular battery order. For it is evident, that the electricity which +passes across the acid from the zinc to the platina in the first cell, and +which has been associated with, or even evolved by, the decomposition of a +definite portion of water in that cell, cannot pass from the zinc to the +platina across the acid in the second cell, without the decomposition of +the same quantity of water there, and the oxidation of the same quantity of +zinc by it (924. 949.). The same result recurs in every other cell; the +electro-chemical equivalent of water must be decomposed in each, before the +current can pass through it; for the quantity of electricity passed and the +quantity of electrolyte decomposed, _must_ be the equivalents of each +other. The action in each cell, therefore, is not to increase the quantity +set in motion in any one cell, but to aid in urging forward that quantity, +the passing of which is consistent with the oxidation of its own zinc; and +in this way it exalts that peculiar property of the current which we +endeavour to express by the term _intensity_, without increasing the +_quantity_ beyond that which is proportionate to the quantity of zinc +oxidized in any single cell of the series. + +991. To prove this, I arranged ten pairs of amalgamated zinc and platina +plates with dilute sulphuric acid in the form of a battery. On completing +the circuit, all the pairs acted and evolved gas at the surfaces of the +platina. This was collected and found to be alike in quantity for each +plate; and the quantity of hydrogen evolved at any one platina plate was in +the same proportion to the quantity of metal dissolved from any one zinc +plate, as was given in the experiment with a single pair (864. &c.). It was +therefore certain, that, just as much electricity and no more had passed +through the series of ten pair of plates as had passed through, or would +have been put into motion by, any single pair, notwithstanding that ten +times the quantity of zinc had been consumed. + +992. This truth has been proved also long ago in another way, by the action +of the evolved current on a magnetic needle; the deflecting power of one +pair of plates in a battery being equal to the deflecting power of the +whole, provided the wires used be sufficiently large to carry the current +of the single pair freely; but the _cause_ of this equality of action could +not be understood whilst the definite action and evolution of electricity +(783. 869.) remained unknown. + +993. The superior decomposing power of a battery over a single pair of +plates is rendered evident in two ways. Electrolytes held together by an +affinity so strong as to resist the action of the current from a single +pair, yield up their elements to the current excited by many pairs; and +that body which is decomposed by the action of one or of few pairs of +metals, &c., is resolved into its _ions_ the more readily as it is acted +upon by electricity urged forward by many alternations. + +994. Both these effects are, I think, easily understood. Whatever +_intensity_ may be, (and that must of course depend upon the nature of +electricity, whether it consist of a fluid or fluids, or of vibrations of +an ether, or any other kind or condition of matter,) there seems to be no +difficulty in comprehending that the _degree_ of intensity at which a +current of electricity is evolved by a first voltaic element, shall be +increased when that current is subjected to the action of a second voltaic +element, acting in conformity and possessing equal powers with the first: +and as the decompositions are merely opposed actions, but exactly of the +same kind as those which generate the current (917.), it seems to be a +natural consequence, that the affinity which can resist the force of a +single decomposing action may be unable to oppose the energies of many +decomposing actions, operating conjointly, as in the voltaic battery. + +995. That a body which can give way to a current of feeble intensity, +should give way more freely to one of stronger force, and yet involve no +contradiction to the law of definite electrolytic action, is perfectly +consistent. All the facts and also the theory I have ventured to put forth, +tend to show that the act of decomposition opposes a certain force to the +passage of the electric current; and, that this obstruction should be +overcome more or less readily, in proportion to the greater or less +intensity of the decomposing current, is in perfect consistency with all +our notions of the electric agent. + +996. I have elsewhere (947.) distinguished the chemical action of zinc and +dilute sulphuric acid into two portions; that which, acting effectually on +the zinc, evolves hydrogen at once upon its surface, and that which, +producing an arrangement of the chemical forces throughout the electrolyte +present, (in this case water,) tends to take oxygen from it, but cannot do +so unless the electric current consequent thereon can have free passage, +and the hydrogen be delivered elsewhere than against the zinc. The electric +current depends altogether upon the second of these; but when the current +can pass, by favouring the electrolytic action it tends to diminish the +former and increase the latter portion. + +997. It is evident, therefore, that when ordinary zinc is used in a voltaic +arrangement, there is an enormous waste of that power which it is the +object to throw into the form of an electric current; a consequence which +is put in its strongest point of view when it is considered that three +ounces and a half of zinc, properly oxidized, can circulate enough +electricity to decompose nearly one ounce of water, and cause the evolution +of about 2100 cubic inches of hydrogen gas. This loss of power not only +takes place during the time the electrodes of the battery are in +communication, being then proportionate to the quantity of hydrogen evolved +against the surface of any one of the zinc plates, but includes also _all_ +the chemical action which goes on when the extremities of the pile are not +in communication. + +998. This loss is far greater with ordinary zinc than with the pure metal, +as M. De la Rive has shown[A]. The cause is, that when ordinary zinc is +acted upon by dilute sulphuric acid, portions of copper, lead, cadmium, or +other metals which it may contain, are set free upon its surface; and +these, being in contact with the zinc, form small but very active voltaic +circles, which cause great destruction of the zinc and evolution of +hydrogen, apparently upon the zinc surface, but really upon the surface of +these incidental metals. In the same proportion as they serve to discharge +or convey the electricity back to the zinc, do they diminish its power of +producing an electric current which shall extend to a greater distance +across the acid, and be discharged only through the copper or platina plate +which is associated with it for the purpose of forming a voltaic apparatus. + + [A] Quarterly Journal of Science, 1831, p. 388; or Bibliotheque + Universelle, 1830, p. 391. + +999. All these evils are removed by the employment of an amalgam of zinc in +the manner recommended by Mr. Kemp[A], or the use of the amalgamated zinc +plates of Mr. Sturgeon (863.), who has himself suggested and objected to +their application in galvanic batteries; for he says, "Were it not on +account of the brittleness and other inconveniences occasioned by the +incorporation of the mercury with the zinc, amalgamation of the zinc +surfaces in galvanic batteries would become an important improvement; for +the metal would last much longer, and remain bright for a considerable +time, even for several successive hours; essential considerations in the +employment of this apparatus[B]." + + [A] Jameson's Edinburgh Journal, October 1828. + + [B] Recent Experimental Researches, p. 42, &c. Mr. Sturgeon is of + course unaware of the definite production of electricity by chemical + action, and is in fact quoting the experiment as the strongest + argument _against_ the chemical theory of galvanism. + +1000. Zinc so prepared, even though impure, does not sensibly decompose the +water of dilute sulphuric acid, but still has such affinity for the oxygen, +that the moment a metal which, like copper or platina, has little or no +affinity, touches it in the acid, action ensues, and a powerful and +abundant electric current is produced. It is probable that the mercury acts +by bringing the surface, in consequence of its fluidity, into one uniform +condition, and preventing those differences in character between one spot +and another which are necessary for the formation of the minute voltaic +circuits referred to (998.). If any difference does exist at the first +moment, with regard to the proportion of zinc and mercury, at one spot on +the _surface_, as compared with another, that spot having the least mercury +is first acted on, and, by solution of the zinc, is soon placed in the same +condition as the other parts, and the whole plate rendered superficially +uniform. One part cannot, therefore, act as a discharger to another; and +hence _all_ the chemical power upon the water at its surface is in that +equable condition (949.), which, though it tends to produce an electric +current through the liquid to another plate of metal which can act as a +discharger (950.), presents no irregularities by which any one part, having +weaker affinities for oxygen, can act as a discharger to another. Two +excellent and important consequences follow upon this state of the metal. +The first is, that _the full equivalent_ of electricity is obtained for the +oxidation of a certain quantity of zinc; the second, that a battery +constructed with the zinc so prepared, and charged with dilute sulphuric +acid, is active only whilst the electrodes are connected, and ceases to act +or be acted upon by the acid the instant the communication is broken. + +1001. I have had a small battery of ten pairs of plates thus constructed, +and am convinced that arrangements of this kind will be very important, +especially in the development and illustration of the philosophical +principles of the instrument. The metals I have used are amalgamated zinc +and platina, connected together by being soldered to platina wires, the +whole apparatus having the form of the couronne des tasses. The liquid used +was dilute sulphuric acid of sp. gr. 1.25. No action took place upon the +metals except when the electrodes were in communication, and then the +action upon the zinc was only in proportion to the decomposition in the +experimental cell; for when the current was retarded there, it was retarded +also in the battery, and no waste of the powers of the metal was incurred. + +1002. In consequence of this circumstance, the acid in the cells remained +active for a very much longer time than usual. In fact, time did not tend +to lower it in any sensible degree: for whilst the metal was preserved to +be acted upon at the proper moment, the acid also was preserved almost at +its first strength. Hence a constancy of action far beyond what can be +obtained by the use of common zinc. + +1003. Another excellent consequence was the renewal, during the interval of +rest, between two experiments of the first and most efficient state. When +an amalgamated zinc and a platina plate, immersed in dilute sulphuric acid, +are first connected, the current is very powerful, but instantly sinks very +much in force, and in some cases actually falls to only an eighth or a +tenth of that first produced (1036.). This is due to the acid which is in +contact with the zinc becoming neutralized by the oxide formed; the +continued quick oxidation of the metal being thus prevented. With ordinary +zinc, the evolution of gas at its surface tends to mingle all the liquid +together, and thus bring fresh acid against the metal, by which the oxide +formed there can be removed. With the amalgamated zinc battery, at every +cessation of the current, the saline solution against the zinc is gradually +diffused amongst the rest of the liquid; and upon the renewal of contact at +the electrodes, the zinc plates are found most favourably circumstanced for +the production of a ready and powerful current. + +1004. It might at first be imagined that amalgamated zinc would be much +inferior in force to common zinc, because, of the lowering of its energy, +which the mercury might be supposed to occasion over the whole of its +surface; but this is not the case. When the electric currents of two pairs +of platina and zinc plates were opposed, the difference being that one of +the zincs was amalgamated and the other not, the current from the +amalgamated zinc was most powerful, although no gas was evolved against it, +and much was evolved at the surface of the unamalgamated metal. Again, as +Davy has shown[A], if amalgamated and unamalgamated zinc be put in contact, +and dipped into dilute sulphuric acid, or other exciting fluids, the former +is positive to the latter, i.e. the current passes from the amalgamated +zinc, through the fluid, to the unprepared zinc. This he accounts for by +supposing that "there is not any inherent and specific property in each +metal which gives it the electrical character, but that it depends upon its +peculiar state--on that form of aggregation which fits it for chemical +change." + + [A] Philosophical Transactions, 1826, p. 405. + +1005. The superiority of the amalgamated zinc is not, however, due to any +such cause, but is a very simple consequence of the state of the fluid in +contact with it; for as the unprepared zinc acts directly and alone upon +the fluid, whilst that which is amalgamated does not, the former (by the +oxide it produces) quickly neutralizes the acid in contact with its +surface, so that the progress of oxidation is retarded, whilst at the +surface of the amalgamated zinc, any oxide formed is instantly removed by +the free acid present, and the clean metallic surface is always ready to +act with full energy upon the water. Hence its superiority (1037.). +1006. The progress of improvement in the voltaic battery and its +applications, is evidently in the contrary direction at present to what it +was a few years ago; for in place of increasing the number of plates, the +strength of acid, and the extent altogether of the instrument, the change +is rather towards its first state of simplicity, but with a far more +intimate knowledge and application of the principles which govern its force +and action. Effects of decomposition can now be obtained with ten pairs of +plates (417.), which required five hundred or a thousand pairs for their +production in the first instance. The capability of decomposing fused +chlorides, iodides, and other compounds, according to the law before +established (380. &c.), and the opportunity of collecting certain of the +products, without any loss, by the use of apparatus of the nature of those +already described (789. 814. &c.), render it probable that the voltaic +battery may become a useful and even economical manufacturing instrument; +for theory evidently indicates that an equivalent of a rare substance may +be obtained at the expense of three or four equivalents of a very common +body, namely, zinc: and practice seems thus far to justify the expectation. +In this point of view I think it very likely that plates of platina or +silver may be used instead of plates of copper with advantage, and that +then the evil arising occasionally from solution of the copper, and its +precipitation on the zinc, (by which the electromotive power of the zinc is +so much injured,) will be avoided (1047.). + + +P iv. _On the Resistance of an Electrolyte to Electrolytic Action, and on +Interpositions._ + +1007. I have already illustrated, in the simplest possible form of +experiment (891. 910.), the resistance established at the place of +decomposition to the force active at the exciting place. I purpose +examining the effects of this resistance more generally; but it is rather +with reference to their practical interference with the action and +phenomena of the voltaic battery, than with any intention at this time to +offer a strict and philosophical account of their nature. Their general and +principal cause is the resistance of the chemical affinities to be +overcome; but there are numerous other circumstances which have a joint +influence with these forces (1034. 1040. &c.), each of which would require +a minute examination before a correct account of the whole could be given. + +1008. As it will be convenient to describe the experiments in a form +different to that in which they were made, both forms shall first be +explained. Plates of platina, copper, zinc, and other metals, about three +quarters of an inch wide and three inches long, were associated together in +pairs by means of platina wires to which they were soldered, fig. 88, the +plates of one pair being either alike or different, as might be required. +These were arranged in glasses, fig. 89, so as to form Volta's crown of +cups. The acid or fluid in the cups never covered the whole of any plate; +and occasionally small glass rods were put into the cups, between the +plates, to prevent their contact. Single plates were used to terminate the +series and complete the connexion with a galvanometer, or with a +decomposing apparatus (899. 968. &c.), or both. Now if fig. 90 be examined +and compared with fig. 91, the latter may be admitted as representing the +former in its simplest condition; for the cups i, ii, and iii of the +former, with their contents, are represented by the cells i, ii, and iii of +the latter, and the metal plates Z and P of the former by the similar +plates represented Z and P in the latter. The only difference, in fact, +between the apparatus, fig. 90, and the trough represented fig. 91, is that +twice the quantity of surface of contact between the metal and acid is +allowed in the first to what would occur in the second. + +1009. When the extreme plates of the arrangement just described, fig. 90, +are connected metallically through the galvanometer _g_, then the whole +represents a battery consisting of two pairs of zinc and platina plates +urging a current forward, which has, however, to decompose water unassisted +by any direct chemical affinity before it can be transmitted across the +cell iii, and therefore before it can circulate. This decomposition of +water, which is opposed to the passage of the current, may, as a matter of +convenience, be considered as taking place either against the surfaces of +the two platina plates which constitute the electrodes in the cell in, or +against the two surfaces of that platina plate which separates the cells ii +and iii, fig. 91, from each other. It is evident that if that plate were +away, the battery would consist of two pairs of plates and two cells, +arranged in the most favourable position for the production of a current. +The platina plate therefore, which being introduced as at _x_, has oxygen +evolved at one surface and hydrogen at the other (that is, if the +decomposing current passes), may be considered as the cause of any +obstruction arising from the decomposition of water by the electrolytic +action of the current; and I have usually called it the interposed plate. + +1010. In order to simplify the conditions, dilute sulphuric acid was first +used in all the cells, and platina for the interposed plates; for then the +initial intensity of the current which tends to be formed is constant, +being due to the power which zinc has of decomposing water; and the +opposing force of decomposition is also constant, the elements of the water +being unassisted in their separation at the interposed plates by any +affinity or secondary action at the electrodes (744.), arising either from +the nature of the plate itself or the surrounding fluid. + +1011. When only one voltaic pair of zinc and platina plates was used, the +current of electricity was entirely stopped to all practical purposes by +interposing one platina plate, fig. 92, i.e. by requiring of the current +that it should decompose water, and evolve both its elements, before it +should pass. This consequence is in perfect accordance with the views +before given (910. 917. 973.). For as the whole result depends upon the +opposition of forces at the places of electric excitement and +electro-decomposition, and as water is the substance to be decomposed at +both before the current can move, it is not to be expected that the zinc +should have such powerful attraction for the oxygen, as not only to be able +to take it from its associated hydrogen, but leave such a surplus of force +as, passing to the second place of decomposition, should be there able to +effect a second separation of the elements of water. Such an effect would +require that the force of attraction between zinc and oxygen should under +the circumstances be _at least_ twice as great as the force of attraction +between the oxygen and hydrogen. + +1012. When two pairs of zinc and platina exciting plates were used, the +current was also practically stopped by one interposed platina plate, fig. +93. There was a very feeble effect of a current at first, but it ceased +almost immediately. It will be referred to, with many other similar +effects, hereafter (1017.). + +1013. Three pairs of zinc and platina plates, fig. 94, were able to produce +a current which could pass an interposed platina plate, and effect the +electrolyzation of water in cell iv. The current was evident, both by the +continued deflection of the galvanometer, and the production of bubbles of +oxygen and hydrogen at the electrodes in cell iv. Hence the accumulated +surplus force of three plates of zinc, which are active in decomposing +water, is more than equal, when added together, to the force with which +oxygen and hydrogen are combined in water, and is sufficient to cause the +separation of these elements from each other. + +1014. The three pairs of zinc and platina plates were now opposed by two +intervening platina plates, fig. 95. In this case the current was stopped. + +1015. Four pairs of zinc and platina plates were also neutralized by two +interposed platina plates, fig. 96. + +1016. Five pairs of zinc and platina, with two interposed platina plates, +fig. 97, gave a feeble current; there was permanent deflection at the +galvanometer, and decomposition in the cells vi and vii. But the current +was very feeble; very much less than when all the intermediate plates were +removed and the two extreme ones only retained: for when they were placed +six inches asunder in one cell, they gave a powerful current. Hence five +exciting pairs, with two interposed obstructing plates, do not give a +current at all comparable to that of a single unobstructed pair. + +1017. I have already said that a _very feeble current_ passed when the +series included one interposed platina and two pairs of zinc and platina +plates (1012.). A similarly feeble current passed in every case, and even +when only one exciting pair and four intervening platina plates were used, +fig. 98, a current passed which could be detected at _x_, both by chemical +action on the solution of iodide of potassium, and by the galvanometer. +This current I believe to be due to electricity reduced in intensity below +the point requisite for the decomposition of water (970. 984.); for water +can conduct electricity of such low intensity by the same kind of power +which it possesses in common with metals and charcoal, though it cannot +conduct electricity of higher intensity without suffering decomposition, +and then opposing a new force consequent thereon. With an electric current +of, or under this intensity, it is probable that increasing the number of +interposed platina plates would not involve an increased difficulty of +conduction. + +1018. In order to obtain an idea of the additional interfering power of +each added platina plate, six voltaic pairs and four intervening platinas +were arranged as in fig. 99; a very feeble current then passed (985. +1017.). When one of the platinas was removed so that three intervened, a +current somewhat stronger passed. With two intervening platinas a still +stronger current passed; and with only one intervening platina a very fair +current was obtained. But the effect of the successive plates, taken in the +order of their interposition, was very different, as might be expected; for +the first retarded the current more powerfully than the second, and the +second more than the third. + +1019. In these experiments both amalgamated and unamalgamated zinc were +used, but the results generally were the same. + +1020. The effects of retardation just described were altered altogether +when changes were made in the _nature of the liquid_ used between the +plates, either in what may be called the _exciting_ or the _retarding_ +cells. Thus, retaining the exciting force the same, by still using pure +dilute sulphuric acid for that purpose, if a little nitric acid were added +to the liquid in the _retarding_ cells, then the transmission of the +current was very much facilitated. For instance, in the experiment with one +pair of exciting plates and one intervening plate (1011.), fig. 92, when a +few drops of nitric acid were added to the contents of cell ii, then the +current of electricity passed with considerable strength (though it soon +fell from other causes (1036; 1040.),) and the same increased effect was +produced by the nitric acid when many interposed plates were used. + +1021. This seems to be a consequence of the diminution of the difficulty of +decomposing water when its hydrogen, instead of being absolutely expelled, +as in the former cases, is transferred to the oxygen of the nitric acid, +producing a secondary result at the _cathode_ (752.); for in accordance +with the chemical views of the electric current and its action already +advanced (913.), the water, instead of opposing a resistance to +decomposition equal to the full amount of the force of mutual attraction +between its oxygen and hydrogen, has that force counteracted in part, and +therefore diminished by the attraction of the hydrogen at the _cathode_ for +the oxygen of the nitric acid which surrounds it, and with which it +ultimately combines instead of being evolved in its free state. + +1022. When a little nitric acid was put into the exciting cells, then again +the circumstances favouring the transmission of the current were +strengthened, for the _intensity_ of the current itself was increased by +the addition (906.). When therefore a little nitric acid was added to both +the _exciting_ and the _retarding_ cells, the current of electricity passed +with very considerable freedom. + +1023. When dilute muriatic acid was used, it produced and transmitted a +current more easily than pure dilute sulphuric acid, but not so readily as +dilute nitric acid. As muriatic acid appears to be decomposed more freely +than water (765.), and as the affinity of zinc for chlorine is very +powerful, it might be expected to produce a current more intense than that +from the use of dilute sulphuric acid; and also to transmit it more freely +by undergoing decomposition at a lower intensity (912.). + +1024. In relation to the effect of these interpositions, it is necessary to +state that they do not appear to be at all dependent upon the size of the +electrodes, or their distance from each other in the acid, except that when +a current _can pass_, changes in these facilitate or retard its passage. +For on repeating the experiment with one intervening and one pair of +exciting plates (1011.), fig. 92, and in place of the interposed plate P +using sometimes a mere wire, and sometimes very large plates (1008.), and +also changing the terminal exciting plates Z and P, so that they were +sometimes wires only and at others of great size, still the results were +the same as those already obtained. + +1025. In illustration of the effect of distance, an experiment like that +described with two exciting pairs and one intervening plate (1012.), fig. +93, was arranged so that the distance between the plates in the third cell +could be increased to six or eight inches, or diminished to the thickness +of a piece of intervening bibulous paper. Still the result was the same in +both cases, the effect not being sensibly greater, when the plates were +merely separated by the paper, than when a great way apart; so that the +principal opposition to the current in this case does not depend upon the +_quantity_ of intervening electrolytic conductor, but on the _relation of +its elements to the intensity of the current_, or to the chemical nature of +the electrodes and the surrounding fluids. + +1026. When the acid was sulphuric acid, _increasing its strength_ in any of +the cells, caused no change in the effects; it did not produce a more +intense current in the exciting cells (908.), or cause the current produced +to traverse the decomposing cells more freely. But if to very weak +sulphuric acid a few drops of nitric acid were added, then either one or +other of those effects could be produced; and, as might be expected in a +case like this, where the exciting or conducting action bore a _direct_ +reference to the acid itself, increasing the strength of this (the nitric +acid), also increased its powers. + +1027. The _nature of the interposed plate_ was now varied to show its +relation to the phenomena either of excitation or retardation, and +amalgamated zinc was first substituted for platina. On employing one +voltaic pair and one interposed zinc plate, fig. 100, there was as powerful +a current, apparently, as if the interposed zinc plate was away. Hydrogen +was evolved against P in cell ii, and against the side of the second zinc +in cell i; but no gas appeared against the side of the zinc in cell ii, nor +against the zinc in cell i. + +1028. On interposing two amalgamated zinc plates, fig. 101, instead of one, +there was still a powerful current, but interference had taken place. On +using three intermediate zinc plates, fig. 102, there was still further +retardation, though a good current of electricity passed. + +1029. Considering the retardation as due to the inaction of the amalgamated +zinc upon the dilute acid, in consequence of the slight though general +effect of diminished chemical power produced by the mercury on the surface, +and viewing this inaction as the circumstance which rendered it necessary +that each plate should have its tendency to decompose water assisted +slightly by the electric current, it was expected that plates of the metal +in the unamalgamated state would probably not require such assistance, and +would offer no sensible impediment to the passing of the current. This +expectation was fully realized in the use of two and three interposed +unamalgamated plates. The electric current passed through them as freely as +if there had been no such plates in the way. They offered no obstacle, +because they could decompose water without the current; and the latter had +only to give direction to a part of the forces, which would have been +active whether it had passed or not. + +1030. Interposed plates of copper were then employed. These seemed at first +to occasion no obstruction, but after a few minutes the current almost +entirely ceased. This effect appears due to the surfaces taking up that +peculiar condition (1010.) by which they tend to produce a reverse current; +for when one or more of the plates were turned round, which could easily be +effected with the couronne des tasses form of experiment, fig. 90, then the +current was powerfully renewed for a few moments, and then again ceased. +Plates of platina and copper, arranged as a voltaic pile with dilute +sulphuric acid, could not form a voltaic trough competent to act for more +than a _few_ minutes, because of this peculiar counteracting effect. + +1031. All these effects of retardation, exhibited by decomposition against +surfaces for which the evolved elements have more or less affinity, or are +altogether deficient in attraction, show generally, though beautifully, the +chemical relations and source of the current, and also the balanced state +of the affinities at the places of excitation and decomposition. In this +way they add to the mass of evidence in favour of the identity of the two; +for they demonstrate, as it were, the antagonism of the _chemical powers_ +at the electromotive part with the _chemical powers_ at the interposed +parts; they show that the first are _producing_ electric effects, and the +second _opposing_ them; they bring the two into direct relation; they prove +that either can determine the other, thus making what appears to be cause +and effect convertible, and thereby demonstrating that both chemical and +electrical action are merely two exhibitions of one single agent or power +(916. &c.). + +1032. It is quite evident, that as water and other electrolytes can conduct +electricity without suffering decomposition (986.), when the electricity is +of sufficiently low intensity, it may not be asserted as absolutely true in +all cases, that whenever electricity passes through an electrolyte, it +produces a definite effect of decomposition. But the quantity of +electricity which can pass in a given time through an electrolyte without +causing decomposition, is so small as to bear no comparison to that +required in a case of very moderate decomposition, and with electricity +above the intensity required for electrolyzation, I have found no sensible +departure as yet from the law of _definite electrolytic action_ developed +in the preceding series of these Researches (783. &c.). + +1033. I cannot dismiss this division of the present Paper without making a +reference to the important experiments of M. Aug. De la Rive on the effects +of interposed plates[A]. As I have had occasion to consider such plates +merely as giving rise to new decompositions, and in that way only causing +obstruction to the passage of the electric current, I was freed from the +necessity of considering the peculiar effects described by that +philosopher. I was the more willing to avoid for the present touching upon +these, as I must at the same time have entered into the views of Sir +Humphry Davy upon the same subject[B] and also those of Marianini[C] and +Hitter[D], which are connected with it. + + [A] Annales de Chimie, tom. xxviii. p 190; and Memoires de Geneve. + + [B] Philosophical Transactions, 1826, p. 413. + + [C] Annales de Chimie, tom. xxxiii. pp. 117, 119, &c. + + [D] Journal de Physique, tom. lvii. pp. 319, 350. + + +P v. _General Remarks on the active Voltaic Battery._ + +1034. When the ordinary voltaic battery is brought into action, its very +activity produces certain effects, which re-act upon it, and cause serious +deterioration of its power. These render it an exceedingly inconstant +instrument as to the _quantity_ of effect which it is capable of producing. +They are already, in part, known and understood; but as their importance, +and that of certain other coincident results, will be more evident by +reference to the principles and experiments already stated and described, I +have thought it would be useful, in this investigation of the voltaic pile, +to notice them briefly here. + +1035. When the battery is in action, it causes such substances to be formed +and arranged in contact with the plates as very much weaken its power, or +even tend to produce a counter current. They are considered by Sir Humphry +Davy as sufficient to account for the phenomena of Ritter's secondary +piles, and also for the effects observed by M.A. De la Rive with interposed +platina plates[A]. + + [A] Philosophical Transactions, 1826, p. 113. + +1036. I have already referred to this consequence (1003.), as capable, in +some cases, of lowering the force of the current to one-eighth or one-tenth +of what it was at the first moment, and have met with instances in which +its interference was very great. In an experiment in which one voltaic pair +and one interposed platina plate were used with dilute sulphuric acid in +the cells fig. 103, the wires of communication were so arranged, that the +end of that marked 3 could be placed at pleasure upon paper moistened in +the solution of iodide of potassium at _x_, or directly upon the platina +plate there. If, after an interval during which the circuit had not been +complete, the wire 3 were placed upon the paper, there was evidence of a +current, decomposition ensued, and the galvanometer was affected. If the +wire 3 were made to touch the metal of _p_, a comparatively strong sudden +current was produced, affecting the galvanometer, but lasting only for a +moment; the effect at the galvanometer ceased, and if the wire 3 were +placed on the paper at _x_, no signs of decomposition occurred. On raising +the wire 3, and breaking the circuit altogether for a while, the apparatus +resumed its first power, requiring, however, from five to ten minutes for +this purpose; and then, as before, on making contact between 3 and _p_, +there was again a momentary current, and immediately all the effects +apparently ceased. + +1037. This effect I was ultimately able to refer to the state of the film +of fluid in contact with the zinc plate in cell i. The acid of that film is +instantly neutralized by the oxide formed; the oxidation of the zinc +cannot, of course, go on with the same facility as before; and the chemical +action being thus interrupted, the voltaic action diminishes with it. The +time of the rest was required for the diffusion of the liquid, and its +replacement by other acid. From the serious influence of this cause in +experiments with single pairs of plates of different metals, in which I was +at one time engaged, and the extreme care required to avoid it, I cannot +help feeling a strong suspicion that it interferes more frequently and +extensively than experimenters are aware of, and therefore direct their +attention to it. + +1038. In considering the effect in delicate experiments of this source of +irregularity of action, in the voltaic apparatus, it must be remembered +that it is only that very small portion of matter which is directly in +contact with the oxidizable metal which has to be considered with reference +to the change of its nature; and this portion is not very readily displaced +from its position upon the surface of the metal (582. 605.), especially if +that metal be rough and irregular. In illustration of this effect, I will +quote a remarkable experiment. A burnished platina plate (569.) was put +into hot strong sulphuric acid for an instant only: it was then put into +distilled water, moved about in it, taken out, and wiped dry: it was put +into a second portion of distilled water, moved about in it, and again +wiped: it was put into a third portion of distilled water, in which it was +moved about for nearly eight seconds; it was then, without wiping, put into +a fourth portion of distilled water, where it was allowed to remain five +minutes. The two latter portions of water were then tested for sulphuric +acid; the third gave no sensible appearance of that substance, but the +fourth gave indications which were not merely evident, but abundant for the +circumstances under which it had been introduced. The result sufficiently +shows with what difficulty that portion of the substance which is in +_contact_ with the metal leaves it; and as the contact of the fluid formed +against the plate in the voltaic circuit must be as intimate and as perfect +as possible, it is easy to see how quickly and greatly it must vary from +the general fluid in the cells, and how influential in diminishing the +force of the battery this effect must be. + +1039. In the ordinary voltaic pile, the influence of this effect will occur +in all variety of degrees. The extremities of a trough of twenty pairs of +plates of Wollaston's construction were connected with the +volta-electrometer, fig. 66. (711.), of the Seventh Series of these +Researches, and after five minutes the number of bubbles of gas issuing +from the extremity of the tube, in consequence of the decomposition of the +water, noted. Without moving the plates, the acid between the copper and +zinc was agitated by the introduction of a feather. The bubbles were +immediately evolved more rapidly, above twice the number being produced in +the same portion of time as before. In this instance it is very evident +that agitation by a feather must have been a very imperfect mode of +restoring the acid in the cells against the plates towards its first equal +condition; and yet imperfect as the means were, they more than doubled the +power of the battery. The _first effect_ of a battery which is known to be +so superior to the degree of action which the battery can sustain, is +almost entirely due to the favourable condition of the acid in contact with +the plates. + +1040. A _second_ cause of diminution in the force of the voltaic battery, +consequent upon its own action, is that extraordinary state of the surfaces +of the metals (969.) which was first described, I believe, by Ritter[A], to +which he refers the powers of his secondary piles, and which has been so +well experimented upon by Marianini, and also by A. De la Rive. If the +apparatus, fig. 103. (1096.), be left in action for an hour or two, with +the wire 3 in contact with the plate _p_, so as to allow a free passage for +the current, then, though the contact be broken for ten or twelve minutes, +still, upon its renewal, only a feeble current will pass, not at all equal +in force to what might be expected. Further, if P^{1} and P^{2} be +connected by a metal wire, a powerful momentary current will pass from +P^{2} to P^{1} through the acid, and therefore in the reverse direction to +that produced by the action of the zinc in the arrangement; and after this +has happened, the general current can pass through the whole of the system +as at first, but by its passage again restores the plates P^{2} and P^{1} +into the former opposing condition. This, generally, is the fact described +by Ritter, Marianini, and De la Rive. It has great opposing influence on +the action of a pile, especially if the latter consist of but a small +number of alternations, and has to pass its current through many +interpositions. It varies with the solution in which the interposed plates +are immersed, with the intensity of the current, the strength of the pile, +the time of action, and especially with accidental discharges of the plates +by inadvertent contacts or reversions of the plates during experiments, and +must be carefully watched in every endeavour to trace the source, strength, +and variations of the voltaic current. Its effect was avoided in the +experiments already described (1036. &c.), by making contact between the +plates P^{1} and P^{2} before the effect dependent upon the state of the +solution in contact with the zinc plate was observed, and by other +precautions. + + [A] Journal de Physique, lvii. p. 349. + +1041. When an apparatus like fig. 98. (1017.) with several platina plates +was used, being connected with a battery able to force a current through +them, the power which they acquired, of producing a reversed current, was +very considerable. + +1042. _Weak and exhausted charges_ should never be used at the same time +with _strong and fresh ones_ in the different cells of a trough, or the +different troughs of a battery: the fluid in all the cells should be alike, +else the plates in the weaker cells, in place of assisting, retard the +passage of the electricity generated in, and transmitted across, the +stronger cells. Each zinc plate so circumstanced has to be assisted in +decomposing power before the whole current can pass between it and the +liquid. So, that, if in a battery of fifty pairs of plates, ten of the +cells contain a weaker charge than the others, it is as if ten decomposing +plates were opposed to the transit of the current of forty pairs of +generating plates (1031.). Hence a serious loss of force, and hence the +reason why, if the ten pairs of plates were removed, the remaining forty +pairs would be much more powerful than the whole fifty. + +1043. Five similar troughs, of ten pairs of plates each, were prepared, +four of them with a good uniform charge of acid, and the fifth with the +partially neutralized acid of a used battery. Being arranged in right +order, and connected with a volta-electrometer (711.), the whole fifty +pairs of plates yielded 1.1 cubic inch of oxygen and hydrogen in one +minute: but on moving one of the connecting wires so that only the four +well-charged troughs should be included in the circuit, they produced with +the same volta-electrometer 8.4 cubical inches of gas in the same time. +Nearly seven-eighths of the power of the four troughs had been lost, +therefore, by their association with the fifth trough. + +1044. The same battery of fifty pairs of plates, after being thus used, was +connected with a volta-electrometer (711.), so that by quickly shifting the +wires of communication, the current of the whole of the battery, or of any +portion of it, could be made to pass through the instrument for given +portions of time in succession. The whole of the battery evolved 0.9 of a +cubic inch of oxygen and hydrogen in half a minute; the forty plates +evolved 4.6 cubic inches in the same time; the whole then evolved 1 cubic +inch in the half-minute; the ten weakly charged evolved 0.4 of a cubic inch +in the time given: and finally the whole evolved 1.15 cubic inch in the +standard time. The order of the observations was that given: the results +sufficiently show the extremely injurious effect produced by the mixture of +strong and weak charges in the same battery[A]. + + [A] The gradual increase in the action of the whole fifty pairs of + plates was due to the elevation of temperature in the weakly charged + trough by the passage of the current, in consequence of which the + exciting energies of the fluid within were increased. + +1045. In the same manner associations of _strong and weak_ pairs of plates +should be carefully avoided. A pair of copper and platina plates arranged +in _accordance_ with a pair of zinc and platina plates in dilute sulphuric +acid, were found to stop the action of the latter, or even of two pairs of +the latter, as effectually almost as an interposed plate of platina +(1011.), or as if the copper itself had been platina. It, in fact, became +an interposed decomposing plate, and therefore a retarding instead of an +assisting pair. + +1046. The _reversal_, by accident or otherwise, of the plates in a battery +has an exceedingly injurious effect. It is not merely the counteraction of +the current which the reversed plates can produce, but their effect also in +retarding even as indifferent plates, and requiring decomposition to be +effected upon their surface, in _accordance_ with the course of the +current, before the latter can pass. They oppose the current, therefore, in +the first place, as interposed platina plates would do (1011-1018.); and to +this they add a force of opposition as counter-voltaic plates. I find that, +in a series of four pairs of zinc and platina plates in dilute sulphuric +acid, if one pair be reversed, it very nearly neutralizes the power of the +whole. + +1047. There are many other causes of reaction, retardation, and +irregularity in the voltaic battery. Amongst them is the not unusual one of +precipitation of copper upon the zinc in the cells, the injurious effect of +which has before been adverted to (1006.). But their interest is not +perhaps sufficient to justify any increase of the length of this paper, +which is rather intended to be an investigation of the theory of the +voltaic pile than a particular account of its practical application[A]. + + [A] For further practical results relating to these points of the + philosophy of the voltaic battery, see Series X. S 17. + 1163.--1160.--_Dec. 1838._ + +_Note_.--Many of the views and experiments in this Series of my +Experimental Researches will be seen at once to be corrections and +extensions of the theory of electro-chemical decomposition, given in the +Fifth and Seventh Series of these Researches. The expressions I would now +alter are those which concern the independence of the evolved elements in +relation to the poles or electrodes, and the reference of their evolution +to powers entirely internal (524. 537. 661.). The present paper fully shows +my present views; and I would refer to paragraphs 891. 904. 910. 917. 918. +947. 963. 1007. 1031. &c., as stating what they are. I hope this note will +be considered as sufficient in the way of correction at present; for I +would rather defer revising the whole theory of electro-chemical +decomposition until I can obtain clearer views of the way in which the +power under consideration can appear at one time as associated with +particles giving them their chemical attraction, and at another as free +electricity (493. 957.).--M.F. + +_Royal Institution, +March 31st, 1834._ + + + + +NINTH SERIES. + + +S 15. _On the influence by induction of an Electric Current on itself:--and +on the inductive action of Electric Currents generally._ + +Received December 18, 1834,--Read January 29, 1835. + + +1048. The following investigations relate to a very remarkable inductive +action of electric currents, or of the different parts of the same current +(74.), and indicate an immediate connexion between such inductive action +and the direct transmission of electricity through conducting bodies, or +even that exhibited in the form of a spark. + +1049. The inquiry arose out of a fact communicated to me by Mr. Jenkin, +which is as follows. If an ordinary wire of short length be used as the +medium of communication between the two plates of an electromotor +consisting of a single pair of metals, no management will enable the +experimenter to obtain an electric shock from this wire; but if the wire +which surrounds an electro-magnet be used, a shock is felt each time the +contact with the electromotor is broken, provided the ends of the wire be +grasped one in each hand. + +1050. Another effect is observed at the same time, which has long been +known to philosophers, namely, that a bright electric spark occurs at the +place of disjunction. + +1051. A brief account of these results, with some of a corresponding +character which I had observed in using long wires, was published in the +Philosophical Magazine for 1834[A]; and I added to them some observations +on their nature. Further investigations led me to perceive the inaccuracy +of my first notions, and ended in identifying these effects with the +phenomena of induction which I had been fortunate enough to develop in the +First Series of these Experimental Researches (1.-59.)[B]. Notwithstanding +this identity, the extension and the results supply, lead me to believe +that they will be found worthy of the attention of the Royal Society. + + [A] Vol. v. pp. 349, 444. + + [B] Philosophical Transactions, 1832, p. 126. + +1052. The _electromotor_ used consisted of a cylinder of zinc introduced +between the two parts of a double cylinder of copper, and preserved from +metallic contact in the usual way by corks. The zinc cylinder was eight +inches high and four inches in diameter. Both it and the copper cylinder +were supplied with stiff wires, surmounted by cups containing mercury; and +it was at these cups that the contacts of wires, helices, or +electro-magnets, used to complete the circuit, were made or broken. These +cups I will call G and E throughout the rest of this paper (1079.). + +1053. Certain _helices_ were constructed, some of which it will be +necessary to describe. A pasteboard tube had four copper wires, one +twenty-fourth of an inch in thickness, wound round it, each forming a helix +in the same direction from end to end: the convolutions of each wire were +separated by string, and the superposed helices prevented from touching by +intervening calico. The lengths of the wires forming the helices were 48, +49.5, 48, and 45 feet. The first and third wires were united together so as +to form one consistent helix of 96 feet in length; and the second and +fourth wires were similarly united to form a second helix, closely +interwoven with the first, and 94.5 feet in length. These helices may be +distinguished by the numbers i and ii. They were carefully examined by a +powerful current of electricity and a galvanometer, and found to have no +communication with each other. + +1054. Another helix was constructed upon a similar pasteboard tube, two +lengths of the same copper wire being used, each forty-six feet long. These +were united into one consistent helix of ninety-two feet, which therefore +was nearly equal in value to either of the former helices, but was not in +close inductive association with them. It may be distinguished by the +number iii. + +1055. A fourth helix was constructed of very thick copper wire, being +one-fifth of an inch in diameter; the length of wire used was seventy-nine +feet, independent of the straight terminal portions. + +1056. The principal _electro-magnet_ employed consisted of a cylindrical +bar of soft iron twenty-five inches long, and one inch and three quarters +in diameter, bent into a ring, so that the ends nearly touched, and +surrounded by three coils of thick copper wire, the similar ends of which +were fastened together; each of these terminations was soldered to a copper +rod, serving as a conducting continuation of the wire. Hence any electric +current sent through the rods was divided in the helices surrounding the +ring, into three parts, all of which, however, moved in the same direction. +The three wires may therefore be considered as representing one wire, of +thrice the thickness of the wire really used. + +1057. Other electro-magnets could be made at pleasure by introducing a soft +iron rod into any of the helices described (1053, &c.). + +1058. The _galvanometer_ which I had occasion to use was rough in its +construction, having but one magnetic needle, and not at all delicate in +its indications. + +1059. The effects to be considered _depend on the conductor_ employed to +complete the communication between the zinc and copper plates of the +electromotor; and I shall have to consider this conductor under four +different forms: as the helix of an electro-magnet (1056); as an ordinary +helix (1053, &c.); as a _long_ extended wire, having its course such that +the parts can exert little or no mutual influence; and as a _short_ wire. +In all cases the conductor was of copper. + +1060. The peculiar effects are best shown by the _electro-magnet_ (1056.). +When it was used to complete the communication at the electromotor, there +was no sensible spark on _making_ contact, but on _breaking_ contact there +was a very large and bright spark, with considerable combustion of the +mercury. Then, again, with respect to the shock: if the hands were +moistened in salt and water, and good contact between them and the wires +retained, no shock could be felt upon _making_ contact at the electromotor, +but a powerful one on _breaking_ contact. + +1061. When the _helix_ i or iii (1053, &c.) was used as the connecting +conductor, there was also a good spark on breaking contact, but none +(sensibly) on making contact. On trying to obtain the shock from these +helices, I could not succeed at first. By joining the similar ends of i and +ii so as to make the two helices equivalent to one helix, having wire of +double thickness, I could just obtain the sensation. Using the helix of +thick wire (1055.) the shock was distinctly obtained. On placing the tongue +between two plates of silver connected by wires with the parts which the +hands had heretofore touched (1064.), there was a powerful shock on +_breaking_ contact, but none on _making_ contact. + +1062. The power of producing these phenomena exists therefore in the simple +helix, as in the electro-magnet, although by no means in the same high +degree. + +1063. On putting a bar of soft iron into the helix, it became an +electro-magnet (1057.), and its power was instantly and greatly raised. On +putting a bar of copper into the helix, no change was produced, the action +being that of the helix alone. The two helices i and ii, made into one +helix of twofold length of wire, produced a greater effect than either i or +ii alone. + +1064. On descending from the helix to the mere _long wire_, the following +effects were obtained, A copper wire, 0.18 of an inch in diameter, and 132 +feet in length, was laid out upon the floor of the laboratory, and used as +the connecting conductor (1059.); it gave no sensible spark on making +contact, but produced a bright one on breaking contact, yet not so bright +as that from the helix (1061.) On endeavouring to obtain the electric shock +at the moment contact was broken, I could not succeed so as to make it pass +through the hands; but by using two silver plates fastened by small wires +to the extremity of the principal wire used, and introducing the tongue +between those plates, I succeeded in obtaining powerful shocks upon the +tongue and gums, and could easily convulse a flounder, an eel, or a frog. +None of these effects could be obtained directly from the electromotor, +i.e. when the tongue, frog, or fish was in a similar, and therefore +comparative manner, interposed in the course of the communication between +the zinc and copper plates, separated everywhere else by the acid used to +excite the combination, or by air. The bright spark and the shock, produced +only on breaking contact, are therefore effects of the same kind as those +produced in a higher degree by the helix, and in a still higher degree by +the electro-magnet. + +1065. In order to compare an extended wire with a helix, the helix i, +containing ninety-six feet, and ninety-six feet of the same-sized wire +lying on the floor of the laboratory, were used alternately as conductors: +the former gave a much brighter spark at the moment of disjunction than the +latter. Again, twenty-eight feet of copper wire were made up into a helix, +and being used gave a good spark on disjunction at the electromotor; being +then suddenly pulled out and again employed, it gave a much smaller spark +than before, although nothing but its spiral arrangement had been changed. + +1066. As the superiority of a helix over a wire is important to the +philosophy of the effect, I took particular pains to ascertain the fact +with certainty. A wire of copper sixty-seven feet long was bent in the +middle so as to form a double termination which could be communicated with +the electromotor; one of the halves of this wire was made into a helix and +the other remained in its extended condition. When these were used +alternately as the connecting wire, the helix half gave by much the +strongest spark. It even gave a stronger spark than when it and the +extended wire were used conjointly as a double conductor. + +1067. When a _short wire_ is used, _all_ these effects disappear. If it be +only two or three inches long, a spark can scarcely be perceived on +breaking the junction. If it be ten or twelve inches long and moderately +thick, a small spark may be more easily obtained. As the length is +increased, the spark becomes proportionately brighter, until from extreme +length the resistance offered by the metal as a conductor begins to +interfere with the principal result. + +1068. The effect of elongation was well shown thus: 114 feet of copper +wire, one-eighteenth of an inch in diameter, were extended on the floor and +used as a conductor; it remained cold, but gave a bright spark on breaking +contact. Being crossed so that the two terminations were in contact near +the extremities, it was again used as a conductor, only twelve inches now +being included in the circuit: the wire became very hot from the greater +quantity of electricity passing through it, and yet the spark on breaking +contact was scarcely visible. The experiment was repeated with a wire +one-ninth of an inch in diameter and thirty-six feet long with the same +results. + +1069. That the effects, and also the action, in all these forms of the +experiment are identical, is evident from the manner in which the former +can be gradually raised from that produced by the shortest wire to that of +the most powerful electro-magnet: and this capability of examining what +will happen by the most powerful apparatus, and then experimenting for the +same results, or reasoning from them, with the weaker arrangements, is of +great advantage in making out the true principles of the phenomena. + +1070. The action is evidently dependent upon the wire which serves as a +conductor; for it varies as that wire varies in its length or arrangement. +The shortest wire may be considered as exhibiting the full effect of spark +or shock which the electromotor can produce by its own direct power; all +the additional force which the arrangements described can excite being due +to some affection of the current, either permanent or momentary, in the +wire itself. That it is a _momentary_ effect, produced only at the instant +of breaking contact, will be fully proved (1089. 1100.). + +1071. No change takes place in the quantity or intensity of the current +during the time the latter is _continued_, from the moment after contact is +made, up to that previous to disunion, except what depends upon the +increased obstruction offered to the passage of the electricity by a long +wire as compared to a short wire. To ascertain this point with regard to +_quantity_, the helix i (1053.) and the galvanometer (1055.) were both made +parts of the metallic circuit used to connect the plates of a small +electromotor, and the deflection at the galvanometer was observed; then a +soft iron core was put into the helix, and as soon as the momentary effect +was over, and the needle had become stationary, it was again observed, and +found to stand exactly at the same division as before. Thus the quantity +passing through the wire when the current was continued was the same either +with or without the soft iron, although the peculiar effects occurring at +the moment of disjunction were very different in degree under such +variation of circumstances. + +1072. That the quality of _intensity_ belonging to the constant current did +not vary with the circumstances favouring the peculiar results under +consideration, so as to yield an explanation of those results, was +ascertained in the following manner. The current excited by an electromotor +was passed through short wires, and its intensity tried by subjecting +different substances to its electrolyzing power (912. 966. &c.); it was +then passed through the wires of the powerful electro-magnet (1056.), and +again examined with respect to its intensity by the same means and found +unchanged. Again, the constancy of the _quantity_ passed in the above +experiment (1071.) adds further proof that the intensity could not have +varied; for had it been increased upon the introduction of the soft iron, +there is every reason to believe that the quantity passed in a given time +would also have increased. + +1073. The fact is, that under many variations of the experiments, the +permanent current _loses_ in force as the effects upon breaking contact +become _exalted_. This is abundantly evident in the comparative experiments +with long and short wires (1068.); and is still more strikingly shown by +the following variation. Solder an inch or two in length of fine platina +wire (about one-hundredth of an inch in diameter) on to one end of the long +communicating wire, and also a similar length of the same platina wire on +to one end of the short communication; then, in comparing the effects of +these two communications, make and break contact between the platina +terminations and the mercury of the cup G or E (1079.). When the short wire +is used, the platina will be _ignited by the constant current_, because of +the quantity of electricity, but the spark on breaking contact will be +hardly visible; on using the longer communicating wire, which by +obstructing will diminish the current, the platina will remain cold whilst +the current passes, but give a bright spark at the moment it ceases: thus +the strange result is obtained of a diminished spark and shock from the +strong current, and increased effects from the weak one. Hence the spark +and shock at the moment of disjunction, although resulting from great +intensity and quantity, of the current _at that moment_, are no direct +indicators or measurers of the intensity or quantity of the constant +current previously passing, and by which they are ultimately produced. + + * * * * * + +1074. It is highly important in using the spark as an indication, by its +relative brightness, of these effects, to bear in mind certain +circumstances connected with its production and appearance (958.). An +ordinary electric spark is understood to be the bright appearance of +electricity passing suddenly through an interval of air, or other badly +conducting matter. A voltaic spark is sometimes of the same nature, but, +generally, is due to the ignition and even combustion of a minute portion +of a good conductor; and that is especially the case when the electromotor +consists of but one or few pairs of plates. This can be very well observed +if either or both of the metallic surfaces intended to touch be solid and +pointed. The moment they come in contact the current passes; it heats, +ignites, and even burns the touching points, and the appearance is as if +the spark passed on making contact, whereas it is only a case of ignition +by the current, contact being previously made, and is perfectly analogous +to the ignition of a fine platina wire connecting the extremities of a +voltaic battery. + +1075. When mercury constitutes one or both of the surfaces used, the +brightness of the spark is greatly increased. But as this effect is due to +the action on, and probable combustion of, the metal, such sparks must only +be compared with other sparks also taken from mercurial surfaces, and not +with such as may be taken, for instance, between surfaces of platina or +gold, for then the appearances are far less bright, though the same +quantity of electricity be passed. It is not at all unlikely that the +commonly occurring circumstance of combustion may affect even the duration +of the light; and that sparks taken between mercury, copper, or other +combustible bodies, will continue for a period sensibly longer than those +passing between platina or gold. + +1076. When the end of a short clean copper wire, attached to one plate of +an electromotor, is brought down carefully upon a surface of mercury +connected with the other plate, a spark, almost continuous, can be +obtained. This I refer to a succession of effects of the following nature: +first, contact,--then ignition of the touching points,--recession of the +mercury from the mechanical results of the heat produced at the place of +contact, and the electro-magnetic condition of the parts at the moment[A], +--breaking of the contact and the production of the peculiar intense effect +dependent thereon,--renewal of the contact by the returning surface of the +undulating mercury,--and then a repetition of the same series of effects, +and that with such rapidity as to present the appearance of a continued +discharge. If a long wire or an electro-magnet be used as the connecting +conductor instead of a short wire, a similar appearance may be produced by +tapping the vessel containing the mercury and making it vibrate; but the +sparks do not usually follow each other so rapidly as to produce an +apparently continuous spark, because of the time required, when the long +wire or electro-magnet is used, both for the full development of the +current (1101. 1106.) and for its complete cessation. + + [A] Quarterly Journal of Science, vol. xii, p. 420. + +1077. Returning to the phenomena in question, the first thought that arises +in the mind is, that the electricity circulates with something like +_momentum or inertia_ in the wire, and that thus a long wire produces +effects at the instant the current is stopped, which a short wire cannot +produce. Such an explanation is, however, at once set aside by the fact, +that the same length of wire produces the effects in very different +degrees, according as it is simply extended, or made into a helix, or forms +the circuit of an electro-magnet (1069.). The experiments to be adduced +(1089.) will still more strikingly show that the idea of momentum cannot +apply. + +1078. The bright spark at the electromotor, and the shock in the arms, +appeared evidently to be due to _one_ current in the long wire, divided +into two parts by the double channel afforded through the body and through +the electromotor; for that the spark was evolved at the place of +disjunction with the electromotor, not by any direct action of the latter, +but by a force immediately exerted in the wire of communication, seemed to +be without doubt (1070.). It followed, therefore, that by using a better +conductor in place of the human body, the _whole_ of this extra current +might be made to pass at that place; and thus be separated from that which +the electromotor could produce by its immediate action, and its _direction_ +be examined apart from any interference of the original and originating +current. This was found to be true; for on connecting the ends of the +principal wire together by a cross wire two or three feet in length, +applied just where the hands had felt the shock, the whole of the extra +current passed by the new channel, and then no better spark than one +producible by a short wire was obtained on disjunction at the electromotor. + +1079. The _current_ thus separated was examined by galvanometers and +decomposing apparatus introduced into the course of this wire. I will +always speak of it as the current in the cross wire or wires, so that no +mistake, as to its place or origin, may occur. In the wood-cut, Z and C +represent the zinc and copper plates of the electromotor; G and E the cups +of mercury where contact is made or broken (1052.); A and B the +terminations of D, the long wire, the helix or the electro-magnet, used to +complete the circuit; N and P are the cross wires, which can either be +brought into contact at _x_, or else have a galvanometer (1058.) or an +electrolyzing apparatus (312. 316.) interposed there. + +[Illustration] + +The production of the _shock_ from the current in the cross wire, whether D +was a long extended wire, or a helix, or an electro-magnet, has been +already described (1060. 1061. 1064.). + +1080. The _spark_ of the cross-wire current could be produced at _x_ in the +following manner: D was made an electro-magnet; the metallic extremities at +_x_ were held close together, or rubbed lightly against each other, whilst +contact was broken at G or E. When the communication was perfect at _x_, +little or no spark appeared at G or E. When the condition of vicinity at +_x_ was favourable for the result required, a bright spark would pass there +at the moment of disjunction, _none_ occurring at G and E: this spark was +the luminous passage of the extra current through the cross-wires. When +there was no contact or passage of current at _x_, then the spark appeared +at G or E, the extra current forcing its way through the electromotor +itself. The same results were obtained by the use of the helix or the +extended wire at D in place of the electro-magnet. + +1081. On introducing a fine platina wire at _x_, and employing the +electro-magnet at D, no visible effects occurred as long as contact was +continued; but on breaking contact at G or E, the fine wire was instantly +ignited and fused. A longer or thicker wire could be so adjusted at _x_ as +to show ignition, without fusion, every time the contact was broken at G +or E. + +1082. It is rather difficult to obtain this effect with helices or wires, +and for very simple reasons: with the helices i, ii, or iii, there was such +retardation of the electric current, from the length of wire used, that a +full inch of platina wire one-fiftieth of an inch in diameter could be +retained ignited at the cross-wires during the _continuance of contact_, by +the portion of electricity passing through it. Hence it was impossible to +distinguish the particular effects at the moments of making or breaking +contact from this constant effect. On using the thick wire helix (1055.), +the same results ensued. + +1083. Proceeding upon the known fact that electric currents of great +quantity but low intensity, though able to ignite thick wires, cannot +produce that effect upon thin ones, I used a very fine platina wire at _x_, +reducing its diameter until a spark appeared at G or E, when contact was +broken there. A quarter of an inch of such wire might be introduced at _x_ +without being ignited by the _continuance_ of contact at G or E; but when +contact was broken at either place, this wire became red-hot; proving, by +this method, the production of the induced current at that moment. + +1084. _Chemical decomposition_ was next effected by the cross-wire current, +an electro-magnet being used at D, and a decomposing apparatus, with +solution of iodide of potassium in paper (1079.), employed at _x_. The +conducting power of the connecting system A B D was sufficient to carry all +the primary current, and consequently no chemical action took place at _x_ +during the _continuance_ of contact at G and E; but when contact was +broken, there was instantly decomposition at _x_. The iodine appeared +against the wire N, and not against the wire P; thus demonstrating that the +current through the cross-wires, when contact was broken, was in the +_reverse direction_ to that marked by the arrow, or that which the +electromotor would have sent through it. + +1085. In this experiment a bright spark occurs at the place of disjunction, +indicating that only a small part of the extra current passed the apparatus +at _x_, because of the small conducting power of the latter. + +1086. I found it difficult to obtain the chemical effects with the simple +helices and wires, in consequence of the diminished inductive power of +these arrangements, and because of the passage of a strong constant current +at _x_ whenever a very active electromotor was used (1082). + +1087. The most instructive set of results was obtained, however, when the +_galvanometer_ was introduced at _x_. Using an electro-magnet at D, and +continuing contact, a current was then indicated by the deflection, +proceeding from P to N, in the direction of the arrow; the cross-wire +serving to carry one part of the electricity excited by the electromotor, +and that part of the arrangement marked A B D, the other and far greater +part, as indicated by the arrows. The magnetic needle was then forced back, +by pins applied upon opposite sides of its two extremities, to its natural +position when uninfluenced by a current; after which, contact being +_broken_ at G or E, it was deflected strongly in the opposite direction; +thus showing, in accordance with the chemical effects (1084), that the +extra current followed a course in the cross-wires _contrary_ to that +indicated by the arrow, i. e. contrary to the one produced by the direct +action of the electromotor[A]. + + [A] It was ascertained experimentally, that if a strong current was + passed through the galvanometer only, and the needle restrained in one + direction as above in its natural position, when the current was + stopped, no vibration of the needle in the opposite direction took + place. + +1088. With the _helix_ only (1061.), these effects could scarcely be +observed, in consequence of the smaller inductive force of this +arrangement, the opposed action from induction in the galvanometer wire +itself, the mechanical condition and tension of the needle from the effect +of blocking (1087.) whilst the current due to continuance of contact was +passing round it; and because of other causes. With the _extended wire_ +(1064.) all these circumstances had still greater influence, and therefore +allowed less chance of success. + +1089. These experiments, establishing as they did, by the quantity, +intensity, and even direction, a distinction between the primary or +generating current and the extra current, led me to conclude that the +latter was identical with the induced current described (6. 26. 74.) in the +First Series of these Researches; and this opinion I was soon able to bring +to proof, and at the same times obtained not the partial (1078.) but entire +separation of one current from the other. + +1090. The double helix (1053.) was arranged so that it should form the +connecting wire between the plates of the electromotor, in being out of the +current, and its ends unconnected. In this condition it acted very well, +and gave a good spark at the time and place of disjunction. The opposite +ends of ii were then connected together so as to form an endless wire, i +remaining unchanged: but now _no spark_, or one scarcely sensible, could be +obtained from the latter at the place of disjunction. Then, again, the ends +of ii were held so nearly together that any current running round that +helix should be rendered visible as a spark; and in this manner a spark was +obtained from ii when the junction of i with the electromotor was broken, +in place of appearing at the disjoined extremity of i itself. + +1091. By introducing a galvanometer or decomposing apparatus into the +circuit formed by the helix ii, I could easily obtain the deflections and +decomposition occasioned by the induced current due to the breaking contact +at helix i, or even to that occasioned by making contact of that helix with +the electromotor; the results in both cases indicating the contrary +directions of the two induced currents thus produced (26.). + +1092. All these effects, except those of decomposition, were reproduced by +two extended long wires, not having the form of helices, but placed close +to each other; and thus it was proved that the _extra current_ could be +removed from the wire carrying the original current to a neighbouring wire, +and was at the same time identified, in direction and every other respect, +with the currents producible by induction (1089.). The case, therefore, of +the bright spark and shock on disjunction may now be stated thus: If a +current be established in a wire, and another wire, forming a complete +circuit, be placed parallel to the first, at the moment the current in the +first is stopped it induces a current in the _same_ direction in the +second, the first exhibiting then but a feeble spark; but if the second +wire be away, disjunction of the first wire induces a current in itself in +the same direction, producing a strong spark. The strong spark in the +single long wire or helix, at the moment of disjunction, is therefore the +equivalent of the current which would be produced in a neighbouring wire if +such second current were permitted. + +1093. Viewing the phenomena as the results of the induction of electrical +currents, many of the principles of action, in the former experiments, +become far more evident and precise. Thus the different effects of short +wires, long wires, helices, and electro-magnets (1069.) may be +comprehended. If the inductive action of a wire a foot long upon a +collateral wire also a foot in length, be observed, it will be found very +small; but if the same current be sent through a wire fifty feet long, it +will induce in a neighbouring wire of fifty feet a far more powerful +current at the moment of making or breaking contact, each successive foot +of wire adding to the sum of action; and by parity of reasoning, a similar +effect should take place when the conducting wire is also that in which the +induced current is formed (74.): hence the reason why a long wire gives a +brighter spark on breaking contact than a short one (1068.), although it +carries much less electricity. + +1094. If the long wire be made into a helix, it will then be still more +effective in producing sparks and shocks on breaking contact; for by the +mutual inductive action of the convolutions each aids its neighbour, and +will be aided in turn, and the sum of effect will be very greatly +increased. + +1095. If an electro-magnet be employed, the effect will be still more +highly exalted; because the iron, magnetized by the power of the continuing +current, will lose its magnetism at the moment the current ceases to pass, +and in so doing will tend to produce an electric current in the wire around +it (37. 38.), in conformity with that which the cessation of current in the +helix itself also tends to produce. + +1096. By applying the laws of the induction of electric currents formerly +developed (6. &c.), various new conditions of the experiments could be +devised, which by their results should serve as tests of the accuracy of +the view just given. Thus, if a long wire be doubled, so that the current +in the two halves shall have opposite actions, it ought not to give a +sensible spark at the moment of disjunction: and this proved to be the +case, for a wire forty feet long, covered with silk, being doubled and tied +closely together to within four inches of the extremities, when used in +that state, gave scarcely a perceptible spark; but being opened out and the +parts separated, it gave a very good one. The two helices i and ii being +joined at their similar ends, and then used at their other extremities to +connect the plates of the electromotor, thus constituted one long helix, of +which one half was opposed in direction to the other half: under these +circumstances it gave scarcely a sensible spark, even when the soft iron +core was within, although containing nearly two hundred feet of wire. When +it was made into one consistent helix of the same length of wire it gave a +very bright spark. + +1097. Similar proofs can be drawn from the mutual inductive action of two +separate currents (1110.); and it is important for the general principles +that the consistent action of two such currents should be established. +Thus, two currents going in the same direction should, if simultaneously +stopped, aid each other by their relative influence; or if proceeding in +contrary directions, should oppose each other under similar circumstances. +I endeavoured at first to obtain two currents from two different +electromotors, and passing them through the helices i and ii, tried to +effect the disjunctions mechanically at the same moment. But in this I +could not succeed; one was always separated before the other, and in that +case produced little or no spark, its inductive power being employed in +throwing a current round the remaining complete circuit (1090.): the +current which was stopped last always gave a bright spark. If it were ever +to become needful to ascertain whether two junctions were accurately broken +at the same moment, these sparks would afford a test for the purpose, +having an infinitesimal degree of perfection. + +1098. I was able to prove the points by other expedients. Two short thick +wires were selected to serve as terminations, by which contact could be +made or broken with the electromotor. The compound helix, consisting of i +and ii (1053.), was adjusted so that the extremities of the two helices +could be placed in communication with the two terminal wires, in such a +manner that the current moving through the thick wires should be divided +into two equal portions in the two helices, these portions travelling, +according to the mode of connexion, either in the same direction or in +contrary directions at pleasure. In this manner two streams could be +obtained, both of which could be stopped simultaneously, because the +disjunction could be broken at G or F by removing a single wire. When the +helices were in contrary directions, there was scarcely a sensible spark at +the place of disjunction; but when they were in accordance there was a very +bright one. + +1099. The helix i was now used constantly, being sometimes associated, as +above, with helix ii in an according direction, and sometimes with helix +iii, which was placed at a little distance. The association i and ii, which +presented two currents able to affect each other by induction, because of +their vicinity, gave a brighter spark than the association i and iii, where +the two streams could not exert their mutual influence; but the difference +was not so great as I expected. + +1100. Thus all the phenomena tend to prove that the effects are due to an +inductive action, occurring at the moment when the principal current is +stopped. I at one time thought they were due to an action continued during +the _whole time_ of the current, and expected that a steel magnet would +have an influence according to its position in the helix, comparable to +that of a soft iron bar, in assisting the effect. This, however, is not the +case; for hard steel, or a magnet in the helix, is not so effectual as soft +iron; nor does it make any difference how the magnet is placed in the +helix, and for very simple reasons, namely, that the effect does not depend +upon a permanent state of the core, but a _change of state_; and that the +magnet or hard steel cannot sink through such a difference of state as soft +iron, at the moment contact ceases, and therefore cannot produce an equal +effect in generating a current of electricity by induction (34. 37.). + + * * * * * + +1101. As an electric current acts by induction with equal energy at the +moment of its commencement as at the moment of its cessation (10. 26.), but +in a contrary direction, the reference of the effects under examination to +an inductive action, would lead to the conclusion that corresponding +effects of an opposite nature must occur in a long wire, a helix, or an +electro-magnet, every time that _contact is made with_ the electromotor. +These effects will tend to establish a resistance for the first moment in +the long conductor, producing a result equivalent to the reverse of a shock +or a spark. Now it is very difficult to devise means fit for the +recognition of such negative results; but as it is probable that some +positive effect is produced at the time, if we knew what to expect, I think +the few facts bearing upon this subject with which I am acquainted are +worth recording. + +1102. The electro-magnet was arranged with an electrolyzing apparatus at +_x_, as before described (1084.), except that the intensity of the chemical +action at the electromotor was increased until the electric current was +just able to produce the feeblest signs of decomposition whilst contact was +continued at G and E (1079.); (the iodine of course appearing against the +end of the cross wire P;) the wire N was also separated from A at _r_, so +that contact there could be made or broken at pleasure. Under these +circumstances the following set of actions was repeated several times: +contact was broken at _r_, then broken at G, next made at _r_, and lastly +renewed at G; thus any current from N to P due to _breaking_ of contact was +avoided, but any additional force to the current from P to N due to +_making_ contact could be observed. In this way it was found, that a much +greater decomposing effect (causing the evolution of iodine against P) +could be obtained by a few completions of contact than by the current which +could pass in a much longer time if the contact was _continued_. This I +attribute to the act of induction in the wire ABD at the moment of contact +rendering that wire a worse conductor, or rather retarding the passage of +the electricity through it for the instant, and so throwing a greater +quantity of the electricity which the electromotor could produce, through +the cross wire passage NP. The instant the induction ceased, ABD resumed +its full power of carrying a constant current of electricity, and could +have it highly increased, as we know by the former experiments (1060.) by +the opposite inductive action brought into activity at the moment contact +at Z or C was _broken_. + +1103. A galvanometer was then introduced at _x_, and the deflection of the +needle noted whilst contact was continued at G and E: the needle was then +blocked as before in one direction (1087.), so that it should not return +when the current ceased, but remain in the position in which the current +could retain it. Contact at G or E was broken, producing of course no +visible effect; it was then renewed, and the needle was instantly +deflected, passing from the blocking pins to a position still further from +its natural place than that which the constant current could give, and thus +showing, by the temporary excess of current in this cross communication, +the temporary retardation in the circuit ABD. + +1104. On adjusting a platina wire at _x_ (1081.) so that it should not be +ignited by the current passing through it whilst contact at G and E was +_continued_, and yet become red-hot by a current somewhat more powerful, I +was readily able to produce its ignition upon _making contact_, and again +upon _breaking contact_. Thus the momentary retardation in ABD on making +contact was again shown by this result, as well also as the opposite result +upon breaking contact. The two ignitions of the wire at _x_ were of course +produced by electric currents moving in opposite directions. + +1105. Using the _helix_ only, I could not obtain distinct deflections at +_x_, due to the extra effect on making contact, for the reasons already +mentioned (1088.). By using a very fine platina wire there (1083.), I did +succeed in obtaining the igniting effect for making contact in the same +manner, though by no means to the same degree, as with the electro-magnet +(1104). + +1106. We may also consider and estimate the effect on _making contact_, by +transferring the force of induction from the wire carrying the original +current to a lateral wire, as in the cases described (1090.); and we then +are sure, both by the chemical and galvanometrical results (1091.), that +the forces upon making and breaking contact, like action and reaction, are +equal in their strength but contrary in their direction. If, therefore, the +effect on making contact resolves itself into a mere retardation of the +current at the first moment of its existence, it must be, in its degree, +equivalent to the high exaltation of that same current at the moment +contact is broken. + +1107. Thus the case, under the circumstances, is, that the intensity and +quantity of electricity moving in a current are smaller when the current +commences or is increased, and greater when it diminishes or ceases, than +they would be if the inductive action occurring at these moments did not +take place; or than they are in the original current wire if the inductive +action be transferred from that wire to a collateral one (1090.). + +1108. From the facility of transference to neighbouring wires, and from the +effects generally, the inductive forces appear to be lateral, i.e. exerted +in a direction perpendicular to the direction of the originating and +produced currents: and they also appear to be accurately represented by the +magnetic curves, and closely related to, if not identical with, magnetic +forces. + +1109. There can be no doubt that the current in one part of a wire can act +by induction upon other parts of the _same_ wire which are lateral to the +first, i.e. in the same vertical section (74.), or in the parts which are +more or less oblique to it (1112.), just as it can act in producing a +current in a neighbouring wire or in a neighbouring coil of the same wire. +It is this which gives the appearance of the current acting upon itself: +but all the experiments and all analogy tend to show that the elements (if +I may so say) of the currents do not act upon themselves, and so cause the +effect in question, but produce it by exciting currents in conducting +matter which is lateral to them. + +1110. It is possible that some of the expressions I have used may seem to +imply, that the inductive action is essentially the action of one current +upon another, or of one element of a current upon another element of the +same current. To avoid any such conclusion I must explain more distinctly +my meaning. If an endless wire be taken, we have the means of generating a +current in it which shall run round the circuit without adding any +electricity to what was previously in the wire. As far as we can judge, the +electricity which appears as a current is the same as that which before was +quiescent in the wire; and though we cannot as yet point out the essential +condition of difference of the electricity at such times, we can easily +recognize the two states. Now when a current acts by induction upon +conducting matter lateral to it, it probably acts upon the electricity in +that conducting matter whether it be in the form of a _current_ or +_quiescent_, in the one case increasing or diminishing the current +according to its direction, in the other producing a current, and the +_amount_ of the inductive action is probably the same in both cases. Hence, +to say that the action of induction depended upon the mutual relation of +two or more currents, would, according to the restricted sense in which the +term current is understood at present (283. 517. 667.), be an error. + +1111. Several of the effects, as, for instances, those with helices(1066.), +with according or counter currents (1097. 1098.), and those on the +production of lateral currents (1090.), appeared to indicate that a current +could produce an effect of induction in a neighbouring wire more readily +than in its own carrying wire, in which case it might be expected that some +variation of result would be produced if a bundle of wires were used as a +conductor instead of a single wire. In consequence the following +experiments were made. A copper wire one twenty-third of an inch in +diameter was cut into lengths of five feet each, and six of these being +laid side by side in one bundle, had their opposite extremities soldered to +two terminal pieces of copper. This arrangement could be used as a +discharging wire, but the general current could be divided into six +parallel streams, which might be brought close together, or, by the +separation of the wires, be taken more or less out of each other's +influence. A somewhat brighter spark was, I think, obtained on breaking +contact when the six wires were close together than when held asunder. + +1112. Another bundle, containing twenty of these wires, was eighteen feet +long: the terminal pieces were one-fifth of an inch in diameter, and each +six inches long. This was compared with nineteen feet in length of copper +wire one-fifth of an inch in diameter. The bundle gave a smaller spark on +breaking contact than the latter, even when its strands were held together +by string: when they were separated, it gave a still smaller spark. Upon +the whole, however, the diminution of effect was not such as I expected: +and I doubt whether the results can be considered as any proof of the truth +of the supposition which gave rise to them. + +1113. The inductive force by which two elements of one current (1109. +1110.) act upon each other, appears to diminish as the line joining them +becomes oblique to the direction of the current and to vanish entirely when +it is parallel. I am led by some results to suspect that it then even +passes into the repulsive force noticed by Ampere[A]; which is the cause of +the elevations in mercury described by Sir Humphry Davy[B], and which again +is probably directly connected with the quality of intensity. + + [A] Recueil d'Observations Electro-Dynamiques, p. 285. + + [B] Philosophical Transactions, 1823, p. 155. + +1114. Notwithstanding that the effects appear only at the making and +breaking of contact, (the current remaining unaffected, seemingly, in the +interval,) I cannot resist the impression that there is some connected and +correspondent effect produced by this lateral action of the elements of the +electric stream during the time of its continuance (60. 242.). An action of +this kind, in fact, is evident in the magnetic relations of the parts of +the current. But admitting (as we may do for the moment) the magnetic +forces to constitute the power which produces such striking and different +results at the commencement and termination of a current, still there +appears to be a link in the chain of effects, a wheel in the physical +mechanism of the action, as yet unrecognised. If we endeavour to consider +electricity and magnetism as the results of two forces of a physical agent, +or a peculiar condition of matter, exerted in determinate directions +perpendicular to each other, then, it appears to me, that we must consider +these two states or forces as convertible into each other in a greater or +smaller degree; i.e. that an element of an electric current has not a +determinate electric force and a determinate magnetic force constantly +existing in the same ratio, but that the two forces are, to a certain +degree, convertible by a process or change of condition at present unknown +to us. How else can a current of a given intensity and quantity be able, by +its direct action, to sustain a state which, when allowed to react, (at the +cessation of the original current,) shall produce a second current, having +an intensity and quantity far greater than the generating one? This cannot +result from a direct reaction of the electric force; and if it result from +a change of electrical into magnetic force, and a reconversion back again, +it will show that they differ in something more than mere direction, as +regards _that agent_ in the conducting wire which constitutes their +immediate cause. + +1115. With reference to the appearance, at different times, of the contrary +effects produced by the making and breaking contact, and their separation +by an intermediate and indifferent state, this separation is probably more +apparent than real. If the conduction of electricity be effected by +vibrations (283.), or by any other mode in which opposite forces are +successively and rapidly excited and neutralized, then we might expect a +peculiar and contrary development of force at the commencement and +termination of the periods during which the conducting action should last +(somewhat in analogy with the colours produced at the outside of an +imperfectly developed solar spectrum): and the intermediate actions, +although not sensible in the same way, may be very important and, for +instance, perhaps constitute the very essence of conductibility. It is by +views and reasons such as these, which seem to me connected with the +fundamental laws and facts of electrical science, that I have been induced +to enter, more minutely than I otherwise should have done, into the +experimental examination of the phenomena described in this paper. + +1116. Before concluding, I may briefly remark, that on using a voltaic +battery of fifty pairs of plates instead of a single pair (1052.), the +effects were exactly of the same kind. The spark on making contact, for the +reasons before given, was very small (1101. 1107.); that on breaking +contact, very excellent and brilliant. The _continuous_ discharge did not +seem altered in character, whether a short wire or the powerful +electro-magnet were used as a connecting discharger. + +1117. The effects produced at the commencement and end of a current, (which +are separated by an interval of time when that current is supplied from a +voltaic apparatus,) must occur at the same moment when a common electric +discharge is passed through a long wire. Whether, if happening accurately +at the same moment, they would entirely neutralize each other, or whether +they would not still give some definite peculiarity to the discharge, is a +matter remaining to be examined; but it is very probable that the peculiar +character and pungency of sparks drawn from a long wire depend in part upon +the increased intensity given at the termination of the discharge by the +inductive action then occurring. + +1118. In the wire of the helix of magneto-electric machines, (as, for +instance, in Mr. Saxton's beautiful arrangement,) an important influence of +these principles of action is evidently shown. From the construction of the +apparatus the current is permitted to move in a complete metallic circuit +of great length during the first instants of its formation: it gradually +rises in strength, and is then suddenly stopped by the breaking of the +metallic circuit; and thus great intensity is given _by induction_ to the +electricity, which at that moment passes (1064. 1060.). This intensity is +not only shown by the brilliancy of the spark and the strength of the +shock, but also by the necessity which has been experienced of +well-insulating the convolutions of the helix, in which the current is +formed: and it gives to the current a force at these moments very far above +that which the apparatus could produce if the principle which forms the +subject of this paper were not called into play. + +_Royal Institution, +December 8th, 1834._ + + + + +TENTH SERIES. + + +S 16. _On an improved form of the Voltaic Battery._ S 17. _Some practical +results respecting the construction and use of the Voltaic Battery._ + +Received June 16,--Read June 18, 1835. + + +1119. I Have lately had occasion to examine the voltaic trough practically, +with a view to improvements in its construction and use; and though I do +not pretend that the results have anything like the importance which +attaches to the discovery of a new law or principle, I still think they are +valuable, and may therefore, if briefly told, and in connexion with former +papers, be worthy the approbation of the Royal Society. + +S 16. _On an improved form of the Voltaic Battery._ + + +1120. In a simple voltaic circuit (and the same is true of the battery) the +chemical forces which, during their activity, give power to the instrument, +are generally divided into two portions; one of these is exerted locally, +whilst the other is transferred round the circle (947. 996.); the latter +constitutes the electric current of the instrument, whilst the former is +altogether lost or wasted. The ratio of these two portions of power may be +varied to a great extent by the influence of circumstances: thus, in a +battery not closed, _all_ the action is local; in one of the ordinary +construction, _much_ is in circulation when the extremities are in +communication: and in the perfect one, which I have described (1001.), +_all_ the chemical power circulates and becomes electricity. By referring +to the quantity of zinc dissolved from the plates (865. 1120.), and the +quantity of decomposition effected in the volta-electrometer (711. 1126,) +or elsewhere, the proportions of the local and transferred actions under +any particular circumstances can be ascertained, and the efficacy of the +voltaic arrangement, or the waste of chemical power at its zinc plates, be +accurately determined. + +1121. If a voltaic battery were constructed of zinc and platina, the latter +metal surrounding the former, as in the double copper arrangement, and the +whole being excited by dilute sulphuric acid, then no insulating divisions +of glass, porcelain or air would be required between the contiguous platina +surfaces; and, provided these did not touch metallically, the same acid +which, being between the zinc and platina, would excite the battery into +powerful action, would, between the two surfaces of platina, produce no +discharge of the electricity, nor cause any diminution of the power of the +trough. This is a necessary consequence of the resistance to the passage of +the current which I have shown occurs at the place of decomposition (1007. +1011.); for that resistance is fully able to stop the current, and +therefore acts as insulation to the electricity of the contiguous plates, +inasmuch as the current which tends to pass between them never has a higher +intensity than that due to the action of a single pair. + +1122. If the metal surrounding the zinc be copper (1045.), and if the acid +be nitro-sulphuric acid (1020.), then a slight discharge between the two +contiguous coppers does take place, provided there be no other channel open +by which the forces may circulate; but when such a channel is permitted, +the return or back discharge of which I speak is exceedingly diminished, in +accordance with the principles laid down in the Eighth Series of these +Researches. + +1123. Guided by these principles I was led to the construction of a voltaic +trough, in which the coppers, passing round both surfaces of the zincs, as +in Wollaston's construction, should not be separated from each other except +by an intervening thickness of paper, or in some other way, so as to +prevent metallic contact, and should thus constitute an instrument compact, +powerful, economical, and easy of use. On examining, however, what had been +done before, I found that the new trough was in all essential respects the +same as that invented and described by Dr. Hare, Professor in the +University of Pennsylvania, to whom I have great pleasure in referring it. + +1124. Dr. Hare has fully described his trough[A]. In it the contiguous +copper plates are separated by thin veneers of wood, and the acid is poured +on to, or off, the plates by a quarter revolution of an axis, to which both +the trough containing the plates, and another trough to collect and hold +the liquid, are fixed. This arrangement I have found the most convenient of +any, and have therefore adopted it. My zinc plates were cut from rolled +metal, and when soldered to the copper plates had the form delineated, fig. +1. These were then bent over a gauge into the form fig. 2, and when packed +in the wooden box constructed to receive them, were arranged as in fig. +3[B], little plugs of cork being used to keep the zinc plates from touching +the copper plates, and a single or double thickness of cartridge paper +being interposed between the contiguous surfaces of copper to prevent them +from coming in contact. Such was the facility afforded by this arrangement, +that a trough of forty pairs of plates could be unpacked in five minutes, +and repacked again in half an hour; and the whole series was not more than +fifteen inches in length. + +[Illustration: Fig. 1.] + +[Illustration: Fig. 2.] + +[Illustration: Fig. 3.] + + [A] Philosophical Magazine, 1824, vol. lxiii. p. 241; or Silliman's + Journal, vol. vii. See also a previous paper by Dr. Hare, Annals of + Philosophy, 1821, vol. i. p. 329, in which he speaks of the + non-necessity of insulation between the coppers. + + [B] The papers between the coppers are, for the sake of distinctness, + omitted in the figure. + +1125. This trough, of forty pairs of plates three inches square, was +compared, as to the ignition of a platina wire, the discharge between +points of charcoal, the shock on the human frame, &c., with forty pairs of +four-inch plates having double coppers, and used in porcelain troughs +divided into insulating cells, the strength of the acid employed to excite +both being the same. In all these effects the former appeared quite equal +to the latter. On comparing a second trough of the new construction, +containing twenty pairs of four-inch plates, with twenty pairs of four-inch +plates in porcelain troughs, excited by acid of the same strength, the new +trough appeared to surpass the old one in producing these effects, +especially in the ignition of wire. + +1126. In these experiments the new trough diminished in its energy much +more rapidly than the one on the old construction, and this was a necessary +consequence of the smaller quantity of acid used to excite it, which in the +case of the forty pairs of new construction was only one-seventh part of +that used for the forty pairs in the porcelain troughs. To compare, +therefore, both forms of the voltaic trough in their decomposing powers, +and to obtain accurate data as to their relative values, experiments of the +following kind were made. The troughs were charged with a known quantity of +acid of a known strength; the electric current was passed through a +volta-electrometer (711.) having electrodes 4 inches long and 2.3 inches in +width, so as to oppose as little obstruction as possible to the current; +the gases evolved were collected and measured, and gave the quantity of +water decomposed. Then the whole of the charge used was mixed together, and +a known part of it analyzed, by being precipitated and boiled with excess +of carbonate of soda, and the precipitate well-washed, dried, ignited, and +weighed. In this way the quantity of metal oxidized and dissolved by the +acid was ascertained; and the part removed from each zinc plate, or from +all the plates, could be estimated and compared with the water decomposed +in the volta-electrometer. To bring these to one standard of comparison, I +have reduced the results so as to express the loss at the plates in +equivalents of zinc for the equivalent of water decomposed at the +volta-electrometer: I have taken the equivalent number of water as 9, and +of zinc as 32.5, and have considered 100 cubic inches of the mixed oxygen +and hydrogen, as they were collected over a pneumatic trough, to result +from the decomposition of 12.68 grains of water. + +1127. The acids used in these experiments were three,--sulphuric, nitric, +and muriatic. The sulphuric acid was strong oil of vitriol; one cubical +inch of it was equivalent to 486 grains of marble. The nitric acid was very +nearly pure; one cubical inch dissolved 150 grains of marble. The muriatic +acid was also nearly pure, and one cubical inch dissolved 108 grains of +marble. These were always mixed with water by volumes, the standard of +volume being a cubical inch. + +1128. An acid was prepared consisting of 200 parts water, 4-1/2 parts +sulphuric acid, and 4 parts nitric acid; and with this both my trough +containing forty pairs of three-inch plates, and four porcelain troughs, +arranged in succession, each containing ten pairs of plates with double +coppers four inches square, were charged. These two batteries were then +used in succession, and the action of each was allowed to continue for +twenty or thirty minutes, until the charge was nearly exhausted, the +connexion with the volta-electrometer being carefully preserved during the +whole time, and the acid in the troughs occasionally mixed together. In +this way the former trough acted so well, that for each equivalent of water +decomposed in the volta-electrometer only from 2 to 2.5 equivalents of zinc +were dissolved from each plate. In four experiments the average was 2.21 +equivalents for each plate, or 88.4 for the whole battery. In the +experiments with the porcelain troughs, the equivalents of consumption at +each plate were 3.51, or 141.6 for the whole battery. In a perfect voltaic +battery of forty pairs of plates (991. 1001.) the consumption would have +been one equivalent for each zinc plate, or forty for the whole. + +1129. Similar experiments were made with two voltaic batteries, one +containing twenty pairs of four-inch plates, arranged as I have described +(1124.), and the other twenty pairs of four-inch plates in porcelain +troughs. The average of five experiments with the former was a consumption +of 3.7 equivalents of zinc from each plate, or 74 from the whole: the +average of three experiments with the latter was 5.5 equivalents from each +plate, or 110 from the whole: to obtain this conclusion two experiments +were struck out, which were much against the porcelain troughs, and in +which some unknown deteriorating influence was supposed to be accidentally +active. In all the experiments, care was taken not to compare _new_ and +_old_ plates together, as that would have introduced serious errors into +the conclusions (1146.). + +1130. When ten pairs of the new arrangement were used, the consumption of +zinc at each plate was 6.76 equivalents, or 67.6 for the whole. With ten +pairs of the common construction, in a porcelain trough, the zinc oxidized +was, upon an average, 15.5 equivalents each plate, or 155 for the entire +trough. + +1131. No doubt, therefore, can remain of the equality or even the great +superiority of this form of voltaic battery over the best previously in +use, namely, that with double coppers, in which the cells are insulated. +The insulation of the coppers may therefore be dispensed with; and it is +that circumstance which principally permits of such other alterations in +the construction of the trough as gives it its practical advantages. + +1132. The advantages of this form of trough are very numerous and great. i. +It is exceedingly compact, for 100 pairs of plates need not occupy a trough +of more than three feet in length, ii. By Dr. Hare's plan of making the +trough turn upon copper pivots which rest upon copper bearings, the latter +afford _fixed_ terminations; and these I have found it very convenient to +connect with two cups of mercury, fastened in the front of the stand of the +instrument. These fixed terminations give the great advantage of arranging +an apparatus to be used in connexion with the battery _before_ the latter +is put into action, iii. The trough is put into readiness for use in an +instant, a single jug of dilute acid being sufficient for the charge of 100 +pairs of four-inch plates, iv. On making the trough pass through a quarter +of a revolution, it becomes active, and the great advantage is obtained of +procuring for the experiment the effect of the _first contact_ of the zinc +and acid, which is twice or sometimes even thrice that which the battery +can produce a minute or two after (1036. 1150.). v. When the experiment is +completed, the acid can be at once poured from between the plates, so that +the battery is never left to waste during an unconnected state of its +extremities; the acid is not unnecessarily exhausted; the zinc is not +uselessly consumed; and, besides avoiding these evils, the charge is mixed +and rendered uniform, which produces a great and good result (1039.); and, +upon proceeding to a second experiment, the important effect of _first +contact_ is again obtained. vi. The saving of zinc is very great. It is not +merely that, whilst in action, the zinc performs more voltaic duty (1128. +1129.), but _all_ the destruction which takes place with the ordinary forms +of battery between the experiments is prevented. This saving is of such +extent, that I estimate the zinc in the new form of battery to be thrice as +effective as that in the ordinary form. vii. The importance of this saving +of metal is not merely that the value of the zinc is saved, but that the +battery is much lighter and more manageable; and also that the surfaces of +the zinc and copper plates may be brought much nearer to each other when +the battery is constructed, and remain so until it is worn out: the latter +is a very important advantage (1148.). viii. Again, as, in consequence of +the saving, thinner plates will perform the duty of thick ones, rolled zinc +may be used; and I have found rolled zinc superior to cast zinc in action; +a superiority which I incline to attribute to its greater purity (1144.). +ix. Another advantage is obtained in the economy of the acid used, which is +proportionate to the diminution of the zinc dissolved. x. The acid also is +more easily exhausted, and is in such small quantity that there is never +any occasion to return an old charge into use. The acid of old charges +whilst out of use, often dissolves portions of copper from the black +flocculi usually mingled with it, which are derived from the zinc; now any +portion of copper in solution in the charge does great harm, because, by +the _local_ action of the acid and zinc, it tends to precipitate upon the +latter, and diminish its voltaic efficacy (1145.). xi. By using a due +mixture of nitric and sulphuric acid for the charge (1139.), no gas is +evolved from the troughs; so that a battery of several hundred pairs of +plates may, without inconvenience, be close to the experimenter. xii. If, +during a series of experiments, the acid becomes exhausted, it can be +withdrawn, and replaced by other acid with the utmost facility; and after +the experiments are concluded, the great advantage of easily washing the +plates is at command. And it appears to me, that in place of making, under +different circumstances, mutual sacrifices of comfort, power, and economy, +to obtain a desired end, all are at once obtained by Dr. Hare's form of +trough. + +1133. But there are some disadvantages which I have not yet had time to +overcome, though I trust they will finally be conquered. One is the extreme +difficulty of making a wooden trough constantly water-tight under the +alternations of wet and dry to which the voltaic instrument is subject. To +remedy this evil, Mr. Newman is now engaged in obtaining porcelain troughs. +The other disadvantage is a precipitation of copper on the zinc plates. It +appears to me to depend mainly on the circumstance that the papers between +the coppers retain acid when the trough is emptied; and that this acid +slowly acting on the copper, forms a salt, which gradually mingles with the +next charge, and is reduced on the zinc plate by the local action (1120.): +the power of the whole battery is then reduced. I expect that by using +slips of glass or wood to separate the coppers at their edges, their +contact can be sufficiently prevented, and the space between them be left +so open that the acid of a charge can be poured and washed out, and so be +removed from _every part_ of the trough when the experiments in which the +latter is used are completed. + +1134. The actual superiority of the troughs which I have constructed on +this plan, I believe to depend, first and principally, on the closer +approximation of the zinc and copper surfaces;--in my troughs they are only +one-tenth of an inch apart (1148.);--and, next, on the superior quality of +the rolled zinc above the cast zinc used in the construction of the +ordinary pile. It cannot be that insulation between the contiguous coppers +is a disadvantage, but I do not find that it is any advantage; for when, +with both the forty pairs of three-inch plates and the twenty pairs of +four-inch plates, I used papers well-soaked in wax[A], these being so large +that when folded at the edges they wrapped over each other, so as to make +cells as insulating as those of the porcelain troughs, still no sensible +advantage in the chemical action was obtained. + + [A] A single paper thus prepared could insulate the electricity of a + trough of forty pairs of plates. + +1135. As, upon principle, there must be a discharge of part of the +electricity from the edges of the zinc and copper plates at the sides of +the trough, I should prefer, and intend having, troughs constructed with a +plate or plates of crown glass at the sides of the trough: the bottom will +need none, though to glaze that and the ends would be no disadvantage. The +plates need not be fastened in, but only set in their places; nor need they +be in large single pieces. + + +S 17. _Some practical results respecting the construction and use of the +Voltaic Battery_ (1034. &c.). + + +1136. The electro-chemical philosopher is well acquainted with some +practical results obtained from the voltaic battery by MM.. Gay-Lussac and +Thenard, and given in the first forty-five pages of their 'Recherches +Physico-Chimiques'. Although the following results are generally of the +same nature, yet the advancement made in this branch of science of late +years, the knowledge of the definite action of electricity, and the more +accurate and philosophical mode of estimating the results by the +equivalents of zinc consumed, will be their sufficient justification. + +1137. _Nature and strength of the acid._--My battery of forty pairs of +three-inch plates was charged with acid consisting of 200 parts water and 9 +oil of vitriol. Each plate lost, in the average of the experiments, 4.66 +equivalents of zinc for the equivalent of water decomposed in the +volta-electrometer, or the whole battery 186.4 equivalents of zinc. Being +charged with a mixture of 200 water and 16 of the muriatic acid, each plate +lost 3.8, equivalents of zinc for the water decomposed, or the whole +battery 152 equivalents of zinc. Being charged with a mixture of 200 water +and 8 nitric acid, each plate lost 1.85, equivalents of zinc for one +equivalent of water decomposed, or the whole battery 74.16 equivalents of +zinc. The sulphuric and muriatic acids evolved much hydrogen at the plates +in the trough; the nitric acid no gas whatever. The relative strengths of +the original acids have already been given (1127.); but a difference in +that respect makes no important difference in the results when thus +expressed by equivalents (1140.). + +1138. Thus nitric acid proves to be the best for this purpose; its +superiority appears to depend upon its favouring the electrolyzation of the +liquid in the cells of the trough upon the principles already explained +(905. 973, 1022.), and consequently favouring the transmission of the +electricity, and therefore the production of transferable power (1120.). + +1139. The addition of nitric acid might, consequently, be expected to +improve sulphuric and muriatic acids. Accordingly, when the same trough was +charged with a mixture of 200 water, 9 oil of vitriol, and 4 nitric acid, +the consumption of zinc was at each plate 2.786, and for the whole battery +111.5, equivalents. When the charge was 200 water, 9 oil of vitriol, and 8 +nitric acid, the loss per plate was 2.26, or for the whole battery 90.4, +equivalents. When the trough was charged with a mixture of 200 water, 16 +muriatic acid, and 6 nitric acid, the loss per plate was 2.11, or for the +whole battery 84.4, equivalents. Similar results were obtained with my +battery of twenty pairs of four-inch plates (1129.). Hence it is evident +that the nitric acid was of great service when mingled with the sulphuric +acid; and the charge generally used after this time for ordinary +experiments consisted of 200 water, 4-1/2 oil of vitriol, and 4 nitric +acid. + +1140. It is not to be supposed that the different strengths of the acids +produced the differences above; for within certain limits I found the +electrolytic effects to be nearly as the strengths of the acids, so as to +leave the expression of force, when given in equivalents, almost constant. +Thus, when the trough was charged with a mixture of 200 water and 8 nitric +acid, each plate lost 1.854 equivalent of zinc. When the charge was 200 +water and 16 nitric acid, the loss per plate was 1.82 equivalent. When it +was 200 water and 32 nitric acid, the loss was 2.1 equivalents. The +differences here are not greater than happen from unavoidable +irregularities, depending on other causes than the strength of acid. + +1141. Again, when a charge consisting of 200 water, 4-1/2 oil of vitriol, +and 4 nitric acid was used, each zinc plate lost 2.16 equivalents; when the +charge with the same battery was 200 water, 9 oil of vitriol, and 8 nitric +acid, each zinc plate lost 2.26 equivalents. + +1142. I need hardly say that no copper is dissolved during the regular +action of the voltaic trough. I have found that much ammonia is formed in +the cells when nitric acid, either pure or mixed with sulphuric acid, is +used. It is produced in part as a secondary result at the cathodes (663.) +of the different portions of fluid constituting the necessary electrolyte, +in the cells. + +1143. _Uniformity of the charge._--This is a most important point, as I +have already shown experimentally (1042. &c.). Hence one great advantage of +Dr. Hare's mechanical arrangement of his trough. + +1144. _Purity of the zinc._--If pure zinc could be obtained, it would be +very advantageous in the construction of the voltaic apparatus (998.). Most +zincs, when put into dilute sulphuric acid, leave more or less of an +insoluble matter upon the surface in the form of a crust, which contains +various metals, as copper, lead, zinc, iron, cadmium, &c., in the metallic +state. Such particles, by discharging part of the transferable power, +render it, as to the whole battery, local; and so diminish the effect. As +an indication connected with the more or less perfect action of the +battery, I may mention that no gas ought to rise from the zinc plates. The +more gas which is generated upon these surfaces, the greater is the local +action and the less the transferable force. The investing crust is also +inconvenient, by preventing the displacement and renewal of the charge upon +the surface of the zinc. Such zinc as, dissolving in the cleanest manner in +a dilute acid, dissolves also the slowest, is the best; zinc which contains +much copper should especially be avoided. I have generally found rolled +Liege or Mosselman's zinc the purest; and to the circumstance of having +used such zinc in its construction attribute in part the advantage of the +new battery (1134.). + +1145. _Foulness of the zinc plates._--After use, the plates of a battery +should be cleaned from the metallic powder upon their surfaces, especially +if they are employed to obtain the laws of action of the battery itself. +This precaution was always attended to with the porcelain trough batteries +in the experiments described (1125, &c.). If a few foul plates are mingled +with many clean ones, they make the action in the different cells +irregular, and the transferable power is accordingly diminished, whilst the +local and wasted power is increased. No old charge containing copper should +be used to excite a battery. + +1146. _New and old plates._--I have found voltaic batteries far more +powerful when the plates were new than when they have been used two or +three times; so that a new and an used battery cannot be compared together, +or even a battery with itself on the first and after times of use. My +trough of twenty pairs of four-inch plates, charged with acid consisting of +200 water, 4-1/2 oil of vitriol, and 4 nitric acid, lost, upon the first +time of being used, 2.82 equivalents per plate. When used after the fourth +time with the same charge, the loss was from 3.26 to 4.47 equivalents per +plate; the average being 3.7 equivalents. The first time the forty pair of +plates (1124.) were used, the loss at each plate was only 1.65 equivalent; +but afterwards it became 2.16, 2.17, 2.52. The first time twenty pair of +four-inch plates in porcelain troughs were used, they lost, per plate, only +3.7 equivalents; but after that, the loss was 5.25, 5.36, 5.9 equivalents. +Yet in all these cases the zincs had been well-cleaned from adhering +copper, &c., before each trial of power. + +1147. With the rolled zinc the fall in force soon appeared to become +constant, i.e. to proceed no further. But with the cast zinc plates +belonging to the porcelain troughs, it appeared to continue, until at last, +with the same charge, each plate lost above twice as much zinc for a given +amount of action as at first. These troughs were, however, so irregular +that I could not always determine the circumstances affecting the amount of +electrolytic action. + +1148. _Vicinity of the copper and zinc._--The importance of this point in +the construction of voltaic arrangements, and the greater power, as to +immediate action, which is obtained when the zinc and copper surfaces are +near to each other than when removed further apart, are well known. I find +that the power is not only greater on the instant, but also that the sum of +transferable power, in relation to the whole sum of chemical action at the +plates, is much increased. The cause of this gain is very evident. Whatever +tends to retard the circulation of the transferable force, (i.e. the +electricity,) diminishes the proportion of such force, and increases the +proportion of that which is local (996. 1120.). Now the liquid in the cells +possesses this retarding power, and therefore acts injuriously, in greater +or less proportion, according to the quantity of it between the zinc and +copper plates, i.e. according to the distances between their surfaces. A +trough, therefore, in which the plates are only half the distance asunder +at which they are placed in another, will produce more transferable, and +less local, force than the latter; and thus, because the electrolyte in the +cells can transmit the current more readily; both the intensity and +quantity of electricity is increased for a given consumption of zinc. To +this circumstance mainly I attribute the superiority of the trough I have +described (1134.). + +1149. The superiority of _double coppers_ over single plates also depends +in part upon diminishing the resistance offered by the electrolyte between +the metals. For, in fact, with double coppers the sectional area of the +interposed acid becomes nearly double that with single coppers, and +therefore it more freely transfers the electricity. Double coppers are, +however, effective, mainly because they virtually double the acting surface +of the zinc, or nearly so; for in a trough with single copper plates and +the usual construction of cells, that surface of zinc which is not opposed +to a copper surface is thrown almost entirely out of voltaic action, yet +the acid continues to act upon it and the metal is dissolved, producing +very little more than local effect (947. 996). But when by doubling the +copper, that metal is opposed to the second surface of the zinc plate, then +a great part of the action upon the latter is converted into transferable +force, and thus the power of the trough as to quantity of electricity is +highly exalted. + +1150. _First immersion of the plates._--The great effect produced at the +first immersion of the plates, (apart from their being new or used +(1146.),) I have attributed elsewhere to the unchanged condition of the +acid in contact with the zinc plate (1003. 1037.): as the acid becomes +neutralized, its exciting power is proportionally diminished. Hare's form +of trough secures much advantage of this kind, by mingling the liquid, and +bringing what may be considered as a fresh surface of acid against the +plates every time it is used immediately after a rest. + +1151. _Number of plates._[A]--The most advantageous number of plates in a +battery used for chemical decomposition, depends almost entirely upon the +resistance to be overcome at the place of action; but whatever that +resistance may be, there is a certain number which is more economical than +either a greater or a less. Ten pairs of four-inch plates in a porcelain +trough of the ordinary construction, acting in the volta-electrometer +(1126.) upon dilute sulphuric acid of spec. grav. 1.314, gave an average +consumption of 15.4 equivalents per plate, or 154 equivalents on the whole. +Twenty pairs of the same plates, with the same acid, gave only a +consumption of 5.5 per plate, or 110 equivalents upon the whole. When forty +pairs of the same plates were used, the consumption was 3.54 equivalents +per plate, or 141.6 upon the whole battery. Thus the consumption of zinc +arranged as _twenty_ plates was more advantageous than if arranged either +as _ten_ or as _forty_. + + [A] Gay-Lussac and Thenard, Recherches Physico-Chimiques, tom. i. p. 29. + +1152. Again, ten pairs of my four-inch plates (1129.) lost 6.76 each, or +the whole ten 67.6 equivalents of zinc, in effecting decomposition; whilst +twenty pairs of the same plates, excited by the same acid, lost 3.7 +equivalents each, or on the whole 74 equivalents. In other comparative +experiments of numbers, ten pairs of the three inch-plates, (1125.) lost +3.725, or 37.25 equivalents upon the whole; whilst twenty pairs lost 2.53 +each, or 50.6 in all; and forty pairs lost on an average 2.21, or 88.4 +altogether. In both these cases, therefore, increase of numbers had not +been advantageous as to the effective production of _transferable chemical +power_ from the _whole quantity of chemical force_ active at the surfaces +of excitation (1120.). + +1153. But if I had used a weaker acid or a worse conductor in the +volta-electrometer, then the number of plates which would produce the most +advantageous effect would have risen; or if I had used a better conductor +than that really employed in the volta-electrometer, I might have reduced +the number even to one; as, for instance, when a thick wire is used to +complete the circuit (865., &c.). And the cause of these variations is very +evident, when it is considered that each successive plate in the voltaic +apparatus does not add anything to the _quantity_ of transferable power or +electricity which the first plate can put into motion, provided a good +conductor be present, but tends only to exalt the _intensity_ of that +quantity, so as to make it more able to overcome the obstruction of bad +conductors (994. 1158.). + +1154. _Large or small plates._[A]--The advantageous use of large or small +plates for electrolyzations will evidently depend upon the facility with +which the transferable power of electricity can pass. If in a particular +case the most effectual number of plates is known (1151.), then the +addition of more zinc would be most advantageously made in increasing the +_size_ of the plates, and not their _number_. At the same time, large +increase in the size of the plates would raise in a small degree the most +favourable number. + + [A] Gay-Lussac and Thenard, Recherches Physico-Chimiques, tom, i. p. 20. + +1155. Large and small plates should not be used together in the same +battery: the small ones occasion a loss of the power of the large ones, +unless they be excited by an acid proportionably more powerful; for with a +certain acid they cannot transmit the same portion of electricity in a +given time which the same acid can evolve by action on the larger plates. + +1156. _Simultaneous decompositions._--When the number of plates in a +battery much surpasses the most favourable proportion (1151--1153.), two or +more decompositions may be effected simultaneously with advantage. Thus my +forty pairs of plates (1124.) produced in one volta-electrometer 22.8 cubic +inches of gas. Being recharged exactly in the same manner, they produced in +each of two volta-electrometers 21 cubical inches. In the first experiment +the whole consumption of zinc was 88.4 equivalents, and in the second only +48.28 equivalents, for the whole of the water decomposed in both +volta-electrometers. + +1157. But when the twenty pairs of four-inch plates (1129.) were tried in +a similar manner, the results were in the opposite direction. With one +volta-electrometer 52 cubic inches of gas were obtained; with two, only +14.6 cubic inches from each. The quantity of charge was not the same in +both cases, though it was of the same strength; but on rendering the +results comparative by reducing them to equivalents (1126.), it was found +that the consumption of metal in the first case was 74, and in the second +case 97, equivalents for the _whole_ of the water decomposed. These +results of course depend upon the same circumstances of retardation, &c., +which have been referred to in speaking of the proper number of plates +(1151.). + +1158. That the _transferring_, or, as it is usually called, _conducting, +power_ of an electrolyte which is to be decomposed, or other interposed +body, should be rendered as good as possible[A], is very evident (1020. +1120.). With a perfectly good conductor and a good battery, nearly all the +electricity is passed, i.e. _nearly all_ the chemical power becomes +transferable, even with a single pair of plates (807.). With an interposed +nonconductor none of the chemical power becomes transferable. With an +imperfect conductor more or less of the chemical power becomes transferable +as the circumstances favouring the transfer of forces across the imperfect +conductor are exalted or diminished: these circumstances are, actual +increase or improvement of the conducting power, enlargement of the +electrodes, approximation of the electrodes, and increased intensity of the +passing current. + + [A] Gay-Lussac and Thenard, Recherches Physico-Chimiques, tom. i. pp. + 13, 15, 22. + +1159. The introduction of common spring water in place of one of the +volta-electrometers used with twenty pairs of four-inch plates (1156.) +caused such obstruction as not to allow one-fifteenth of the transferable +force to pass which would have circulated without it. Thus +fourteen-fifteenths of the available force of the battery were destroyed, +local force, (which was rendered evident by the evolution of gas from the +being converted into zincs,) and yet the platina electrodes in the water +were three inches long, nearly an inch wide, and not a quarter of an inch +apart. + +1160. These points, i.e. the increase of conducting power, the enlargement +of the electrodes, and their approximation, should be especially attended +to in _volta-electrometers_. The principles upon which their utility depend +are so evident that there can be no occasion for further development of +them here. + +_Royal Institution, +October 11, 1834._ + + + + +ELEVENTH SERIES. + +S 18. _On Induction._ P i. _Induction an action of contiguous particles._ +P ii. _Absolute charge of matter._ P iii. _Electrometer and inductive +apparatus employed._ P iv. _Induction in curved lines._ P v. _Specific +inductive capacity._ P vi. _General results as to induction._ + +Received November 30,--Read December 21, 1837. + + +P i. _Induction an action of contiguous particles._ + + +1161. The science of electricity is in that state in which every part of it +requires experimental investigation; not merely for the discovery of new +effects, but what is just now of far more importance, the development of +the means by which the old effects are produced, and the consequent more +accurate determination of the first principles of action of the most +extraordinary and universal power in nature:--and to those philosophers who +pursue the inquiry zealously yet cautiously, combining experiment with +analogy, suspicious of their preconceived notions, paying more respect to a +fact than a theory, not too hasty to generalize, and above all things, +willing at every step to cross-examine their own opinions, both by +reasoning and experiment, no branch of knowledge can afford so fine and +ready a field for discovery as this. Such is most abundantly shown to be +the case by the progress which electricity has made in the last thirty +years: Chemistry and Magnetism have successively acknowledged its +over-ruling influence; and it is probable that every effect depending upon +the powers of inorganic matter, and perhaps most of those related to +vegetable and animal life, will ultimately be found subordinate to it. + +1162. Amongst the actions of different kinds into which electricity has +conventionally been subdivided, there is, I think, none which excels, or +even equals in importance, that called _Induction_. It is of the most +general influence in electrical phenomena, appearing to be concerned in +every one of them, and has in reality the character of a first, essential, +and fundamental principle. Its comprehension is so important, that I think +we cannot proceed much further in the investigation of the laws of +electricity without a more thorough understanding of its nature; how +otherwise can we hope to comprehend the harmony and even unity of action +which doubtless governs electrical excitement by friction, by chemical +means, by heat, by magnetic influence, by evaporation, and even by the +living being? + +1163. In the long-continued course of experimental inquiry in which I have +been engaged, this general result has pressed upon me constantly, namely, +the necessity of admitting two forces, or two forms or directions of a +force (516. 517.), combined with the impossibility of separating these two +forces (or electricities) from each other, either in the phenomena of +statical electricity or those of the current. In association with this, the +impossibility under any circumstances, as yet, of absolutely charging +matter of any kind with one or the other electricity only, dwelt on my +mind, and made me wish and search for a clearer view than any that I was +acquainted with, of the way in which electrical powers and the particles of +matter are related; especially in inductive actions, upon which almost all +others appeared to rest. + +1164. When I discovered the general fact that electrolytes refused to yield +their elements to a current when in the solid state, though they gave them +forth freely if in the liquid condition (380. 394. 402.), I thought I saw +an opening to the elucidation of inductive action, and the possible +subjugation of many dissimilar phenomena to one law. For let the +electrolyte be water, a plate of ice being coated with platina foil on its +two surfaces, and these coatings connected with any continued source of the +two electrical powers, the ice will charge like a Leyden arrangement, +presenting a case of common induction, but no current will pass. If the ice +be liquefied, the induction will fall to a certain degree, because a +current can now pass; but its passing is dependent upon a _peculiar +molecular arrangement_ of the particles consistent with the transfer of the +elements of the electrolyte in opposite directions, the degree of discharge +and the quantity of elements evolved being exactly proportioned to each +other (377. 783.). Whether the charging of the metallic coating be effected +by a powerful electrical machine, a strong and large voltaic battery, or a +single pair of plates, makes no difference in the principle, but only in +the degree of action (360). Common induction takes place in each case if +the electrolyte be solid, or if fluid, chemical action and decomposition +ensue, provided opposing actions do not interfere; and it is of high +importance occasionally thus to compare effects in their extreme degrees, +for the purpose of enabling us to comprehend the nature of an action in its +weak state, which may be only sufficiently evident to us in its stronger +condition (451.). As, therefore, in the electrolytic action, _induction_ +appeared to be the _first_ step, and _decomposition_ the _second_ (the +power of separating these steps from each other by giving the solid or +fluid condition to the electrolyte being in our hands); as the induction +was the same in its nature as that through air, glass, wax, &c. produced by +any of the ordinary means; and as the whole effect in the electrolyte +appeared to be an action of the particles thrown into a peculiar or +polarized state, I was led to suspect that common induction itself was in +all cases an _action of contiguous particles_[A], and that electrical +action at a distance (i.e. ordinary inductive action) never occurred except +through the influence of the intervening matter. + + [A] The word _contiguous_ is perhaps not the best that might have been + used here and elsewhere; for as particles do not touch each other it + is not strictly correct. I was induced to employ it, because in its + common acceptation it enabled me to state the theory plainly and with + facility. By contiguous particles I mean those which are next.--_Dec. + 1838._ + +1165. The respect which I entertain towards the names of Epinus, Cavendish, +Poisson, and other most eminent men, all of whose theories I believe +consider induction as an action at a distance and in straight lines, long +indisposed me to the view I have just stated; and though I always watched +for opportunities to prove the opposite opinion, and made such experiments +occasionally as seemed to bear directly on the point, as, for instance, the +examination of electrolytes, solid and fluid, whilst under induction by +polarized light (951. 955.), it is only of late, and by degrees, that the +extreme generality of the subject has urged me still further to extend my +experiments and publish my view. At present I believe ordinary induction in +all cases to be an action of contiguous particles consisting in a species +of polarity, instead of being an action of either particles or masses at +sensible distances; and if this be true, the distinction and establishment +of such a truth must be of the greatest consequence to our further progress +in the investigation of the nature of electric forces. The linked condition +of electrical induction with chemical decomposition; of voltaic excitement +with chemical action; the transfer of elements in an electrolyte; the +original cause of excitement in all cases; the nature and relation of +conduction and insulation of the direct and lateral or transverse action +constituting electricity and magnetism; with many other things more or less +incomprehensible at present, would all be affected by it, and perhaps +receive a full explication in their reduction under one general law. + +1166. I searched for an unexceptionable test of my view, not merely in the +accordance of known facts with it, but in the consequences which would flow +from it if true; especially in those which would not be consistent with the +theory of action at a distance. Such a consequence seemed to me to present +itself in the direction in which inductive action could be exerted. If in +straight lines only, though not perhaps decisive, it would be against my +view; but if in curved lines also, that would be a natural result of the +action of contiguous particles, but, as I think, utterly incompatible with +action at a distance, as assumed by the received theories, which, according +to every fact and analogy we are acquainted with, is always in straight +lines. + +1167. Again, if induction be an action of contiguous particles, and also +the first step in the process of electrolyzation (1164. 919.), there seemed +reason to expect some particular relation of it to the different kinds of +matter through which it would be exerted, or something equivalent to a +_specific electric induction_ for different bodies, which, if it existed, +would unequivocally prove the dependence of induction on the particles; and +though this, in the theory of Poisson and others, has never been supposed +to be the case, I was soon led to doubt the received opinion, and have +taken great pains in subjecting this point to close experimental +examination. + +1168. Another ever-present question on my mind has been, whether +electricity has an actual and independent existence as a fluid or fluids, +or was a mere power of matter, like what we conceive of the attraction of +gravitation. If determined either way it would be an enormous advance in +our knowledge; and as having the most direct and influential bearing on my +notions, I have always sought for experiments which would in any way tend +to elucidate that great inquiry. It was in attempts to prove the existence +of electricity separate from matter, by giving an independent charge of +either positive or negative power only, to some one substance, and the +utter failure of all such attempts, whatever substance was used or whatever +means of exciting or _evolving_ electricity were employed, that first drove +me to look upon induction as an action of the particles of matter, each +having _both_ forces developed in it in exactly equal amount. It is this +circumstance, in connection with others, which makes me desirous of placing +the remarks on absolute charge first, in the order of proof and argument, +which I am about to adduce in favour of my view, that electric induction is +an action of the contiguous particles of the insulating medium or +_dielectric_[A]. + + [A] I use the word _dielectric_ to express that substance through or + across which the electric forces are acting.--_Dec. 1838._ + + +P ii. _On the absolute charge of matter._ + +1169. Can matter, either conducting or non-conducting, be charged with one +electric force independently of the other, in any degree, either in a +sensible or latent state? + +1170. The beautiful experiments of Coulomb upon the equality of action of +_conductors_, whatever their substance, and the residence of _all_ the +electricity upon their surfaces[A], are sufficient, if properly viewed, to +prove that _conductors cannot be bodily charged_; and as yet no means of +communicating electricity to a conductor so as to place its particles in +relation to one electricity, and not at the same time to the other in +exactly equal amount, has been discovered. + + [A] Memoires de l'Academie, 1786, pp. 67. 69. 72; 1787, p. 452. + +1171. With regard to electrics or non-conductors, the conclusion does not +at first seem so clear. They may easily be electrified bodily, either by +communication (1247.) or excitement; but being so charged, every case in +succession, when examined, came out to be a case of induction, and not of +absolute charge. Thus, glass within conductors could easily have parts not +in contact with the conductor brought into an excited state; but it was +always found that a portion of the inner surface of the conductor was in an +opposite and equivalent state, or that another part of the glass itself was +in an equally opposite state, an _inductive_ charge and not an _absolute_ +charge having been acquired. + +1172. Well-purified oil of turpentine, which I find to be an excellent +liquid insulator for most purposes, was put into a metallic vessel, and, +being insulated, an endeavour was made to charge its particles, sometimes +by contact of the metal with the electrical machine, and at others by a +wire dipping into the fluid within; but whatever the mode of communication, +no electricity of one kind only was retained by the arrangement, except +what appeared on the exterior surface of the metal, that portion being +present there only by an inductive action through the air to the +surrounding conductors. When the oil of turpentine was confined in glass +vessels, there were at first some appearances as if the fluid did receive +an absolute charge of electricity from the charging wire, but these were +quickly reduced to cases of common induction jointly through the fluid, the +glass, and the surrounding air. + +1173. I carried these experiments on with air to a very great extent. I had +a chamber built, being a cube of twelve feet. A slight cubical wooden frame +was constructed, and copper wire passed along and across it in various +directions, so as to make the sides a large net-work, and then all was +covered in with paper, placed in close connexion with the wires, and +supplied in every direction with bands of tin foil, that the whole might be +brought into good metallic communication, and rendered a free conductor in +every part. This chamber was insulated in the lecture-room of the Royal +Institution; a glass tube about six feet in length was passed through its +side, leaving about four feet within and two feet on the outside, and +through this a wire passed from the large electrical machine (290.) to the +air within. By working the machine, the air in this chamber could be +brought into what is considered a highly electrified state (being, in fact, +the same state as that of the air of a room in which a powerful machine is +in operation), and at the same time the outside of the insulated cube was +everywhere strongly charged. But putting the chamber in communication with +the perfect discharging train described in a former series (292.), and +working the machine so as to bring the air within to its utmost degree of +charge if I quickly cut off the connexion with the machine, and at the same +moment or instantly after insulated the cube, the air within had not the +least power to communicate a further charge to it. If any portion of the +air was electrified, as glass or other insulators may be charged (1171.), +it was accompanied by a corresponding opposite action _within_ the cube, +the whole effect being merely a case of induction. Every attempt to charge +air bodily and independently with the least portion of either electricity +failed. + +1174 I put a delicate gold-leaf electrometer within the cube, and then +charged the whole by an _outside_ communication, very strongly, for some +time together; but neither during the charge or after the discharge did the +electrometer or air within show the least signs of electricity. I charged +and discharged the whole arrangement in various ways, but in no case could +I obtain the least indication of an absolute charge; or of one by induction +in which the electricity of one kind had the smallest superiority in +quantity over the other. I went into the cube and lived in it, and using +lighted candles, electrometers, and all other tests of electrical states, I +could not find the least influence upon them, or indication of any thing +particular given by them, though all the time the outside of the cube was +powerfully charged, and large sparks and brushes were darting off from +every part of its outer surface. The conclusion I have come to is, that +non-conductors, as well as conductors, have never yet had an absolute and +independent charge of one electricity communicated to them, and that to all +appearance such a state of matter is impossible. + +1175. There is another view of this question which may be taken under the +supposition of the existence of an electric fluid or fluids. It may be +impossible to have one fluid or state in a free condition without its +producing by induction the other, and yet possible to have cases in which +an isolated portion of matter in one condition being uncharged, shall, by a +change of state, evolve one electricity or the other: and though such +evolved electricity might immediately induce the opposite state in its +neighbourhood, yet the mere evolution of one electricity without the other +in the _first instance_, would be a very important fact in the theories +which assume a fluid or fluids; these theories as I understand them +assigning not the slightest reason why such an effect should not occur. + +1176. But on searching for such cases I cannot find one. Evolution by +friction, as is well known, gives both powers in equal proportion. So does +evolution by chemical action, notwithstanding the great diversity of bodies +which may be employed, and the enormous quantity of electricity which can +in this manner be evolved (371. 376. 861. 868. 961.). The more promising +cases of change of state, whether by evaporation, fusion, or the reverse +processes, still give both forms of the power in _equal_ proportion; and +the cases of splitting of mica and other crystals, the breaking of sulphur, +&c., are subject to the same law of limitation. + +1177. As far as experiment has proceeded, it appears, therefore, impossible +either to evolve or make disappear one electric force without equal and +corresponding change in the other. It is also equally impossible +experimentally to charge a portion of matter with one electric force +independently of the other. Charge always implies _induction_, for it can +in no instance be effected without; and also the presence of the _two_ +forms of power, equally at the moment of the development and afterwards. +There is no _absolute_ charge of matter with one fluid; no latency of a +single electricity. This though a negative result is an exceedingly +important one, being probably the consequence of a natural impossibility, +which will become clear to us when we understand the true condition and +theory of the electric power. + +1178. The preceding considerations already point to the following +conclusions: bodies cannot be charged absolutely, but only relatively, and +by a principle which is the same with that of _induction_. All _charge_ is +sustained by induction. All phenomena of _intensity_ include the principle +of induction. All _excitation_ is dependent on or directly related to +induction. All _currents_ involve previous intensity and therefore previous +induction. INDUCTION appears to be the essential function both the first +development and the consequent phenomena of electricity. + + +P iii. _Electrometer and inductive apparatus employed._ + +1179. Leaving for a time the further consideration of the preceding facts +until they can be collated with other results bearing directly on the great +question of the nature of induction, I will now describe the apparatus I +have had occasion to use; and in proportion to the importance of the +principles sought to be established is the necessity of doing this so +clearly, as to leave no doubt of the results behind. + +1180. _Electrometer._--The measuring instrument I have employed has been +the torsion balance electrometer of Coulomb, constructed, generally, +according to his directions[A], but with certain variations and additions, +which I will briefly describe. The lower part was a glass cylinder eight +inches in height and eight inches in diameter; the tube for the torsion +thread was seventeen inches in length. The torsion thread itself was not of +metal, but glass, according to the excellent suggestion of the late Dr. +Ritchie[B]. It was twenty inches in length, and of such tenuity that when +the shell-lac lever and attached ball, &c. were connected with it, they +made about ten vibrations in a minute. It would bear torsion through four +revolutions or 1440 deg., and yet, when released, return accurately to its +position; probably it would have borne considerably more than this without +injury. The repelled ball was of pith, gilt, and was 0.3 of an inch in +diameter. The horizontal stem or lever supporting it was of shell-lac, +according to Coulomb's direction, the arm carrying the ball being 2.4 +inches long, and the other only 1.2 inches: to this was attached the vane, +also described by Coulomb, which I found to answer admirably its purpose of +quickly destroying vibrations. That the inductive action within the +electrometer might be uniform in all positions of the repelled ball and in +all states of the apparatus, two bands of tin foil, about an inch wide +each, were attached to the inner surface of the glass cylinder, going +entirely round it, at the distance of 0.4 of an inch from each other, and +at such a height that the intermediate clear surface was in the same +horizontal plane with the lever and ball. These bands were connected with +each other and with the earth, and, being perfect conductors, always +exerted a uniform influence on the electrified balls within, which the +glass surface, from its irregularity of condition at different times, I +found, did not. For the purpose of keeping the air within the electrometer +in a constant state as to dryness, a glass dish, of such size as to enter +easily within the cylinder, had a layer of fused potash placed within it, +and this being covered with a disc of fine wire-gauze to render its +inductive action uniform at all parts, was placed within the instrument at +the bottom and left there. + + [A] Memoires de l'Academie, 1785, p. 570. + + [B] Philosophical Transactions, 1830. + +1181. The moveable ball used to take and measure the portion of electricity +under examination, and which may be called the _repelling_, or the +_carrier_, ball, was of soft alder wood, well and smoothly gilt. It was +attached to a fine shell-lac stem, and introduced through a hole into the +electrometer according to Coulomb's method: the stem was fixed at its upper +end in a block or vice, supported on three short feet; and on the surface +of the glass cover above was a plate of lead with stops on it, so that when +the carrier ball was adjusted in its right position, with the vice above +bearing at the same time against these stops, it was perfectly easy to +bring away the carrier-ball and restore it to its place again very +accurately, without any loss of time. + +1182. It is quite necessary to attend to certain precautions respecting +these balls. If of pith alone they are bad; for when very dry, that +substance is so imperfect a conductor that it neither receives nor gives a +charge freely, and so, after contact with a charged conductor, it is liable +to be in an uncertain condition. Again, it is difficult to turn pith so +smooth as to leave the ball, even when gilt, so free from irregularities of +form, as to retain its charge undiminished for a considerable length of +time. When, therefore, the balls are finally prepared and gilt they should +be examined; and being electrified, unless they can hold their charge with +very little diminution for a considerable time, and yet be discharged +instantly and perfectly by the touch of an uninsulated conductor, they +should be dismissed. + +1183. It is, perhaps, unnecessary to refer to the graduation of the +instrument, further than to explain how the observations were made. On a +circle or ring of paper on the outside of the glass cylinder, fixed so as +to cover the internal lower ring of tinfoil, were marked four points +corresponding to angles of 90 deg.; four other points exactly corresponding to +these points being marked on the upper ring of tinfoil within. By these and +the adjusting screws on which the whole instrument stands, the glass +torsion thread could be brought accurately into the centre of the +instrument and of the graduations on it. From one of the four points on the +exterior of the cylinder a graduation of 90 deg. was set off, and a +corresponding graduation was placed upon the upper tinfoil on the opposite +side of the cylinder within; and a dot being marked on that point of the +surface of the repelled ball nearest to the side of the electrometer, it +was easy, by observing the line which this dot made with the lines of the +two graduations just referred to, to ascertain accurately the position of +the ball. The upper end of the glass thread was attached, as in Coulomb's +original electrometer, to an index, which had its appropriate graduated +circle, upon which the degree of torsion was ultimately to be read off. + +1184. After the levelling of the instrument and adjustment of the glass +thread, the blocks which determine the place of the _carrier ball_ are to +be regulated (1181.) so that, when the carrier arrangement is placed +against them, the centre of the ball may be in the radius of the instrument +corresponding to 0 deg. on the lower graduation or that on the side of the +electrometer, and at the same level and distance from the centre as the +_repelled ball_ on the suspended torsion lever. Then the torsion index is +to be turned until the ball connected with it (the repelled ball) is +accurately at 30 deg., and finally the graduated arc belonging to the torsion +index is to be adjusted so as to bring 0 deg. upon it to the index. This state +of the instrument was adopted as that which gave the most direct expression +of the experimental results, and in the form having fewest variable errors; +the angular distance of 30 deg. being always retained as the standard distance +to which the balls were in every case to be brought, and the whole of the +torsion being read off at once on the graduated circle above. Under these +circumstances the distance of the balls from each other was not merely the +same in degree, but their position in the instrument, and in relation to +every part of it, was actually the same every time that a measurement was +made; so that all irregularities arising from slight difference of form and +action in the instrument and the bodies around were avoided. The only +difference which could occur in the position of anything within, consisted +in the deflexion of the torsion thread from a vertical position, more or +less, according to the force of repulsion of the balls; but this was so +slight as to cause no interfering difference in the symmetry of form within +the instrument, and gave no error in the amount of torsion force indicated +on the graduation above. + +1185. Although the constant angular distance of 30 deg. between the centres of +the balls was adopted, and found abundantly sensible, for all ordinary +purposes, yet the facility of rendering the instrument far more sensible by +diminishing this distance was at perfect command; the results at different +distances being very easily compared with each other either by experiment, +or, as they are inversely as the squares of the distances, by calculation. + +1186. The Coulomb balance electrometer requires experience to be +understood; but I think it a very valuable instrument in the hands of those +who will take pains by practice and attention to learn the precautions +needful in its use. Its insulating condition varies with circumstances, and +should be examined before it is employed in experiments. In an ordinary and +fair condition, when the balls were so electrified as to give a repulsive +torsion force of 100 deg. at the standard distance of 30 deg., it took nearly four +hours to sink to 50 deg. at the same distance; the average loss from 400 deg. to +300 deg. being at the rate of 2 deg..7 per minute, from 300 deg. to 200 deg. of 1 deg..7 per +minute, from 200 deg. to 100 deg. of 1 deg..3 per minute, and from 100 deg. to 50 deg. of 0 deg..87 +per minute. As a complete measurement by the instrument may be made in much +less than a minute, the amount of loss in that time is but small, and can +easily be taken into account. + +1187. _The inductive apparatus._--My object was to examine inductive action +carefully when taking place through different media, for which purpose it +was necessary to subject these media to it in exactly similar +circumstances, and in such quantities as should suffice to eliminate any +variations they might present. The requisites of the apparatus to be +constructed were, therefore, that the inducing surfaces of the conductors +should have a constant form and state, and be at a constant distance from +each other; and that either solids, fluids, or gases might be placed and +retained between these surfaces with readiness and certainty, and for any +length of time. + +1188. The apparatus used may be described in general terms as consisting of +two metallic spheres of unequal diameter, placed, the smaller within the +larger, and concentric with it; the interval between the two being the +space through which the induction was to take place. A section of it is +given (Plate VII. fig. 104.) on a scale of one-half: _a, a_ are the two +halves of a brass sphere, with an air-tight joint at _b_, like that of the +Magdeburg hemispheres, made perfectly flush and smooth inside so as to +present no irregularity; _c_ is a connecting piece by which the apparatus +is joined to a good stop-cock _d_, which is itself attached either to the +metallic foot _e_, or to an air-pump. The aperture within the hemisphere at +_f_ is very small: _g_ is a brass collar fitted to the upper hemisphere, +through which the shell-lac support of the inner ball and its stem passes; +_h_ is the inner ball, also of brass; it screws on to a brass stem _i_, +terminated above by a brass ball B, _l, l_ is a mass of shell-lac, moulded +carefully on to _i_, and serving both to support and insulate it and its +balls _h_, B. The shell-lac stem _l_ is fitted into the socket _g_, by a +little ordinary resinous cement, more fusible than shell-lac, applied at +_mm_ in such a way as to give sufficient strength and render the apparatus +air-tight there, yet leave as much as possible of the lower part of the +shell-lac stem untouched, as an insulation between the ball _h_ and the +surrounding sphere _a, a_. The ball _h_ has a small aperture at _n_, so +that when the apparatus is exhausted of one gas and filled with another, +the ball _h_ may itself also be exhausted and filled, that no variation of +the gas in the interval _o_ may occur during the course of an experiment. + +1189. It will be unnecessary to give the dimensions of all the parts, since +the drawing is to a scale of one-half: the inner ball has a diameter 2.33 +inches, and the surrounding sphere an internal diameter of 3.57 inches. +Hence the width of the intervening space, through which the induction is to +take place, is 0.62 of an inch; and the extent of this place or plate, i.e. +the surface of a medium sphere, may be taken as twenty-seven square inches, +a quantity considered as sufficiently large for the comparison of different +substances. Great care was taken in finishing well the inducing surfaces of +the ball _h_ and sphere _a, a_; and no varnish or lacquer was applied to +them, or to any part of the metal of the apparatus. + +1190. The attachment and adjustment of the shell-lac stem was a matter +requiring considerable care, especially as, in consequence of its cracking, +it had frequently to be renewed. The best lac was chosen and applied to the +wire _i_, so as to be in good contact with it everywhere, and in perfect +continuity throughout its own mass. It was not smaller than is given by +scale in the drawing, for when less it frequently cracked within a few +hours after it was cold. I think that very slow cooling or annealing +improved its quality in this respect. The collar _g_ was made as thin as +could be, that the lac might be as wide there as possible. In order that at +every re-attachment of the stem to the upper hemisphere the ball _h_ might +have the same relative position, a gauge _p_ (fig. 105.) was made of wood, +and this being applied to the ball and hemisphere whilst the cement at _m_ +was still soft, the bearings of the ball at _qq_, and the hemisphere at +_rr_, were forced home, and the whole left until cold. Thus all difficulty +in the adjustment of the ball in the sphere was avoided. + +1191. I had occasion at first to attach the stem to the socket by other +means, as a band of paper or a plugging of white silk thread; but these +were very inferior to the cement, interfering much with the insulating +power of the apparatus. + +1192. The retentive power of this apparatus was, when in good condition, +better than that of the electrometer (1186.), i.e. the proportion of loss +of power was less. Thus when the apparatus was electrified, and also the +balls in the electrometer, to such a degree, that after the inner ball had +been in contact with the top _k_ of the ball of the apparatus, it caused a +repulsion indicated by 600 deg. of torsion force, then in falling from 600 deg. to +400 deg. the average loss was 8 deg..6 per minute; from 400 deg. to 300 deg. the average +loss was 2 deg..6 per minute; from 300 deg. to 200 deg. it was 1 deg..7 per minute; from +200 deg. to 170 deg. it was 1 deg. per minute. This was after the apparatus had been +charged for a short time; at the first instant of charging there is an +apparent loss of electricity, which can only be comprehended hereafter +(1207. 1250.). + +1193. When the apparatus loses its insulating power suddenly, it is almost +always from a crack near to or within the brass socket. These cracks are +usually transverse to the stem. If they occur at the part attached by +common cement to the socket, the air cannot enter, and thus constituting +vacua, they conduct away the electricity and lower the charge, as fast +almost as if a piece of metal had been introduced there. Occasionally stems +in this state, being taken out and cleared from the common cement, may, by +the careful application of the heat of a spirit-lamp, be so far softened +and melted as to restore the perfect continuity of the parts; but if that +does not succeed in replacing things in a good condition, the remedy is a +new shell-lac stem. + +1194. The apparatus when in order could easily be exhausted of air and +filled with any given gas; but when that gas was acid or alkaline, it could +not properly be removed by the air-pump, and yet required to be perfectly +cleared away. In such cases the apparatus was opened and emptied of gas; +and with respect to the inner ball _h_, it was washed out two or three +times with distilled water introduced at the screw-hole, and then being +heated above 212 deg., air was blown through to render the interior perfectly +dry. + +1195. The inductive apparatus described is evidently a Leyden phial, with +the advantage, however, of having the _dielectric_ or insulating medium +changed at pleasure. The balls _h_ and B, with the connecting wire _i_, +constitute the charged conductor, upon the surface of which all the +electric force is resident by virtue of induction (1178.). Now though the +largest portion of this induction is between the ball _h_ and the +surrounding sphere _aa_, yet the wire _i_ and the ball B determine a part +of the induction from their surfaces towards the external surrounding +conductors. Still, as all things in that respect remain the same, whilst +the medium within at _oo_, may be varied, any changes exhibited by the +whole apparatus will in such cases depend upon the variations made in the +interior; and these were the changes I was in search of, the negation or +establishment of such differences being the great object of my inquiry. I +considered that these differences, if they existed, would be most +distinctly set forth by having two apparatus of the kind described, +precisely similar in every respect; and then, _different insulating media_ +being within, to charge one and measure it, and after dividing the charge +with the other, to observe what the ultimate conditions of both were. If +insulating media really had any specific differences in favouring or +opposing inductive action through them, such differences, I conceived, +could not fail of being developed by such a process. + +1196. I will wind up this description of the apparatus, and explain the +precautions necessary to their use, by describing the form and order of the +experiments made to prove their equality when both contained common air. In +order to facilitate reference I will distinguish the two by the terms App. +i. and App. ii. + +1197. The electrometer is first to be adjusted and examined (1184.), and +the app. i. and ii. are to be perfectly discharged. A Leyden phial is to be +charged to such a degree that it would give a spark of about one-sixteenth +or one-twentieth of an inch in length between two balls of half an inch +diameter; and the carrier ball of the electrometer being charged by this +phial, is to be introduced into the electrometer, and the lever ball +brought by the motion of the torsion index against it; the charge is thus +divided between the balls, and repulsion ensues. It is useful then to bring +the repelled ball to the standard distance of 30 deg. by the motion of the +torsion index, and observe the force in degrees required for this purpose; +this force will in future experiments be called _repulsion of the balls_. + +1198. One of the inductive apparatus, as, for instance, app. i., is now to +be charged from the Leyden phial, the latter being in the state it was in +when used to charge the balls; the carrier ball is to be brought into +contact with the top of its upper ball (_k_, fig. 104.), then introduced +into the electrometer, and the repulsive force (at the distance of 30 deg.) +measured. Again, the carrier should be applied to the app. i. and the +measurement repeated; the apparatus i. and ii. are then to be joined, so as +to _divide_ the charge, and afterwards the force of each measured by the +carrier ball, applied as before, and the results carefully noted. After +this both i. and ii. are to be discharged; then app. ii. charged, measured, +divided with app. i., and the force of each again measured and noted. If in +each case the half charges of app. i. and ii. are equal, and are together +equal to the whole charge before division, then it may be considered as +proved that the two apparatus are precisely equal in power, and fit to be +used in cases of comparison between different insulating media or +_dielectrics_. + +1199. But the _precautions_ necessary to obtain accurate results are +numerous. The apparatus i. and ii. must always be placed on a thoroughly +uninsulating medium. A mahogany table, for instance, is far from +satisfactory in this respect, and therefore a sheet of tinfoil, connected +with an extensive discharging train (292.), is what I have used. They must +be so placed also as not to be too near each other, and yet equally exposed +to the inductive influence of surrounding objects; and these objects, +again, should not be disturbed in their position during an experiment, or +else variations of induction upon the external ball B of the apparatus may +occur, and so errors be introduced into the results. The carrier ball, when +receiving its portion of electricity from the apparatus, should always be +applied at the same part of the ball, as, for instance, the summit _k_, and +always in the same way; variable induction from the vicinity of the head, +hands, &c. being avoided, and the ball after contact being withdrawn +upwards in a regular and constant manner. + +1200. As the stem had occasionally to be changed (1190.), and the change +might occasion slight variations in the position of the ball within, I made +such a variation purposely, to the amount of an eighth of an inch (which is +far more than ever could occur in practice), but did not find that it +sensibly altered the relation of the apparatus, or its inductive condition +_as a whole_. Another trial of the apparatus was made as to the effect of +dampness in the air, one being filled with very dry air, and the other with +air from over water. Though this produced no change in the result, except +an occasional tendency to more rapid dissipation, yet the precaution was +always taken when working with gases (1290.) to dry them perfectly. + +1201. It is essential that the interior of the apparatus should be +perfectly free from _dust or small loose particles_, for these very rapidly +lower the charge and interfere on occasions when their presence and action +would hardly be expected. To breathe on the interior of the apparatus and +wipe it out quietly with a clean silk handkerchief, is an effectual way of +removing them; but then the intrusion of other particles should be +carefully guarded against, and a dusty atmosphere should for this and +several other reasons be avoided. + +1202. The shell-lac stem requires occasionally to be well-wiped, to remove, +in the first instance, the film of wax and adhering matter which is upon +it; and afterwards to displace dirt and dust which will gradually attach to +it in the course of experiments. I have found much to depend upon this +precaution, and a silk handkerchief is the best wiper. + +1203. But wiping and some other circumstances tend to give a charge to the +surface of the shell-lac stem. This should be removed, for, if allowed to +remain, it very seriously affects the degree of charge given to the carrier +ball by the apparatus (1232.). This condition of the stem is best observed +by discharging the apparatus, applying the carrier ball to the stem, +touching it with the finger, insulating and removing it, and examining +whether it has received any charge (by induction) from the stem; if it has, +the stem itself is in a charged state. The best method of removing the +charge I have found to be, to cover the finger with a single fold of a silk +handkerchief, and breathing on the stem, to wipe it immediately after with +the finger; the ball B and its connected wire, &c. being at the same time +_uninsulated_: the wiping place of the silk must not be changed; it then +becomes sufficiently damp not to excite the stem, and is yet dry enough to +leave it in a clean and excellent insulating condition. If the air be +dusty, it will be found that a single charge of the apparatus will bring on +an electric state of the outside of the stem, in consequence of the +carrying power of the particles of dust; whereas in the morning, and in a +room which has been left quiet, several experiments can be made in +succession without the stem assuming the least degree of charge. + +1204. Experiments should not be made by candle or lamp light except with +much care, for flames have great and yet unsteady powers of affecting and +dissipating electrical charges. + +1205. As a final observation on the state of the apparatus, they should +retain their charges well and uniformly, and alike for both, and at the +same time allow of a perfect and instantaneous discharge, giving afterwards +no charge to the carrier ball, whatever part of the ball B it may be +applied to (1218.). + +1206. With respect to the balance electrometer, all the precautions that +need be mentioned, are, that the carrier ball is to be preserved during the +first part of an experiment in its electrified state, the loss of +electricity which would follow upon its discharge being avoided; and that +in introducing it into the electrometer through the hole in the glass plate +above, care should be taken that it do not touch, or even come near to, the +edge of the glass. + +1207. When the whole charge in one apparatus is divided between the two, +the gradual fall, apparently from dissipation, in the apparatus which has +_received_ the half charge is greater than in the one _originally_ charged. +This is due to a peculiar effect to be described hereafter (1250. 1251.), +the interfering influence of which may be avoided to a great extent by +going through the steps of the process regularly and quickly; therefore, +after the original charge has been measured, in app. i. for instance, i. +and ii. are to be symmetrically joined by their balls B, the carrier +touching one of these balls at the same time; it is first to be removed, +and then the apparatus separated from each other; app. ii. is next quickly +to be measured by the carrier, then app. i.; lastly, ii. is to be +discharged, and the discharged carrier applied to it to ascertain whether +any residual effect is present (1205.), and app. i. being discharged is +also to be examined in the same manner and for the same purpose. + +1208. The following is an example of the division of a charge by the two +apparatus, air being the dielectric in both of them. The observations are +set down one under the other in the order in which they were taken, the +left-hand numbers representing the observations made on app. i., and the +right-hand numbers those on app. ii. App. i. is that which was originally +charged, and after two measurements, the charge was divided with app. ii. + +App. i. App. ii. + Balls 160 deg. + + . . . . 0 deg. +254 deg. . . . . +250 . . . . +divided and instantly taken + . . . . 122 +124 . . . . + 1 . . . . after being discharged. + . . . . 2 after being discharged. + +1209. Without endeavouring to allow for the loss which must have been +gradually going on during the time of the experiment, let us observe the +results of the numbers as they stand. As 1 deg. remained in app. i. in an +undischargeable state, 249 deg. may be taken as the utmost amount of the +transferable or divisible charge, the half of which is 124 deg..5. As app. ii. +was free of charge in the first instance, and immediately after the +division was found with 122 deg., this amount _at least_ may be taken as what +it had received. On the other hand 124 deg. minus 1 deg., or 123 deg., may be taken as +the half of the transferable charge retained by app. i. Now these do not +differ much from each other, or from 124 deg..5, the half of the full amount of +transferable charge; and when the gradual loss of charge evident in the +difference between 254 deg. and 250 deg. of app. i. is also taken into account, +there is every reason to admit the result as showing an equal division of +charge, _unattended by any disappearance of power_ except that due to +dissipation. + +1210. I will give another result, in which app. ii. was first charged, and +where the residual action of that apparatus was greater than in the former +case. + +App. i. App. ii. + Balls 150 deg. + + . . . . 152 deg. + . . . . 148 +divided and instantly taken + 70 deg. . . . . + . . . . 78 + . . . . 5 immediately after discharge. + 0 . . . . immediately after discharge. + +1211. The transferable charge being 148 deg. - 5 deg., its half is 71 deg..5, which is +not far removed from 70 deg., the half charge of i.; or from 73 deg., the half +charge of ii.: these half charges again making up the sum of 143 deg., or just +the amount of the whole transferable charge. Considering the errors of +experiment, therefore, these results may again be received as showing that +the apparatus were equal in inductive capacity, or in their powers of +receiving charges. + +1212. The experiments were repeated with charges of negative electricity +with the same general results. + +1213. That I might be sure of the sensibility and action of the apparatus, +I made such a change in one as ought upon principle to increase its +inductive force, i.e. I put a metallic lining into the lower hemisphere of +app. i., so as to diminish the thickness of the intervening air in that +part, from 0.62 to 0.435 of an inch: this lining was carefully shaped and +rounded so that it should not present a sudden projection within at its +edge, but a gradual transition from the reduced interval in the lower part +of the sphere to the larger one in the upper. + +1214. This change immediately caused app. i. to produce effects indicating +that it had a greater aptness or capacity for induction than app. ii. Thus, +when a transferable charge in app. ii. of 469 deg. was divided with app. i., +the former retained a charge of 225 deg., whilst the latter showed one of 227 deg., +i.e. the former had lost 244 deg. in communicating 227 deg. to the latter: on the +other hand, when app. i. had a transferable charge in it of 381 deg. divided by +contact with app. ii., it lost 181 deg. only, whilst it gave to app. ii. as +many as 194:--the sum of the divided forces being in the first instance +_less_, and in the second instance _greater_ than the original undivided +charge. These results are the more striking, as only one-half of the +interior of app. i. was modified, and they show that the instruments are +capable of bringing out differences in inductive force from amongst the +errors of experiment, when these differences are much less than that +produced by the alteration made in the present instance. + + +P iv. _Induction in curved lines._ + +1215. Amongst those results deduced from the molecular view of induction +(1166.), which, being of a peculiar nature, are the best tests of the truth +or error of the theory, the expected action in curved lines is, I think, +the most important at present; for, if shown to take place in an +unexceptionable manner, I do not see how the old theory of action at a +distance and in straight lines can stand, or how the conclusion that +ordinary induction is an action of contiguous particles can be resisted. + +1216. There are many forms of old experiments which might be quoted as +favourable to, and consistent with the view I have adopted. Such are most +cases of electro-chemical decomposition, electrical brushes, auras, sparks, +&c.; but as these might be considered equivocal evidence, inasmuch as they +include a current and discharge, (though they have long been to me +indications of prior molecular action (1230.)) I endeavoured to devise such +experiments for first proofs as should not include transfer, but relate +altogether to the pure simple inductive action of statical electricity. + +1217. It was also of importance to make these experiments in the simplest +possible manner, using not more than one insulating medium or dielectric at +a time, lest differences of slow conduction should produce effects which +might erroneously be supposed to result from induction in curved lines. It +will be unnecessary to describe the steps of the investigation minutely; I +will at once proceed to the simplest mode of proving the facts, first in +air and then in other insulating media. + +1218. A cylinder of solid shell-lac, 0.9 of an inch in diameter and seven +inches in length, was fixed upright in a wooden foot (fig. 106.): it was +made concave or cupped at its upper extremity so that a brass ball or other +small arrangement could stand upon it. The upper half of the stem having +been excited _negatively_ by friction with warm flannel, a brass ball, B, 1 +inch in diameter, was placed on the top, and then the whole arrangement +examined by the carrier ball and Coulomb's electrometer (1180. &c.). For +this purpose the balls of the electrometer were charged _positively_ to +about 360 deg., and then the carrier being applied to various parts of the ball +B, the two were uninsulated whilst in contact or in position, then +insulated[A], separated, and the charge of the carrier examined as to its +nature and force. Its electricity was always positive, and its force at the +different positions _a, b, c, d,_ &c. (figs. 106. and 107.) observed in +succession, was as follows: + +at _a_ above 1000 deg. + _b_ it was 149 + _c_ 270 + _d_ 512 + _b_ 130 + + [A] It can hardly be necessary for me to say here, that whatever + general state the carrier ball acquired in any place where it was + uninsulated and then insulated, it retained on removal from that + place, notwithstanding that it might pass through other places that + would have given to it, if uninsulated, a different condition. + +1219. To comprehend the full force of these results, it must first be +understood, that all the charges of the ball B and the carrier are charges +by induction, from the action of the excited surface of the shell-lac +cylinder; for whatever electricity the ball B received by _communication_ +from the shell-lac, either in the first instance or afterwards, was removed +by the uninsulating contacts, only that due to induction remaining; and +this is shown by the charges taken from the ball in this its uninsulated +state being always positive, or of the contrary character to the +electricity of the shell-lac. In the next place, the charges at _a_, _c_, +and _d_ were of such a nature as might be expected from an inductive action +in straight lines, but that obtained at _b_ is _not so_: it is clearly a +charge by induction, but _induction_ in _a curved line_; for the carrier +ball whilst applied to _b_, and after its removal to a distance of six +inches or more from B, could not, in consequence of the size of B, be +connected by a straight line with any part of the excited and inducing +shell-lac. + +1220. To suppose that the upper part of the _uninsulated_ ball B, should in +some way be retained in an electrified state by that portion of the surface +of the ball which is in sight of the shell-lac, would be in opposition to +what we know already of the subject. Electricity is retained upon the +surface of conductors only by induction (1178.); and though some persons +may not be prepared as yet to admit this with respect to insulated +conductors, all will as regards uninsulated conductors like the ball B; and +to decide the matter we have only to place the carrier ball at _e_ (fig. +107.), so that it shall not come in contact with B, uninsulate it by a +metallic rod descending perpendicularly, insulate it, remove it, and +examine its state; it will be found charged with the same kind of +electricity as, and even to a _higher degree_ (1224.) than, if it had been +in contact with the summit of B. + +1221. To suppose, again, that induction acts in some way _through or +across_ the metal of the ball, is negatived by the simplest considerations; +but a fact in proof will be better. If instead of the ball B a small disc +of metal be used, the carrier may be charged at, or above the middle of its +upper surface: but if the plate be enlarged to about 1-1/2 or 2 inches in +diameter, C (fig. 108.), then no charge will be given to the carrier at +_f_, though when applied nearer to the edge at _g_, or even _above the +middle_ at _h_, a charge will be obtained; and this is true though the +plate may be a mere thin film of gold-leaf. Hence it is clear that the +induction is not _through_ the metal, but through the surrounding air or +_dielectric_, and that in curved lines. + +1222. I had another arrangement, in which a wire passing downwards through +the middle of the shell-lac cylinder to the earth, was connected with the +ball B (fig. 109.) so as to keep it in a constantly uninsulated state. This +was a very convenient form of apparatus, and the results with it were the +same as those just described. + +1223. In another case the ball B was supported by a shell-lac stem, +independently of the excited cylinder of shell-lac, and at half an inch +distance from it; but the effects were the same. Then the brass ball of a +charged Leyden jar was used in place of the excited shell-lac to produce +induction; but this caused no alteration of the phenomena. Both positive +and negative inducing charges were tried with the same general results. +Finally, the arrangement was inverted in the air for the purpose of +removing every possible objection to the conclusions, but they came out +exactly the same. + +1224. Some results obtained with a brass hemisphere instead of the ball B +were exceedingly interesting, It was 1.36 of an inch in diameter, (fig. +110.), and being placed on the top of the excited shell-lac cylinder, the +carrier ball was applied, as in the former experiments (1218.), at the +respective positions delineated in the figure. At _i_ the force was 112 deg., +at _k_ 108 deg., at _l_ 65 deg., at _m_ 35 deg.; the inductive force gradually +diminishing, as might have been expected, to this point. But on raising the +carrier to the position _n_, the charge increased to 87 deg.; and on raising it +still higher to _o_, the charge still further increased to 105 deg.: at a +higher point still, _p_, the charge taken was smaller in amount, being 98 deg., +and continued to diminish for more elevated positions. Here the induction +fairly turned a corner. Nothing, in fact, can better show both the curved +lines or courses of the inductive action, disturbed as they are from their +rectilineal form by the shape, position, and condition of the metallic +hemisphere; and also a _lateral tension,_ so to speak, of these lines on +one another:--all depending, as I conceive, on induction being an action of +the contiguous particles of the dielectric, which being thrown into a state +of polarity and tension, are in mutual relation by their forces in all +directions. + +1225. As another proof that the whole of these actions were inductive I may +state a result which was exactly what might be expected, namely, that if +uninsulated conducting matter was brought round and near to the excited +shell-lac stem, then the inductive force was directed towards it, and could +not be found on the top of the hemisphere. Removing this matter the lines +of force resumed their former direction. The experiment affords proofs of +the lateral tension of these lines, and supplies a warning to remove such +matter in repeating the above investigation. + +1226. After these results on curved inductive action in air I extended the +experiments to other gases, using first carbonic acid and then hydrogen: +the phenomena were precisely those already described. In these experiments +I found that if the gases were confined in vessels they required to be very +large, for whether of glass or earthenware, the conducting power of such +materials is so great that the induction of the excited shell-lac cylinder +towards them is as much as if they were metal; and if the vessels be small, +so great a portion of the inductive force is determined towards them that +the lateral tension or mutual repulsion of the lines of force before spoken +of, (1224.) by which their inflexion is caused, is so much relieved in +other directions, that no inductive charge will be given to the carrier +ball in the positions _k, l, m, n, o, p_ (fig. 110.). A very good mode of +making the experiment is to let large currents of the gases ascend or +descend through the air, and carry on the experiments in these currents. + +1227. These experiments were then varied by the substitution of a liquid +dielectric, namely, _oil of turpentine_, in place of air and gases. A dish +of thin glass well-covered with a film of shell-lac (1272.), which was +found by trial to insulate well, had some highly rectified oil of +turpentine put into it to the depth of half an inch, and being then placed +upon the top of the brass hemisphere (fig. 110.), observations were made +with the carrier ball as before (1224.). The results were the same, and the +circumstance of some of the positions being within the fluid and some +without, made no sensible difference. + +1228. Lastly, I used a few solid dielectrics for the same purpose, and with +the same results. These were shell-lac, sulphur, fused and cast borate of +lead, flint glass well-covered with a film of lac, and spermaceti. The +following was the form of experiment with sulphur, and all were of the same +kind. A square plate of the substance, two inches in extent and 0.6 of an +inch in thickness, was cast with a small hole or depression in the middle +of one surface to receive the carrier ball. This was placed upon the +surface of the metal hemisphere (fig. 112.) arranged on the excited lac as +in former cases, and observations were made at _n, o, p_, and _q_. Great +care was required in these experiments to free the sulphur or other solid +substance from any charge it might previously have received. This was done +by breathing and wiping (1203.), and the substance being found free from +all electrical excitement, was then used in the experiment; after which it +was removed and again examined, to ascertain that it had received no +charge, but had acted really as a dielectric. With all these precautions +the results were the same: and it is thus very satisfactory to obtain the +curved inductive action through _solid bodies_, as any possible effect from +the translation of charged particles in fluids or gases, which some persons +might imagine to be the case, is here entirely negatived. + +1229. In these experiments with solid dielectrics, the degree of charge +assumed by the carrier ball at the situations _n, o, p_ (fig. 112.), was +decidedly greater than that given to the ball at the same places when air +only intervened between it and the metal hemisphere. This effect is +consistent with what will hereafter be found to be the respective relations +of these bodies, as to their power of facilitating induction through them +(1269. 1273. 1277.). + +1230. I might quote _many_ other forms of experiment, some old and some +new, in which induction in curved or contorted lines takes place, but think +it unnecessary after the preceding results; I shall therefore mention but +two. If a conductor A, (fig. 111.) be electrified, and an uninsulated +metallic ball B, or even a plate, provided the edges be not too thin, be +held before it, a small electrometer at _c_ or at _d_, uninsulated, will +give signs of electricity, opposite in its nature to that of A, and +therefore caused by induction, although the influencing and influenced +bodies cannot be joined by a right line passing through the air. Or if, the +electrometers being removed, a point be fixed at the back of the ball in +its uninsulated state as at C, this point will become luminous and +discharge the conductor A. The latter experiment is described by +Nicholson[A], who, however, reasons erroneously upon it. As to its +introduction here, though it is a case of discharge, the discharge is +preceded by induction, and that induction must be in curved lines. + + [A] Encyclopaedia Britannica, vol. vi. p. 504. + +1231. As argument against the received theory of induction and in favour of +that which I have ventured to put forth, I cannot see how the preceding +results can be avoided. The effects are clearly inductive effects produced +by electricity, not in currents but in its statical state, and this +induction is exerted in lines of force which, though in many experiments +they may be straight, are here curved more or less according to +circumstances. I use the term _line of inductive force_ merely as a +temporary conventional mode of expressing the direction of the power in +cases of induction; and in the experiments with the hemisphere (1224.), it +is curious to see how, when certain lines have terminated on the under +surface and edge of the metal, those which were before lateral to them +_expand and open out from each other_, some bending round and terminating +their action on the upper surface of the hemisphere, and others meeting, as +it were, above in their progress outwards, uniting their forces to give an +increased charge to the carrier ball, at an _increased distance_ from the +source of power, and influencing each other so as to cause a second flexure +in the contrary direction from the first one. All this appears to me to +prove that the whole action is one of contiguous particles, related to each +other, not merely in the lines which they may be conceived to form through +the dielectric, between the _inductric_ and the _inducteous_ surfaces +(1483.), but in other lateral directions also. It is this which gives an +effect equivalent to a lateral repulsion or expansion in the lines of force +I have spoken of, and enables induction to turn a corner (1304.). The +power, instead of being like that of gravity, which causes particles to act +on each other through straight lines, whatever other particles may be +between them, is more analogous to that of a series of magnetic needles, or +to the condition of the particles considered as forming the whole of a +straight or a curved magnet. So that in whatever way I view it, and with +great suspicion of the influence of favourite notions over myself, I cannot +perceive how the ordinary theory applied to explain induction can be a +correct representation of that great natural principle of electrical +action. + +1232. I have had occasion in describing the precautions necessary in the +use of the inductive apparatus, to refer to one founded on induction in +curved lines (1203.); and after the experiments already described, it will +easily be seen how great an influence the shell-lac stem may exert upon the +charge of the carrier ball when applied to the apparatus (1218.), unless +that precaution be attended to. + +1233. I think it expedient, next in the course of these experimental +researches, to describe some effects due to _conduction_, obtained with +such bodies as glass, lac, sulphur, &c., which had not been anticipated. +Being understood, they will make us acquainted with certain precautions +necessary in investigating the great question of specific inductive +capacity. + +1234. One of the inductive apparatus already described (1187, &c.) had a +hemispherical cup of shell-lac introduced, which being in the interval +between the inner bull and the lower hemisphere, nearly occupied the space +there; consequently when the apparatus was charged, the lac was the +dielectric or insulating medium through which the induction took place in +that part. When this apparatus was first charged with electricity (1198.) +up to a certain intensity, as 400 deg., measured by the COULOMB'S electrometer +(1180.), it sank much faster from that degree than if it had been +previously charged to a higher point, and had gradually fallen to 400 deg.; or +than it would do if the charge were, by a second application, raised up +again to 400 deg.; all other things remaining the same. Again, if after having +been charged for some time, as fifteen or twenty minutes, it was suddenly +and perfectly discharged, even the stem having all electricity removed from +it (1203.), then the apparatus being left to itself, would gradually +recover a charge, which in nine or ten minutes would rise up to 50 deg. or 60 deg., +and in one instance to 80 deg.. + +1235. The electricity, which in these cases returned from an apparently +latent to a sensible state, was always of the same kind as that which had +been given by the charge. The return took place at both the inducing +surfaces; for if after the perfect discharge of the apparatus the whole was +insulated, as the inner ball resumed a positive state the outer sphere +acquired a negative condition. + +1236. This effect was at once distinguished from that produced by the +excited stem acting in curved lines of induction (1203. 1232.), by the +circumstance that all the returned electricity could be perfectly and +instantly discharged. It appeared to depend upon the shell-lac within, and +to be, in some way, due to electricity evolved from it in consequence of a +previous condition into which it had been brought by the charge of the +metallic coatings or balls. + +1237. To examine this state more accurately, the apparatus, with the +hemispherical cup of shell-lac in it, was charged for about forty-five +minutes to above 600 deg. with positive electricity at the balls _h_ and B. +(fig. 104.) above and within. It was then discharged, opened, the shell-lac +taken out, and its state examined; this was done by bringing the carrier +ball near the shell-lac, uninsulating it, insulating it, and then observing +what charge it had acquired. As it would be a charge by induction, the +state of the ball would indicate the opposite state of electricity in that +surface of the shell-lac which had produced it. At first the lac appeared +quite free from any charge; but gradually its two surfaces assumed opposite +states of electricity, the concave surface, which had been next the inner +and positive ball; assuming a positive state, and the convex surface, which +had been in contact with the negative coating, acquiring a negative state; +these states gradually increased in intensity for some time. + +1238. As the return action was evidently greatest instantly after the +discharge, I again put the apparatus together, and charged it for fifteen +minutes as before, the inner ball positively. I then discharged it, +instantly removing the upper hemisphere with the interior ball, and, +leaving the shell-lac cup in the lower uninsulated hemisphere, examined its +inner surface by the carrier ball as before (1237.). In this way I found +the surface of the shell-lac actually _negative_, or in the reverse state +to the ball which had been in it; this state quickly disappeared, and was +succeeded by a positive condition, gradually increasing in intensity for +some time, in the same manner as before. The first negative condition of +the surface opposite the positive charging ball is a natural consequence of +the state of things, the charging ball being in contact with the shell-lac +only in a few points. It does not interfere with the general result and +peculiar state now under consideration, except that it assists in +illustrating in a very marked manner the ultimate assumption by the +surfaces of the shell-lac of an electrified condition, similar to that of +the metallic surfaces opposed to or against them. + +1239. _Glass_ was then examined with respect to its power of assuming this +peculiar state. I had a thick flint-glass hemispherical cup formed, which +would fit easily into the space _o_ of the lower hemisphere (1188. 1189.); +it had been heated and varnished with a solution of shell-lac in alcohol, +for the purpose of destroying the conducting power of the vitreous surface +(1254.). Being then well-warmed and experimented with, I found it could +also assume the _same state_, but not apparently to the same degree, the +return action amounting in different cases to quantities from 6 deg. to 18 deg.. + +1240. _Spermaceti_ experimented with in the same manner gave striking +results. When the original charge had been sustained for fifteen or twenty +minutes at about 500 deg., the return charge was equal to 95 deg. or 100 deg., and was +about fourteen minutes arriving at the maximum effect. A charge continued +for not more than two or three seconds was here succeeded by a return +charge of 50 deg. or 60 deg.. The observations formerly made (1234.) held good with +this substance. Spermaceti, though it will insulate a low charge for some +time, is a better conductor than shell-lac, glass, and sulphur; and this +conducting power is connected with the readiness with which it exhibits the +particular effect under consideration. + +1241. _Sulphur._--I was anxious to obtain the amount of effect with this +substance, first, because it is an excellent insulator, and in that respect +would illustrate the relation of the effect to the degree of conducting +power possessed by the dielectric (1247.); and in the next place, that I +might obtain that body giving the smallest degree of the effect now under +consideration for the investigation of the question of specific inductive +capacity (1277.). + +1242. With a good hemispherical cup of sulphur cast solid and sound, I +obtained the return charge, but only to an amount of 17 deg. or 18 deg.. Thus glass +and sulphur, which are bodily very bad conductors of electricity, and +indeed almost perfect insulators, gave very little of this return charge. + +1243. I tried the same experiment having _air_ only in the inductive +apparatus. After a continued high charge for some time I could obtain a +little effect of return action, but it was ultimately traced to the +shell-lac of the stem. + +1244. I sought to produce something like this state with one electric power +and without induction; for upon the theory of an electric fluid or fluids, +that did not seem impossible, and then I should have obtained an absolute +charge (1169. 1177.), or something equivalent to it. In this I could not +succeed. I excited the outside of a cylinder of shell-lac very highly for +some time, and then quickly discharging it (1203.), waited and watched +whether any return charge would appear, but such was not the case. This is +another fact in favour of the inseparability of the two electric forces +(1177.), and another argument for the view that induction and its +concomitant phenomena depend upon a polarity of the particles of matter. + +1245. Although inclined at first to refer these effects to a peculiar +masked condition of a certain portion of the forces, I think I have since +correctly traced them to known principles of electrical action. The effects +appear to be due to an actual penetration of the charge to some distance +within the electric, at each of its two surfaces, by what we call +_conduction_; so that, to use the ordinary phrase, the electric forces +sustaining the induction are not upon the metallic surfaces only, but upon +and within the dielectric also, extending to a greater or smaller depth +from the metal linings. Let _c_ (fig. 113.) be the section of a plate of +any dielectric, _a_ and _b_ being the metallic coatings; let _b_ be +uninsulated, and _a_ be charged positively; after ten or fifteen minutes, +if _a_ and _b_ be discharged, insulated, and immediately examined, no +electricity will appear in them; but in a short time, upon a second +examination, they will appear charged in the same way, though not to the +same degree, as they were at first. Now suppose that a portion of the +positive force has, under the coercing influence of all the forces +concerned, penetrated the dielectric and taken up its place at the line +_p_, a corresponding portion of the negative force having also assumed its +position at the line _n_; that in fact the electric at these two parts has +become charged positive and negative; then it is clear that the induction +of these two forces will be much greater one towards the other, and less in +an external direction, now that they are at the small distance _np_ from +each other, than when they were at the larger interval _ab_. Then let _a_ +and _b_ be discharged; the discharge destroys or neutralizes all external +induction, and the coatings are therefore found by the carrier ball +unelectrified; but it also removes almost the whole of the forces by which +the electric charge was driven into the dielectric, and though probably a +part of that charge goes forward in its passage and terminates in what we +call discharge, the greater portion returns on its course to the surfaces +of _c_, and consequently to the conductors _a_ and _b_, and constitutes the +recharge observed. + +1246. The following is the experiment on which I rest for the truth of this +view. Two plates of spermaceti, _d_ and, _f_ (fig. 114.), were put together +to form the dielectric, _a_ and _b_ being the metallic coatings of this +compound plate, as before. The system was charged, then discharged, +insulated, examined, and found to give no indications of electricity to the +carrier ball. The plates _d_ and _f_were then separated from each other, +and instantly _a_ with _d_ was found in a positive state, and _b_ with _f_ +in a negative state, nearly all the electricity being in the linings _a_ +and _b_. Hence it is clear that, of the forces sought for, the positive was +in one-half of the compound plate and the negative in the other half; for +when removed bodily with the plates from each other's inductive influence, +they appeared in separate places, and resumed of necessity their power of +acting by induction on the electricity of surrounding bodies. Had the +effect depended upon a peculiar relation of the contiguous particles of +matter only, then each half-plate, _d_ and _f_, should have shown positive +force on one surface and negative on the other. + +1247. Thus it would appear that the best solid insulators, such as +shell-lac, glass, and sulphur, have conductive properties to such an +extent, that electricity can penetrate them bodily, though always subject +to the overruling condition of induction (1178.). As to the depth to which +the forces penetrate in this form of charge of the particles, +theoretically, it should be throughout the mass, for what the charge of the +metal does for the portion of dielectric next to it, should be close by the +charged dielectric for the portion next beyond it again; but probably in +the best insulators the sensible charge is to a very small depth only in +the dielectric, for otherwise more would disappear in the first instance +whilst the original charge is sustained, less time would be required for +the assumption of the particular state, and more electricity would +re-appear as return charge. + +1248. The condition of _time_ required for this penetration of the charge +is important, both as respects the general relation of the cases to +conduction, and also the removal of an objection that might otherwise +properly be raised to certain results respecting specific inductive +capacities, hereafter to be given (1269. 1277.) + +1249. It is the assumption for a time of this charged state of the glass +between the coatings in the Leyden jar, which gives origin to a well-known +phenomenon, usually referred to the diffusion of electricity over the +uncoated portion of the glass, namely, the _residual charge_. The extent of +charge which can spontaneously be recovered by a large battery, after +perfect uninsulation of both surfaces, is very considerable, and by far the +largest portion of this is due to the return of electricity in the manner +described. A plate of shell-lac six inches square, and half an inch thick, +or a similar plate of spermaceti an inch thick, being coated on the sides +with tinfoil as a Leyden arrangement, will show this effect exceedingly +well. + + * * * * * + +1250. The peculiar condition of dielectrics which has now been described, +is evidently capable of producing an effect interfering with the results +and conclusions drawn from the use of the two inductive apparatus, when +shell-lac, glass, &c. is used in one or both of them (1192. 1207.), for +upon dividing the charge in such cases according to the method described +(1198. 1207.), it is evident that the apparatus just receiving its half +charge must fall faster in its tension than the other. For suppose app. i. +first charged, and app. ii. used to divide with it; though both may +actually lose alike, yet app. i., which has been diminished one-half, will +be sustained by a certain degree of return action or charge (1234.), whilst +app. ii. will sink the more rapidly from the coming on of the particular +state. I have endeavoured to avoid this interference by performing the +whole process of comparison as quickly as possible, and taking the force of +app. ii. immediately after the division, before any sensible diminution of +the tension arising from the assumption of the peculiar state could be +produced; and I have assumed that as about three minutes pass between the +first charge of app. i. and the division, and three minutes between the +division and discharge, when the force of the non-transferable electricity +is measured, the contrary tendencies for those periods would keep that +apparatus in a moderately steady and uniform condition for the latter +portion of time. + +1251. The particular action described occurs in the shell-lac of the stems, +as well as in the _dielectric_ used within the apparatus. It therefore +constitutes a cause by which the outside of the stems may in some +operations become charged with electricity, independent of the action of +dust or carrying particles (1203.). + + +P v. _On specific induction, or specific inductive capacity._ + +1252. I now proceed to examine the great question of specific inductive +capacity, i.e. whether different dielectric bodies actually do possess any +influence over the degree of induction which takes place through them. If +any such difference should exist, it appeared to me not only of high +importance in the further comprehension of the laws and results of +induction, but an additional and very powerful argument for the theory I +have ventured to put forth, that the whole depends upon a molecular action, +in contradistinction to one at sensible distances. + +The question may be stated thus: suppose A an electrified plate of metal +suspended in the air, and B and C two exactly similar plates, placed +parallel to and on each side of A at equal distances and uninsulated; A +will then induce equally towards B and C. If in this position of the plates +some other dielectric than air, as shell-lac, be introduced between A and +C, will the induction between them remain the same? Will the relation of C +and B to A be unaltered, notwithstanding the difference of the dielectrics +interposed between them?[A] + + [A] Refer for the practical illustration of this statement to the + supplementary note commencing 1307, &c.--_Dec. 1838._ + +1253. As far as I recollect, it is assumed that no change will occur under +such variation of circumstances, and that the relations of B find C to A +depend entirely upon their distance. I only remember one experimental +illustration of the question, and that is by Coulomb[A], in which he shows +that a wire surrounded by shell-lac took exactly the same quantity of +electricity from a charged body as the same wire in air. The experiment +offered to me no proof of the truth of the supposition: for it is not the +mere films of dielectric substances surrounding the charged body which have +to be examined and compared, but the _whole mass_ between that body and the +surrounding conductors at which the induction terminates. Charge depends +upon induction (1171. 1178.); and if induction is related to the particles +of the surrounding dielectric, then it is related to _all_ the particles of +that dielectric inclosed by the surrounding conductors, and not merely to +the few situated next to the charged body. Whether the difference I sought +for existed or not, I soon found reason to doubt the conclusion that might +be drawn from Coulomb's result; and therefore had the apparatus made, +which, with its use, has been already described (1187, &c.), and which +appears to me well-suited for the investigation of the question. + + [A] Memoires de l'Academie, 1787, pp. 452, 453. + +1254. Glass, and many bodies which might at first be considered as very fit +to test the principle, proved exceedingly unfit for that purpose. Glass, +principally in consequence of the alkali it contains, however well-warmed +and dried it may be, has a certain degree of conducting power upon its +surface, dependent upon the moisture of the atmosphere, which renders it +unfit for a test experiment. Resin, wax, naphtha, oil of turpentine, and +many other substances were in turn rejected, because of a slight degree of +conducting power possessed by them; and ultimately shell-lac and sulphur +were chosen, after many experiments, as the dielectrics best fitted for the +investigation. No difficulty can arise in perceiving how the possession of +a feeble degree of conducting power tends to make a body produce effects, +which would seem to indicate that it had a greater capability of allowing +induction through it than another body perfect in its insulation. This +source of error has been that which I have found most difficult to obviate +in the proving experiments. + + * * * * * + +1255. _Induction through shell-lac._--As a preparatory experiment, I first +ascertained generally that when a part of the surface of a thick plate of +shell-lac was excited or charged, there was no sensible difference in the +character of the induction sustained by that charged part, whether exerted +through the air in the one direction, or through the shell-lac of the plate +in the other; provided the second surface of the plate had not, by contact +with conductors, the action of dust, or any other means, become charged +(1203.). Its solid condition enabled it to retain the excited particles in +a permanent position, but that appeared to be all; for these particles +acted just as freely through the shell-lac on one side as through the air +on the other. The same general experiment was made by attaching a disc of +tinfoil to one side of the shell-lac plate, and electrifying it, and the +results were the same. Scarcely any other solid substance than shell-lac +and sulphur, and no liquid substance that I have tried, will bear this +examination. Glass in its ordinary state utterly fails; yet it was +essentially necessary to obtain this prior degree of perfection in the +dielectric used, before any further progress could be made in the principal +investigation. + +1256. _Shell-lac and air_ were compared in the first place. For this +purpose a thick hemispherical cup of shell-lac was introduced into the +lower hemisphere of one of the inductive apparatus (1187, &c.), so as +nearly to fill the lower half of the space _o, o_ (fig. 104.) between it +and the inner ball; and then charges were divided in the manner already +described (1198. 1207.), each apparatus being used in turn to receive the +first charge before its division by the other. As the apparatus were known +to have equal inductive power when air was in both (1209. 1211.), any +differences resulting from the introduction of the shell-lac would show a +peculiar action in it, and if unequivocally referable to a specific +inductive influence, would establish the point sought to be sustained. I +have already referred to the precautions necessary in making the +experiments (1199, &c.); and with respect to the error which might be +introduced by the assumption of the peculiar state, it was guarded against, +as far as possible, in the first place, by operating quickly (1248); and, +afterwards, by using that dielectric as glass or sulphur, which assumed the +peculiar state most slowly, and in the least degree (1239. 1241.). + +1257. The shell-lac hemisphere was put into app. i., and app. ii. left +filled with air. The results of an experiment in which the charge through +air was divided and reduced by the shell-lac app. were as follows: + +App. i. Lac. App. ii. Air. + Balls 255 deg.. + + 0 deg. . . . . + . . . . 304 deg. + . . . . 297 + Charge divided. + 113 . . . . + . . . . 121 + 0 . . . . after being discharged. + . . . . 7 after being discharged. + +1258. Here 297 deg., minus 7 deg., or 290 deg., may be taken as the divisible charge of +app. ii. (the 7 deg. being fixed stem action (1203. 1232.)), of which 145 deg. is +the half. The lac app. i. gave 113 deg. as the power or tension it had acquired +after division; and the air app. ii. gave 121 deg., minus 7 deg., or 114 deg., as the +force it possessed from what it retained of the divisible charge of 290 deg.. +These two numbers should evidently be alike, and they are very nearly so, +indeed far within the errors of experiment and observation, but these +numbers differ very much from 145 deg., or the force which the half charge +would have had if app. i. had contained air instead of shell-lac; and it +appears that whilst in the division the induction through the air has lost +176 deg. of force, that through the lac has only gained 113 deg.. + +1259. If this difference be assumed as depending entirely on the greater +facility possessed by shell-lac of allowing or causing inductive action +through its substance than that possessed by air, then this capacity for +electric induction would be inversely as the respective loss and gain +indicated above; and assuming the capacity of the air apparatus as 1, that +of the shell-lac apparatus would be 176/113 or 1.55. + +1260. This extraordinary difference was so unexpected in its amount, as to +excite the greatest suspicion of the general accuracy of the experiment, +though the perfect discharge of app. i. after the division, showed that the +113 deg. had been taken and given up readily. It was evident that, if it really +existed, it ought to produce corresponding effects in the reverse order; +and that when induction through shell-lac was converted into induction +through air, the force or tension of the whole ought to be _increased_. The +app. i. was therefore charged in the first place, and its force divided +with app. ii. The following were the results: + +App. i. Lac. App. ii. Air. + . . . . 0 deg. + 215 deg. . . . . + 204 . . . . + Charge divided. + . . . . 118 + 118 . . . . + . . . . 0 after being discharged. + 0 . . . . after being discharged. + +1261. Here 204 deg. must be the utmost of the divisible charge. The app. i. and +app. ii. present 118 deg. as their respective forces; both now much _above_ the +half of the first force, or 102 deg., whereas in the former case they were +below it. The lac app. i. has lost only 86 deg., yet it has given to the air +app. ii. 118 deg., so that the lac still appears much to surpass the air, the +capacity of the lac app. i. to the air app. ii. being as 1.37 to 1. + +1262. The difference of 1.55 and 1.37 as the expression of the capacity for +the induction of shell-lac seems considerable, but is in reality very +admissible under the circumstances, for both are in error in _contrary +directions_. Thus in the last experiment the charge fell from 215 deg. to 204 deg. +by the joint effects of dissipation and absorption (1192. 1250.), during +the time which elapsed in the electrometer operations, between the +applications of the carrier ball required to give those two results. Nearly +an equal time must have elapsed between the application of the carrier +which gave the 204 deg. result, and the division of the charge between the two +apparatus; and as the fall in force progressively decreases in amount +(1192.), if in this case it be taken at 6 deg. only, it will reduce the whole +transferable charge at the time of division to 198 deg. instead of 204 deg.; this +diminishes the loss of the shell-lac charge to 80 deg. instead of 86 deg.; and then +the expression of specific capacity for it is increased, and, instead of +1.37, is 1.47 times that of air. + +1263. Applying the same correction to the former experiment in which air +was _first_ charged, the result is of the _contrary_ kind. No shell-lac +hemisphere was then in the apparatus, and therefore the loss would be +principally from dissipation, and not from absorption: hence it would be +nearer to the degree of loss shown by the numbers 304 deg. and 297 deg., and being +assumed as 6 deg. would reduce the divisible charge to 284 deg.. In that case the +air would have lost 170 deg., and communicated only 113 deg. to the shell-lac; and +the relative specific capacity of the latter would appear to be 1.50, which +is very little indeed removed from 1.47, the expression given by the second +experiment when corrected in the same way. + +1264. The shell-lac was then removed from app. i. and put into app. ii. and +the experiments of division again made. I give the results, because I think +the importance of the point justifies and even requires them. + +App. i. Air. App. ii. Lac. + Balls 200 deg.. + + . . . . 0 deg.. + 286 deg. . . . . + 283 . . . . + Charge divided. + . . . . 110 + 109 . . . . + . . . . 0.25 after discharge. +Trace . . . . after discharge. + +Here app. i. retained 109 deg., having lost 174 deg. in communicating 110 deg. to app. +ii.; and the capacity of the air app. is to the lac app., therefore, as 1 +to 1.58. If the divided charge be corrected for an assumed loss of only 3 deg., +being the amount of previous loss in the same time, it will make the +capacity of the shell-lac app. 1.55 only. + +1265. Then app. ii. was charged, and the charge divided thus: + +App. i. Air. App. ii. Lac, + 0 deg. . . . . + . . . . 250 deg. + . . . . 251 + Charge divided. + 146 . . . . + . . . . 149 +a little . . . . after discharge. + . . . . a little after discharge. + +Here app. i. acquired a charge of 146 deg., while app. ii. lost only 102 deg. in +communicating that amount of force; the capacities being, therefore, to +each other as 1 to 1.43. If the whole transferable charge be corrected for +a loss of 4 deg. previous to division, it gives the expression of l.49 for the +capacity of the shell-lac apparatus. + +1266. These four expressions of 1.47, 1.50, 1.55, and 1.49 for the power of +the shell-lac apparatus, through the different variations of the +experiment, are very near to each other; the average is close upon 1.5, +which may hereafter be used as the expression of the result. It is a very +important result; and, showing for this particular piece of shell-lac a +decided superiority over air in allowing or causing the act of induction, +it proved the growing necessity of a more close and rigid examination of +the whole question. + +1267. The shell-lac was of the best quality, and had been carefully +selected and cleaned; but as the action of any conducting particles in it +would tend, virtually, to diminish the quantity or thickness of the +dielectric used, and produce effects as if the two inducing surfaces of the +conductors in that apparatus were nearer together than in the one with air +only, I prepared another shell-lac hemisphere, of which the material had +been dissolved in strong spirit of wine, the solution filtered, and then +carefully evaporated. This is not an easy operation, for it is difficult to +drive off the last portions of alcohol without injuring the lac by the heat +applied; and unless they be dissipated, the substance left conducts too +well to be used in these experiments. I prepared two hemispheres this way, +one of them unexceptionable; and with it I repeated the former experiments +with all precautions. The results were exactly of the same kind; the +following expressions for the capacity of the shell-lac apparatus, whether +it were app. i. or ii., being given directly by the experiments, 1.46, +1.50, 1.52, 1.51; the average of these and several others being very nearly +1.5. + +1268. As a final check upon the general conclusion, I then actually brought +the surfaces of the air apparatus, corresponding to the place of the +shell-lac in its apparatus, nearer together, by putting a metallic lining +into the lower hemisphere of the one not containing the lac (1213.). The +distance of the metal surface from the carrier ball was in this way +diminished from 0.62 of an inch to 0.435 of an inch, whilst the interval +occupied by the lac in the other apparatus remained O.62 of an inch as +before. Notwithstanding this change, the lac apparatus showed its former +superiority; and whether it or the air apparatus was charged first, the +capacity of the lac apparatus to the air apparatus was by the experimental +results as 1.45 to 1. + +1269. From all the experiments I have made, and their constant results, I +cannot resist the conclusion that shell-lac does exhibit a case of +_specific inductive capacity_. I have tried to check the trials in every +way, and if not remove, at least estimate, every source of error. That the +final result is not due to common conduction is shown by the capability of +the apparatus to retain the communicated charge; that it is not due to the +conductive power of inclosed small particles, by which they could acquire a +polarized condition as conductors, is shown by the effects of the shell-lac +purified by alcohol; and, that it is not due to any influence of the +charged state, formerly described (1250.), first absorbing and then +evolving electricity, is indicated by the _instantaneous_ assumption and +discharge of those portions of the power which are concerned in the +phenomena, that instantaneous effect occurring in these cases, as in all +others of ordinary induction, by charged conductors. The latter argument is +the more striking in the case where the air apparatus is employed to divide +the charge with the lac apparatus, for it obtains its portion of +electricity in an _instant_, and yet is charged far above the _mean_. + +1270. Admitting for the present the general fact sought to be proved; then +1.5, though it expresses the capacity of the apparatus containing the +hemisphere of shell-lac, by no means expresses the relation of lac to air. +The lac only occupies one-half of the space _o, o_, of the apparatus +containing it, through which the induction is sustained; the rest is filled +with air, as in the other apparatus; and if the effect of the two upper +halves of the globes be abstracted, then the comparison of the shell-lac +powers in the lower half of the one, with the power of the air in the lower +half of the other, will be as 2:1; and even this must be less than the +truth, for the induction of the upper part of the apparatus, i.e. of the +wire and ball B. (fig. 104.) to external objects, must be the same in both, +and considerably diminish the difference dependent upon, and really +producible by, the influence of the shell-lac within. + + * * * * * + +1271. _Glass._--I next worked with glass as the dielectric. It involved the +possibility of conduction on its surface, but it excluded the idea of +conducting particles within its substance (1267.) other than those of its +own mass. Besides this it does not assume the charged state (1239.) so +readily, or to such an extent, as shell-lac. + +1272. A thin hemispherical cup of glass being made hot was covered with a +coat of shell-lac dissolved in alcohol, and after being dried for many +hours in a hot place, was put into the apparatus and experimented with. It +exhibited effects so slight, that, though they were in the direction +indicating a superiority of glass over air, they were allowed to pass as +possible errors of experiment; and the glass was considered as producing no +sensible effect. + +1273. I then procured a thick hemispherical flint glass cup resembling that +of shell-lac (1239.), but not filling up the space _o, o_, so well. Its +average thickness was 0.4 of an inch, there being an additional thickness +of air, averaging 0.22 of an inch, to make up the whole space of 0.62 of an +inch between the inductive metallic surfaces. It was covered with a film of +shell-lac as the former was, (1272.) and being made very warm, was +introduced into the apparatus, also warmed, and experiments made with it as +in the former instances (1257. &c.). The general results were the same as +with shell-lac, i.e. glass surpassed air in its power of favouring +induction through it. The two best results as respected the state of the +apparatus for retention of charge, &c., gave, when the air apparatus was +charged first 1.336, and when the glass apparatus was charged first 1.45, +as the specific inductive capacity for glass, both being without +correction. The average of nine results, four with the glass apparatus +first charged, and five with the air apparatus first charged, gave 1.38 as +the power of the glass apparatus; 1.22 and 1.46 being the minimum and +maximum numbers with all the errors of experiment upon them. In all the +experiments the glass apparatus took up its inductive charge instantly, and +lost it as readily (1269.); and during the short time of each experiment, +acquired the peculiar state in a small degree only, so that the influence +of this state, and also of conduction upon the results, must have been +small. + +1274. Allowing specific inductive capacity to be proved and active in this +case, and 1.38 as the expression for the glass apparatus, then the specific +inductive capacity of flint glass will be above 1.76, not forgetting that +this expression is for a piece of glass of such thickness as to occupy not +quite two-thirds of the space through which the induction is sustained +(1253. 1273.). + + * * * * * + +1275. _Sulphur._--The same hemisphere of this substance was used in app. +ii. as was formerly referred to (1242.). The experiments were well made, +i.e. the sulphur itself was free from charge both before and after each +experiment, and no action from the stem appeared (1203. 1232.), so that no +correction was required on that account. The following are the results when +the air apparatus was first charged and divided: + +App. i. Air, App. ii. Sulphur. + Balls 280 deg.. + + 0 deg. . . . . + . . . . 0 deg. + 438 . . . . + 434 . . . . + Charge divided. + . . . . 162 + 164 . . . . + . . . . 160 + 162 . . . . + . . . . 0 after discharge. + 0 . . . . after discharge. + +Here app. i. retained 164 deg., having lost 276 deg. in communicating 162 deg. to app. +ii., and the capacity of the air apparatus is to that of the sulphur +apparatus as 1 to 1.66. + +1276. Then the sulphur apparatus was charged first, thus: + + . . . . 0 deg. + 0 deg. . . . . + . . . . 395 + . . . . 388 + Charge divided. + 237 . . . . + . . . . 238 + 0 . . . . after discharge. + . . . . 0 after discharge. + +Here app. ii. retained 238 deg., and gave up 150 deg. in communicating a charge of +237 deg. to app. i., and the capacity of the air apparatus is to that of the +sulphur apparatus as 1 to 1.58. These results are very near to each other, +and we may take the mean 1.62 as representing the specific inductive +capacity of the sulphur apparatus; in which case the specific inductive +capacity of sulphur itself as compared to air = 1 (1270.) will be about or +above 2.24. + +1277. This result with sulphur I consider as one of the most +unexceptionable. The substance when fused was perfectly clear, pellucid, +and free from particles of dirt (1267.), so that no interference of small +conducting bodies confused the result. The substance when solid is an +excellent insulator, and by experiment was found to take up, with great +slowness, that state (1244. 1242.) which alone seemed likely to disturb the +conclusion. The experiments themselves, also, were free from any need of +correction. Yet notwithstanding these circumstances, so favourable to the +exclusion of error, the result is a higher specific inductive capacity for +sulphur than for any other body as yet tried; and though this may in part +be clue to the sulphur being in a better shape, i.e. filling up more +completely the space _o, o_, (fig. 104.) than the cups of shell-lac and +glass, still I feel satisfied that the experiments altogether fully prove +the existence of a difference between dielectrics as to their power of +favouring an inductive action through them; which difference may, for the +present, be expressed by the term _specific inductive capacity_. + +1278. Having thus established the point in the most favourable cases that I +could anticipate, I proceeded to examine other bodies amongst solids, +liquids, and gases. These results I shall give with all convenient brevity. + + * * * * * + +1279. _Spermaceti._--A good hemisphere of spermaceti being tried as to +conducting power whilst its two surfaces were still in contact with the +tinfoil moulds used in forming it, was found to conduct sensibly even +whilst warm. On removing it from the moulds and using it in one of the +apparatus, it gave results indicating a specific inductive capacity between +1.3 and 1.6 for the apparatus containing it. But as the only mode of +operation was to charge the air apparatus, and then after a quick contact +with the spermaceti apparatus, ascertain what was left in the former +(1281.), no great confidence can be placed in the results. They are not in +opposition to the general conclusion, but cannot be brought forward as +argument in favour of it. + + * * * * * + +1280. I endeavoured to find some liquids which would insulate well, and +could be obtained in sufficient quantity for these experiments. Oil of +turpentine, native naphtha rectified, and the condensed oil gas fluid, +appeared by common experiments to promise best as to insulation. Being left +in contact with fused carbonate of potassa, chloride of lime, and quick +lime for some days and then filtered, they were found much injured in +insulating power; but after distillation acquired their best state, though +even then they proved to be conductors when extensive metallic contact was +made with them. + +1281. _Oil of turpentine rectified._--I filled the lower half of app. i. +with the fluid: and as it would not hold a charge sufficiently to enable me +first to measure and then divide it, I charged app. ii. containing air, and +dividing its charge with app. i. by a quick contact, measured that +remaining in app. ii.: for, theoretically, if a quick contact would divide +up to equal tension between the two apparatus, yet without sensible loss +from the conducting power of app. i.; and app. ii. were left charged to a +degree of tension above half the original charge, it would indicate that +oil of turpentine had less specific inductive capacity than air; or, if +left charged below that mean state of tension, it would imply that the +fluid had the greater inductive capacity. In an experiment of this kind, +app. ii. gave as its charge 390 deg. before division with app. i., and 175 deg. +afterwards, which is less than the half of 390 deg.. Again, being at 176 deg. +before division, it was 79 deg. after, which is also less than half the divided +charge. Being at 79 deg., it was a third time divided, and then fell to 36 deg., +less than the half of 79 deg.. Such are the best results I could obtain; they +are not inconsistent with the belief that oil of turpentine has a greater +specific capacity than air, but they do not prove the fact, since the +disappearance of more than half the charge may be due to the conducting +power merely of the fluid. + +1282. _Naphtha._--This liquid gave results similar in their nature and +direction to those with oil of turpentine. + + * * * * * + +1283. A most interesting class of substances, in relation to specific +inductive capacity, now came under review, namely, the gases or aeriform +bodies. These are so peculiarly constituted, and are bound together by so +many striking physical and chemical relations, that I expected some +remarkable results from them: air in various states was selected for the +first experiments. + +1284. _Air, rare and dense._--Some experiments of division (1208.) seemed +to show that dense and rare air were alike in the property under +examination. A simple and better process was to attach one of the apparatus +to an air-pump, to charge it, and then examine the tension of the charge +when the air within was more or less rarefied. Under these circumstances it +was found, that commencing with a certain charge, that charge did not +change in its tension or force as the air was rarefied, until the +rarefaction was such that _discharge_ across the space _o_, _o_ (fig. 104.) +occurred. This discharge was proportionate to the rarefaction; but having +taken place, and lowered the tension to a certain degree, that degree was +not at all affected by restoring the pressure and density of the air to +their first quantities. + + inches of mercury. +Thus at a pressure of 30 the charge was 88 deg. +Again 30 the charge was 88 +Again 30 the charge was 87 +Reduced to 11 the charge was 87 +Raised again to 30 the charge was 86 +Being now reduced to 3.4 the charge fell to 81 +Raised again to 30 the charge was still 81 + +1285. The charges were low in these experiments, first that they might not +pass off at low pressure, and next that little loss by dissipation might +occur. I now reduced them still lower, that I might rarefy further, and for +this purpose in the following experiment used a measuring interval in the +electrometer of only 15 deg. (1185.). The pressure of air within the apparatus +being reduced to 1.9 inches of mercury, the charge was found to be 29 deg.; +then letting in air till the pressure was 30 inches, the charge was still +29 deg.. + +1286. These experiments were repeated with pure oxygen with the same +consequences. + +1287. This result of _no variation_ in the electric tension being produced +by variation in the density or pressure of the air, agrees perfectly with +those obtained by Mr. Harris[A], and described in his beautiful and +important investigations contained in the Philosophical Transactions; +namely that induction is the same in rare and dense air, and that the +divergence of an electrometer under such variations of the air continues +the same, provided no electricity pass away from it. The effect is one +entirely independent of that power which dense air has of causing a higher +charge to be _retained_ upon the surface of conductors in it than can be +retained by the same conductors in rare air; a point I propose considering +hereafter. + + [A] Philosophical Transactions, 1834, pp. 223, 224, 237, 244. + +1288. I then compared _hot and cold air_ together, by raising the +temperature of one of the inductive apparatus as high as it could be +without injury, and then dividing charges between it and the other +apparatus containing cold air. The temperatures were about 50 deg. and 200 deg., +Still the power or capacity appeared to be unchanged; and when I +endeavoured to vary the experiment, by charging a cold apparatus and then +warming it by a spirit lamp, I could obtain no proof that the inductive +capacity underwent any alteration. + +1289. I compared _damp and dry air_ together, but could find no difference +in the results. + + * * * * * + +1290. _Gases._--A very long series of experiments was then undertaken for +the purpose of comparing _different gases_ one with another. They were all +found to insulate well, except such as acted on the shell-lac of the +supporting stem; these were chlorine, ammonia, and muriatic acid. They were +all dried by appropriate means before being introduced into the apparatus. +It would have been sufficient to have compared each with air; but, in +consequence of the striking result which came out, namely, that _all had +the same power of_ or _capacity for_, sustaining induction through them, +(which perhaps might have been expected after it was found that no +variation of density or pressure produced any effect,) I was induced to +compare them, experimentally, two and two in various ways, that no +difference might escape me, and that the sameness of result might stand in +full opposition to the contrast of property, composition, and condition +which the gases themselves presented. + +1291. The experiments were made upon the following pairs of gases. + + 1. Nitrogen and Oxygen. + 2. Oxygen Air. + 3. Hydrogen Air. + 4. Muriatic acid gas Air. + 5. Oxygen Hydrogen. + 5. Oxygen Carbonic acid. + 7. Oxygen Olefiant gas. + 8. Oxygen Nitrous gas. + 9. Oxygen Sulphurous acid. +10. Oxygen Ammonia. +11. Hydrogen Carbonic acid. +12 Hydrogen Olefiant gas. +13. Hydrogen Sulphurous acid. +14. Hydrogen Fluo-silicic acid. +15. Hydrogen Ammonia. +16, Hydrogen Arseniuretted hydrogen. +17. Hydrogen Sulphuretted hydrogen. +18, Nitrogen Olefiant gas. +19. Nitrogen Nitrous gas. +20. Nitrogen Nitrous oxide. +21. Nitrogen Ammonia. +22. Carbonic oxide Carbonic acid. +23. Carbonic oxide Olefiant gas. +24. Nitrous oxide Nitrous gas. +25. Ammonia Sulphurous acid. + +1292. Notwithstanding the striking contrasts of all kinds which these gases +present of property, of density, whether simple or compound, anions or +cations (665.), of high or low pressure (1284. 1286.), hot or cold (1288.), +not the least difference in their capacity to favour or admit electrical +induction through them could be perceived. Considering the point +established, that in all these gases induction takes place by an action of +contiguous particles, this is the more important, and adds one to the many +striking relations which hold between bodies having the gaseous condition +and form. Another equally important electrical relation, which will be +examined in the next paper[A], is that which the different gases have to +each other at the _same pressure_ of causing the retention of the _same or +different degrees of charge_ upon conductors in them. These two results +appear to bear importantly upon the subject of electrochemical excitation +and decomposition; for as _all_ these phenomena, different as they seem to +be, must depend upon the electrical forces of the particles of matter, the +very distance at which they seem to stand from each other will do much, if +properly considered, to illustrate the principle by which they are held in +one common bond, and subject, as they must be, to one common law. + + [A] See in relation to this point 1382. &c.--_Dec. 1838._ + +1293. It is just possible that the gases may differ from each other in +their specific inductive capacity, and yet by quantities so small as not to +be distinguished in the apparatus I have used. It must be remembered, +however, that in the gaseous experiments the gases occupy all the space _o, +o_, (fig. 104.) between the inner and the outer ball, except the small +portion filled by the stem; and the results, therefore, are twice as +delicate as those with solid dielectrics. + +1294. The insulation was good in all the experiments recorded, except Nos. +10, 15, 21, and 25, being those in which ammonia was compared with other +gases. When shell-lac is put into ammoniacal gas its surface gradually +acquires conducting power, and in this way the lac part of the stem within +was so altered, that the ammonia apparatus could not retain a charge with +sufficient steadiness to allow of division. In these experiments, +therefore, the other apparatus was charged; its charge measured and divided +with the ammonia apparatus by a quick contact, and what remained untaken +away by the division again measured (1281.). It was so nearly one-half of +the original charge, as to authorize, with this reservation, the insertion +of ammoniacal gas amongst the other gases, as having equal power with them. + + +P vi. _General results as to induction._ + +1295. Thus _induction_ appears to be essentially an action of contiguous +particles, through the intermediation of which the electric force, +originating or appearing at a certain place, is propagated to or sustained +at a distance, appearing there as a force of the same kind exactly equal in +amount, but opposite in its direction and tendencies (1164.). Induction +requires no sensible thickness in the conductors which may be used to limit +its extent; an uninsulated leaf of gold may be made very highly positive on +one surface, and as highly negative on the other, without the least +interference of the two states whilst the inductions continue. Nor is it +affected by the nature of the limiting conductors, provided time be +allowed, in the case of those which conduct slowly, for them to assume +their final state (1170.). + +1296. But with regard to the _dielectrics_ or insulating media, matters are +very different (1167.). Their thickness has an immediate and important +influence on the degree of induction. As to their quality, though all gases +and vapours are alike, whatever their state; yet amongst solid bodies, and +between them and gases, there are differences which prove the existence of +_specific inductive capacities_, these differences being in some cases very +great. + +1297. The direct inductive force, which may be conceived to be exerted in +lines between the two limiting and charged conducting surfaces, is +accompanied by a lateral or transverse force equivalent to a dilatation or +repulsion of these representative lines (1224.); or the attractive force +which exists amongst the particles of the dielectric in the direction of +the induction is accompanied by a repulsive or a diverging force in the +transverse direction (1304.). + +1298. Induction appears to consist in a certain polarized state of the +particles, into which they are thrown by the electrified body sustaining +the action, the particles assuming positive and negative points or parts, +which are symmetrically arranged with respect to each other and the +inducting surfaces or particles[A]. The state must be a forced one, for it +is originated and sustained only by force, and sinks to the normal or +quiescent state when that force is removed. It can be _continued_ only in +insulators by the same portion of electricity, because they only can retain +this state of the particles (1304). + + [A] The theory of induction which I am stating does not pretend to + decide whether electricity be a fluid or fluids, or a mere power or + condition of recognized matter. That is a question which I may be + induced to consider in the next or following series of these + researches. + +1299. The principle of induction is of the utmost generality in electric +action. It constitutes charge in every ordinary case, and probably in every +case; it appears to be the cause of all excitement, and to precede every +current. The degree to which the particles are affected in this their +forced state, before discharge of one kind or another supervenes, appears +to constitute what we call _intensity_. + +1300. When a Leyden jar is _charged_, the particles of the glass are forced +into this polarized and constrained condition by the electricity of the +charging apparatus. _Discharge_ is the return of these particles to their +natural state from their state of tension, whenever the two electric forces +are allowed to be disposed of in some other direction. + +1301. All charge of conductors is on their surface, because being +essentially inductive, it is there only that the medium capable of +sustaining the necessary inductive state begins. If the conductors are +hollow and contain air or any other dielectric, still no _charge_ can +appear upon that internal surface, because the dielectric there cannot +assume the polarized state throughout, in consequence of the opposing +actions in different directions. + +1302. The known influence of _form_ is perfectly consistent with the +corpuscular view of induction set forth. An electrified cylinder is more +affected by the influence of the surrounding conductors (which complete the +condition of charge) at the ends than at the middle, because the ends are +exposed to a greater sum of inductive forces than the middle; and a point +is brought to a higher condition than a ball, because by relation to the +conductors around, more inductive force terminates on its surface than on +an equal surface of the ball with which it is compared. Here too, +especially, can be perceived the influence of the lateral or transverse +force (1297.), which, being a power of the nature of or equivalent to +repulsion, causes such a disposition of the lines of inductive force in +their course across the dielectric, that they must accumulate upon the +point, the end of the cylinder, or any projecting part. + +1303. The influence of _distance_ is also in harmony with the same view. +There is perhaps no distance so great that induction cannot take place +through it[A]; but with the same constraining force (1298.) it takes place +the more easily, according as the extent of dielectric through which it is +exerted is lessened. And as it is assumed by the theory that the particles +of the dielectric, though tending to remain in a normal state, are thrown +into a forced condition during the induction; so it would seem to follow +that the fewer there are of these intervening particles opposing their +tendency to the assumption of the new state, the greater degree of change +will they suffer, i.e. the higher will be the condition they assume, and +the larger the amount of inductive action exerted through them. + + [A] I have traced it experimentally from a ball placed in the middle + of the large cube formerly described (1173.) to the sides of the cube + six feet distant, and also from the same ball placed in the middle of + our large lecture-room to the walls of the room at twenty-six feet + distance, the charge sustained upon the ball in these cases being + solely due to induction through these distances. + +1304. I have used the phrases _lines of inductive force_ and _curved lines_ +of force (1231. 1297. 1298. 1302.) in a general sense only, just as we +speak of the lines of magnetic force. The lines are imaginary, and the +force in any part of them is of course the resultant of compound forces, +every molecule being related to every other molecule in _all_ directions by +the tension and reaction of those which are contiguous. The transverse +force is merely this relation considered in a direction oblique to the +lines of inductive force, and at present I mean no more than that by the +phrase. With respect to the term _polarity_ also, I mean at present only a +disposition of force by which the same molecule acquires opposite powers on +different parts. The particular way in which this disposition is made will +come into consideration hereafter, and probably varies in different bodies, +and so produces variety of electrical relation[A]. All I am anxious about +at present is, that a more particular meaning should not be attached to the +expressions used than I contemplate. Further inquiry, I trust, will enable +us by degrees to restrict the sense more and more, and so render the +explanation of electrical phenomena day by day more and more definite. + + [A] See now 1685. &c.--_Dec. 1838._ + +1305. As a test of the probable accuracy of my views, I have throughout +this experimental examination compared them with the conclusions drawn by +M. Poisson from his beautiful mathematical inquiries[A]. I am quite unfit +to form a judgment of these admirable papers; but as far as I can perceive, +the theory I have set forth and the results I have obtained are not in +opposition to such of those conclusions as represent the final disposition +and state of the forces in the limited number of cases be has considered. +His theory assumes a very different mode of action in induction to that +which I have ventured to support, and would probably find its mathematical +test in the endeavour to apply it to cases of induction in curved lines. To +my feeling it is insufficient in accounting for the retention of +electricity upon the surface of conductors by the pressure of the air, an +effect which I hope to show is simple and consistent according to the +present view[B]; and it does not touch voltaic electricity, or in any way +associate it and what is called ordinary electricity under one common +principle. + + [A] Memoires de L'Institut, 1811, tom. xii. the first page 1, and the +second paging 163. + + [B] Refer to 1377, 1378, 1379, 1398.--_Dec. 1838._ + +I have also looked with some anxiety to the results which that +indefatigable philosopher Harris has obtained in his investigation of the +laws of induction[A], knowing that they were experimental, and having a +full conviction of their exactness; but I am happy in perceiving no +collision at present between them and the views I have taken. + + [A] Philosophical Transactions, 1834, p. 213. + +1306. Finally, I beg to say that I put forth my particular view with doubt +and fear, lest it should not bear the test of general examination, for +unless true it will only embarrass the progress of electrical science. It +has long been on my mind, but I hesitated to publish it until the +increasing persuasion of its accordance with all known facts, and the +manner in which it linked together effects apparently very different in +kind, urged me to write the present paper. I as yet see no inconsistency +between it and nature, but, on the contrary, think I perceive much new +light thrown by it on her operations; and my next papers will be devoted to +a review of the phenomena of conduction, electrolyzation, current, +magnetism, retention, discharge, and some other points, with an application +of the theory to these effects, and an examination of it by them. + + +_Royal Institution, +November 16, 1837._ + + * * * * * + +_Supplementary Note to Experimental Researches in Electricity._ + +_Eleventh Series._ + +Received March 29, 1838. + + +1307. I have recently put into an experimental form that general statement +of the question of _specific inductive capacity_ which is given at No. 1252 +of Series XI., and the result is such as to lead me to hope the Council of +the Royal Society will authorize its addition to the paper in the form of a +supplementary note. Three circular brass plates, about five inches in +diameter, were mounted side by side upon insulating pillars; the middle +one, A, was a fixture, but the outer plates B and C were moveable on +slides, so that all three could be brought with their sides almost into +contact, or separated to any required distance. Two gold leaves were +suspended in a glass jar from insulated wires; one of the outer plates B +was connected with one of the gold leaves, and the other outer plate with +the other leaf. The outer plates B and C were adjusted at the distance of +an inch and a quarter from the middle plate A, and the gold leaves were +fixed at two inches apart; A was then slightly charged with electricity, +and the plates B and C, with their gold leaves, thrown out of insulation +_at the same time_, and then left insulated. In this state of things A was +charged positive inductrically, and B and C negative inducteously; the same +dielectric, air, being in the two intervals, and the gold leaves hanging, +of course, parallel to each other in a relatively unelectrified state. + +1308. A plate of shell-lac three-quarters of an inch in thickness, and four +inches square, suspended by clean white silk thread, was very carefully +deprived of all charge (1203.) (so that it produced no effect on the gold +leaves if A were uncharged) and then introduced between plates A and B; the +electric relation of the three plates was immediately altered, and the gold +leaves attracted each other. On removing the shell-lac this attraction +ceased; on introducing it between A and C it was renewed; on removing it +the attraction again ceased; and the shell-lac when examined by a delicate +Coulomb electrometer was still without charge. + +1309. As A was positive, B and C were of course negative; but as the +specific inductive capacity of shell-lac is about twice that of air +(1270.), it was expected that when the lac was introduced between A and B, +A would induce more towards B than towards C; that therefore B would become +more negative than before towards A, and consequently, because of its +insulated condition, be positive externally, as at its back or at the gold +leaves; whilst C would be less negative towards A, and therefore negative +outwards or at the gold leaves. This was found to be the case; for on +whichever side of A the shell-lac was introduced the external plate at that +side was positive, and the external plate on the other side negative +towards each other, and also to uninsulated external bodies. + +1310. On employing a plate of sulphur instead of shell-lac, the same +results were obtained; consistent with the conclusions drawn regarding the +high specific inductive capacity of that body already given (1276.). + +1311. These effects of specific inductive capacity can be exalted in +various ways, and it is this capability which makes the great value of the +apparatus. Thus I introduced the shell-lac between A and B, and then for a +moment connected B and C, uninsulated them, and finally left them in the +insulated state; the gold leaves were of course hanging parallel to each +other. On removing the shell-lac the gold leaves attracted each other; on +introducing the shell-lac between A and C this attraction was _increased_, +(as had been anticipated from theory,) and the leaves came together, though +not more than four inches long, and hanging three inches apart. + +1312. By simply bringing the gold leaves nearer to each other I was able to +show the difference of specific inductive capacity when only thin plates of +shell-lac were used, the rest of the dielectric space being filled with +air. By bringing B and C nearer to A another great increase of sensibility +was made. By enlarging the size of the plates still further power was +gained. By diminishing the extent of the wires, &c. connected with the gold +leaves, another improvement resulted. So that in fact the gold leaves +became, in this manner, as delicate a test of _specific inductive action_ +as they are, in Bennet's and Singer's electrometers, of ordinary electrical +charge. + +1313. It is evident that by making the three plates the sides of cells, +with proper precautions as regards insulation, &c., this apparatus may be +used in the examination of gases, with far more effect than the former +apparatus (1187. 1290), and may, perhaps, bring out differences which have +as yet escaped me (1292. 1293.) + +1314. It is also evident that two metal plates are quite sufficient to form +the instrument; the state of the single inducteous plate when the +dielectric is changed, being examined either by bringing a body excited in +a known manner towards its gold leaves, or, what I think will be better, +employing a carrier ball in place of the leaf, and examining that ball by +the Coulomb electrometer (1180.). The inductive and inducteous surfaces may +even be balls; the latter being itself the carrier ball of the Coulomb's +electrometer (1181. 1229.). + +1315. To increase the effect, a small condenser may be used with great +advantage. Thus if, when two inducteous plates are used, a little condenser +were put in the place of the gold leaves, I have no doubt the three +principal plates might be reduced to an inch or even half an inch in +diameter. Even the gold leaves act to each other for the time as the plates +of a condenser. If only two plates were used, by the proper application of +the condenser the same reduction might take place. This expectation is +fully justified by an effect already observed and described (1229.). + +1316. In that case the application of the instrument to very extensive +research is evident. Comparatively small masses of dielectrics could be +examined, as diamonds and crystals. An expectation, that the specific +inductive capacity of crystals will vary in different directions, according +as the lines of inductive force (1304.) are parallel to, or in other +positions in relation to the axes of the crystals, can be tested[A]: I +purpose that these and many other thoughts which arise respecting specific +inductive action and the polarity of the particles of dielectric matter, +shall be put to the proof as soon as I can find time. + + [A] Refer for this investigation to 1680-1698.--_Dec. 1838._ + +1317. Hoping that this apparatus will form an instrument of considerable +use, I beg to propose for it (at the suggestion of a friend) the name of +_Differential Inductometer_. + +_Royal Institution, +March 29, 1838._ + + + + +TWELFTH SERIES. + +S 18. _On Induction (continued)._ P vii. _Conduction, or conductive +discharge._ P viii. _Electrolytic discharge._ P ix. _Disruptive +discharge--Insulation--Spark--Brush--Difference of discharge at the +positive and negative surfaces of conductors._ + +Received January 11,--Read February 8, 1838. + + +1318. I Proceed now, according to my promise, to examine, by the great +facts of electrical science, that theory of induction which I have ventured +to put forth (1165. 1295. &c.). The principle of induction is so universal +that it pervades all electrical phenomena; but the general case which I +purpose at present to go into consists of insulation traced into and +terminating with discharge, with the accompanying effects. This case +includes the various _modes_ of discharge, and also the condition and +characters of a current; the elements of magnetic action being amongst the +latter. I shall necessarily have occasion to speak theoretically, and even +hypothetically; and though these papers profess to be experimental +researches, I hope that, considering the facts and investigations contained +in the last series in support of the particular view advanced, I shall not +be considered as taking too much liberty on the present occasion, or as +departing too far from the character which they ought to have, especially +as I shall use every opportunity which presents itself of returning to that +strong test of truth, experiment. + +1319. Induction has as yet been considered in these papers only in cases of +insulation; opposed to insulation is _discharge_. The action or effect +which may be expressed by the general term _discharge_, may take place, as +far as we are aware at present, in several modes. Thus, that which is +called simply _conduction_ involves no chemical action, and apparently no +displacement of the particles concerned. A second mode may be called +_electrolytic discharge_; in it chemical action does occur, and particles +must, to a certain degree, be displaced. A third mode, namely, that by +sparks or brushes, may, because of its violent displacement of the +particles of the _dielectric_ in its course, be called the _disruptive +discharge_; and a fourth may, perhaps, be conveniently distinguished for a +time by the words _convection_, or _carrying discharge_, being that in +which discharge is effected either by the carrying power of solid +particles, or those of gases and liquids. Hereafter, perhaps, all these +modes may appear as the result of one common principle, but at present they +require to be considered apart; and I will now speak of the _first_ mode, +for amongst all the forms of discharge, that which we express by the term +conduction appears the most simple and the most directly in contrast with +insulation. + + +P vii. _Conduction, or conductive discharge._ + +1320. Though assumed to be essentially different, yet neither Cavendish nor +Poisson attempt to explain by, or even state in, their theories, what the +essential difference between insulation and conduction is. Nor have I +anything, perhaps, to offer in this respect, _except_ that, according to my +view of induction, insulation and conduction depend upon the same molecular +action of the dielectrics concerned; are only extreme degrees of _one +common condition_ or effect; and in any sufficient mathematical theory of +electricity must be taken as cases of the same kind. Hence the importance +of the endeavour to show the connection between them under my theory of the +electrical relations of contiguous particles. + +1321. Though the action of the insulating dielectric in the charged Leyden +jar, and that of the wire in discharging it, may seem very different, they +may be associated by numerous intermediate links, which carry us on from +one to the other, leaving, I think, no necessary connection unsupplied. We +may observe some of these in succession for information respecting the +whole case. + +1322. Spermnceti has been examined and found to be a dielectric, through +which induction can take place (1240. 1246.), its specific inductive +capacity being about or above 1.8 (1279.), and the inductive action has +been considered in it, as in all other substances, an action of contiguous +particles. + +1323. But spermaceti is also a _conductor_, though in so low a degree that +we can trace the process of conduction, as it were, step by step through +the mass (1247.); and even when the electric force has travelled through it +to a certain distance, we can, by removing the coercitive (which is at the +same time the inductive) force, cause it to return upon its path and +reappear in its first place (1245. 1246.). Here induction appears to be a +necessary preliminary to conduction. It of itself brings the contiguous +particles of the dielectric into a certain condition, which, if retained by +them, constitutes _insulation_, but if lowered by the communication of +power from one particle to another, constitutes _conduction_. + +1324. If _glass_ or _shell-lac_ be the substances under consideration, the +same capabilities of suffering either induction or conduction through them +appear (1233. 1239. 1247.), but not in the same degree. The conduction +almost disappears (1239. 1242.); the induction therefore is sustained, i.e. +the polarized state into which the inductive force has brought the +contiguous particles is retained, there being little discharge action +between them, and therefore the _insulation_ continues. But, what discharge +there is, appears to be consequent upon that condition of the particles +into which the induction throws them; and thus it is that ordinary +insulation and conduction are closely associated together or rather are +extreme cases of one common condition. + +1325. In ice or water we have a better conductor than spermaceti, and the +phenomena of induction and insulation therefore rapidly disappear, because +conduction quickly follows upon the assumption of the inductive state. But +let a plate of cold ice have metallic coatings on its sides, and connect +one of these with a good electrical machine in work, and the other with the +ground, and it then becomes easy to observe the phenomena of induction +through the ice, by the electrical tension which can be obtained and +continued on both the coatings (419. 426.). For although that portion of +power which at one moment gave the inductive condition to the particles is +at the next lowered by the consequent discharge due to the conductive act, +it is succeeded by another portion of force from the machine to restore the +inductive state. If the ice be converted into water the same succession of +actions can be just as easily proved, provided the water be distilled, and +(if the machine be not powerful enough) a voltaic battery be employed. + +1326. All these considerations impress my mind strongly with the +conviction, that insulation and ordinary conduction cannot be properly +separated when we are examining into their nature; that is, into the +general law or laws under which their phenomena are produced. They appear +to me to consist in an action of contiguous particles dependent on the +forces developed in electrical excitement; these forces bring the particles +into a state of tension or polarity, which constitutes both _induction_ and +_insulation_; and being in this state, the continuous particles have a +power or capability of communicating their forces one to the other, by +which they are lowered, and discharge occurs. Every body appears to +discharge (444. 987.); but the possession of this capability in a _greater +or smaller degree_ in different bodies, makes them better or worse +conductors, worse or better insulators; and both _induction_ and +_conduction_ appear to be the same in their principle and action (1320.), +except that in the latter an effect common to both is raised to the highest +degree, whereas in the former it occurs in the best cases, in only an +almost insensible quantity. + +1327. That in our attempts to penetrate into the nature of electrical +action, and to deduce laws more general than those we are at present +acquainted with, we should endeavour to bring apparently opposite effects +to stand side by side in harmonious arrangement, is an opinion of long +standing, and sanctioned by the ablest philosophers. I hope, therefore, I +may be excused the attempt to look at the highest cases of conduction as +analogous to, or even the same in kind with, those of induction and +insulation. + +1328. If we consider the slight penetration of sulphur (1241. 1242.) or +shell-lac (1234.) by electricity, or the feebler insulation sustained by +spermaceti (1279. 1240.), as essential consequences and indications of +their _conducting_ power, then may we look on the resistance of metallic +wires to the passage of electricity through them as _insulating_ power. Of +the numerous well-known cases fitted to show this resistance in what are +called the perfect conductors, the experiments of Professor Wheatstone best +serve my present purpose, since they were carried to such an extent as to +show that _time_ entered as an element into the conditions of conduction[A] +even in metals. When discharge was made through a copper wire 2640 feet in +length, and 1/15th of an inch in diameter, so that the luminous sparks at +each end of the wire, and at the middle, could be observed in the same +place, the latter was found to be sensibly behind the two former in time, +they being by the conditions of the experiment simultaneous. Hence a proof +of retardation; and what reason can be given why this retardation should +not be of the same kind as that in spermaceti, or in lac, or sulphur? But +as, in them, retardation is insulation, and insulation is induction, why +should we refuse the same relation to the same exhibitions of force in the +metals? + + [A] Philosophical Transactions, 1834, p. 583. + +1329. We learn from the experiment, that if _time_ be allowed the +retardation is gradually overcome; and the same thing obtains for the +spermaceti, the lac, and glass (1248.); give but time in proportion to the +retardation, and the latter is at last vanquished. But if that be the case, +and all the results are alike in kind, the only difference being in the +length of time, why should we refuse to metals the previous inductive +action, which is admitted to occur in the other bodies? The diminution of +_time_ is no negation of the action; nor is the lower degree of tension +requisite to cause the forces to traverse the metal, as compared to that +necessary in the cases of water, spermaceti, or lac. These differences +would only point to the conclusion, that in metals the particles under +induction can transfer their forces when at a lower degree of tension or +polarity, and with greater facility than in the instances of the other +bodies. + +1330. Let us look at Mr. Wheatstone's beautiful experiment in another point +of view, If, leaving the arrangement at the middle and two ends of the long +copper wire unaltered, we remove the two intervening portions and replace +them by wires of iron or platina, we shall have a much greater retardation +of the middle spark than before. If, removing the iron, we were to +substitute for it only five or six feet of water in a cylinder of the same +diameter as the metal, we should have still greater retardation. If from +water we passed to spermaceti, either directly or by gradual steps through +other bodies, (even though we might vastly enlarge the bulk, for the +purpose of evading the occurrence of a spark elsewhere (1331.) than at the +three proper intervals,) we should have still greater retardation, until at +last we might arrive, by degrees so small as to be inseparable from each +other, at actual and permanent insulation. What, then, is to separate the +principle of these two extremes, perfect conduction and perfect insulation, +from each other; since the moment we leave in the smallest degree +perfection at either extremity, we involve the element of perfection at the +opposite end? Especially too, as we have not in nature the case of +perfection either at one extremity or the other, either of insulation or +conduction. + +1331. Again, to return to this beautiful experiment in the various forms +which may be given to it: the forces are not all in the wire (after they +have left the Leyden jar) during the whole time (1328.) occupied by the +discharge; they are disposed in part through the surrounding dielectric +under the well-known form of induction; and if that dielectric be air, +induction takes place from the wire through the air to surrounding +conductors, until the ends of the wire are electrically related through its +length, and discharge has occurred, i.e. for the _time_ during which the +middle spark is retarded beyond the others. This is well shown by the old +experiment, in which a long wire is so bent that two parts (Plate VIII. +fig. 115.), _a, b_, near its extremities shall approach within a short +distance, as a quarter of an inch, of each other in the air. If the +discharge of a Leyden jar, charged to a sufficient degree, be sent through +such a wire, by far the largest portion of the electricity will pass as a +spark across the air at the interval, and not by the metal. Does not the +middle part of the wire, therefore, act here as an insulating medium, +though it be of metal? and is not the spark through the air an indication +of the tension (simultaneous with _induction_) of the electricity in the +ends of this single wire? Why should not the wire and the air both be +regarded as dielectrics; and the action at its commencement, and whilst +there is tension, as an inductive action? If it acts through the contorted +lines of the wire, so it also does in curved and contorted lines through +air (1219, 1224, 1231.), and other insulating dielectrics (1228); and we +can apparently go so far in the analogy, whilst limiting the case to the +inductive action only, as to show that amongst insulating dielectrics some +lead away the lines of force from others (1229.), as the wire will do from +worse conductors, though in it the principal effect is no doubt due to the +ready discharge between the particles whilst in a low state of tension. The +retardation is for the time insulation; and it seems to me we may just as +fairly compare the air at the interval _a, b_ (fig. 115.) and the wire in +the circuit, as two bodies of the same kind and acting upon the same +principles, as far as the first inductive phenomena are concerned, +notwithstanding the different forms of discharge which ultimately +follow[A], as we may compare, according to Coulomb's investigations[B] +_different lengths_ of different insulating bodies required to produce the +same amount of insulating effect. + + [A] These will be examined hereafter (1348. &c.). + + [B] Memoires de l'Academie, 1785, p. 612. or Ency. Britann. First + Supp. vol. i. p. 614. + +1332. This comparison is still more striking when we take into +consideration the experiment of Mr. Harris, in which he stretched a fine +wire across a glass globe, the air within being rarefied[A]. On sending a +charge through the joint arrangement of metal and rare air, as much, if not +more, electricity passed by the latter as by the former. In the air, +rarefied as it was, there can be no doubt the discharge was preceded by +induction (1284.); and to my mind all the circumstances indicate that the +same was the case with the metal; that, in fact, both substances are +dielectrics, exhibiting the same effects in consequence of the action of +the same causes, the only variation being one of degree in the different +substances employed. + + [A] Philosophical Transactions, 1834, p, 212. + +1333. Judging on these principles, velocity of discharge through the _same +wire_ may be varied greatly by attending to the circumstances which cause +variations of discharge through spermaceti or sulphur. Thus, for instance, +it must vary with the tension or intensity of the first urging force (1234. +1240.), which tension is charge and induction. So if the two ends of the +wire, in Professor Wheatstone's experiment, were immediately connected with +two large insulated metallic surfaces exposed to the air, so that the +primary act of induction, after making the contact for discharge, might be +in part removed from the internal portion of the wire at the first instant, +and disposed for the moment on its surface jointly with the air and +surrounding conductors, then I venture to anticipate that the middle spark +would be more retarded than before; and if these two plates were the inner +and outer coating of a large jar or a Leyden battery, then the retardation +of that spark would be still greater. + +1334. Cavendish was perhaps the first to show distinctly that discharge was +not always by one channel[A], but, if several are present, by many at once. +We may make these different channels of different bodies, and by +proportioning their thicknesses and lengths, may include such substances as +air, lac, spermaceti, water, protoxide of iron, iron and silver, and by +_one_ discharge make each convey its proportion of the electric force. +Perhaps the air ought to be excepted, as its discharge by conduction is +questionable at present (1336.); but the others may all be limited in their +mode of discharge to pure conduction. Yet several of them suffer previous +induction, precisely like the induction through the air, it being a +necessary preliminary to their discharging action. How can we therefore +separate any one of these bodies from the others, as to the _principles and +mode_ of insulating and conducting, except by mere degree? All seem to me +to be dielectrics acting alike, and under the same common laws. + + [A] _Philosophical Transactions_, 1776, p. 197. + +1335. I might draw another argument in favour of the general sameness, in +nature and action, of good and bad conductors (and all the bodies I refer +to are conductors more or less), from the perfect equipoise in action of +very different bodies when opposed to each other in magneto-electric +inductive action, as formerly described (213.), but am anxious to be as +brief as is consistent with the clear examination of the probable truth of +my views. + +1336. With regard to the possession by the gases of any conducting power +of the simple kind now under consideration, the question is a very +difficult one to determine at present. Experiments seem to indicate that +they do insulate certain low degrees of tension perfectly, and that the +effects which may have appeared to be occasioned by _conduction_ have been +the result of the carrying power of the charged particles, either of the +air or of dust, in it. It is equally certain, however, that with higher +degrees of tension or charge the particles discharge to one another, and +that is conduction. If the gases possess the power of insulating a certain +low degree of tension continuously and perfectly, such a result may be due +to their peculiar physical state, and the condition of separation under +which their particles are placed. But in that, or in any case, we must not +forget the fine experiments of Cagniard de la Tour[A], in which he has +shown that liquids and their vapours can be made to pass gradually into +each other, to the entire removal of any marked distinction of the two +states. Thus, hot dry steam and cold water pass by insensible gradations +into each other; yet the one is amongst the gases as an insulator, and the +other a comparatively good conductor. As to conducting power, therefore, +the transition from metals even up to gases is gradual; substances make but +one series in this respect, and the various cases must come under one +condition and law (444.). The specific differences of bodies as to +conducting power only serves to strengthen the general argument, that +conduction, like insulation, is a result of induction, and is an action of +contiguous particles. + + [A] Annales de Chimie, xxi. pp. 127, 178, or Quarterly Journal of + Science, xv. 145. + +1337. I might go on now to consider induction and its concomitant, +_conduction_, through mixed dielectrics, as, for instance, when a charged +body, instead of acting across air to a distant uninsulated conductor, acts +jointly through it and an interposed insulated conductor. In such a case, +the air and the conducting body are the mixed dielectrics; and the latter +assumes a polarized condition as a mass, like that which my theory assumes +_each particle_ of the air to possess at the same time (1679). But I fear +to be tedious in the present condition of the subject, and hasten to the +consideration of other matter. + +1338. To sum up, in some degree, what has been said, I look upon the first +effect of an excited body upon neighbouring matters to be the production of +a polarized state of their particles, which constitutes _induction_; and +this arises from its action upon the particles in immediate contact with +it, which again act upon those contiguous to them, and thus the forces are +transferred to a distance. If the induction remain undiminished, then +perfect insulation is the consequence; and the higher the polarized +condition which the particles can acquire or maintain, the higher is the +intensity which may be given to the acting forces. If, on the contrary, the +contiguous particles, upon acquiring the polarized state, have the power to +communicate their forces, then conduction occurs, and the tension is +lowered, conduction being a distinct act of discharge between neighbouring +particles. The lower the state of tension at which this discharge between +the particles of a body takes place, the better conductor is that body. In +this view, insulators may be said to be bodies whose particles can retain +the polarized state; whilst conductors are those whose particles cannot be +permanently polarized. If I be right in my view of induction, then I +consider the reduction of these two effects (which have been so long held +distinct) to an action of contiguous particles obedient to one common law, +as a very important result; and, on the other hand, the identity of +character which the two acquire when viewed by the theory (1326.), is +additional presumptive proof in favour of the correctness of the latter. + + * * * * * + +1339. That heat has great influence over simple conduction is well known +(445.), its effect being, in some cases, almost an entire change of the +characters of the body (432. 1340.). Harris has, however, shown that it in +no respect affects gaseous bodies, or at least air[A]; and Davy has taught +us that, as a class, metals have their conducting power _diminished_ by +it[B]. + + [A] _Philosophical Transactions_, 1834, p. 230 + + [B] Ibid. 1821, p. 431. + +1340. I formerly described a substance, sulphuret of silver, whose +conducting power was increased by heat (433. 437. 438.); and I have since +then met with another as strongly affected in the same way: this is +fluoride of lead. When a piece of that substance, which had been fused and +cooled, was introduced into the circuit of a voltaic battery, it stopped +the current. Being heated, it acquired conducting powers before it was +visibly red-hot in daylight; and even sparks could be taken against it +whilst still solid. The current alone then raised its temperature (as in +the case of sulphuret of silver) until it fused, after which it seemed to +conduct as well as the metallic vessel containing it; for whether the wire +used to complete the circuit touched the fused fluoride only, or was in +contact with the platina on which it was supported, no sensible difference +in the force of the current was observed. During all the time there was +scarcely a trace of decomposing action of the fluoride, and what did occur, +seemed referable to the air and moisture of the atmosphere, and not to +electrolytic action. + +1341. I have now very little doubt that periodide of mercury (414. 448. +691.) is a case of the same kind, and also corrosive sublimate (692.). I am +also inclined to think, since making the above experiments, that the +anomalous action of the protoxide of antimony, formerly observed and +described (693. 801.), may be referred in part to the same cause. + +1342. I have no intention at present of going into the particular relation +of heat and electricity, but we may hope hereafter to discover by +experiment the law which probably holds together all the above effects with +those of the _evolution_ and the _disappearance_ of heat by the current, +and the striking and beautiful results of thermo-electricity, in one common +bond. + + +P viii. _Electrolytic discharge._ + +1343. I have already expressed in a former paper (1164.), the view by which +I hope to associate ordinary induction and electrolyzation. Under that +view, the discharge of electric forces by electrolyzation is rather an +effect superadded, in a certain class of bodies, to those already described +as constituting induction and insulation, than one independent of and +distinct from these phenomena. + +1344. Electrolytes, as respects their insulating and conducting forces, +belong to the general category of bodies (1320. 1334.); and if they are in +the solid state (as nearly all can assume that state), they retain their +place, presenting then no new phenomenon (426. &c.); or if one occur, being +in so small a proportion as to be almost unimportant. When liquefied, they +also belong to the same list whilst the electric intensity is below a +certain degree; but at a given intensity (910. 912. 1007.), fixed for each, +and very low in all known cases, they play a new part, causing discharge in +proportion (783.) to the development of certain chemical effects of +combination and decomposition; and at this point, move out from the general +class of insulators and conductors, to form a distinct one by themselves. +The former phenomena have been considered (1320. 1338.); it is the latter +which have now to be revised, and used as a test of the proposed theory of +induction. + +1345. The theory assumes, that the particles of the dielectric (now an +electrolyte) are in the first instance brought, by ordinary inductive +action, into a polarized state, and raised to a certain degree of tension +or intensity before discharge commences; the inductive state being, in +fact, a _necessary preliminary_ to discharge. By taking advantage of those +circumstances which bear upon the point, it is not difficult to increase +the tension indicative of this state of induction, and so make the state +itself more evident. Thus, if distilled water be employed, and a long +narrow portion of it placed between the electrodes of a powerful voltaic +battery, we have at once indications of the intensity which can be +sustained at these electrodes by the inductive action through the water as +a dielectric, for sparks may be obtained, gold leaves diverged, and Leyden +bottles charged at their wires. The water is in the condition of the +spermaceti (1322. 1323.) a bad conductor and a bad insulator; but what it +does insulate is by virtue of inductive action, and that induction is the +preparation for and precursor of discharge (1338.). + +1346. The induction and tension which appear at the limits of the portion +of water in the direction of the current, are only the sums of the +induction and tension of the contiguous particles between those limits; and +the limitation of the inductive tension, to a certain degree shows (time +entering in each case as an important element of the result), that when the +particles have acquired a certain relative state, _discharge_, or a +transfer of forces equivalent to ordinary conduction, takes place. + +1347. In the inductive condition assumed by water before discharge comes +on, the particles polarized are the particles of the _water_ that being the +dielectric used[A]; but the discharge between particle and particle is not, +as before, a mere interchange of their powers or forces at the polar parts, +but an actual separation of them into their two elementary particles, the +oxygen travelling in one direction, and carrying with it its amount of the +force it had acquired during the polarization, and the hydrogen doing the +same thing in the other direction, until they each meet the next +approaching particle, which is in the same electrical state with that they +have left, and by association of their forces with it, produce what +constitutes discharge. This part of the action may be regarded as a +carrying one (1319. 1572. 1622.), performed by the constituent particles of +the dielectric. The latter is always a compound body (664. 823.); and by +those who have considered the subject and are acquainted with the +philosophical view of transfer which was first put forth by Grotthuss[B], +its particles may easily be compared to a series of metallic conductors +under inductive action, which, whilst in that state, are divisible into +these elementary moveable halves. + + [A] See 1699-1708.--_Dec. 1838_ + + [B] Annales de Chimie, lviii. 60. and lxiii, 20. + +1348. Electrolytic discharge depends, of necessity, upon the non-conduction +of the dielectric as a whole, and there are two steps or acts in the +process: first a polarization of the molecules of the substance and then a +lowering of the forces by the separation, advance in opposite directions, +and recombination of the elements of the molecules, these being, as it +were, the halves of the originally polarized conductors or particles. + +1349. These views of the decomposition of electrolytes and the consequent +effect of discharge, which, as to the particular case, are the same with +those of Grotthuss (481.) and Davy (482.), though they differ from those of +Biot (487.), De la Rive (490.), and others, seem to me to be fully in +accordance not merely with the theory I have given of induction generally +(1165.), but with all the known _facts_ of common induction, conduction, +and electrolytic discharge; and in that respect help to confirm in my mind +the truth of the theory set forth. The new mode of discharge which +electrolyzation presents must surely be an evidence of the _action of +contiguous particles_; and as this appears to depend directly upon a +previous inductive state, which is the same with common induction, it +greatly strengthens the argument which refers induction in all cases to an +action of contiguous particles also (1295, &c.). + +1350. As an illustration of the condition of the polarized particles in a +dielectric under induction, I may describe an experiment. Put into a glass +vessel some clear rectified oil of turpentine, and introduce two wires +passing through glass tubes where they coincide with the surface of the +fluid, and terminating either in balls or points. Cut some very clean dry +white silk into small particles, and put these also into the liquid: then +electrify one of the wires by an ordinary machine and discharge by the +other. The silk will immediately gather from all parts of the liquid, and +form a band of particles reaching from wire to wire, and if touched by a +glass rod will show considerable tenacity; yet the moment the supply of +electricity ceases, the band will fall away and disappear by the dispersion +of its parts. The _conduction_ by the silk is in this case very small; and +after the best examination I could give to the effects, the impression on +my mind is, that the adhesion of the whole is due to the polarity which +each filament acquires, exactly as the particles of iron between the poles +of a horse-shoe magnet are held together in one mass by a similar +disposition of forces. The particles of silk therefore represent to me the +condition of the molecules of the dielectric itself, which I assume to be +polar, just as that of the silk is. In all cases of conductive discharge +the contiguous polarized particles of the body are able to effect a +neutralization of their forces with greater or less facility, as the silk +does also in a very slight degree. Further we are not able to carry the +parallel, except in imagination; but if we could divide each particle of +silk into two halves, and let each half travel until it met and united with +the next half in an opposite state, it would then exert its carrying power +(1347.), and so far represent electrolytic discharge. + +1351. Admitting that electrolytic discharge is a consequence of previous +induction, then how evidently do its numerous cases point to induction in +curved lines (521. 1216.), and to the divergence or lateral action of the +lines of inductive force (1231.), and so strengthen that part of the +general argument in the former paper! If two balls of platina, forming the +electrodes of a voltaic battery, are put into a large vessel of dilute +sulphuric acid, the whole of the surfaces are covered with the respective +gases in beautifully regulated proportions, and the mind has no difficulty +in conceiving the direction of the curved lines of discharge, and even the +intensity of force of the different lines, by the quantity of gas evolved +upon the different parts of the surface. From this condition of the lines +of inductive force arise the general effects of diffusion; the appearance +of the anions or cathions round the edges and on the further side of the +electrodes when in the form of plates; and the manner in which the current +or discharge will follow all the forms of the electrolyte, however +contorted. Hence, also, the effects which Nobili has so well examined and +described[A] in his papers on the distribution of currents in conducting +masses. All these effects indicate the curved direction of the currents or +discharges which occur in and through the dielectrics, and these are in +every case _preceded_ by equivalent inductive actions of the contiguous +particles. + + [A] Bibliotheque Universelle, 1835, lix. 263. 416. + +1352. Hence also the advantage, when the exciting forces are weak or +require assistance, of enlarging the mass of the electrolyte; of increasing +the size of the electrodes; of making the coppers surround the zincs:--all +is in harmony with the view of induction which I am endeavouring to +examine; I do not perceive as yet one fact against it. + +1353. There are many points of _electrolytic discharge_ which ultimately +will require to be very closely considered, though I can but slightly touch +upon them. It is not that, as far as I have investigated them, they present +any contradiction to the view taken (for I have carefully, though +unsuccessfully, sought for such cases), but simply want of time as yet to +pursue the inquiry, which prevents me from entering upon them here. + +1354. One point is, that different electrolytes or dielectrics require +different initial intensities for their decomposition (912.). This may +depend upon the degree of polarization which the particles require before +electrolytic discharge commences. It is in direct relation to the chemical +affinity of the substances concerned; and will probably be found to have a +relation or analogy to the specific inductive capacity of different bodies +(1252. 1296.). It thus promises to assist in causing the great truths of +those extensive sciences, which are occupied in considering the forces of +the particles of matter, to fall into much closer order and arrangement +than they have heretofore presented. + +1355. Another point is the facilitation of electrolytic conducting power or +discharge by the addition of substances to the dielectric employed. This +effect is strikingly shown where water is the body whose qualities are +improved, but, as yet, no general law governing all the phenomena has been +detected. Thus some acids, as the sulphuric, phosphoric, oxalic, and +nitric, increase the power of water enormously; whilst others, as the +tartaric and citric acids, give but little power; and others, again, as the +acetic and boracic acids, do not produce a change sensible to the +voltameter (739.). Ammonia produces no effect, but its carbonate does. The +caustic alkalies and their carbonates produce a fair effect. Sulphate of +soda, nitre (753.), and many soluble salts produce much effect. Percyanide +of mercury and corrosive sublimate produce no effect; nor does iodine, gum, +or sugar, the test being a voltameter. In many cases the added substance is +acted on either directly or indirectly, and then the phenomena are more +complicated; such substances are muriatic acid (758.), the soluble +protochlorides (766.), and iodides (769.), nitric acid (752.), &c. In other +cases the substance added is not, when alone, subject to or a conductor of +the powers of the voltaic battery, and yet both gives and receives power +when associated with water. M. de la Rive has pointed this result out in +sulphurous acid[A], iodine and bromine[B]; the chloride of arsenic produces +the same effect. A far more striking case, however, is presented by that +very influential body sulphuric acid (681.): and probably phosphoric acid +also is in the same peculiar relation. + + [A] Quarterly Journal, xxvii. 407. or Bibliotheque Universelle, xl. + 205. Kemp says sulphurous acid is a very good conductor, Quarterly + Journal, 1831, p. 613. + + [B] Quarterly Journal, xxiv, 465. or Annales de Chimie, xxxv. 161. + +1356. It would seem in the cases of those bodies which suffer no change +themselves, as sulphuric acid (and perhaps in all), that they affect water +in its conducting power only as an electrolyte; for whether little or much +improved, the decomposition is proportionate to the quantity of electricity +passing (727. 730.), and the transfer is therefore due to electrolytic +discharge. This is in accordance with the fact already stated as regards +water (984.), that the conducting power is not improved for electricity of +force below the electrolytic intensity of the substance acting as the +dielectric; but both facts (and some others) are against the opinion which +I formerly gave, that the power of salts, &c. might depend upon their +assumption of the liquid state by solution in the water employed (410.). It +occurs to me that the effect may perhaps be related to, and have its +explanation in differences of specific inductive capacities. + +1357. I have described in the last paper, cases, where shell-lac was +rendered a conductor by absorption of ammonia (1294.). The same effect +happens with muriatic acid; yet both these substances, when gaseous, are +non-conductors; and the ammonia, also when in strong solution (718.). Mr. +Harris has mentioned instances[A] in which the conducting power of metals +is seriously altered by a very little alloy. These may have no relation to +the former cases, but nevertheless should not be overlooked in the general +investigation which the whole question requires. + + [A] Philosophical Transactions, 1827, p. 22. + +1358. Nothing is perhaps more striking in that class of dielectrics which +we call electrolytes, than the extraordinary and almost complete suspension +of their peculiar mode of effecting discharge when they are rendered +_solid_ (380, &c.), even though the intensity of the induction acting +through them may be increased a hundredfold or more (419.). It not only +establishes a very general relation between the physical properties of +these bodies and electricity acting by induction through them, but draws +both their physical and chemical relations so near together, as to make us +hope we shall shortly arrive at the full comprehension of the influence +they mutually possess over each other. + + +P ix. _Disruptive discharge and insulation._ + +1359. The next form of discharge has been distinguished by the adjective +_disruptive_ (1319.), as it in every case displaces more or less the +particles amongst and across which it suddenly breaks. I include under it, +discharge in the form of sparks, brushes, and glow (1405.), but exclude the +cases of currents of air, fluids, &c., which, though frequently +accompanying the former, are essentially distinct in their nature. + +1360. The conditions requisite for the production of an electric spark in +its simplest form are well-known. An insulating dielectric must be +interposed between two conducting surfaces in opposite states of +electricity, and then if the actions be continually increased in strength, +or otherwise favoured, either by exalting the electric state of the two +conductors, or bringing them nearer to each other, or diminishing the +density of the dielectric, a _spark_ at last appears, and the two forces +are for the time annihilated, for _discharge_ has occurred. + +1361. The conductors (which may be considered as the termini of the +inductive action) are in ordinary cases most generally metals, whilst the +dielectrics usually employed are common air and glass. In my view of +induction, however, every dielectric becomes of importance, for as the +results are considered essentially dependent on these bodies, it was to be +expected that differences of action never before suspected would be evident +upon close examination, and so at once give fresh confirmation of the +theory, and open new doors of discovery into the extensive and varied +fields of our science. This hope was especially entertained with respect to +the gases, because of their high degree of insulation, their uniformity in +physical condition, and great difference in chemical properties. + +1362. All the effects prior to the discharge are inductive; and the degree +of tension which it is necessary to attain before the spark passes is +therefore, in the examination I am now making of the new view of induction, +a very important point. It is the limit of the influence which the +dielectric exerts in resisting discharge; it is a measure, consequently, of +the conservative power of the dielectric, which in its turn may be +considered as becoming a measure, and therefore a representative of the +intensity of the electric forces in activity. + +1363. Many philosophers have examined the circumstances of this limiting +action in air, but, as far as I know, none have come near Mr. Harris as to +the accuracy with, and the extent to, which he has carried on his +investigations[A]. Some of his results I must very briefly notice, +premising that they are all obtained with the use of air as the +_dielectric_ between the conducting surfaces. + + [A] Philosophical Transactions, 1834, p. 225. + +1364. First as to the _distance_ between the two balls used, or in other +words, the _thickness_ of the dielectric across which the induction was +sustained. The quantity of electricity, measured by a unit jar, or +otherwise on the same principle with the unit jar, in the charged or +inductive ball, necessary to produce spark discharge, was found to vary +exactly with the distance between the balls, or between the discharging +points, and that under very varied and exact forms of experiment[A]. + + [A] Philosophical Transactions, 1834, p. 225. + +1365. Then with respect to variation in the _pressure_ or _density_ of the +air. The quantities of electricity required to produce discharge across a +_constant_ interval varied exactly with variations of the density; the +quantity of electricity and density of the air being in the same simple +ratio. Or, if the quantity was retained the same, whilst the interval and +density of the air were varied, then these were found in the inverse simple +ratio of each other, the same quantity passing across twice the distance +with air rarefied to one-half[A]. + + [A] Philosophical Transactions, 1834, p.229. + +1366. It must be remembered that these effects take place without any +variation of the _inductive_ force by condensation or rarefaction of the +air. That force remains the same in air[A], and in all gases (1284. 1292.), +whatever their rarefaction may be. + + [A] Philosophical Transactions, 1834, p. 237, 244. + +1367. Variation of the _temperature_ of the air produced no variation of +the quantity of electricity required to cause discharge across a given +interval[A]. + + [A] Philosophical Transactions, 1834, p. 230 + +Such are the general results, which I have occasion for at present, +obtained by Mr. Harris, and they appear to me to be unexceptionable. + +1368. In the theory of induction founded upon a molecular action of the +dielectric, we have to look to the state of that body principally for the +cause and determination of the above effects. Whilst the induction +continues, it is assumed that the particles of the dielectric are in a +certain polarized state, the tension of this state rising higher in each +particle as the induction is raised to a higher degree, either by +approximation of the inducing surfaces, variation of form, increase of the +original force, or other means; until at last, the tension of the particles +having reached the utmost degree which they can sustain without subversion +of the whole arrangement, discharge immediately after takes place. + +1369. The theory does not assume, however, that _all_ the particles of the +dielectric subject to the inductive action are affected to the same amount, +or acquire the same tension. What has been called the lateral action of the +lines of inductive force (1231. 1297.), and the diverging and occasionally +curved form of these lines, is against such a notion. The idea is, that any +section taken through the dielectric across the lines of inductive force, +and including _all of them,_ would be equal, in the sum of the forces, to +the sum of the forces in any other section; and that, therefore, the whole +amount of tension for each such section would be the same. + +1370. Discharge probably occurs, not when all the particles have attained +to a certain degree of tension, but when that particle which is most +affected has been exalted to the subverting or turning point (1410.). For +though _all_ the particles in the line of induction resist charge, and are +associated in their actions so as to give a sum of resisting force, yet +when any one is brought up to the overturning point, _all_ must give way in +the case of a spark between ball and ball. The breaking down of that one +must of necessity cause the whole barrier to be overturned, for it was at +its utmost degree of resistance when it possessed the aiding power of that +one particle, in addition to the power of the rest, and the power of that +one is now lost. Hence _tension_ or _intensity_[A] may, according to the +theory, be considered as represented by the particular condition of the +particles, or the amount in them of forced variation from their normal +state (1298. 1368.). + + [A] See Harris on proposed particular meaning of these terms, + Philosophical Transactions, 1834, p. 222. + +1371. The whole effect produced by a charged conductor on a distant +conductor, insulated or not, is by my theory assumed to be due to an action +propagated from particle to particle of the intervening and insulating +dielectric, all the particles being considered as thrown for the time into +a forced condition, from which they endeavour to return to their normal or +natural state. The theory, therefore, seems to supply an easy explanation +of the influence of _distance_ in affecting induction (1303. 1364.). As the +distance is diminished induction increases; for there are then fewer +particles in the line of inductive force to oppose their united resistance +to the assumption of the forced or polarized state, and _vice versa._ +Again, as the distance diminishes, discharge across happens with a lower +charge of electricity; for if, as in Harris's experiments (1364), the +interval be diminished to one-half, then half the electricity required to +discharge across the first interval is sufficient to strike across the +second; and it is evident, also, that at that time there are only half the +number of interposed molecules uniting their forces to resist the +discharge. + +1372. The effect of enlarging the conducting surfaces which are opposed to +each other in the act of induction, is, if the electricity be limited in +its supply, to lower the intensity of action; and this follows as a very +natural consequence from the increased area of the dielectric across which +the induction is effected. For by diffusing the inductive action, which at +first was exerted through one square inch of sectional area of the +dielectric, over two or three square inches of such area, twice or three +times the number of molecules of the dielectric are brought into the +polarized condition, and employed in sustaining the inductive action, and +consequently the tension belonging to the smaller number on which the +limited force was originally accumulated, must fall in a proportionate +degree. + +1373. For the same reason diminishing these opposing surfaces must increase +the intensity, and the effect will increase until the surfaces become +points. But in this case, the tension of the particles of the dielectric +next the points is higher than that of particles midway, because of the +lateral action and consequent bulging, as it were, of the lines of +inductive force at the middle distance (1369.). + +1374. The more exalted effects of induction on a point _p_, or any small +surface, as the rounded end of a rod, when it is opposed to a large +surface, as that of a ball or plate, rather than to another point or end, +the distance being in both cases the same, fall into harmonious relation +with my theory (1302.). For in the latter case, the small surface _p_ is +affected only by those particles which are brought into the inductive +condition by the equally small surface of the opposed conductor, whereas +when that is a ball or plate the lines of inductive force from the latter +are concentrated, as it were, upon the end _p_. Now though the molecules of +the dielectric against the large surface may have a much lower state of +tension than those against the corresponding smaller surface, yet they are +also far more numerous, and, as the lines of inductive force converge +towards a point, are able to communicate to the particles contained in any +cross section (1369.) nearer the small surface an amount of tension equal +to their own, and consequently much higher for each individual particle; so +that, at the surface of the smaller conductor, the tension of a particle +rises much, and if that conductor were to terminate in a point, the tension +would rise to an infinite degree, except that it is limited, as before +(1368.), by discharge. The nature of the discharge from small surfaces and +points under induction will be resumed hereafter (1425. &c.) + +1375. _Rarefaction_ of the air does not alter the _intensity_ of inductive +action (1284. 1287.); nor is there any reason, as far as I can perceive, +why it should. If the quantity of electricity and the distance remain the +same, and the air be rarefied one-half, then, though one-half of the +particles of the dielectric are removed, the other half assume a double +degree of tension in their polarity, and therefore the inductive forces are +balanced, and the result remains unaltered as long as the induction and +insulation are sustained. But the case of _discharge_ is very different; +for as there are only half the number of dielectric particles in the +rarefied atmosphere, so these are brought up to the discharging intensity +by half the former quantity of electricity; discharge, therefore, ensues, +and such a consequence of the theory is in perfect accordance with Mr. +Harris's results (1365.). + +1376. The _increase_ of electricity required to cause discharge over the +same distance, when the pressure of the air or its density is increased, +flows in a similar manner, and on the same principle (1375.), from the +molecular theory. + +1377. Here I think my view of induction has a decided advantage over +others, especially over that which refers the retention of electricity on +the surface of conductors in air to the _pressure of the atmosphere_ +(1305.). The latter is the view which, being adopted by Poisson and +Biot[A], is also, I believe, that generally received; and it associates two +such dissimilar things, as the ponderous air and the subtile and even +hypothetical fluid or fluids of electricity, by gross mechanical relations; +by the bonds of mere static pressure. My theory, on the contrary, sets out +at once by connecting the electric forces with the particles of matter; it +derives all its proofs, and even its origin in the first instance, from +experiment; and then, without any further assumption, seems to offer at +once a full explanation of these and many other singular, peculiar, and, I +think, heretofore unconnected effects. + + [A] Encyclopaedia Britannica, Supplement, vol. iv. Article Electricity, + pp. 76, 81. &c. + +1378. An important assisting experimental argument may here be adduced, +derived from the difference of specific inductive capacity of different +dielectrics (1269. 1274. 1278.). Consider an insulated sphere electrified +positively and placed in the centre of another and larger sphere +uninsulated, a uniform dielectric, as air, intervening. The case is really +that of my apparatus (1187.), and also, in effect, that of any ball +electrified in a room and removed to some distance from irregularly-formed +conductors. Whilst things remain in this state the electricity is +distributed (so to speak) uniformly over the surface of the electrified +sphere. But introduce such a dielectric as sulphur or lac, into the space +between the two conductors on one side only, or opposite one part of the +inner sphere, and immediately the electricity on the latter is diffused +unequally (1229. 1270. 1309.), although the form of the conducting +surfaces, their distances, and the _pressure_ of the atmosphere remain +perfectly unchanged. + +1379. Fusinieri took a different view from that of Poisson, Biot, and +others, of the reason why rarefaction of air caused easy diffusion of +electricity. He considered the effect as due to the removal of the +_obstacle_ which the air presented to the expansion of the substances from +which the electricity passed[A]. But platina balls show the phenomena _in +vacuo_ as well as volatile metals and other substances; besides which, when +the rarefaction is very considerable, the electricity passes with scarcely +any resistance, and the production of no sensible heat; so that I think +Fusinieri's view of the matter is likely to gain but few assents. + + [A] Bib. Univ. 1831, xlviii. 375. + +1380. I have no need to remark upon the discharging or collecting power of +flame or hot air. I believe, with Harris, that the mere heat does nothing +(1367.), the rarefaction only being influential. The effect of rarefaction +has been already considered generally (1375.); and that caused by the heat +of a burning light, with the pointed form of the wick, and the carrying +power of the carbonaceous particles which for the time are associated with +it, are fully sufficient to account for all the effects. + +1381. We have now arrived at the important question, how will the inductive +tension requisite for insulation and disruptive discharge be sustained in +gases, which, having the same physical state and also the _same +pressure_ and the _same temperature_ as _air_, differ from it in specific +gravity, in chemical qualities, and it may be in peculiar relations, which +not being as yet recognized, are purely electrical (1361.)? + +1382. Into this question I can enter now only as far as is essential for +the present argument, namely, that insulation and inductive tension do not +depend merely upon the charged conductors employed, but also, and +essentially, upon the interposed dielectric, in consequence of the +molecular action of its particles (1292.). + +1383. A glass vessel _a_ (fig. 127.)[A] was ground at the top and bottom so +as to be closed by two ground brass plates, _b_ and _c_; _b_ carried a +stuffing-box, with a sliding rod _d_ terminated by a brass ball _s_ below, +and a ring above. The lower plate was connected with a foot, stop-cock, and +socket, _e_, _f_ and _g_; and also with a brass ball _l_, which by means of +a stem attached to it and entering the socket _g_, could be fixed at +various heights. The metallic parts of this apparatus were not varnished, +but the glass was well-covered with a coat of shell-lac previously +dissolved in alcohol. On exhausting the vessel at the air-pump it could be +filled with any other gas than air, and, in such cases, the gas so passed +in was dried whilst entering by fused chloride of calcium. + + [A] The drawing is to a scale of 1/6. + +1384. The other part of the apparatus consisted of two insulating pillars, +_h_ and _i_, to which were fixed two brass balls, and through these passed +two sliding rods, _k_ and _m_, terminated at each end by brass balls; _n_ +is the end of an insulated conductor, which could be rendered either +positive or negative from an electrical machine; _o_ and _p_ are wires +connecting it with the two parts previously described, and _q_ is a wire +which, connecting the two opposite sides of the collateral arrangements, +also communicates with a good discharging train _r_ (292.). + +1385. It is evident that the discharge from the machine electricity may +pass either between _s_ and _l_, or S and L. The regulation adopted in the +first experiments was to keep _s_ and _l_ with their distance _unchanged_, +but to introduce first one gas and then another into the vessel _a_, and +then balance the discharge at the one place against that at the other; for +by making the interval at _a_ sufficiently small, all the discharge would +pass there, or making it sufficiently large it would all occur at the +interval _v_ in the receiver. On principle it seemed evident, that in this +way the varying interval _u_ might be taken as a measure, or rather +indication of the resistance to discharge through the gas at the constant +interval _v_. The following are the constant dimensions. + + Ball _s_ 0.93 of an inch. + Ball S 0.96 of an inch. + Ball _l_ 2.02 of an inch. + Ball L 0.62 of an inch. + Interval _v_ 0.62 of an inch. + +1386. On proceeding to experiment it was found that when air or any gas was +in the receiver _a_, the interval _u_ was not a fixed one; it might be +altered through a certain range of distance, and yet sparks pass either +there or at _v_ in the receiver. The extremes were therefore noted, i.e. +the greatest distance short of that at which the discharge _always_ took +place at _v_ in the gas, and the least distance short of that at which it +_always_ took place at _u_ in the air. Thus, with air in the receiver, the +extremes at _u_ were 0.56 and 0.79 of an inch, the range of 0.23 between +these distances including intervals at which sparks passed occasionally +either at one place or the other. + +1387. The small balls _s_ and S could be rendered either positive or +negative from the machine, and as gases were expected and were found to +differ from each other in relation to this change (1399.), the results +obtained under these differences of charge were also noted. + +1388. The following is a Table of results; the gas named is that in the +vessel _a_. The smallest, greatest, and mean interval at _u_ in air is +expressed in parts of an inch, the interval _v_ being constantly 0.62 of an +inch. + + Smallest. Greatest. Mean. + _ +| Air, _s_ and S, pos. 0.60 0.79 0.695 +|_Air, _s_ and S, neg. 0.59 0.68 0.635 + _ +| Oxygen, _s_ and S, pos. 0.41 0.60 0.505 +|_Oxygen, _s_ and S, neg. 0.50 0.52 0.510 + _ +| Nitrogen, _s_ and S, pos. 0.55 0.68 0.615 +|_Nitrogen, _s_ and S, neg. 0.59 0.70 0.645 + _ +| Hydrogen, _s_ and S, pos. 0.30 0.44 0.370 +|_Hydrogen, _s_ and S, neg. 0.25 0.30 0.275 + _ +| Carbonic acid, _s_ and S, pos. 0.56 0.72 0.640 +|_Carbonic acid, _s_ and S, neg. 0.58 0.60 0.590 + _ +| Olefiant gas, _s_ and S, pos. 0.64 0.86 0.750 +|_Olefiant gas, _s_ and S, neg. 0.69 0.77 0.730 + _ +| Coal gas, _s_ and S, pos. 0.37 0.61 0.490 +|_Coal gas, _s_ and S, neg. 0.47 0.58 0.525 + _ +| Muriatic acid gas, _s_ and S, pos. 0.89 1.32 1.105 +|_Muriatic acid gas, _s_ and S, neg. 0.67 0.75 0.710 + +1389. The above results were all obtained at one time. On other occasions +other experiments were made, which gave generally the same results as to +order, though not as to numbers. Thus: + + Hydrogen, _s_ and S, pos. 0.23 0.57 0.400 + Carbonic acid, _s_ and S, pos. 0.51 1.05 0.780 + Olefiant gas, _s_ and S, pos. 0.66 1.27 0.965 + +I did not notice the difference of the barometer on the days of +experiment[A]. + + [A] Similar experiments in different gases are described at 1507. + 1508.--_Dec. 1838._ + +1390. One would have expected only two distances, one for each interval, +for which the discharge might happen either at one or the other; and that +the least alteration of either would immediately cause one to predominate +constantly over the other. But that under common circumstances is not the +case. With air in the receiver, the variation amounted to 0.2 of an inch +nearly on the smaller interval of 0.6, and with muriatic acid gas, the +variation was above 0.4 on the smaller interval of 0.9. Why is it that when +a fixed interval (the one in the receiver) will pass a spark that cannot go +across 0.6 of air at one time, it will immediately after, and apparently +under exactly similar circumstances, not pass a spark that can go across +0.8 of air? + +1391. It is probable that part of this variation will be traced to +particles of dust in the air drawn into and about the circuit (1568.). I +believe also that part depends upon a variable charged condition of the +surface of the glass vessel _a_. That the whole of the effect is not +traceable to the influence of circumstances in the vessel _a_, may be +deduced from the fact, that when sparks occur between balls in free air +they frequently are not straight, and often pass otherwise than by the +shortest distance. These variations in air itself, and at different parts +of the very same balls, show the presence and influence of circumstances +which are calculated to produce effects of the kind now under +consideration. + +1392. When a spark had passed at either interval, then, generally, more +tended to appear at the _same_ interval, as if a preparation had been made +for the passing of the latter sparks. So also on continuing to work the +machine quickly the sparks generally followed at the same place. This +effect is probably due in part to the warmth of the air heated by the +preceding spark, in part to dust, and I suspect in part, to something +unperceived as yet in the circumstances of discharge. + +1393. A very remarkable difference, which is _constant_ in its direction, +occurs when the electricity communicated to the balls _s_ and S is changed +from positive to negative, or in the contrary direction. It is that the +range of variation is always greater when the small bulls are positive than +when they are negative. This is exhibited in the following Table, drawn +from the former experiments. + + Pos. Neg. +In Air the range was 0.19 0.09 + Oxygen 0.19 0.02 + Nitrogen 0.18 0.11 + Hydrogen 0.14 0.05 + Carbonic acid 0.16 0.02 + Olefiant gas 0.22 0.08 + Coal gas 0.24 0.12 + Muriatic acid 0.43 0.08 + +I have no doubt these numbers require considerable correction, but the +general result is striking, and the differences in several cases very +great. + + * * * * * + +1394. Though, in consequence of the variation of the striking distance +(1386.), the interval in air fails to be a measure, as yet, of the +insulating or resisting power of the gas in the vessel, yet we may for +present purposes take the mean interval as representing in some degree that +power. On examining these mean intervals as they are given in the third +column (1388.), it will be very evident, that gases, when employed as +dielectrics, have peculiar electrical relations to insulation, and +therefore to induction, very distinct from such as might be supposed to +depend upon their mere physical qualities of specific gravity or pressure. + +1395. First, it is clear that at the _same pressure_ they are not alike, +the difference being as great as 37 and 110. When the small balls are +charged positively, and with the same surfaces and the same pressure, +muriatic acid gas has three times the insulating or restraining power +(1362.) of hydrogen gas, and nearly twice that of oxygen, nitrogen, or air. + +1396. Yet it is evident that the difference is not due to specific gravity, +for though hydrogen is the lowest, and therefore lower than oxygen, oxygen +is much beneath nitrogen, or olefiant gas; and carbonic acid gas, though +considerably heavier than olefiant gas or muriatic acid gas, is lower than +either. Oxygen as a heavy, and olefiant as a light gas, are in strong +contrast with each other; and if we may reason of olefiant gas from +Harris's results with air (1365.), then it might be rarefied to two-thirds +its usual density, or to a specific gravity of 9.3 (hydrogen being 1), and +having neither the same density nor pressure as oxygen, would have equal +insulating powers with it, or equal tendency to resist discharge. + +1397. Experiments have already been described (1291. 1292.) which show that +the gases are sensibly alike in their inductive capacity. This result is +not in contradiction with the existence of great differences in their +restraining power. The same point has been observed already in regard to +dense and rare air (1375.). + +1398. Hence arises a new argument proving that it cannot be mere pressure +of the atmosphere which prevents or governs discharge (1377. 1378.), but a +specific electric quality or relation of the gaseous medium. Hence also +additional argument for the theory of molecular inductive action. + +1399. Other specific differences amongst the gases may be drawn from the +preceding series of experiments, rough and hasty as they are. Thus the +positive and negative series of mean intervals do not give the same +differences. It has been already noticed that the negative numbers are +lower than the positive (1393.), but, besides that, the _order_ of the +positive and negative results is not the same. Thus, on comparing the mean +numbers (which represent for the present insulating tension,) it appears +that in air, hydrogen, carbonic acid, olefiant gas and muriatic acid, the +tension rose higher when the smaller ball was made positive than when +rendered negative, whilst in oxygen, nitrogen, and coal gas, the reverse +was the case. Now though the numbers cannot be trusted as exact, and though +air, oxygen, and nitrogen should probably be on the same side, yet some of +the results, as, for instance, those with muriatic acid, fully show a +peculiar relation and difference amongst gases in this respect. This was +further proved by making the interval in air 0.8 of an inch whilst muriatic +acid gas was in the vessel _a_; for on charging the small balls _s_ and S +positively, _all_ the discharge took place through the _air_; but on +charging them negatively, _all_ the discharge took place through the +_muriatic acid gas_. + +1400. So also, when the conductor _n_ was connected _only_ with the +muriatic acid gas apparatus, it was found that the discharge was more +facile when the small ball _s_ was negative than when positive; for in the +latter case, much of the electricity passed off as brush discharge through +the air from the connecting wire _p_ but in the former case, it all seemed +to go through the muriatic acid. + +1401. The consideration, however, of positive and negative discharge across +air and other gases will be resumed in the further part of this, or in the +next paper (1465. 1525.). + +1402. Here for the present I must leave this part of the subject, which had +for its object only to observe how far gases agreed or differed as to their +power of retaining a charge on bodies acting by induction through them. All +the results conspire to show that Induction is an action of contiguous +molecules (1295. &c.); but besides confirming this, the first principle +placed for proof in the present inquiry, they greatly assist in developing +the specific properties of each gaseous dielectric, at the same time +showing that further and extensive experimental investigation is necessary, +and holding out the promise of new discovery as the reward of the labour +required. + + * * * * * + +1403. When we pass from the consideration of dielectrics like the gases to +that of bodies having the liquid and solid condition, then our reasonings +in the present state of the subject assume much more of the character of +mere supposition. Still I do not perceive anything adverse to the theory, +in the phenomena which such bodies present. If we take three insulating +dielectrics, as air, oil of turpentine, and shell-lac, and use the same +balls or conductors at the same intervals in these three substances, +increasing the intensity of the induction until discharge take place, we +shall find that it must be raised much higher in the fluid than for the +gas, and higher still in the solid than for the fluid. Nor is this +inconsistent with the theory; for with the liquid, though its molecules are +free to move almost as easily as those of the gas, there are many more +particles introduced into the given interval; and such is also the case +when the solid body is employed. Besides that with the solid, the cohesive +force of the body used will produce some effect; for though the production +of the polarized states in the particle of a solid may not be obstructed, +but, on the contrary, may in some cases be even favoured (1164. 1344.) by +its solidity or other circumstances, yet solidity may well exert an +influence on the point of final subversion, (just as it prevents discharge +in an electrolyte,) and so enable inductive intensity to rise to a much +higher degree. + +1404. In the cases of solids and liquids too, bodies may, and most probably +do, possess specific differences as to their ability of assuming the +polarized state, and also as to the extent to which that polarity must rise +before discharge occurs. An analogous difference exists in the specific +inductive capacities already pointed out in a few substances (1278.) in the +last paper. Such a difference might even account for the various degrees of +insulating and conducting power possessed by different bodies, and, if it +should be found to exist, would add further strength to the argument in +favour of the molecular theory of inductive action. + + * * * * * + +1405. Having considered these various cases of sustained insulation in +non-conducting dielectrics up to the highest point which they can attain, +we find that they terminate at last in _disruptive discharge_; the peculiar +condition of the molecules of the dielectric which was necessary to the +continuous induction, being equally essential to the occurrence of that +effect which closes all the phenomena. This discharge is not only in its +appearance and condition different to the former modes by which the +lowering of the powers was effected (1320. 1343.), but, whilst really the +same in principle, varies much from itself in certain characters, and thus +presents us with the forms of _spark_, _brush_, and _glow_ (1359.). I will +first consider _the spark_, limiting it for the present to the case of +discharge between two oppositely electrified conducting surfaces. + +_The electric spark or flash._ + +1406. The _spark_ is consequent upon a discharge or lowering of the +polarized inductive state of many dielectric particles, by a particular +action of a few of the particles occupying a very small and limited space; +all the previously polarized particles returning to their first or normal +condition in the inverse order in which they left it, and uniting their +powers meanwhile to produce, or rather to continue, (1417.--1436.) the +discharge effect in the place where the subversion of force first occurred. +My impression is, that the few particles situated where discharge occurs +are not merely pushed apart, but assume a peculiar state, a highly exulted +condition for the time, i.e. have thrown upon them all the surrounding +forces in succession, and rising up to a proportionate intensity of +condition, perhaps equal to that of chemically combining atoms, discharge +the powers, possibly in the same manner as they do theirs, by some +operation at present unknown to us; and so the end of the whole. The +ultimate effect is exactly as if a metallic wire had been put into the +place of the discharging particles; and it does not seem impossible that +the principles of action in both cases, may, hereafter, prove to be the +same. + +1407. The _path of the spark_, or of the discharge, depends on the degree +of tension acquired by the particles in the line of discharge, +circumstances, which in every common case are very evident and by the +theory easy to understand, rendering it higher in them than in their +neighbours, and, by exalting them first to the requisite condition, causing +them to determine the course of the discharge. Hence the selection of the +path, and the solution of the wonder which Harris has so well described[A] +as existing under the old theory. All is prepared amongst the molecules +beforehand, by the prior induction, for the path either of the electric +spark or of lightning itself. + + [A] Nautical Magazine, 1834, p 229. + +1408. The same difficulty is expressed as a principle by Nobili for voltaic +electricity, almost in Mr. Harris's words, namely[A], "electricity directs +itself towards the point where it can most easily discharge itself," and +the results of this as a principle he has well wrought out for the case of +voltaic currents. But the _solution_ of the difficulty, or the proximate +cause of the effects, is the same; induction brings the particles up to or +towards a certain degree of tension (1370.); and by those which first +attain it, is the discharge first and most efficiently performed. + + [A] Bibliotheque Universelle, 1835, lix. 275. + +1409. The _moment_ of discharge is probably determined by that molecule of +the dielectric which, from the circumstances, has its tension most quickly +raised up to the maximum intensity. In all cases where the discharge passes +from conductor to conductor this molecule must be on the surface of one of +them; but when it passes between a conductor and a nonconductor, it is, +perhaps, not always so (1453.). When this particle has acquired its maximum +tension, then the whole barrier of resistance is broken down in the line or +lines of inductive action originating at it, and disruptive discharge +occurs (1370.): and such an inference, drawn as it is from the theory, +seems to me in accordance with Mr. Harris's facts and conclusions +respecting the resistance of the atmosphere, namely, that it is not really +greater at any one discharging distance than another[A]. + + [A] Philosophical Transactions, 1834, pp. 227, 229. + +1410. It seems probable, that the tension of a particle of the same +dielectric, as air, which is requisite to produce discharge, is a _constant +quantity_, whatever the shape of the part of the conductor with which it is +in contact, whether ball or point; whatever the thickness or depth of +dielectric throughout which induction is exerted; perhaps, even, whatever +the state, as to rarefaction or condensation of the dielectric; and +whatever the nature of the conductor, good or bad, with which the particle +is for the moment associated. In saying so much, I do not mean to exclude +small differences which may be caused by the reaction of neighbouring +particles on the deciding particle, and indeed, it is evident that the +intensity required in a particle must be related to the condition of those +which are contiguous. But if the expectation should be found to approximate +to truth, what a generality of character it presents! and, in the +definiteness of the power possessed by a particular molecule, may we not +hope to find an immediate relation to the force which, being electrical, is +equally definite and constitutes chemical affinity? + +1411. Theoretically it would seem that, at the moment of discharge by the +spark in one line of inductive force, not merely would all the other lines +throw their forces into this one (1406.), but the lateral effect, +equivalent to a repulsion of these lines (1224. 1297.), would be relieved +and, perhaps, followed by a contrary action, amounting to a collapse or +attraction of these parts. Having long sought for some transverse force in +statical electricity, which should be the equivalent to magnetism or the +transverse force of current electricity, and conceiving that it might be +connected with the transverse action of the lines of inductive force, +already described (1297.), I was desirous, by various experiments, of +bringing out the effect of such a force, and making it tell upon the +phenomena of electro-magnetism and magneto-electricity[A]. + + [A] See further investigations of this subject, 1658-1666. + 1709-1735.--_Dec. 1838._ + +1412. Amongst other results, I expected and sought for the mutual +affection, or even the lateral coalition of two similar sparks, if they +could be obtained simultaneously side by side, and sufficiently near to +each other. For this purpose, two similar Leyden jars were supplied with +rods of copper projecting from their balls in a horizontal direction, the +rods being about 0.2 of an inch thick, and rounded at the ends. The jars +were placed upon a sheet of tinfoil, and so adjusted that their rods, _a_ +and _b_, were near together, in the position represented in plan at fig. +116: _c_ and _d_ were two brass balls connected by a brass rod and +insulated: _e_ was also a brass ball connected, by a wire, with the ground +and with the tinfoil upon which the Leyden jars were placed. By laying an +insulated metal rod across from _a_ to _b_, charging the jars, and removing +the rod, both the jars could be brought up to the same intensity of charge +(1370.). Then, making the ball _e_ approach the ball _d_, at the moment the +spark passed there, two sparks passed between the rods _n_, _o_, and the +ball _c_; and as far as the eye could judge, or the conditions determine, +they were simultaneous. + +1413. Under these circumstances two modes of discharge took place; either +each end had its own particular spark to the ball, or else one end only was +associated by a spark with the ball, but was at the same time related to +the other end by a spark between the two. + +1414. When the ball _c_ was about an inch in diameter, the ends _n_ and +_o_, about half an inch from it, and about 0.4 of an inch from each other, +the two sparks to the ball could be obtained. When for the purpose of +bringing the sparks nearer together, the ends, _n_ and _o_, were brought +closer to each other, then, unless very carefully adjusted, only one end +had a spark with the ball, the other having a spark to it; and the least +variation of position would cause either _n_ or _o_ to be the end which, +giving the direct spark to the ball, was also the one through, or by means +of which, the other discharged its electricity. + +1415. On making the ball _c_ smaller, I found that then it was needful to +make the interval between the ends _n_ and _o_ larger in proportion to the +distance between them and the ball _c_. On making _c_ larger, I found I +could diminish the interval, and so bring the two simultaneous separate +sparks closer together, until, at last, the distance between them was not +more at the widest part than 0.6 of their whole length. + +1416. Numerous sparks were then passed and carefully observed. They were +very rarely straight, but either curved or bent irregularly. In the average +of cases they were, I think, decidedly convex towards each other; perhaps +two-thirds presented more or less of this effect, the rest bulging more or +less outwards. I was never able, however, to obtain sparks which, +separately leaving the ends of the wires _n_ and _o_, conjoined into one +spark before they reached or communicated with the ball _c_. At present, +therefore, though I think I saw a tendency in the sparks to unite, I cannot +assert it as a fact. + +1417. But there is one very interesting effect here, analogous to, and it +may be in part the same with, that I was searching for: I mean the +increased facility of discharge where the spark passes. For instance, in +the cases where one end, as _n_, discharged the electricity of both ends to +the ball _c_, fig. 116, the electricity of the other end _o_, had to pass +through an interval of air 1.5 times as great as that which it might have +taken, by its direct passage between the end and the ball itself. In such +cases, the eye could not distinguish, even by the use of Wheatstone's +means[A], that the spark from the end _n_, which contained both portions of +electricity, was a double spark. It could not have consisted of two sparks +taking separate courses, for such an effect would have been visible to the +eye; but it is just possible, that the spark of the first end _n_ and its +jar, passing at the smallest interval of time before that of the other _o_ +had heated and expanded the air in its course, and made it so much more +favourable to discharge, that the electricity of the end _o_ preferred +leaping across to it and taking a very circuitous route, rather than the +more direct one to the ball. It must, however, be remarked, in answer to +this supposition, that the one spark between _d_ and _e_ would, by its +influence, tend to produce simultaneous discharges at _n_ and _o_, and +certainly did so, when no preponderance was given to one wire over the +other, as to the previous inductive effect (1414.). + + [A] Philosophical Transactions, 1834, pp. 584, 585. + +1418. The fact, however, is, that disruptive discharge is favourable to +itself. It is at the outset a case of tottering equilibrium: and if _time_ +be an element in discharge, in however minute a proportion (1436.), then +the commencement of the act at any point favours its continuance and +increase there, and portions of power will be discharged by a course which +they would not otherwise have taken. + +1419. The mere heating and expansion of the air itself by the first portion +of electricity which passes, must have a great influence in producing this +result. + +1420. As to the result itself, we see its effect in every electric spark; +for it is not the whole quantity which passes that determines the +discharge, but merely that small portion of force which brings the deciding +molecule (1370.) up to its maximum tension; then, when its forces are +subverted and discharge begins, all the rest passes by the same course, +from the influence of the favouring circumstances just referred to; and +whether it be the electricity on a square inch, or a thousand square inches +of charged glass, the discharge is complete. Hereafter we shall find the +influence of this effect in the formation of brushes (1435.); and it is not +impossible that we may trace it producing the jagged spark and the forked +lightning. + + * * * * * + +1421. The characters of the electric spark in _different gases_ vary, and +the variation _may_ be due simply to the effect of the heat evolved at the +moment. But it may also be due to that specific relation of the particles +and the electric forces which I have assumed as the basis of a theory of +induction; the facts do not oppose such a view; and in that view the +variation strengthens the argument for molecular action, as it would seem +to show the influence of the latter in every part of the electrical effect +(1423. 1454.). + +1422. The appearances of the sparks in different gases have often been +observed and recorded[A], but I think it not out of place to notice briefly +the following results; they were obtained with balls of brass, (platina +surfaces would have been better,) and at common pressures. In _air_, the +sparks have that intense light and bluish colour which are so well known, +and often have faint or dark parts in their course, when the quantity of +electricity passing is not great. In _nitrogen_, they are very beautiful, +having the same general appearance as in air, but have decidedly more +colour of a bluish or purple character, and I thought were remarkably +sonorous. In _oxygen_, the sparks were whiter than in air or nitrogen, and +I think not so brilliant. In _hydrogen_, they had a very fine crimson +colour, not due to its rarity, for the character passed away as the +atmosphere was rarefied (1459.)[B]. Very little sound was produced in this +gas; but that is a consequence of its physical condition[C]. In _carbonic +acid gas_, the colour was similar to that of the spark in air, but with a +little green in it: the sparks were remarkably irregular in form, more so +than in common air: they could also, under similar circumstances as to size +of ball, &c., be obtained much longer than in air, the gas showing a +singular readiness to cause the discharge in the form of spark. In +_muriatic acid gas_, the spark was nearly white: it was always bright +throughout, never presenting those dark parts which happen in air, +nitrogen, and some other gases. The gas was dry, and during the whole +experiment the surface of the glass globe within remained quite dry and +bright. In _coal gas_, the spark was sometimes green, sometimes red, and +occasionally one part was green and another red: black parts also occur +very suddenly in the line of the spark, i.e. they are not connected by any +dull part with bright portions, but the two seem to join directly one with +the other. + + [A] See Van Marum's description of the Teylerian machine, vol. i. p. + 112, and vol. ii. p. 196; also Ency. Britan., vol. vi., Article + Electricity, pp. 505, 507. + + [B] Van Marum says they are about four times as large in hydrogen as + in air. vol. i. p. 122. + + [C] Leslie. Cambridge Phil. Transactions, 267. + +1423. These varieties of character impress my mind with a feeling, that +they are due to a direct relation of the electric powers to the particles +of the dielectric through which the discharge occurs, and are not the mere +results of a casual ignition or a secondary kind of action of the +electricity, upon the particles which it finds in its course and thrusts +aside in its passage (1454.). + +1424. The spark may be obtained in media which are far denser than air, as +in oil of turpentine, olive oil, resin, glass, &c.: it may also be obtained +in bodies which being denser likewise approximate to the condition of +conductors, as spermaceti, water, &c. But in these cases, nothing occurs +which, as far as I can perceive, is at all hostile to the general views I +have endeavoured to advocate. + +_The electrical brush._ + +1425. The _brush_ is the next form of disruptive discharge which I shall +consider. There are many ways of obtaining it, or rather of exalting its +characters; and all these ways illustrate the principles upon which it is +produced. If an insulated conductor, connected with the positive conductor +of an electrical machine, have a metal rod 0.3 of an inch in diameter +projecting from it outwards from the machine, and terminating by a rounded +end or a small ball, it will generally give good brushes; or, if the +machine be not in good action, then many ways of assisting the formation of +the brush can be resorted to; thus, the hand or any _large_ conducting +surface may be approached towards the termination to increase inductive +force (1374.): or the termination may be smaller and of badly conducting +matter, as wood: or sparks may be taken between the prime conductor of the +machine and the secondary conductor to which the termination giving brushes +belongs: or, which gives to the brushes exceedingly fine characters and +great magnitude, the air around the termination may be rarefied more or +less, either by heat or the air-pump; the former favourable circumstances +being also continued. + +1426. The brush when obtained by a powerful machine on a ball about 0.7 of +an inch in diameter, at the end of a long brass rod attached to the +positive prime conductor, had the general appearance as to form represented +in fig. 117: a short conical bright part or root appeared at the middle +part of the ball projecting directly from it, which, at a little distance +from the ball, broke out suddenly into a wide brush of pale ramifications +having a quivering motion, and being accompanied at the same time with a +low dull chattering sound. + +1427. At first the brush seems continuous, but Professor Wheatstone has +shown that the whole phenomenon consists of successive intermitting +discharges[A]. If the eye be passed rapidly, not by a motion of the head, +but of the eyeball itself, across the direction of the brush, by first +looking steadfastly about 10 deg. or 15 deg. above, and then instantly as much +below it, the general brush will be resolved into a number of individual +brushes, standing in a row upon the line which the eye passed over; each +elementary brush being the result of a single discharge, and the space +between them representing both the time during which the eye was passing +over that space, and that which elapsed between one discharge and another. + + [A] Philosophical Transactions, 1834, p. 586. + +1428. The single brushes could easily be separated to eight or ten times +their own width, but were not at the same time extended, i.e. they did not +become more indefinite in shape, but, on the contrary, less so, each being +more distinct in form, ramification, and character, because of its +separation from the others, in its effects upon the eye. Each, therefore, +was instantaneous in its existence (1436.). Each had the conical root +complete (1426.). + +1429. On using a smaller ball, the general brush was smaller, and the +sound, though weaker, more continuous. On resolving the brush into its +elementary parts, as before, these were found to occur at much shorter +intervals of time than in the former case, but still the discharge was +intermitting. + +1430. Employing a wire with a round end, the brush was still smaller, but, +as before, separable into successive discharges. The sound, though feebler, +was higher in pitch, being a distinct musical note. + +1431. The sound is, in fact, due to the recurrence of the noise of each +separate discharge, and these, happening at intervals nearly equal under +ordinary circumstances, cause a definite note to be heard, which, rising in +pitch with the increased rapidity and regularity of the intermitting +discharges, gives a ready and accurate measure of the intervals, and so may +be used in any case when the discharge is heard, even though the +appearances may not be seen, to determine the element of _time_. So when, +by bringing the hand towards a projecting rod or ball, the pitch of the +tone produced by a brushy discharge increases, the effect informs us that +we have increased the induction (1374.), and by that means increased the +rapidity of the alternations of charge and discharge. + +1432. By using wires with finer terminations, smaller brushes were +obtained, until they could hardly be distinguished as brushes; but as long +as _sound_ was heard, the discharge could be ascertained by the eye to be +intermitting; and when the sound ceased, the light became _continuous_ as a +glow (1359. 1405. 1526-1543.). + +1433. To those not accustomed to use the eye in the manner I have +described, or, in cases where the recurrence is too quick for any +unassisted eye, the beautiful revolving mirror of Professor Wheatstone[A] +will be useful for such developments of condition as those mentioned above. +Another excellent process is to produce the brush or other luminous +phenomenon on the end of a rod held in the hand opposite to a charged +positive or negative conductor, and then move the rod rapidly from side to +side whilst the eye remains still. The successive discharges occur of +course in different places, and the state of things before, at, and after a +single coruscation or brush can be exceedingly well separated. + + [A] Philosophical Transactions, 1834, pp. 581, 585. + +1434. The _brush_ is in reality a discharge between a bad or a +non-conductor and either a conductor or another non-conductor. Under common +circumstances, the brush is a discharge between a conductor and air, and I +conceive it to take place in something like the following manner. When the +end of an electrified rod projects into the middle of a room, induction +takes place between it and the walls of the room, across the dielectric, +air; and the lines of inductive force accumulate upon the end in greater +quantity than elsewhere, or the particles of air at the end of the rod are +more highly polarized than those at any other part of the rod, for the +reasons already given (1374.). The particles of air situated in sections +across these lines of force are least polarized in the sections towards the +walls and most polarized in those nearer to the end of the wires (1369.): +thus, it may well happen, that a particle at the end of the wire is at a +tension that will immediately terminate in discharge, whilst in those even +only a few inches off, the tension is still beneath that point. But suppose +the rod to be charged positively, a particle of air A, fig. 118, next it, +being polarized, and having of course its negative force directed towards +the rod and its positive force outwards; the instant that discharge takes +place between the positive force of the particle of the rod opposite the +air and the negative force of the particle of air towards the rod, the +whole particle of air becomes positively electrified; and when, the next +instant, the discharged part of the rod resumes its positive state by +conduction from the surface of metal behind, it not only acts on the +particles beyond A, by throwing A into a polarized state again, but A +itself, because of its charged state, exerts a distinct inductive act +towards these further particles, and the tension is consequently so much +exalted between A and B, that discharge takes place there also, as well as +again between the metal and A. + +1435. In addition to this effect, it has been shown, that, the act of +discharge having once commenced, the whole operation, like a case of +unstable equilibrium, is hastened to a conclusion (1370. 1418.), the rest +of the act being facilitated in its occurrence, and other electricity than +that which caused the first necessary tension hurrying to the spot. When, +therefore, disruptive discharge has once commenced at the root of a brush, +the electric force which has been accumulating in the conductor attached to +the rod, finds a more ready discharge there than elsewhere, and will at +once follow the course marked out as it were for it, thus leaving the +conductor in a partially discharged state, and the air about the end of the +wire in a charged condition; and the time necessary for restoring the full +charge of the conductor, and the dispersion of the charged air in a greater +or smaller degree, by the joint forces of repulsion from the conductor and +attraction towards the walls of the room, to which its inductive action is +directed, is just that time which forms the interval between brush and +brush (1420. 1427. 1431. 1447.). + +1436. The words of this description are long, but there is nothing in the +act or the forces on which it depends to prevent the discharge being +_instantaneous_, as far as we can estimate and measure it. The +consideration of _time_ is, however, important in several points of view +(1418.), and in reference to disruptive discharge, it seemed from theory +far more probable that it might be detected in a brush than in a spark; for +in a brush, the particles in the line through which the discharge passes +are in very different states as to intensity, and the discharge is already +complete in its act at the root of the brush, before the particles at the +extremity of the ramifications have yet attained their maximum intensity. + +1437. I consider _brush_ discharge as probably a successive effect in this +way. Discharge begins at the root (1426. 1553.), and, extending itself in +succession to all parts of the single brush, continues to go on at the root +and the previously formed parts until the whole brush is complete; then, by +the fall in intensity and power at the conductor, it ceases at once in all +parts, to be renewed, when that power has risen again to a sufficient +degree. But in a _spark_, the particles in the line of discharge being, +from the circumstances, nearly alike in their intensity of polarization, +suffer discharge so nearly at the same moment as to make the time quite +insensible to us. + +1438. Mr. Wheatstone has already made experiments which fully illustrate +this point. He found that the brush generally had a sensible duration, but +that with his highest capabilities he could not detect any such effect in +the spark[A]. I repeated his experiment on the brush, though with more +imperfect means, to ascertain whether I could distinguish a longer duration +in the stem or root of the brush than in the extremities, and the +appearances were such as to make me think an effect of this kind was +produced. + + [A] Philosophical Transactions, 1836, pp. 586, 590. + +1439. That the discharge breaks into several ramifications, and by them +passes through portions of air alike, or nearly alike, as to polarization +and the degree of tension the particles there have acquired, is a very +natural result of the previous state of things, and rather to be expected +than that the discharge should continue to go straight out into space in a +single line amongst those particles which, being at a distance from the end +of the rod, are in a lower state of tension than those which are near: and +whilst we cannot but conclude, that those parts where the branches of a +single brush appear, are more favourably circumstanced for discharge than +the darker parts between the ramifications, we may also conclude, that in +those parts where the light of concomitant discharge is equal, there the +circumstances are nearly equal also. The single successive brushes are by +no means of the same particular shape even when they are observed without +displacement of the rod or surrounding objects (1427. 1433.), and the +successive discharges may be considered as taking place into the mass of +air around, through different roads at each brush, according as minute +circumstances, such as dust, &c. (1391. 1392.), may have favoured the +course by one set of particles rather than another. + +1440. Brush discharge does not essentially require any current of the +medium in which the brush appears: the current almost always occurs, but is +a consequence of the brush, and will be considered hereafter (1562-1610.). +On holding a blunt point positively charged towards uninsulated water, a +star or glow appeared on the point, a current of air passed from it, and +the surface of the water was depressed; but on bringing the point so near +that sonorous brushes passed, then the current of air instantly ceased, and +the surface of the water became level. + +1441. The discharge by a brush is not to all the particles of air that are +near the electrified conductor from which the brush issues; only those +parts where the ramifications pass are electrified: the air in the central +dark parts between them receives no charge, and, in fact, at the time of +discharge, has its electric and inductive tension considerably lowered. For +consider fig. 128 to represent a single positive brush;--the induction +before the discharge is from the end of the rod outwards, in diverging +lines towards the distant conductors, as the walls of the room, &c., and a +particle at _a_ has polarity of a certain degree of tension, and tends with +a certain force to become charged; but at the moment of discharge, the air +in the ramifications _b_ and _d_, acquiring also a positive state, opposes +its influence to that of the positive conductor on _a_, and the tension of +the particle at _a_ is therefore diminished rather than increased. The +charged particles at _b_ and _d_ are now inductive bodies, but their lines +of inductive action are still outwards towards the walls of the room; the +direction of the polarity and the tendency of other particles to charge +from these, being governed by, or in conformity with, these lines of force. + +1442. The particles that are charged are probably very highly charged, but, +the medium being a non-conductor, they cannot communicate that state to +their neighbours. They travel, therefore, under the influence of the +repulsive and attractive forces, from the charged conductor towards the +nearest uninsulated conductor, or the nearest body in a different state to +themselves, just as charged particles of dust would travel, and are then +discharged; each particle acting, in its course, as a centre of inductive +force upon any bodies near which it may come. The travelling of these +charged particles when they are numerous, causes wind and currents, but +these will come into consideration under _carrying discharge_ (1319. 1562. +&c.). + +1443. When air is said to be electrified, and it frequently assumes this +state near electrical machines, it consists, according to my view, of a +mixture of electrified and unelectrified particles, the latter being in +very large proportion to the former. When we gather electricity from air, +by a flame or by wires, it is either by the actual discharge of these +particles, or by effects dependent on their inductive action, a case of +either kind being produceable at pleasure. That the law of equality between +the two forces or forms of force in inductive action is as strictly +preserved in these as in other cases, is fully shown by the fact, formerly +stated (1173. 1174.), that, however strongly air in a vessel might be +charged positively, there was an exactly equal amount of negative force on +the inner surface of the vessel itself, for no residual portion of either +the one or the other electricity could be obtained. + +1444. I have nowhere said, nor does it follow, that the air is charged only +where the luminous brush appears. The charging may extend beyond those +parts which are visible, i.e. particles to the right or left of the lines +of light may receive electricity, the parts which are luminous being so +only because much electricity is passing by them to other parts (1437.); +just as in a spark discharge the light is greater as more electricity +passes, though it has no necessary relation to the quantity required to +commence discharge (1370. 1420.). Hence the form we see in a brush may by +no means represent the whole quantity of air electrified; for an invisible +portion, clothing the visible form to a certain depth, may, at the same +time, receive its charge (1552.). + +1445. Several effects which I have met with in muriatic acid gas tend to +make me believe, that that gaseous body allows of a dark discharge. At the +same time, it is quite clear from theory, that in some gases, the reverse +of this may occur, i.e. that the charging of the air may not extend even so +far as the light. We do not know as yet enough of the electric light to be +able to state on what it depends, and it is very possible that, when +electricity bursts forth into air, all the particles of which are in a +state of tension, light may be evolved by such as, being very near to, are +not of, those which actually receive a charge at the time. + +1446. The further a brush extends in a gas, the further no doubt is the +charge or discharge carried forward; but this may vary between different +gases, and yet the intensity required for the first moment of discharge not +vary in the same, but in some other proportion. Thus with respect to +nitrogen and muriatic acid gases, the former, as far as my experiments have +proceeded, produces far finer and larger brushes than the latter (1458. +1462.), but the intensity required to commence discharge is much higher for +the muriatic acid than the nitrogen (1395.). Here again, therefore, as in +many other qualities, specific differences are presented by different +gaseous dielectrics, and so prove the special relation of the latter to the +act and the phenomena of induction. + +1447. To sum up these considerations respecting the character and condition +of the brush, I may state that it is a spark to air; a diffusion of +electric force to matter, not by conduction, but disruptive discharge, a +dilute spark which, passing to very badly conducting matter, frequently +discharges but a small portion of the power stored up in the conductor; for +as the air charged reacts on the conductor, whilst the conductor, by loss +of electricity, sinks in its force (1435.), the discharge quickly ceases, +until by the dispersion of the charged air and the renewal of the excited +conditions of the conductor, circumstances have risen up to their first +effective condition, again to cause discharge, and again to fall and rise, + +1448. The brush and spark gradually pass into one another, Making a small +ball positive by a good electrical machine with a large prime conductor, +and approaching a large uninsulated discharging ball towards it, very +beautiful variations from the spark to the brush may be obtained. The +drawings of long and powerful sparks, given by Van Marum[A], Harris[B], and +others, also indicate the same phenomena. As far as I have observed, +whenever the spark has been brushy in air of common pressures, the whole of +the electricity has not been discharged, but only portions of it, more or +less according to circumstances; whereas, whenever the effect has been a +distinct spark throughout the whole of its course, the discharge has been +perfect, provided no interruption had been made to it elsewhere, in the +discharging circuit, than where the spark occurred. + + [A] Description of the Teylerian machine, vol. i. pp. 28. 32.; vol. + ii. p. 226, &c. + + [B] Philosophical Transactions, 1834, p. 213. + +1449. When an electrical brush from an inch to six inches in length or more +is issuing into free air, it has the form given, fig. 117. But if the hand, +a ball, of any knobbed conductor be brought near, the extremities of the +coruscations turn towards it and each other, and the whole assumes various +forms according to circumstances, as in figs. 119, 120, and 121. The +influence of the circumstances in each case is easily traced, and I might +describe it here, but that I should be ashamed to occupy the time of the +Society in things so evident. But how beautifully does the curvature of the +ramifications illustrate the curved form of the lines of inductive force +existing previous to the discharge! for the former are consequences of the +latter, and take their course, in each discharge, where the previous +inductive tension had been raised to the proper degree. They represent +these curves just as well as iron filings represent magnetic curves, the +visible effects in both cases being the consequences of the action of the +forces in _the places where_ the effects appear. The phenomena, therefore, +constitute additional and powerful testimony (1216. 1230.) to that already +given in favour both of induction through dielectrics in curved lines +(1231.), and of the lateral relation of these lines, by an effect +equivalent to a repulsion producing divergence, or, as in the cases +figured, the bulging form. + +1450. In reference to the theory of molecular inductive action, I may also +add, the proof deducible from the long brushy ramifying spark which, may be +obtained between a small ball on the positive conductor of an electrical +machine, and a larger one at a distance (1448. 1504.). What a fine +illustration that spark affords of the previous condition of _all_ the +particles of the dielectric between the surfaces of discharge, and how +unlike the appearances are to any which would be deduced from the theory +which assumes inductive action to be action at a distance, in straight +lines only; and charge, as being electricity retained upon the surface of +conductors by the mere pressure of the atmosphere! + + * * * * * + +1451. When the brush is obtained in rarefied air, the appearances vary +greatly, according to circumstances, and are exceedingly beautiful. +Sometimes a brush may be formed of only six or seven branches, these being +broad and highly luminous, of a purple colour, and in some parts an inch or +more apart: by a spark discharge at the prime conductor (1455.) single +brushes may be obtained at pleasure. Discharge in the form of a brush is +favoured by rarefaction of the air, in the same manner and for the same +reason as discharge in the form of a spark (1375.); but in every case there +is previous induction and charge through the dielectric, and polarity of +its particles (1437.), the induction being, as in any other instance, +alternately raised by the machine and lowered by the discharge. In certain +experiments the rarefaction was increased to the utmost degree, and the +opposed conducting surfaces brought as near together as possible without +producing glow (1529.): the brushes then contracted in their lateral +dimensions, and recurred so rapidly as to form an apparently continuous arc +of light from metal to metal. Still the discharge could be observed to +intermit (1427.), so that even under these high conditions, induction +preceded each single brush, and the tense polarized condition of the +contiguous particles was a necessary preparation for the discharge itself. + +1452. The brush form of disruptive discharge may be obtained not only in +air and gases, but also in much denser media. I procured it in _oil of +turpentine_ from the end of a wire going through a glass tube into the +fluid contained in a metal vessel. The brush was small and very difficult +to obtain; the ramifications were simple, and stretched out from each +other, diverging very much. The light was exceedingly feeble, a perfectly +dark room being required for its observation. When a few solid particles, +as of dust or silk, were in the liquid, the brush was produced with much +greater facility. + +1453. The running together or coalescence of different lines of discharge +(1412.) is very beautifully shown in the brush in air. This point may +present a little difficulty to those who are not accustomed to see in every +discharge an equal exertion of power in opposite directions, a positive +brush being considered by such (perhaps in consequence of the common phrase +_direction of a current_) as indicating a breaking forth in different +directions of the original force, rather than a tendency to convergence and +union in one line of passage. But the ordinary case of the brush may be +compared, for its illustration, with that in which, by holding the knuckle +opposite to highly excited glass, a discharge occurs, the ramifications of +a brush then leading from the glass and converging into a spark on the +knuckle. Though a difficult experiment to make, it is possible to obtain +discharge between highly excited shell-lac and the excited glass of a +machine: when the discharge passes, it is, from the nature of the charged +bodies, brush at each end and spark in the middle, beautifully illustrating +that tendency of discharge to facilitate like action, which I have +described in a former page (1418.). + +1454. The brush has _specific characters_ in different gases, indicating a +relation to the particles of these bodies even in a stronger degree than +the spark (1422. 1423.). This effect is in strong contrast with the +non-variation caused by the use of different substances as _conductors_ +from which the brushes are to originate. Thus, using such bodies as wood, +card, charcoal, nitre, citric acid, oxalic acid, oxide of lead, chloride of +lead, carbonate of potassa, potassa fusa, strong solution of potash, oil of +vitriol, sulphur, sulphuret of antimony, and haematite, no variation in the +character of the brushes was obtained, except that (dependent upon their +effect as better or worse conductors) of causing discharge with more or +less readiness and quickness from the machine[A]. + + [A] Exception must, of course, be made of those cases where the root + of the brush, becoming a spark, causes a little diffusion or even + decomposition of the matter there, and so gains more or less of a + particular colour at that part. + +1455. The following are a few of the effects I observed in different gasses +at the positively charged surfaces, and with atmospheres varying in their +pressure. The general effect of rarefaction was the same for all the gases: +at first, sparks passed; these gradually were converted into brushes, which +became larger and more distinct in their ramifications, until, upon further +rarefaction, the latter began to collapse and draw in upon each other, till +they formed a stream across from conductor to conductor: then a few lateral +streams shot out towards the glass of the vessel from the conductors; these +became thick and soft in appearance, and were succeeded by the full +constant glow which covered the discharging wire. The phenomena varied with +the size of the vessel (1477.), the degree of rarefaction, and the +discharge of electricity from the machine. When the latter was in +successive sparks, they were most beautiful, the effect of a spark from a +small machine being equal to, and often surpassing, that produced by the +_constant_ discharge of a far more powerful one. + +1456. _Air._--Fine positive brushes are easily obtained in air at common +pressures, and possess the well-known purplish light. When the air is +rarefied, the ramifications are very long, filling the globe (1477.); the +light is greatly increased, and is of a beautiful purple colour, with an +occasional rose tint in it. + +1457. _Oxygen._--At common pressures, the brush is very close and +compressed, and of a dull whitish colour. In rarefied oxygen, the form and +appearance are better, the colour somewhat purplish, but all the characters +very poor compared to those in air. + +1458. _Nitrogen_ gives brushes with great facility at the positive surface, +far beyond any other gas I have tried: they are almost always fine in form, +light, and colour, and in rarefied nitrogen, are magnificent. They surpass +the discharges in any other gas as to the quantity of light evolved. + +1459. _Hydrogen_, at common pressures, gave a better brush than oxygen, but +did not equal nitrogen; the colour was greenish gray. In rarefied hydrogen, +the ramifications were very fine in form and distinctness, but pale in +colour, with a soft and velvety appearance, and not at all equal to those +in nitrogen. In the rarest state of the gas, the colour of the light was a +pale gray green. + +1460. _Coal gas._--The brushes were rather difficult to produce, the +contrast with nitrogen being great in this respect. They were short and +strong, generally of a greenish colour, and possessing much of the spark +character: for, occurring on both the positive and negative terminations, +often when there was a dark interval of some length between the two +brushes, still the quick, sharp sound of the spark was produced, as if the +discharge had been sudden through this gas, and partaking, in that respect, +of the character of a spark. In rare coal gas, the brush forms were better, +but the light very poor and the colour gray. + +1461. _Carbonic acid gas_ produces a very poor brush at common pressures, +as regards either size, light, or colour; and this is probably connected +with the tendency which this gas has to discharge the electricity as a +spark (1422.). In rarefied carbonic acid, the brush is better in form, but +weak as to light, being of a dull greenish or purplish line, varying with +the pressure and other circumstances. + +1462. _Muriatic acid gas._--It is very difficult to obtain the brush in +this gas at common pressures. On gradually increasing the distance of the +rounded ends, the sparks suddenly ceased when the interval was about an +inch, and the discharge, which was still through the gas in the globe, was +silent and dark. Occasionally a very short brush could for a few moments be +obtained, but it quickly disappeared. Even when the intermitting spark +current (1455.) from the machine was used, still I could only with +difficulty obtain a brush, and that very short, though I used rods with +rounded terminations (about 0.25 of an inch in diameter) which had before +given them most freely in air and nitrogen. During the time of this +difficulty with the muriatic gas, magnificent brushes were passing off from +different parts of the machine into the surrounding air. On rarefying the +gas, the formation of the brush was facilitated, but it was generally of a +low squat form, very poor in light, and very similar on both the positive +and negative surfaces. On rarefying the gas still more, a few large +ramifications were obtained of a pale bluish colour, utterly unlike those +in nitrogen. + + * * * * * + +1463. In all the gases, the different forms of disruptive discharge may be +linked together and gradually traced from one extreme to the other, i.e. +from the spark to the glow (1405. 1526.), or, it may be, to a still further +condition to be called dark discharge (1544-1560.); but it is, +nevertheless, very surprising to see what a specific character each keeps +whilst under the predominance of the general law. Thus, in muriatic acid, +the brush is very difficult to obtain, and there comes in its place almost +a dark discharge, partaking of the readiness of the spark action. Moreover, +in muriatic acid, I have _never_ observed the spark with any dark interval +in it. In nitrogen, the spark readily changes its character into that of +brush. In carbonic acid gas, there seems to be a facility to occasion spark +discharge, whilst yet that gas is unlike nitrogen in the facility of the +latter to form brushes, and unlike muriatic acid in its own facility to +continue the spark. These differences add further force, first to the +observations already made respecting the spark in various gases (1422. +1423.), and then, to the proofs deducible from it, of the relation of the +electrical forces to the particles of matter. + +1464. The peculiar characters of nitrogen in relation to the electric +discharge (1422. 1458.) must, evidently, have an important influence over +the form and even the occurrence of lightning. Being that gas which most +readily produces coruscations, and, by them, extends discharge to a greater +distance than any other gas tried, it is also that which constitutes +four-fifths of our atmosphere; and as, in atmospheric electrical phenomena, +one, and sometimes both the inductive forces are resident on the particles +of the air, which, though probably affected as to conducting power by the +aqueous particles in it, cannot be considered as a good conductor; so the +peculiar power possessed by nitrogen, to originate and effect discharge in +the form of a brush or of ramifications, has, probably, an important +relation to its electrical service in nature, as it most seriously affects +the character and condition of the discharge when made. The whole subject +of discharge from and through gases is of great interest, and, if only in +reference to atmospheric electricity, deserves extensive and close +experimental investigation. + +_Difference of discharge at the positive and negative conducting surfaces._ + +1465. I have avoided speaking of this well-known phenomenon more than was +quite necessary, that I might bring together here what I have to say on the +subject. When the brush discharge is observed in air at the positive and +negative surfaces, there is a very remarkable difference, the true and full +comprehension of which would, no doubt, be of the utmost importance to the +physics of electricity; it would throw great light on our present subject, +i.e. the molecular action of dielectrics under induction, and its +consequences; and seems very open to, and accessible by, experimental +inquiry. + +1466. The difference in question used to be expressed in former times by +saying, that a point charged positively gave brushes into the air, whilst +the same point charged negatively gave a star. This is true only of bad +conductors, or of metallic conductors charged intermittingly, or otherwise +controlled by collateral induction. If metallic points project _freely_ +into the air, the positive and negative light upon them differ very little +in appearance, and the difference can be observed only upon close +examination. + +1467. The effect varies exceedingly under different circumstances, but, as +we must set out from some position, may perhaps be stated thus: if a +metallic wire with a rounded termination in free air be used to produce the +brushy discharge, then the brushes obtained when the wire is charged +negatively are very poor and small, by comparison with those produced when +the charge is positive. Or if a large metal ball connected with the +electrical machine be charged _positively_, and a fine uninsulated point be +gradually brought towards it, a star appears on the point when at a +considerable distance, which, though it becomes brighter, does not change +its form of a star until it is close up to the ball: whereas, if the ball +be charged negatively, the point at a considerable distance has a star on +it as before; but when brought nearer, (in my case to the distance of 1-1/2 +inch,) a brush formed on it, extending to the negative ball; and when still +nearer, (at 1/8 of an inch distance,) the brush ceased, and bright sparks +passed. These variations, I believe, include the whole series of +differences, and they seem to show at once, that the negative surface tends +to retain its discharging character unchanged, whilst the positive surface, +under similar circumstances, permits of great variation. + +1468. There are several points in the character of the negative discharge +to air which it is important to observe. A metal rod, 0.3 of an inch in +diameter, with a rounded end projecting into the air, was charged +negatively, and gave a short noisy brush (fig. 122.). It was ascertained +both by sight (1427. 1433.) and sound (1431.), that the successive +discharges were very rapid in their recurrence, being seven or eight times +more numerous in the same period, than those produced when the rod was +charged positively to an equal degree. When the rod was positive, it was +easy, by working the machine a little quicker, to replace the brush by a +glow (1405. 1463.), but when it was negative no efforts could produce this +change. Even by bringing the hand opposite the wire, the only effect was to +increase the number of brush discharges in a given period, raising at the +same time the sound to a higher pitch. + +1469. A point opposite the negative brush exhibited a star, and as it was +approximated caused the size and sound of the negative brush to diminish, +and, at last, to cease, leaving the negative end silent and dark, yet +effective as to discharge. + +1470. When the round end of a smaller wire (fig. 123.) was advanced towards +the negative brush, it (becoming positive by induction) exhibited the quiet +glow at 8 inches distance, the negative brush continuing. When nearer, the +pitch of the sound of the negative brush rose, indicating quicker +intermittences (1431.); still nearer, the positive end threw off +ramifications and distinct brushes; at the same time, the negative brush +contracted in its lateral directions and collected together, giving a +peculiar narrow longish brush, in shape like a hair pencil, the two brushes +existing at once, but very different in their form and appearance, and +especially in the more rapid recurrence of the negative discharges than of +the positive. On using a smaller positive wire for the same experiment, the +glow first appeared on it, and then the brush, the negative brush being +affected at the same time; and the two at one distance became exceedingly +alike in appearance, and the sounds, I thought, were in unison; at all +events they were in harmony, so that the intermissions of discharge were +either isochronous, or a simple ratio existed between the intervals. With a +higher action of the machine, the wires being retained unaltered, the +negative surface became dark and silent, and a glow appeared on the +positive one. A still higher action changed the latter into a spark. Finer +positive wires gave other variations of these effects, the description of +which I must not allow myself to go into here. + +1471. A thinner rod was now connected with the negative conductor in place +of the larger one (1468.), its termination being gradually diminished to a +blunt point, as in fig. 124; and it was beautiful to observe that, +notwithstanding the variation of the brush, the same general order of +effects was produced. The end gave a small sonorous negative brush, which +the approach of the hand or a large conducting surface did not alter, until +it was so near as to produce a spark. A fine point opposite to it was +luminous at a distance; being nearer it did not destroy the light and sound +of the negative brush, but only tended to have a brush produced on itself, +which, at a still less distance, passed into a spark joining the two +surfaces. + +1472. When the distinct negative and positive brushes are produced +simultaneously in relation to each other in air, the former almost always +has a contracted form, as in fig. 125, very much indeed resembling the +figure which the positive brush itself has when influenced by the lateral +vicinity of positive parts acting by induction. Thus a brush issuing from a +point in the re-entering angle of a positive conductor has the same +compressed form (fig. 126.). + +1473. The character of the negative brush is not affected by the chemical +nature of the substances of the conductors (1454.), but only by their +possession of the conducting power in a greater or smaller degree. + +1474. Rarefaction of common air about a negative ball or blunt point +facilitated the development of the negative brush, the effect being, I +think, greater than on a positive brush, though great on both. Extensive +ramifications could be obtained from a ball or end electrified negatively +to the plate of the air-pump on which the jar containing it stood. + +1475. A very important variation of the relative forms and conditions of +the positive and negative brush takes place on varying the dielectric in +which they are produced. The difference is so very great that it points to +a specific relation of this form of discharge to the particular gas in +which it takes place, and opposes the idea that gases are but obstructions +to the discharge, acting one like another and merely in proportion to their +pressure (1377.). + +1476. In _air_, the superiority of the positive brush is well known (1467. +1472.). In _nitrogen_, it is as great or even greater than in air (1458.). +In _hydrogen_, the positive brush loses a part of its superiority, not +being so good as in nitrogen or air; whilst the negative brush does not +seem injured (1459.). In _oxygen_, the positive brush is compressed and +poor (1457); whilst the negative did not become less: the two were so alike +that the eye frequently could not tell one from the other, and this +similarity continued when the oxygen was gradually rarefied. In _coal gas_, +the brushes are difficult of production as compared to nitrogen (1460.), +and the positive not much superior to the negative in its character, either +at common or low pressures. In _carbonic acid gas_, this approximation of +character also occurred. In _muriatic acid gas_, the positive brush was +very little better than the negative, and both difficult to produce (1462.) +as compared with the facility in nitrogen or air. + +1477. These experiments were made with rods of brass about a quarter of an +inch thick having rounded ends, these being opposed in a glass globe 7 +inches in diameter, containing the gas to be experimented with. The +electric machine was used to communicate directly, sometimes the positive, +and sometimes the negative state, to the rod in connection with it. + +1478. Thus we see that, notwithstanding there is a general difference in +favour of the superiority of the positive brush over the negative, that +difference is at its maximum in nitrogen and air; whilst in carbonic acid, +muriatic acid, coal gas, and oxygen, it diminishes, and at last almost +disappears. So that in this particular effect, as in all others yet +examined, the evidence is in favour of that view which refers the results +to a direct relation of the electric forces with the molecules of the +matter concerned in the action (1421. 1423. 1463.). Even when special +phenomena arise under the operation of the general law, the theory adopted +seems fully competent to meet the case. + +1479. Before I proceed further in tracing the probable cause of the +difference between the positive and negative brush discharge, I wish to +know the results of a few experiments which are in course of preparation: +and thinking this Series of Researches long enough, I shall here close it +with the expectation of being able in a few weeks to renew the inquiry, and +entirely redeem my pledge (1306.). + +_Royal Institution, +Dec. 23rd, 1837._ + + + + +THIRTEENTH SERIES. + + +S 18. _On Induction (continued)._ P ix. _Disruptive discharge +(continued)--Peculiarities of positive and negative discharge either as +spark or brush--Glow discharge--Dark discharge._ P x. _Convection, or +carrying discharge._ P xi. _Relation of a vacuum to electrical phenomena._ +S 19. _Nature of the electrical current._ + +Received February 22,--Read March 15, 1838. + + +P ix. _Disruptive discharge (continued)._ + + +1480. Let us now direct our attention to the general difference of the +positive and negative disruptive discharge, with the object of tracing, as +far as possible, the cause of that difference, and whether it depends on +the charged conductors principally, or on the interposed dielectric; and as +it appears to be great in air and nitrogen (1476.), let us observe the +phenomena in air first. + +1481. The general case is best understood by a reference to surfaces of +considerable size rather than to points, which involve (as a secondary +effect) the formation of currents (1562). My investigation, therefore, was +carried on with balls and terminations of different diameters, and the +following are some of the principal results. + +1482. If two balls of very different dimensions, as for instance one-half +an inch, and the other three inches in diameter, be arranged at the ends of +rods so that either can be electrified by a machine and made to discharge +by sparks to the other, which is at the same time uninsulated; then, as is +well known, far longer sparks are obtained when the small ball is positive +and the large ball negative, than when the small ball is negative and the +large ball positive. In the former case, the sparks are 10 or 12 inches in +length; in the latter, an inch or an inch and a half only. + + * * * * * + +1483. But previous to the description of further experiments, I will +mention two words, for which with many others I am indebted to a friend, +and which I think it would be expedient to introduce and use. It is +important in ordinary inductive action, to distinguish at which charged +surface the induction originates and is sustained: i.e. if two or more +metallic balls, or other masses of matter, are in inductive relation, to +express which are charged originally, and which are brought by them into +the opposite electrical condition. I propose to call those bodies which are +originally charged, _inductric_ bodies; and those which assume the opposite +state, in consequence of the induction, _inducteous_ bodies. This +distinction is not needful because there is any difference between the sums +of the _inductric_ and the _inducteous_ forces; but principally because, +when a ball A is inductric, it not merely brings a ball B, which is +opposite to it, into an inducteous state, but also many other surrounding +conductors, though some of them may be a considerable distance off, and the +consequence is, that the balls do not bear the same precise relation to +each other when, first one, and then the other, is made the inductric ball; +though, in each case, the _same ball_ be made to assume the _same state._ + +1484, Another liberty which I may also occasionally take in language I will +explain and limit. It is that of calling a particular spark or brush, +_positive_ or _negative_, according as it may be considered as +_originating_ at a positive or a negative surface. We speak of the brush as +positive or negative when it shoots out from surfaces previously in those +states; and the experiments of Mr. Wheatstone go to prove that it _really +begins_ at the charged surface, and from thence extends into the air (1437. +1438.) or other dielectric. According to my view, _sparks_ also originate +or are determined at one particular spot (1370.), namely, that where the +tension first rises up to the maximum degree; and when this can be +determined, as in the simultaneous use of large and small balls, in which +case the discharge begins or is determined by the latter, I would call that +discharge which passes _at once_, a positive spark, if it was at the +positive surface that the maximum intensity was first obtained; or a +negative spark, if that necessary intensity was first obtained at the +negative surface. + + * * * * * + +1485. An apparatus was arranged, as in fig. 129. (Plate VIII.): A and B +were brass balls of very different diameters attached to metal rods, moving +through sockets on insulating pillars, so that the distance between the +balls could be varied at pleasure. The large ball A, 2 inches in diameter, +was connected with an insulated brass conductor, which could be rendered +positive or negative directly from a cylinder machine: the small ball B, +0.25 of an inch in diameter, was connected with a discharging train (292.) +and perfectly uninsulated. The brass rods sustaining the balls were 0.2 of +an inch in thickness. + +1486. When the large ball was _positive_ and inductric (1483.), negative +sparks occurred until the interval was 0.49 of an inch; then mixed brush +and spark between that and 0.51; and from 0.52 and upwards, negative brush +alone. When the large ball was made _negative_ and inductric, then positive +spark alone occurred until the interval was as great as 1.15 inches; spark +and brush from that up to 1.55; and to have the positive brush alone, it +required an interval of at least 1.65 inches. + +1487. The balls A and B were now changed for each other. Then making the +small ball B inductric _positively_, the positive sparks alone continued +only up to 0.67; spark and brush occurred from 0.68 up to 0.72; and +positive brush alone from 0.74 and upwards. Rendering the small ball B +inductric and _negative_, negative sparks alone occurred up to 0.40; then +spark and brush at 0.42; whilst from 0.44 and upwards the noisy negative +brush alone took place. + +1488. We thus find a great difference as the balls are rendered inductric +or inducteous; the small ball rendered _positive_ inducteously giving a +spark nearly twice as long as that produced when it was charged positive +inductrically, and a corresponding difference, though not, under the +circumstances, to the same extent, was manifest, when it was rendered +_negative_[A]. + + [A] For similar experiments on different gases, see 1518.--_Dec. 1838._ + +1489. Other results are, that the small ball rendered positive gives a much +longer spark than when it is rendered negative, and that the small ball +rendered negative gives a brush more readily than when positive, in +relation to the effect produced by increasing the distance between the two +balls. + +1490. When the interval was below 0.4 of an inch, so that the small ball +should give sparks, whether positive or negative, I could not observe that +there was any constant difference, either in their ready occurrence or the +number which passed in a given time. But when the interval was such that +the small ball when negative gave a brush, then the discharges from it, as +separate negative brushes, were far more numerous than the corresponding +discharges from it when rendered positive, whether those positive +discharges were as sparks or brushes. + +1491. It is, therefore, evident that, when a ball is discharging +electricity in the form of brushes, the brushes are far more numerous, and +each contains or carries off far less electric force when the electricity +so discharged is negative, than when it is positive. + +1492. In all such experiments as those described, the point of change from +spark to brush is very much governed by the working state of the electrical +machine and the size of the conductor connected with the discharging ball. +If the machine be in strong action and the conductor large, so that much +power is accumulated quickly for each discharge, then the interval is +greater at which the sparks are replaced by brushes; but the general effect +is the same[A]. + + [A] For similar experiments in different gases, see 1510-1517.--_Dec. + 1838._ + +1493. These results, though indicative of very striking and peculiar +relations of the electric force or forces, do not show the relative degrees +of charge which the small ball acquires before discharge occurs, i.e. they +do not tell whether it acquires a higher condition in the negative, or in +the positive state, immediately preceding that discharge. To illustrate +this important point I arranged two places of discharge as represented, fig +130. A and D are brass balls 2 inches diameter, B and C are smaller brass +balls 0.25 of an inch in diameter; the forks L and R supporting them were +of brass wire 0.2 of an inch in diameter; the space between the large and +small ball on the same fork was 5 inches, that the two places of discharge +_n_ and _o_ might be sufficiently removed from each other's influence. The +fork L was connected with a projecting cylindrical conductor, which could +be rendered positive or negative at pleasure, by an electrical machine, and +the fork R was attached to another conductor, but thrown into an +uninsulated state by connection with a discharging train (292.). The two +intervals or places of discharge _n_ and _o_ could be varied at pleasure, +their extent being measured by the occasional introduction of a diagonal +scale. It is evident, that, as the balls A and B connected with the same +conductor are always charged at once, and that discharge may take place to +either of the balls connected with the discharging train, the intervals of +discharge _n_ and _o_ may be properly compared to each other, as respects +the influence of large and small balls when charged positively and +negatively in air. + +1494. When the intervals _n_ and _o_ were each made = 0.9 of an inch, and +the balls A and B inductric _positively_, the discharge was all at _n_ from +the small ball of the conductor to the large ball of the discharging train, +and mostly by positive brush, though once by a spark. When the balls A and +B were made inductric _negatively_, the discharge was still from the same +small ball, at _n_, by a constant negative brush. + +1495. I diminished the intervals _n_ and _o_ to 0.6 of an inch. When A and +B were inductric _positively_, all the discharge was at _n_ as a positive +brush: when A and B were inductric _negatively_, still all the discharge +was at _n_, as a negative brush. + +1496. The facility of discharge at the positive and negative small balls, +therefore, did not appear to be very different. If a difference had +existed, there were always two small balls, one in each state, that the +discharge might happen at that most favourable to the effect. The only +difference was, that one was in the inductric, and the other in the +inducteous state, but whichsoever happened for the time to be in that +state, whether positive or negative, had the advantage. + +1497. To counteract this interfering influence, I made the interval _n_ = +0.79 and interval _o_ = 0.58 of an inch. Then, when the balls A and B were +_inductric positive_, the discharge was about equal at both intervals. +When, on the other hand, the balls A and B were inductric _negative_, there +was discharge, still at both, but most at _n_, as if the small ball +_negative_ could discharge a little easier than the same ball _positive_. + +1498. The small balls and terminations used in these and similar +experiments may very correctly be compared, in their action, to the same +balls and ends when electrified in free air at a much greater distance from +conductors, than they were in those cases from each other. In the first +place, the discharge, even when as a spark, is, according to my view, +determined, and, so to speak, begins at a spot on the surface of the small +ball (1374.), occurring when the intensity there has risen up to a certain +maximum degree (1370.); this determination of discharge at a particular +spot first, being easily traced from the spark into the brush, by +increasing the distance, so as, at last, even to render the time evident +which is necessary for the production of the effect (1436. 1438.). In the +next place, the large balls which I have used might be replaced by larger +balls at a still greater distance, and so, by successive degrees, may be +considered as passing into the sides of the rooms; these being under +general circumstances the inducteous bodies, whilst the small ball rendered +either positive or negative is the inductric body. + +1499. But, as has long been recognised, the small ball is only a blunt end, +and, electrically speaking, a point only a small ball; so that when a point +or blunt end is throwing out its brushes into the air, it is acting exactly +as the small balls have acted in the experiments already described, and by +virtue of the same properties and relations. + +1500. It may very properly be said with respect to the experiments, that +the large negative ball is as essential to the discharge as the small +positive ball, and also that the large negative ball shows as much +superiority over the large positive ball (which is inefficient in causing a +spark from its opposed small negative ball) as the small positive ball does +over the small negative ball; and probably when we understand the real +cause of the difference, and refer it rather to the condition of the +particles of the dielectric than to the sizes of the conducting balls, we +may find much importance in such an observation. But for the present, and +whilst engaged in investigating the point, we may admit, what is the fact, +that the forces are of higher intensity at the surfaces of the smaller +balls than at those of the larger (1372. 1374.); that the former, +therefore, determine the discharge, by first rising up to that exalted +condition which is necessary for it; and that, whether brought to this +condition by induction towards the walls of a room or the large balls I +have used, these may fairly be compared one with the other in their +influence and actions. + +1501. The conclusions I arrive at are: first, that when two equal small +conducting surfaces equally placed in air are electrified, one positively +and the other negatively, that which is negative can discharge to the air +at a tension a little lower than that required for the positive ball: +second, that when discharge does take place, much more passes at each time +from the positive than from the negative surface (1491.). The last +conclusion is very abundantly proved by the optical analysis of the +positive and negative brushes already described (1468.), the latter set of +discharges being found to recur five or six times oftener than the +former[A]. + + [A] A very excellent mode of examining the relation of small positive + and negative surfaces would be by the use of drops of gum water, + solutions, or other liquids. See onwards (1581. 1593.). + +1502. If, now, a small ball be made to give brushes or brushy sparks by a +powerful machine, we can, in some measure, understand and relate the +difference perceived when it is rendered positive or negative. It is known +to give when positive a much larger and more powerful spark than when +negative, and with greater facility (1482.): in fact, the spark, although +it takes away so much more electricity at once, commences at a tension +higher only in a small degree, if at all. On the other hand, if rendered +negative, though discharge may commence at a lower degree, it continues but +for a very short period, very little electricity passing away each time. +These circumstances are directly related; for the extent to which the +positive spark can reach, and the size and extent of the positive brush, +are consequences of the capability which exists of much electricity passing +off at one discharge from the positive surface (1468. 1501.). + +1503. But to refer these effects only to the form and size of the +conductor, would, according to my notion of induction, be a very imperfect +mode of viewing the whole question (1523. 1600.). I apprehend that the +effects are due altogether to the mode in which the particles of the +interposed dielectric polarize, and I have already given some experimental +indications of the differences presented by different electrics in this +respect (1475. 1476.). The modes of polarization, as I shall have occasion +hereafter to show, may be very diverse in different dielectrics. With +respect to common air, what seems to be the consequence of a superiority in +the positive force at the surface of the small ball, may be due to the more +exalted condition of the negative polarity of the particles of air, or of +the nitrogen in it (the negative part being, perhaps, more compressed, +whilst the positive part is more diffuse, or _vice versa_ (1687. &c.)); for +such a condition could determine certain effects at the positive ball which +would not take place to the same degree at the negative ball, just as well +as if the positive ball had possessed some special and independent power of +its own. + +1504. The opinion, that the effects are more likely to be dependent upon +the dielectric than the ball, is supported by the character of the two +discharges. If a small positive ball be throwing off brushes with +ramifications ten inches long, how can the ball affect that part of a +ramification which is five inches from it? Yet the portion beyond that +place has the same character as that preceding it, and no doubt has that +character impressed by the same general principle and law. Looking upon the +action of the contiguous particles of a dielectric as fully proved, I see, +in such a ramification, a propagation of discharge from particle to +particle, each doing for the one next it what was done for it by the +preceding particle, and what was done for the first particle by the charged +metal against which it was situated. + +1505. With respect to the general condition and relations of the positive +and negative brushes in dense or rare air, or in other media and gases, if +they are produced at different times and places they are of course +independent of each other. But when they are produced from opposed ends or +balls at the same time, in the same vessel of gas (1470. 1477.), they are +frequently related; and circumstances may be so arranged that they shall be +isochronous, occurring in equal numbers in equal times; or shall occur in +multiples, i.e. with two or three negatives to one positive; or shall +alternate, or be quite irregular. All these variations I have witnessed; +and when it is considered that the air in the vessel, and also the glass of +the vessel, can take a momentary charge, it is easy to comprehend their +general nature and cause. + + * * * * * + +1506. Similar experiments to those in air (1485. 1493.) were made in +different gases, the results of which I will describe as briefly as +possible. The apparatus is represented fig. 131, consisting of a bell-glass +eleven inches in diameter at the widest part, and ten and a half inches +high up to the bottom of the neck. The balls are lettered, as in fig. 130, +and are in the same relation to each other; but A and B were on separate +sliding wires, which, however, were generally joined by a cross wire, _w_, +above, and that connected with the brass conductor, which received its +positive or negative charge from the machine. The rods of A and B were +graduated at the part moving through the stuffing-box, so that the +application of a diagonal scale applied there, told what was the distance +between these balls and those beneath them. As to the position of the balls +in the jar, and their relation to each other, C and D were three and a +quarter inches apart, their height above the pump plate five inches, and +the distance between any of the balls and the glass of the jar one inch and +three quarters at least, and generally more. The balls A and D were two +inches in diameter, as before (1493.); the balls B and C only 0.15 of an +inch in diameter. + +Another apparatus was occasionally used in connection with that just +described, being an open discharger (fig. 132.), by which a comparison of +the discharge in air and that in gases could be obtained. The balls E and +F, each 0.6 of an inch in diameter, were connected with sliding rods and +other balls, and were insulated. When used for comparison, the brass +conductor was associated at the same time with the balls A and B of figure +131 and ball E of this apparatus (fig. 132.); whilst the balls C, D and F +were connected with the discharging train. + +1507. I will first tabulate the results as to the _restraining power_ of +the gases over discharge. The balls A and C (fig. 131.) were thrown out of +action by distance, and the effects at B and D, or the interval _n_ in the +gas, compared with those at the interval _p_ in the air, between E and F +(fig. 132.). The Table sufficiently explains itself. It will be understood +that all discharge was in the air, when the interval there was less than +that expressed in the first or third columns of figures; and all the +discharge in the gas, when the interval in air was greater than that in the +second or fourth column of figures. At intermediate distances the discharge +was occasionally at both places, i.e. sometimes in the air, sometimes in +the gas. + + _____________________________________________________________________ +| | | +| | Interval _p_ in parts of an inch | +|_________________|___________________________________________________| +| | | | +| | When the small ball B | When the small ball B | +| Constant inter- | was inductric and | was inductric and | +| val _n_ between | _positive_ the | _negative_ the | +| B and D = 1 | discharge was all | discharge was all | +| inch | at _p_ in at _n_ in | at _p_ in at _n_ in | +| | air before the gas | air before the gas | +| | after | after | +|_________________|_________________________|_________________________| +| | _p_ = | _p_ = | _p_ = | _p_ = | +|In Air | 0.10 | 0.50 | 0.28 | 0.33 | +|In Nitrogen | 0.30 | 0.65 | 0.31 | 0.40 | +|In Oxygen | 0.33 | 0.52 | 0.27 | 0.30 | +|In Hydrogen | 0.20 | 0.10 | 0.22 | 0.24 | +|In Coal Gas | 0.20 | 0.90 | 0.20 | 0.27 | +|In Carbonic Acid | 0.61 | 1.30 | 0.30 | 0.15 | +|_________________|____________|____________|____________|____________| + +1508. These results are the same generally, as far as they go, as those of +the like nature in the last series (1388.), and confirm the conclusion that +different gases restrain discharge in very different proportions. They are +probably not so good as the former ones, for the glass jar not being +varnished, acted irregularly, sometimes taking a certain degree of charge +as a non-conductor, and at other times acting as a conductor in the +conveyance and derangement of that charge. Another cause of difference in +the ratios is, no doubt, the relative sizes of the discharge balls in air; +in the former case they were of very different size, here they were alike. + +1509. In future experiments intended to have the character of accuracy, the +influence of these circumstances ought to be ascertained, and, above all +things, the gases themselves ought to be contained in vessels of metal, and +not of glass. + + * * * * * + +1510. The next set of results are those obtained when the intervals _n_ and +_o_ (fig. 131.) were made equal to each other, and relate to the greater +facility of discharge at the small ball, when rendered positive or negative +(1493.). + +1511. In _air_, with the intervals = 0.4 of an inch, A and B being +inductric and positive, discharge was nearly equal at _n_ and _o_; when A +and B were inductric and negative, the discharge was mostly at _n_ by +negative brush. When the intervals were = 0.8 of an inch, with A and B +inductric positively, all discharge was at _n_ by positive brush; with A +and B inductric negatively, all the discharge was at _n_ by a negative +brush. It is doubtful, therefore, from these results, whether the negative +ball has any greater facility than the positive. + +1512. _Nitrogen._--Intervals _n_ and _o_ = 0.4 of an inch: A, B inductric +positive, discharge at both intervals, most at _n_, by positive sparks; A, +B inductric negative, discharge equal at _n_ and _o_. The intervals made = +0.8 of an inch: A, B inductric positive, discharge all at _n_ by positive +brush; A, B inductric negative, discharge most at _o_ by positive brush. In +this gas, therefore, though the difference is not decisive, it would seem +that the positive small ball caused the most ready discharge. + +1513. _Oxygen._--Intervals _n_ and _o_ = 0.4 of an inch: A, B inductric +positive, discharge nearly equal; inductric negative, discharge mostly at +_n_ by negative brush. Made the intervals = 0.8 of an inch: A, B inductric +positive, discharge both at _n_ and _o_; inductric negative, discharge all +at _o_ by negative brush. So here the negative small ball seems to give the +most ready discharge. + +1514. _Hydrogen._--Intervals _n_ and _o_ = 0.4 of an inch: A, B inductric +positive, discharge nearly equal: inductric negative, discharge mostly at +_o_. Intervals = 0.8 of an inch: A and B inductric positive, discharge +mostly at _n_, as positive brush; inductric negative, discharge mostly at +_o_, as positive brush. Here the positive discharge seems most facile. + +1515. _Coal gas._--_n_ and _o_ = 0.4 of an inch: A, B inductric positive, +discharge nearly all at _o_ by negative spark: A, B inductric negative, +discharge nearly all at _n_ by negative spark. Intervals = 0.8 of an inch, +and A, B inductric positive, discharge mostly at _o_ by negative brush: A, +B inductric negative, discharge all at _n_ by negative brush. Here the +negative discharge most facile. + +1516. _Carbonic acid gas._--_n_ and _o_ = 0.1 of an inch: A, B inductric +positive, discharge nearly all at _o_, or negative: A, B inductric +negative, discharge nearly all at _n_, or negative. Intervals = 0.8 of an +inch: A, B inductric positive, discharge mostly at _o_, or negative. A, B +inductric negative, discharge all at _n_, or negative. In this case the +negative had a decided advantage in facility of discharge. + +1517. Thus, if we may trust this form of experiment, the negative small +ball has a decided advantage in facilitating disruptive discharge over the +positive small ball in some gases, as in carbonic acid gas and coal gas +(1399.), whilst in others that conclusion seems more doubtful; and in +others, again, there seems a probability that the positive small ball may +be superior. All these results were obtained at very nearly the same +pressure of the atmosphere. + + * * * * * + +1518. I made some experiments in these gases whilst in the air jar (fig. +131.), as to the change from spark to brush, analogous to those in the open +air already described (1486. 1487.). I will give, in a Table, the results +as to when brush began to appear mingled with the spark; but the after +results were so varied, and the nature of the discharge in different gases +so different, that to insert the results obtained without further +investigation, would be of little use. At intervals less than those +expressed the discharge was always by spark. + + _______________________________________________________________________ +| | | | +| | Discharge between | Discharge between | +| | balls B and D. | balls A and C. | +| |___________________________|___________________________| +| | | | | | +| | Small ball | Small ball | Large ball | Large ball | +| | B inductric | B inductric | A inductric | A inductric | +| | _pos_. | _neg_. | _pos_. | _neg_. | +|_______________|_____________|_____________|_____________|_____________| +| | | | | | +| Air | 0.55 | 0.30 | 0.40 | 0.75 | +| Nitrogen | 0.30 | 0.40 | 0.52 | 0.41 | +| Oxygen | 0.70 | 0.30 | 0.45 | 0.82 | +| Hydrogen | 0.20 | 0.10 | | | +| Coal gas | 0.13 | 0.30 | 0.30 | 0.44 | +| Carbonic acid | 0.82 | 0.43 | 1.60 | {above 1.80;| +| | | | | had not | +| | | | | space.) | +|_______________|_____________|_____________|_____________|_____________| + +1519. It is to be understood that sparks occurred at much higher intervals +than these; the table only expresses that distance beneath which all +discharge was as spark. Some curious relations of the different gases to +discharge are already discernible, but it would be useless to consider them +until illustrated by further experiments. + + * * * * * + +1520. I ought not to omit noticing here, that Professor Belli of Milan has +published a very valuable set of experiments on the relative dissipation of +positive and negative electricity in the air[A]; he finds the latter far +more ready, in this respect, than the former. + + [A] Bibliotheque Universelle, 1836, September, p. 152. + +1521. I made some experiments of a similar kind, but with sustained high +charges; the results were less striking than those of Signore Belli, and I +did not consider them as satisfactory. I may be allowed to mention, in +connexion with the subject, an interfering effect which embarrassed me for +a long time. When I threw positive electricity from a given point into the +air, a certain intensity was indicated by an electrometer on the conductor +connected with the point, but as the operation continued this intensity +rose several degrees; then making the conductor negative with the same +point attached to it, and all other things remaining the same, a certain +degree of tension was observed in the first instance, which also gradually +rose as the operation proceeded. Returning the conductor to the positive +state, the tension was at first low, but rose as before; and so also when +again made negative. + +1522. This result appeared to indicate that the point which had been giving +off one electricity, was, by that, more fitted for a short time to give off +the other. But on closer examination I found the whole depended upon the +inductive reaction of that air, which being charged by the point, and +gradually increasing in quantity before it, as the positive or negative +issue was continued, diverted and removed a part of the inductive action of +the surrounding wall, and thus apparently affected the powers of the point, +whilst really it was the dielectric itself that was causing the change of +tension. + + * * * * * + +1523. The results connected with the different conditions of positive and +negative discharge will have a far greater influence on the philosophy of +electrical science than we at present imagine, especially if, as I believe, +they depend on the peculiarity and degree of polarized condition which the +molecules of the dielectrics concerned acquire (1503. 1600.). Thus, for +instance, the relation of our atmosphere and the earth within it, to the +occurrence of spark or brush, must be especial and not accidental (1464.). +It would not else consist with other meteorological phenomena, also of +course dependent on the special properties of the air, and which being +themselves in harmony the most perfect with the functions of animal and +vegetable life, are yet restricted in their actions, not by loose +regulations, but by laws the most precise. + +1524. Even in the passage through air of the voltaic current we see the +peculiarities of positive and negative discharge at the two charcoal +points; and if these discharges are made to take place simultaneously to +mercury, the distinction is still more remarkable, both as to the sound and +the quantity of vapour produced. + +1525. It seems very possible that the remarkable difference recently +observed and described by my friend Professor Daniell[A], namely, that when +a zinc and a copper ball, the same in size, were placed respectively in +copper and zinc spheres, also the same in size, and excited by electrolytes +or dielectrics of the same strength and nature, the zinc ball far surpassed +the zinc sphere in action, may also be connected with these phenomena; for +it is not difficult to conceive how the polarity of the particles shall be +affected by the circumstance of the positive surface, namely the zinc, +being the larger or the smaller of the two inclosing the electrolyte. It is +even possible, that with different electrolytes or dielectrics the ratio +may be considerably varied, or in some cases even inverted. + + [A] Philosophical Transactions, 1838, p. 47. + + * * * * * + +_Glow discharge._ + +1526. That form of disruptive discharge which appears as a _glow_ (1359. +1405.), is very peculiar and beautiful: it seems to depend on a quick and +almost continuous charging of the air close to, and in contact with, the +conductor. + +1527. _Diminution of the charging surface_ will produce it. Thus, when a +rod 0.3 of an inch in diameter, with a rounded termination, was rendered +positive in free air, it gave fine brushes from the extremity, but +occasionally these disappeared, and a quiet phosphorescent continuous glow +took their place, covering the whole of the end of the wire, and extending +a very small distance from the metal into the air. With a rod 0.2 of an +inch in diameter the glow was more readily produced. With still smaller +rods, and also with blunt conical points, it occurred still more readily; +and with a fine point I could not obtain the brush in free air, but only +this glow. The positive glow and the positive star are, in fact, the same. + +1528. _Increase of power in the machine_ tends to produce the glow; for +rounded terminations which will give only brushes when the machine is in +weak action, will readily give the glow when it is in good order. + +1529. _Rarefaction of the air_ wonderfully favours the glow phenomena. A +brass ball, two and a half inches in diameter, being made positively +inductric in an air-pump receiver, became covered with glow over an area of +two inches in diameter, when the pressure was reduced to 4.4 inches of +mercury. By a little adjustment the ball could be covered all over with +this light. Using a brass ball 1.25 inches in diameter, and making it +inducteously positive by an inductric negative point, the phenomena, at +high degrees of rarefaction, were exceedingly beautiful. The glow came over +the positive ball, and gradually increased in brightness, until it was at +last very luminous; and it also stood up like a low flame, half an inch or +more in height. On touching the sides of the glass jar this lambent flame +was affected, assumed a ring form, like a crown on the top of the ball, +appeared flexible, and revolved with a comparatively slow motion, i.e. +about four or five times in a second. This ring-shape and revolution are +beautifully connected with the mechanical currents (1576.) taking place +within the receiver. These glows in rarefied air are often highly exalted +in beauty by a spark discharge at the conductor (1551. _Note_.). + +1530. To obtain a _negative glow_ in air at common pressures is difficult. +I did not procure it on the rod 0.3 of an inch in diameter by my machine, +nor on much smaller rods; and it is questionable as yet, whether, even on +fine points, what is called the negative star is a very reduced and minute, +but still intermitting brush, or a glow similar to that obtained on a +positive point. + +1531. In rarefied air the negative glow can easily be obtained. If the +rounded ends of two metal rods, about O.2 of an inch in diameter, are +introduced into a globe or jar (the air within being rarefied), and being +opposite to each other, are about four inches apart, the glow can be +obtained on both rods, covering not only the ends, but an inch or two of +the part behind. On using _balls_ in the air-pump jar, and adjusting the +distance and exhaustion, the negative ball could be covered with glow, +whether it were the inductric or the inducteous surface. + +1532. When rods are used it is necessary to be aware that, if placed +concentrically in the jar or globe, the light on one rod is often reflected +by the sides of the vessel on to the other rod, and makes it apparently +luminous, when really it is not so. This effect may be detected by shifting +the eye at the time of observation, or avoided by using blackened rods. + +1533. It is curious to observe the relation _of glow, brush_, and _spark_ +to each other, as produced by positive or negative surfaces; thus, +beginning with spark discharge, it passes into brush much sooner when the +surface at which the discharge commences (1484.) is negative, than it does +when positive; but proceeding onwards in the order of change, we find that +the positive brush passes into _glow_ long before the negative brush does. +So that, though each presents the three conditions in the same general +order, the series are not precisely the same. It is probable, that, when +these points are minutely examined, as they must be shortly, we shall find +that each different gas or dielectric presents its own peculiar results, +dependent upon the mode in which its particles assume polar electric +condition. + +1534. The glow occurs in all gases in which I have looked for it. These are +air, nitrogen, oxygen, hydrogen, coal gas, carbonic acid, muriatic acid, +sulphurous acid and ammonia. I thought also that I obtained it in oil of +turpentine, but if so it was very dull and small. + +1535. The glow is always accompanied by a wind proceeding either directly +out from the glowing part, or directly towards it; the former being the +most general case. This takes place even when the glow occurs upon a ball +of considerable size: and if matters be so arranged that the ready and +regular access of air to a part exhibiting the glow be interfered with or +prevented, the glow then disappears. + +1536. I have never been able to analyse or separate the glow into visible +elementary intermitting discharges (1427. 1433.), nor to obtain the other +evidence of intermitting action, namely an audible sound (1431.). The want +of success, as respects trials made by ocular means, may depend upon the +large size of the glow preventing the separation of the visible images: +and, indeed, if it does intermit, it is not likely that all parts intermit +at once with a simultaneous regularity. + +1537. All the effects tend to show, that _glow_ is due to a continuous +charge or discharge of air; in the former case being accompanied by a +current from, and in the latter by one to, the place of the glow. As the +surrounding air comes up to the charged conductor, on attaining that spot +at which the tension of the particles is raised to the sufficient degree +(1370. 1410.), it becomes charged, and then moves off, by the joint action +of the forces to which it is subject; and, at the same time that it makes +way for other particles to come and be charged in turn, actually helps to +form that current by which they are brought into the necessary position. +Thus, through the regularity of the forces, a constant and quiet result is +produced; and that result is, the charging of successive portions of air, +the production of a current, and of a continuous glow. + +1538. I have frequently been able to make the termination of a rod, which, +when left to itself, would produce a brush, produce in preference a glow, +simply by aiding the formation of a current of air at its extremity; and, +on the other hand, it is not at all difficult to convert the glow into +brushes, by affecting the current of air (1574. 1579.) or the inductive +action near it. + +1539. The transition from glow, on the one hand, to brush and spark, on the +other, and, therefore, their connexion, may be established in various ways. +Those circumstances which tend to facilitate the charge of the air by the +excited conductor, and also those which tend to keep the tension at the +same degree notwithstanding the discharge, assist in producing the glow; +whereas those which tend to resist the charge of the air or other +dielectric, and those which favour the accumulation of electric force prior +to discharge, which, sinking by that act, has to be exalted before the +tension can again acquire the requisite degree, favour intermitting +discharge, and, therefore, the production of brush or spark. Thus, +rarefaction of the air, the removal of large conducting surfaces from the +neighbourhood of the glowing termination, the presentation of a sharp point +towards it, help to sustain or produce the glow: but the condensation of +the air, the presentation of the hand or other large surface, the gradual +approximation of a discharging ball, tend to convert the glow into brush or +even spark. All these circumstances may be traced and reduced, in a manner +easily comprehensible, to their relative power of assisting to produce, +either a _continuous_ discharge to the air, which gives the glow; or an +_interrupted_ one, which produces the brush, and, in a more exalted +condition, the spark. + +1540. The rounded end of a brass rod, 0.3 of an inch in diameter, was +covered with a positive glow by the working of an electrical machine: on +stopping the machine, so that the charge of the connected conductor should +fall, the glow changed for a moment into brushes just before the discharge +ceased altogether, illustrating the necessity for a certain high continuous +charge, for a certain sized termination. Working the machine so that the +intensity should be just low enough to give continual brushes from the end +in free air, the approach of a fine point changed these brushes into a +glow. Working the machine so that the termination presented a continual +glow in free air, the gradual approach of the hand caused the glow to +contract at the very end of the wire, then to throw out a luminous point, +which, becoming a foot stalk (1426.), finally produced brushes with large +ramifications. All these results are in accordance with what is stated +above (1539.). + +1541. Greasing the end of a rounded wire will immediately make it produce +brushes instead of glow. A ball having a blunt point which can be made to +project more or less beyond its surface, at pleasure, can be made to +produce every gradation from glow, through brush, to spark. + +1542. It is also very interesting and instructive to trace the transition +from spark to glow, through the intermediate condition of stream, between +ends in a vessel containing air more or less rarefied; but I fear to be +prolix. + +1543. All the effects show, that the glow is in its nature exactly the same +as the luminous part of a brush or ramification, namely a charging of air; +the only difference being, that the glow has a continuous appearance from +the constant renewal of the same action in the same place, whereas the +ramification is due to a momentary, independent and intermitting action of +the same kind. + + * * * * * + +_Dark discharge._ + +1544. I will now notice a very remarkable circumstance in the luminous +discharge accompanied by negative glow, which may, perhaps, be correctly +traced hereafter into discharges of much higher intensity. Two brass rods, +0.3 of an inch in diameter, entering a glass globe on opposite sides, had +their ends brought into contact, and the air about them very much rarefied. +A discharge of electricity from the machine was then made through them, and +whilst that was continued the ends were separated from each other. At the +moment of separation a continuous glow came over the end of the negative +rod, the positive termination remaining quite dark. As the distance was +increased, a purple stream or haze appeared on the end of the positive rod, +and proceeded directly outwards towards the negative rod; elongating as the +interval was enlarged, but never joining the negative glow, there being +always a short dark space between. This space, of about 1/16th or 1/20th of +an inch, was apparently invariable in its extent and its position, relative +to the negative rod; nor did the negative glow vary. Whether the negative +end were inductric or inducteous, the same effect was produced. It was +strange to see the positive purple haze diminish or lengthen as the ends +were separated, and yet this dark space and the negative glow remain +unaltered (fig. 133). + +1545. Two balls were then used in a large air-pump receiver, and the air +rarefied. The usual transitions in the character of the discharge took +place; but whenever the luminous stream, which appears after the spark and +the brush have ceased, was itself changed into glow at the balls, the dark +space occurred, and that whether the one or the other ball was made +inductric, or positive, or negative. + +1546. Sometimes when the negative ball was large, the machine in powerful +action, and the rarefaction high, the ball would be covered over half its +surface with glow, and then, upon a hasty observation, would seem to +exhibit no dark space: but this was a deception, arising from the +overlapping of the convex termination of the negative glow and the concave +termination of the positive stream. More careful observation and experiment +have convinced me, that when the negative glow occurs, it never visibly +touches the luminous part of the positive discharge, but that the dark +space is always there. + +1547. This singular separation of the positive and negative discharge, as +far as concerns their luminous character, under circumstances which one +would have thought very favourable to their coalescence, is probably +connected with their differences when in the form of brush, and is perhaps +even dependent on the same cause. Further, there is every likelihood that +the dark parts which occur in feeble sparks are also connected with these +phenomena[A]. To understand them would be very important, for it is quite +clear that in many of the experiments, indeed in all that I have quoted, +discharge is taking place across the dark part of the dielectric to an +extent quite equal to what occurs in the luminous part. This difference in +the result would seem to imply a distinction in the modes by which the two +electric forces are brought into equilibrium in the respective parts; and +looking upon all the phenomena as giving additional proofs, that it is to +the condition of the particles of the dielectric we must refer for the +principles of induction and discharge, so it would be of great importance +if we could know accurately in what the difference of action in the dark +and the luminous parts consisted. + + [A] See Professor Johnson's experiments. Silliman's Journal, xxv. p. 57. + +1548. The dark discharge through air (1552.), which in the case mentioned +is very evident (1544.), leads to the inquiry, whether the particles of air +are generally capable of effecting discharge from one to another without +becoming luminous; and the inquiry is important, because it is connected +with that degree of tension which is necessary to originate discharge +(1368. 1370.). Discharge between _air and conductors_ without luminous +appearances are very common; and non-luminous discharges by carrying +currents of air and other fluids (1562. 1595.) are also common enough: but +these are not cases in point, for they are not discharges between +insulating particles. + +1549. An arrangement was made for discharge between two balls (1485.) (fig. +129.) but, in place of connecting the inducteous ball directly with the +discharging train, it was put in communication with the inside coating of a +Leyden jar, and the discharging train with the outside coating. Then +working the machine, it was found that whenever sonorous and luminous +discharge occurred at the balls A B, the jar became charged; but that when +these did not occur, the jar acquired no charge: and such was the case when +small rounded terminations were used in place of the balls, and also in +whatever manner they were arranged. Under these circumstances, therefore, +discharge even between the air and conductors was always luminous. + +1550. But in other cases, the phenomena are such as to make it almost +certain, that dark discharge can take place across air. If the rounded end +of a metal rod, 0.15 of an inch in diameter, be made to give a good +negative brush, the approach of a smaller end or a blunt point opposite to +it will, at a certain distance, cause a diminution of the brush, and a glow +will appear on the positive inducteous wire, accompanied by a current of +air passing from it. Now, as the air is being charged both at the positive +and negative surfaces, it seems a reasonable conclusion, that the charged +portions meet somewhere in the interval, and there discharge to each other, +without producing any luminous phenomena. It is possible, however, that the +air electrified positively at the glowing end may travel on towards the +negative surface, and actually form that atmosphere into which the visible +negative brushes dart, in which case dark discharge need not, of necessity, +occur. But I incline to the former opinion, and think, that the diminution +in size of the negative brush, as the positive glow comes on to the end of +the opposed wire, is in favour of that view. + +1551. Using rarefied air as the dielectric, it is very easy to obtain +luminous phenomena as brushes, or glow, upon both conducting balls or +terminations, whilst the interval is dark, and that, when the action is so +momentary that I think we cannot consider currents as effecting discharge +across the dark part. Thus if two balls, about an inch in diameter, and 4 +or more inches apart, have the air rarefied about them, and are then +interposed in the course of discharge, an interrupted or spark current +being produced at the machine[A], each termination may be made to show +luminous phenomena, whilst more or less of the interval is quite dark. The +discharge will pass as suddenly as a retarded spark (295. 334.), i.e. in an +interval of time almost inappreciably small, and in such a case, I think it +must have passed across the dark part as true disruptive discharge, and not +by convection. + + [A] By spark current I mean one passing in a series of spark between + the conductor of the machine and the apparatus: by a continuous + current one that passes through metallic conductors, and in that + respect without interruption at the same place. + +1552. Hence I conclude that dark disruptive discharge may occur (1547. +1550.); and also, that, in the luminous brush, the visible ramifications +may not show the full extent of the disruptive discharge (1444. 1452.), but +that each may have a dark outside, enveloping, as it were, every part +through which the discharge extends. It is probable, even, that there are +such things as dark discharges analogous in form to the brush and the +spark, but not luminous in any part (1445.). + +1553. The occurrence of dark discharge in any case shows at how low a +tension disruptive discharge may occur (1548,), and indicates that the +light of the ultimate brush or spark is in no relation to the intensity +required (1368. 1370.). So to speak, the discharge begins in darkness, and +the light is a mere consequence of the quantity which, after discharge has +commenced, flows to that spot and there finds its most facile passage +(1418. 1435.). As an illustration of the growth generally of discharge, I +may remark that, in the experiments on the transition in oxygen of the +discharge from spark to brush (1518.), every spark was immediately preceded +by a short brush. + +1554. The phenomena relative to dark discharge in other gases, though +differing in certain characters from those in air, confirm the conclusions +drawn above. The two rounded terminations (1544.) (fig. 133.), were placed +in _muriatic acid gas_ (1445. 1463.) at the pressure of 6.5 inches of +mercury, and a continuous machine current of electricity sent through the +apparatus: bright sparks occurred until the interval was about or above an +inch, when they were replaced by squat brushy intermitting glows upon both +terminations, with a dark part between. When the current at the machine was +in spark, then each spark caused a discharge across the muriatic acid gas, +which, with a certain interval, was bright; with a larger interval, was +straight across and flamy, like a very exhausted and sudden, but not a +dense sharp spark; and with a still larger interval, produced a feeble +brush on the inductric positive end, and a glow on the inducteous negative +end, the dark part being between (1544.); and at such times, the spark at +the conductor, instead of being sudden and sonorous, was dull and quiet +(334.). + +1555. On introducing more muriatic acid gas, until the pressure was 29.97 +inches, the same terminations gave bright sparks within at small distances; +but when they were about an inch or more apart, the discharge was generally +with very small brushes and glow, and frequently with no light at all, +though electricity had passed through the gas. Whenever the bright spark +did pass through the muriatic acid gas at this pressure, it was bright +throughout, presenting no dark or dull space. + +1556. In _coal gas_, at common pressures, when the distance was about an +inch, the discharge was accompanied by short brushes on the ends, and a +dark interval of half an inch or more between them, notwithstanding the +discharge had the sharp quick sound of a dull spark, and could not have +depended in the dark part on _convection_ (1562.). + +1557. This gas presents several curious points in relation to the bright +and dark parts of spark discharge. When bright sparks passed between the +rod ends 0.3 of an inch in diameter (1544.), very sudden dark parts would +occur next to the brightest portions of the spark. Again with these ends +and also with balls (1422.), the bright sparks would be sometimes red, +sometimes green, and occasionally green and red in different parts of the +same spark. Again, in the experiments described (1518.), at certain +intervals a very peculiar pale, dull, yet sudden discharge would pass, +which, though apparently weak, was very direct in its course, and +accompanied by a sharp snapping noise, as if quick in its occurrence. + +1558. _Hydrogen_ frequently gave peculiar sparks, one part being bright +red, whilst the other was a dull pale gray, or else the whole spark was +dull and peculiar. + +1559. _Nitrogen_ presents a very remarkable discharge, between two balls of +the respective diameters of 0.15 and 2 inches (1506. 1518.), the smaller +one being rendered negative either directly inducteously. The peculiar +discharge occurs at intervals between 0.42 and 0.68, and even at 1.4 inches +when the large ball was inductric positively; it consisted of a little +brushy part on the small negative ball, then a dark space, and lastly a +dull straight line on the large positive ball (fig. 134.). The position of +the dark space was very constant, and is probably in direct relation to the +dark space described when negative glow was produced (1544.). When by any +circumstance a bright spark was determined, the contrast with the peculiar +spark described was very striking; for it always had a faint purple part, +but the place of this part was constantly near the positive ball. + +1560. Thus dark discharge appears to be decidedly established. But its +establishment is accompanied by proofs that it occurs in different degrees +and modes in different gases. Hence then another specific action, added to +the many (1296. 1398. 1399. 1423. 1454. 1503.) by which the electrical +relations of insulating dielectrics are distinguished and established, and +another argument in favour of that molecular theory of induction, which is +at present under examination[A]. + + [A] I cannot resist referring here by a note to Biot's philosophical + view of the nature of the light of the electric discharge, Annales de + Chimie, liii. p. 321. + + * * * * * + +1561. What I have had to say regarding disruptive discharge has extended to +some length, but I hope will be excused in consequence of the importance of +the subject. Before concluding my remarks, I will again intimate in the +form of a query, whether we have not reason to consider the tension or +retention and after discharge in air or other insulating dielectrics, as +the same thing with retardation and discharge in a metal wire, differing +only, but almost infinitely, in degree (1334. 1336.). In other words, can +we not, by a gradual chain of association, carry up discharge from its +occurrence in air, through spermaceti and water, to solutions, and then on +to chlorides, oxides and metals, without any essential change in its +character; and, at the same time, connecting the insensible conduction of +air, through muriatic acid gas and the dark discharge, with the better +conduction of spermaceti, water, and the all but perfect conduction of the +metals, associate the phenomena at both extremes? and may it not be, that +the retardation and ignition of a wire are effects exactly correspondent in +their nature to the retention of charge and spark in air? If so, here again +the two extremes in property amongst dielectrics will be found to be in +intimate relation, the whole difference probably depending upon the mode +and degree in which their particles polarize under the influence of +inductive actions (1338. 1603. 1610.). + + * * * * * + +P x. _Convection, or carrying discharge._ + +1562. The last kind of discharge which I have to consider is that effected +by the motion of charged particles from place to place. It is apparently +very different in its nature to any of the former modes of discharge +(1319.), but, as the result is the same, may be of great importance in +illustrating, not merely the nature of discharge itself, but also of what +we call the electric current. It often, as before observed, in cases of +brush and glow (1440. 1535.), joins its effect to that of disruptive +discharge, to complete the act of neutralization amongst the electric +forces. + +1563. The particles which being charged, then travel, may be either of +insulating or conducting matter, large or small. The consideration in the +first place of a large particle of conducting matter may perhaps help our +conceptions. + +1564. A copper boiler 3 feet in diameter was insulated and electrified, but +so feebly, that dissipation by brushes or disruptive discharge did not +occur at its edges or projecting parts in a sensible degree. A brass ball, +2 inches in diameter, suspended by a clean white silk thread, was brought +towards it, and it was found that, if the ball was held for a second or two +near any part of the charged surface of the boiler, at such distance (two +inches more or less) as not to receive any direct charge from it, it became +itself charged, although insulated the whole time; and its electricity was +the _reverse_ of that of the boiler. + +1565. This effect was the strongest opposite the edges and projecting parts +of the boiler, and weaker opposite the sides, or those extended portions of +the surface which, according to Coulomb's results, have the weakest charge. +It was very strong opposite a rod projecting a little way from the boiler. +It occurred when the copper was charged negatively as well as positively: +it was produced also with small balls down to 0.2 of an inch and less in +diameter, and also with smaller charged conductors than the copper. It is, +indeed, hardly possible in some cases to carry an insulated ball within an +inch or two of a charged plane or convex surface without its receiving a +charge of the contrary kind to that of the surface. + +1566. This effect is one of induction between the bodies, not of +communication. The ball, when related to the positive charged surface by +the intervening dielectric, has its opposite sides brought into contrary +states, that side towards the boiler being negative and the outer side +positive. More inductric action is directed towards it than would have +passed across the same place if the ball had not been there, for several +reasons; amongst others, because, being a conductor, the resistance of the +particles of the dielectric, which otherwise would have been there, is +removed (1298.); and also, because the reacting positive surface of the +ball being projected further out from the boiler than when there is no +introduction of conducting matter, is more free therefore to act through +the rest of the dielectric towards surrounding conductors, and so favours +the exaltation of that inductric polarity which is directed in its course. +It is, as to the exaltation of force upon its outer surface beyond that +upon the inductric surface of the boiler, as if the latter were itself +protuberant in that direction. Thus it acquires a state like, but higher +than, that of the surface of the boiler which causes it; and sufficiently +exalted to discharge at its positive surface to the air, or to affect small +particles, as it is itself affected by the boiler, and they flying to it, +take a charge and pass off; and so the ball, as a whole, is brought into +the contrary inducteous state. The consequence is, that, if free to move, +its tendency, under the influence of all the forces, to approach the boiler +is increased, whilst it at the same time becomes more and more exalted in +its condition, both of polarity and charge, until, at a certain distance, +discharge takes place, it acquires the same state as the boiler, is +repelled, and passing to that conductor most favourably circumstanced to +discharge it, there resumes its first indifferent condition. + +1567. It seems to me, that the manner in which inductric bodies affect +uncharged floating or moveable conductors near them, is very frequently of +this nature, and generally so when it ends in a carrying operation (1562. +1602.). The manner in which, whilst the dominant inductric body cannot give +off its electricity to the air, the inducteous body _can_ effect the +discharge of the same kind of force, is curious, and, in the case of +elongated or irregularly shaped conductors, such as filaments or particles +of dust, the effect will often be very ready, and the consequent attraction +immediate. + +1568. The effect described is also probably influential in causing those +variations in spark discharge referred to in the last series (1386. 1390. +1391.): for if a particle of dust were drawn towards the axis of induction +between the balls, it would tend, whilst at some distance from that axis, +to commence discharge at itself, in the manner described (1566.), and that +commencement might so far facilitate the act (1417. 1420.) as to make the +complete discharge, as spark, pass through the particle, though it might +not be the shortest course from ball to ball. So also, with equal balls at +equal distances, as in the experiments of comparison already described +(1493. 1506.), a particle being between one pair of balls would cause +discharge there in preference; or even if a particle were between each, +difference of size or shape would give one for the time a predominance over +the other. + +1569. The power of particles of dust to carry off electricity in cases of +high tension is well known, and I have already mentioned some instances of +the kind in the use of the inductive apparatus (1201.). The general +operation is very well shown by large light objects, as the toy called the +electrical spider; or, if smaller ones are wanted for philosophical +investigation, by the smoke of a glowing green wax taper, which, presenting +a successive stream of such particles, makes their course visible. + +1570. On using oil of turpentine as the dielectric, the action and course +of small conducting carrying particles in it can be well observed. A few +short pieces of thread will supply the place of carriers, and their +progressive action is exceedingly interesting. + +1571. A very striking effect was produced on oil of turpentine, which, +whether it was due to the carrying power of the particles in it, or to any +other action of them, is perhaps as yet doubtful. A portion of that fluid +in a glass vessel had a large uninsulated silver dish at the bottom, and an +electrified metal rod with a round termination dipping into it at the top. +The insulation was very good, and the attraction and other phenomena +striking. The rod end, with a drop of gum water attached to it, was then +electrified in the fluid; the gum water soon spun off in fine threads, and +was quickly dissipated through the oil of turpentine. By the time that four +drops had in this way been commingled with a pint of the dielectric, the +latter had lost by far the greatest portion of its insulating power; no +sparks could be obtained in the fluid; and all the phenomena dependent upon +insulation had sunk to a low degree. The fluid was very slightly turbid. +Upon being filtered through paper only, it resumed its first clearness, and +now insulated as well as before. The water, therefore, was merely diffused +through the oil of turpentine, not combined with or dissolved in it: but +whether the minute particles acted as carriers, or whether they were not +rather gathered together in the line of highest inductive tension (1350.), +and there, being drawn into elongated forms by the electric forces, +combined their effects to produce a band of matter having considerable +conducting power, as compared with the oil of turpentine, is as yet +questionable. + +1572. The analogy between the action of solid conducting carrying particles +and that of the charged particles of fluid insulating substances, acting as +dielectrics, is very evident and simple; but in the latter case the result +is, necessarily, currents in the mobile media. Particles are brought by +inductric action into a polar state; and the latter, after rising to a +certain tension (1370.), is followed by the communication of a part of the +force originally on the conductor; the particles consequently become +charged, and then, under the joint influence of the repellent and +attractive forces, are urged towards a discharging place, or to that spot +where these inductric forces are most easily compensated by the contrary +inducteous forces. + +1573. Why a point should be so exceedingly favourable to the production of +currents in a fluid insulating dielectric, as air, is very evident. It is +at the extremity of the point that the intensity necessary to charge the +air is first acquired (1374.); it is from thence that the charged particle +recedes; and the mechanical force which it impresses on the air to form a +current is in every way favoured by the shape and position of the rod, of +which the point forms the termination. At the same time, the point, having +become the origin of an active mechanical force, does, by the very act of +causing that force, namely, by discharge, prevent any other part of the rod +from acquiring the same necessary condition, and so preserves and sustains +its own predominance. + +1574. The very varied and beautiful phenomena produced by sheltering or +enclosing the point, illustrate the production of the current exceedingly +well, and justify the same conclusions; it being remembered that in such +cases the effect upon the discharge is of two kinds. For the current may be +interfered with by stopping the access of fresh uncharged air, or retarding +the removal of that which has been charged, as when a point is electrified +in a tube of insulating matter closed at one extremity; or the _electric +condition_ of the point itself may be altered by the relation of other +parts in its neighbourhood, also rendered electric, as when the point is in +a metal tube, by the metal itself, or when it is in the glass tube, by a +similar action of the charged parts of the glass, or even by the +surrounding air which has been charged, and which cannot escape. + +1575. Whenever it is intended to observe such inductive phenomena in a +fluid dielectric as have a direct relation to, and dependence upon, the +fluidity of the medium, such, for instance, as discharge from points, or +attractions and repulsions, &c., then the mass of the fluid should be +great, and in such proportion to the distance between the inductric and +inducteous surfaces as to include all the _lines of inductive force_ +(1369.) between them; otherwise, the effects of currents, attraction, &c., +which are the resultants of all these forces, cannot be obtained. The +phenomena, which occur in the open air, or in the middle of a globe filled +with oil of turpentine, will not take place in the same media if confined +in tubes of glass, shell-lac, sulphur, or other such substances, though +they be excellent insulating dielectrics; nor can they be expected: for in +such cases, the polar forces, instead of being all dispersed amongst fluid +particles, which tend to move under their influence, are now associated in +many parts with particles that, notwithstanding their tendency to motion, +are constrained by their solidity to remain quiescent. + +1576. The varied circumstances under which, with conductors differently +formed and constituted, currents can occur, all illustrate the same +simplicity of production. A _ball_, if the intensity be raised sufficiently +on its surface, and that intensity be greatest on a part consistent with +the production of a current of air up to and off from it, will produce the +effect like a point (1537); such is the case whenever the glow occurs upon +a ball, the current being essential to that phenomenon. If as large a +sphere as can well be employed with the production of glow be used, the +glow will appear at the place where the current leaves the ball, and that +will be the part directly opposite to the connection of the ball and rod +which supports it; but by increasing the tension elsewhere, so as to raise +it above the tension upon that spot, which can easily be effected +inductively, then the place of the glow and the direction of the current +will also change, and pass to that spot which for the time is most +favourable for their production (1591.). + +1577. For instance, approaching the hand towards the ball will tend to +cause brush (1539.), but by increasing the supply of electricity the +condition of glow may be preserved; then on moving the hand about from side +to side the position of the glow will very evidently move with it. + +1578. A point brought towards a glowing ball would at twelve or fourteen +inches distance make the glow break into brush, but when still nearer, glow +was reproduced, probably dependent upon the discharge of wind or air +passing from the point to the ball, and this glow was very obedient to the +motion of the point, following it in every direction. + +1579. Even a current of wind could affect the place of the glow; for a +varnished glass tube being directed sideways towards the ball, air was +sometimes blown through it at the ball and sometimes not. In the former +case, the place of the glow was changed a little, as if it were blown away +by the current, and this is just the result which might have been +anticipated. All these effects illustrate beautifully the general causes +and relations, both of the glow and the current of air accompanying it +(1574.). + +1580. Flame facilitates the production of a current in the dielectric +surrounding it. Thus, if a ball which would not occasion a current in the +air have a flame, whether large or small, formed on its surface, the +current is produced with the greatest ease; but not the least difficulty +can occur in comprehending the effective action of the flame in this case, +if its relation, as part of the surrounding dielectric, to the electrified +ball, be but for a moment considered (1375. 1380.). + +1581. Conducting fluid terminations, instead of rigid points, illustrate in +a very beautiful manner the formation of the currents, with their effects +and influence in exalting the conditions under which they were commenced. +Let the rounded end of a brass rod, 0.3 of an inch or thereabouts in +diameter, point downwards in free air; let it be amalgamated, and have a +drop of mercury suspended from it; and then let it be powerfully +electrized. The mercury will present the phenomenon of _glow_; a current of +air will rush along the rod, and set off from the mercury directly +downwards; and the form of the metallic drop will be slightly affected, the +convexity at a small part near the middle and lower part becoming greater, +whilst it diminishes all round at places a little removed from this spot. +The change is from the form of _a_ (fig. 135.) to that of _b_, and is due +almost, if not entirely, to the mechanical force of the current of air +sweeping over its surface. + +1582. As a comparative observation, let it be noticed, that a ball +gradually brought towards it converts the glow into brushes, and ultimately +sparks pass from the most projecting part of the mercury. A point does the +same, but at much smaller distances. + +1583. Take next a drop of strong solution of muriate of lime; being +electrified, a part will probably be dissipated, but a considerable +portion, if the electricity be not too powerful, will remain, forming a +conical drop (fig. 136.), accompanied by a strong current. If glow be +produced, the drop will be smooth on the surface. If a short low brush is +formed, a minute tremulous motion of the liquid will be visible; but both +effects coincide with the principal one to be observed, namely, the regular +and successive charge of air, the formation of a wind or current, and the +form given by that current to the fluid drop, if a discharge ball be +gradually brought toward the cone, sparks will at last pass, and these will +be from the apex of the cone to the approached ball, indicating a +considerable degree of conducting power in this fluid. + +1584. With a drop of water, the effects were of the same kind, and were +best obtained when a portion of gum water or of syrup hung from a ball +(fig. 137.). When the machine was worked slowly, a fine large quiet conical +drop, with concave lateral outline, and a small rounded end, was produced, +on which the glow appeared, whilst a steady wind issued, in a direction +from the point of the cone, of sufficient force to depress the surface of +uninsulated water held opposite to the termination. When the machine was +worked more rapidly some of the water was driven off; the smaller pointed +portion left was roughish on the surface, and the sound of successive brush +discharges was heard. With still more electricity, more water was +dispersed; that which remained was elongated and contracted, with an +alternating motion; a stronger brush discharge was heard, and the +vibrations of the water and the successive discharges of the individual +brushes were simultaneous. When water from beneath was brought towards the +drop, it did not indicate the same regular strong contracted current of air +as before; and when the distance was such that sparks passed, the water +beneath was _attracted_ rather than driven away, and the current of air +_ceased_. + +1585. When the discharging ball was brought near the drop in its first +quiet glowing state (1582.), it converted that glow into brushes, and +caused the vibrating motion of the drop. When still nearer, sparks passed, +but they were always from the metal of the rod, over the surface of the +water, to the point, and then across the air to the ball. This is a natural +consequence of the deficient conducting power of the fluid (1584. 1585.). + +1586. Why the drop vibrated, changing its form between the periods of +discharging brushes, so as to be more or less acute at particular instants, +to be most acute when the brush issued forth, and to be isochronous in its +action, and how the quiet glowing liquid drop, on assuming the conical +form, facilitated, as it were, the first action, are points, as to theory, +so evident, that I will not stop to speak of them. The principal thing to +observe at present is, the formation of the carrying current of air, and +the manner in which it exhibits its existence and influence by giving form +to the drop. + +1587. That the drop, when of water, or a better conductor than water, is +formed into a cone principally by the current of air, is shown amongst +other ways (1594.) thus. A sharp point being held opposite the conical +drop, the latter soon lost its pointed form; was retraced and became round; +the current of air from it ceased, and was replaced by one from the point +beneath, which, if the latter were held near enough to the drop, actually +blew it aside, and rendered it concave in form. + +1588. It is hardly necessary to say what happened with still worse +conductors than water, as oil, or oil of turpentine; the fluid itself was +then spun out into threads and carried off, not only because the air +rushing over its surface helped to sweep it away, but also because its +insulating particles assumed the same charged state as the particles of +air, and, not being able to discharge to them in a much greater decree than +the air particles themselves could do, were carried off by the same causes +which urged those in their course. A similar effect with melted sealing-wax +on a metal point forms an old and well-known experiment. + +1589. A drop of gum water in the exhausted receiver of the air-pump was not +sensibly affected in its form when electrified. When air was let in, it +begun to show change of shape when the pressure was ten inches of mercury. +At the pressure of fourteen or fifteen inches the change was more sensible, +and as the air increased in density the effects increased, until they were +the same as those in the open atmosphere. The diminished effect in the rare +air I refer to the relative diminished energy of its current; that +diminution depending, in the first place, on the lower electric condition +of the electrified ball in the rarefied medium, and in the next, on the +attenuated condition of the dielectric, the cohesive force of water in +relation to rarefied air being something like that of mercury to dense air +(1581.), whilst that of water in dense air may be compared to that of +mercury in oil of turpentine (1597.). + +1590. When a ball is covered with a thick conducting fluid, as treacle or +syrup, it is easy by inductive action to determine the wind from almost any +part of it (1577.); the experiment, which before was of rather difficult +performance, being rendered facile in consequence of the fluid enabling +that part, which at first was feeble in its action, to rise into an exalted +condition by assuming a pointed form. + +1591. To produce the current, the electric intensity must rise and continue +at _one spot_, namely, at the origin of the current, higher than elsewhere, +and then, air having a uniform and ready access, the current is produced. +If no current be allowed (1574.), then discharge may take place by brush or +spark. But whether it be by brush or spark, or wind, it seems very probable +that the initial intensity or tension at which a particle of a given +gaseous dielectric charges, or commences discharge, is, under the +conditions before expressed, always the same (1410.). + +1592. It is not supposed that all the air which enters into motion is +electrified; on the contrary, much that is not charged is carried on into +the stream. The part which is really charged may be but a small proportion +of that which is ultimately set in motion (1442.). + + +1593. When a drop of gum water (1584.) is made _negative_, it presents a +larger cone than when made positive; less of the fluid is thrown off, and +yet, when a ball is approached, sparks can hardly be obtained, so pointed +is the cone, and so free the discharge. A point held opposite to it did not +cause the retraction of the cone to such an extent as when it was positive. +All the effects are so different from those presented by the positive cone, +that I have no doubt such drops would present a very instructive method of +investigating the difference of positive and negative discharge in air and +other dielectrics (1480. 1501.). + +1594. That I may not be misunderstood (1587.), I must observe here that I +do not consider the cones produced as the result _only_ of the current of +air or other insulating dielectric over their surface. When the drop is of +badly conducting matter, a part of the effect is due to the electrified +state of the particles, and this part constitutes almost the whole when the +matter is melted sealing-wax, oil of turpentine, and similar insulating +bodies (1588.). But even when the drop is of good conducting matter, as +water, solutions, or mercury, though the effect above spoken of will then +be insensible (1607.), still it is not the mere current of air or other +dielectric which produces all the change of form; for a part is due to +those attractive forces by which the charged drop, if free to move, would +travel along the line of strongest induction, and not being free to move, +has its form elongated until the _sum_ of the different forces tending to +produce this form is balanced by the cohesive attraction of the fluid. The +effect of the attractive forces are well shown when treacle, gum water, or +syrup is used; for the long threads which spin out, at the same time that +they form the axes of the currents of air, which may still be considered as +determined at their points, are like flexible conductors, and show by their +directions in what way the attractive forces draw them. + +1595. When the phenomena of currents are observed in dense insulating +dielectrics, they present us with extraordinary degrees of mechanical +force. Thus, if a pint of well-rectified and filtered (1571.) oil of +turpentine be put into a glass vessel, and two wires be dipped into it in +different places, one leading to the electrical machine, and the other to +the discharging train, on working the machine the fluid will be thrown into +violent motion throughout its whole mass, whilst at the same time it will +rise two, three or four inches up the machine wire, and dart off jets from +it into the air. + +1596. If very clean uninsulated mercury be at the bottom of the fluid, and +the wire from the machine be terminated either by a ball or a point, and +also pass through a glass tube extending both above and below the surface +of the oil of turpentine, the currents can be better observed, and will be +seen to rush down the wire, proceeding directly from it towards the +mercury, and there, diverging in all directions, will ripple its surface +strongly, and mounting up at the sides of the vessel, will return to +re-enter upon their course. + +1597. A drop of mercury being suspended from an amalgamated brass ball, +preserved its form almost unchanged in air (1581.); but when immersed in +the oil of turpentine it became very pointed, and even particles of the +metal could be spun out and carried off by the currents of the dielectric. +The form of the liquid metal was just like that of the syrup in air +(1584.), the point of the cone being quite as fine, though not so long. By +bringing a sharp uninsulated point towards it, it could also be effected in +the same manner as the syrup drop in air (1587.), though not so readily, +because of the density and limited quantity of the dielectric. + +1598. If the mercury at the bottom of the fluid be connected with the +electrical machine, whilst a rod is held in the hand terminating in a ball +three quarters of an inch, less or more, in diameter, and the ball be +dipped into the electrified fluid, very striking appearances ensue. When +the ball is raised again so as to be at a level nearly out of the fluid, +large portions of the latter will seem to cling to it (fig. 138.). If it be +raised higher, a column of the oil of turpentine will still connect it with +that in the basin below (fig. 139.). If the machine be excited into more +powerful action, this will become more bulky, and may then also be raised +higher, assuming the form (fig. 140); and all the time that these effects +continue, currents and counter-currents, sometimes running very close +together, may be observed in the raised column of fluid. + +1599. It is very difficult to decide by sight the direction of the currents +in such experiments as these. If particles of silk are introduced they +cling about the conductors; but using drops of water and mercury the course +of the fluid dielectric seems well indicated. Thus, if a drop of water be +placed at the end of a rod (1571.) over the uninsulated mercury, it is soon +swept away in particles streaming downwards towards the mercury. If another +drop be placed on the mercury beneath the end of the rod, it is quickly +dispersed in all directions in the form of streaming particles, the +attractive forces drawing it into elongated portions, and the currents +carrying them away. If a drop of mercury be hung from a ball used to raise +a column of the fluid (1598.), then the shape of the drop seems to show +currents travelling in the fluid in the direction indicated by the arrows +(fig. 141.). + +1600. A very remarkable effect is produced on these phenomena, connected +with positive and negative charge and discharge, namely, that a ball +charged positively raises a much higher and larger column of the oil of +turpentine than when charged negatively. There can be no doubt that this is +connected with the difference of positive and negative action already +spoken of (1480. 1525.), and tends much to strengthen the idea that such +difference is referable to the particles of the dielectric rather than to +the charged conductors, and is dependent upon the mode in which these +particles polarize (1503. 1523.). + +1601. Whenever currents travel in insulating dielectrics they really effect +discharge; and it is important to observe, though a very natural result, +that it is indifferent which way the current or particles travel, as with +reversed direction their state is reversed. The change is easily made, +either in air or oil of turpentine, between two opposed rods, for an +insulated ball being placed in connexion with either rod and brought near +its extremity, will cause the current to set towards it from the opposite +end. + +1602. The two currents often occur at once, as when both terminations +present brushes, and frequently when they exhibit the glow (1531.). In such +cases, the charged particles, or many of them, meet and mutually discharge +each other (1518. 1612.). If a smoking wax taper be held at the end of an +insulating rod towards a charged prime conductor, it will very often happen +that two currents will form, and be rendered visible by its vapour, one +passing as a fine filament of smoky particles directly to the charged +conductor, and the other passing as directly from the same taper wick +outwards, and from the conductor: the principles of inductric action and +charge, which were referred to in considering the relation of a carrier +ball and a conductor (1566.), being here also called into play. + + * * * * * + +1603. The general analogy and, I think I may say, identity of action found +to exist as to insulation and conduction (1338. 1561.) when bodies, the +best and the worst in the classes of insulators or conductors, were +compared, led me to believe that the phenomena of _convection_ in badly +conducting media were not without their parallel amongst the best +conductors, such even as the metals. Upon consideration, the cones produced +by Davy[A] in fluid metals, as mercury and tin, seemed to be cases in +point, and probably also the elongation of the metallic medium through +which a current of electricity was passing, described by Ampere (1113)[B]; +for it is not difficult to conceive, that the diminution of convective +effect, consequent upon the high conducting power of the metallic media +used in these experiments, might be fully compensated for by the enormous +quantity of electricity passing. In fact, it is impossible not to expect +_some_ effect, whether sensible or not, of the kind in question, when such +a current is passing through a fluid offering a sensible resistance to the +passage of the electricity, and, thereby, giving proof of a certain degree +of insulating power (1328.). + + [A] Philosophical Transactions, 1823, p. 155. + + [B] Bibliotheque Universelle, xxi, 417. + +1604. I endeavoured to connect the convective currents in air, oil of +turpentine, &c. and those in metals, by intermediate cases, but found this +not easy to do. On taking bodies, for instance, which, like water, adds, +solutions, fused salts or chlorides, &c., have intermediate conducting +powers, the minute quantity of electricity which the common machine can +supply (371. 861.) is exhausted instantly, so that the cause of the +phenomenon is kept either very low in intensity, or the instant of time +during which the effect lasts is so small, that one cannot hope to observe +the result sought for. If a voltaic battery be used, these bodies are all +electrolytes, and the evolution of gas, or the production of other changes, +interferes and prevents observation of the effect required. + +1605. There are, nevertheless, some experiments which illustrate the +connection. Two platina wires, forming the electrodes of a powerful voltaic +battery, were placed side by side, near each other, in distilled water, +hermetically sealed up in a strong glass tube, some minute vegetable fibres +being present in the water. When, from the evolution of gas and the +consequent increased pressure, the bubbles formed on the electrodes were so +small as to produce but feebly ascending currents, then it could be +observed that the filaments present were attracted and repelled between the +two wires, as they would have been between two oppositely charged surfaces +in air or oil of turpentine, moving so quickly as to displace and disturb +the bubbles and the currents which these tended to form. Now I think it +cannot be doubted, that under similar circumstances, and with an abundant +supply of electricity, of sufficient tension also, convective currents +might have been formed; the attractions and repulsions of the filaments +were, in fact, the elements of such currents (1572.), and therefore water, +though almost infinitely above air or oil of turpentine as a conductor, is +a medium in which similar currents can take place. + +1606. I had an apparatus made (fig. 142.) in which _a_ is a plate of +shell-lac, _b_ a fine platina wire passing through it, and having only the +section of the wire exposed above; _c_ a ring of bibulous paper resting on +the shell-lac, and _d_ distilled water retained by the paper in its place, +and just sufficient in quantity to cover the end of the wire _b_; another +wire, _e_, touched a piece of tinfoil lying in the water, and was also +connected with a discharging train; in this way it was easy, by rendering +_b_ either positive or negative, to send a current of electricity by its +extremity into the fluid, and so away by the wire _e_. + +1607. On connecting _b_ with the conductor of a powerful electrical +machine, not the least disturbance of the level of the fluid over the end +of the wire during the working of the machine could be observed; but at the +same time there was not the smallest indication of electrical charge about +the conductor of the machine, so complete was the discharge. I conclude +that the quantity of electricity passed in a _given time_ had been too +small, when compared with the conducting power of the fluid to produce the +desired effect. + +1608. I then charged a large Leyden battery (291.), and discharged it +through the wire _b_, interposing, however, a wet thread, two feet long, to +prevent a spark in the water, and to reduce what would else have been a +sudden violent discharge into one of more moderate character, enduring for +a sensible length of time (334.). I now did obtain a very brief elevation +of the water over the end of the wire; and though a few minute bubbles of +gas were at the same time formed there, so as to prevent me from asserting +that the effect was unequivocally the same as that obtained by DAVY in the +metals, yet, according to my best judgement, it was partly, and I believe +principally, of that nature. + +1609. I employed a voltaic battery of 100 pair of four-inch plates for +experiments of a similar nature with electrolytes. In these cases the +shell-lac was cupped, and the wire _b_ 0.2 of an inch in diameter. +Sometimes I used a positive amalgamated zinc wire in contact with dilute +sulphuric acid; at others, a negative copper wire in a solution of sulphate +of copper; but, because of the evolution of gas, the precipitation of +copper, &c., I was not able to obtain decided results. It is but right to +mention, that when I made use of mercury, endeavouring to repeat DAVY's +experiment, the battery of 100 pair was not sufficient to produce the +elevations[A]. + + [A] In the experiments at the Royal Institution, Sir H. Davy used, I + think, 500 or 600 pairs of plates. Those at the London Institution + were made with the apparatus of Mr. Pepys (consisting of an enormous + single pair of plates), described in the Philosophical Transactions + for 1832, p. 187. + +1610. The latter experiments (1609.) may therefore be considered as failing +to give the hoped-for proof, but I have much confidence in the former +(1605. 1608.), and in the considerations (1603.) connected with them. If I +have rightly viewed them, and we may be allowed to compare the currents at +points and surfaces in such extremely different bodies as air and the +metals, and admit that they are effects of the _same_ kind, differing only +in degree and in proportion to the insulating or conducting power of the +dielectric used, what great additional argument we obtain in favour of that +theory, which in the phenomena of insulation and conduction also, as in +these, would link _the same_ apparently dissimilar substances together +(1336. 1561.); and how completely the general view, which refers all the +phenomena to the direct action of the molecules of matter, seems to embrace +the various isolated phenomena as they successively come under +consideration! + + * * * * * + +1611. The connection of this convective or carrying effect, which depends +upon a certain degree of insulation, with conduction; i.e. the occurrence +of both in so many of the substances referred to, as, for instance, the +metals, water, air, &c., would lead to many very curious theoretical +generalizations, which I must not indulge in here. One point, however, I +shall venture to refer to. Conduction appears to be essentially an action +of contiguous particles, and the considerations just stated, together with +others formerly expressed (1326, 1336, &c.), lead to the conclusion, that +all bodies conduct, and by the same process, air as well as metals; the +only difference being in the necessary degree of force or tension between +the particles which must exist before the act of conduction or transfer +from one particle to another can take place. + +1612. The question then arises, what is this limiting condition which +separates, as it were, conduction and insulation from each other? Does it +consist in a difference between the two contiguous particles, or the +contiguous poles of these particles, in the nature and amount of positive +and negative force, no communication or discharge occurring unless that +difference rises up to a certain degree, variable for different bodies, but +always the same for the same body? Or is it true that, however small the +difference between two such particles, if _time_ be allowed, equalization +of force will take place, even with the particles of such bodies as air, +sulphur or lac? In the first case, insulating power in any particular body +would be proportionate to the degree of the assumed necessary difference of +force; in the second, to the _time_ required to equalize equal degrees of +difference in different bodies. With regard to airs, one is almost led to +expect a permanent difference of force; but in all other bodies, time seems +to be quite sufficient to ensure, ultimately, complete conduction. The +difference in the modes by which insulation may be sustained, or conduction +effected, is not a mere fanciful point, but one of great importance, as +being essentially connected with the molecular theory of induction, and the +manner in which the particles of bodies assume and retain their polarized +state. + + * * * * * + +P xi. _Relation of a vacuum to electrical phenomena._ + +1613. It would seem strange, if a theory which refers all the phenomena of +insulation and conduction, i.e. all electrical phenomena, to the action of +contiguous particles, were to omit to notice the assumed possible case of a +_vacuum_. Admitting that a vacuum can be produced, it would be a very +curious matter indeed to know what its relation to electrical phenomena +would be; and as shell-lac and metal are directly opposed to each other, +whether a vacuum would be opposed to them both, and allow neither of +induction or conduction across it. Mr. Morgan[A] has said that a vacuum +does not conduct. Sir H. Davy concluded from his investigations, that as +perfect a vacuum as could be made[B] did conduct, but does not consider the +prepared spaces which he used as absolute vacua. In such experiments I +think I have observed the luminous discharge to be principally on the inner +surface of the glass; and it does not appear at all unlikely, that, if the +vacuum refused to conduct, still the surface of glass next it might carry +on that action. + + [A] Philosophical Transactions, 1785, p. 272 + + [B] Ibid. 1822, p. 64. + +1614. At one time, when I thought inductive force was exerted in right +lines, I hoped to illustrate this important question by making experiments +on induction with metallic mirrors (used only as conducting vessels) +exposed towards a very clear sky at night time, and of such concavity that +nothing but the firmament could be visible from the lowest part of the +concave _n_, fig. 143. Such mirrors, when electrified, as by connexion with +a Leyden jar, and examined by a carrier ball, readily gave electricity at +the lowest part of their concavity if in a room; but I was in hopes of +finding that, circumstanced as before stated, they would give little or +none at the same spot, if the atmosphere above really terminated in a +vacuum. I was disappointed in the conclusion, for I obtained as much +electricity there as before; but on discovering the action of induction in +curved lines (1231.), found a full and satisfactory explanation of the +result. + +1615. My theory, as far as I have ventured it, does not pretend to decide +upon the consequences of a vacuum. It is not at present limited +sufficiently, or rendered precise enough, either by experiments relating to +spaces void of matter, or those of other kinds, to indicate what would +happen in the vacuum case. I have only as yet endeavoured to establish, +what all the facts seem to prove, that when electrical phenomena, as those +of induction, conduction, insulation and discharge occur, they depend on, +and are produced by the action of _contiguous_ particles of matter, the +next existing particle being considered as the contiguous one; and I have +further assumed, that these particles are polarized; that each exhibits the +two forces, or the force in two directions (1295. 1298.); and that they act +at a distance, only by acting on the _contiguous_ and intermediate +particles. + +1616. But assuming that a perfect vacuum were to intervene in the course of +the lines of inductive action (1304.), it does not follow from this theory, +that the particles on opposite sides of such a vacuum could not act on each +other. Suppose it possible for a positively electrified particle to be in +the centre of a vacuum an inch in diameter, nothing in my present views +forbids that the particle should act at the distance of half an inch on all +the particles forming the inner superficies of the bounding sphere, and +with a force consistent with the well-known law of the squares of the +distance. But suppose the sphere of an inch were full of insulating matter, +the electrified particle would not then, according to my notion, act +directly on the distant particles, but on those in immediate association +with it, employing _all_ its power in polarizing them; producing in them +negative force equal in amount to its own positive force and directed +towards the latter, and positive force of equal amount directed outwards +and acting in the same manner upon the layer of particles next in +succession. So that ultimately, those particles in the surface of a sphere +of half an inch radius, which were acted on _directly_ when that sphere was +a vacuum, will now be acted on _indirectly_ as respects the central +particle or source of action, i.e. they will be polarized in the same way, +and with the same amount of force. + + +S 19. _Nature of the electric current._ + + +1617. The word _current_ is so expressive in common language, that when +applied in the consideration of electrical phenomena we can hardly divest +it sufficiently of its meaning, or prevent our minds from being prejudiced +by it (283. 511.). I shall use it in its common electrical sense, namely, +to express generally a certain condition and relation of electrical forces +supposed to be in progression. + +1618. A current is produced both by excitement and discharge; and +whatsoever the variation of the two general causes may be, the effect +remains the same. Thus excitement may occur in many ways, as by friction, +chemical action, influence of heat, change of condition, induction, &c.; +and discharge has the forms of conduction, electrolyzation, disruptive +discharge, and convection; yet the current connected with these actions, +when it occurs, appears in all cases to be the same. This constancy in the +character of the current, notwithstanding the particular and great +variations which may be made in the mode of its occurrence, is exceedingly +striking and important; and its investigation and development promise to +supply the most open and advantageous road to a true and intimate +understanding of the nature of electrical forces. + +1619. As yet the phenomena of the current have presented nothing in +opposition to the view I have taken of the nature of induction as an action +of contiguous particles. I have endeavoured to divest myself of prejudices +and to look for contradictions, but I have not perceived any in conductive, +electrolytic, convective, or disruptive discharge. + +1620. Looking at the current as a _cause_, it exerts very extraordinary and +diverse powers, not only in its course and on the bodies in which it +exists, but collaterally, as in inductive or magnetic phenomena. + +1621. _Electrolytic action._--One of its direct actions is the exertion of +pure chemical force, this being a result which has now been examined to a +considerable extent. The effect is found to be _constant_ and _definite_ +for the quantity of electric force discharged (783. &c.); and beyond that, +the _intensity_ required is in relation to the intensity of the affinity or +forces to be overcome (904. 906. 911.). The current and its consequences +are here proportionate; the one may be employed to represent the other; no +part of the effect of either is lost or gained; so that the case is a +strict one, and yet it is the very case which most strikingly illustrates +the doctrine that induction is an action of contiguous particles (1164. +1343.). + +1622. The process of electrolytic discharge appears to me to be in close +analogy, and perhaps in its nature identical with another process of +discharge, which at first seems very different from it, I mean _convection_ +(1347. 1572.). In the latter case the particles may travel for yards across +a chamber; they may produce strong winds in the air, so as to move +machinery; and in fluids, as oil of turpentine, may even shake the hand, +and carry heavy metallic bodies about[A]; and yet I do not see that the +force, either in kind or action, is at all different to that by which a +particle of hydrogen leaves one particle of oxygen to go to another, or by +which a particle of oxygen travels in the contrary direction. + + [A] If a metallic vessel three or four inches deep, containing oil of + turpentine, be insulated and electrified, and a rod with a ball (an + inch or more in diameter) at the end have the ball immersed in the + fluid whilst the end is held in the hand, the mechanical force + generated when the ball is moved to and from the sides of the vessel + will soon be evident to the experimenter. + +1623. Travelling particles of the air can effect chemical changes just as +well as the contact of a fixed platina electrode, or that of a combining +electrode, or the ions of a decomposing electrolyte (453. 471.); and in the +experiment formerly described, where eight places of decomposition were +rendered active by one current (469.), and where charged particles of air +in motion were the only electrical means of connecting these parts of the +current, it seems to me that the action of the particles of the electrolyte +and of the air were essentially the same. A particle of air was rendered +positive; it travelled in a certain determinate direction, and coming to an +electrolyte, communicated its powers; an equal amount of positive force was +accordingly acquired by another particle (the hydrogen), and the latter, so +charged, travelled as the former did, and in the same direction, until it +came to another particle, and transferred its power and motion, making that +other particle active. Now, though the particle of air travelled over a +visible and occasionally a large space, whilst the particle of the +electrolyte moved over an exceedingly small one; though the air particle +might be oxygen, nitrogen, or hydrogen, receiving its charge from force of +high intensity, whilst the electrolytic particle of hydrogen had a natural +aptness to receive the positive condition with extreme facility; though the +air particle might be charged with very little electricity at a very high +intensity by one process, whilst the hydrogen particle might be charged +with much electricity at a very low intensity by another process; these are +not differences of kind, as relates to the final discharging action of +these particles, but only of degree; not essential differences which make +things unlike, but such differences as give to things, similar in their +nature, that great variety which fits them for their office in the system +of the universe. + +1624. So when a particle of air, or of dust in it, electrified at a +negative point, moves on through the influence of the inductive forces +(1572.) to the next positive surface, and after discharge passes away, it +seems to me to represent exactly that particle of oxygen which, having been +rendered negative in the electrolyte, is urged by the same disposition of +inductive forces, and going to the positive platina electrode, is there +discharged, and then passes away, as the air or dust did before it. + +1625. _Heat_ is another direct effect of the _current_ upon substances in +which it occurs, and it becomes a very important question, as to the +relation of the electric and heating forces, whether the latter is always +definite in amount[A]. There are many cases, even amongst bodies which +conduct without change, that at present are irreconcileable with the +assumption that it is[B]; but there are also many which indicate that, when +proper limitations are applied, the heat produced is definite. Harris has +shown this for a given length of current in a metallic wire, using common +electricity[C]; and De la Rive has proved the same point for voltaic +electricity by his beautiful application of Breguet's thermometer[D]. + + [A] See De la Rive's Researches, Bib. Universelle, 1829, xl. p. 40. + + [B] Amongst others, Davy, Philosophical Transactions, 1821, p. 438. + Pelletier's important results, Annales de Chimie, 1834, lvi. p. 371. + and Becquerel's non-heating current, Bib. Universelle, 1835, lx. 218. + + [C] Philosophical Transactions, 1824, pp. 225. 228. + + [D] Annales de Chimie, 1836, lxii. 177. + +1626. When the production of heat is observed in electrolytes under +decomposition, the results are still more complicated. But important steps +have been taken in the investigation of this branch of the subject by De la +Rive[A] and others; and it is more than probable that, when the right +limitations are applied, constant and definite results will here also be +obtained. + + [A] Bib. Universelle, 1829, xl. 49; and Ritchie, Phil. Trans. 1832. p. + 296. + + * * * * * + +1627. It is a most important part of the character of the current, and +essentially connected with its very nature, that it is always the same. The +two forces are everywhere in it. There is never one current of force or one +fluid only. Any one part of the current may, as respects the presence of +the two forces there, be considered as precisely the same with any other +part; and the numerous experiments which imply their possible separation, +as well as the theoretical expressions which, being used daily, assume it, +are, I think, in contradiction with facts (511, &c.). It appears to me to +be as impossible to assume a current of positive or a current of negative +force alone, or of the two at once with any predominance of one over the +other, as it is to give an absolute charge to matter (516. 1169. 1177.). + +1628. The establishment of this truth, if, as I think, it be a truth, or on +the other hand the disproof of it, is of the greatest consequence. If, as a +first principle, we can establish, that the centres of the two forces, or +elements of force, never can be separated to any sensible distance, or at +all events not further than the space between two contiguous particles +(1615.), or if we can establish the contrary conclusion, how much more +clear is our view of what lies before us, and how much less embarrassed the +ground over which we have to pass in attaining to it, than if we remain +halting between two opinions! And if, with that feeling, we rigidly test +every experiment which bears upon the point, as far as our prejudices will +let us (1161.), instead of permitting them with a theoretical expression to +pass too easily away, are we not much more likely to attain the real truth, +and from that proceed with safety to what is at present unknown? + +1629. I say these things, not, I hope, to advance a particular view, but to +draw the strict attention of those who are able to investigate and judge of +the matter, to what must be a turning point in the theory of electricity; +to a separation of two roads, one only of which can be right: and I hope I +may be allowed to go a little further into the facts which have driven me +to the view I have just given. + +1630. When a wire in the voltaic circuit is heated, the temperature +frequently rises first, or most at one end. If this effect were due to any +relation of positive or negative as respects the current, it would be +exceedingly important. I therefore examined several such cases; but when, +keeping the contacts of the wire and its position to neighbouring things +unchanged, I altered the direction of the current, I found that the effect +remained unaltered, showing that it depended, not upon the direction of the +current, but on other circumstances. So there is here no evidence of a +difference between one part of the circuit and another. + +1631. The same point, i.e. uniformity in every part, may be illustrated by +what may be considered as the inexhaustible nature of the current when +producing particular effects; for these effects depend upon transfer only, +and do not consume the power. Thus a current which will heat one inch of +platina wire will heat a hundred inches (853. note). If a current be +sustained in a constant state, it will decompose the fluid in one +voltameter only, or in twenty others if they be placed in the circuit, in +each to an amount equal to that in the single one. + +1632. Again, in cases of disruptive discharge, as in the spark, there is +frequently a dark part (1422.) which, by Professor Johnson, has been called +the neutral point[A]; and this has given rise to the use of expressions +implying that there are two electricities existing separately, which, +passing to that spot, there combine and neutralize each other[B]. But if +such expressions are understood as correctly indicating that positive +electricity alone is moving between the positive ball and that spot, and +negative electricity only between the negative ball and that spot, then +what strange conditions these parts must be in; conditions, which to my +mind are every way unlike those which really occur! In such a case, one +part of a current would consist of positive electricity only, and that +moving in one direction; another part would consist of negative electricity +only, and that moving in the other direction; and a third part would +consist of an accumulation of the two electricities, not moving in either +direction, but mixing up together! and being in a relation to each other +utterly unlike any relation which could be supposed to exist in the two +former portions of the discharge. This does not seem to me to be natural. +In a current, whatever form the discharge may take, or whatever part of the +circuit or current is referred to, as much positive force as is there +exerted in one direction, so much negative force is there exerted in the +other. If it were not so we should have bodies electrified not merely +positive and negative, but on occasions in a most extraordinary manner, one +being charged with five, ten, or twenty times as much of both positive and +negative electricity in equal quantities as another. At present, however, +there is no known fact indicating such states. + + [A] Silliman's Journal, 1834, xxv. p. 57. + + [B] Thomson on Heat and Electricity, p. 171. + +1633. Even in cases of convection, or carrying discharge, the statement +that the current is everywhere the same must in effect be true (1627.); for +how, otherwise, could the results formerly described occur? When currents +of air constituted the mode of discharge between the portions of paper +moistened with iodide of potassium or sulphate of soda (465. 469.), +decomposition occurred; and I have since ascertained that, whether a +current of positive air issued from a spot, or one of negative air passed +towards it, the effect of the evolution of iodine or of acid was the same, +whilst the reversed currents produced alkali. So also in the magnetic +experiments (307.) whether the discharge was effected by the introduction +of a wire, or the occurrence of a spark, or the passage of convective +currents either one way or the other (depending on the electrified state of +the particles), the result was the same, being in all cases dependent upon +the perfect current. + +1634. Hence, the section of a current compared with other sections of the +same current must be a constant quantity, if the actions exerted be of the +same kind; or if of different kinds, then the forms under which the effects +are produced are equivalent to each other, and experimentally convertible +at pleasure. It is in sections, therefore, we must look for identity of +electrical force, even to the sections of sparks and carrying actions, as +well as those of wires and electrolytes. + +1635. In illustration of the utility and importance of establishing that +which may be the true principle, I will refer to a few cases. The doctrine +of unipolarity, as formerly stated, and I think generally understood[A], is +evidently inconsistent with my view of a current (1627.); and the later +singular phenomena of poles and flames described by Erman and others[B] +partake of the same inconsistency of character. If a unipolar body could +exist, i.e. one that could conduct the one electricity and not the other, +what very new characters we should have a right to expect in the currents +of single electricities passing through them, and how greatly ought they to +differ, not only from the common current which is supposed to have both +electricities travelling in opposite directions in equal amount at the same +time, but also from each other! The facts, which are excellent, have, +however, gradually been more correctly explained by Becquerel[C], +Andrews[D], and others; and I understand that Professor Ohms[E] has +perfected the work, in his close examination of all the phenomena; and +after showing that similar phenomena can take place with good conductors, +proves that with soap, &c. many of the effects are the mere consequences of +the bodies evolved by electrolytic action. + + [A] Erman, Annales de Chimie, 1807. lxi. p. 115. Davy's Elements, p. + 168. Biot, Ency. Brit. Supp, iv. p. 444. Becquerel, Traite, i. p. 167. + De la Rive, Bib. Univ. 1837. vii. 392. + + [B] Erman, Annales de Chimie, 1824. xxv. 278. Becquerel, Ibid. xxxvi. + p. 329 + + [C] Becquerel, Annales de Chimie, 1831. xlvi. p. 283. + + [D] Andrews, Philosophical Magazine, 1836. ix. 182. + + [E] Schweigger's Jahrbuch de Chimie, &c. 1830. Heft 8. Not + understanding German, it is with extreme regret I confess I have not + access, and cannot do justice, to the many most valuable papers in + experimental electricity published in that language. I take this + opportunity also of stating another circumstance which occasions me + great trouble, and, as I find by experience, may make, me seemingly + regardless of the labours of others:--it is a gradual loss of memory + for some years past; and now, often when I read a memoir, I remember + that I have seen it before, and would have rejoiced if at the right + time I could have recollected and referred to it in the progress of my + own papers.--M.F. + +1636. I conclude, therefore, that the _facts_ upon which the doctrine of +unipolarity was founded are not adverse to that unity and indivisibility of +character which I have stated the current to possess, any more than the +phenomena of the pile itself (which might well bear comparison with those +of unipolar bodies,) are opposed to it. Probably the effects which have +been called effects of unipolarity, and the peculiar differences of the +positive and negative surface when discharging into air, gases, or other +dielectrics (1480. 1525.) which have been already referred to, may have +considerable relation to each other[A]. + + [A] See also Hare in Silliman's Journal, 1833. xxiv. 246. + + * * * * * + +1637. M. de la Rive has recently described a peculiar and remarkable effect +of heat on a current when passing between electrodes and a fluid[A]. It is, +that if platina electrodes dip into acidulated water, no change is produced +in the passing current by making the positive electrode hotter or colder; +whereas making the negative electrode hotter increased the deflexion of a +galvanometer affected by the current, from 12 deg. to 30 deg. and even 45 deg., whilst +making it colder diminished the current in the same high proportions. + + [A] Bibliotheque Universelle, 1837, vii. 388. + +1638. That one electrode should have this striking relation to heat whilst +the other remained absolutely without, seem to me as incompatible with what +I conceived to be the character of a current as unipolarity (1627. 1635.), +and it was therefore with some anxiety that I repeated the experiment. The +electrodes which I used were platina; the electrolyte, water containing +about one sixth of sulphuric acid by weight: the voltaic battery consisted +of two pairs of amalgamated zinc and platina plates in dilute sulphuric +acid, and the galvanometer in the circuit was one with two needles, and +gave when the arrangement was complete a deflexion of 10 deg. or 12 deg.. + +1639. Under these circumstances heating either electrode increased the +current; heating both produced still more effect. When both were heated, if +either were cooled, the effect on the current fell in proportion. The +proportion of effect due to heating this or that electrode varied, but on +the whole heating the negative seemed to favour the passage of the current +somewhat more than heating the positive. Whether the application of heat +were by a flame applied underneath, or one directed by a blowpipe from +above, or by a hot iron or coal, the effect was the same. + +1640. Having thus removed the difficulty out of the way of my views +regarding a current, I did not pursue this curious experiment further. It +is probable, that the difference between my results and those of M. de la +Rive may depend upon the relative values of the currents used; for I +employed only a weak one resulting from two pairs of plates two inches long +and half an inch wide, whilst M. de la Rive used four pairs of plates of +sixteen square inches in surface. + + * * * * * + +1641. Electric discharges in the atmosphere in the form of balls of fire +have occasionally been described. Such phenomena appear to me to be +incompatible with all that we know of electricity and its modes of +discharge. As _time_ is an element in the effect (1418. 1436.) it is +possible perhaps that an electric discharge might really pass as a ball +from place to place; but as every thing shows that its velocity must be +almost infinite, and the time of its duration exceedingly small, it is +impossible that the eye should perceive it as anything else than a line of +light. That phenomena of balls of fire may appear in the atmosphere, I do +not mean to deny; but that they have anything to do with the discharge of +ordinary electricity, or are at all related to lightning or atmospheric +electricity, is much more than doubtful. + + * * * * * + +1642. All these considerations, and many others, help to confirm the +conclusion, drawn over and over again, that the current is an indivisible +thing; an axis of power, in every part of which both electric forces are +present in equal amount[A] (517. 1627.). With conduction and +electrolyzation, and even discharge by spark, such a view will harmonize +without hurting any of our preconceived notions; but as relates to +convection, a more startling result appears, which must therefore be +considered. + + [A] I am glad to refer here to the results obtained by Mr. Christie + with magneto-electricity, Philosophical Transactions, 1833, p. 113 + note. As regards the current in a wire, they confirm everything that I + am contending for. + +1643. If two balls A and B be electrified in opposite states and held +within each other's influence, the moment they move towards each other, a +current, or those effects which are understood by the word current, will be +produced. Whether A move towards B, or B move in the opposite direction +towards A, a current, and in both cases having the same _direction_, will +result. If A and B move from each other, then a _current_ in the opposite +direction, or equivalent effects, will be produced. + +1644. Or, as charge exists only by induction (1178. 1299.), and a body when +electrified is necessarily in relation to other bodies in the opposite +state; so, if a ball be electrified positively in the middle of a room and +be then moved in any direction, effects will be produced, as _current_ in +the same direction (to use the conventional mode of expression) had +existed: or, if the ball be negatively electrified, and then moved, effects +as if a current in a direction contrary to that of the motion had been +formed, will be produced. + +1645. I am saying of a single particle or of two what I have before said, +in effect, of many (1633.). If the former account of currents be true, then +that just stated must be a necessary result. And, though the statement may +seem startling at first, it is to be considered that, according to my +theory of induction, the charged conductor or particle is related to the +distant conductor in the opposite state, or that which terminates the +extent of the induction, by all the intermediate particles (1165, 1295.), +these becoming polarized exactly as the particles of a solid electrolyte do +when interposed between the two electrodes. Hence the conclusion regarding +the unity and identity of the current in the case of convection, jointly +with the former cases, is not so strange as it might at first appear. + + * * * * * + +1646. There is a very remarkable phenomenon or effect of the electrolytic +discharge, first pointed out, I believe, by Mr. Porrett, of the +accumulation of fluid under decomposing action in the current on one side +of an interposed diaphragm[A]. It is a mechanical result; and as the liquid +passes from the positive towards the negative electrode in all the known +cases, it seems to establish a relation to the polar condition of the +dielectric in which the current exists (1164. 1525.). It has not as yet +been sufficiently investigated by experiment; for De la Rive says[B], it +requires that the water should be a bad conductor, as, for instance, +distilled water, the effect not happening with strong solutions; whereas, +Dutrochet says[C] the contrary is the case, and that, the effect is not +directly due to the electric current. + + [A] Annals of Philosophy, 1816. viii. p. 75. + + [B] Annales de Chimie, 1835. xxviii. p. 196. + + [C] Annales de Chimie, 1832, xlix. p. 423. + +1647. Becquerel, in his Traite de l'Electricite, has brought together the +considerations which arise for and against the opinion, that the effect +generally is an electric effect[A]. Though I have no decisive fact to quote +at present, I cannot refrain from venturing an opinion, that the effect is +analogous both to combination and convection (1623.), being a case of +carrying due to the relation of the diaphragm and the fluid in contact with +it, through which the electric discharge is jointly effected; and further, +that the peculiar relation of positive and negative small and large +surfaces already referred to (1482. 1503. 1525.), may be the direct cause +of the fluid and the diaphragm travelling in contrary but determinate +directions. A very valuable experiment has been made by M. Becquerel with +particles of clay[B], which will probably bear importantly on this point. + + [A] Vol. iv. p. 192, 197. + + [B] Traite de l'Electricite, i. p. 285. + + * * * * * + +1648. _As long as_ the terms _current_ and _electro-dynamic_ are used to +express those relations of the electric forces in which progression of +either fluids or effects are supposed to occur (283.), _so long_ will the +idea of velocity be associated with them; and this will, perhaps, be more +especially the case if the hypothesis of a fluid or fluids be adopted. + +1649. Hence has arisen the desire of estimating this velocity either +directly or by some effect dependent on it; and amongst the endeavours to +do this correctly, may be mentioned especially those of Dr. Watson[A] in +1748, and of Professor Wheatstone[B] in 1834; the electricity in the early +trials being supposed to travel from end to end of the arrangement, but in +the later investigations a distinction occasionally appearing to be made +between the transmission of the effect and of the supposed fluid by the +motion of whose particles that effect is produced. + + [A] Philosophical Transactions, 1748. + + [B] Ibid. 1834, p. 583. + +1650. Electrolytic action has a remarkable bearing upon this question of +the velocity of the current, especially as connected with the theory of an +electric fluid or fluids. In it there is an evident transfer of power with +the transfer of each particle of the anion or cathion present, to the next +particles of the cathion or anion; and as the amount of power is definite, +we have in this way a means of localizing as it were the force, identifying +it by the particle and dealing it out in successive portions, which leads, +I think, to very striking results. + +1651. Suppose, for instance, that water is undergoing decomposition by the +powers of a voltaic battery. Each particle of hydrogen as it moves one way, +or of oxygen as it moves in the other direction, will transfer a certain +amount of electrical force associated with it in the form of chemical +affinity (822. 852. 918.) onwards through a distance, which is equal to +that through which the particle itself has moved. This transfer will be +accompanied by a corresponding movement in the electrical forces throughout +every part of the circuit formed (1627. 1634.), and its effects may be +estimated, as, for instance, by the heating of a wire (853.) at any +particular section of the current however distant. If the water be a cube +of an inch in the side, the electrodes touching, each by a surface of one +square inch, and being an inch apart, then, by the time that a tenth of it, +or 25.25 grs., is decomposed, the particles of oxygen and hydrogen +throughout the mass may be considered as having moved relatively to each +other in opposite directions, to the amount of the tenth of an inch; i.e. +that two particles at first in combination will after the motion be the +tenth of an inch apart. Other motions which occur in the fluid will not at +all interfere with this result; for they have no power of accelerating or +retarding the electric discharge, and possess in fact no relation to it. + +1652. The quantity of electricity in 25.25 grains of water is, according to +an estimate of the force which I formerly made (861.), equal to above 24 +millions of charges of a large Leyden battery; or it would have kept any +length of a platina wire 1/104 of an inch in diameter red-hot for an hour +and a half (853.). This result, though given only as an approximation, I +have seen no reason as yet to alter, and it is confirmed generally by the +experiments and results of M. Pouillet[A]. According to Mr. Wheatstone's +experiments, the influence or effects of the current would appear at a +distance of 576,000 miles in a second[B]. We have, therefore, in this view +of the matter, on the one hand, an enormous quantity of power equal to a +most destructive thunder-storm appearing instantly at the distance of +576,000 miles from its source, and on the other, a quiet effect, in +producing which the power had taken an hour and a half to travel through +the tenth of an inch: yet these are the equivalents to each other, being +effects observed at the sections of one and the same current (1634.). + + [A] Becquerel, Traite de l'Electricite, v. p. 278. + + [B] Philosophical Transactions, 1834, p. 589. + + * * * * * + +1653. It is time that I should call attention to the lateral or transverse +forces of the _current_. The great things which have been achieved by +Oersted, Arago, Ampere, Davy, De la Rive, and others, and the high degree +of simplification which has been introduced into their arrangement by the +theory of Ampere, have not only done their full service in advancing most +rapidly this branch of knowledge, but have secured to it such attention +that there is no necessity for urging on its pursuit. I refer of course to +magnetic action and its relations; but though this is the only recognised +lateral action of the current, there is great reason for believing that +others exist and would by their discovery reward a close search for them +(951.). + +1654. The magnetic or transverse action of the current seems to be in a +most extraordinary degree independent of those variations or modes of +action which it presents directly in its course; it consequently is of the +more value to us, as it gives us a higher relation of the power than any +that might have varied with each mode of discharge. This discharge, whether +it be by conduction through a wire with infinite velocity (1652.), or by +electrolyzation with its corresponding and exceeding slow motion (1651.), +or by spark, and probably even by convection, produces a transverse +magnetic action always the same in kind and direction. + +1655. It has been shown by several experimenters, that whilst the discharge +is of the _same kind_ the amount of lateral or magnetic force is very +constant (216. 366. 367. 368. 376.). But when we wish to compare discharge +of different kinds, for the important purpose of ascertaining whether the +same amount of current will in its _different forms_ produce the same +amount of transverse action, we find the data very imperfect. Davy noticed, +that when the electric current was passing through an aqueous solution it +affected a magnetic needle[A], and Dr. Ritchie says, that the current in +the electrolyte is as magnetic as that in a metallic wire[B], and has +caused water to revolve round a magnet as a wire carrying the current would +revolve. + + [A] Philosophical Transactions, 1821, p. 426. + + [B] Ibid. 1832, p. 294. + +1656. Disruptive discharge produces its magnetic effects: a strong spark, +passed transversely to a steel needle, will magnetise it as well as if the +electricity of the spark were conducted by a metallic wire occupying the +line of discharge; and Sir H. Davy has shown that the discharge of a +voltaic battery in vacuo is affected and has motion given to it by +approximated magnets[A]. + + [A] Philosophical Transactions, 1821, p. 427. + +1657. Thus the three very different modes of discharge, namely, conduction, +electrolyzation, and disruptive discharge, agree in producing the important +transverse phenomenon of magnetism. Whether convection or carrying +discharge will produce the same phenomenon has not been determined, and the +few experiments I have as yet had time to make do not enable me to answer +in the affirmative. + + * * * * * + +1658. Having arrived at this point in the consideration of the current and +in the endeavour to apply its phenomena as tests of the truth or fallacy of +the theory of induction which I have ventured to set forth, I am now very +much tempted to indulge in a few speculations respecting its lateral action +and its possible connexion with the transverse condition of the lines of +ordinary induction (1165, 1304.)[A]. I have long sought and still seek for +an effect or condition which shall be to statical electricity what magnetic +force is to current electricity (1411.); for as the lines of discharge are +associated with a certain transverse effect, so it appeared to me +impossible but that the lines of tension or of inductive action, which of +necessity precede that discharge, should also have their correspondent +transverse condition or effect (951.). + + [A] Refer for further investigations to 1709.--1736.--_Dec. 1838._ + +1659. According to the beautiful theory of Ampere, the transverse force of +a current may be represented by its attraction for a similar current and +its repulsion of a contrary current. May not then the equivalent transverse +force of static electricity be represented by that lateral tension or +repulsion which the lines of inductive action appear to possess (1304.)? +Then again, when current or discharge occurs between two bodies, previously +under inductrical relations to each other, the lines of inductive force +will weaken and fade away, and, as their lateral repulsive tension +diminishes, will contract and ultimately disappear in the line of +discharge. May not this be an effect identical with the attractions of +similar currents? i.e. may not the passage of static electricity into +current electricity, and that of the lateral tension of the lines of +inductive force into the lateral attraction of lines of similar discharge, +have the same relation and dependences, and run parallel to each other? + +1660. The phenomena of induction amongst currents which I had the good +fortune to discover some years ago (6. &c. 1048.) may perchance here form a +connecting link in the series of effects. When a current is first formed, +it tends to produce a current in the contrary direction in all the matter +around it; and if that matter have conducting properties and be fitly +circumstanced, such a current is produced. On the contrary, when the +original current is stopped, one in the same direction tends to form all +around it, and, in conducting matter properly arranged, will be excited. + +1661. Now though we perceive the effects only in that portion of matter +which, being in the neighbourhood, has conducting properties, yet +hypothetically it is probable, that the nonconducting matter has also its +relations to, and is affected by, the disturbing cause, though we have not +yet discovered them. Again and again the relation of conductors and +non-conductors has been shown to be one not of opposition in kind, but only +of degree (1334, 1603.); and, therefore, for this, as well as for other +reasons, it is probable, that what will affect a conductor will affect an +insulator also; producing perhaps what may deserve the term of the +electrotonic state (60. 242. 1114.). + +1662. It is the feeling of the necessity of some lateral connexion between +the lines of electric force (1114.); of some link in the chain of effects +as yet unrecognised, that urges me to the expression of these speculations. +The same feeling has led me to make many experiments on the introduction of +insulating dielectrics having different inductive capacities (1270. 1277.) +between magnetic poles and wires carrying currents, so as to pass across +the lines of magnetic force. I have employed such bodies both at rest and +in motion, without, as yet, being able to detect any influence produced by +them; but I do by no means consider the experiments as sufficiently +delicate, and intend, very shortly, to render them more decisive[A]. + + [A] See onwards 1711.--1726.--_Dec. 1838._ + +1663. I think the hypothetical question may at present be put thus: can +such considerations as those already generally expressed (1658.) account +for the transverse effects of electrical currents? are two such currents in +relation to each other merely by the inductive condition of the particles +of matter between them, or are they in relation by some higher quality and +condition (1654.), which, acting at a distance and not by the intermediate +particles, has, like the force of gravity, no relation to them? + +1664. If the latter be the case, then, when electricity is acting upon and +in matter, its direct and its transverse action are essentially different +in their nature; for the former, if I am correct, will depend upon the +contiguous particles, and the latter will not. As I have said before, this +may be so, and I incline to that view at present; but I am desirous of +suggesting considerations why it may not, that the question may be +thoroughly sifted. + +1665. The transverse power has a character of polarity impressed upon it. +In the simplest forms it appears as attraction or repulsion, according as +the currents are in the same or different directions: in the current and +the magnet it takes up the condition of tangential forces; and in magnets +and their particles produces poles. Since the experiments have been made +which have persuaded me that the polar forces of electricity, as in +induction and electrolytic action (1298. 1343.), show effects at a distance +only by means of the polarized contiguous and intervening particles, I have +been led to expect that _all polar forces_ act in the same general manner; +and the other kinds of phenomena which one can bring to bear upon the +subject seem fitted to strengthen that expectation. Thus in +crystallizations the effect is transmitted from particle to particle; and +in this manner, in acetic acid or freezing water a crystal a few inches or +even a couple of feet in length will form in less than a second, but +progressively and by a transmission of power from particle to particle. +And, as far as I remember, no case of polar action, or partaking of polar +action, except the one under discussion, can be found which does not act by +contiguous particles[A]. It is apparently of the nature of polar forces +that such should be the case, for the one force either finds or developed +the contrary force near to it, and has, therefore, no occasion to seek for +it at a distance. + + [A] I mean by contiguous particles those which are next to each other, + not that there is _no_ space between them. See (1616.). + +1666. But leaving these hypothetical notions respecting the nature of the +lateral action out of sight, and returning to the direct effects, I think +that the phenomena examined and reasoning employed in this and the two +preceding papers tend to confirm the view first taken (1464.), namely, that +ordinary inductive action and the effects dependent upon it are due to an +action of the contiguous particles of the dielectric interposed between the +charged surfaces or parts which constitute, as it were, the terminations of +the effect. The great point of distinction and power (if it have any) in +the theory is, the making the dielectric of essential and specific +importance, instead of leaving it as it were a mere accidental circumstance +or the simple representative of space, having no more influence over the +phenomena than the space occupied by it. I have still certain other results +and views respecting the nature of the electrical forces and excitation, +which are connected with the present theory; and, unless upon further +consideration they sink in my estimation, I shall very shortly put them +into form as another series of these electrical researches. + +_Royal Institution. +February 14th, 1838._ + + + + +FOURTEENTH SERIES. + + +S 20. _Nature of the electric force or forces._ S 21. _Relation of the +electric and magnetic forces._ S 22. _Note on electrical excitation._ + +Received June 21, 1838.--Read June 21, 1838. + +S 20. _Nature of the electric force or forces._ + + +1667. The theory of induction set forth and illustrated in the three +preceding series of experimental researches does not assume anything new as +to the nature of the electric force or forces, but only as to their +distribution. The effects may depend upon the association of one electric +fluid with the particles of matter, as in the theory of Franklin, Epinus, +Cavendish, and Mossotti; or they may depend upon the association of two +electric fluids, as in the theory of Dufay and Poisson; or they may not +depend upon anything which can properly be called the electric fluid, but +on vibrations or other affections of the matter in which they appear. The +theory is unaffected by such differences in the mode of viewing the nature +of the forces; and though it professes to perform the important office of +stating _how_ the powers are arranged (at least in inductive phenomena), it +does not, as far as I can yet perceive, supply a single experiment which +can be considered as a distinguishing test of the truth of any one of these +various views, + +1668. But, to ascertain how the forces are arranged, to trace them in their +various relations to the particles of matter, to determine their general +laws, and also the specific differences which occur under these laws, is as +important as, if not more so than, to know whether the forces reside in a +fluid or not; and with the hope of assisting in this research, I shall +offer some further developments, theoretical and experimental, of the +conditions under which I suppose the particles of matter are placed when +exhibiting inductive phenomena. + +1669. The theory assumes that all the _particles_, whether of insulating or +conducting matter, are as wholes conductors. + +1670. That not being polar in their normal state, they can become so by the +influence of neighbouring charged particles, the polar state being +developed at the instant, exactly as in an insulated conducting _mass_ +consisting of many particles. + +1671. That the particles when polarized are in a forced state, and tend to +return to their normal or natural condition. + +1672. That being as wholes conductors, they can readily be charged, either +_bodily_ or _polarly_. + +1673. That particles which being contiguous[A] are also in the line of +inductive action can communicate or transfer their polar forces one to +another _more_ or _less_ readily. + + [A] See note to 1164.--_Dec. 1838._ + +1674. That those doing so less readily require the polar forces to be +raised to a higher degree before this transference or communication takes +place. + +1675. That the _ready_ communication of forces between contiguous particles +constitutes _conduction_, and the _difficult_ communication _insulation_; +conductors and insulators being bodies whose particles naturally possess +the property of communicating their respective forces easily or with +difficulty; having these differences just as they have differences of any +other natural property. + +1676. That ordinary induction is the effect resulting from the action of +matter charged with excited or free electricity upon insulating matter, +tending to produce in it an equal amount of the contrary state. + +1677. That it can do this only by polarizing the particles contiguous to +it, which perform the same office to the next, and these again to those +beyond; and that thus the action is propagated from the excited body to the +next conducting mass, and there renders the contrary force evident in +consequence of the effect of communication which supervenes in the +conducting mass upon the polarization of the particles of that body +(1675.). + +1678. That therefore induction can only take place through or across +insulators; that induction is insulation, it being the necessary +consequence of the state of the particles and the mode in which the +influence of electrical forces is transferred or transmitted through or +across such insulating media. + +1679. The particles of an insulating dielectric whilst under induction may +be compared to a series of small magnetic needles, or more correctly still +to a series of small insulated conductors. If the space round a charged +globe were filled with a mixture of an insulating dielectric, as oil of +turpentine or air, and small globular conductors, as shot, the latter being +at a little distance from each other so as to be insulated, then these +would in their condition and action exactly resemble what I consider to be +the condition and action of the particles of the insulating dielectric +itself (1337.). If the globe were charged, these little conductors would +all be polar; if the globe were discharged, they would all return to their +normal state, to be polarized again upon the recharging of the globe. The +state developed by induction through such particles on a mass of conducting +mutter at a distance would be of the contrary kind, and exactly equal in +amount to the force in the inductric globe. There would be a lateral +diffusion of force (1224. 1297.), because each polarized sphere would be in +an active or tense relation to all those contiguous to it, just as one +magnet can affect two or more magnetic needles near it, and these again a +still greater number beyond them. Hence would result the production of +curved lines of inductive force if the inducteous body in such a mixed +dielectric were an uninsulated metallic ball (1219. &c.) or other properly +shaped mass. Such curved lines are the consequences of the two electric +forces arranged as I have assumed them to be: and, that the inductive force +can be directed in such curved lines is the strongest proof of the presence +of the two powers and the polar condition of the dielectric particles. + +1680. I think it is evident, that in the case stated, action at a distance +can only result through an action of the contiguous conducting particles. +There is no reason why the inductive body should polarize or affect +_distant_ conductors and leave those _near_ it, namely the particles of the +dielectric, unaffected: and everything in the form of fact and experiment +with conducting masses or particles of a sensible size contradicts such a +supposition. + +1681. A striking character of the electric power is that it is limited and +exclusive, and that the two forces being always present are exactly equal +in amount. The forces are related in one of two ways, either as in the +natural normal condition of an uncharged insulated conductor; or as in the +charged state, the latter being a case of induction. + +1682. Cases of induction are easily arranged so that the two forces being +limited in their direction shall present no phenomena or indications +external to the apparatus employed, Thus, if a Leyden jar, having its +external coating a little higher than the internal, be charged and then its +charging ball and rod removed, such jar will present no electrical +appearances so long as its outside is uninsulated. The two forces which may +be said to be in the coatings, or in the particles of the dielectric +contiguous to them, are entirely engaged to each other by induction through +the glass; and a carrier ball (1181.) applied either to the inside or +outside of the jar will show no signs of electricity. But if the jar be +insulated, and the charging ball and rod, in an uncharged state and +suspended by an insulating thread of white silk, be restored to their +place, then the part projecting above the jar will give electrical +indications and charge the carrier, and at the same time the _outside_ +coating of the jar will be found in the opposite state and inductric +towards external surrounding objects. + +1683. These are simple consequences of the theory. Whilst the charge of the +inner coating could induce only through the glass towards the outer +coating, and the latter contained no more of the contrary force than was +equivalent to it, no induction external to the jar could be perceived; but +when the inner coating was extended by the rod and ball so that it could +induce through the air towards external objects, then the tension of the +polarized glass molecules would, by their tendency to return to the normal +state, fall a little, and a portion of the charge passing to the surface of +this new part of the inner conductor, would produce inductive action +through the air towards distant objects, whilst at the same time a part of +the force in the outer coating previously directed inwards would now be at +liberty, and indeed be constrained to induct outwards through the air, +producing in that outer coating what is sometimes called, though I think +very improperly, free charge. If a small Leyden jar be converted into that +form of apparatus usually known by the name of the electric well, it will +illustrate this action very completely. + +1684. The terms _free charge_ and _dissimulated electricity_ convey +therefore erroneous notions if they are meant to imply any difference as to +the mode or kind of action. The charge upon an insulated conductor in the +middle of a room is in the same relation to the walls of that room as the +charge upon the inner coating of a Leyden jar is to the outer coating of +the same jar. The one is not more _free_ or more _dissimulated_ than the +other; and when sometimes we make electricity appear where it was not +evident before, as upon the outside of a charged jar, when, after +insulating it, we touch the inner coating, it is only because we divert +more or less of the inductive force from one direction into another; for +not the slightest change is in such circumstances impressed upon the +character or action of the force. + + * * * * * + +1685. Having given this general theoretical view, I will now notice +particular points relating to the nature of the assumed electric polarity +of the insulating dielectric particles. + +1686. The polar state may be considered in common induction as a forced +state, the particles tending to return to their normal condition. It may +probably be raised to a very high degree by approximation of the inductric +and inducteous bodies or by other circumstances; and the phenomena of +electrolyzation (861. 1652. 1796.) seem to imply that the quantity of power +which can thus be accumulated on a single particle is enormous. Hereafter +we may be able to compare corpuscular forces, as those of gravity, +cohesion, electricity, and chemical affinity, and in some way or other from +their effects deduce their relative equivalents; at present we are not able +to do so, but there seems no reason to doubt that their electrical, which +are at the same time their chemical forces (891. 918.), will be by far the +most energetic. + +1687. I do not consider the powers when developed by the polarization as +limited to two distinct points or spots on the surface of each particle to +be considered as the poles of an axis, but as resident on large portions of +that surface, as they are upon the surface of a conductor of sensible size +when it is thrown into a polar state. But it is very probable, +notwithstanding, that the particles of different bodies may present +specific differences in this respect, the powers not being equally diffused +though equal in quantity; other circumstances also, as form and quality, +giving to each a peculiar polar relation. It is perhaps to the existence of +some such differences as these that we may attribute the specific actions +of the different dielectrics in relation to discharge(1394. 1508.). Thus +with respect to oxygen and nitrogen singular contrasts were presented when +spark and brush discharge were made to take place in these gases, as may be +seen by reference to the Table in paragraph 1518 of the Thirteenth Series; +for with nitrogen, when the small, negative or the large positive ball was +rendered inductric, the effects corresponded with those which in oxygen +were produced when the small positive or the large negative ball was +rendered inductric. + +1688. In such solid bodies as glass, lac, sulphur, &c., the particles +appear to be able to become polarized in all directions, for a mass when +experimented upon so as to ascertain its inductive capacity in three or +more directions (1690.), gives no indication of a difference. Now as the +particles are fixed in the mass, and as the direction of the induction +through them must change with its change relative to the mass, the constant +effect indicates that they can be polarized electrically in any direction. +This accords with the view already taken of each particle as a whole being +a conductor (1669.), and, as an experimental fact, helps to confirm that +view. + +1689. But though particles may thus be polarized in _any_ direction under +the influence of powers which are probably of extreme energy (1686.), it +does not follow that each particle may not tend to polarize to a greater +degree, or with more facility, in one direction than another; or that +different kinds may not have specific differences in this respect, as they +have differences of conducting and other powers (1296. 1326. 1395.). I +sought with great anxiety for a relation of this nature; and selecting +crystalline bodies as those in which all the particles are symmetrically +placed, and therefore best fitted to indicate any result which might depend +upon variation of the direction of the forces to the direction of the +particles in which they were developed, experimented very carefully with +them. I was the more strongly stimulated to this inquiry by the beautiful +electrical condition of the crystalline bodies tourmaline and boracite, and +hoped also to discover a relation between electric polarity and that of +crystallization, or even of cohesion itself (1316.). My experiments have +not established any connexion of the kind sought for. But as I think it of +equal importance to show either that there is or is not such a relation, I +shall briefly describe the results. + +1690. The form of experiment was as follows. A brass ball 0.73 of an inch +in diameter, fixed at the end of a horizontal brass rod, and that at the +end of a brass cylinder, was by means of the latter connected with a large +Leyden battery (291.) by perfect metallic communications, the object being +to keep that ball, by its connexion with the charged battery in an +electrified state, very nearly uniform, for half an hour at a time. This +was the inductric ball. The inducteous ball was the carrier of the torsion +electrometer (1229. 1314.); and the dielectric between them was a cube cut +from a crystal, so that two of its faces should be perpendicular to the +optical axis, whilst the other four were parallel to it. A small projecting +piece of shell-lac was fixed on the inductric ball at that part opposite to +the attachment of the brass rod, for the purpose of preventing actual +contact between the ball and the crystal cube. A coat of shell-lac was also +attached to that side of the carrier ball which was to be towards the cube, +being also that side which was furthest from the repelled ball in the +electrometer when placed in its position in that instrument. The cube was +covered with a thin coat of shell-lac dissolved in alcohol, to prevent the +deposition of damp upon its surface from the air. It was supported upon a +small table of shell-lac fixed on the top of a stem of the same substance, +the latter being of sufficient strength to sustain the cube, and yet +flexible enough from its length to act as a spring, and allow the cube to +bear, when in its place, against the shell-lac on the inductric ball. + +[Illustration:] + +1691. Thus it was easy to bring the inducteous ball always to the same +distance from the inductric bull, and to uninsulate and insulate it again +in its place; and then, after measuring the force in the electrometer +(1181.), to return it to its place opposite to the inductric ball for a +second observation. Or it was easy by revolving the stand which supported +the cube to bring four of its faces in succession towards the inductric +ball, and so observe the force when the lines of inductive action (1304.) +coincided with, or were transverse to, the direction of the optical axis of +the crystal. Generally from twenty to twenty-eight observations were made +in succession upon the four vertical faces of a cube, and then an average +expression of the inductive force was obtained, and compared with similar +averages obtained at other times, every precaution being taken to secure +accurate results. + +1692. The first cube used was of _rock crystal_; it was 0.7 of an inch in +the side. It presented a remarkable and constant difference, the average of +not less than 197 observations, giving 100 for the specific inductive +capacity in the direction coinciding with the optical axis of the cube, +whilst 93.59 and 93.31 were the expressions for the two transverse +directions. + +1693. But with a second cube of rock crystal corresponding results were not +obtained. It was 0.77 of an inch in the side. The average of many +experiments gave 100 for the specific inductive capacity coinciding with +the direction of the optical axis, and 98.6 and 99.92 for the two other +directions. + +1694. Lord Ashley, whom I have found ever ready to advance the cause of +science, obtained for me the loan of three globes of rock crystal belonging +to Her Grace the Duchess of Sutherland for the purposes of this +investigation. Two had such fissures as to render them unfit for the +experiments (1193. 1698.). The third, which was very superior, gave me no +indications of any difference in the inductive force for different +directions. + +1695. I then used cubes of Iceland spar. One 0.5 of an inch in diameter +gave 100 for the axial direction, and 98.66 and 95.74 for the two cross +directions. The other, 0.8 of an inch in the side, gave 100 for the axial +direction, whilst 101.73 and 101.86 were the numbers for the cross +direction. + +1696. Besides these differences there were others, which I do not think it +needful to state, since the main point is not confirmed. For though the +experiments with the first cube raised great expectation, they have not +been generalized by those which followed. I have no doubt of the results as +to that cube, but they cannot as yet be referred to crystallization. There +are in the cube some faintly coloured layers parallel to the optical axis, +and the matter which colours them may have an influence; but then the +layers are also nearly parallel to a cross direction, and if at all +influential should show some effect in that direction also, which they did +not. + +1697. In some of the experiments one half or one part of a cube showed a +superiority to another part, and this I could not trace to any charge the +different parts had received. It was found that the varnishing of the cubes +prevented any communication of charge to them, except (in a few +experiments) a small degree of the negative state, or that which was +contrary to the state of the inductric ball (1564. 1566.). + +1698. I think it right to say that, as far as I could perceive, the +insulating character of the cubes used was perfect, or at least so nearly +perfect, as to bear a comparison with shell-lac, glass, &c. (1255). As to +the cause of the differences, other than regular crystalline structure, +there may be several. Thus minute fissures in the crystal insensible to the +eye may be so disposed as to produce a sensible electrical difference +(1193.). Or the crystallization may be irregular; or the substance may not +be quite pure; and if we consider how minute a quantity of matter will +alter greatly the conducting power of water, it will seem not unlikely that +a little extraneous matter diffused through the whole or part of a cube, +may produce effects sufficient to account for all the irregularities of +action that have been observed. + +1699. An important inquiry regarding the electrical polarity of the +particles of an insulating dielectric, is, whether it be the molecules of +the particular substance acted on, or the component or ultimate particles, +which thus act the part of insulated conducting polarizing portions +(1669.). + +1700. The conclusion I have arrived at is, that it is the molecules of the +substance which polarize as wholes (1347.); and that however complicated +the composition of a body may be, all those particles or atoms which are +held together by chemical affinity to form one molecule of the resulting +body act as one conducting mass or particle when inductive phenomena and +polarization are produced in the substance of which it is a part. + +1701. This conclusion is founded on several considerations. Thus if we +observe the insulating and conducting power of elements when they are used +as dielectrics, we find some, as sulphur, phosphorus, chlorine, iodine, +&c., whose particles insulate, and therefore polarize in a high degree; +whereas others, as the metals, give scarcely any indication of possessing a +sensible proportion of this power (1328.), their particles freely +conducting one to another. Yet when these enter into combination they form +substances having no direct relation apparently, in this respect, to their +elements; for water, sulphuric acid, and such compounds formed of +insulating elements, conduct by comparison freely; whilst oxide of lead, +flint glass, borate of lead, and other metallic compounds containing very +high proportions of conducting matter, insulate excellently well. Taking +oxide of lead therefore as the illustration, I conceive that it is not the +particles of oxygen and lead which polarize separately under the act of +induction, but the molecules of oxide of lead which exhibit this effect, +all the elements of one particle of the resulting body, being held together +as parts of one conducting individual by the bonds of chemical affinity; +which is but another term for electrical force (918.). + +1702. In bodies which are electrolytes we have still further reason for +believing in such a state of things. Thus when water, chloride of tin, +iodide of lead, &c. in the solid state are between the electrodes of the +voltaic battery, their particles polarize as those of any other insulating +dielectric do (1164.); but when the liquid state is conferred on these +substances, the polarized particles divide, the two halves, each in a +highly charged state, travelling onwards until they meet other particles in +an opposite and equally charged state, with which they combine, to the +neutralization of their chemical, i.e. their electrical forces, and the +reproduction of compound particles, which can again polarize as wholes, and +again divide to repeat the same series of actions (1347.). + +1703. But though electrolytic particles polarize as wholes, it would appear +very evident that in them it is not a matter of entire indifference _how_ +the particle polarizes (1689.), since, when free to move (380, &c.) the +polarities are ultimately distributed in reference to the elements; and +sums of force equivalent to the polarities, and very definite in kind and +amount, separate, as it were, from each other, and travel onwards with the +elementary particles. And though I do not pretend to know what an atom is, +or how it is associated or endowed with electrical force, or how this force +is arranged in the cases of combination and decomposition, yet the strong +belief I have in the electrical polarity of particles when under inductive +action, and the hearing of such an opinion on the general effects of +induction, whether ordinary or electrolytic, will be my excuse, I trust, +for a few hypothetical considerations. + +1704 In electrolyzation it appears that the polarized particles would +(because of the gradual change which has been induced upon the chemical, +i.e. the electrical forces of their elements (918.)) rather divide than +discharge to each other without division (1348.); for if their division, +i.e. their decomposition and recombination, be prevented by giving them the +solid state, then they will insulate electricity perhaps a hundredfold more +intense than that necessary for their electrolyzation (419, &c.). Hence the +tension necessary for direct conduction in such bodies appears to be much +higher than that for decomposition (419. 1164. 1344.). + +1705. The remarkable stoppage of electrolytic conduction by solidification +(380. 1358.), is quite consistent with these views of the dependence of +that process on the polarity which is common to all insulating matter when +under induction, though attended by such peculiar electro-chemical results +in the case of electrolytes. Thus it may be expected that the first effect +of induction is so to polarize and arrange the particles of water that the +positive or hydrogen pole of each shall be from the positive electrode and +towards the negative electrode, whilst the negative or oxygen pole of each +shall be in the contrary direction; and thus when the oxygen and hydrogen +of a particle of water have separated, passing to and combining with other +hydrogen and oxygen particles, unless these new particles of water could +turn round they could not take up that position necessary for their +successful electrolytic polarization. Now solidification, by fixing the +water particles and preventing them from assuming that essential +preliminary position, prevents also their electrolysis (413.); and so the +transfer of forces in that manner being prevented (1347. 1703.), the +substance acts as an ordinary insulating dielectric (for it is evident by +former experiments (419. 1704.) that the insulating tension is higher than +the electrolytic tension), induction through it rises to a higher degree, +and the polar condition of the molecules as wholes, though greatly exalted, +is still securely maintained. + +1706. When decomposition happens in a fluid electrolyte, I do not suppose +that all the molecules in the same sectional plane (1634.) part with and +transfer their electrified particles or elements at once. Probably the +_discharge force_ for that plane is summed up on one or a few particles, +which decomposing, travelling and recombining, restore the balance of +forces, much as in the case of spark disruptive discharge (1406.); for as +those molecules resulting from particles which have just transferred power +must by their position (1705.) be less favourably circumstanced than +others, so there must be some which are most favourably disposed, and +these, by giving way first, will for the time lower the tension and produce +discharge. + +1707. In former investigations of the action of electricity (821, &c.) it +was shown, from many satisfactory cases, that the quantity of electric +power transferred onwards was in proportion to and was definite for a given +quantity of matter moving as anion or cathion onwards in the electrolytic +line of action; and there was strong reason to believe that each of the +particles of matter then dealt with, had associated with it a definite +amount of electrical force, constituting its force of chemical affinity, +the chemical equivalents and the electro-chemical equivalents being the +same (836.). It was also found with few, and I may now perhaps say with no +exceptions (1341.), that only those compounds containing elements in single +proportions could exhibit the characters and phenomena of electrolytes +(697.); oxides, chlorides, and other bodies containing more than one +proportion of the electro-negative element refusing to decompose under the +influence of the electric current. + +1708. Probable reasons for these conditions and limitations arise out of +the molecular theory of induction. Thus when a liquid dielectric, as +chloride of tin, consists of molecules, each composed of a single particle +of each of the elements, then as these can convey equivalent opposite +forces by their separation in opposite directions, both decomposition and +transfer can result. But when the molecules, as in the bichloride of tin, +consist of one particle or atom of one element, and two of the other, then +the simplicity with which the particles may be supposed to be arranged and +to act, is destroyed. And, though it may be conceived that when the +molecules of bichloride of tin are polarized as wholes by the induction +across them, the positive polar force might accumulate on the one particle +of tin whilst the negative polar force accumulated on the two particles of +chlorine associated with it, and that these might respectively travel right +and left to unite with other two of chlorine and one of tin, in analogy +with what happens in cases of compounds consisting of single proportions, +yet this is not altogether so evident or probable. For when a particle of +tin combines with two of chlorine, it is difficult to conceive that there +should not be some relation of the three in the resulting molecule +analogous to fixed position, the one particle of metal being perhaps +symmetrically placed in relation to the two of chlorine: and, it is not +difficult to conceive of such particles that they could not assume that +position dependent both on their polarity and the relation of their +elements, which appears to be the first step in the process of +electrolyzation (1345. 1705.). + + +S 21. _Relation of the electric and magnetic forces._ + + +1709. I have already ventured a few speculations respecting the probable +relation of magnetism, as the transverse force of the current, to the +divergent or transverse force of the lines of inductive action belonging to +static electricity (1658, &c.). + +1710. In the further consideration of this subject it appeared to me to be +of the utmost importance to ascertain, if possible, whether this lateral +action which we call magnetism, or sometimes the induction of electrical +currents (26. 1048, &c.), is extended to a distance _by the action of the +intermediate particles_ in analogy with the induction of static +electricity, or the various effects, such as conduction, discharge, &c., +which are dependent on that induction; or, whether its influence at a +distance is altogether independent of such intermediate particles (1662.). + +1711. I arranged two magneto-electric helices with iron cores end to end, +but with an interval of an inch and three quarters between them, in which +interval was placed the end or pole of a bar magnet. It is evident, that on +moving the magnetic pole from one core towards the other, a current would +tend to form in both helices, in the one because of the lowering, and in +the other because of the strengthening of the magnetism induced in the +respective soft iron cores. The helices were connected together, and also +with a galvanometer, so that these two currents should coincide in +direction, and tend by their joint force to deflect the needle of the +instrument. The whole arrangement was so effective and delicate, that +moving the magnetic pole about the eighth of an inch to and fro two or +three times, in periods equal to those required for the vibrations of the +galvanometer needle, was sufficient to cause considerable vibration in the +latter; thus showing readily the consequence of strengthening the influence +of the magnet on the one core and helix, and diminishing it on the other. + +1712. Then without disturbing the distances of the magnet and cores, plates +of substances were interposed. Thus calling the two cores A and B, a plate +of shell-lac was introduced between the magnetic pole and A for the time +occupied by the needle in swinging one way; then it was withdrawn for the +time occupied in the return swing; introduced again for another equal +portion of time; withdrawn for another portion, and so on eight or nine +times; but not the least effect was observed on the needle. In other cases +the plate was alternated, i.e. it was introduced between the magnet and A +for one period of time, withdrawn and introduced between the magnet and B +for the second period, withdrawn and restored to its first place for the +third period, and so on, but with no effect on the needle. + +1713. In these experiments _shell-lac_ in plates 0.9 of an inch in +thickness, _sulphur_ in a plate 0.9 of an inch in thickness, and _copper_ +in a plate 0.7 of an inch in thickness were used without any effect. And I +conclude that bodies, contrasted by the extremes of conducting and +insulating power, and opposed to each other as strongly as metals, air, and +sulphur, show no difference with respect to magnetic forces when placed in +their lines of action, at least under the circumstances described. + +1714. With a plate of iron, or even a small piece of that metal, as the +head of a nail, a very different effect was produced, for then the +galvanometer immediately showed its sensibility, and the perfection of the +general arrangement. + +1715. I arranged matters so that a plate of _copper_ 0.2 of an inch in +thickness, and ten inches in diameter, should have the part near the edge +interposed between the magnet and the core, in which situation it was first +rotated rapidly, and then held quiescent alternately, for periods according +with that required for the swinging of the needle; but not the least effect +upon the galvanometer was produced. + +1716. A plate of shell-lac 0.6 of an inch in thickness was applied in the +same manner, but whether rotating or not it produced no effect. + +1717. Occasionally the plane of rotation was directly across the magnetic +curve: at other times it was made as oblique as possible; the direction of +the rotation being also changed in different experiments, but not the least +effect was produced. + +1718. I now removed the helices with their soft iron cores, and replaced +them by two _flat helices_ wound upon card board, each containing forty-two +feet of silked copper wire, and having no associated iron. Otherwise the +arrangement was as before, and exceedingly sensible; for a very slight +motion of the magnet between the helices produced an abundant vibration of +the galvanometer needle. + +1719. The introduction of plates of shell-lac, sulphur, or copper into the +intervals between the magnet and these helices (1713.), produced not the +least effect, whether the former were quiescent or in rapid revolution +(1715.). So here no evidence of the influence of the intermediate particles +could be obtained (1710.). + +1720. The magnet was then removed and replaced by a flat helix, +corresponding to the two former, the three being parallel to each other. +The middle helix was so arranged that a voltaic current could be sent +through it at pleasure. The former galvanometer was removed, and one with a +double coil employed, one of the lateral helices being connected with one +coil, and the other helix with the other coil, in such manner that when a +voltaic current was sent through the middle helix its inductive action +(26.) on the lateral helices should cause currents in them, having contrary +directions in the coils of the galvanometer. By a little adjustment of the +distances these induced currents were rendered exactly equal, and the +galvanometer needle remained stationary notwithstanding their frequent +production in the instrument. I will call the middle coil C, and the +external coils A and B. + +1721. A plate of copper 0.7 of an inch thick and six inches square, was +placed between coils C and B, their respective distances remaining +unchanged; and then a voltaic current from twenty pairs of 4 inch plates +was sent through the coil C, and intermitted, in periods fitted to produce +an effect on the galvanometer (1712.). if any difference had been produced +in the effect of C on A and B. But notwithstanding the presence of air in +one interval and copper in the other, the inductive effect was exactly +alike on the two coils, and as if air had occupied both intervals. So that +notwithstanding the facility with which any induced currents might form in +the thick copper plate, the coil outside of it was just as much affected by +the central helix C as if no such conductor as the copper had been there +(65.). + +1722. Then, for the copper plate was substituted one of sulphur 0.9 of an +inch thick; still the results were exactly the same, i.e. there was no +action at the galvanometer. + +1723. Thus it appears that when a voltaic current in one wire is exerting +its inductive action to produce a contrary or a similar current in a +neighbouring wire, according as the primary current is commencing or +ceasing, it makes not the least difference whether the intervening space is +occupied by such insulating bodies as air, sulphur and shell-lac, or such +conducting bodies as copper, and the other non-magnetic metals. + +1724. A correspondent effect was obtained with the like forces when +resident in a magnet thus. A single flat helix (1718.) was connected with a +galvanometer, and a magnetic pole placed near to it; then by moving the +magnet to and from the helix, or the helix to and from the magnet, currents +were produced indicated by the galvanometer. + +1725. The thick copper plate (1721.) was afterwards interposed between the +magnetic pole and the helix; nevertheless on moving these to and fro, +effects, exactly the same in direction and amount, were obtained as if the +copper had not been there. So also on introducing a plate of sulphur into +the interval, not the least influence on the currents produced by motion of +the magnet or coils could be obtained. + +1726. These results, with many others which I have not thought it needful +to describe, would lead to the conclusion that (judging by the _amount_ of +effect produced at a distance by forces transverse to the electric current, +i.e. magnetic forces,) the intervening matter, and therefore the +intervening particles, have nothing to do with the phenomena; or in other +words, that though the inductive force of static electricity is transmitted +to a distance by the action of the intermediate particles (1164. 1666.), +the transverse inductive force of currents, which can also act at a +distance, is not transmitted by the intermediate particles in a similar +way. + +1727. It is however very evident that such a conclusion cannot be +considered as proved. Thus when the metal copper is between the pole and +the helix (1715. 1719. 1725.) or between the two helices (1721.) we know +that its particles are affected, and can by proper arrangements make their +peculiar state for the time very evident by the production of either +electrical or magnetical effects. It seems impossible to consider this +effect on the particles of the intervening matter as independent of that +produced by the inductric coil or magnet C, on the inducteous coil or core +A (1715. 1721.); for since the inducteous body is equally affected by the +inductric body whether these intervening and affected particles of copper +are present or not (1723. 1725.), such a supposition would imply that the +particles so affected had no reaction back on the original inductric +forces. The more reasonable conclusion, as it appears to me, is, to +consider these affected particles as efficient in continuing the action +onwards from the inductric to the inducteous body, and by this very +communication producing the effect of _no loss_ of induced power at the +latter. + +1728. But then it may be asked what is the relation of the particles of +insulating bodies, such as air, sulphur, or lac, when _they_ intervene in +the line of magnetic action? The answer to this is at present merely +conjectural. I have long thought there must be a particular condition of +such bodies corresponding to the state which causes currents in metals and +other conductors (26. 53. 191. 201. 213.); and considering that the bodies +are insulators one would expect that state to be one of tension. I have by +rotating non-conducting bodies near magnetic poles and poles near them, and +also by causing powerful electric currents to be suddenly formed and to +cease around and about insulators in various directions, endeavoured to +make some such state sensible, but have not succeeded. Nevertheless, as any +such state must be of exceedingly low intensity, because of the feeble +intensity of the currents which are used to induce it, it may well be that +the state may exist, and may be discoverable by some more expert +experimentalist, though I have not been able to make it sensible. + +1729. It appears to me possible, therefore, and even probable, that +magnetic action may be communicated to a distance by the action of the +intervening particles, in a manner having a relation to the way in which +the inductive forces of static electricity are transferred to a distance +(1677.); the intervening particles assuming for the time more or less of a +peculiar condition, which (though with a very imperfect idea) I have +several times expressed by the term _electro-tonic state_ (60. 242. 1114. +1661.). I hope it will not be understood that I hold the settled opinion +that such is the case. I would rather in fact have proved the contrary, +namely, that magnetic forces are quite independent of the matter +intervening between the inductric and the inductions bodies; but I cannot +get over the difficulty presented by such substances as copper, silver, +lead, gold, carbon, and even aqueous solutions (201. 213.), which though +they are known to assume a peculiar state whilst intervening between the +bodies acting and acted upon (1727.), no more interfere with the final +result than those which have as yet had no peculiarity of condition +discovered in them. + +1730. A remark important to the whole of this investigation ought to be +made here. Although I think the galvanometer used as I have described it +(1711. 1720.) is quite sufficient to prove that the final amount of action +on each of the two coils or the two cores A and B (1713. 1719.) is equal, +yet there is an effect which _may_ be consequent on the difference of +action of two interposed bodies which it would not show. As time enters as +an element into these actions[A] (125.), it is very possible that the +induced actions on the helices or cores A, B, though they rise to the same +degree when air and copper, or air and lac are contrasted as intervening +substances, do not do so in the same time; and yet, because of the length +of time occupied by a vibration of the needle, this difference may not be +visible, both effects rising to their maximum in periods so short as to +make no sensible portion of that required for a vibration of the needle, +and so exert no visible influence upon it. + + [A] See Annnles de Chimie, 1833, tom. li. pp. 422, 428. + + * * * * * + +1731. If the lateral or transverse force of electrical currents, or what +appears to be the same thing, magnetic power, could be proved to be +influential at a distance independently of the intervening contiguous +particles, then, as it appears to me, a real distinction of a high and +important kind, would be established between the natures of these two +forces (1654. 1664.). I do not mean that the powers are independent of each +other and might be rendered separately active, on the contrary they are +probably essentially associated (1654.), but it by no means follows that +they are of the same nature. In common statical induction, in conduction, +and in electrolyzation, the forces at the opposite extremities of the +particles which coincide with the lines of action and have commonly been +distinguished by the term electric, are polar, and in the cases of +contiguous particles act only to insensible distances; whilst those which +are transverse to the direction of these lines, and are called magnetic, +are circumferential, act at a distance, and if not through the mediation of +the intervening particles, have their relations to ordinary matter entirely +unlike those of the electrical forces with which they are associated. + +1732. To decide this question of the identity or distinction of the two +kinds of power, and establish their true relation, would be exceedingly +important. The question seems fully within the reach of experiment, and +offers a high reward to him who will attempt its settlement. + +1733. I have already expressed a hope of finding an effect or condition +which shall be to statical electricity what magnetic force is to current +electricity (1658.). If I could have proved to my own satisfaction that +magnetic forces extended their influence to a distance by the conjoined +action of the intervening particles in a manner analogous to that of +electrical forces, then I should have thought that the natural tension of +the lines of inductive action (1659.), or that state so often hinted at as +the electro-tonic state (1661. 1662.), was this related condition of +statical electricity. + +1734. It may be said that the state of _no lateral action_ is to static or +inductive force the equivalent of _magnetism_ to current force; but that +can only be upon the view that electric and magnetic action are in their +nature essentially different (1664.). If they are the same power, the whole +difference in the results being the consequence of the difference of +_direction_, then the normal or _undeveloped_ state of electric force will +correspond with the state of _no lateral action_ of the magnetic state of +the force; the electric current will correspond with the lateral effects +commonly called magnetism; but the state of static induction which is +between the normal condition and the current will still require a +corresponding lateral condition in the magnetic series, presenting its own +peculiar phenomena; for it can hardly be supposed that the normal electric, +and the inductive or polarized electric, condition, can both have the same +lateral relation. If magnetism be a separate and a higher relation of the +powers developed, then perhaps the argument which presses for this third +condition of that force would not be so strong. + +1735. I cannot conclude these general remarks upon the relation of the +electric and magnetic forces without expressing my surprise at the results +obtained with the copper plate (1724. 1725.). The experiments with the flat +helices represent one of the simplest cases of the induction of electrical +currents (1720.); the effect, as is well known, consisting in the +production of a momentary current in a wire at the instant when a current +in the contrary direction begins to pass through a neighbouring parallel +wire, and the production of an equally brief current in the reverse +direction when the determining current is stopped (26.). Such being the +case, it seems very extraordinary that this induced current which takes +place in the helix A when there is only air between A and C (1720.). should +be equally strong when that air is replaced by an enormous mass of that +excellently conducting metal copper (1721.). It might have been supposed +that this mass would have allowed of the formation and discharge of almost +any quantity of currents in it, which the helix C was competent to induce, +and so in some degree have diminished if not altogether prevented the +effect in A: instead of which, though we can hardly doubt that an infinity +of currents are formed at the moment in the copper plate, still not the +smallest diminution or alteration of the effect in A appears (65.). Almost +the only way of reconciling this effect with generally received notions is, +as it appears to me, to admit that magnetic action is communicated by the +action of the intervening particles (1729. 1733.). + +1736. This condition of things, which is very remarkable, accords perfectly +with the effects observed in solid helices where wires are coiled over +wires to the amount of five or six or more layers in succession, no +diminution of effect on the outer ones being occasioned by those within. + + +S _22. Note on electrical excitation._ + + +1737. That the different modes in which electrical excitement takes place +will some day or other be reduced under one common law can hardly be +doubted, though for the present we are bound to admit distinctions. It will +be a great point gained when these distinctions are, not removed, but +understood. + +1738. The strict relation of the electrical and chemical powers renders the +chemical mode of excitement the most instructive of all, and the case of +two isolated combining particles is probably the simplest that we possess. +Here however the action is local, and we still want such a test of +electricity as shall apply to it, to cases of current electricity, and also +to those of static induction. Whenever by virtue of the previously combined +condition of some of the acting particles (923.) we are enabled, as in the +voltaic pile, to expand or convert the local action into a current, then +chemical action can be traced through its variations to the production of +_all_ the phenomena of tension and the static state, these being in every +respect the same as if the electric forces producing them had been +developed by friction. + +1739. It was Berzelius, I believe, who first spoke of the aptness of +certain particles to assume opposite states when in presence of each other +(959.). Hypothetically we may suppose these states to increase in intensity +by increased approximation, or by heat, &c. until at a certain point +combination occurs, accompanied by such an arrangement of the forces of the +two particles between themselves as is equivalent to a discharge, producing +at the same time a particle which is throughout a conductor (1700.). + +1740. This aptness to assume an excited electrical state (which is probably +polar in those forming non-conducting matter) appears to be a primary fact, +and to partake of the nature of induction (1162.), for the particles do not +seem capable of retaining their particular state independently of each +other (1177.) or of matter in the opposite state. What appears to be +definite about the particles of matter is their assumption of a +_particular_ state, as the positive or negative, in relation to each other, +and not of either one or other indifferently; and also the acquirement of +force up to a certain amount. + +1741. It is easily conceivable that the same force which causes local +action between two free particles shall produce current force if one of the +particles is previously in combination, forming part of an electrolyte +(923. 1738.). Thus a particle of zinc, and one of oxygen, when in presence +of each other, exert their inductive forces (1740.), and these at last rise +up to the point of combination. If the oxygen be previously in union with +hydrogen, it is held so combined by an analogous exertion and arrangement +of the forces; and as the forces of the oxygen and hydrogen are for the +time of combination mutually engaged and related, so when the superior +relation of the forces between the oxygen and zinc come into play, the +induction of the former or oxygen towards the metal cannot be brought on +and increased without a corresponding deficiency in its induction towards +the hydrogen with which it is in combination (for the amount of force in a +particle is considered as definite), and the latter therefore has its force +turned towards the oxygen of the next particle of water; thus the effect +may be considered as extended to sensible distances, and thrown into the +condition of static induction, which being discharged and then removed by +the action of other particles produces currents. + +1742. In the common voltaic battery, the current is occasioned by the +tendency of the zinc to take the oxygen of the water from the hydrogen, the +effective action being at the place where the oxygen leaves the previously +existing electrolyte. But Schoenbein has arranged a battery in which the +effective action is at the other extremity of this essential part of the +arrangement, namely, where oxygen goes to the electrolyte[A]. The first may +be considered as a case where the current is put into motion by the +abstraction of oxygen from hydrogen, the latter by that of hydrogen from +oxygen. The direction of the electric current is in both cases the same, +when referred to the direction in which the elementary particles of the +electrolyte are moving (923. 962.), and both are equally in accordance with +the hypothetical view of the inductive action of the particles just +described (1740.). + + [A] Philosophical Magazine, 1838, xii. 225, 315. also De la Rive's + results with peroxide of manganese. Annales de Chimie, 1836, lxi. p. + 40.--_Dec. 1838._ + +1743. In such a view of voltaic excitement, the action of the particles may +be divided into two parts, that which occurs whilst the force in a particle +of oxygen is rising towards a particle of zinc acting on it, and falling +towards the particle of hydrogen with which it is associated (this being +the progressive period of the inductive action), and that which occurs when +the change of association takes place, and the particle of oxygen leaves +the hydrogen and combines with the zinc. The former appears to be that +which produces the current, or if there be no current, produces the state +of tension at the termination of the battery; whilst the latter, by +terminating for the time the influence of the particles which have been +active, allows of others coming into play, and so the effect of current is +continued. + +1744. It seems highly probable, that excitement by friction may very +frequently be of the same character. Wollaston endeavoured to refer such +excitement to chemical action[A]; but if by chemical action ultimate union +of the acting particles is intended, then there are plenty of cases which +are opposed to such a view. Davy mentions some such, and for my own part I +feel no difficulty in admitting other means of electrical excitement than +chemical action, especially if by chemical action is meant a final +combination of the particles. + + [A] Philosophical Transactions, 1801, p. 427. + +1745. Davy refers experimentally to the opposite states which two particles +having opposite chemical relations can assume when they are brought into +the close vicinity of each other, but _not_ allowed to combine[A]. This, I +think, is the first part of the action already described (1743.); but in my +opinion it cannot give rise to a continuous current unless combination take +place, so as to allow other particles to act successively in the same +manner, and not even then unless one set of the particles be present as an +element of an electrolyte (923. 963.); i.e. mere quiescent contact alone +without chemical action does not in such cases produce a _current_. + + [A] Philosophical Transactions, 1807, p. 31. + +1746. Still it seems very possible that such a relation may produce a high +charge, and thus give rise to excitement by friction. When two bodies are +rubbed together to produce electricity in the usual way, one at least must +be an insulator. During the act of rubbing, the particles of opposite kinds +must be brought more or less closely together, the few which are most +favourably circumstanced being in such close contact as to be short only of +that which is consequent upon chemical combination. At such moments they +may acquire by their mutual induction (1740.) and partial discharge to each +other, very exalted opposite states, and when, the moment after, they are +by the progress of the rub removed from each other's vicinity, they will +retain this state if both bodies be insulators, and exhibit them upon their +complete separation. + +1747. All the circumstances attending friction seem to me to favour such a +view. The irregularities of form and pressure will cause that the particles +of the two rubbing surfaces will be at very variable distances, only a few +at once being in that very close relation which is probably necessary for +the development of the forces; further, those which are nearest at one time +will be further removed at another, and others will become the nearest, and +so by continuing the friction many will in succession be excited. Finally, +the lateral direction of the separation in rubbing seems to me the best +fitted to bring many pairs of particles, first of all into that close +vicinity necessary for their assuming the opposite states by relation to +each other, and then to remove them from each other's influence whilst they +retain that state. + +1748. It would be easy, on the same view, to explain hypothetically, how, +if one of the rubbing bodies be a conductor, as the amalgam of an +electrical machine, the state of the other when it comes from under the +friction is (as a mass) exalted; but it would be folly to go far into such +speculation before that already advanced has been confirmed or corrected by +fit experimental evidence. I do not wish it to be supposed that I think all +excitement by friction is of this kind; on the contrary, certain +experiments lead me to believe, that in many cases, and perhaps in all, +effects of a thermo-electric nature conduce to the ultimate effect; and +there are very probably other causes of electric disturbance influential at +the same time, which we have not as yet distinguished. + +_Royal Institution. +June, 1838._ + + + + +INDEX. + + * * * * * + +N.B. A dash rule represents the _italics_ immediately preceding it. The +references are sometimes to the individual paragraph, and sometimes to that +in conjunction with those which follow. + + * * * * * + +_Absolute_ charge of matter, 1169. +---- quantity of electricity in matter, 852, 861, 873. +Acetate of potassa, its electrolysis, 749. +Acetates, their electrolysis, 774. +Acetic acid, its electrolysis, 773. +_Acid_, nitric, formed in air by a spark, 324. +----, or alkali, alike in exciting the pile, 932. +----, transference of, 525. +---- _for battery_, its nature and strength, 1128, 1137. +---- ----, nitric, the best, 1138. +---- ----, effect of different strengths, 1139. +---- _in voltaic pile_, does not evolve the electricity, 925, 933. +---- ----, its use, 925. +Acids and bases, their relation in the voltaic pile, 927, 933. +Active battery, general remarks on, 1034, 1136. +Adhesion of fluids to metals, 1038. +Advantages of a new voltaic battery, 1132. +_Affinities, chemical_, opposed voltaically, 891, 904, 910. +----, their relation in the active pile, 949. +_Air_, its attraction by surfaces, 622. +----, _charge of_, 1173. +----, ----, by brush, 1434, 1441. +----, ----, by glow, 1537, 1543. +----, convective currents in, 1572, 1576, 1581. +----, dark discharge in, 1548. +----, disruptive discharge in, 1359, 1406, 1425, 1526. +----, induction in, 1208, 1215, 1284, 1362. +----, its insulating and conducting power, 411, 1332, 1336, 1362. +----, its rarefaction facilitates discharge, 1375. +----, electrified, 1443. +----, electro-chemical decompositions in, 454, 1623. +----, hot, discharges voltaic battery, 271, 274. +----, poles of, 455, 461, 559. +----, _positive and negative_ brush in, 1467, 1472, 1476. +----, ---- glow in, 1526, 1530. +----, ---- spark in, 1485. +----, rarefied, brush in, 1451, 1456. +----, retention of electricity on conductors by, 1377, 1398. +----, _specific inductive capacity of_, 1284. +----, ----, not varied by temperature or pressure, 1287, 1288. +_Alkali_ has strong exciting power in voltaic pile, 884, 931, 941. +----, transference of, 525. +_Amalgamated zinc_, its condition, 1000. +----, how prepared, 863. +----, its valuable use, 863, 999. +---- battery, 1001. +_Ammonia_, nature of its electrolysis, 748. +----, solution of, a bad conductor, 554, 748. +Ampere's inductive results, 78, 255, 379 _note_. +_Anions_ defined, 665, 824. +----, table of, 847. +---- related through the entire circuit, 963. +----, their action in the voltaic pile, 924. +----, their direction of transfer, 962, +Anode defined, 663. +_Antimony_, its relation to magneto-electric induction, 139. +----, chloride of, not an electrolyte, 690, 796. +----, oxide of, how affected by the electric current, 801. +---- _supposed new_ protoxide, 693. +---- ----, sulphuret, 694. +_Animal electricity_, its general characters considered, 351. +---- is identical with other electricities, 354, 360. +----, its chemical force, 355. +----, enormous amount, 359. +----, evolution of heat, 353, +----, magnetic force, 351. +----, physiological effects, 357. +----, spark, 358. +----, tension, 352. +Apparatus, inductive, 1187. _See_ Inductive apparatus. +_Arago's magnetic phenomena_, their nature, 81, 120. +----, reason why no effect if no motion, 126, +----, direction of motion accounted for, 121. +----, due to induced electric currents, 119, 248. +----, like electro-magnetic rotations in principle, 121. +----, not due to direct induction of magnetism, 128, 138, 215, 243, 248. +----, obtained with electro-magnets, 129. +----, produced by conductors only, 130, 215. +----, time an element in, 124. +----, Babbage and Hershel's results explained, 127. +Arago's experiment, Sturgeon's form of, 219. +Associated voltaic circles, 989. +_Atmospheric_ balls of fire, 1611. +----, electricity, its chemical action, 336. +Atomic number judged of from electrochemical equivalent, 851. +_Atoms of matter_, 869, 1703. +----, their electric power, 856, 860. +Attraction of particles, its influence in Doebereiner's phenomena, 619. +_Attractions_, electric, their force, 1022 _note_. +----, _chemic, produce_ current force, 852, 918, 947, 996, 1741. +----, ---- local force, 852, 921, 947, 959, 1739. +----, hygrometric, 621. +Aurora borealis referred to magneto-electric induction, 192. +Axis of power, the electric current on, 517, 1627, 1642. + +Balls of fire, atmospheric, 1611. +Barlow's revolving globe, magnetic effects explained, 137, 160. +Barry, decomposed bodies by atmospheric electricity, 338. +Bases and acids, their relation in the pile, 927. +Battery, Leyden, that generally used, 291. +_Battery, voltaic_, its nature, 856, 989. +----, _origin of its power_, 878, 989. +----, ---- not in contact, 887, 915, +----, ---- chemical, 879, 916, 919, 1741. +----, ----, oxidation of the zinc, 919, 944. +----, its circulating force, 858, 1120. +----, its local force, 1120. +----, quantity of electricity circulating, 990. +----, intensity of electricity circulating, 990, 993. +----, _intensity of its current_, 909, 994. +----, ---- increased, 905, 989. +----, _its diminution in power_, 1035. +----, ---- _from_ adhesion of fluid, 1003, 1136. +----, ---- ---- peculiar state of metal, 1040. +----, ---- ---- exhaustion of charge, 1042. +----, ---- ---- irregularity of plates, 1045, 1146. +----, use of metallic contact in, 893, 896. +----, _electrolytes essential to it_, 921. +----, ----, why, 858, 923. +----, state of metal and electrolyte before contact, 916. +----, conspiring action of associated affinities, 989. +----, purity of its zinc, 1144. +----, use of amalgamated zinc in, 999. +----, _plates, their_ number, 1151. +----, ---- size, 1154. +----, ---- vicinity, 1148. +----, ---- immersion, 1150. +----, ---- relative age, 1146. +----, ---- foulness, 1145. +----, _excited by_ acid, 880, 926, 1137. +----, ---- alkali, 931, 934, 941. +----, ---- sulphuretted solutions, 943. +----, the acid, its use, 925, +----, acid for, 1128, 1137. +----, nitric acid best for, 1137. +----, construction of, 989, 1001, 1121. +----, with numerous alternations, 989. +----, Hare's, 1123. +----, general remarks on, 1031. 1136. +----, simultaneous decompositions with, 1156. +----, practical results with, 1136. +----, _improved_, 1001, 1006, 1120. +----, ----, its construction, 1124. +----, ----, power, 1125, 1128. +----, ----, advantages, 1132. +----, ----, disadvantages, 1132. +Batteries, voltaic, compared, 1126. +Becquerel, his important secondary results, 745, 784. +Berzelius, his view of combustion, 870, 959. +Biot's theory of electro-chemical decomposition, 486. +Bismuth, its relation to magneto-electric induction, 139. +_Bodies_ classed in relation to the electric current, 823. +---- classed in relation to magnetism, 255. +Bodies electrolyzable, 824. +Bonijol decomposed substances by atmospheric electricity, 336. +Boracic acid a bad conductor, 408. +_Brush, electric_, 1425. +----, produced, 1425. +----, not affected by nature of conductors, 1454, 1473. +----, is affected by the dielectrics, 1455, 1463, 1475. +----, not dependent on current of air, 1440. +----, proves molecular action of dielectric, 1449, 1450. +----, its analysis, 1427, 1433. +----, nature, 1434, 1441, 1447. +----, form, 1428, 1449, 1451. +----, _ramifications_, 1439. +---- ----, their coalescence, 1453. +----, sound, 1426, 1431. +----, requisite intensity for, 1446. +---- has sensible duration, 1437. +---- is intermitting, 1427, 1431, 1451. +----, _light of_, 1444, 1445, 1451. +----, ----, in different gases, 1446, 1454. +----, dark? 1444, 1552. +----, passes into spark, 1448. +----, spark and glow relation of, 1533, 1539, 1542. +----, in gases, 1454, 1463, 1476. +----, oxygen, 1457, 1476. +----, nitrogen, 1458, 1476. +----, hydrogen, 1459, 1476. +----, coal-gas, 1460, 1476. +----, carbonic acid gas, 1461, 1476. +----, muriatic acid gas, 1462, 1476. +----, rare air, 1451, 1455, 1474. +----, oil of turpentine, 1452. +----, positive, 1455, 1467, 1484. +----, _negative_, 1468, 1472, 1484. +----, ----, of rapid recurrence, 1468, 1491. +----, positive and negative in different gases, 1455, 1475, 1506. + +_Capacity, specific inductive_, 1252. +----. _See_ Specific inductive capacity. +_Carbonic acid gas_ facilitates formation of spark, 1463. +----, brush in, 1461, 1476. +----, glow in, 1534. +----, spark in, 1422, 1463. +----, _positive and negative_ brush in, 1476. +----, ---- discharge in, 1546. +----, non-interference of, 645, 652. +Carbonic oxide gas, interference of, 645, 652. +_Carrying discharge_, 1562. +----. _See_ Discharge convective. +Cathode described, 663, 824. +_Cations_, or cathions, described, 665, 824. +----, table of, 817. +----, direction of their transfer, 962. +Cations, are in relation through the entire circuit, 963. +_Characters of_ electricity, table of, 360. +---- the electric current, constant, 1618, 1627. +---- voltaic electricity, 268. +---- ordinary electricity, 284. +---- magneto-electricity, 343. +---- thermo-electricity, 349. +---- animal electricity, 351. +_Charge_, free, 1684. +---- is always induction, 1171, 1177, 1300, 1682. +---- on surface of conductors: why, 1301. +----. _influence of_ form on, 1302. +----, ---- distance on, 1303. +----, loss of, by convection, 1569. +----, removed from good insulators, 1203. +---- of matter, absolute, 1169. +---- _of air_, 1173. +---- ---- by brush, 1434, 1441. +---- ---- by glow, 1526, 1537, 1543. +---- of particles in air, 1564. +---- of oil of turpentine, 1172. +---- of inductive apparatus divided, 1208. +----, residual, of a Leyden jar, 1249. +----, _chemical, for battery_, good, 1137. +-----, ----, weak and exhausted, 1042, 1143. +_Chemical action_, the, exciting the pile is oxidation, 921. +---- _superinduced by_ metals, 564. +---- ---- platina, 564, 617, 630. +---- tested by iodide of potassium, 315. +Chemical actions, distant, opposed to each other, 891, 910, 1007. +_Chemical affinity_ influenced by mechanical forces, 656. +---- transferable through metals, 918. +---- statical or local, 852, 921, 917, 959. +---- current, 852, 918, 947, 996. +_Chemical decomposition by_ voltaic electricity, 278, 450, 661. +---- common electricity, 309, 453. +---- magneto-electricity, 346. +---- thermo-electricity, 349. +---- animal electricity, 355. +----. _See_ Decomposition electro-chemical. +Chemical and electrical forces identical, 877, 918, 947, 960, 965, 1031. +_Chloride of_ antimony not an electrolyte, 690. +---- _lead_, its electrolysis, 794, 815. +---- ----, electrolytic intensity for, 978. +---- _silver_, its electrolysis, 541, 813, 902. +---- ----, electrolytic intensity for, 979. +---- tin, its electrolysis, 789, 819. +_Chlorides in_ solution, their electrolysis, 766. +---- fusion, their electrolysis, 789, 813. +Circle of anions and cathions, 963. +_Circles_, simple voltaic, 875. +----, associated voltaic, 989. +Circuit, voltaic, relation of bodies in, 962. +_Classification of bodies in relation to_ magnetism, 255. +---- the electric current, 823, 817. +Cleanliness of metals and other solids, 633. +_Clean platina_, its characters, 633, 717. +----, _its power of effecting combination_, 590, 605, 617, 632. +----, ----. _See_ Plates of platina. +_Coal gas_, brush in, 1460. +----, dark discharge in, 1556. +----, positive and negative brush in, 1476. +----, positive and negative discharge in, 1515. +----, spark in, 1422. +Colladon on magnetic force of common electricity, 289. +Collectors, magneto-electric, 86. +_Combination effected by_ metals, 564, 608. +---- solids, 564, 618. +---- poles of platina, 566. +---- _platina_, 564, 568, 571, 590, 630. +---- ----, as plates, 569. +---- ----, as sponge, 609, 636. +---- ----, cause of, 590, 616, 625, 656. +---- ----, how, 630. +---- ----, interferences with, 638, 652, 655. +---- ---- _retarded by_ olefiant gas, 640. +---- ---- ---- carbonic oxide, 645, 652. +---- ---- ---- sulphuret of carbon, 650. +---- ---- ---- ether, 651. +---- ---- ---- other substances, 649, 653, 654. +Comparison of voltaic batteries, 1126, 1146. +_Conditions_, general, of voltaic decomposition, 669. +----, new, of electro-chemical decomposition, 453. +_Conducting power_ measured by a magnet, 216. +---- of solid electrolytes, 419. +---- of water, constant, 984. +_Conduction_, 418, 1320. +----, its nature, 1320, 1326, 1611. +----, of two kinds, 987. +----, preceded by induction, 1329, 1332, 1338. +---- and insulation, cases of the same kind, 1320, 1326, 1336, 1338, 1561. +----, its relation to the intensity of the current conducted, 419. +---- common to all bodies, 444, 449. +---- by a vacuum, 1613. +---- by lac, 1234, 1324. +---- by sulphur, 1241, 1328. +---- by glass, 1239, 1324. +---- by spermaceti, 1240, 1323. +---- by gases, 1336. +----, slow, 1233, 1245, 1328. +---- affected by temperature, 445, 1339. +---- by metals diminished by heat, 432, 445. +---- increased by heat, 432, 441, 445. +---- of electricity and heat, relation of, 416. +----, _simple, can occur in electrolytes_, 967, 983. +----, ---- with very feeble currents, 970. +---- by electrolytes without decomposition, 968, 1017, 1032. +---- and decomposition associated in electrolytes, 413, 676, 854. +---- facilitated in electrolytes, 1355. +---- _by water_ bad, 1159. +---- ---- improved by dissolved bodies, 984, 1355. +----, electrolytic, stopped, 380, 1358, 1705. +---- of currents stopped by ice, 381. +---- conferred by liquefaction, 394, 410. +---- _taken away by solidification_, 394, 1705. +---- ---- why, 910, 1705. +----, _new law of_, 380, 394, 410. +----, ----, supposed exception to, 691, 1340. +----, general results as to, 443. +Conductive discharge, 1320. +_Conductors_, electrolytic, 474. +----, magneto-electric, 86. +----, their nature does not affect the electric brush, 1454. +----, size of, affects discharge, 1372. +----, form of, affects discharge, 1374, 1425. +----, _distribution of electricity on_, 1368. +----, ----, _affected by_ form, 1374. +----, ----, ---- distance, 1364, 1371. +----, ----, ---- air pressure, 1375. +----, ----, irregular with equal pressure, 1378. +Constancy of electric current, 1618. +_Constitution of electrolytes as to_ proportions, 679, 697, 830, 1708. +---- liquidity, 394, 823. +_Contact of metals_ not necessary for electrolyzation, 879. +----, its use in the voltaic battery, 893. +---- not necessary for spark, 915, 956. +_Contiguous particles_, their relation to induction, 1165, 1679. +---- active in electrolysis, 1349, 1703. +_Convection_, 1562, 1642. +---- or convective discharge. _See_ Discharge convective. +Copper, iron, and sulphur circle, 943. +Coruscations of lightning, 1464. +_Coulomb's electrometer_, 1180. +----, precautions in its use, 1182, 1186, 1206. +Crystals, induction through, 1689. +Cube, large, electrified, 1173. +Cubes of crystals, induction through, 1692, 1695. +Current chemical affinity, 852, 918, 947, 996. +Current, voltaic, without metallic contact, 879, 887. +_Current, electric_, 1617. +----, defined, 282, 511. +----, nature of, 511, 667, 1617, 1627. +----, variously produced, 1618. +----, _produced by_ chemical action, 879, 916, 1741. +----, ---- animals, 351. +----, ---- friction, 301, 307, 311. +----, ---- heat, 349, +----, ---- discharge of static electricity, 296, 307, 363. +----, ---- _induction by_ other currents, 6, 1089. +----, ---- ---- magnets, 30, 88, 344. +----, evolved in the moving earth, 181. +----, in the earth, 187. +----, natural standard of direction, 663. +----, none of one electricity, 1627, 1632, 1635. +----, two forces everywhere in it, 1627, 1632, 1635, 1642. +----, one, and indivisible, 1627. +----, an axis of power, 517, 1642. +----, constant in its characters, 1618, 1627. +----, inexhaustibility of, 1631. +----, _its velocity in_ conduction, 1648. +----, ---- electrolyzation, 1651. +----, regulated by a fine wire, 853, _note_. +----, affected by heat, 1637. +----, stopped by solidification, 381. +----, _its section_, 498, 504, 1634. +----, ---- presents a constant force, 1634. +----, _produces_ chemical phenomena, 1621. +----, ---- heat, 1625. +----, its heating power uniform, 1630. +----, produces magnetism, 1653. +----, Porrett's effects produced by, 1646. +----, _induction of_, 1, 6, 232, 241, 1101, 1048. +----, ----, on itself, 1048. +----, ----. _See_ Induction of electric current. +----, its inductive force lateral, 1108. +----, induced in different metals, 193, 213, 201, 211. +----, _its transverse effects_, 1653. +----, ---- constant, 1655. +----, _its transverse forces_, 1658. +----, ---- are in relation to contiguous particles, 1664. +----, ---- their polarity of character, 1665. +---- and magnet, their relation remembered, 38, _note_. +_Currents_ in air by convection, 1572, 1581. +----, metals by convection, 1603. +----, oil of turpentine by convection, 1595, 1598. +Curved lines, induction in, 1215. +Curves, magnetic, their relation to dynamic induction, 217, 232. + +Daniell on the size of the voltaic metals, 1525. +_Dark discharge_,1444, 1544. +----. _See_ Discharge, dark. +Dates of some facts and publications, 139, _note after_. +_Davy's_ theory of electro-chemical decomposition, 482, 500. +---- electro-chemical views, 965. +---- mercurial cones, convective phenomena, 1603. +_Decomposing force_ alike in every section of the current, 501, 505. +----, variation of, on each particle, 503. +_Decomposition_ and conduction associated in electrolytes, 413, 854. +----, primary and secondary results of, 742, 777. +---- _by common electricity_, 309, 454. +---- ----, precautions, 322. +_Decomposition, electro-chemical_, 450, 669. +----, nomenclature of, 661. +----, new terms relating to, 662. +----, its distinguishing character, 309. +----, by common electricity, 309, 454. +----, by a single pair of plates, 862, 897, 904, 931. +----, by the electric current, 1621. +----, without metallic contact, 880, 882. +----, its cause, 891, 904, 910. +----, not due to direct attraction or repulsion of poles, 493, 497, 536, + 542, 5460. +----, _dependent on_ previous induction, 1345. +----, ---- the electric current, 493, 510, 524, 854. +----, ---- intensity of current, 905. +----, ---- chemical affinity of particles, 519, 525, 519. +----, resistance to, 891, 910, 1007. +----, intensity requisite for, 966, 1354. +----, stopped by solidification, 380, 1358, 1705. +----, retarded by interpositions, 1007. +----, assisted by dissolved bodies, 1355. +----, division of the electrolyte, 1347, 1623, 1701. +----, transference, 519, 525, 538, 550, 1347, 1706. +----, why elements appear at the poles, 535. +----, uncombined bodies do not travel, 544, 546. +----, circular series of effects, 562, 962. +----, simultaneous, 1156, +----, _definite_, 329, 372, 377, 504, 704, 714, 722, 726, 732, 764, 783, + 807, 821, 960. +----, ---- independent of variations of electrodes, 714, 722, 807, 832. +----, necessary intensity of current, 911, 966, 1345, 1354. +----, influence of water in, 472. +----, in air, 451, 461, 469. +----, some general conditions of, 669. +----, new conditions of, 453. +----, primary results, 742. +----, secondary results, 702, 742, 748, 777. +----, of acetates, 774. +----, acetic acid, 773. +----, ammonia, 748. +----, _chloride of_ antimony, 690, 796. +----, ---- lead, 794, 815. +----, ---- silver, 541, 813, 979. +----, _chlorides in_ solution, 766. +----, ---- fusion, 789, 913. +----, fused electrolytes, 789. +----, hydriodic acid and iodides, 767, 787. +----, hydrocyanic acid and cyanides, 771. +----, hydrofluoric acid and fluorides, 770. +----, _iodide of_ lead, 802, 818. +----, ---- potassium, 805. +----, muriatic acid, 758, 780. +----, nitre, 753. +----, nitric acid, 752. +----, _oxide_ antimony, 801. +----, ---- lead, 797. +----, protochloride of tin, 789, 819. +----, protiodide of tin, 804. +----, sugar, gum, &c., 776. +----, of sulphate of magnesia, 495. +----, sulphuric acid, 757. +----, sulphurous acid, 755. +----, tartaric acid, 775. +----, water, 704, 785, 807. +----, _theory of_, 477, 1345. +----, ----, by A. de la Rive, 489, 507, 514, 543. +----, ----, Biot, 486. +----, ----, Davy, 482, 500. +----, ----, Grotthuss, 481, 499, 515. +----, ----, Hachette, 491, 513, +----, ----, Riffault and Chompre, 485, 507, 512. +----, author's theory, 518, 524, 1345, 1623, 1703, 1766. +_Definite_ decomposing action of electricity, 329, 372, 377, 504, 704, 783, + 821. +----, magnetic action of electricity, 216, 362, 367, 377. +----, _electro-chemical action_, 822, 869, 960. +----, ----, general principles of, 822, 862. +----, ----, _in chloride of lead_, 815. +----, ----, ---- silver, 813. +----, ----, in hydriodic acid, 767, 787. +----, ----, iodide of lead, 802, 818. +----, ----, muriatic acid, 758, 786, +----, ----, protochloride of tin, 819. +----, ----, water, 732, 785, 807. +Degree in measuring electricity, proposal for, 736. +_De la Rive_ on heat at the electrodes, 1637. +----, his theory of electro-chemical decomposition, 489, 507, 514, 543. +_Dielectrics_, what, 1168. +----, their importance in electrical actions, 1666. +----, their relation to static induction, 1296. +----, their condition under induction, 1369, 1679. +----, their nature affects the brush, 1455. +----, their specific electric actions, 1296, 1398, 1423, 1454, 1503, 1560. +Difference of positive and negative discharge, 1465, 1480, 1485. +Differential inductometer, 1307. +_Direction of_ ions in the circuit, 962. +----, the electric current, 563. +----, the magneto-electric current, 114, 116. +----, the induced volta-electric current, 19, 26, 1091. +Disruptive discharge, 1359, 1405. _See_ Discharge, disruptive. +_Discharge, electric_, as balls of fire, 1641. +----, of Leyden jar, 1300. +----, _of voltaic battery by_ hot air, 271, 274. +----, ---- points, 272. +----, velocity of, in metal, varied, 1333. +----, varieties of, 1319. +----, brush, 1425. _See_ Brush. +----, carrying, 1562. _See_ Discharge, convective. +----, conductive, 1320. _See_ Conduction. +----, dark, 1444, 1544. +----, disruptive, 1359, 1405. +----, electrolytic, 1343, 1622, 1704. +----, glow, 1526. _See_ Glow. +----, positive and negative, 1465. +----, spark, 1406. _See_ Spark, electric. +_Discharge, connective_, 1442, 1562, 1601, 1623, 1633, 1642. +----, in insulating media, 1562, 1572. +----, in good conductors, 1603. +----, _with fluid terminations in_ air, 1581, 1589. +----, ---- liquids, 1597. +----, from a ball, 1576, 1590. +----, influence of points in, 1573. +----, _affected by_ mechanical causes, 1579. +----, ---- flame, 1580. +----, with glow, 1576. +----, _charge of a particle in_ air, 1564. +----, ---- oil of turpentine, 1570. +----, charge of air by, 1442, 1592. +----, _currents produced in_ air, 1572, 1581, 1591. +----, ---- oil of turpentine, 1595, 1598. +----, direction of the currents, 1599, 1645. +----, Porrett's effects, 1646, +----, positive and negative, 1593, 1600, 1643. +----, related to electrolytic discharge, 1622, 1633. +_Discharge, dark_, 1444, 1544, 1560. +----, with negative glow, 1544. +----, between positive and negative glow, 1547. +----, in air, 1548. +----, muriatic acid gas, 1554. +----, coal gas, 1556. +----, hydrogen, 1558. +----, nitrogen, 1559. +_Discharge, disruptive_, 1405. +----, preceded by induction, 1362. +----, determined by one particle, 1370, 1409. +----, necessary intensity, 1409, 1553. +----, determining intensity constant, 1410. +----, related to particular dielectric, 1503. +----, facilitates like action, 1417, 1435, 1453, 1553. +----, its time, 1418, 1436, 1498, 1641. +----, _varied by_ form of conductors, 1302, 1372, 1374. +----, ---- change in the dielectric, 1395, 1422,1454. +----, ---- rarefaction of air, 1365, 1375, 1451. +----, ---- temperature, 1367, 1380. +----, ---- distance of conductors, 1303, 1364, 1371. +----, ---- size of conductors, 1372. +----, in liquids and solids, 1403. +----, in _different gases_, 1381, 1388, 1421. +----, ---- not alike, 1395. +----, ---- specific differences, 1399, 1422, 1687. +----, _positive and negative_, 1393, 1399, 1465, 1524. +----, ----, distinctions, 1467, 1475, 1482. +----, ----, differences, 1485, 1501. +----, ----, relative facility, 1496, 1520. +----, ----, dependent on the dielectric, 1503. +----, ----, in different gases, 1506, 1510, 1518, 1687. +----, ----, of voltaic current, 1524. +----, brush, 1425. +----, collateral, 1412. +----, dark, 1444, 1544, 1560. +----, glow, 1526. +----, spark, 1406. +----, theory of, 1308, 1406, 1434. +_Discharge, electrolytic_, 1164, 1343, 1621, 1703, 1706. +----, previous induction, 1345, 1351. +----, necessary intensity, 912, 966, 1346, 1354. +----, division of the electrolyte, 1347, 1704. +----, stopped by solidifying the electrolyte, 380, 1358, 1705. +----, facilitated by added bodies, 1355. +----, in curved lines, 521, 1216, 1351. +----, proves action of contiguous particles, 1349. +----, positive and negative, 1525. +----, velocity of electric current in, 1650. +----, related to convective discharge, 1622. +----, theory of, 1344, 1622, 1704. +Discharging train generally used, 292. +Disruptive discharge, 1405. _See_ Discharge, disruptive. +Dissimulated electricity, 1684. +_Distance, its influence_ in induction, 1303, 1364,1371. +---- over disruptive discharge, 1364, 1371. +Distant chemical actions, connected and opposed, 891, 909. +Distinction of magnetic and magneto-electric action, 138, 215, 243, 253. +Division of a charge by inductive apparatus, 1208. +Doebereiner on combination effected by platina, 609, 610. +Dulong and Thenard on combination by platina and solids, 609, 611. +Dust, charge of its particles, 1567. + +Earth, natural magneto-electric induction in, 181, 190, 192. +_Elasticity of_ gases, 626. +---- gaseous particles, 658. +_Electric_ brush, 1425. _See_ Brush, electric. +---- condition of particles of matter, 862, 1669. +---- conduction, 1320. _See_ Conduction. +---- _current_ defined, 283, 511. +---- ----, nature of, 511, 1617, 1627. +---- ----. _See_ Current, electric. +---- ----, _induction of_, 6, 232, 241, 1048, 1101. _See_ Induction of + electric current. +---- ----, ----, on itself, 1048. +---- discharge, 1319. _See_ Discharge. +---- force, nature of, 1667. _See_ Forces. +---- induction, 1162. _See_ Induction. +---- inductive capacity, 1252. _See_ Specific inductive capacity. +---- polarity, 1685. _See_ Polarity, electric. +---- spark, 1406. _See_ Spark, electric. +---- and magnetic forces, their relation, 118, 1411, 1653, 1658, 1709, + 1731. +Electrics, charge of, 1171, 1247. +_Electrical_ excitation, 1737. _See_ Excitation. +---- machine generally used, 290. +---- battery generally used, 291. +---- and chemical forces identical, 877, 917, 947, 960, 965, 1031. +_Electricities_, their identity, however excited, 265, 360. +----, one or two, 516, 1667. +----, _two_, 1163. +----, ----, their independent existence, 1168. +----, ----, their inseparability, 1168, 1177, 1244. +----, ----, never separated in the current, 1628. +_Electricity_, quantity of, in matter, 852, 861. +----, _its distribution on conductors_, 1368. +----, ---- _influenced by_ form, 1302, 1374. +----, ---- ---- distance, 1303, 1364, 1371. +----, ---- ---- air's pressure, 1375. +----, relation of a vacuum to, 1613. +----, dissimulated, 1684. +----, common and voltaic, measured, 361, 860. +----, _its definite_ decomposing action, 329, 377, 783, 1621. +----, ---- heating action, 1625. +----, ---- magnetic action, 216, 366. +----, animal, its characters, 351. +----, magneto-, its characters, 343. +----, ordinary, its characters, 284. +----, thermo-, its characters, 349. +----, voltaic, its characters, 268. +_Electricity from magnetism_, 27, 36, 57, 83, 135, 140. +----, _on magnetisation of soft iron by_ currents, 27, 34, 57, 113. +---- ---- magnets, 36, 44. +----, _employing_ permanent magnets, 39, 84, 112. +----, ---- terrestrial magnetic force, 140, 150, 161. +----, ---- _moving conductors_, 55, 83, 132, 139, 149, 161, 171. +----, ---- ---- essential condition, 217. +---- _by revolving plate_, 83, 149, 240. +---- ---- a constant source of electricity, 89, 90, 154. +---- ----, law of evolution, 114. +---- ----, direction of the current evolved, 91, 99, 110, 116, 117. +---- ----, course of the currents in the plate, 123, 150. +---- by a revolving globe, 137, 160. +---- by plates, 94, 101. +---- by a wire, 49, 55, 109, 112, 137. +----, conductors and magnet may move together, 218. +----, _current produced_ in a single wire, 49, 55, 170. +----, ---- a ready source of electricity, 46, _note_. +----, ---- momentary, 28, 30, 47. +----, ---- permanent, 89, 154. +----, ---- deflects galvanometer, 30, 39, 46. +----, ---- makes magnets, 34. +----, ----, shock of, 56. +----, ----, spark of, 32. +----, ---- traverses fluids, 23, 33. +----, ----, its direction, 30, 38, 41, 52, 53, 54, 78, 91, 99, 114, 142, + 166, 220, 222. +----, effect of approximation and recession, 18, 39, 50. +----, the essential condition, 217. +----, general expression of the effects, 256. +----, from magnets alone, 220. +_Electricity of the voltaic pile_, 875. +---- _its source_, 875. +---- ---- not metallic contact, 887, 915. +---- ---- is in chemical action, 879, 916, 919, 1738, 1741. +_Electro-chemical decomposition_, 450, 661. +----, nomenclature, 661. +----, general conditions of, 669. +----, new conditions of, 453, +----, influence of water in, 472. +----, primary and secondary results, 742. +----, definite, 732, 783. +----, theory of, 477. +----. _See_ also Decomposition, electrochemical. +_Electro-chemical equivalents_, 824, 833, 835, 855. +----, table of, 847. +----, how ascertained, 837. +---- always consistent, 835. +---- same as chemical equivalents, 836, 839. +---- able to determine atomic number, 851. +Electro-chemical excitation, 878, 919, 1738. +Electrode defined, 662. +_Electrodes_ affected by heat, 1637. +----, _varied in_ size, 714, 722. +----, ---- nature, 807. +----. _See_ Poles. +Electrolysis, resistance to, 1007. +_Electrolyte_ defined, 664. +---- _exciting, solution of_ acid, 881, 925. +---- ---- alkali, 931, 941. +---- _exciting_, water, 944, 945. +---- ---- sulphuretted solution, 943. +_Electrolytes_, their necessary constitution, 669, 823, 829, 858, 921, + 1347, 1708. +---- consist of single proportionals of elements, 679, 697, 830, 1707. +---- _essential to voltaic pile_, 921. +---- ----, why, 858, 923. +---- conduct and decompose simultaneously, 413. +---- can conduct feeble currents without decomposition, 967. +----, as ordinary conductors, 970, 983, 1344. +----, solid, their insulating and conducting power, 419. +----, real conductive power not affected by dissolved matters, 1356. +----, needful conducting power, 1158. +---- are good conductors when fluid, 394, 823. +_Electrolytes non-conductors when solid_ 381, 394. +----, why, 910, 1705. +----, the exception, 1032. +_Electrolytes_, their particles polarize as wholes, 1700. +----, polarized light sent across, 951. +----, relation of their moving elements to the passing current, 923, 1704. +----, their resistance to decomposition, 891, 1007, 1705. +----, and metal, their states in the voltaic pile, 946. +----, salts considered as, 698. +----, acids not of this class, 681. +_Electrolytic_ action of the current, 478, 518, 1620. +---- conductors, 474. +---- discharge, 1343. _See_ Discharge, electrolytic. +---- induction, 1164, 1343. +---- _intensity_, 911, 966, 983. +---- ---- varies for different bodies, 912, 986, 1354. +---- ---- of chloride of lead, 978. +---- ---- chloride of silver, 979. +---- ---- sulphate of soda, 975. +---- ---- water, 968, 981. +---- ---- its natural relation, 987. +_Electrolyzation_, 450, 661, 1164, 1347, 1704. _See_ Decomposition + electro-chemical. +---- defined, 664. +---- facilitated, 394, 417, 549, 1355. +---- in a single circuit, 863, 879. +----, intensity needful for, 919, 966, +---- of chloride of silver, 541, 979. +---- sulphate of magnesia, 495. +---- and conduction associated, 413, 676. +Electro-magnet, inductive effects in, 1060. +Electro-magnetic induction definite, 216, 366. +_Electrometer, Coulomb's_, described, 1180. +----, how used, 1183. +_Electro-tonic state_, 60, 231, 242, 1114, 1661, 1729. +---- _considered common to all_ metals, 66. +---- ---- conductors, 76. +---- is a state of tension, 71. +---- is dependent on particles, 73. +Elementary bodies probably ions, 849. +_Elements evolved_ by force of the current, 493, 520, 524. +---- at the poles, why, 535. +---- determined to either pole, 552, 681, 757. +----, transference of, 454, 538. +----, if not combined, do not travel, 544, 546. +_Equivalents_, electro-chemical, 824, 833, 855. +----, chemical and electro-chemical, the same, 836, 839. +Ether, interference of, 651. +_Evolution_ of electricity, 1162, 1737. +---- of one electric force impossible, 1175. +---- of elements at the poles, why, 535. +_Excitation_, electrical, 1737. +---- by chemical action, 878, 916, 1739. +---- by friction, 1744. +Exclusive induction, 1681. + +Flame favours convectivc discharge, 1580. +Flowing water, electric currents in, 190. +Fluid terminations for convection, 1581. +Fluids, their adhesion to metals, 1038. +Fluoride of lead, hot, conducts well, 1340. +_Force, chemical_, local, 947, 959, 1739. +----, circulating, 917, 947, 996, 1120. +_Force_, electric, nature of, 1163, 1667. +----, inductive, of currents, its nature, 60, 1113, 1735. +_Forces, electric_, two, 1163. +----, inseparable, 1163, 1177, 1244, 1627. +---- and chemical, are the same, 877, 916. +---- _and magnetic_, relation of, 1411, 1653, 1658, 1709. +---- ----, are they essentially different? 1663, 1731. +_Forces, exciting, of voltaic apparatus_, 887, 916. +----, exalted, 905, 994, 1138, 1148. +_Forces_, polar, 1665. +---- _of the current_, direct, 1620. +---- ----, lateral or transverse, 1653, 1709. +_Form, its influence on_ induction, 1302, 1374. +---- discharge, 1372, 1374. +Fox, his terrestrial electric currents, 187. +_Friction_ electricity, its characters, 284. +----, excitement by, 1744. +Fusion, conduction consequent upon, 394, 402. +Fusinieri, on combination effected by platina, 613. + +_Galvanometer_, affected by common electricity, 289, 366. +----, a correct measure of electricity, 367, _note_. +_Gases_, their elasticity, 626, 657. +----, conducting power, 1336. +----, _insulating power_, 1381, 1507. +----, ---- not alike, 1395, 1508. +----, _specific inductive capacity_, 1283, 1290. +----, ---- alike in all, 1292. +----, specific influence on brush and spark, 1463, 1687. +----, discharge, disruptive, through, 1381. +----, brush in, 1454. +----, spark in, 1421. +----, _positive and negative brushes in_, 1475. +----, ----, their differences, 1476. +----, positive and negative discharge in, 1393, 1506, 1687. +----, solubility of, in cases of electrolyzation, 717, 728. +----, from water, spontaneous recombination of, 566. +----, mixtures of, affected by platina plates, 571. +----, mixed, relation of their particles, 625. +_General_ principles of definite electrolytic action, 822. +---- remarks on voltaic batteries, 1031, 1136. +---- _results as to_ conduction, 443. +---- ---- induction, 1295. +_Glass_, its conducting power, 1239. +----, its specific inductive capacity, 1271. +----, _its attraction for_ air, 622. +----, ---- water, 1251. +_Globe, revolving of Barlow_, effects explained, 137, 160. +----, is magnetic, 164. +_Glow_, 1405, 1525. +----, produced, 1527. +----, positive, 1527. +----, negative, 1530. +----, favoured by rarefaction of air, 1529. +----, is a continuous charge of air, 1526, 1537, 1543. +----, occurs in all gases, 1534. +----, accompanied by a wind, 1535. +----, its nature, 1543, +----, discharge, 1526. +----, brush and spark relation of, 1533, 1538, 1539, 1542. +Grotthuss' theory of electro-chemical decomposition, 481, 499, 515. +_Growth of a_ brush, 1437. +---- spark, 1553. + +Hachette's view of electro-chemical decomposition, 491. +Hare's voltaic trough, 1123, 1132. +Harris on induction in air, 1363. +_Heat_ affects the two electrodes, 1637. +---- increases the conducting power of some bodies, 432, 438, 1340. +----, its conduction related to that of electricity, 416. +----, as a result of the electric current, 853, _note_, 1625, 1630. +---- _evolved by_ animal electricity, 353. +---- ---- common electricity, 287. +---- ---- magneto-electricity, 344. +---- ---- thermo-electricity, 349. +---- ---- voltaic electricity, 276. +Helix, inductive effects in, 1061, 1094. +Hydriodic acid, its electrolyses, 767, 787. +Hydrocyanic acid, its electrolyses, 771, 788. +Hydrofluoric acid, not electrolysable, 770. +_Hydrogen_, brush in, 1459. +----, _positive and negative_ brush in, 1476. +----, ---- discharge in, 1514. +_Hydrogen and oxygen combined by_ platina plates, 570, 605. +---- spongy platina, 609. + +_Ice_, its conducting power, 419. +---- a non-conductor of voltaic currents, 381. +Iceland crystal, induction across, 1695. +_Identity_, of electricities, 265, 360. +---- of chemical and electrical forces, 877, 917, 947, 961, 1031. +Ignition of wire by electric current, 853, _note_, 1630. +Improved voltaic battery, 1006, 1120. +Increase of cells in voltaic battery, effect of, 990. +Inducteous surfaces, 1483. +_Induction apparatus_, 1187. +----, fixing the stem, 1190, 1193, 1200. +----, precautions, 1194, 1199, 1213, 1232, 1250. +----, removal of charge, 1203. +----, retention of charge, 1205, 1207. +----, a charge divided, 1208. +----, peculiar effects with, 1233. +_Induction, static_, 1161. +----, an action of contiguous particles, 1165, 1231, 1253, 1295, 1450, + 1668, 1679. +----, consists in a polarity of particles, 1298, 1670, 1679. +----, continues only in insulators, 1298, 1324, 1338. +----, intensity of, sustained, 1362. +----, _influenced by the_ form of conductors, 1302. +----, ---- distance of conductors, 1303. +----, ---- relation of the bounding surfaces, 1483. +----, charge, a case of, 1171, 1177, 1300. +----, exclusive action, 1681. +----, towards space, 1614. +----, across a vacuum, 1614. +---- _through_ air, 1217, 1284. +---- ---- different gases, 1381, 1395. +---- ---- crystals, 1689, +---- ---- lac, 1228, 1255, 1308. +---- ---- metals, 1329, 1332. +---- ---- all bodies, 1331, 1334. +----, _its relation to_ other electrical actions, 1165, 1178. +----, ---- insulation, 1324, 13602, 1368, 1678. +----, ---- conduction, 1320. +----, ---- discharge, 1319, 1323, 1362. +----, ---- electrolyzation, 1164, 1343. +----, ---- intensity, 1178, 1362. +----, ---- excitation, 1178, 1740. +----, its relation to charge, 1177, 1299. +---- an essential general electric function, 1178, 1299. +----, general results as to, 1295. +----, theory of, 1165, 1231, 1295, 1667, 1669. +---- _in curved lines_, 1166, 1215, 1679. +---- ----, _through_ air, 1218, 1449. +---- ----, ---- other gases, 1226. +---- ----, ---- lac, 1228. +---- ----, ---- sulphur, 1228. +---- ----, ---- oil of turpentine, 1227. +_induction, specific_, 1167, 1252, 1307. +----, _the problem_ stated, 1252. +----, ---- solved, 1307. +----, _of air_, 1284. +----, ----, invariable, 1287, 1288. +----, _of gases_, 1283, 1290. +----, ---- alike in all, 1292. +----, of shell-lac, 1256, 1269. +----, glass, 1271. +----, sulphur, 1275. +----, spermaceti, 1279. +----, certain fluid insulators, 1280. +_Induction of electric currents_, 6, 34, 232, 241, 1048, 1089, 1101, 1660, + 1718. +----, on aiming the principal current, 10, 238, 1101. +----, on stopping the principal current, 10, 17, 238, 1087, 1100. +---- by approximation, 18, 236. +---- by increasing distance, 19, 237. +---- _effective through_ conductors, 1719, 1721, 1735. +---- ---- insulators, 1719, 1722, 1735. +---- in different metals, 193, 202, 211, 213. +---- in the moving earth, 181. +---- in flowing water, 190. +---- in revolving plates, 85, 240. +----, _the induced current, its_ direction, 26, 232. +----, ---- duration, 19, 47, 89. +----, ----, traverses fluids, 20, 23. +----, ----, its intensity in different conductors, 183, 193, 201, 211, 213. +----, ----, not obtained by Leyden discharge, 24. +----, Ampere's results, 78, 255, 379, _note_. +_Induction of a current on itself_, 1048, 1109. +----, apparatus used, 1052. +----, _in a_ long wire, 1064, 1068, 1092, 1118. +----, ---- doubled wire, 1096. +----, ---- helix, 1053, 1061. +---- in doubled helices, 1096. +---- in an electro-magnet, 1056, 1060. +----, wire and helix compared, 1065. +----, short wire, effects with, 1067. +----, action momentary, 1070, 1091, 1100. +----, causes no permanent change in the current, 1071. +----, not due to momentum, 1077. +----, induced current separated, 1078, 1089. +----, _effect at_ breaking contact, 1060, 1081, 1084, 1087. +----, ---- making contact, 1101, 1106. +----, _effects produced_, shock, 1060, 1064, 1079. +----, ---- spark, 1060, 1064, 1080. +----, ---- chemical decomposition, 1084. +----, ---- ignition of wire, 1081, 1104. +----, cause is in the conductor, 1059, 1070. +----, general principles of the action, 1093, 1107. +----, direction of the forces lateral, 1108. +_induction, magnetic_, 255, 1658, 1710. +----, by intermediate particles, 1663, 1710, 1729, 1735. +----, _through_ quiescent bodies, 1712, 1719, 1720, 1735. +----, ---- moving bodies, 1715, 1716, 1719. +---- and magneto-electric, distinguished, 138, 215, 243, 253. +_Induction_, magneto-electric, 27, 58, 81, 140, 193, 1709. _See_ Arago's + magnetic phenomena. +----, magnelectric, 58. +----, electrolytic, 1164, 1345, 1702, 1740. +----, volta-electric, 26. +Inductive capacity, specific, 1167, 1252. +_Inductive force of currents_ lateral, 26, 1108. +----, its nature, 1113, 1660, 1663, 1709. +_Inductive force, lines of_, 1231, 1297, 1304. +----, often curved, 1219, 1224, 1230. +----, exhibited by the brush, 1449. +----, their lateral relation, 1231, 1297, 1304. +----, their relation to magnetism, 1411, 1658, 1709. +Inductometer, differential, 1307, 1317. +Inductric surfaces, 1483. +Inexhaustible nature of the electric current, 1631. +Inseparability of the two electric forces, 1163, 1177, 1244, 1628. +Insulating power of different gases, 1388, 1395, 1507. +_Insulation_, 1320, 1359, 1361. +----, its nature, 1321. +---- is sustained induction, 1324. +----, degree of induction sustained, 1362. +---- _dependent on the_ dielectrics, 1368. +---- ---- distance in air, 1303, 1364, 1371. +---- ---- density of air, 1365, 1375. +---- ---- induction, 1368. +---- ---- form of conductors, 1302, 1374. +----, as affected by temperature of air, 1367, 1380. +---- _in different gases_, 1381, 1388. +---- ---- differs, 1395. +---- in liquids and solids, 1403. +---- in metals, 1328, 1331, 1332. +---- and conduction not essentially different, 1320, 1326, 1336, 1338, + 1561. +----, its relation to induction, 1324, 1362, 1368, 1678. +_Insulators_, liquid, good, 1172. +----, solid, good, 1254. +----, the best conduct, 1233, 1241, 1245, 1247, 1254. +---- tested as to conduction, 1255. +---- and conductors, relation of, 1328, 1334, 1338. +_Intensity_, its influence in conduction, 419. +----, inductive, how represented, 1370. +----, relative, of magneto-electric currents, 183, 193, 211, 213. +---- of disruptive discharge constant, 1410. +----, electrolytic, 912, 966, 983, 1354. +---- necessary for electrolyzation, 911, 966. +---- _of the current of single circles_, 904. +---- ---- increased, 906. +---- of electricity in the voltaic battery, 990, 993. +---- of voltaic current increased, 906, 990. +_Interference with combining power of platina_, 638, 655. +---- by olefiant gas, 640. +---- carbonic oxide, 645. +---- sulphuret of carbon, 650. +---- ether, 651. +Interpositions, their retarding effects, 1018. +_Iodides in_ solution, their electrolysis, 769. +---- fusion, their electrolysis, 802, 813. +_Iodide_ of lead, electrolysed, 802, 818. +---- of potassium, test of chemical action, 316. +_Ions_, what, 665, 824, 833, 834, 849. +---- not transferable alone, 542, 547, 826. +----, table of, 847. +_Iron_, both magnetic and magneto-electric at once, 138, 254. +----, copper and sulphur circles, 943. + +Jenkin, his shock by one pair of plates, 1049. + +Kemp, his amalgam of zinc, 999. +Knight, Dr. Gowin, his magnet, 44. + +_Lac_, charge removed from, 1203. +----, induction through, 1255. +----, specific inductive capacity of, 1256, 1269. +----, effects of its conducting power, 1234. +----, its relation to conduction and insulation, 1324. +_Lateral_ direction of inductive forces of currents, 26, 1108. +---- forces of the current, 1653, 1709. +_Law of_ conduction, new, 380, 394, 410. +---- magneto-electric induction, 114. +---- volta-electric induction, 26. +_Lead_, chloride of, electrolysed, 794, 815. +----, fluoride of, conducts well when heated, 1340. +----, iodide of, electrolysed, 802, 818. +----, oxide of, electrolysed, 797. +_Leyden jar_, condition of its charge, 1682. +----, its charge, nature of, 1300. +----, its discharge, 1300. +----, its residual charge, 1249. +_Light_, polarized, passed across electrolytes, 951. +----, _electric_, 1405, 1445, 1560, _note_. +----, ----, spark, 1406, 1553. +----, ----, brush, 1425, 1444, 1445. +----, ----, glow, 1526. +Lightning, 1420, 1404, 1641. +_Lines of inductive force_, 1231, 1304, +---- often curved, 1219, 1224, 1230. +----, as shown by the brush, 1449. +----, their lateral relation, 1231, 1297, 1304. +----, their relation to magnetism, 1411, 1658, 1709. +Liquefaction, conduction consequent upon, 380, 394, 410. +Liquid bodies which are non-conductors, 405. +Local chemical affinity, 947, 959, 961, 1739. + +_Machine_, electric, evolution of electricity by, 1748. +------, magneto-electric, 135, 154, 158, 1118. +_Magnelectric_ induction, 58. +----, collectors or conductors, 86. +_Magnesia_, sulphate, decomposed against water, 494, 533. +----, transference of, 495. +_Magnet_, a measure of conducting power, 216. +---- _and_ current, their relation remembered, 38, _note_. +---- ---- plate revolved together, 218. +---- ---- cylinder revolved together, 219. +---- revolved alone, 220, 223. +---- and moving conductors, their general relation, 256. +---- made by induced current, 13, 14. +----, electricity from, 36, 220, 223. +_Magnetic_ bodies, but few, 255. +----, curves, their inductive relation, 217, 232. +---- _effects of_ voltaic electricity, 277. +---- ---- common electricity, 288, 367. +---- ---- magneto-electricity, 27, 83, 345. +---- ---- thermo-electricity, 349. +---- ---- animal electricity, 354. +---- and electric forces, their relation, 118, 1411, 1653, 1658, 1709, + 1731. +---- forces active through intermediate particles, 1663, 1710, 1729, 1735. +---- _forces of the current_, 1653. +---- ---- very constant, 1654. +---- deflection by common electricity, 289, 296. +---- phenomena of Arago explained, 81. +---- induction. _See_ Induction, magnetic. +---- _induction through_ quiescent bodies, 1712, 1719, 1720, 1735. +---- ---- moving bodies, 1715, 1719. +---- and magneto-electric action distinguished, 138, 215, 243, 253. +_Magnetism_, electricity evolved by, 27. +----, its relation to the lines of inductive force, 1411, 1658, 1709. +---- bodies classed in relation to, 255. +_Magneto-electric currents_, their intensity, 183, 193, 211, 213. +----, their direction, 114, 110. +---- traverse fluids, 33. +---- momentary, 30. +---- permanent, 89. +---- in all conductors, 193, 213. +_Magneto-electric induction_, 27, 58. +----, terrestrial, 110, 181. +----, law of, 114. +----. _See_ Arago's magnetic phenomena. +_Magneto-electric machines_, 135, 154, 158. +----, inductive effects in their wires, 1118, +_Magneto-electricity_, its general characters considered, 343, &c. +---- identical with other electricities, 360. +----, its tension, 343. +----, evolution of heat, 344. +----, magnetic force, 345. +----, chemical force, 346. +----, spark, 348. +----, physiological effects, 347. +----. _See_ Induction, magnetic. +_Matter_, atoms of, 869, 1703. +----, new condition of, 60, 231, 242, 1114, 1661, 1729. +----, quantity of electricity in, 852, 861, 873, 1652. +----, absolute charge of, 1169. +_Measures of electricity_, galvanometer, 367, _note_. +----, voltameter, 704, 736, 739. +----, metal precipitated, 740, 842. +Measure of specific inductive capacity, 1307, 1600. +_Measurement of_ common and voltaic electricities, 361, 860, 1652. +---- _electricity_, degree, 736, 738. +---- ---- by voltameter, 704, 736, 739. +---- ---- by galvanometer, 367, _note_. +---- ---- by metal precipitated, 740, 842. +Mechanical forces affect chemical affinity, 656. +Mercurial terminations for convection, 1581. +_Mercury_, periodide of, an exception to the law of conduction? 691, 1341. +----, perchloride of, 692, 1341. +_Metallic contact_ not necessary for electrolyzation, 879. +---- not essential to the voltaic current, 879, 887, 915. +---- its use in the pile, 893, 896. +Metallic poles, 557. +Metal and electrolyte, their state, 946. +_Metals_, adhesion of fluids to, 1038. +----, _their power of inducing combination_ 564, 608. +----, ---- interfered with, 638. +----, static induction in, 1329, 1332. +----, different, currents induced in, 193, 211. +----, generally secondary results of electrolysis, 746. +---- transfer chemical force, 918. +----, transference of, 539, 545. +---- insulate in a certain degree, 1328. +----, convective currents in, 1603. +----, but few magnetic, 255. +Model of relation of magnetism and electricity, 116. +Molecular inductive action, 1164, 1669. +_Motion_ essential to magneto-electric induction, 39, 217, 256. +---- across magnetic curves, 217. +---- _of conductor and magnet, relative_, 114. +---- ---- not necessary, 218. +Moving magnet is electric, 220. +_Muriatic acid gas_, its high insulating power, 1395. +----, brush in, 1462. +----, dark discharge in, 1554. +----, glow in, 1534. +----, positive and negative brush in, 1476. +----, _spark in_, 1422, 1463. +----, ----, has no dark interval, 1463, 1555. +_Muriatic acid_ decomposed by common electricity, 314. +----, its electrolysis (primary), 758, 786. + +Nascent state, its relation to combination, 658, 717. +_Natural_ standard of direction for current, 663. +---- relation of electrolytic intensity, 987. +_Nature of the electric_ current, 1617. +---- force or forces, 1667. +_Negative_ current, none, 1627, 1632. +---- _discharge_, 1465, 1484. +---- ----, as Spark, 1467, 1482. +---- ----, as brush, 1466, 1502. +---- spark or brush, 1484, 1502. +_Negative and positive discharge_, 1465, 1482, 1525 +---- in different gases, 1393. +_New_ electrical condition of matter, 60, 231, 242, 1114, 1661, 1729. +---- law of conduction, 380, 394, 410. +_Nitric acid_ formed by spark in air, 324. +---- _favours_ excitation of current, 906, 1138 +---- ---- transmission of current, 1020. +---- is best for excitation of battery, 1137. +----, nature of its electrolysis, 752. +_Nitrogen_ determined to either pole, 554, 748, 752. +---- a secondary result of electrolysis, 746, 748. +----, brush in, 1458. +----, dark discharge in, 1559. +----, glow in, 1534. +----, spark in, 1422, 1463. +----, _positive and negative_ brush in, 1476. +----, ---- discharge in, 1512. +----, its influence on lightning, 1464. +Nomenclature, 662, 1483. +Nonconduction by solid electrolytes, 381, 1358, 1705. +Note on electrical excitation, 1737. +Nuclei, their action, 623, 657. + +Olefiant gas, interference of, 610, 652. +_Ordinary electricity_, its tension, 285. +---- evolution of heat, 287. +---- magnetic force, 288, 362. +---- _chemical force_, 309, 454. +---- ----, precautions, 322. +---- spark, 333. +---- physiological effect, 332. +---- general characters considered, 284. +----, identity with other electricities, 360. +Origin of the force of the voltaic pile, 878, 910, 919. +Oxidation the origin of the electric current in the voltaic pile, 919, 930. +Oxide of lead electrolysed, 797. +_Oxygen_, brush in, 1457. +----, _positive and negative_ brush in, 1476, +----, ---- discharge in, 1513. +----, solubility of, in cases of electrolyzation, 717, 728. +----, spark in, 1422. +---- _and hydrogen combined by_ platina plates, 570, 605, 630. +---- ---- spongy platina, 609, 636. +---- ---- other metals, 608. + +_Particles_, their nascent state, 658. +---- in air, how charged, 1564. +----, neighbouring, their relation to each other, 619, 624, 657. +----, contiguous, active in induction, 1165, 1677. +---- of a dielectric, their inductive condition, 1369, 1410, 1669. +----, polarity of, when under induction, 1298, 1676. +----, _how polarised_, 1669, 1679. +----, ----, in any direction, 1689. +----, ----, as wholes or elements, 1699. +----, ----, in electrolytes, 1702. +----, crystalline, 1689. +----, contiguous, active in electrolysis, 1349, 1702. +----, _their_ action in electrolyzation, 520, 1343, 1703. +----, ---- local chemical action, 961, 1739. +----, ---- relation to electric action, 73. +----, ---- electric action, 1669, 1679, 1740. +Path of the electric spark, 1107. +Phosphoric acid not an electrolyte, 682. +_Physiological effects of_ voltaic-electricity, 279. +---- common electricity, 332. +---- magneto-electricity, 56, 347. +---- thermo-electricity, 349. +---- animal electricity, 357. +_Pile, voltaic_, electricity of, 875. +----. _See_ Battery, voltaic. +_Plates of platina_ effect combination, 568, 571, 590, 630. +---- _prepared by_ electricity, 570, 585, 588. +---- ---- friction, 591. +---- ---- heat, 595. +---- ---- chemical cleansing, 599, 605, +----, clean, their general properties, 633, 717. +----, _their power preserved_, 576. +----, ---- in water, 580. +----, _their power diminished by_ action, 581. +----, ---- exposure to air, 636. +----, _their power affected by_ washing in water, 582. +----, ---- heat, 584, 597. +----, ---- presence of certain gases, 638, 655. +----, their power, cause of, 590, 616, 630. +----, _theory of their action_, Doebereiner's, 610. +----, ----, Dulong and Thenard's, 611. +----, ----, Fusinieri's, 613. +----, ----, author's, 619, 626, 630, 656. +_Plates of voltaic battery_ foul, 1145. +----, new and old, 1116. +----, vicinity of, 1148. +----, immersion of, 1003, 1150. +----, number of, 989, 1151. +----, large or small, 1154. +_Platina_, clean, its characters, 633, 717. +---- attracts matter from the air, 634. +----, spongy, its state, 637. +----, _clean, its power of effecting combination_, 564, 590, 605, 617, 630. +----, ---- interfered with, 638. +----, _its action retarded by_ olefiant gas, 640, 652. +----, ----, carbonic oxide, 645, 652. +----. _See_ Combination, Plates of platina, and Interference. +---- poles, recombination effected by, 567, 588. +Plumbago poles for chlorides, 794. +Poisson's theory of electric induction, 1305. +_Points_, favour convective discharge, 1573. +----, fluid for convection, 1581. +_Polar_ forces, their character, 1665. +---- decomposition by common electricity, 312, 321, 469. +_Polarity_, meaning intended, 1304, 1685. +---- of particles under induction, 1298, 1676. +----, _electric_, 1070, 1085. +----, ----, its direction, 1688, 1703, +----, ----, its variation, 1687. +----, ----, its degree, 1686. +----, ----, in crystals, 1689. +----, ----, in molecules or atoms, 1699. +----, ----, in electrolytes, 1702. +Polarized light across electrolytes, 951. +_Poles, electric_, their nature, 461, 498, 556, 662. +----, appearance of evolved bodies at, accounted for, 535. +---- one element to either? 552, 681, 757. +----, of air, 455, 461, 559. +----, of water, 491, 558. +----, of metal, 557. +----, of platina, recombination effected by, 567, 588. +----, of plumbago, 794. +Poles, magnetic, distinguished, 44, _note_. +Porrett's peculiar effects, 1646. +_Positive_ current none, 1627, 1632. +---- _discharge_, 1465, 1480. +---- ----, as spark, 1467, 1482. +---- ----, as brush, 1467, 1476. +---- spark or brush, 1484, 1502. +---- _and negative_, convective discharge, 1600. +---- ---- _disruptive discharge_, 1465, 1482, 1485, 1525. +---- ---- ---- in different gases, 1393. +---- ---- voltaic discharge, 1524. +---- ---- electrolytic discharge, 1525. +Potassa acetate, nature of its electrolysis, 749. +Potassium, iodide of, electrolysed, 805. +Power of voltaic batteries estimated, 1126. +Powers, their state of tension in the pile, 949. +Practical results with the voltaic battery, 1136. +Pressure of air retains electricity, explained, 1377, 1398. +Primary electrolytical results, 742. +Principles, general, of definite electrolytic action, 822. +Proportionals in electrolytes, single, 679, 697. + +_Quantity of electricity in_ matter, 852, 861, 873, 1652. +---- voltaic battery, 990. + +Rarefaction of air facilitates discharge, why, 1375. +Recombination, spontaneous, of gases from water, 566. +_Relation_, by measure, of electricities, 361. +---- of magnets and moving conductors, 256. +---- of magnetic induction to intervening bodies, 1662, 1728. +---- of a current and magnet, to remember, 38, _note_. +---- of electric and magnetic forces, 118, 1411, 1653, 1658,1709, 1731. +---- of conductors and insulators, 1321, 1326, 1334, 1338. +---- of conduction and induction, 1320, 1337. +---- _of induction and_ disruptive discharge, 1362. +---- ---- electrolyzation, 1164, 1343. +---- ---- excitation, 1178, 1740. +---- ---- charge, 1171, 1177, 1300. +---- of insulation and induction, 1324, 1362, 1368, 1678. +----, lateral, of lines of inductive force, 1231, 1297, 1304. +---- of a vacuum to electricity, 1613. +---- of spark, brush, and glow, 1533, 1539, 1542. +---- of gases to positive and negative discharge, 1510. +---- of neighbouring particles to each other, 619, 624. +---- _of elements in_ decomposing electrolytes, 923, 1702. +---- ---- exciting electrolytes, 921. +---- of acids and bases voltaically, 927, 933. +Remarks on the active battery, 1034, 1136. +Residual charge of a Leyden jar, 1249. +_Resistance_ to electrolysis, 891, 904, 911, 1007. +---- of an electrolyte to decomposition, 1007. +_Results_ of electrolysis, primary or secondary, 742, 777. +----, practical, with the voltaic battery, 1136. +----, general, as to induction, 1295, 1669. +Retention of electricity by pressure of the atmosphere explained, 1377, + 1398. +_Revolving_ plate. _See_ Arago's phenomena. +---- _globe, Barlow's_, effect explained, 137, 160, 169. +---- ----, magnetic, 164. +---- ----, direction of currents in, 161, 166. +Riffault's and Chompre's theory of electro-chemical decomposition, 485, + 507, 512. +Rock crystal, induction across, 1692. +Room, insulated and electrified, 1173. +Rotation of the earth a cause of magneto-electric induction, 181. + +Salts considered as electrolytes, 698. +Scale of electrolytic intensities, 912. +_Secondary electrolytical results_, 702, 742, 748, 777. +---- become measures of the electric current, 843. +_Sections of the current_, 498, 1634. +----, decomposing force alike in all, 501, 1621. +_Sections of lines of inductive action_, 1369. +----, amount of force constant, 1369. +Shock, strong, with one voltaic pair, 1049. +_Silver, chloride of_, its electrolyzation, 541, 813, 902. +----, electrolytic intensity for, 979. +Silver, sulphuret of, hot, conducts well, 433. +_Simple voltaic circles_, 875. +----, decomposition effected by, 897, 904, 931. +Single and many pairs of plates, relation of, 990. +_Single voltaic circuits_, 875. +---- without metallic contact, 879. +---- with metallic contact, 893. +---- their force exalted, 906. +---- _give_ strong shocks, 1049. +---- ---- a bright spark, 1050. +_Solid electrolytes are non-conductors_, 394, 402, 1358. +----, why, 910, 1705. +_Solids, their power of inducing combination_, 564, 618. +---- interfered with, 638. +Solubility of gases in cases of electrolyzation, 717, 728. +_Source of electricity in the voltaic pile_, 875. +---- is chemical action, 879, 916, 919, 1741. +Spark, 1360, 1406. +_Spark, electric, its_ conditions, 1360, 1406, 1553. +---- path, 1407. +---- light, 1553. +---- insensible duration or time, 1438. +---- accompanying dark parts, 1547, 1632. +---- determination, 1370. 1409. +_Spark is affected by the_ dielectrics, 1395, 1421. +---- size of conductor, 1372. +---- form of conductor, 1302, 1374. +---- rarefaction of air, 1375. +_Spark_, atmospheric or lightning, 1464, 1641. +----, negative, 1393, 1467, 1482, 1484, 1502. +----, positive, 1393, 1448, 1467, 1482, 1484, 1502. +----, ragged, 1420, 1448. +----, when not straight, why, 1568. +----, variation in its length, 1381. +----, tendency to its repetition, 1392. +----, facilitates discharge, 1417, 1553. +----, passes into brush, 1448. +----, preceded by induction, 1362. +----, forms nitric acid in air, 324. +----, in gases, 1383, 1421. +----, in air, 1422. +----, in nitrogen, 1422, 1463. +----, in oxygen, 1422. +----, in hydrogen, 1422. +----, in carbonic acid, 1422, 1463. +----, in muriatic acid gas, 1422, 1463. +----, in coal-gas, 1422. +----, in liquids, 1424. +----, precautions, 958, 1074. +----, voltaic, without metallic contact, 915, 956. +---- from single voltaic pair, 1050. +---- from common and voltaic electricity assimilated, 334. +----, first magneto-electric, 32. +---- of voltaic electricity, 280. +---- of common electricity, 333. +---- of magneto-electricity, 348. +---- of thermo-electricity, 349. +---- of animal electricity, 358. +----, brush and glow related, 1533, 1539, 1542. +Sparks, their expected coalition, 1412. +Specific induction. _See_ Induction, specific, 1252. +_Specific inductive capacity_, 1252. +----, apparatus for, 1187. +---- of lac, 1256, 1270, 1308. +---- of sulphur, 1275, 1310. +---- of air, 1284. +---- of gases, 1283, 1290. +---- of glass, 1271. +_Spermaceti_, its conducting power, 1240, 1323. +----, its relation to conduction and insulation, 1322. +Standard of direction in the current, 663. +State, electrotonic, 60, 231, 242, 1114, 1661, 1729. +Static induction. _See_ Induction, static. +_Sturgeon_, his form of Arago's experiment, 249. +----, use of amalgamated zinc by, 863, 999. +_Sulphate of soda_, decomposed by common electricity, 317. +----, electrolytic intensity for, 975. +_Sulphur_ determined to either pole, 552, 681, 757. +----, its conducting power, 1241, 1245. +----, its specific inductive capacity, 1275. +----, copper and iron, circle, 943. +_Sulphuret of_ carbon, interference of, 650. +---- silver, hot, conducts well, 433. +Sulphuretted solution excites the pile, 943. +_Sulphuric acid_, conduction by, 409, 681. +----, magneto-electric induction on, 200, 213. +---- in voltaic pile, its use, 925. +---- not an electrolyte, 681. +----, its transference, 525. +----, its decomposition, 681, 757. +Sulphurous acid, its decomposition, 755. +_Summary of_ conditions of conduction, 443. +---- molecular inductive theory, 1669. + +_Table of_ discharge in gases, 1388. +---- electric effects, 360. +---- electro-chemical equivalents, 847. +---- electrolytes affected by fusion, 402. +---- insulation in gases, 1388. +---- ions, anions, and cathions, 847. +Tartaric acid, nature of its electrolysis, 775. +_Tension_, inductive, how represented, 1370. +---- of voltaic electricity, 268. +---- of common electricity, 285. +---- of thermo-electricity, 349. +---- of magneto-electricity, 343. +---- of animal electricity, 352. +---- of zinc and electrolyte in the voltaic pile, 949. +Terrestrial electric currents, 187. +_Terrestrial magneto-electric induction_, 140. +---- cause of aurora borealis, 192. +----, _electric currents produced by_, 141, 150. +----, ----, _in helices_ alone, 148. +----, ----, ---- with iron, 141, 146. +----, ----, ---- with a magnet, 147. +----, ---- a single wire, 170. +----, ---- a revolving plate, 149. +----, ---- a revolving ball, 160. +----, ---- the earth, 173. +Test between magnetic and magneto-electric action, 215, 243. +_Theory of_ combination of gases by clean platina, 619, 626, 630, 656. +---- electro-chemical decomposition, 477, 661, 1623, 1704. +---- the voltaic apparatus, 875, 1741. +---- static induction, 1165, 1231, 1295, 1666, 1667. +---- disruptive discharge, 1368, 1406, 1434. +---- Arago's phenomena, 120. +_Thermo-electricity_, its general characters, 349. +---- identical with other electricities, 360. +----, its evolution of heat, 349. +----, magnetic, force, 349. +----, physiological effects, 349. +----, spark, 349. +Time, 59, 68, 124, 1248, 1328, 1346, 1418, 1431, 1436, 1439, 1612, 1641, + 1730. +_Tin_, iodide of, electrolysed, 804. +----, protochloride, electrolysis of, definite, 789, 819. +_Torpedo_, nature of its electric discharge, 359. +----, its enormous amount of electric force, 359. +Transfer of elements and the current, their relation, 923, 962. +_Transference_ is simultaneous in opposite directions, 542, 828. +----, uncombined bodies do not travel, 544, 546, 826. +---- _of elements_, 454, 507, 539, 550, 826. +---- ---- across great intervals, 455, 468. +---- ----, its nature, 519, 525, 538, 549. +---- of chemical force, 918. +Transverse forces of the current, 1653, 1709. +Travelling of charged particles, 1563. +Trough, voltaic. _See_ Battery, voltaic. +_Turpentine, oil of_, a good fluid insulator, 1172. +----, its insulating power destroyed, 1571. +---- charged, 1172. +----, brush in, 1452, +----, electric motions in, 1588, 1595, +----, convective currents in, 1595, 1598. + +Unipolarity, 1635. + +Vacuum, its relation to electricity, 1613. +Vaporization, 657. +_Velocity of_ conduction in metals varied, 1333. +---- the electric discharge, 1641, 1649. +---- conductive and electrolytic discharge, difference of, 1650. +Vicinity of plates in voltaic battery, 1148. +Volta-electric induction, 26. +_Volta-electrometer_, 704, 736. +----, fluid decomposed in it, water, 706, 728, 732. +----, forms of, 707, 734. +---- _tested for variation of_ electrodes, 714, 722. +---- ---- fluid within, 727. +---- ---- intensity, 723. +----, strength of acid used in, 728,733. +----, _its indications by_ oxygen and hydrogen, 736. +----, ---- hydrogen, 734. +----, ---- oxygen, 735. +----, how used, 737. +Voltameter, 704. +_Voltaic battery_, its nature, 875, 989. +----, remarks on, 1034, 1136. +----, improved, 1001, 1119. +----, practical results with, 1136. +----. _See_ Battery, voltaic. +_Voltaic circles, simple_, 875. +----, decomposition by, 897. +Voltaic circles associated, or battery, 989. +_Voltaic circuit_, relation of bodies in, 962. +----, defined, 282, 511. +----, origin of, 916, 1741. +----, its direction, 663, 925, +----, intensity increased, 905, 990. +----, produced by oxidation of zinc, 919, 930. +---- not due to combination of oxide and acid, 925, 933. +----, _its relation to the_ combining oxygen, 921, 962. +----, ---- combining sulphur, 943. +----, ---- the transferred elements, 923, 962. +----, relation of bodies in, 962. +Voltaic current, 1617. _See_ Current, electric. +Voltaic discharge, positive and negative, 1524. +Voltaic decomposition, 450, 600. _See_ Decomposition, electro-chemical. +_Voltaic electricity_, identical with electricity, otherwise evolved, 268, + 360. +----, _discharged by_ points, 272. +----, ---- hot air, 271, 274. +----, its tension, 268, 275. +----, evolution of heat by, 276. +----, its magnetic force, 277. +----, its chemical force, 278. +----, its spark, 280. +----, its physiological effects, 279. +----, its general characters considered, 268. +_Voltaic pile_ distinguished, 856, _note_. +----, electricity of, 875. +----, depends on chemical action, 872. +----, relation of acid and bases in the, 927. +----. _See_ Battery, voltaic. +_Voltaic spark_ without contact, 915, 956. +----, precautions, 958, 1074. +Voltaic trough, 989. _See_ Battery, voltaic. + + +_Water_, flowing, electric currents in, 190. +----, retardation of current by, 1159. +----, _its direct conducting power_, 1017, 1159, 1355. +----, ---- constant, 984. +----, electro-chemical decomposition against, 494, 532. +----, poles of, 494, 533, 558. +----, its influence in electro-chemical decomposition, 472. +---- is the great electrolyte, 924. +----, _the exciting electrolyte when_ pure, 944. +----, ---- acidulated, 880, 926, 1137. +----, ---- alkalized, 931, 934, 941. +----, electrolytic intensity for, 968, 981, 1017. +---- electrolyzed in a single circuit, 862. +----, its electrolysis definite, 732, 785, 807. +----, decomposition of by fine wires, 327. +----, quantity of electricity in its elements, 853, 861. +----, determined to either pole, 553. +_Wheatstone's_ analysis of the electric brush, 1427. +---- measurement of conductive velocity in metals, 1328. +_Wire, ignition of, by the electric current_, 853, _note_, 1631. +---- is uniform throughout, 1630. +_Wire_ a regulator of the electric current, 853, _note_. +----, velocity of conduction in, varied, 1333. +----, single, a current induced in, 170. +----, long, inductive effects in, 1064, 1118. +_Wollaston on_ decomposition by common electricity, 309. +---- decomposition of water by points, 327. + +_Zinc, amalgamated_, its condition, 863, 1000. +----, used in pile, 999. +_Zinc_, how amalgamated, 863. +----, of troughs, its purity, 1144. +----, its relation to the electrolyte, 949. +----, its oxidation is the source of power in the pile, 919. +---- _plates of troughs_, foul, 1145. +---- ----, new and old, 1146. +----, waste of, in voltaic batteries, 997. + + +THE END. + +PRINTED BY RICHARD AND JOHN E. 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