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diff --git a/39053-h/39053-h.htm b/39053-h/39053-h.htm new file mode 100644 index 0000000..798d510 --- /dev/null +++ b/39053-h/39053-h.htm @@ -0,0 +1,7388 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" + "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> +<!-- $Id: header.txt 236 2009-12-07 18:57:00Z vlsimpson $ --> + +<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> + <head> + <meta http-equiv="Content-Type" content="text/html;charset=UTF-8" /> + <meta http-equiv="Content-Style-Type" content="text/css" /> + <title> + The Project Gutenberg eBook of Electric Bells and All About Them, by S. R. Bottone. + </title> + <style type="text/css"> + +body { + margin-left: 10%; + margin-right: 10%; +} + + h1,h2,h3,h4,h5,h6 { + text-align: center; /* all headings centered */ + clear: both; +} + +p { + margin-top: .75em; + text-align: justify; + margin-bottom: .75em; +} + +hr { + width: 33%; + margin-top: 2em; + margin-bottom: 2em; + margin-left: auto; + margin-right: auto; + clear: both; +} + +hr.long { + width: 65%; +} + +table { + margin-left: auto; + margin-right: auto; +} + +td.in1 { + padding-left: 0.75em; +} + +td.padlr { + padding-left: 1em; + padding-right: 1em; +} + +.bigbrace { + font-size: 600%; +} + +.pagenum { /* uncomment the next line for invisible page numbers */ + /* visibility: hidden; */ + position: absolute; + left: 92%; + font-size: smaller; + text-align: right; +} /* page numbers */ + +.recipe_amount { + position: absolute; + left: 80%; +} /* recipes on page 48 and 49 + +.linenum { + position: absolute; + top: auto; + left: 4%; +} /* poetry number */ + +.blockquot { + margin-left: 5%; + margin-right: 10%; +} + +.sidenote { + width: 20%; + padding-bottom: .5em; + padding-top: .5em; + padding-left: .5em; + padding-right: .5em; + margin-left: 1em; + float: right; + clear: right; + margin-top: 1em; + font-size: smaller; + color: black; + background: #eeeeee; + border: dashed 1px; +} + +.bb {border-bottom: solid 2px;} + +.bl {border-left: solid 2px;} + +.bt {border-top: solid 2px;} + +.br {border-right: solid 2px;} + +.bbox {border: solid 2px;} + +.center {text-align: center;} + +.smcap {font-variant: small-caps;} + +.u {text-decoration: underline;} + +/* Images */ +.figcenter { + margin: auto; + text-align: center; +} + +.figleft { + float: left; + clear: left; + margin-left: 0; + margin-bottom: 1em; + margin-top: 1em; + margin-right: 1em; + padding: 0; + text-align: center; +} + +.figright { + float: right; + clear: right; + margin-left: 1em; + margin-bottom: + 1em; + margin-top: 1em; + margin-right: 0; + padding: 0; + text-align: center; +} + +a img {border: none;} /* suppress image border */ + +p.caption {font-weight: bold; text-align: center} + +/* Footnotes */ +.footnotes {border: dashed 1px;} + +.footnote {margin-left: 10%; margin-right: 10%; font-size: 0.9em;} + +.footnote .label {position: absolute; right: 84%; text-align: right;} + +.fnanchor { + vertical-align: super; + font-size: .8em; + text-decoration: + none; +} + +/* Poetry */ +.poem { + margin-left:10%; + margin-right:10%; + text-align: left; +} + +.poem br {display: none;} + +.poem .stanza {margin: 1em 0em 1em 0em;} + +.poem span.i0 { + display: block; + margin-left: 0em; + padding-left: 3em; + text-indent: -3em; +} + +.poem span.i2 { + display: block; + margin-left: 2em; + padding-left: 3em; + text-indent: -3em; +} + +.poem span.i4 { + display: block; + margin-left: 4em; + padding-left: 3em; + text-indent: -3em; +} + +div.trans-note { + border-style: solid; + border-width: 1px; + margin: 2em 15%; + padding: 1em; + text-align: center; +} /* transcriber's note */ + +ul { + list-style-type: none +} /* no bullets on lists */ + +li.indent1 { + padding-left: 1.0em; +} /* indented list item */ + +li.indent2 { + padding-left: 2.0em; +} /* double indented list item */ + + + </style> + </head> +<body> + + +<pre> + +Project Gutenberg's Electric Bells and All About Them, by S. R. Bottone + +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: Electric Bells and All About Them + A Practical Book for Practical Men + +Author: S. R. Bottone + +Release Date: March 4, 2012 [EBook #39053] + +Language: English + +Character set encoding: UTF-8 + +*** START OF THIS PROJECT GUTENBERG EBOOK ELECTRIC BELLS AND ALL ABOUT THEM *** + + + + +Produced by Simon Gardner, Chris Curnow and the Online +Distributed Proofreading Team at http://www.pgdp.net (This +file was produced from images generously made available +by The Internet Archive) + + + + + + +</pre> + + +<div class="trans-note"> +<h4>Transcriber's Notes</h4> + +<p>Inconsistent spellings (e.g. depolariser & depolarizer) and hyphenation +(e.g. guttapercha & gutta-percha) are retained as in the original text. +Minor punctuation errors are corrected without comment. Changes which +have been made to the text (in the case of typographical errors) are +listed at <a href="#Transcribers_Notes">the end of the book</a>.</p> + +<p class="center"><a href="images/i_cover.png">[cover image]</a></p> +<p class="center"><a href="#CONTENTS">Table of Contents</a>.</p> +<p class="center"><a href="#LIST_OF_ILLUSTRATIONS">List of Illustrations</a>.</p> +<p class="center"><a href="#INDEX">Index</a>.</p> + +</div> +<p><!-- Page i --><span class="pagenum"><a name="Page_i" id="Page_i">[Pg i]</a></span></p> + + + +<h1> ELECTRIC BELLS AND<br /> + ALL ABOUT THEM.</h1> + +<p class="center"> A Practical Book for Practical Men.</p> + +<p class="center"> <i>WITH MORE THAN 100 ILLUSTRATIONS.</i></p> + +<p class="center"> BY + S. R. BOTTONE,</p> + +<p class="center"> CERTIFICATED BY SOUTH KENSINGTON (LATE OF THE COLLEGIO + DEL CARMINE, TURIN, AND OF THE ISTITUTO + BELLINO, NOVARA);</p> + +<p class="center"> <i>Author of "The Dynamo," "Electrical Instruments for + Amateurs," &c.</i></p> + +<p class="center"> LONDON: + <span class="smcap">WHITTAKER & CO., Paternoster Square, E.C.</span></p> + +<p class="center"> 1889.</p> + +<p class="center"> (<i>All rights reserved.</i>)</p> +<p><!-- Page iii --><span class="pagenum"><a name="Page_iii" id="Page_iii">[Pg iii]</a></span></p> + + + +<h2>PREFACE.</h2> + + +<p>So rapidly has the use of electric bells and similiar +signalling appliances extended, in modern houses, +offices, hotels, lifts, and ships, that every bell-fitter +must have felt the need of accurate knowledge of the +manner in which these instruments act and are made.</p> + +<p>In the following pages the author has attempted to +supply this need, by giving full details as to the construction +of batteries, bells, pushes, detectors, etc., the +mode of wiring, testing, connecting up, localizing faults, +and, in point of fact, by directing careful attention to +every case that can present itself to the electric-bell +fitter.</p> + +<p> +<span class="smcap">Carshalton, Surrey</span>,<br /> +<i>November, 1888</i>.</p> + + + +<hr class="long" /> +<p><!-- Page v --><span class="pagenum"><a name="Page_v" id="Page_v">[Pg v]</a></span></p> +<h2><a name="CONTENTS" id="CONTENTS"></a>CONTENTS.</h2> + + + + +<div class="center"> +<table border="0" cellpadding="4" cellspacing="0" summary=""> +<tr><td align="right"><span class="smcap">chap.</span></td><td align="right" colspan="3"><span class="smcap">page</span></td></tr> +<tr><td align="right">I.</td><td align="left">Preliminary Considerations</td><td align="right"><a href="#Page_1">1</a></td></tr> +<tr><td align="right"> II.</td><td align="left">On the Choice of Batteries for Electric Bell Work</td><td align="right"><a href="#Page_18">18</a></td></tr> +<tr><td align="right">III.</td><td align="left">On Electric Bells and other Signalling Appliances</td><td align="right"><a href="#Page_59">59</a></td></tr> +<tr><td align="right"> IV.</td><td align="left">On Contacts, Pushes, Switches, Keys, Alarms, and Relays</td><td align="right"><a href="#Page_109">109</a></td></tr> +<tr><td align="right">V.</td><td align="left">On Wiring, Connecting up, and Localising Faults</td><td align="right"><a href="#Page_144">144</a></td></tr> +</table></div> + +<p><!-- Page vii --><span class="pagenum"><a name="Page_vii" id="Page_vii">[Pg vii]</a></span></p> + + + +<hr class="long" /> +<h2><a name="LIST_OF_ILLUSTRATIONS" id="LIST_OF_ILLUSTRATIONS"></a>LIST OF ILLUSTRATIONS.</h2> + + + + +<div class="center"> +<table border="0" cellpadding="4" cellspacing="0" summary="list of illustrations"> +<tr><td align="left"><span class="smcap">Fig.</span></td><td align="right" colspan="3"><span class="smcap">Page</span></td></tr> +<tr><td align="left" class="in1"> <a href="#FIG_1">1</a>.</td><td align="left">Direction of current in cell</td><td align="right">9</td></tr> +<tr><td align="left" class="in1"> <a href="#FIG_2">2</a>.</td><td align="left">Direction of current out of cell</td><td align="right">10</td></tr> +<tr><td align="left" class="in1"> <a href="#FIG_3">3</a>.</td><td align="left">Bar and horse-shoe magnets</td><td align="right">14</td></tr> +<tr><td align="left" class="in1"> <a href="#FIG_4">4</a>.</td><td align="left">The Dynamo</td><td align="right">16</td></tr> +<tr><td align="left" class="in1"> <a href="#FIG_5">5</a>.</td><td align="left">The Smee cell</td><td align="right">28</td></tr> +<tr><td align="left" class="in1"> <a href="#FIG_6">6</a>.</td><td align="left">The Daniell cell</td><td align="right">30</td></tr> +<tr><td align="left" class="in1"> <a href="#FIG_7">7</a>.</td><td align="left">The Gravity cell</td><td align="right">32</td></tr> +<tr><td align="left" class="in1"> <a href="#FIG_8">8</a>.</td><td align="left">The Leclanché cell and parts</td><td align="right">34</td></tr> +<tr><td align="left" class="in1"> <a href="#FIG_9">9</a>.</td><td align="left">The Agglomerate cell</td><td align="right">40</td></tr> +<tr><td align="left"><a href="#FIG_10">10</a>.</td><td align="left">The Judson cell</td><td align="right">42</td></tr> +<tr><td align="left"><a href="#FIG_11">11</a>.</td><td align="left">The Battery in box</td><td align="right">43</td></tr> +<tr><td align="left"><a href="#FIG_12">12</a>.</td><td align="left">The Gent cell</td><td align="right">44</td></tr> +<tr><td align="left"><a href="#FIG_13">13</a>.</td><td align="left">The Bichromate cell</td><td align="right">48</td></tr> +<tr><td align="left"><a href="#FIG_14">14</a>.</td><td align="left">The Fuller cell</td><td align="right">50</td></tr> +<tr><td align="left"><a href="#FIG_15">15</a>.</td><td align="left">The Cells coupled in series</td><td align="right">54</td></tr> +<tr><td align="left"><a href="#FIG_16">16</a>.</td><td align="left">The Cells coupled in Parallel</td><td align="right">57</td></tr> +<tr><td align="left"><a href="#FIG_17">17</a>.</td><td align="left">Outline of electric bell</td><td align="right">61</td></tr> +<tr><td align="left"><a href="#FIG_18">18</a>.</td><td align="left">Frame of bell</td><td align="right">62</td></tr> +<tr><td align="left"><a href="#FIG_19">19</a>.</td><td align="left">E-shaped frame</td><td align="right">63</td></tr> +<tr><td align="left"><a href="#FIG_20">20</a>.</td><td align="left">Electro-magnet, old form</td><td align="right">64</td></tr> +<tr><td align="left"><a href="#FIG_20A">20<span class="smcap">A</span></a>.</td><td align="left">Electro-magnet, modern form</td><td align="right">65</td></tr> +<tr><td align="left"><a href="#FIG_21">21</a>.</td><td align="left">Magnet frame</td><td align="right">66</td></tr> +<tr><td align="left"><a href="#FIG_21A">21<span class="smcap">A</span></a>.</td><td align="left">Winder</td><td align="right">72</td></tr> +<tr><td align="left"><a href="#FIG_22">22</a>.</td><td align="left">Mode of joining electromagnet wires</td><td align="right">73</td></tr> +<tr><td align="left"><a href="#FIG_23">23</a>.</td><td align="left">Armature spring</td><td align="right">74</td></tr> +<tr><td align="left"><a href="#FIG_24">24</a>.</td><td align="left">Armature spring Another form</td><td align="right">74</td></tr> +<tr><td align="left"><a href="#FIG_25">25</a>.</td><td align="left">Platinum tipped screw</td><td align="right">75</td></tr> +<tr><td align="left"><a href="#FIG_26">26</a>.</td><td align="left">Platinum tipped spring</td><td align="right">76</td></tr> +<tr><td align="left"><a href="#FIG_27">27</a>.</td><td align="left">Binding screws</td><td align="right">77</td></tr> +<tr><td align="left"><a href="#FIG_28">28</a>.</td><td align="left">Bell or gong</td><td align="right">78</td></tr> +<tr><td align="left"><a href="#FIG_29">29</a>.</td><td align="left">Pillar and nuts</td><td align="right">78</td></tr> +<tr><td align="left"><a href="#FIG_30">30</a>.</td><td align="left">Washers</td><td align="right">78</td></tr> +<tr><td align="left"><a href="#FIG_31">31</a>.</td><td align="left">Trembling bell</td><td align="right">81</td></tr> +<tr><td align="left"><a href="#FIG_32">32</a>.</td><td align="left">Bell action enclosed in case</td><td align="right">88</td></tr> +<tr><td align="left"><a href="#FIG_33A">33</a>.</td><td align="left">Ordinary trembling bells</td><td align="right">90</td></tr> +<tr><td align="left"><a href="#FIG_34">34</a>.</td><td align="left">Single stroke bell</td><td align="right">91</td></tr> +<tr><td align="left"><a href="#FIG_35">35</a>.</td><td align="left">Continuous ring bell</td><td align="right">94</td></tr> +<tr><td align="left"><a href="#FIG_36">36</a>.</td><td align="left">Release action</td><td align="right">95</td></tr> +<tr><td align="left"><a href="#FIG_37">37</a>.</td><td align="left">Continuous ringing with relay</td><td align="right">96</td></tr> +<tr><td align="left"><a href="#FIG_38">38</a>.</td><td align="left">Continuous ringing action with indicator</td><td align="right">97</td></tr> +<tr><td align="left"><a href="#FIG_39">39</a>.</td><td align="left">Relay and detent lever for indicator</td><td align="right">97</td></tr> +<tr><td align="left"><a href="#FIG_40">40</a>.</td><td align="left">Callow's attachment</td><td align="right">99</td></tr> +<tr><td align="left"><a href="#FIG_40A">40<span class="smcap">A</span></a>.</td><td align="left">Thorpe's arrangement</td><td align="right">101</td></tr> +<tr><td align="left"><a href="#FIG_41">41</a>.</td><td align="left">Jensen bell, <i>section</i></td><td align="right">102</td></tr> +<tr><td align="left"><a href="#FIG_42">42</a>.</td><td align="left">Jensen bell, <i>exterior</i></td><td align="right">104</td></tr> +<tr><td align="left"><a href="#FIG_43A">43<span class="smcap">A</span></a>.</td><td align="left">Circular bell</td><td align="right">106</td></tr> +<tr><td align="left"><a href="#FIG_43B">43<span class="smcap">B</span></a>.</td><td align="left">Mining bell</td><td align="right">106</td></tr> +<tr><td align="left"><a href="#FIG_44">44</a>.</td><td align="left">Electric trumpet (Binswanger's)</td><td align="right">107</td></tr> +<tr><td align="left"><a href="#FIG_45">45</a>.</td><td align="left">Various forms of pushes</td><td align="right">110</td></tr> +<tr><td align="left"><a href="#FIG_46">46</a>.</td><td align="left">Pressel</td><td align="right">111</td></tr> +<tr><td align="left"><a href="#FIG_47">47</a>.</td><td align="left">Pull</td><td align="right">112</td></tr> +<tr><td align="left"><a href="#FIG_48">48</a>.</td><td align="left">Bedroom pull</td><td align="right">113</td></tr> +<tr><td align="left"><a href="#FIG_49A">49<span class="smcap">A</span></a>.</td><td align="left">Bedroom pull Another form</td><td align="right">114<!-- Page viii --><span class="pagenum"><a name="Page_viii" id="Page_viii">[Pg viii]</a></span></td></tr> +<tr><td align="left"><a href="#FIG_49B">49<span class="smcap">B</span></a>.</td><td align="left">Floor contact, ball form</td><td align="right">114</td></tr> +<tr><td align="left"><a href="#FIG_50">50</a>.</td><td align="left">Burglar alarm</td><td align="right">115</td></tr> +<tr><td align="left"><a href="#FIG_51">51</a>.</td><td align="left">Burglar alarm <i>Another form</i></td><td align="right">115</td></tr> +<tr><td align="left"><a href="#FIG_52">52</a>.</td><td align="left">Floor contact</td><td align="right">115</td></tr> +<tr><td align="left"><a href="#FIG_53">53</a>.</td><td align="left">Door contact</td><td align="right">116</td></tr> +<tr><td align="left"><a href="#FIG_54">54</a>.</td><td align="left">Sash contact</td><td align="right">117</td></tr> +<tr><td align="left"><a href="#FIG_55">55</a>.</td><td align="left">Shop door contact</td><td align="right">117</td></tr> +<tr><td align="left"><a href="#FIG_56A">56<span class="smcap">A</span></a>.</td><td align="left">Closed circuit system, <i>single</i></td><td align="right">119</td></tr> +<tr><td align="left"><a href="#FIG_56B">56<span class="smcap">B</span></a>.</td><td align="left">Closed circuit system, <i>double</i></td><td align="right">119</td></tr> +<tr><td align="left"><a href="#FIG_57">57</a>.</td><td align="left">Modified gravity, Daniell</td><td align="right">120</td></tr> +<tr><td align="left"><a href="#FIG_58">58</a>.</td><td align="left">Contact for closed circuit</td><td align="right">121</td></tr> +<tr><td align="left"><a href="#FIG_59">59</a>.</td><td align="left">Thermometer alarm</td><td align="right">122</td></tr> +<tr><td align="left"><a href="#FIG_60">60</a>.</td><td align="left">Fire alarm</td><td align="right">123</td></tr> +<tr><td align="left"><a href="#FIG_61">61<span class="smcap">A</span></a>.</td><td align="left">Fire alarm Another form</td><td align="right">123</td></tr> +<tr><td align="left"><a href="#FIG_61">61<span class="smcap">B</span></a>.</td><td align="left">Fire alarm Another form in action</td><td align="right">123</td></tr> +<tr><td align="left"><a href="#FIG_62">62</a>.</td><td align="left">Binswanger's "watch alarm" contact</td><td align="right">125</td></tr> +<tr><td align="left"><a href="#FIG_63">63</a>.</td><td align="left">Watchman's electric tell-tale clock</td><td align="right">126</td></tr> +<tr><td align="left"><a href="#FIG_64">64</a>.</td><td align="left">Lever switch, <i>two-way</i></td><td align="right">128</td></tr> +<tr><td align="left"><a href="#FIG_65">65</a>.</td><td align="left">Morse key, <i>double contact</i></td><td align="right">133</td></tr> +<tr><td align="left"><a href="#FIG_66">66</a>.</td><td align="left">Relay</td><td align="right">134</td></tr> +<tr><td align="left"><a href="#FIG_67">67</a>.</td><td align="left">Indicator, drop</td><td align="right">137</td></tr> +<tr><td align="left"><a href="#FIG_68">68</a>.</td><td align="left">Indicator, Semaphore</td><td align="right">138</td></tr> +<tr><td align="left"><a href="#FIG_69">69</a>.</td><td align="left">Indicator, Fall back</td><td align="right">139</td></tr> +<tr><td align="left"><a href="#FIG_70">70</a>.</td><td align="left">Indicator, Pendulum</td><td align="right">140</td></tr> +<tr><td align="left"><a href="#FIG_71">71</a>.</td><td align="left">Indicator, Coupled up</td><td align="right">142</td></tr> +<tr><td align="left"><a href="#FIG_72">72</a>.</td><td align="left">Indicator, Gent's tripolar</td><td align="right">143</td></tr> +<tr><td align="left"><a href="#FIG_73">73</a>.</td><td align="left">Soldering iron and wires</td><td align="right">148</td></tr> +<tr><td align="left"><a href="#FIG_74">74</a>.</td><td align="left">Push, interior of</td><td align="right">151</td></tr> +<tr><td align="left"><a href="#FIG_75">75</a>.</td><td align="left">Bell, battery and push</td><td align="right">159</td></tr> +<tr><td align="left"><a href="#FIG_76">76</a>.</td><td align="left">Bell, battery and push And earth return</td><td align="right">160</td></tr> +<tr><td align="left"><a href="#FIG_77">77</a>.</td><td align="left">Bell, and two pushes</td><td align="right">161</td></tr> +<tr><td align="left"><a href="#FIG_78">78</a>.</td><td align="left">Bell, two pushes and one pull</td><td align="right">161</td></tr> +<tr><td align="left"><a href="#FIG_79">79</a>.</td><td align="left">Two bells in parallel</td><td align="right">162</td></tr> +<tr><td align="left"><a href="#FIG_80">80</a>.</td><td align="left">Two bells in parallel Another mode</td><td align="right">162</td></tr> +<tr><td align="left"><a href="#FIG_81">81</a>.</td><td align="left">Two bells in parallel with two-way switch</td><td align="right">163</td></tr> +<tr><td align="left"><a href="#FIG_82">82</a>.</td><td align="left">Series coupler</td><td align="right">163</td></tr> +<tr><td align="left"><a href="#FIG_83">83</a>.</td><td align="left">Bell with local battery and relay</td><td align="right">164</td></tr> +<tr><td align="left"><a href="#FIG_84">84</a>.</td><td align="left">Continuous ringing bell with wire return</td><td align="right">165</td></tr> +<tr><td align="left"><a href="#FIG_85">85</a>.</td><td align="left">Bells with Morse keys for signalling</td><td align="right">165</td></tr> +<tr><td align="left"><a href="#FIG_86">86</a>.</td><td align="left">Bells with double contact pushes for signalling</td><td align="right">166</td></tr> +<tr><td align="left"><a href="#FIG_87">87</a>.</td><td align="left">Bells with double contact with one battery only</td><td align="right">167</td></tr> +<tr><td align="left"><a href="#FIG_88">88</a>.</td><td align="left">Two-way signalling with one battery only</td><td align="right">168</td></tr> +<tr><td align="left"><a href="#FIG_89">89</a>.</td><td align="left">Complete installation of bells, batteries, pushes, etc.</td><td align="right">169</td></tr> +<tr><td align="left"><a href="#FIG_90">90</a>.</td><td align="left">Mode of getting out plan or design</td><td align="right">170</td></tr> +<tr><td align="left"><a href="#FIG_91">91</a>.</td><td align="left">Lift fitted with bells</td><td align="right">173</td></tr> +<tr><td align="left"><a href="#FIG_92">92</a>.</td><td align="left">Magneto bell: generator</td><td align="right">174</td></tr> +<tr><td align="left"><a href="#FIG_93">93</a>.</td><td align="left">Magneto bell: Receiver</td><td align="right">175</td></tr> +<tr><td align="left"><a href="#FIG_94">94</a>.</td><td align="left">Magneto bell: Combined</td><td align="right">176</td></tr> +<tr><td align="left"><a href="#FIG_95">95</a>.</td><td align="left">Detector or galvanometer</td><td align="right">176</td></tr> +</table></div> + + + +<hr /> + +<p><!-- Page 1 --><span class="pagenum"><a name="Page_1" id="Page_1">[Pg 1]</a></span></p> +<h1><a name="ELECTRIC_BELLS" id="ELECTRIC_BELLS"></a>ELECTRIC BELLS.</h1> + + + +<h2><a name="CHAPTER_I" id="CHAPTER_I"></a>CHAPTER I.</h2> + +<h3>PRELIMINARY CONSIDERATIONS.</h3> + + +<p><a name="SEC_1" id="SEC_1"></a>§ 1. <span class="smcap">Electricity.</span>—The primary cause of all the +effects which we are about to consider resides in a force +known as <i>electricity</i>, from the Greek name of amber +(electron), this being the body in which the manifestations +were first observed. The ancients were acquainted +with a few detached facts, such as the attractive power +acquired by amber after friction; the benumbing shocks +given by the torpedo; the aurora borealis; the lightning +flash; and the sparks or streams of light which, +under certain conditions, are seen to issue from the +human body. Thales, a Grecian philosopher, who +flourished about 600 years <span class="smcap">B.C.</span>, observed the former +of these facts, but nearly twenty centuries elapsed +before it was suspected that any connection existed +between these phenomena.</p> + + +<p><a name="SEC_2" id="SEC_2"></a>§ 2. According to the present state of our knowledge,<!-- Page 2 --><span class="pagenum"><a name="Page_2" id="Page_2">[Pg 2]</a></span> +it would appear that electricity is a mode of motion in +the constituent particles (or atoms) of bodies very +similar to, if not identical with, <i>heat</i> and <i>light</i>. These, +like <i>sound</i>, are known to be dependent on undulatory +motion; but, whilst <i>sound</i> is elicited by the vibration of +a body <i>as a whole</i>, electricity appears to depend, in its +manifestations, upon some motion (whether rotary, +oscillatory, or undulatory, it is not known) of the atoms +themselves.</p> + +<p>However this be, it is certain that whatever tends to +set up molecular motion, tends also to call forth a display +of electricity. Hence we have several practical means +at our disposal for evoking electrical effects. These +may be conveniently divided into three classes, viz.:—1st, +mechanical; 2nd, chemical; 3rd, changes of temperature. +Among the <i>mechanical</i> may be ranged friction, +percussion, vibration, trituration, cleavage, etc. Among +the <i>chemical</i> we note the action of acids and alkalies +upon metals. Every chemical action is accompanied by +electrical effects; but not all such actions are convenient +sources of electricity. <i>Changes of temperature</i>, +whether sudden or gradual, call forth electricity, but the +displays are generally more striking in the former than +in the latter case, owing to the accumulated effect being +presented in a shorter time.</p> + + +<p><a name="SEC_3" id="SEC_3"></a>§ 3. We may now proceed to study a few of these +methods of evoking electricity, so as to familiarise ourselves +with the leading properties.</p> + +<p>If we rub any resinous substance (such as amber, +copal, resin, sealing-wax, ebonite, etc.) with a piece of<!-- Page 3 --><span class="pagenum"><a name="Page_3" id="Page_3">[Pg 3]</a></span> +warm, dry flannel, we shall find that it acquires the +power of attracting light bodies, such as small pieces of +paper, straw, pith, etc. After remaining in contact +with the rubbed (or electrified) substance for a short +time, the paper, etc., will fly off as if repelled; and this +apparent repulsion will be more evident and more +quickly produced if the experiment be performed over a +metal tray. If a small pith-ball, the size of a pea, be +suspended from the ceiling by a piece of fine cotton, +previously damped and then approached by an ebonite +comb which has been briskly rubbed, it will be vigorously +attracted, and never repelled; but if for the +cotton there be substituted a thread or fibre of very fine +dry silk, the pith-ball will be first <i>attracted</i> and then +<i>repelled</i>. This is owing to the fact that the damp +cotton allows the electricity to escape along it: <i>id est</i>, +damp cotton is a <span class="smcap">CONDUCTOR</span> of electricity, while silk +does not permit its dissipation; or, in other words, silk +is a <span class="smcap">NON-CONDUCTOR</span>. All bodies with which we are +acquainted are found, on trial, to fall under one or other +of the two heads—viz., conductors and non-conductors. +Nature knows no hard lines, so that we find that even the +worst conductors will permit the escape of some electricity, +while the very best conductors oppose a measurable +resistance to its passage. Between the limits of good +conductors, on the one hand, and non-conductors (or +insulators) on the other, we have bodies possessing varying +degrees of conductivity.</p> + + +<p><a name="SEC_4" id="SEC_4"></a>§ 4. As a knowledge of which bodies are, and which +are not, conductors of electricity is absolutely essential<!-- Page 4 --><span class="pagenum"><a name="Page_4" id="Page_4">[Pg 4]</a></span> +to every one aspiring to apply electricity to any practical +purpose, the following table is subjoined, giving the +names of the commoner bodies, beginning with those +which most readily transmit electricity, or are <i>good</i> conductors, +and ending with those which oppose the highest +resistance to its passage, or are insulators, or non-conductors:—</p> + + +<p class="center"><a name="SEC_5" id="SEC_5"></a>§ 5. TABLE OF CONDUCTORS AND INSULATORS. +<!-- Page 5 --><span class="pagenum"><a name="Page_5" id="Page_5">[Pg 5]</a></span></p> + + +<div class="center"> +<table border="0" cellpadding="4" cellspacing="0" summary="Table of conductors and insulators"> +<tr><th align="center" class="bt">Quality.</th><th align="center" class="bt" colspan="3">Name of Substance.</th><th align="center" class="bt">Relative Resistance.</th></tr> +<tr><td align="left" class="bt" rowspan="24" valign="middle">Good Conductors</td><td align="left" class="bt" colspan="3">Silver, annealed</td><td align="right" class="bt">1.</td></tr> +<tr><td align="left" colspan="3">Copper, annealed</td><td align="right">1.063</td></tr> +<tr><td align="left" colspan="3">Silver, hard drawn</td><td align="right">1.086</td></tr> +<tr><td align="left" colspan="3">Copper, hard drawn</td><td align="right">1.086</td></tr> +<tr><td align="left" colspan="3">Gold, annealed</td><td align="right">1.369</td></tr> +<tr><td align="left" colspan="3">Gold, hard drawn</td><td align="right">1.393</td></tr> +<tr><td align="left" colspan="3">Aluminium, annealed</td><td align="right">1.935</td></tr> +<tr><td align="left" colspan="3">Zinc, pressed</td><td align="right">3.741</td></tr> +<tr><td align="left" colspan="3">Brass (variable)</td><td align="right">5.000</td></tr> +<tr><td align="left" colspan="3">Platinum, annealed</td><td align="right">6.022</td></tr> +<tr><td align="left" colspan="3">Iron</td><td align="right">6.450</td></tr> +<tr><td align="left" colspan="3">Steel, soft</td><td align="right">6.500</td></tr> +<tr><td align="left" colspan="3">Gold and silver alloy, 2 to 1</td><td align="right">7.228</td></tr> +<tr><td align="left" colspan="3">Nickel, annealed</td><td align="right">8.285</td></tr> +<tr><td align="left" colspan="3">Tin, pressed</td><td align="right">8.784</td></tr> +<tr><td align="left" colspan="3">Lead, pressed</td><td align="right">13.050</td></tr> +<tr><td align="left" colspan="3">German silver (variable)</td><td align="right">13.920</td></tr> +<tr><td align="left" colspan="3">Platinum-silver alloy, 1 to 2</td><td align="right">16.210</td></tr> +<tr><td align="left" colspan="3">Steel, hard</td><td align="right">25.000</td></tr> +<tr><td align="left" colspan="3">Antimony, pressed</td><td align="right">23.600</td></tr> +<tr><td align="left" colspan="3">Mercury</td><td align="right">62.730</td></tr> +<tr><td align="left" colspan="3">Bismuth</td><td align="right">87.230</td></tr> +<tr><td align="left" colspan="3">Graphite</td><td align="right">145.000</td></tr> +<tr><td align="left" colspan="3">Nitric Acid</td><td align="right">976000.000</td></tr> +<tr><td align="left" class="bt" rowspan="5" valign="middle">Imperfect Conductors</td><td align="left" class="bt" colspan="3">Hydrochloric acid</td><td align="left" class="bt"><a name="FNanchor_1_1" id="FNanchor_1_1"></a><a href="#Footnote_1_1" class="fnanchor">[1]</a></td></tr> +<tr><td align="left" colspan="3">Sulphuriacid</td><td align="right">1032020.000</td></tr> +<tr><td align="left" colspan="3">Solutions of metallic salts</td><td align="right">varies with strength</td></tr> +<tr><td align="left" colspan="3">Metallic sulphides</td><td align="left"><a href="#Footnote_1_1" class="fnanchor">[1]</a></td></tr> +<tr><td align="left" colspan="3">Distilled water</td><td align="left"><a href="#Footnote_1_1" class="fnanchor">[1]</a> 6754208.000</td></tr> +<tr><td align="left" class="bt" rowspan="10" valign="middle">Inferior Conductors.</td><td align="left" class="bt" colspan="3">Metallic salts, solid</td><td align="left" class="bt"><a href="#Footnote_1_1" class="fnanchor">[1]</a></td></tr> +<tr><td align="left">Linen</td><td align="left" rowspan="4"><span class="bigbrace">}</span></td><td align="left" rowspan="4" valign="middle">and other forms of cellulose</td><td align="left" valign="middle" rowspan="4"><a href="#Footnote_1_1" class="fnanchor">[1]</a></td></tr> +<tr><td align="left">Cotton</td></tr> +<tr><td align="left">Hemp</td></tr> +<tr><td align="left">Paper</td></tr> +<tr><td align="left" colspan="3">Alcohol</td><td align="left"><a href="#Footnote_1_1" class="fnanchor">[1]</a></td></tr> +<tr><td align="left" colspan="3">Ether</td><td align="left"><a href="#Footnote_1_1" class="fnanchor">[1]</a></td></tr> +<tr><td align="left" colspan="3">Dry Wood</td><td align="left"><a href="#Footnote_1_1" class="fnanchor">[1]</a></td></tr> +<tr><td align="left" colspan="3">Dry Ice</td><td align="left"><a href="#Footnote_1_1" class="fnanchor">[1]</a></td></tr> +<tr><td align="left" colspan="3">Metallic Oxides</td><td align="left"><a href="#Footnote_1_1" class="fnanchor">[1]</a></td></tr> +<tr><td align="left" class="bt" rowspan="15" valign="middle">Non-conductors,<br /> or Insulators.</td><td align="left" class="bt" colspan="3">Ice, at 25 c.</td><td align="left" class="bt"><a href="#Footnote_1_1" class="fnanchor">[1]</a></td></tr> +<tr><td align="left" colspan="3">Fats and oils</td><td align="left"><a href="#Footnote_1_1" class="fnanchor">[1]</a></td></tr> +<tr><td align="left" colspan="3">Caoutchouc</td><td align="right">1000000000000.</td></tr> +<tr><td align="left" colspan="3">Guttapercha</td><td align="right">1000000000000.</td></tr> +<tr><td align="left" colspan="3">Dry air, gases, and vapours</td><td align="left"><a href="#Footnote_1_1" class="fnanchor">[1]</a></td></tr> +<tr><td align="left" colspan="3">Wool</td><td align="left"><a href="#Footnote_1_1" class="fnanchor">[1]</a></td></tr> +<tr><td align="left" colspan="3">Ebonite</td><td align="right">1300000000000.</td></tr> +<tr><td align="left" colspan="3">Diamond</td><td align="left"><a href="#Footnote_1_1" class="fnanchor">[1]</a></td></tr> +<tr><td align="left" colspan="3">Silk</td><td align="left"><a href="#Footnote_1_1" class="fnanchor">[1]</a></td></tr> +<tr><td align="left" colspan="3">Glass</td><td align="left"><a href="#Footnote_1_1" class="fnanchor">[1]</a></td></tr> +<tr><td align="left" colspan="3">Wax</td><td align="left"><a href="#Footnote_1_1" class="fnanchor">[1]</a></td></tr> +<tr><td align="left" colspan="3">Sulphur</td><td align="left"><a href="#Footnote_1_1" class="fnanchor">[1]</a></td></tr> +<tr><td align="left" colspan="3">Resin</td><td align="left"><a href="#Footnote_1_1" class="fnanchor">[1]</a></td></tr> +<tr><td align="left" colspan="3">Amber</td><td align="left"><a href="#Footnote_1_1" class="fnanchor">[1]</a></td></tr> +<tr><td align="left" colspan="3">Shellac</td><td align="left"><a href="#Footnote_1_1" class="fnanchor">[1]</a></td></tr> +<tr><td align="left" class="bb"></td><td align="left" class="bb" colspan="3">Paraffin</td><td align="right" class="bb">1500000000000.</td></tr> +</table></div> + + +<div class="footnote"><p><a name="Footnote_1_1" id="Footnote_1_1"></a><a href="#FNanchor_1_1"><span class="label">[1]</span></a> These have not been accurately measured.</p></div> + +<p>The figures given as indicating the relative resistance +of the above bodies to the passage of electricity must +be taken as approximate only, since the conductivity of +all these bodies varies very largely with their purity, and +with the temperature. Metals become worse conductors +when heated; liquids and non-metals, on the contrary, +become better conductors.</p> + +<p>It must be borne in mind that <i>dry air</i> is one of the<!-- Page 6 --><span class="pagenum"><a name="Page_6" id="Page_6">[Pg 6]</a></span> +<i>best insulators</i>, or worst <i>conductors</i>, with which we are +acquainted; while damp air, on the contrary, owing to +the facility with which it deposits <i>water</i> on the surface +of bodies, is highly conducive to the escape of electricity.</p> + + +<p><a name="SEC_6" id="SEC_6"></a>§ 6. If the experiment described at <a href="#SEC_3">§ 3</a> be repeated, +substituting a glass rod for the ebonite comb, it will be +found that the pith-ball will be first attracted and then +repelled, as in the case with the ebonite; and if of +two similar pith-balls, each suspended by a fibre of silk, +one be treated with the excited ebonite and the other +with the glass rod, until repulsion occurs, and then +approached to each other, the two balls will be found to +attract each other. This proves that the electrical condition +of the excited ebonite and of the excited glass +must be different; for had it been the same, the two +balls would have repelled one another. Farther, it will +be found that the <i>rubber</i> with which the ebonite or the +glass rod have been excited has also acquired electrical +properties, attracting the pith-ball, previously repelled by +the rod. From this we may gather that when one body +acting on another, either mechanically or chemically, +sets up an electrical condition in one of the two bodies, +a similar electrical condition, but in the opposite sense, +is produced in the other: in point of fact, that it is +impossible to excite any one body without exciting +a corresponding but opposite state in the other. (We +may take, as a rough mechanical illustration of this, the +effect which is produced on the pile of two pieces of +plush or fur, on being drawn across one another in +opposite directions. On examination we shall find that<!-- Page 7 --><span class="pagenum"><a name="Page_7" id="Page_7">[Pg 7]</a></span> +both the piles have been laid down, the upper in the one +direction, the lower in the other.) For a long time +these two electrical states were held to depend upon two +distinct electricities, which were called respectively +<i>vitreous</i> and <i>resinous</i>, to indicate the nature of the bodies +from which they were derived. Later on (when it was +found that the theory of a single electricity could be +made to account for all the phenomena, provided it was +granted that some electrified bodies acquired more, +while others acquired less than their natural share of +electricity), the two states were known as <i>positive</i> and +<i>negative</i>; and these names are still retained, although it +is pretty generally conceded that electricity is not an +entity in itself, but simply a mode of motion.</p> + + +<p><a name="SEC_7" id="SEC_7"></a>§ 7. It is usual, in treatises on electricity, to give a +long list of the substances which acquire a positive or a +negative condition when rubbed against one another. +Such a table is of very little use, since the slightest +modification in physical condition will influence very +considerably the result. For example: if two similar +sheets of glass be rubbed over one another, no change +in electrical condition is produced; but if one be roughed +while the other is left polished, this latter becomes +positively, while the former becomes negatively, electrified. +So, also, if one sheet of glass be warmed, while the +other be left cold, the colder becomes positively, and +the latter negatively, excited. As a general law, <i>that +body, the particles of which are more easily displaced, +becomes negatively electrified</i>.</p> + + +<p><a name="SEC_8" id="SEC_8"></a>§ 8. As, however, the electricity set up by friction<!-- Page 8 --><span class="pagenum"><a name="Page_8" id="Page_8">[Pg 8]</a></span> +has not hitherto found any practical application in +electric bell-ringing or signalling, we need not to go +more deeply into this portion of the subject, but pass +at once to the electricity elicited by the action of acids, +or their salts, on metals.</p> + +<p>Here, as might be expected from the law enunciated +above, the metal more acted on by the acid becomes +negatively electrified, while the one less acted on +becomes positive.<a name="FNanchor_2_2" id="FNanchor_2_2"></a><a href="#Footnote_2_2" class="fnanchor">[2]</a> The following table, copied from +Ganot, gives an idea of the electrical condition which the +commoner metals and graphite assume when two of +them are immersed at the same time in dilute acid:—</p> + +<div class="center"> +<table border="0" cellpadding="0" cellspacing="0" summary=""> +<tr> +<td rowspan="13" valign="middle">The portion immersed in the acid fluid.</td> +<td align="center">⎧</td><td align="center">↓</td><td align="left" class="padlr">Zinc.</td><td align="center">↑</td><td align="center">⎫</td> +<td rowspan="13" valign="middle">The portion out of the acid fluid.</td> +</tr> +<tr><td align="center">⎪</td><td align="center">↓</td><td align="left" class="padlr">Cadmium.</td><td align="center">↑</td><td align="center">⎪</td></tr> +<tr><td align="center">⎪</td><td align="center">↓</td><td align="left" class="padlr">Tin.</td><td align="center">↑</td><td align="center">⎪</td></tr> +<tr><td align="center">⎪</td><td align="center">↓</td><td align="left" class="padlr">Lead.</td><td align="center">↑</td><td align="center">⎪</td></tr> +<tr><td align="center">⎪</td><td align="center">↓</td><td align="left" class="padlr">Iron.</td><td align="center">↑</td><td align="center">⎪</td></tr> +<tr><td align="center">⎪</td><td align="center">↓</td><td align="left" class="padlr">Nickel.</td><td align="center">↑</td><td align="center">⎪</td></tr> +<tr><td align="center">⎪</td><td align="center">↓</td><td align="left" class="padlr">Bismuth.</td><td align="center">↑</td><td align="center">⎪</td></tr> +<tr><td align="center">⎪</td><td align="center">↓</td><td align="left" class="padlr">Antimony.</td><td align="center">↑</td><td align="center">⎪</td></tr> +<tr><td align="center">⎪</td><td align="center">↓</td><td align="left" class="padlr">Copper.</td><td align="center">↑</td><td align="center">⎪</td></tr> +<tr><td align="center">⎪</td><td align="center">↓</td><td align="left" class="padlr">Silver.</td><td align="center">↑</td><td align="center">⎪</td></tr> +<tr><td align="center">⎪</td><td align="center">↓</td><td align="left" class="padlr">Gold.</td><td align="center">↑</td><td align="center">⎪</td></tr> +<tr><td align="center">⎪</td><td align="center">↓</td><td align="left" class="padlr">Platinum.</td><td align="center">↑</td><td align="center">⎪</td></tr> +<tr><td align="center">⎩</td><td align="center">↓</td><td align="left" class="padlr">Graphite.</td><td align="center">↑</td><td align="center">⎭</td></tr> +</table></div> + + +<p>The meaning of the above table is, that if we test the +electrical condition of any two of its members when +immersed in an acid fluid, we shall find that the ones at +the head of the list are <i>positive</i> to those below them, but +negative to those above them, if the test have reference +to the condition of the parts <i>within</i> the fluid. On the<!-- Page 9 --><span class="pagenum"><a name="Page_9" id="Page_9">[Pg 9]</a></span> +contrary, we shall find that any member of the list will +be found to be <i>negative</i> to any one below it, or <i>positive</i> +to any above it, if tested from the portion <span class="smcap">NOT</span> immersed +in the acid fluid.</p> + +<div class="figcenter" style="width: 400px;"> +<a name="FIG_1" id="FIG_1"></a> +<img src="images/i_018.png" width="400" height="293" alt="" title="Direction of current in cell" /> +<p class="caption">Fig. 1.</p> +</div> + +<hr /> + +<div class="figcenter" style="width: 278px;"> +<a name="FIG_2" id="FIG_2"></a> +<img src="images/i_019.png" width="278" height="400" alt="" title="Direction of current out of cell" /> +<p class="caption">Fig. 2.</p> +</div> + + +<p><a name="SEC_9" id="SEC_9"></a>§ 9. A very simple experiment will make this quite +clear. Two strips, one of copper and the other of zinc, +1" wide by 4" long, have a 12" length of copper wire +soldered to one extremity of each. A small flat piece +of cork, about 1" long by 1" square section, is placed +between the two plates, at the end where the wires have +been soldered, this portion being then lashed together by +a few turns of waxed string. (The plates should not +touch each other at any point.) If this combination +(which constitutes a very primitive galvanic couple) be<!-- Page 10 --><span class="pagenum"><a name="Page_10" id="Page_10">[Pg 10]</a></span> +immersed in a tumbler three-parts filled with water, +rendered just sour by the addition of a few drops of +sulphuric or hydrochloric acid, we shall get a manifestation +of electrical effects. If a delicately poised +magnetic needle be allowed to take up its natural +position of north and south, and then the wires proceeding +from the two metal strips twisted in contact, so +as to be parallel to and over the needle, as shown in +<a href="#FIG_1">Fig. 1</a>, the needle will be impelled out of its normal +position, and be deflected more or less out of the line of<!-- Page 11 --><span class="pagenum"><a name="Page_11" id="Page_11">[Pg 11]</a></span> +the wire. If the needle be again allowed to come to +rest <span class="smcap">N.</span> and <span class="smcap">S.</span> (the battery or couple having been +removed), and then the tumbler be held close over the +needle, as in <a href="#FIG_2">Fig. 2</a>, so that the needle points from +the copper to the zinc strip, the needle will be again +impelled or deflected out of its natural position, but in +this case in the opposite direction.</p> + + +<p><a name="SEC_10" id="SEC_10"></a>§ 10. It is a well-known fact that if a wire, or any +other conductor, along which the electric undulation (or, +as is usually said, the electric current) is passing, be +brought over and parallel to a suspended magnetic +needle, pointing north and south, the needle is +immediately deflected from this north and south +position, and assumes a new direction, more or less +east and west, according to the amplitude of the +current and the nearness of the conductor to the +needle. Moreover, the direction in which the north +pole of the needle is impelled is found to be dependent +upon the direction in which the electric waves (or +current) enter the conducting body or wire. The law +which regulates the direction of these deflections, and +which is known, from the name of its originator, as +Ampère's law, is briefly as follows:—</p> + + +<p><a name="SEC_11" id="SEC_11"></a>§ 11. "If a current be caused to flow <i>over</i> and parallel +to a freely suspended magnetic needle, previously +pointing north and south, the north pole will be +impelled to the <span class="smcap">LEFT</span> of the <i>entering</i> current. If, on +the contrary, the wire, or conductor, be placed +<i>below</i> the needle, the deflection will, under similar +circumstances, be in the opposite direction, viz.: the<!-- Page 12 --><span class="pagenum"><a name="Page_12" id="Page_12">[Pg 12]</a></span> +north pole will be impelled to the <span class="smcap">RIGHT</span> of the +<i>entering</i> current." In both these cases the observer is +supposed to be looking along the needle, with its <span class="smcap">N.</span> +seeking pole pointing at him.</p> + + +<p><a name="SEC_12" id="SEC_12"></a>§ 12. From a consideration of the above law, in +connection with the experiments performed at <a href="#SEC_9">§ 9</a>, +it will be evident that inside the tumbler the zinc is +<i>positive</i> to the copper strip; while, viewed from the +outside conductor, the copper is positive to the zinc +strip.<a name="FNanchor_3_3" id="FNanchor_3_3"></a><a href="#Footnote_3_3" class="fnanchor">[3]</a></p> + + +<p><a name="SEC_13" id="SEC_13"></a>§ 13. A property of current electricity, which is the +fundamental basis of electric bell-ringing, is that of +conferring upon iron and steel the power of attracting +iron and similar bodies, or, as it is usually said, of +rendering iron magnetic. If a soft iron rod, say about +4" long by ½" diameter, be wound evenly from end to +end with three or four layers of cotton-covered copper +wire, say No. 20 gauge, and placed in proximity to a +few iron nails, etc., no attractive power will be evinced; +but let the two free ends of the wire be placed in metallic +contact with the wires leading from the simple battery +described at <a href="#SEC_9">§ 9</a>, and it will be found that the iron has +become powerfully magnetic, capable of sustaining +several ounces weight of iron and steel, so long as the +wires from the battery are in contact with the wire +encircling the iron; or, in other words, "<i>the soft iron is a +magnet, so long as an electric current flows round it</i>." +If contact between the battery wires and the coiled wires<!-- Page 13 --><span class="pagenum"><a name="Page_13" id="Page_13">[Pg 13]</a></span> +be broken, the iron loses all magnetic power, and +the nails, etc., drop off immediately. A piece of soft +iron thus coiled with covered or "insulated" wire, no +matter what its shape may be, is termed an "electro-magnet." +Their chief peculiarities, as compared with +the ordinary permanent steel magnets or lodestones, are, +first, their great attractive and sustaining power; secondly, +the rapidity, nay, instantaneity, with which they lose all +attractive force on the cessation of the electric flow +around them. It is on these two properties that their +usefulness in bell-ringing depends.</p> + + +<p><a name="SEC_14" id="SEC_14"></a>§ 14. If, instead of using a <i>soft</i> iron bar in the above +experiment, we had substituted one of <i>hard</i> iron, or +steel, we should have found two remarkable differences +in the results. In the first place, the bar would have +been found to retain its magnetism instead of losing it +immediately on contact with the battery being broken; +and, in the second place, the attractive power elicited +would have been much less than in the case of soft iron. +It is therefore of the highest importance, in all cases +where rapid and powerful magnetisation is desired, that +the <i>cores</i> of the electro-magnets should be of the very +softest iron. Long annealing and gradual cooling +conduce greatly to the softness of iron.</p> + +<div class="figcenter" style="width: 400px;"> +<a name="FIG_3" id="FIG_3"></a> +<img src="images/i_023.png" width="400" height="322" alt="" title="Bar and horse-shoe magnets" /> +<p class="caption">Fig. 3. +<br /> +<span class="smcap">Magnets</span>, showing Lines of Force.</p> +</div> + + +<p><a name="SEC_15" id="SEC_15"></a>§ 15. There is yet another source of electricity which +must be noticed here, as it has already found application +in some forms of electric bells and signalling, and which +promises to enter into more extended use. If we +sprinkle some iron filings over a bar magnet, or a horse-shoe +magnet, we shall find that the filings arrange<!-- Page 14 --><span class="pagenum"><a name="Page_14" id="Page_14">[Pg 14]</a></span> +themselves in a definite position along the lines of +greatest attractive force; or, as scientists usually say, the +iron filings arrange themselves in the direction of the +lines of force. The entire space acted on by the +magnet is usually known as its "field." <a href="#FIG_3">Fig. 3</a> gives +an idea of the distribution of the iron filings, and also +of the general direction of the lines of force. It is found +that if a body be moved before the poles of a magnet +in such a direction as to cut the lines of force, electricity +is excited in that body, and also around the magnet. +The ordinary magneto-electric machines of the shops +are illustrations of the application of this property of +magnets. They consist essentially in a horse-shoe<!-- Page 15 --><span class="pagenum"><a name="Page_15" id="Page_15">[Pg 15]</a></span> +magnet, in front of which is caused to rotate, by means +of appropriate gearing, or wheel and band, an iron +bobbin, or pair of bobbins, coiled with wire. The ends of +the wire on the bobbins are brought out and fastened +to insulated portions of the spindle, and revolve with it. +Two springs press against the spindle, and pick up the +current generated by the motion of the iron bobbins +before the poles of the magnet. It is quite indifferent +whether we use permanent steel magnets or electro-magnets +to produce this effect. If we use the latter, +and more especially if we cause a portion of the current +set up to circulate round the electro-magnet to maintain +its power, we designate the apparatus by the name of +<span class="smcap">Dynamo</span>.</p> + +<div class="figcenter" style="width: 400px;"> +<a name="FIG_4" id="FIG_4"></a> +<img src="images/i_025.png" width="400" height="249" alt="" title="The Dynamo" /> +<p class="caption">Fig. 4. +<br /> +<span class="smcap">Typical Dynamo</span>, showing essential portions.</p> +</div> + + +<p><a name="SEC_16" id="SEC_16"></a>§ 16. Our space will not permit of a very extended +description of the dynamo, but the following brief outline +of its constructive details will be found useful to +the student. A mass of soft iron (shape immaterial) +is wound with many turns of insulated copper wire, in +such a manner that, were an electrical current sent along +the wire, the mass of iron would become strongly north +at one extremity, and south at the other. As prolongations +of the electro-magnet thus produced are +affixed two masses of iron facing one another, and so +fashioned or bored out as to allow a ring, or cylinder of +soft iron, to rotate between them. This cylinder, or ring +of iron, is also wound with insulated wire, two or more +ends of which are brought out in a line with the spindle +on which it rotates, and fastened down to as many +insulated sections of brass cylinder placed around the<!-- Page 16 --><span class="pagenum"><a name="Page_16" id="Page_16">[Pg 16]</a></span> +circumference of the spindle. Two metallic springs, +connected to binding screws which form the "terminals" +of the machine, serve to collect the electrical wave set up +by the rotation of the coiled cylinder (or "armature") +before the poles of the electro-magnet. The annexed +cut (<a href="#FIG_4">Fig. 4</a>) will assist the student in getting a clear +idea of the essential portions in a dynamo:—<span class="smcap">E</span> is the +mass of wrought iron wound with insulated wire, and +known as the <i>field-magnet</i>. <span class="smcap">N</span> and <span class="smcap">S</span> are cast-iron +prolongations of the same, and are usually bolted to the +field-magnet. When current is passing these become +powerfully magnetic. <span class="smcap">A</span> is the rotating iron ring, or +cylinder, known as the <i>armature</i>, which is also wound +with insulated wire, <span class="smcap">B</span>, the ends of which are brought +out and connected to the insulated brass segments<!-- Page 17 --><span class="pagenum"><a name="Page_17" id="Page_17">[Pg 17]</a></span> +known as the <i>commutator</i>, <span class="smcap">C</span>. Upon this commutator +press the two springs <span class="smcap">D</span> and <span class="smcap">D'</span>, known as the <i>brushes</i>, +which serve to collect the electricity set up by the +rotation of the armature. These <i>brushes</i> are in electrical +connection with the two terminals of the machine <span class="smcap">F F'</span>, +whence the electric current is transmitted where required; +the latter being also connected with the wire encircling +the field-magnet, <span class="smcap">E</span>.</p> + +<p>When the iron mass stands in the direction of the +earth's magnetic meridian, even if it have not previously +acquired a little magnetism from the hammering, etc., to +which it was subjected during fitting, it becomes weakly +magnetic. On causing the armature to rotate by +connecting up the pulley at the back of the shaft (not +shown in cut) with any source of power, a very small +current is set up in the wires of the armature, due to the +weak magnetism of the iron mass of the field-magnet. +As this current (or a portion of it) is caused to circulate +around this iron mass, through the coils of wire surrounding +the field-magnet, this latter becomes more powerfully +magnetic (<a href="#SEC_13">§ 13</a>), and, being more magnetically active, sets +up a more powerful electrical disturbance in the armature.</p> + +<p>This increased electrical activity in the armature +increases the magnetism of this field-magnet as before, +and this again reacts on the armature; and these +cumulative effects rapidly increase, until a limit is +reached, dependent partly on the speed of rotation, +partly on the magnetic saturation of the iron of which +the dynamo is built up, and partly on the amount of +resistance in the circuit.</p> + +<div class="footnote"><p><a name="Footnote_2_2" id="Footnote_2_2"></a><a href="#FNanchor_2_2"><span class="label">[2]</span></a> This refers, of course, to those portions of the metals which are out of +the acid. For reasons which will be explained farther on, the condition of +the metals in the acid is just the opposite to this.</p></div> + +<div class="footnote"><p><a name="Footnote_3_3" id="Footnote_3_3"></a><a href="#FNanchor_3_3"><span class="label">[3]</span></a> From some recent investigations, it would appear that what we usually +term the negative is really the point at which the undulation takes its rise.</p></div> + + + +<hr class="long" /> +<p><!-- Page 18 --><span class="pagenum"><a name="Page_18" id="Page_18">[Pg 18]</a></span></p> +<h2><a name="CHAPTER_II" id="CHAPTER_II"></a>CHAPTER II.</h2> + +<h3>ON THE CHOICE OF BATTERIES FOR ELECTRIC BELL +WORK.</h3> + + +<p><a name="SEC_17" id="SEC_17"></a>§ 17. If we immerse a strip of ordinary commercial +sheet zinc in dilute acid (say sulphuric acid 1 part +by measure, water 16 parts by measure<a name="FNanchor_4_4" id="FNanchor_4_4"></a><a href="#Footnote_4_4" class="fnanchor">[4]</a>), we shall find +that the zinc is immediately acted on by the acid, +being rapidly corroded and dissolved, while at the same +time a quantity of bubbles of gas are seen to collect +around, and finally to be evolved at the surface of the +fluid in contact with the plate. Accompanying this +chemical action, and varying in a degree proportionate +to the intensity of the action of the acid on the zinc, +we find a marked development of <i>heat</i> and <i>electricity</i>. +If, while the bubbling due to the extrication of gas be +still proceeding, we immerse in the same vessel a strip +of silver, or copper, or a rod of graphite, taking care +that contact <i>does not</i> take place between the two +elements, no perceptible change takes place in the<!-- Page 19 --><span class="pagenum"><a name="Page_19" id="Page_19">[Pg 19]</a></span> +condition of things; but if we cause the two strips +to touch, either by inclining the upper extremities so +as to bring them in contact out of the fluid like a +letter Λ, or by connecting the upper extremities +together by means of a piece of wire (or other conductor +of electricity), or by causing their lower +extremities in the fluid to touch, we notice a very +peculiar change. The extrication of bubbles around +the zinc strip ceases entirely or almost entirely, while +the other strip (silver, copper, or graphite) becomes +immediately the seat of the evolution of the gaseous +bubbles. Had these experiments been performed with +chemically pure metallic zinc, instead of the ordinary +impure commercial metal, we should have found some +noteworthy differences in behaviour. In the first place, +the zinc would have been absolutely unattacked by the +acid before the immersion of the other strip; and, +secondly, all evolution of gas would entirely cease when +contact between the two strips was broken.</p> + +<p>As the property which zinc possesses of causing the +extrication of gas (under the above circumstances) has +a considerable influence on the efficiency of a battery, +it is well to understand thoroughly what chemical +action takes place which gives rise to this evolution of gas.</p> + + +<p><a name="SEC_18" id="SEC_18"></a>§ 18. All acids may be conveniently regarded as +being built up of two essential portions, viz.: firstly, a +strongly electro-negative portion, which may either +be a single body, such as <i>chlorine</i>, <i>iodine</i>, <i>bromine</i>, etc., +or a compound radical, such as <i>cyanogen</i>; secondly, +the strongly electro-positive body <i>hydrogen</i>.<!-- Page 20 --><span class="pagenum"><a name="Page_20" id="Page_20">[Pg 20]</a></span></p> + +<p>Representing, for brevity's sake, hydrogen by the +letter H., and chlorine, bromine, iodine, etc., respectively +by Cl., Br., and I., the constitution of the acids derived +from these bodies may be conveniently represented by:—</p> + + + +<div class="center"> +<table border="0" cellpadding="4" cellspacing="0" summary="representation of acids"> +<tr><td align="center">H Cl</td><td align="center">H Br</td><td align="center">H I</td></tr> +<tr><td align="center">┗━━┛</td><td align="center">┗━━┛</td><td align="center">┗━━┛</td></tr> +<tr><td align="center">Hydrochloric<br /> Acid<a name="FNanchor_5_5" id="FNanchor_5_5"></a><a href="#Footnote_5_5" class="fnanchor">[5]</a>.</td><td align="center">Hydrobromic<br /> Acid.</td><td align="center">Hydriodic<br /> Acid.</td></tr> +</table></div> + + + +<p>and the more complex acids, in which the electro-negative +component is a compound, such as sulphuric +acid (built up of 1 atom of sulphur and 4 atoms of +oxygen, united to 2 atoms of hydrogen) or nitric acid +(consisting of 1 nitrogen atom, 6 oxygen atoms, and +1 hydrogen atom), may advantageously be retained +in memory by the aid of the abbreviations:—</p> + + + +<div class="center"> +<table border="0" cellpadding="4" cellspacing="0" summary=""> +<tr><td align="center">H<sub>2</sub>SO<sub>4</sub></td><td align="center"> </td><td align="center">HNO<sub>6</sub></td></tr> +<tr><td align="center">┗━━━┛</td><td align="center"> </td><td align="center">┗━━┛</td></tr> +<tr><td align="center">Sulphuric<br /> Acid<a name="FNanchor_6_6" id="FNanchor_6_6"></a><a href="#Footnote_6_6" class="fnanchor">[6]</a>.</td><td align="center">and</td><td align="center">Nitric<br /> Acid<a name="FNanchor_7_7" id="FNanchor_7_7"></a><a href="#Footnote_7_7" class="fnanchor">[7]</a>.</td></tr> +</table></div> + + + + +<p>When zinc <i>does</i> act on an acid, it displaces the hydrogen +contained in it, and takes its place; the acid +losing at the same time its characteristic sourness and +corrosiveness, becoming, as chemists say, <i>neutralized</i>. +<i>One</i> atom of zinc can replace <i>two</i> atoms of hydrogen, +so that one atom of zinc can replace the hydrogen in +two equivalents of such acids as contain only one atom +of hydrogen.</p> + +<p>This power of displacement and replacement possessed +by zinc is not peculiar to this metal, but is<!-- Page 21 --><span class="pagenum"><a name="Page_21" id="Page_21">[Pg 21]</a></span> +possessed also by many other bodies, and is of very +common occurrence in chemistry; and may be roughly +likened to the substitution of a new brick for an old +one in a building, or one girder for another in an arch.</p> + +<p>It will be well, therefore, to remember that in all +batteries in which acids are used to excite electricity +by their behaviour along with zinc, the following +chemical action will also take place, according to which +acid is employed:—</p> + + + +<div class="center"> +<table border="0" cellpadding="4" cellspacing="0" summary=""> +<tr><td align="center">Hydrochloric Acid</td><td align="center">and</td><td align="center">Zinc,</td><td align="center">equal</td><td align="center">Zinc Chloride</td><td align="center">and</td><td align="center">Hydrogen Gas.</td></tr> +<tr><td align="center">2HCl</td><td align="center">+</td><td align="center">Zn</td><td align="center">=</td><td align="center">ZnCl<sub>2</sub></td><td align="center">+</td><td align="center">H<sub>2</sub></td></tr> +</table></div> + + +<p>or:—</p> + + + +<div class="center"> +<table border="0" cellpadding="4" cellspacing="0" summary=""> +<tr><td align="center">Sulphuric Acid</td><td align="center">and</td><td align="center">Zinc,</td><td align="center">equal</td><td align="center">Zinc Sulphate</td><td align="center">and</td><td align="center">Hydrogen Gas.</td></tr> +<tr><td align="center">H<sub>2</sub>SO<sub>4</sub></td><td align="center">+</td><td align="center">Zn</td><td align="center">=</td><td align="center">ZnSO<sub>4</sub></td><td align="center">+</td><td align="center">H<sub>2</sub></td></tr> +</table></div> + + +<p>Or we may put this statement into a general form, +covering all cases in which zinc is acted on by a compound +body containing hydrogen, representing the other +or electro-negative portion of the compound by X:—</p> + +<p class="center"> +Zn + H<sub>2</sub>X = ZnX + H<sub>2</sub><br /> +</p> + +<p>the final result being in every case the corrosion and +solution of the zinc, and the extrication of the hydrogen +gas displaced.</p> + + +<p><a name="SEC_19" id="SEC_19"></a>§ 19. We learn from the preceding statements that +no electricity can be manifested in a battery or cell +(as such a combination of zinc acid and metal is called) +without consumption of zinc. On the contrary, we may +safely say that the more rapidly the <i>useful</i> consumption +of zinc takes place, the greater will be the electrical +effects produced. But here it must be borne in mind<!-- Page 22 --><span class="pagenum"><a name="Page_22" id="Page_22">[Pg 22]</a></span> +that if the zinc is being consumed when we are <i>not</i> +using the cell or battery, that consumption is sheer +waste, quite as much as if we were compelled to burn +fuel in an engine whether the latter were doing work +or not. For this reason the use of commercial zinc, in +its ordinary condition, is not advisable in batteries in +which acids are employed, since the zinc is consumed +in such, whether the battery is called upon to do +electrical work (by placing its plates in connection +through some conducting circuit) or not. This serious +objection to the employment of commercial zinc could +be overcome by the employment of chemically purified +zinc, were it not that the price of this latter is so +elevated as practically to preclude its use for this +purpose. Fortunately, it is possible to confer, on the +ordinary crude zinc of commerce, the power of resisting +the attacks of the acid (so long as the plates are not +metallically connected; or, in other words, so long as +the "circuit is broken"), by causing it to absorb +superficially a certain amount of mercury (quicksilver). +The modes of doing this, which is technically known +as <i>amalgamating the zinc</i>, are various, and, as it is +an operation which every one who has the care of +batteries is frequently called upon to perform, the +following working details will be found useful:—</p> + + +<p><a name="SEC_20" id="SEC_20"></a>§ 20. To amalgamate zinc, it should first be washed +with a strong solution of common washing soda, to +remove grease, then rinsed in running water; the +zinc plates, or rods, should then be dipped into a vessel +containing acidulated water (<a href="#SEC_17">§ 17</a>), and as soon as<!-- Page 23 --><span class="pagenum"><a name="Page_23" id="Page_23">[Pg 23]</a></span> +bubbles of hydrogen gas begin to be evolved, +transferred to a large flat dish containing water. While +here, a few drops of mercury are poured on each +plate, and caused to spread quickly over the surface +of the zinc by rubbing briskly with an old nail-brush +or tooth-brush. Some operators use a kind of +mop, made of pieces of rag tied on the end of a stick, +and there is no objection to this; others recommend the +use of the fingers for rubbing in the mercury. This +latter plan, especially if many plates have to be done, is +very objectionable: firstly, on the ground of health, since +the mercury is slowly but surely absorbed by the system, +giving rise to salivation, etc.; and, secondly, because any +jewellery, etc., worn by the wearer will be whitened and +rendered brittle. When the entire surface of the zinc +becomes resplendent like a looking-glass, the rubbing +may cease, and the zinc plate be reared up on edge, to +allow the superfluous mercury to drain off. This should +be collected for future operations. It is important that +the mercury used for this purpose should be pure. +Much commercial mercury contains lead and tin. These +metals can be removed by allowing the mercury to +stand for some time in a vessel containing dilute nitric +acid, occasional agitation being resorted to, in order to +bring the acid into general contact with the mercury. +All waste mercury, drainings, brushings from old plates, +etc., should be thus treated with nitric acid, and finally +kept covered with water. Sprague, in his admirable +work on electricity, says:—"Whenever the zinc shows +a grey granular surface (or rather before this), brush it<!-- Page 24 --><span class="pagenum"><a name="Page_24" id="Page_24">[Pg 24]</a></span> +well and re-amalgamate, remembering that a saving of +mercury is no economy, and a free use of it no waste; +for it may all be recovered with a little care. Keep a +convenient sized jar, or vessel, solely for washing zinc in, +and brush into this the dirty grey powder which forms, +and is an amalgam of mercury with zinc, lead, tin, etc., +and forms roughnesses which reduce the protection of the +amalgamation. Rolled sheet zinc should always be used +in preference to cast. This latter is very hard to amalgamate, +and has less electro-motive power<a name="FNanchor_8_8" id="FNanchor_8_8"></a><a href="#Footnote_8_8" class="fnanchor">[8]</a>; but for rods +for use in porous jars, and particularly with saline +solutions, cast-zinc is very commonly used. In this +case great care should be taken to use good zinc +cuttings, removing any parts with solder on them, and +using a little nitre as a flux, which will remove a portion +of the foreign metals."</p> + + +<p><a name="SEC_21" id="SEC_21"></a>§ 21. Another and very convenient mode of amalgamating +zinc, specially useful where solid rods or masses +of zinc are to be used, consists in weighing up the +zinc and setting aside four parts of mercury (by weight) +for every hundred of the zinc thus weighed up. The +zinc should then be melted in a ladle, with a little tallow +or resin over the top as a flux. As soon as melted, the +mercury should be added in and the mixture stirred with +a stick. It should then be poured into moulds of the +desired shape. This is, perhaps, the best mode of +amalgamating cast zincs.</p> + + +<p><a name="SEC_22" id="SEC_22"></a>§ 22. Some operators recommend the use of mercurial +salts (such as mercury nitrate, etc.) as advan<!-- Page 25 --><span class="pagenum"><a name="Page_25" id="Page_25">[Pg 25]</a></span>tageous +for amalgamating; but, apart from the fact that +these salts are generally sold at a higher rate than the +mercury itself, the amalgamation resulting, unless a very +considerable time be allowed for the mercuric salts to +act, is neither so deep nor so satisfactory as in the case +of mercury alone. It may here be noted, that although +the effect of mercury in protecting the zinc is very +marked in those batteries in which acids are used as the +exciting fluids, yet this action is not so observable in the +cases in which solutions of <i>salts</i> are used as exciters; +and in a few, such as the Daniell cell and its congeners, +the use of amalgamated zinc is positively a disadvantage.</p> + + +<p><a name="SEC_23" id="SEC_23"></a>§ 23. If, having thus amalgamated the zinc plate of +the little battery described and figured at <a href="#SEC_9">§ 9</a>, we repeat +the experiment therein illustrated, namely, of joining +the wires proceeding from the two plates over a suspended +magnetic needle, and leave them so united, we +shall find that the magnetic needle, which was originally +very much deflected out of the line of the magnetic +meridian (north and south), will very quickly return +near to its old and normal position; and this will be +found to take place long before the zinc has been all +consumed, or the acid all neutralised. Of course, this +points to a rapid falling off in the transmission of the +electric disturbance along the united wires; for had <i>that</i> +continued of the same intensity, the deflection of the +needle would evidently have remained the same likewise. +What, then, can have caused this rapid loss of +power? On examining (without removing from the<!-- Page 26 --><span class="pagenum"><a name="Page_26" id="Page_26">[Pg 26]</a></span> +fluid) the surface of the copper plate, we shall find that +it is literally covered with a coating of small bubbles of +hydrogen gas, and, if we agitate the liquid or the plates, +many of them will rise to the surface, while the +magnetic needle will at the same time give a larger +deflection. If we entirely remove the plates from the +acid fluid, and brush over the surface of the copper +plate with a feather or small pledget of cotton wool +fastened to a stick, we shall find, on again immersing +the plates in the acid, that the effect on the needle is +almost, if not quite, as great as at first; thus proving +that the sudden loss of electrical energy was greatly due +to the adhesion of the free hydrogen gas to the copper +plate. This peculiar phenomenon, which is generally +spoken of as the <i>polarisation of the negative plate</i>, acts in +a twofold manner towards checking the electrical energy +of the battery. In the first place, the layer of hydrogen +(being a bad conductor of electricity) presents a great +resistance to the transmission of electrical energy from +the zinc plate where it is set up to the copper (or +other) plate whence it is transmitted to the wires, or +<i>electrodes</i>. Again, the <i>copper</i> or other receiving plate, in +order that the electric energy should be duly received +and transmitted, should be more electro-negative than +the zinc plate; but the hydrogen gas which is evolved, +and which thus adheres to the negative plate, is actually +very highly electro-positive, and thus renders the copper +plate incapable of receiving or transmitting the electric +disturbance. This state of things may be roughly +likened to that of two exactly equal and level tanks, <span class="smcap">Z<!-- Page 27 --><span class="pagenum"><a name="Page_27" id="Page_27">[Pg 27]</a></span></span> +and <span class="smcap">C</span>, connected by a straight piece of tubing. If <span class="smcap">Z</span> be +full and <span class="smcap">C</span> have an outlet, it is very evident that <span class="smcap">Z</span> can +and will discharge itself into <span class="smcap">C</span> until exhausted; but if <span class="smcap">C</span> +be allowed to fill up to the same level as <span class="smcap">Z</span>, then no +farther flow can take place between the two.</p> + +<p>It is, therefore, very evident that to ensure anything +like constancy in the working of a battery, at least until +all the zinc be consumed or all the acid exhausted, some +device for removing the liberated hydrogen must be put +into practice. The following are some of the means +that have been adopted by practical men:—</p> + + +<p><a name="SEC_24" id="SEC_24"></a>§ 24. <i>Roughening the surface of the negative plate</i>, +which renders the escape of the hydrogen gas easier. +This mode was adopted by Smee in the battery which +bears his name. It consists of a sheet of silver, placed +between two plates of zinc, standing in a cell containing +dilute sulphuric acid, as shown at <a href="#FIG_5">Fig. 5</a>.</p> + +<div class="figcenter" style="width: 328px;"> +<a name="FIG_5" id="FIG_5"></a> +<img src="images/i_037.png" width="328" height="400" alt="" title="The Smee cell" /> +<p class="caption">Fig. 5.</p> +</div> + +<p>The silver sheet, before being placed in position, is +<i>platinised</i>; that is to say, its surface is covered (by electro-deposition) +with a coating of platinum, in the form +of a fine black powder. This presents innumerable +points of escape for the hydrogen gas; and for this +reason this battery falls off much less rapidly than the +plain zinc and smooth copper form. A modification of +Smee's battery which, owing to the large negative surface +presented, is very advantageous, is Walker's graphite +cell. In this we have a plate of zinc between two plates +of gas-carbon ("scurf"), or graphite. The surface of +this body is naturally much rougher than metal sheets; +and this roughness of surface is further assisted by<!-- Page 28 --><span class="pagenum"><a name="Page_28" id="Page_28">[Pg 28]</a></span> +coating the surface with platinum, as in the case of +the Smee. The chief objection to the use of graphite is +its porosity, which causes it to suck up the acid fluid in +which the plates stand, and this, of course, corrodes the +brass connections, or binding screws.</p> + +<p>Other <i>mechanical</i> means of removing the hydrogen +have been suggested, such as brushing the surface of the +plate, keeping the liquid in a state of agitation by boiling +or siphoning; but the only really efficient practical +means with which we are at present acquainted are +<i>chemical</i> means. Thus, if we can have present at the +negative plate some substance which is greedy of +hydrogen, and which shall absorb it or combine with +it, we shall evidently have solved the problem. This +was first effected by Professor Daniell; and the battery<!-- Page 29 --><span class="pagenum"><a name="Page_29" id="Page_29">[Pg 29]</a></span> +known by his name still retains its position as one of the +simplest and best of the "constant" forms of battery. +The term "constant," as applied to batteries, does not +mean that the battery is a constancy, and will run for +ever, but simply that so long as there is in the battery any +fuel (zinc, acid, etc.), the electrical output of that battery +will be constant. The Daniell cell consists essentially +in a rod or plate of zinc immersed in dilute sulphuric +acid, and separated from the copper or collecting plate +by a porous earthen pot or cell. Around the porous +cell, and in contact with the copper plate, is placed a +solution of sulphate of copper, which is maintained +saturate by keeping crystals of sulphate of copper (blue +stone, blue vitriol) in the solution. Sulphate of copper +is a compound built up of copper Cu, and of sulphur +oxide SO<sub>4</sub>. When the dilute sulphuric acid acts on the +zinc plate or rod (<a href="#SEC_18">§ 18</a>), sulphate of zinc is formed, which +dissolves in the water, and hydrogen is given off:—</p> + + + +<div class="center"> +<table border="0" cellpadding="4" cellspacing="0" summary=""> +<tr><td align="center">Zn</td><td align="center">+</td><td align="center">H<sub>2</sub>SO<sub>4</sub></td><td align="center">=</td><td align="center">ZnSO<sub>4</sub></td><td align="center">+</td><td align="center">H<sub>2</sub>.</td></tr> +<tr><td align="center">Zinc</td><td align="center">and</td><td align="center">sulphuric acid</td><td align="center">produce</td><td align="center">zinc sulphate</td><td align="center">and</td><td align="center">free hydrogen.</td></tr> +</table></div> + + +<p>Now this free hydrogen, by a series of molecular +interchanges, is carried along until it passes through the +porous cell, and finds itself in contact with the solution +of copper sulphate. Here, as the hydrogen has a greater +affinity for, or is more greedy of, the sulphur oxide, SO<sub>4</sub>, +than the copper is, it turns the latter out, takes its place, +setting the copper free, and forming, with the sulphur +oxide, sulphuric acid. The liberated copper goes, and +adheres to the copper plate, and, far from detracting from<!-- Page 30 --><span class="pagenum"><a name="Page_30" id="Page_30">[Pg 30]</a></span> +its efficacy, as the liberated hydrogen would have done, +actually increases its efficiency, as it is deposited in a +roughened form, which presents a large surface for the +collection of the electricity. The interchange which +takes place when the free hydrogen meets the sulphate +of copper (outside the porous cells) is shown in the +following equation:—</p> + + + +<div class="center"> +<table border="0" cellpadding="4" cellspacing="0" summary=""> +<tr><td align="center">H<sub>2</sub></td><td align="center">+</td><td align="center">CuSO<sub>4</sub></td><td align="center">=</td><td align="center">H<sub>2</sub>SO<sub>4</sub></td><td align="center">+</td><td align="center">Cu.</td></tr> +<tr><td align="center">Free hydrogen</td><td align="center">and</td><td align="center">copper sulphate</td><td align="center">produce</td><td align="center">sulphuric acid</td><td align="center">and</td><td align="center">free copper.</td></tr> +</table></div> + + +<div class="figcenter" style="width: 330px;"> +<a name="FIG_6" id="FIG_6"></a> +<img src="images/i_039.png" width="330" height="400" alt="Fig. 6. Daniell Cell." title="" /> +<p class="caption">Fig. 6. Daniell Cell.</p> +</div> + + +<p><a name="SEC_25" id="SEC_25"></a>§ 25. The original form given to this, the Daniell +cell, is shown at <a href="#FIG_6">Fig. 6</a>, in which <span class="smcap">Z</span> is the zinc rod standing +in the porous pot <span class="smcap">P</span>, in which is placed the dilute +sulphuric acid. A containing vessel, <span class="smcap">V</span>, of glazed earthenware, +provided with a perforated shelf, <span class="smcap">S</span>, on which +are placed the crystals of sulphate of copper, serves<!-- Page 31 --><span class="pagenum"><a name="Page_31" id="Page_31">[Pg 31]</a></span> +to hold the copper sheet, <span class="smcap">C</span>, and the solution of sulphate +of copper. <span class="smcap">T</span> and <span class="smcap">T'</span> are the terminals from which the +electricity is led where desired.</p> + +<p>In another form, the copper sheet itself takes the form +and replaces the containing vessel <span class="smcap">V</span>; and since the +copper is not corroded, but actually increases in thickness +during action, this is a decided advantage. A +modification, in which the porous cell is replaced by +<i>sand</i> or by <i>sawdust</i>, is also constructed, and known as +"Minotto's" cell: this, owing to the greater thickness +of the porous layer, offers more resistance, and gives, +consequently, less current. By taking advantage of the +greater specific gravity (<i>weight, bulk for bulk</i>) of the +solution of sulphate of copper over that of water or +dilute sulphuric acid, it is possible to construct a battery +which shall act in a manner precisely similar to a +Daniell, without the employment of any porous partition +whatsoever. <a href="#FIG_7">Fig. 7</a> illustrates the construction of +one of these, known as "Gravity Daniells."</p> + +<div class="figcenter" style="width: 376px;"> +<a name="FIG_7" id="FIG_7"></a> +<img src="images/i_041.png" width="376" height="400" alt="Fig. 7. Gravity Cell." title="" /> +<p class="caption">Fig. 7. Gravity Cell.</p> +</div> + +<p>In this we have a plate, disc, or spiral of copper, <span class="smcap">C</span>, +connected by an insulated copper wire to the terminal <span class="smcap">T'</span>. +Over this is placed a layer of crystals of copper sulphate; +the jar is then filled nearly to the top with dilute sulphuric +acid, or with a strong solution of sulphate of zinc +(which is more lasting in its effects, but not so energetic +as the dilute sulphuric acid), and on the surface of this, +connected to the other terminal, <span class="smcap">T</span>, is allowed to rest +a thick disc of zinc, <span class="smcap">Z</span>. Speaking of these cells, Professor +Ayrton, in his invaluable "Practical Electricity," +says:—"All gravity cells have the disadvantage that<!-- Page 32 --><span class="pagenum"><a name="Page_32" id="Page_32">[Pg 32]</a></span> +they cannot be moved about; otherwise the liquids +mix, and the copper sulphate solution, coming into contact +with the zinc plate, deposits copper on it. This +impairs the action, by causing the zinc to act electrically, +like a copper one. Indeed, without any shaking, the +liquids mix by diffusion, even when a porous pot is +employed; hence a Daniell's cell is found to keep in +better order if it be always allowed to send a weak +current when not in use, since the current uses up the +copper sulphate solution, instead of allowing it to +diffuse." The use of a solution of zinc sulphate to act +on the zinc rod, or plate, is always to be preferred in the +Daniell cell, when long duration is of more consequence +than energetic action.</p> + + +<p><a name="SEC_26" id="SEC_26"></a>§ 26. There are many other bodies which can be used +in batteries to absorb the hydrogen set free. Of several +of these we need only take a passing notice, as the<!-- Page 33 --><span class="pagenum"><a name="Page_33" id="Page_33">[Pg 33]</a></span> +batteries furnished by their use are unfit for electric bell +work. Of these we may mention nitric acid, which +readily parts with a portion of the oxygen (<a href="#SEC_18">§ 18</a>) and +reconverts the free hydrogen into water. This acid is +used as the "depolarizer"<a name="FNanchor_9_9" id="FNanchor_9_9"></a><a href="#Footnote_9_9" class="fnanchor">[9]</a> in the "Grove" and in the +"Bunsen" cell. Another very energetic "depolariser" +is chromic acid, either in solution, in dilute sulphuric +acid, or in the form of potassic dichromate (bichromate +of potash: bichrome). As one form of chromic cell has +found favour with some bell-fitters, we shall study its +peculiarities farther on.</p> + +<p>Another class of bodies which readily part with their +oxygen, and thus act as depolarisers, are the oxides of +lead and manganese. This latter oxide forms the basis +of one of the most useful cells for electric bell work, +namely: the one known as the "Leclanché." As the +battery has been, and will probably remain, long a +favourite, the next paragraph will be devoted to its +consideration.</p> + + +<p><a name="SEC_27" id="SEC_27"></a>§ 27. The Leclanché cell, in its original form, consists +in a rod or block of gas carbon (retort scurf: graphite) +standing in an upright porous pot. Around this, so as +to reach nearly to the top of the porous cell, is tightly +packed a mixture of little lumps of graphite and black +oxide of manganese (manganic dioxide: black wad), +the porous cell itself being placed in an outer containing +vessel, which usually takes the form of a square glass +bottle. A zinc rod stands in one corner of the bottle,<!-- Page 34 --><span class="pagenum"><a name="Page_34" id="Page_34">[Pg 34]</a></span> +and is prevented from coming into actual contact with +the porous cell by having an indiarubber ring slipped +over its upper and lower extremities. The glass containing +vessel is then filled to about two-thirds of its height +with a solution of ammonium chloride (sal ammoniac) in +water, of the strength of about 2 oz. of the salt to each +pint of water. This soon permeates the porous cell and +reaches the mixture inside. The general appearance +of the Leclanché cell is well shown at <a href="#FIG_8">Fig. 8</a>.</p> + +<div class="figcenter" style="width: 400px;"> +<a name="FIG_8" id="FIG_8"></a> +<img src="images/i_043.png" width="400" height="289" alt="Fig. 8." title="The Leclanché cell and parts" /> +<p class="caption">Fig. 8.</p> +</div> + +<p>In order to ensure a large surface of contact for the +terminal of the carbon rod or plate, it is customary to +cast a leaden cap on the top thereof; and, as the porosity<!-- Page 35 --><span class="pagenum"><a name="Page_35" id="Page_35">[Pg 35]</a></span> +of the graphite, or carbon, is very apt to allow the fluid in +the battery to creep up to and corrode the terminal, and +thus oppose resistance to the passage of electricity, the +upper end of the carbon, before the lead cap is cast on, +is soaked for some time in melted paraffin wax, at a temperature +of 110° Centigrade: that is somewhat hotter than +boiling water heat. This, if left on the outside, would +prevent the passage of electricity almost entirely; so +lateral holes are drilled into the carbon before the cap +is finally cast on. The action that takes place in the +Leclanché cell may be summarised as follows:—</p> + +<p>When the zinc, Zn, is acted on by the ammonium +chloride, 2NH<sub>4</sub>Cl, the zinc seizes the chlorine and forms +with it zinc chloride, ZnCl<sub>2</sub>, while the ammonium, 2NH<sub>4</sub>, +is liberated. But this ammonium, 2NH<sub>4</sub>, does not escape. +Being electro-positive, it is impelled towards the negative +plate, and in its passage thereto meets with another +molecule of ammonium chloride, from which it displaces +the ammonium, in this wise: 2NH<sub>4</sub> + 2NH<sub>4</sub>Cl = 2NH<sub>4</sub>Cl ++ 2NH<sub>4</sub>; in other words, this electro-positive ammonium +is able, by virtue of its electrical charge, to displace +the ammonium from the combined chloride. In so +doing, it sets the liberated ammonium in an electro-positive +condition, as it was itself, losing at the same +time its electrical charge. This interchange of molecules +goes on (as we saw in the case of the Daniell's cell, <a href="#SEC_24">§ 24</a>) +until the surface of the carbon is reached. Here, as +there is no more ammonium chloride to decompose, the +ammonium 2NH<sub>4</sub> immediately splits up into ammonia +<!-- Page 36 --><span class="pagenum"><a name="Page_36" id="Page_36">[Pg 36]</a></span>2NH<sub>3</sub> and free hydrogen H<sub>2</sub>. The ammonia escapes, +and may be detected by its smell; while the hydrogen +H<sub>2</sub>, finding itself in contact with the oxide of manganese, +2MnO<sub>2</sub>, seizes one atom of its oxygen, O, becoming +thereby converted into water H<sub>2</sub>O; while the manganese +dioxide, 2MnO<sub>2</sub>, by losing one atom of oxygen, is +reduced to the form of a lower oxide of manganese, +known as manganese sesquioxide, Mn<sub>2</sub>O<sub>3</sub>. Expressed +in symbols, this action may be formulated as below:—</p> + +<p>In the zinc compartment—</p> + +<p class="center"> +Zn + 2NH<sub>4</sub>Cl = ZnCl<sub>2</sub> + 2NH<sub>3</sub> + H<sub>2</sub><br /> +</p> + +<p>In the peroxide of manganese compartment—</p> + +<p class="center"> +H<sub>2</sub> + 2MnO<sub>2</sub> = Mn<sub>2</sub>O<sub>3</sub> + H<sub>2</sub>O.<br /> +</p> + +<p>Ammonia gas therefore slowly escapes while this +battery is in action, and this corrodes all the brass work +with which it comes into contact, producing a bluish green +verdigris. If there be not sufficient ammonium chloride +in solution, the water alone acts on the zinc: zinc oxide +is produced, which renders the solution milky. Should +this be the case, more sal ammoniac must be added. It +is found that for every 50 grains of zinc consumed in this +battery, about 82 grains of sal ammoniac and 124 grains +of manganese dioxide are needed to neutralize the +hydrogen set free. It is essential for the efficient working +of this battery that both the manganese dioxide and +the carbon should be free from powder, otherwise it will +cake together, prevent the passage of the liquid, and +present a much smaller surface to the electricity, than if +in a granular form. For this reason, that manganese +dioxide should be preferred which is known as the<!-- Page 37 --><span class="pagenum"><a name="Page_37" id="Page_37">[Pg 37]</a></span> +"needle" form, and both this and the carbon should be +sifted to remove dust.</p> + + +<p><a name="SEC_28" id="SEC_28"></a>§ 28. In the admirable series of papers on electric bell +fitting which was published in the <i>English Mechanic</i>, +Mr. F. C. Allsop, speaking of the Leclanché cell, says:—"A +severe and prolonged test, extending over many years, +has proved that for general electric bell work the +Leclanché has no equal; though, in large hotels, etc., +where the work is likely to be very heavy, it may, +perhaps, be preferable to employ a form of the Fuller +bichromate battery. It is very important that the +battery employed should be a thoroughly reliable one +and set up in a proper manner, as a failure in the battery +causes a breakdown in the communication throughout +the whole building, whilst the failure of a push or wire +only affects that portion of the building in which the +push or wire is fixed. A common fault is that of +putting in (with a view to economy) only just enough +cells (when first set up) to do the necessary work. This +is false economy, as when the cells are but slightly +exhausted the battery power becomes insufficient; +whereas, if another cell or two had been added, the +battery would have run a much longer time without +renewal, owing to the fact that each cell could have +been reduced to a lower state of exhaustion, yet still the +battery would have furnished the necessary power; and +the writer has always found that the extra expense of +the surplus cells is fully repaid by the increased length +of time the battery runs without renewal."</p> + + +<p><a name="SEC_29" id="SEC_29"></a>§ 29. Another form of Leclanché, from which great<!-- Page 38 --><span class="pagenum"><a name="Page_38" id="Page_38">[Pg 38]</a></span> +things were expected at its introduction, is the one +known as the "Agglomerate block," from the fact that, +instead of simply placing the carbon and manganese +together loosely in a porous cell, solid blocks are +formed by compressing these materials, under a +pressure of several tons, around a central carbon core, +to which the terminal is attached in the usual manner. +The following are some of the compositions used in the +manufacture of agglomerate blocks:—</p> + +<p class="center">No. 1.</p> + + + +<div class="center"> +<table border="0" cellpadding="4" cellspacing="0" summary=""> +<tr><td align="left">Manganese dioxide</td><td align="right">40</td><td align="left">parts.</td></tr> +<tr><td align="left">Powdered gas carbon</td><td align="right">55</td><td align="left">parts.</td></tr> +<tr><td align="left">Gum lac resin</td><td align="right">5</td><td align="left">parts.</td></tr> +</table></div> + + +<p class="center">No. 2.</p> + + + +<div class="center"> +<table border="0" cellpadding="4" cellspacing="0" summary=""> +<tr><td align="left">Manganese dioxide (pyrolusite)</td><td align="right">40</td><td align="left">parts.</td></tr> +<tr><td align="left">Gas carbon (powdered)</td><td align="right">52</td><td align="left">parts.</td></tr> +<tr><td align="left">Gum lac resin</td><td align="right">5</td><td align="left">parts.</td></tr> +<tr><td align="left">Potassium bisulphate</td><td align="right">3</td><td align="left">parts.</td></tr> +</table></div> + + +<p>These are to be thoroughly incorporated, forced into +steel moulds (containing the central carbon core) at a +temperature of 100° C. (212° Fahr.), under a pressure of +300 atmospheres, say 4,500 lbs. to the square inch.</p> + +<p class="center">No. 3.</p> + +<p class="center"> +<i>Barbier and Leclanché's Patent.</i></p> + + + +<div class="center"> +<table border="0" cellpadding="4" cellspacing="0" summary=""> +<tr><td align="left">Manganese dioxide</td><td align="right">49</td><td align="left">parts.</td></tr> +<tr><td align="left">Graphite</td><td align="right">44</td><td align="left">parts.</td></tr> +<tr><td align="left">Pitch ("brai gras")</td><td align="right">9</td><td align="left">parts.</td></tr> +<tr><td align="left">Sulphur</td><td align="right">⅗</td><td align="left">parts.</td></tr> +<tr><td align="left">Water</td><td align="right">⅖</td><td align="left">parts.</td></tr> +</table></div> + +<p><!-- Page 39 --><span class="pagenum"><a name="Page_39" id="Page_39">[Pg 39]</a></span></p> + +<p>The materials having been reduced to fine powder, +and the proportion of water stated having been added, +are intimately mixed together by hand or mechanically. +The moist mixture is moulded at the ordinary temperature, +either by a simple compressing press, or by a press +in which two pistons moving towards each other compress +the block on two opposite faces; or the mixture +may be compressed by drawing, as in the manufacture +of electric light carbon. After compression, the +products are sufficiently solid to be manipulated. They +are then put in a stove, or oven, the temperature +of which is gradually raised to about 350° C. (about +662° Fahr.); a temperature which is insufficient to +decompose the depolarising substance (manganese +dioxide), but sufficient to drive out first the volatile +parts of the agglomerating material, and then to transform +its fixed parts in a body unattackable by the +ammonia of the cell. During the gradual heating, or +baking, which lasts about two hours, what remains of +the water in the agglomerate is driven off; then come the +more volatile oils contained in the pitch, and finally the +sulphur. The sulphur is added to the mixture, not as an +agglomerative, but as a chemical re-agent (and this is a +characteristic feature in the invention), acting on what +remains of the pitch, as it acts on all carbo-hydrides at +a high temperature, transforming it partially into +volatile sulphuretted compounds, which are expelled by +the heat, and partially into a fixed and unattackable +body, somewhat similar to vulcanite. The action of +the sulphur on the pitch can very well be likened to its<!-- Page 40 --><span class="pagenum"><a name="Page_40" id="Page_40">[Pg 40]</a></span> +action on caoutchouc (which is likewise a hydro-carbon) +during the process of vulcanisation.</p> + +<div class="figleft" style="width: 183px;"> +<a name="FIG_9" id="FIG_9"></a> +<img src="images/i_049.png" width="183" height="400" alt="Fig. 9." title="The Agglomerate cell" /> +<p class="caption">Fig. 9.</p> +</div> + +<p>These agglomerate blocks, however prepared, are +placed in glass or porcelain containing vessels, as shown +in <a href="#FIG_9">Fig. 9</a>, with a rod of zinc, separated from actual +contact with the carbon by means of a couple of crossed +indiarubber bands, which serve at the same time to +hold the zinc rods upright. The exciting solution, as +in the case of the ordinary Leclanché consists in a +solution of ammonium chloride.</p> + +<p>Among the various advantages claimed +for the agglomerate form of Leclanché over +the ordinary type, may be mentioned the +following:—</p> + +<p>1st.—The depolarising power of the manganese +oxide is used to the best advantage, +and that, owing to this, the electro-motive +force of the battery is kept at the same +point.</p> + +<p>2nd.—That, owing to the absence of the +porous cell, there is less internal resistance +in the battery and therefore more available current.</p> + +<p>3rd.—That the resistance of the battery remains pretty +constant, whatever work be put upon it.</p> + +<p>4th.—That, owing to the fact that the liquid comes +into contact with both elements immediately, the battery +is ready for use directly on being charged.</p> + +<p>5th.—That the renewal or recharging is exceedingly +easy, since the elements can be removed together, fresh +solution added, or new depolarising blocks substituted.<!-- Page 41 --><span class="pagenum"><a name="Page_41" id="Page_41">[Pg 41]</a></span></p> + +<p>But when this battery came to be put to the test of +practical work, it was found the block form could not be +credited with all these advantages, and that their chief +superiority over the old cell consisted rather in their +lower internal resistance than in anything else. Even +this is not an advantage in the case of bell work, except +when several bells are arranged <i>in parallel</i>, so that a +large current is required. The blocks certainly polarise +more quickly than the old form, and it does not appear +that they depolarise any more rapidly. Probably the +enormous pressure to which the blocks are subjected, in +the first two processes, renders the composition almost +impermeable to the passage of the fluid, so that depolarisation +cannot take place very rapidly. Another and +serious objection to these blocks is that, after a little +work, pieces break away from the blocks and settle on +the zinc. This sets up a "short circuit," and the zincs +are consumed whether the battery is in action or not.</p> + +<p>The author has had no opportunity for making any +practical tests with the blocks prepared by process No. 3, +but he is under the impression that the blocks would be +even more friable than those prepared under greater +pressure.</p> + + +<div class="figleft" style="width: 199px;"> +<a name="FIG_10" id="FIG_10"></a> +<img src="images/i_051.png" width="199" height="420" alt="Fig. 10." title="The Judson cell" /> +<p class="caption">Fig. 10.</p> +</div> + +<p><a name="SEC_30" id="SEC_30"></a>§ 30. A third form of Leclanché, and one which has +given considerable satisfaction, is the one known as +"Judson's Patent." This consists, as shown at <a href="#FIG_10">Fig. +10</a>, in a cylinder of corrugated carbon encased in an +outer coating of an insulating composition. Inside the +cell are two or more thin carbon sheets, cemented to the +sides of the cell by Prout's elastic glue, or some similar<!-- Page 42 --><span class="pagenum"><a name="Page_42" id="Page_42">[Pg 42]</a></span> +compound, so as to leave spaces, which are filled in with +granular carbon and manganese. The surface of the +plates is perforated, so as to allow ready access to the +exciting fluid. The zinc rod, which is affixed to the +cover, stands in the centre of the cell, touching it at no +part. Owing to the very large surface presented by the +corrugations in the carbon, and by the perforated carbon +plates, the internal resistance of this form +of battery is very low; hence the current, +if employed against a small outer resistance, +is large. But this, except in the case of +bells arranged in parallel, is of no great +advantage.</p> + + +<p><a name="SEC_31" id="SEC_31"></a>§ 31. The ordinary form of Leclanché is +found in market in three sizes, viz., No. 1, +No. 2, and No. 3. Unfortunately, all makers +do not use these numbers in the same manner, +so that while some call the smallest, or +<i>pint</i> size, No. 1, others give this name to the +largest, or <i>three-pint</i>, size. No. 2 is always +quart size, and this is the one commonly +employed. When several cells are employed +to work a number of bells, it is well, in order +that they may not receive injury, that they be enclosed +in a wooden box. As it is necessary that the batteries +should be inspected from time to time, boxes are +specially made with doubled hinged top and side, so +that when the catch is released these fall flat; thus +admitting of easy inspection or removal of any individual +cell. This form of battery box is shown at <a href="#FIG_11">Fig. 11</a>.<!-- Page 43 --><span class="pagenum"><a name="Page_43" id="Page_43">[Pg 43]</a></span></p> + +<div class="figcenter" style="width: 400px;"> +<a name="FIG_11" id="FIG_11"></a> +<img src="images/i_052.png" width="400" height="292" alt="Fig. 11. Battery in Box." title="" /> +<p class="caption">Fig. 11. Battery in Box.</p> +</div> + + +<p><a name="SEC_32" id="SEC_32"></a>§ 32. There are certain ills to which the Leclanché +cells are liable that require notice here. The first is +<i>creeping</i>. By creeping is meant the gradual crystallisation +of the sal ammonium up the inside and round +the outside of the glass containing jar. There are +two modes of preventing this. The first consists in +filling in the neck with melted pitch, two small funnel-like +tubes being previously inserted to admit of the +addition of fresh sal ammoniac solution, and for the +escape of gas. This mode cannot be recommended, as +it is almost impossible to remove the pitch (in case it be +required to renew the zinc, etc.) without breaking the +glass vessel. The best way to remove the pitch is to<!-- Page 44 --><span class="pagenum"><a name="Page_44" id="Page_44">[Pg 44]</a></span> +place the cell in a large saucepan of cold water, and +set it on a fire until the water boils. The pitch is, +by this treatment, so far softened that the elements +can be removed and the pitch scraped away with a +knife.</p> + +<div class="figleft" style="width: 254px;"> +<a name="FIG_12" id="FIG_12"></a> +<img src="images/i_053.png" width="254" height="400" alt="Fig. 12." title="The Gent cell" /> +<p class="caption">Fig. 12.</p> +</div> + +<p>By far the better mode is to +rub round the inside and outside +of the neck of the jar with +tallow, or melted paraffin wax, +to the depth of an inch or +thereabouts. This effectually +prevents creeping and the consequent +loss of current. Messrs. +Gent, of Leicester, have introduced +a very neat modification +of the Leclanché cell, with a +view to obviate altogether the +evils deriving from creeping. +This cell is illustrated at <a href="#FIG_12">Fig. +12</a>, and the following is the +description supplied by the +patentees:—"All who have had experience of batteries in +which a solution of salts is used are aware of the difficulty +experienced in preventing it creeping over the outside of +the jar, causing local loss, and oftentimes emptying the +jar of its solution. Many devices have been tried to +prevent this, but the only effectual one is our patent +insulated jar, in which a recess surrounds the top of the +jar, this recess being filled with a material to which the +salts will not adhere, thus keeping the outside of the<!-- Page 45 --><span class="pagenum"><a name="Page_45" id="Page_45">[Pg 45]</a></span> +jar perfectly clean. It is specially adapted for use in +hot climates, and is the only cell in which jars may +touch each other and yet retain their insulations. We +confidently recommend a trial of this cell. Its price is +but little in excess of the ordinary Leclanché." The +battery should be set up in as cool a place as possible, +as heat is very conducive to creeping. It is also +important that the battery should be placed as near +as convenient to the bell.</p> + +<p>Sometimes the zincs are seen to become coated with +a black substance, or covered with crystals, rapidly +wasting away at the same time, although doing little or +no work; a strong smell of ammonia being given off at +the same time. When this occurs, it points to an +electrical leakage, or short circuit, and this, of course, +rapidly exhausts the battery. It is of the utmost importance +to the effective working of any battery that +not the slightest leakage or <i>local action</i> should be +allowed to take place. However slight such loss be, it +will eventually ruin the battery. This leakage may be +taking place in the battery, as a porous cell may be +broken, and carbon may be touching the zinc; or out of +the battery, along the conducting wires, by one touching +the other, or through partial conductivity of a damp +wall, a metallic staple, etc., or by creeping. If loss or +local action has taken place, it is best, after discovering +and repairing the faults (see also <i>testing wires</i>), +to replace the old zincs by new ones, which are not +costly.</p> + + +<p><a name="SEC_33" id="SEC_33"></a>§ 33. There is yet a modification of the Leclanché<!-- Page 46 --><span class="pagenum"><a name="Page_46" id="Page_46">[Pg 46]</a></span> +which is sometimes used to ring the large bells in hotels, +etc., known as the Leclanché reversed, since the zinc is +placed in the porous pot, this latter being stood in the +centre of the stoneware jar, the space between the two +being packed with broken carbon and manganese +dioxide. By this means a very much larger negative +surface is obtained. In the Grenet cell, the porous cell +is replaced by a canvas bag, which is packed full of +lumps of graphite and carbon dioxide, a central rod of +carbon being used as the electrode. This may be used in +out-of-the-way places where porous cells are not readily +obtainable, but I cannot recommend them for durability.</p> + + +<p><a name="SEC_34" id="SEC_34"></a>§ 34. The only other type of battery which it will be +needful to notice in connection with bell work is one +in which the depolariser is either chromic acid or a +compound of chromic acid with potash or lime. Chromic +acid consists of hydrogen united to the metal chromium +and oxygen. Potassic dichromate (bichromate of +potash: bichrome) contains potassium, chromium, and +oxygen. If we represent potassium by K, chromium by +Cr, and oxygen by O, we can get a fair idea of its constitution +by expressing it as K<sub>2</sub>Cr<sub>2</sub>O<sub>7</sub>, by which it is +shown that one molecule of this body contains two atoms +of potassium united to two atoms of chromium and seven +atoms of oxygen. Bichromate of potash readily parts +with its oxygen; and it is upon this, and upon the +relatively large amount of oxygen it contains, that its +efficiency as a depolariser depends. Unfortunately, +bichromate of potash is not very soluble in water; one +pint of water will not take up much more than three<!-- Page 47 --><span class="pagenum"><a name="Page_47" id="Page_47">[Pg 47]</a></span> +ounces of this salt. Hence, though the solution of +potassium bichromate is an excellent depolariser as long +as it contains any of the salt, it soon becomes exhausted. +When bichromate of potash is used in a cell along with +sulphuric acid and water, sulphate of potash and +chromic acid are formed, thus:—</p> + + + +<div class="center"> +<table border="0" cellpadding="4" cellspacing="0" summary=""> +<tr><td align="center">K<sub>2</sub>Cr<sub>2</sub>O<sub>7</sub></td><td align="center">+</td><td align="center">H<sub>2</sub>SO<sub>4</sub></td><td align="center">+</td><td align="center">H<sub>2</sub>O</td><td align="center">=</td><td align="center">K<sub>2</sub>SO<sub>4</sub></td><td align="center">+</td><td align="center">2H<sub>2</sub>CrO<sub>4</sub></td></tr> +<tr><td align="center">┗━━━┛</td><td align="center"> </td><td align="center">┗━━┛</td><td align="center"> </td><td align="center">┗━┛</td><td align="center"> </td><td align="center">┗━━┛</td><td align="center"> </td><td align="center">┗━━━┛</td></tr> +<tr><td align="center">1 molecule of bichrome.</td><td align="center">&</td><td align="center">1 molecule of sulphuric acid.</td><td align="center">&</td><td align="center">1 molecule of water.</td><td align="center">give</td><td align="center">1 molecule of sulphate of potash.</td><td align="center">&</td><td align="center">2 molecules of chromic acid.</td></tr> +</table></div> + + +<p>From this we learn that before the potassium +bichromate enters into action in the battery, it is +resolved into chromic acid. Chromic acid is now +prepared cheaply on a large scale, so that potassium +bichromate may always be advantageously replaced by +chromic acid in these batteries; the more so as chromic +acid is extremely soluble in water. In the presence of +the hydrogen evolved during the action of the battery +(<a href="#SEC_18">§ 18</a>) chromic acid parts with a portion of its oxygen, +forming water and sesquioxide of chromium, Cr<sub>2</sub>O<sub>3</sub>, and +this, finding itself in contact with the sulphuric acid, +always used to increase the conductivity of the liquid, +forms sulphate of chromium. The action of the +hydrogen upon the chromic acid is shown in the +following equation:—</p> + + + +<div class="center"> +<table border="0" cellpadding="4" cellspacing="0" summary=""> +<tr><td align="center">2H<sub>2</sub>CrO<sub>4</sub></td><td align="center">+</td><td align="center">3H<sub>2</sub></td><td align="center">=</td><td align="center">5H<sub>2</sub>O</td><td align="center">+</td><td align="center">Cr<sub>2</sub>O<sub>3</sub></td></tr> +<tr><td align="center">┗━━━┛</td><td align="center"> </td><td align="center">┗━┛</td><td align="center"> </td><td align="center">┗━━┛</td><td align="center"> </td><td align="center">┗━━┛</td></tr> +<tr><td align="center">2 molecules of chromic acid.</td><td align="center">&</td><td align="center">3 molecules of hydrogen.</td><td align="center">give</td><td align="center">5 molecules of water.</td><td align="center">&</td><td align="center">1 molecule of chromium sesquioxide.</td></tr> +</table></div> +<p><!-- Page 48 --><span class="pagenum"><a name="Page_48" id="Page_48">[Pg 48]</a></span></p> + +<div class="figright" style="width: 222px;"> +<a name="FIG_13" id="FIG_13"></a> +<img src="images/i_057.png" width="222" height="400" alt="Fig. 13." title="The Bichromate cell" /> +<p class="caption">Fig. 13.</p> +</div> + + +<p><a name="SEC_35" id="SEC_35"></a>§ 35. The "bottle" form of the bichromate or chromic +acid battery (as illustrated at <a href="#FIG_13">Fig. 13</a>) is much employed +where powerful currents of short duration are required. +It consists of a globular bottle with a rather long wide +neck, in which are placed two long narrow graphite +plates, electrically connected to each +other and to one of the binding screws +on the top. Between these two plates +is a sliding rod, carrying at its lower +extremity the plate of zinc. This sliding +rod can be lowered and raised, or retained +in any position, by means of +a set screw. The zinc is in metallic +connection with the other binding screw. +This battery (which, owing to the facility +with which the zinc can be removed +from the fluid, is extremely convenient and economical +for short experiments) may be charged with either of +the following fluids:—</p> + +<p class="center"><span class="smcap">First Recipe.</span></p> + +<p class="center"><i>Bichromate Solution.</i></p> + +<p> +Bichromate of potash (finely powdered) <span class="recipe_amount">3 oz.</span><br /> +Boiling water <span class="recipe_amount">1 pint.</span><br /> +</p> + +<p>Stir with a glass rod, allow to cool, then add, in a fine +stream, with constant stirring,</p> + +<p> +Strong sulphuric acid (oil of vitriol) <span class="recipe_amount">3 fluid oz.</span><br /> +</p> + +<p>The mixture should be made in a glazed earthern +vessel, and allowed to cool before using.<!-- Page 49 --><span class="pagenum"><a name="Page_49" id="Page_49">[Pg 49]</a></span></p> + +<p class="center"><span class="smcap">Second Recipe.</span></p> + +<p class="center"><i>Chromic Acid Solution.</i></p> + +<p> +Chromic acid (chromic trioxide) <span class="recipe_amount">3 oz.</span><br /> +Water <span class="recipe_amount">1 pint.</span><br /> +</p> + +<p>Stir together till dissolved, then add gradually, with +stirring,</p> + +<p> +Sulphuric acid <span class="recipe_amount">3 oz.</span><br /> +</p> + +<p>This also must not be used till cold.</p> + +<p>In either case the bottle must not be more than three +parts filled with the exciting fluid, to allow plenty of +room for the zinc to be drawn right out of the liquid +when not in use.</p> + + +<p><a name="SEC_36" id="SEC_36"></a>§ 36. The effects given by the above battery, though +very powerful, are too transient to be of any service +in continuous bell work. The following modification, +known as the "Fuller" cell, is, however, useful where +powerful currents are required, and, when carefully set +up, may be made to do good service for five or six +months at a stretch. The "Fuller" cell consists in an +outer glass or glazed earthern vessel, in which stands a +porous pot. In the porous pot is placed a large block +of amalgamated zinc, that is cast around a stout +copper rod, which carries the binding screw. This rod +must be carefully protected from the action of the fluid, +by being cased in an indiarubber tube. The amalgamation +of the zinc must be kept up by putting a small +quantity of mercury in the porous cell. The porous +cells must be paraffined to within about half an inch of +the bottom, to prevent too rapid diffusion of the liquids,<!-- Page 50 --><span class="pagenum"><a name="Page_50" id="Page_50">[Pg 50]</a></span> +and the cells themselves should be chosen rather thick +and close in texture, as otherwise the zinc will be rapidly +corroded. Water alone is used as the exciting fluid in +the porous cell along with the zinc. Speaking of this +form of cell, Mr. Perren-Maycock says:—"The base of +the zinc is more acted on (when bichromate crystals are +used), because the porous cells rest on the crystals; +therefore let it be well paraffined, +as also the top edge. Instead of +paraffining the pot in strips all +round (as many operators do) +paraffin the pot all round, except at +one strip about half an inch wide, +and let this face the carbon plate. +If this be done, the difference in +internal resistance between the cell +with paraffined pot and the same +cell with pot unparaffined will be +little; but if the portion that is +unparaffined be turned away from +the carbon, it will make very nearly +an additional 1 ohm resistance. It +is necessary to have an ounce or so +of mercury in each porous cell, covering the foot of the +zinc; or the zincs may be cast short, but of large diameter, +hollowed out at the top to hold mercury, and +suspended in the porous pot. The zinc is less acted on +then, for when the bichromate solution diffuses into the +porous pot, it obviously does so more at the bottom +than at the top."<!-- Page 51 --><span class="pagenum"><a name="Page_51" id="Page_51">[Pg 51]</a></span></p> + +<div class="figcenter" style="width: 216px;"> +<a name="FIG_14" id="FIG_14"></a> +<img src="images/i_059.png" width="216" height="400" alt="Fig. 14." title="The Fuller cell" /> +<p class="caption">Fig. 14.</p> +</div> + +<p><a href="#FIG_14">Fig. 14</a> illustrates the form usually given to the +modification of the Fuller cell as used for bell and +signalling work.</p> + + +<p><a name="SEC_37" id="SEC_37"></a>§ 37. Before leaving the subject of batteries, there +are certain points in connection therewith that it is +absolutely essential that the practical man should +understand, in order to be able to execute any work +satisfactorily. In the first place, it must be borne in +mind that a cell or battery, when at work, is continually +setting up electric undulations, somewhat in the same +way that an organ pipe, when actuated by a pressure +of air, sets up a continuous sound wave. Whatever +sets up the electric disturbance, whether it be the action +of sulphuric acid on zinc, or caustic potash on iron, etc., +is called <i>electromotive force</i>, generally abbreviated E.M.F. +Just in the same manner that the organ pipe could give +no sound if the pressure of air were alike inside and +out, so the cell, or battery, cannot possibly give <i>current</i>, +or evidence of electric flow, unless there is some means +provided to allow the <i>tension</i>, or increased atomic motion +set up by the electromotive force, to distribute itself +along some line of conductor or conductors not subjected +to the same pressure or E.M.F. In other words, +the "current" of electricity will always tend to flow +from that body which has the highest tension, towards +the body where the strain or tension is less. In a cell +in which zinc and carbon, zinc and copper, or zinc and +silver are the two elements, with an acid as an +excitant, the zinc during the action of the acid +becomes of higher "potential" than the other element,<!-- Page 52 --><span class="pagenum"><a name="Page_52" id="Page_52">[Pg 52]</a></span> +and consequently the undulations take place towards +the negative plate (be it carbon, copper, or silver). +But by this very action the negative plate immediately +reaches a point of equal tension, so that no current +is possible. If, however, we now connect the two +plates together by means of any conductor, say +a copper wire, then the strain to which the carbon +plate is subjected finds its exit along the wire and +the zinc plate, which is continually losing its strain +under the influence of the acid, being thus at a lower +potential (electrical level, strain) than the carbon, can +and does actually take in and pass on the electric +vibrations. It is therefore evident that no true "current" +can pass unless the two elements of a battery are +connected up by a conductor. When this connection +is made, the circuit is called a "<i>closed circuit</i>." If, on +the contrary, there is no electrical connection between +the negative and positive plates of a cell or battery, +the circuit is said to be open, or <i>broken</i>. It may be that +the circuit is closed by some means that is not desirable, +that is to say, along some line or at some time when and +where the flow is not wanted; as, for instance, the outside +of a cell may be <i>wet</i>, and one of the wires resting against +it, when of course "leakage" will take place as the +circuit will be closed, though no useful work will be done. +On the other hand, we may actually take advantage of +the practically unlimited amount of the earth's surface, +and of its cheapness as a conductor to make it act as a +portion of the conducting line. It is perfectly true that +the earth is a very poor conductor as compared with<!-- Page 53 --><span class="pagenum"><a name="Page_53" id="Page_53">[Pg 53]</a></span> +metals. Let us say, for the sake of example, that damp +earth conducts 100,000 times worse than copper. It +will be evident that if a copper wire 1/20 of an inch in +section could convey a given electric current, the same +length of earth having a section of 5,000 inches would +carry the same current equally well, and cost virtually +nothing, beyond the cost of a metal plate, or sack of +coke, presenting a square surface of a little over 70 inches +in the side at each end of the line. This mode of completing +the circuit is known as "the earth plate."</p> + + +<p><a name="SEC_38" id="SEC_38"></a>§ 38. The next point to be remembered in connection +with batteries is, that the electromotive force +(E.M.F.) depends on the <i>nature</i> of the elements (zinc +and silver, zinc and carbon, etc.) and the excitants used +in the cell, and has absolutely nothing whatever to do +with their <i>size</i>. This may be likened to difference of +temperature in bodies. Thus, whether we have a block +of ice as large as an iceberg or an inch square, the temperature +will never exceed 32°F. as long as it remains +ice; and whether we cause a pint or a thousand gallons +of water to boil (under ordinary conditions), its temperature +will not exceed 212°F. The only means we +have of increasing the E.M.F., or "tension," or "potential," +of any given battery, is by connecting up its +constituent cells in <i>series</i>; that is to say, connecting the +carbon or copper plate of the one cell to the zinc of the +next, and so on. By this means we increase the E.M.F. +just in the same degree as we add on cells. The accepted +standard for the measure of electromotive force is +called a VOLT, and 1 volt is practically a trifle less than<!-- Page 54 --><span class="pagenum"><a name="Page_54" id="Page_54">[Pg 54]</a></span> +the E.M.F. set up by a single Daniell's cell; the exact +amount being 1·079 volt, or 1-1/12 volt very nearly. The +E.M.F. of the Leclanché is very nearly 1·6 volt, or +nearly 1 volt and 2/3. Thus in <a href="#FIG_15">Fig. 15</a>, which illustrates +3 Leclanché cells set up in series, we should get</p> + + + +<div class="center"> +<table border="0" cellpadding="4" cellspacing="0" summary=""> +<tr><td align="center">1·6</td><td align="center">volt</td></tr> +<tr><td align="center">1·6</td><td align="center">"</td></tr> +<tr><td align="center">1·6</td><td align="center">"</td></tr> +<tr><td align="center" class="bt">4·8</td><td align="center" class="bt">volts</td></tr> +</table></div> + + +<p>as the total electromotive force of the combination.</p> + +<div class="figcenter" style="width: 400px;"> +<a name="FIG_15" id="FIG_15"></a> +<img src="images/i_063.png" width="400" height="196" alt="Fig. 15." title="The Cells coupled in series" /> +<p class="caption">Fig. 15.</p> +</div> + + +<p><a name="SEC_39" id="SEC_39"></a>§ 39. The <i>current</i>, or amplitude of the continuous +vibrations kept up in the circuit, depends upon two +things: 1st, the electromotive force; 2nd, the resistance +in the circuit. There is a certain amount of resemblance +between the flow of water under pressure and +electricity in this respect. Let us suppose we have a<!-- Page 55 --><span class="pagenum"><a name="Page_55" id="Page_55">[Pg 55]</a></span> +constant "head" of water at our disposal, and allow it +to flow through a tube presenting 1 inch aperture. We +get a certain definite flow of water, let us say 100 +gallons of water per hour. More we do not get, owing +to the resistance opposed by the narrowness of the tube +to a greater flow. If now we double the capacity of the +exit tube, leaving the pressure or "head" of water the +same, we shall double the flow of water. Or we may +arrive at the same result by doubling the "head" or +pressure of water, which will then cause a double quantity +of water to flow out against the same resistance in +the tube, or conductor. Just in the same way, if we +have a given pressure of electric strain, or E.M.F., we +can get a greater or lesser flow or "current" by having +less or more resistance in the circuit. The standard of +flowing current is called an <span class="smcap">Ampère</span>; and 1 ampère is +that current which, in passing through a solution of +sulphate of copper, will deposit 18·35 grains of copper +per hour. The unit of resistance is known as an <span class="smcap">Ohm</span>. +The resistance known as 1 ohm is very nearly that of a +column of mercury 1 square millimètre (1/25 of an inch) +in section, and 41¼ inches in height; or 1 foot of No. +41 gauge pure copper wire, 33/10000 of an inch in diameter, +at a temperature of 32° Fahr., or 0° Centigrade.</p> + + +<p><a name="SEC_40" id="SEC_40"></a>§ 40. Professor Ohm, who made a special study of +the relative effects of the resistance inserted in the circuit, +the electromotive force, and the current produced, +enunciated the following law, which, after him, has been +called "<span class="smcap">Ohm's Law</span>." It is that if we divide the number +of electromotive force units (volts) employed by<!-- Page 56 --><span class="pagenum"><a name="Page_56" id="Page_56">[Pg 56]</a></span> +the number of resistance units (ohms) in the entire circuit, +we get the number of current units (ampères) flowing +through the circuit. This, expressed as an equation +is shown below:</p> + +<p class="center">E/R = C or Electromotive force/Resistance = Current.</p> + +<p>Or if we like to use the initials of volts, ampères, and +ohms, instead of the general terms, E, R, and C, we +may write V/R = A, or Volts/Ohms = Ampères.</p> + +<p>From this it appears that 1 volt will send a current +of 1 ampère through a total resistance of 1 ohm, since +1 divided by 1 equals 1. So also 1 volt can send a +current of 4 ampères through a resistance of ¼ of an +ohm, since 1 divided by ¼ is equal to 4. We can therefore +always double the current by halving the resistance; +or we may obtain the same result by doubling the +E.M.F., allowing the resistance to remain the same. +In performing this with batteries we must bear in mind +that the metals, carbon, and liquids in a battery do +themselves set up resistance. This resistance is known +as "<i>internal resistance</i>," and must always be reckoned +in these calculations. We can <i>halve</i> the internal resistance +by <i>doubling</i> the size of the negative plate, or what +amounts to the same thing by connecting two similar +cells "<i>in parallel</i>;" that is to say, with both their zincs +together, to form a positive plate of double size, and both +carbons or coppers together to form a single negative of +twice the dimensions of that in one cell. Any number<!-- Page 57 --><span class="pagenum"><a name="Page_57" id="Page_57">[Pg 57]</a></span> +of cells thus coupled together "<i>in parallel</i>" have their +resistances reduced just in proportion as their number +is increased; hence 8 cells, each having a resistance of +1 ohm if coupled together <i>in parallel</i> would have a +joint resistance of ⅛ ohm only. The E.M.F. would +remain the same, since this does not depend on the size +of the plate (see <a href="#SEC_38">§ 38</a>). The arrangement of cells in +parallel is shown at <a href="#FIG_16">Fig. 16</a>, where three Leclanché cells +are illustrated thus coupled. The following little table +gives an idea of the E.M.F. in volts, and the internal<!-- Page 58 --><span class="pagenum"><a name="Page_58" id="Page_58">[Pg 58]</a></span> +resistance in ohms, of the cells mostly used in electric +bell work.</p> + +<div class="figcenter" style="width: 357px;"> +<a name="FIG_16" id="FIG_16"></a> +<img src="images/i_066.png" width="357" height="400" alt="Fig. 16." title="The Cells coupled in Parallel" /> +<p class="caption">Fig. 16.</p> +</div> + +<hr /> + +<p class="center">TABLE SHOWING E.M.F. AND R. OF BATTERIES.</p> + + + +<div class="center"> +<table border="0" cellpadding="4" cellspacing="0" summary=""> +<tr><th align="left">Name of Cell.</th><th align="left">Capacity of Cell.</th><th align="left">Electromotive <br />force in Volts.</th><th align="left">Resistance <br />in Ohms.</th></tr> +<tr><td align="left">Daniell</td><td align="left">2 quarts</td><td align="left">1·079</td><td align="left" class="in1">1</td></tr> +<tr><td align="left">Daniell Gravity</td><td align="left">2 quarts</td><td align="left">1·079</td><td align="left">10</td></tr> +<tr><td align="left">Leclanché</td><td align="left">1 pint</td><td align="left">1·60</td><td align="left" class="in1">1·13</td></tr> +<tr><td align="left">Leclanché</td><td align="left">2 pints</td><td align="left">1·60</td><td align="left" class="in1">1·10</td></tr> +<tr><td align="left">Leclanché</td><td align="left">3 pints</td><td align="left">1·60</td><td align="left" class="in1">0·87</td></tr> +<tr><td align="left">Agglomerate</td><td align="left">1 pint</td><td align="left">1·55</td><td align="left" class="in1">0·70</td></tr> +<tr><td align="left">Agglomerate</td><td align="left">2 pints</td><td align="left">1·55</td><td align="left" class="in1">0·60</td></tr> +<tr><td align="left">Agglomerate</td><td align="left">3 pints</td><td align="left">1·55</td><td align="left" class="in1">0·50</td></tr> +<tr><td align="left">Fuller</td><td align="left">1 quart</td><td align="left">1·80</td><td align="left" class="in1">0·50</td></tr> +</table></div> + + +<p>From this it is evident that if we joined up the two +plates of a Fuller cell with a short wire presenting no +appreciable resistance, we should get a current of (1·80 +divided by 0·50) 3·6 ampères along the wire; whereas if a +gravity Daniell were employed the current flowing in +the same wire would only be a little over 1/10 of an +ampère, since 1·079/10 = 0·1079. But every wire, no matter +how short or how thick, presents <i>some</i> resistance; so we +must always take into account both the internal resistance +(that of the battery itself) and the external resistance +(that of the wires, etc., leading to the bells or +indicators) in reckoning for any given current from any +cell or cells.</p> + +<div class="footnote"><p><a name="Footnote_4_4" id="Footnote_4_4"></a><a href="#FNanchor_4_4"><span class="label">[4]</span></a> In mixing sulphuric acid with water, the acid should be added in +a fine stream, with constant stirring, to the water, and not the water to the +acid, lest the great heat evolved should cause the acid to be scattered about.</p></div> + +<div class="footnote"><p><a name="Footnote_5_5" id="Footnote_5_5"></a><a href="#FNanchor_5_5"><span class="label">[5]</span></a> Spirits of salt.</p></div> + +<div class="footnote"><p><a name="Footnote_6_6" id="Footnote_6_6"></a><a href="#FNanchor_6_6"><span class="label">[6]</span></a> Oil of vitriol.</p></div> + +<div class="footnote"><p><a name="Footnote_7_7" id="Footnote_7_7"></a><a href="#FNanchor_7_7"><span class="label">[7]</span></a> Aquafortis.</p></div> + +<div class="footnote"><p><a name="Footnote_8_8" id="Footnote_8_8"></a><a href="#FNanchor_8_8"><span class="label">[8]</span></a> Power to set up a current of electricity.</p></div> + +<div class="footnote"><p><a name="Footnote_9_9" id="Footnote_9_9"></a><a href="#FNanchor_9_9"><span class="label">[9]</span></a> Depolarizer is the technical name given to any body which, by absorbing +the free hydrogen, removes the false polarity of the negative plate.</p></div> + + + +<hr class="long" /> +<p><!-- Page 59 --><span class="pagenum"><a name="Page_59" id="Page_59">[Pg 59]</a></span></p> +<h2><a name="CHAPTER_III" id="CHAPTER_III"></a>CHAPTER III. +<br /> +ON ELECTRIC BELLS AND OTHER SIGNALLING +APPLIANCES.</h2> + + +<p><a name="SEC_41" id="SEC_41"></a>§ 41. An electric bell is an arrangement of a cylindrical +soft iron core, or cores, surrounded by coils of +insulated copper wire. On causing a current of electricity +to flow round these coils, the iron becomes, <i>for +the time being</i>, powerfully magnetic (see <a href="#SEC_13">§ 13</a>). A piece +of soft iron (known as the <i>armature</i>), supported by a +spring, faces the magnet thus produced. This armature +carries at its free extremity a rod with a bob, clapper or +hammer, which strikes a bell, or gong, when the armature, +under the influence of the pull of the magnet, is +drawn towards it. In connection with the armature +and clapper is a device whereby the flow of the current +can be rapidly interrupted, so that on the cessation of +the current the iron may lose its magnetism, and allow +the spring to withdraw the clapper from against the bell. +This device is known as the "contact breaker" and +varies somewhat in design, according to whether the +bell belongs to the <i>trembling</i>, the <i>single stroke</i>, or the +<i>continuous ringing</i> class.</p> + + +<p><a name="SEC_42" id="SEC_42"></a>§ 42. In order that the electric bell-fitter may have an<!-- Page 60 --><span class="pagenum"><a name="Page_60" id="Page_60">[Pg 60]</a></span> +intelligent conception of his work, he should <i>make</i> a +small electric bell himself. By so doing, he will gain +more practical knowledge of what are the requisites of +a good bell, and where defects may be expected in any +he may be called upon to purchase or examine, than he +can obtain from pages of written description. For +this reason I reproduce here (with some trifling additions +and modifications) Mr. G. Edwinson's directions +for making an electric bell:—<a name="FNanchor_10_10" id="FNanchor_10_10"></a><a href="#Footnote_10_10" class="fnanchor">[10]</a></p> + +<p><i>How to make a bell.</i>—The old method of doing this +was to take a piece of round iron, bend it into the form +of a horse-shoe, anneal it (by leaving it for several +hours in a bright fire, and allowing it to cool gradually +as the fire goes out), wind on the wire, and fix it as a +magnet on a stout board of beech or mahogany; a bell +was then screwed to another part of the board, a piece +of brass holding the hammer and spring being fastened to +another part. Many bells made upon this plan are still +offered for sale and exchange, but their performance is +always liable to variation and obstruction, from the following +causes:—To insure a steady, uniform vibratory +stroke on the bell, its hammer must be nicely adjusted +to move within a strictly defined and limited space; the +least fractional departure from this adjustment results in +an unsatisfactory performance of the hammer, and often +a total failure of the magnet to move it. In bells constructed +on the old plan, the wooden base is liable to +expansion and contraction, varying with the change of +weather and the humidity, temperature, etc., of the room<!-- Page 61 --><span class="pagenum"><a name="Page_61" id="Page_61">[Pg 61]</a></span> +in which the bells are placed. Thus a damp, foggy +night may cause the wood to swell and place the hammer +out of range of the bell, while a dry, hot day may alter +the adjustment in the opposite direction. Such failures +as these, from the above causes alone, have often brought +electric bells into disrepute. +Best made bells are, therefore, +now made with metallic +(practically inexpansible) +bases, and it is this kind I +recommend to my readers.</p> + +<div class="figright" style="width: 222px;"> +<a name="FIG_17" id="FIG_17"></a> +<img src="images/i_070.png" width="222" height="400" alt="Fig. 17." title="Outline of electric bell" /> +<p class="caption">Fig. 17.</p> +</div> + +<div class="figright" style="width: 243px;"> +<a name="FIG_18" id="FIG_18"></a> +<img src="images/i_071.png" width="243" height="400" alt="Fig. 18." title="Frame of bell" /> +<p class="caption">Fig. 18.</p> +</div> + +<div class="figright" style="width: 258px;"> +<a name="FIG_19" id="FIG_19"></a> +<img src="images/i_072.png" width="258" height="400" alt="Fig. 19." title="E-shaped frame" /> +<p class="caption">Fig. 19.</p> +</div> + +<p><i>The Base</i>, to which all the +other parts are fastened, is +made of ¾ in. mahogany or +teak, 6 in. by 4 in., shaped +as shown at <a href="#FIG_17">Fig. 17</a>, with a +smooth surface and French +polished. To this is attached +the metallic base-plate, +which may be cut out +of sheet-iron, or sheet-brass +(this latter is better, as iron +disturbs the action of the +magnet somewhat), and +shaped as shown in <a href="#FIG_18">Fig. 18</a>; +or it may be made of cast-iron, or cast in brass; or a substitute +for it may be made in wrought-iron, or brass, as +shown in <a href="#FIG_19">Fig. 19</a>. I present these various forms to suit +the varied handicrafts of my readers; for instance, a +worker in sheet metal may find it more convenient to<!-- Page 62 --><span class="pagenum"><a name="Page_62" id="Page_62">[Pg 62]</a></span> +manufacture his bell out of the parts sketched in Figs. +<a href="#FIG_17">17</a>, <a href="#FIG_18">18</a>, <a href="#FIG_20A">20<sup>A</sup></a>, <a href="#FIG_21">21</a>, <a href="#FIG_23">23</a>, <a href="#FIG_24">24<sup>A</sup></a>, and <a href="#FIG_25">25</a>; but, on the other hand, +a smith or engineer might prefer the improved form +shown at <a href="#FIG_31">Fig. 31</a>, and select the parts shown at Figs. <a href="#FIG_20A">20<sup>A</sup></a>, +<a href="#Page_22">22</a>, <a href="#FIG_19">19</a>, choosing either to forge the horse-shoe magnet, +<a href="#FIG_20">Fig. 20</a>, or to turn up the +two cores, as shown at +<a href="#FIG_21">Fig. 21</a> (<span class="smcap">A</span>), to screw into +the metal base, <a href="#FIG_21">Fig. 21</a> <span class="smcap">B</span>, +or to be fastened by nuts, +as shown at <a href="#FIG_19">Fig. 19</a>. The +result will be the same in +the end, if good workmanship +is employed, and +the proper care taken in +fixing and adjusting the +parts. A tin-plate worker +may even cut his base-plate +out of stout block +tin, and get as good results +as if the bell were made +by an engineer. In some +makes, the base-plate is +cut or stamped out of +thick sheet-iron, in the +form shown by the dotted lines on <a href="#FIG_18">Fig. 18</a>, and +when thus made, the part <span class="smcap">A</span> is turned up at right angles +to form a bracket for the magnet cores, the opposite +projection is cut off, and a turned brass pillar is inserted +at <span class="smcap">B</span> to hold the contact screw, or contact breaker (<a href="#SEC_41">§ 41</a>).<!-- Page 63 --><span class="pagenum"><a name="Page_63" id="Page_63">[Pg 63]</a></span></p> + +<p>The <i>Magnet</i> may be formed as shown at <a href="#FIG_20">Fig. 20</a>, or at +<a href="#FIG_20A">Fig. 20<sup>A</sup></a>. Its essential parts are: 1st. Two soft iron +cores (in some forms a single core is now employed); +2nd. An iron base, or yoke, to hold the cores together; +3rd. Two bobbins wound with wire. The old form of +magnet is shown at <a href="#FIG_20">Fig. 20</a>. In this form the cores and +yoke are made out of one +piece of metal. A length +of round Swedish iron is +bent round in the shape of a +horseshoe; this is rendered +thoroughly soft by annealing, +as explained further on. +It is absolutely essential +that the iron be very soft +and well annealed, otherwise +the iron cores retain +a considerable amount of +magnetism when the current +is not passing, which makes +the bell sluggish in action, +and necessitates a higher +battery power to make it +work (see <a href="#SEC_14">§ 14</a>). Two bobbins of insulated wire +are fitted on the cores, and the magnet is held in +its place by a transverse strip of brass or iron secured +by a wood screw passing between the two bobbins. The +size of the iron, the wire, the bobbins, and the method +of winding is the same as in the form next described, +the only difference being that the length of the iron<!-- Page 64 --><span class="pagenum"><a name="Page_64" id="Page_64">[Pg 64]</a></span> +core, before bending to the horse-shoe form, must be +such as to allow of the two straight portions of the legs +to be 2 in. in length, and stand 1⅜ apart when bent. +We may now consider the construction of a magnet of +the form shown at <a href="#FIG_20A">Fig. 20<sup>A</sup></a>. To make the cores of +such a magnet, to ring a 2½ in. bell, get two 2 inch +lengths of 5/16 in. best Swedish round iron, straighten +them, smooth them in a lathe, and reduce ¼ in. of one +end of each to 4/16 of an in., leaving a sharp shoulder, +as shown at <a href="#FIG_21">Fig. 21</a> <span class="smcap">A</span>. Next, get a 2-in. length of +angle iron, drill in it two holes 1⅜ apart, of the exact +diameter of the turned ends of the cores, and rivet these +securely in their places; this may be done by fastening +the cores or legs in a vice whilst they are being rivetted.<!-- Page 65 --><span class="pagenum"><a name="Page_65" id="Page_65">[Pg 65]</a></span> +Two holes should be also bored in the other flange to +receive the two screws, which are to hold the magnet to +the base, as shown at <a href="#FIG_21">Fig. 21</a> <span class="smcap">B</span>. The magnet is now +quite equal to the horse-shoe form, and must be made +quite soft by annealing. This is done by heating it in +a clear coal fire to a bright red heat, then burying it in +hot ashes, and allowing it to cool gradually for a period +of from 12 to 24 hours; or perhaps a better guide to +the process will be to say, bury the iron in the hot +ashes and leave it there until both it and they are quite +cold. The iron must be brought to a bright cherry red +heat before allowing it to cool, to soften it properly, +and on no account must the cooling be hurried, or the +metal will be <i>hard</i>. Iron is rendered hard by hammering, +by being rapidly cooled, either in cold air or water,<!-- Page 66 --><span class="pagenum"><a name="Page_66" id="Page_66">[Pg 66]</a></span> +and hard iron retains magnetism for a longer time than +soft iron. As we wish to have a magnet that will only +act as such when a current of electricity is passing +around it, and shall return to the state of a simple +piece of unmagnetised iron when the current is broken, +we take the precaution of having it of soft iron. Many +bells have failed to act properly, because this precaution +has been neglected, the "residual" (or remaining) +magnetism holding down the +armature after contact has +been broken. When the +magnet has been annealed, its +legs should be polished with a +piece of emery cloth, and the +ends filed up level and smooth. +If it is intended to fasten the +cores into the base-plate, this +also should be annealed, unless +it be made of brass, in which +case a thin strip of soft iron +should connect the back ends +of the two legs before they are +attached to the brass base (an iron yoke is preferable, as +it certainly is conducive to better effects to have a massive +iron yoke, than to have a mere strip as the connecting +piece). It will also be readily understood and conceded +that the cores should be cut longer when they are to be +fastened by nuts, to allow a sufficient length for screwing +the ends to receive the nuts. The length and size of the +legs given above are suitable for a 2½ in. bell only;<!-- Page 67 --><span class="pagenum"><a name="Page_67" id="Page_67">[Pg 67]</a></span> +for larger bells the size increases 1/16 of an inch, and the +length ¼ of an inch, for every ½ in. increase in the +diameter of the bell.</p> + +<div class="figcenter" style="width: 400px;"> +<a name="FIG_20" id="FIG_20"></a> +<img src="images/i_073.png" width="400" height="331" alt="Fig. 20." title="Electro-magnet, old form" /> +<p class="caption">Fig. 20.</p> +</div> + +<hr /> + +<div class="figcenter" style="width: 400px;"> +<a name="FIG_20A" id="FIG_20A"></a> +<img src="images/i_074.png" width="400" height="336" alt="Fig. 20 A." title="Electro-magnet, modern form" /> +<p class="caption">Fig. 20 A.</p> +</div> + +<div class="figright" style="width: 339px;"> +<a name="FIG_21" id="FIG_21"></a> +<img src="images/i_075.png" width="339" height="400" alt="Fig. 21." title="Magnet frame" /> +<p class="caption">Fig. 21.</p> +</div> + +<p>The <i>Bobbins</i>, on which the wire that serves to carry +the magnetising current is to be wound, next demand +our attention. They may be turned out of boxwood, +ebony, or ebonite, or out of any hard wood strong +enough and dense enough to allow of being turned +down thin in the body, a very necessary requirement to +bring the convolutions of wire as near the coil as possible +without touching it. Some amateurs use the +turned ends of cotton reels or spools, and glue them +on to a tube of paper formed on the cores themselves. +If this tube be afterwards well covered with melted +paraffin wax, the plan answers admirably, but of course +the bobbins become fixtures on the magnets. There +are some persons who are clever enough to make firm +bobbins out of brown paper (like rocket cases), with reel +ends, that can be slipped off and on the magnet cores. +To these I would say, "by all means at your command, +do so if you can." The size of the bobbins for a 2½ in. +bell should be: length 1¾ in., diameter of heads ¾ of an +in., the length increasing ¼ of an in. and the diameter ⅛ of +an in. for every additional ½ in. in the diameter of +the bell. The holes throughout the bobbins should be +of a size to fit the iron cores exactly, and the cores +should project ⅛ of an inch above the end of the +bobbins when these are fitted on. The wire to be +wound on the bobbins is sold by all dealers in electrical +apparatus. It is copper wire, covered with cotton or<!-- Page 68 --><span class="pagenum"><a name="Page_68" id="Page_68">[Pg 68]</a></span> +with silk, to ensure insulation. Mention has already +been made of what is meant by insulation at <a href="#SEC_3">§ 3</a>, but, in +order to refresh the reader's memory, Mr. G. Edwinson's +words are quoted here. "To insulate, as understood +by electricians, means to protect from leakage of +the electric current, by interposing a bad conductor of +electricity between two good conductors, thus insulating<a name="FNanchor_11_11" id="FNanchor_11_11"></a><a href="#Footnote_11_11" class="fnanchor">[11]</a> +or detaching them from electric contact."</p> + +<p>The following list will enable my readers to see +at a glance the value of the substances mentioned +here as conductors or insulators, the best conductors +being arranged from the top downwards, and the bad +conductors or insulators opposed to them in similar +order, viz., the worst conductors or best insulators being +at the top:—</p> + + + +<div class="center"> +<table border="0" cellpadding="4" cellspacing="0" summary=""> +<tr><th align="center"><i>Conductors.</i></th><th align="center"><i>Insulators.</i></th></tr> +<tr><td align="left">Silver.</td><td align="left">Paraffin Wax.</td></tr> +<tr><td align="left">Copper.</td><td align="left">Guttapercha.</td></tr> +<tr><td align="left">Iron.</td><td align="left">Indiarubber.</td></tr> +<tr><td align="left">Brass.</td><td align="left">Shellac.</td></tr> +<tr><td align="left">All Other Metals.</td><td align="left">Varnishes.</td></tr> +<tr><td align="left">Metallic Solutions.</td><td align="left">Sealing Wax.</td></tr> +<tr><td align="left">Metallic Salts.</td><td align="left">Silk and Cotton.</td></tr> +<tr><td align="left">Wet Stone.</td><td align="left">Dry Clothing.</td></tr> +<tr><td align="left">Wet Wood.</td><td align="left">Dry Wood.</td></tr> +<tr><td align="left"></td><td align="left">Oil, Dirt and Rust.</td></tr> +</table></div> + + +<p>See also the more extended list given at <a href="#SEC_5">§ 5</a> for a more +complete and exact classification.<!-- Page 69 --><span class="pagenum"><a name="Page_69" id="Page_69">[Pg 69]</a></span></p> + +<p>It will be seen, on reference to the above, that copper +is a good conductor, being excelled by silver alone in +this respect; and that silk and cotton are bad conductors. +When, therefore, a copper wire is bound round with silk +or with cotton, even if two or more strands of such a +covered wire be superimposed, since these are electrically +separated by the non-conducting covering, no escape of +electricity from one strand to the other can take place, and +the strands are said to be insulated. If the copper wire +had been coiled <i>naked</i> round a bobbin, each convolution +touching its neighbour, the current would not have +circled round the whole length of the coils of wire, but +would have leapt across from one coil to the other, and +thus the desired effect would not have been obtained. +A similar result, differing only in degree, would occur +if a badly insulating wire were used, say one in which +the covering had been worn in places, or had been badly +wound, so as to expose patches of bare copper wire. If +the insulation of a wire be suspected, it should be +immersed in hot melted paraffin wax, and then hung up +to drain and cool. The size of wire to be used on a +2½ in. bell should be No. 24 B. W. G., the size falling two +numbers for each ½ in. increase in the diameter of +the bell. In these wires the higher the number, the +finer the size, No. 6 being 1/5 and No. 40 being 1/200 of an +inch in diameter. Silk-covered wire has an advantage +over cotton-covered wire, inasmuch as the insulating +material occupies less space, hence the convolutions of +wire lie closer together. This is important, as the +current has less effect on the iron if removed further<!-- Page 70 --><span class="pagenum"><a name="Page_70" id="Page_70">[Pg 70]</a></span> +from it, the decrease being as the <i>square</i> of the distance +that the current is removed from the wire. Magnets +coiled with silk-covered wire admit also of better finish, +but for most purposes cotton-covered wire will give +satisfaction, especially if well paraffined. This wire +must be wound on the bobbins, from end to end +regularly, with the coils side by side, as a reel of cotton +is wound. This may be done on a lathe, but a little +practice will be necessary before the inexperienced hand +can guide the wire in a regular manner. If, however, +the spool of wire have a metal rod passed up its centre, +and this be held in the hand at a distance of a foot or +more from the bobbin on the lathe, the wire will almost +guide itself on, providing the guiding hand be allowed +to follow its course. With a little care, the wire for +these little magnets may be wound entirely by hand. +Before commencing to wind on the bobbins, just measure +off 8 in. of the wire (not cutting it off) and coil this +length around a pencil, to form a small coil or helix. +The pencil may then be withdrawn from the helix thus +formed, which serves to connect the wire with one of the +points of contact. This free end is to be fastened outside +the bobbin by a nick in the head; or the ⅛ in. +length, before being formed into a helix, may be +pushed through a small hole made on the head of the +bobbin, so that 8 in. project <i>outside</i> the bobbin, +which projecting piece may be coiled into a helix as +above described. The wire should now be wound +exactly as a reel of cotton is wound, in close coils from +end to end, and then back again, until three layers of<!-- Page 71 --><span class="pagenum"><a name="Page_71" id="Page_71">[Pg 71]</a></span> +wire have been laid on, so that the coiling finishes at the +opposite end to that at which it began. To prevent this +uncoiling, it should be fastened by tying down tightly +with a turn or two of strong silk. The wire should now +be cut from the hank, leaving about 2 in. of free +wire projecting at the finishing end of each bobbin. In +cases where many bobbins have to be wound, either for +bells, for relays, or for indicator coils, a device similar to +that illustrated at <a href="#FIG_21A">Fig. 21 <span class="smcap">A</span></a> may be employed. This +<i>electric bobbin winder</i> consists in a table which can be +stood on a lathe or near any other driving wheel. Two +carriers, <span class="smcap">C C</span>, somewhat similar to the back centre and +poppet head of a lathe, hollow inside, and furnished +with a spring and sliding piston spindle, stand one at +each end of this table. The sliding spindle of the one +carries at its extremity a pulley, <span class="smcap">A</span>, by means of which +motion can be transmitted from the band of the driving +wheel. The sliding spindles, <span class="smcap">B B</span>, are fitted with recesses +and screws, <span class="smcap">H H H H</span>, by means of which the temporary +wooden cores, or the permanent iron cores, of the bobbins +can be held while the bobbins are being wound. The +bobbin is placed as shown at <span class="smcap">D</span>; a flat piece of metal, <span class="smcap">E</span>, +hinged at <span class="smcap">G</span>, presses against the bobbin, owing to the +spring <span class="smcap">F</span>. The centre figure shows details of the carrier, +<span class="smcap">C</span>, in section. At the bottom is shown the spool of wire +on a standard <span class="smcap">L</span>. The wire passes from this spot between +the two indiarubber rollers, <span class="smcap">M M</span>, on to the bobbin <span class="smcap">D</span>.</p> + +<div class="figcenter" style="width: 594px;"> +<a name="FIG_21A" id="FIG_21A"></a> +<img src="images/i_081.png" width="594" height="600" alt="Fig. 21 A." title="Winder" /> +<p class="caption">Fig. 21 A.</p> +</div> + +<p>When the bobbins have been wound, they may be +slipped over the magnet cores. They should fit pretty +tightly; if they do not, a roll of paper may be put round<!-- Page 72 --><span class="pagenum"><a name="Page_72" id="Page_72">[Pg 72]</a></span> +the magnet cores, to ensure their not slipping when +the bell is at work. The helix ends of the bobbins +should stand uppermost, as shown at <a href="#FIG_22">Fig. 22 <span class="smcap">A</span></a>. A short +length of the lower free ends of wire (near the base or +yoke) should now be bared of their covering, cleaned<!-- Page 73 --><span class="pagenum"><a name="Page_73" id="Page_73">[Pg 73]</a></span> +with emery paper, twisted together tightly, as shown at +<a href="#FIG_22">Fig. 22 <span class="smcap">B</span></a>, soldered together, and any excess of wire cut off +with a sharp pair of pliers. To prevent any chance +electrical leakage between this bared portion of the wire +and the iron, it should be carefully coated with a little +melted guttapercha, or Prout's electric glue.</p> + +<div class="figcenter" style="width: 400px;"> +<a name="FIG_22" id="FIG_22"></a> +<img src="images/i_082a.png" width="400" height="332" alt="Fig. 22." title="Mode of joining electromagnet wires" /> +<p class="caption">Fig. 22.</p> +</div> + +<p>Of course, if the operator has any skill at winding, he +may wind both bobbins with one continuous length of +wire, thus avoiding joins, taking care that the direction +of the winding in the finished coils be as shown at +<a href="#FIG_22">Fig. 22 <span class="smcap">B</span></a>; that is to say, that the wire from the <i>under</i> +side of one bobbin, should pass <i>over</i> to the next in the +same way as the curls of the letter <span title="[rotated S in original text]">S</span>.</p> + +<div class="figcenter" style="width: 400px;"> +<a name="FIG_23" id="FIG_23"></a> +<img src="images/i_083a.png" width="400" height="134" alt="Fig. 23." title="Armature spring" /> +<p class="caption">Fig. 23.</p> +</div> + +<hr /> + +<div class="figcenter" style="width: 400px;"> +<a name="FIG_24" id="FIG_24"></a> +<img src="images/i_083b.png" width="400" height="140" alt="Fig. 24." title="Armature spring Another form" /> +<p class="caption">Fig. 24.</p> +</div> + +<div class="figright" style="width: 300px;"> +<a name="FIG_25" id="FIG_25"></a> +<img src="images/i_084.png" width="300" height="352" alt="Fig. 25." title="Platinum tipped screw" /> +<p class="caption">Fig. 25.</p> +</div> + +<div class="figright" style="width: 300px;"> +<a name="FIG_26" id="FIG_26"></a> +<img src="images/i_085.png" width="300" height="72" alt="Fig. 26." title="Platinum tipped spring" /> +<p class="caption">Fig. 26.</p> +</div> + +<div class="figright" style="width: 300px;"> +<a name="FIG_27" id="FIG_27"></a> +<img src="images/i_086.png" width="300" height="348" alt="Fig. 27." title="Binding screws" /> +<p class="caption">Fig. 27.</p> +</div> + +<p>The part that next claims our consideration is the<!-- Page 74 --><span class="pagenum"><a name="Page_74" id="Page_74">[Pg 74]</a></span> +<i>armature</i>, with its fittings. The armature is made out of +5/16 square bar iron, of the best quality, soft, and well +annealed, and filed up smooth and true. The proportionate +length is shown at Figs. <a href="#FIG_23">23</a> and <a href="#FIG_24">24</a>; and the +size of the iron for other bells is regulated in the same +ratio as that of the cores. Two methods of making and +attaching the springs and hammers are shown. <a href="#FIG_24">Fig. 24</a> +shows the section of an armature fitted with back spring +and contact spring in one piece. This is cut out of hard +sheet-brass, as wide as the armature, filed or hammered +down to the desired degree of springiness, then filed up +true on the edges. It may be attached to the iron of the +armature, either by soldering, by rivetting, or by means<!-- Page 75 --><span class="pagenum"><a name="Page_75" id="Page_75">[Pg 75]</a></span> +of two small screws. Rivetting is, perhaps, the best mode, +as it is not liable to shake loose by the vibration of the +hammer. The spring at its shank end may be screwed +or rivetted to the bracket. Mr. Edwinson considers +this the better form of contact spring. The other form +is made in two pieces, as shown at <a href="#FIG_23">Fig. 23</a>, where two +strips of hard brass are cut off, of the width of +the armature, and the edges filed. A slot is then +cut in the back end of the armature to receive the two +brass strips, and these are soldered into it. The top +strip is then bent back over the armature +to form the contact-spring, the other strip +being soldered or rivetted to a small +bracket of angle brass. In either case +a short rod of stout hard brass wire is +rivetted or screwed into the free end of +the armature, and to the end of this rod +is screwed or soldered the metal bead, +or bob, which forms the hammer or +"clapper" of the bell. The next portion +to be made is the contact pillar, or bracket, with its +screw, as shown at <a href="#FIG_25">Fig. 25</a>. This may either be a +short stout pillar of ¼ in. brass rod, about 1 in. high, +tapped on one side to receive the screw, which should be +fitted with a back nut; or it may, as shown in the figure, +be made out of a stout piece of angle brass. The exact +size and length of the screw is immaterial; it must, however, +be long enough to reach (when put in its place +behind the contact spring) the spring itself, and still have +a few threads behind the back nut to spare. The screw<!-- Page 76 --><span class="pagenum"><a name="Page_76" id="Page_76">[Pg 76]</a></span> +should be nicely fitted to the pillar, and the lock nut +should clench it well, as when once the adjustment of +the parts is found which gives good ringing, it is advisable +that no motion should take place, lest the perfection +of ringing be interfered with. Some makers use a "set +screw" at the side of the pillar wherewith to hold the +contact screw; others split the pillar and "spring" it +against the contact screw; but, all things considered, the +back nut gives the greatest satisfaction. When the bell +is in action, a tiny spark is produced at every make and +break of contact between the contact spring and this +screw. This spark soon corrodes the end of the screw +and the back of the spring if brass alone is used, as this +latter rusts under the influence of the spark. To +prevent this, a piece of platinum must be soldered or +rivetted to the spring, at the point where the screw +touches, as shown at <a href="#FIG_26">Fig. 26</a>, and also at the extremity +of the contact screw itself. It +is better to rivet the platinum +than to solder it, as the platinum +is very apt to absorb the solder, +in which case it rusts quickly, and the goodness of +the contact is soon spoiled, when the bell ceases to +ring. To rivet the platinum piece on to the spring, +as shown at <a href="#FIG_26">Fig. 26</a>, it is only needful to procure +a short length of No. 16 platinum wire, say ⅛ in., +then, having drilled a corresponding hole at the +desired spot in the contact spring, put the platinum wire +half way through the hole, and give it one or two sharp +blows on an anvil, with a smooth (pened) hammer.<!-- Page 77 --><span class="pagenum"><a name="Page_77" id="Page_77">[Pg 77]</a></span></p> + +<div class="figcenter" style="width: 400px;"> +<a name="FIG_28" id="FIG_28"></a> +<img src="images/i_087a1.png" width="400" height="400" alt="Fig. 28." title="Bell or gong" /> +<p class="caption">Fig. 28.</p> +</div> + +<hr /> + +<div class="figcenter" style="width: 385px;"> +<a name="FIG_29" id="FIG_29"></a> +<img src="images/i_087a2.png" width="385" height="400" alt="Fig. 29." title="Pillar and nuts" /> +<p class="caption">Fig. 29.</p> +</div> + +<p>This will at once rivet it in its place, and spread it +sufficiently to make a good surface for contact. The +screw must likewise be tipped with platinum, by having +a small hole bored in the centre of its extremity, of the +same diameter as the platinum wire, which must then +be pushed in, and rivetted by hammering the end, and +burring the sides of the screw. Whichever method be +adopted, care must be taken that the platinum tip on +the screw and the speck on the contact spring are +adjusted so as to touch exactly in their centres. It will +be hardly worth while for the amateur +to cast or even turn up his own bells +(which are generally of the class known +as clock gongs), as these can now be +procured so cheaply already nickelled +(<a href="#FIG_28">see Fig. 28</a>). The bell must be +adjusted on its pillar (<a href="#FIG_29">see Fig. 29<sup>A</sup></a>), +which is itself screwed into a hole in +the base-plate, where it is held by a +nut. The adjustment of the bell is effected by placing +it over the shoulder of the pillar, and then clenching it +down by screwing over it one or other of the nuts shown +at <a href="#FIG_29">Fig. 29</a>. The bell should clear the base, and should +be at such a height as to be struck on its edge by the +hammer or clapper attached to the armature, Figs. <a href="#FIG_23">23</a> +and <a href="#FIG_24">24</a>. We still need, to complete our bell, two +binding screws, which may take either of the forms shown +at <a href="#FIG_27">Fig. 27</a>; and an insulating washer, or collar, made +of ebonite or boxwood, soaked in melted paraffin, to +prevent the contact pillar (<a href="#FIG_25">Fig. 25</a>) making electrical<!-- Page 78 --><span class="pagenum"><a name="Page_78" id="Page_78">[Pg 78]</a></span> +contact with the metal base. The best shape to be given +to these washers is shown at <a href="#FIG_30">Fig. 30</a>. They consist in +two thin circlets of wood or ebonite, that will just not +meet when dropped, one on the one side, and one on the +other of the hole through which the shank of the contact +pillar passes when set up on the base-plate. If a wooden +base be used below the metal base-plate, +then only one washer, or collar, need be +used—that is, the one <i>above</i>—since the +screw of the pillar will pass into the wood, +and this is not a conductor. If the metal +base alone be used, both washers must be +employed, and a small nut (not so large as the washer) +used to tighten up and hold the pillar firm and immovable +in its place opposite the contact spring.</p> + +<div class="figcenter" style="width: 322px;"> +<a name="FIG_30" id="FIG_30"></a> +<img src="images/i_087b.png" width="322" height="247" alt="Fig. 30." title="Washers" /> +<p class="caption">Fig. 30.</p> +</div> + +<p>Having now all the parts at hand, we can proceed to +fit them together, which is done as follows:—The bell +pillar, with its bell attached, is fastened by its shank<!-- Page 79 --><span class="pagenum"><a name="Page_79" id="Page_79">[Pg 79]</a></span> +into the hole shown near <span class="smcap">B</span>, <a href="#FIG_17">Fig. 17</a>, where it is screwed +up tight by the square nut shown at <a href="#FIG_29">Fig. 29 <i>c</i></a>. In the +same manner, we must fasten the contact pillar, or bracket, +shown at <a href="#FIG_24">Fig. 24 <span class="smcap">A</span></a>. Whichever form be used, we must +take great care that it be insulated from metallic contact +with the metal base-plate by washers, as shown at +<a href="#FIG_30">Fig. 30</a> (similar washers must be used for the two binding +screws if the <i>whole</i> base-plate be made in metal). +This being done, the metal frame, <a href="#FIG_18">Fig. 18</a>, is put in +position on the wooden base, as shown at <a href="#FIG_17">Fig. 17</a>, and +screwed down thereto by the screws indicated at <i>s s s</i>. +The magnet may then be screwed down to the metal +frame as shown. The small bracket of angle brass +marked <span class="smcap">B</span>, in Figs. <a href="#FIG_23">23</a> and <a href="#FIG_24">24</a>, is next screwed into its +place; that is, in such a position that the armature stands +squarely facing the poles of the electro-magnet, but not +quite touching them (say 1/16 of an inch for a 2½ in. +bell). In setting up this and the contact pillar, the +greatest care must be taken that the platinum tip of the +contact screw, <a href="#FIG_25">Fig. 25</a>, should touch lightly the centre +of the platinum speck at the back of the spring, Figs. +<a href="#FIG_23">23</a> and <a href="#FIG_24">24</a>, shown full size at <a href="#FIG_26">Fig. 26</a>.</p> + +<p>The free ends of the helically coiled electro-magnet +wires should now be inserted into short lengths of small +indiarubber tubing (same as used for feeding bottles), the +extremities being drawn through and 1 in. of the copper +wire bared of its covering for the purpose of making +good metallic contact with the connections. One of these +ends is to be soldered, or otherwise metallically connected, +to the angle brass carrying the armature, spring<!-- Page 80 --><span class="pagenum"><a name="Page_80" id="Page_80">[Pg 80]</a></span> +and clapper, the other being similarly connected with +the left-hand binding-screw, shown at <a href="#FIG_17">Fig. 17</a>. Another +short length of wire (also enclosed in rubber tubing) +must be arranged to connect the contact screw pillar +<a href="#FIG_17">Fig. 17</a>, with the right-hand binding-screw. When +this has been done, we may proceed to test the working +of the bell by connecting up the binding screws with +the wires proceeding from a freshly-charged Leclanché +cell. If all have been properly done, and the connections +duly made, the armature should begin to vibrate +at once, causing the "bob," or hammer, to strike the +bell rapidly; that is, provided the platinum tipped screw +touches the platinum speck on the contact spring. +Should this not be the case, the screw must be turned +until the platinum tip touches the platinum speck. The +armature will now begin to vibrate. It may be that +the clapper runs too near the bell, so that it gives a +harsh, thuddy buzz instead of a clear, ringing sound; or, +possibly, the clapper is "set" too far from the bell to +strike it. In either case a little bending of the brass +wire carrying the clapper (either from or towards the +bell, as the case may dictate) will remedy the defect. +It is also possible that the armature itself may have +been set too near, or too far from the electro-magnet. +In the latter case, the clapper will not vibrate strongly +enough, in the former the vibration will be too short, +and the clapper may even stick to the poles of the +electros, especially if these have not been carefully annealed. +A little bending of the spring, to or from the +magnets, will remedy these deficiencies, unless the dis<!-- Page 81 --><span class="pagenum"><a name="Page_81" id="Page_81">[Pg 81]</a></span>tance +be very much too great, in which case the bending +of the spring would take the platinum tip out of the +centre of the platinum speck.</p> + +<div class="figright" style="width: 209px;"> +<a name="FIG_31" id="FIG_31"></a> +<img src="images/i_090.png" width="209" height="400" alt="Fig. 31." title="Trembling bell" /> +<p class="caption">Fig. 31.</p> +</div> + + +<p><a name="SEC_43" id="SEC_43"></a>§ 43. Having thus constructed an efficient electric bell +we may proceed to study its action and notice some of +the defects to which it may +be subject. In the first place, +if we connect up the bell with +the battery as shown in <a href="#FIG_17">Fig. 17</a>, +viz., the left-hand binding-screw +with the wire proceeding +from the carbon of the +Leclanché, and the right-hand +screw with the wire from the +zinc, then, if the platinum +tipped screw touches the +platinum speck, at the back +of the contact spring, a current +of electricity flows from the +left-hand binding-screw all +round the coils of the electro-magnets, +passes along the +contact spring and platinum +speck, thence to the platinum +tipped screw along the short +length of wire to the right-hand binding-screw, +whence it returns to the zinc element of the battery, +thus completing the circuit. The current, in thus +passing around the electro-magnet cores, converts +them, <i>pro tem.</i>, into a powerful magnet (see <a href="#SEC_13">§ 13</a>); con<!-- Page 82 --><span class="pagenum"><a name="Page_82" id="Page_82">[Pg 82]</a></span>sequently, +the armature, with its contact spring and +hammer, is pulled towards the electro-magnets and at +the same time gives a blow to the bell. Now, if instead +of having the platinum speck attached to a flexible +spring, it had been attached bodily to the rigid iron +armature, directly the electro-magnets felt the influence +of the current, the platinum speck would have also been +pulled out of contact with the platinum screw, therefore +the electro-magnet cores would have <i>immediately</i> lost +their magnetism (see <a href="#SEC_13">§ 13</a>, last five lines). This would +have been disadvantageous, for two reasons: 1st, because +the <i>stroke</i> of the hammer would have been very +short, and consequently the ring of the bell very weak; +and, 2nd, because, as even the softest iron requires +some appreciable time for the electric current to flow +round it to magnetise it to its full capacity, it would need +a much greater battery power to produce a given stroke, +if the contact were so very short. The use of an elastic +contact spring is, therefore, just to lengthen the time of +contact. But the electro-magnets, even when the flexible +spring is used, do actually pull the platinum speck +out of contact with the platinum screw. When this +takes place, the circuit is broken, and no more current +can flow round the electro-magnets, the spring reasserts +its power, and the contact is again made between the +contact screw and contact spring, to be again rapidly +broken, each break and make contact being accompanied +by a correspondingly rapid vibration of the armature, +with its attendant clapper, which thus sets up that +characteristic rapid ringing which has earned for these<!-- Page 83 --><span class="pagenum"><a name="Page_83" id="Page_83">[Pg 83]</a></span> +bells the name of trembling, chattering, or vibrating +bells.</p> + + +<p><a name="SEC_44" id="SEC_44"></a>§ 44. From a careful consideration of the last two +sections it will be evident that the possible defects of +electric bells may be classed under four heads: viz., 1st, +Bad contacts; 2nd, Bad adjustment of the parts; 3rd, +Defective insulation; 4th, Warpage or shrinkage of +base. We will consider these in the above order. +Firstly, then, as to bad contacts. Many operators are +content with simply turning the terminal wires round +the base of the binding-screws. Unless the binding-screws +are firmly held down on to the wires by means +of a back nut, a great loss is sure to occur at these +points, as the wires may have been put on with sweaty +hands, when a film of oxide soon forms, which greatly +lowers the conductivity of the junction. Again, at the +junction points of the wires with the contact angle brass +and contact pillar, some workmen solder the junctions, +using "killed spirits" as a flux. A soldered contact is +certainly the best, electrically speaking, but "killed +spirits," or chloride of zinc, should never be used as a +flux in any apparatus or at any point that cannot be +washed in abundance of water, as chloride of zinc is very +<i>deliquescent</i> (runs to water), rottens the wire, and spoils +the insulation of the adjacent parts. If solder be used +at any parts, let <i>resin</i> be used as a flux. Even if any +excess of resin remain on the work, it does no harm +and does not destroy the insulation of any of the other +portions. Another point where bad contact may arise +is at the platinum contacts. Platinum is a metal which<!-- Page 84 --><span class="pagenum"><a name="Page_84" id="Page_84">[Pg 84]</a></span> +does not rust easily, even under the influence of the +electric spark given at the point of contact. Therefore, +it is preferred to every other metal (except, perhaps, +iridium) for contact breakers. Platinum is an expensive +metal, the retail price being about 30s. an ounce, and as +it is nearly twice as heavy as lead (Lead 11. Platinum +21·5) very little goes to an ounce. For cheap bells, +therefore, there is a great temptation to use some other +white metal, such as silver, german silver, platinoid, etc.</p> + +<p>The tip of the platinum screw may be tested for its +being veritably platinum in the following mode: Touch +the tip with the stopper of a bottle containing aquafortis, +so as to leave a tiny drop on the extreme point of the +suspected platinum. If it boils up green, or turns black, +it is <i>not</i> platinum; if it remains unaltered, it may be +silver or platinum. After it has stood on the tip for a +minute, draw it along a piece of white paper, so as to +produce a streak of the acid. Expose the paper for a +few minutes to sunlight. If the streak turns violet or +pinky violet, the metal is <i>silver</i>; if the paper simply shows +a slightly yellowish streak, the metal is platinum. The +tip of the platinum screw must be carefully dried and +cleaned after this trial before being replaced.</p> + +<p>Secondly, as to bad adjustment. It is evident that +the magnets and the armature must stand at a certain +distance apart to give the best effects with a given +battery power. The distance varies from 1/24 in. in the very +smallest, to ⅛ in. in large bells. Sometimes (but only in +very badly made instruments) the armature adheres to +the poles of the electro-magnet. This is due to <i>residual</i><!-- Page 85 --><span class="pagenum"><a name="Page_85" id="Page_85">[Pg 85]</a></span> +<i>magnetism</i> (see <a href="#SEC_14">§ 14</a>), and points to hard or unannealed +iron in the cores or armature. As a make-shift, this +defect may be partially remedied by pasting a thin piece +of paper over that surface of the armature which faces +the poles of the electro-magnets. Another bad adjustment +is when the platinum screw does not touch fairly +on the centre of the platinum speck, but touches the +spring or the solder. Rust is then sure to form, which +destroys the goodness of the contact. To adjust the +contact spring at the right distance from the platinum +screw, hold the hammer against the bell or gong. The +armature should now <i>just not touch</i> the poles of the +electro-magnet. Now screw up the platinum screw +until it <i>clears</i> the contact spring by about the thickness +of a sheet of brown paper (say 1/50 of an inch). Let the +hammer go, and notice whether the contact spring makes +good contact with the platinum screw. This may be +tried by the Leclanché cell as well, so as to make sure +of the character of the <i>ringing</i>. When this has been +satisfactorily adjusted the back-nut or set screw may be +tightened, to insure that the vibration of the hammer +shall not alter the adjustment. It sometimes happens +that the spring that bears the armature is itself either +too strong (or set back too far) or too weak. In the +former case, the electro-magnet cannot pull the armature +with sufficient force to give a good blow; in the latter, +the spring cannot return the armature, with its attendant +contact spring, back to its place against the platinum +screw. To ascertain which of these two defects obtains, +it is only necessary, while the bell is in action, to press<!-- Page 86 --><span class="pagenum"><a name="Page_86" id="Page_86">[Pg 86]</a></span> +the spring lightly with a bit of wire, first <i>towards</i> and +then <i>away</i> from the electro-magnets. If the ringing is +improved in the first case, the spring is too strong; if +improvement takes place in the latter case, the spring +is too weak. The third source of inefficient action, +defective insulation, is not likely to occur in a newly-made +bell, except by gross carelessness. Still, it may +be well to point out where electrical leakage is likely to +occur, and how its presence may be ascertained, localized, +and remedied. If the wire used to wind the electro-magnet +be old, badly covered, or bared in several places +in winding, it probably will allow the current to "short +circuit," instead of traversing the whole length of the +coils. If this be the case, the magnet will be very weak: +the magnet of a 2½-in. bell should be able to sustain +easily a 1 lb. weight attached by a piece of string to a +smooth piece of ½-in. square iron placed across its poles, +when energized by a single pint Leclanché cell. If it +will not do this, the insulation may be suspected. If +the wire has been wound on the bare cores (without +bobbins), as is sometimes done, bared places in the wire +may be touching the iron. This may be ascertained +by connecting one pole of a bottle bichromate, or other +powerful battery, with one of the wires of the electro-magnet +coils, and drawing the other pole of the battery +across the clean iron faces of the electro-magnet poles. +If there is any leakage, sparks will appear on making +and breaking contact. Nothing but unwinding and +rewinding with a well covered wire can remedy these +defects. The other points where the insulation may<!-- Page 87 --><span class="pagenum"><a name="Page_87" id="Page_87">[Pg 87]</a></span> +be defective are between the binding screws and the +base, if this be all of metal; or between the contact +spring block and the base, and the contact pillar. It is also +probable (if the connecting wires have not been covered +with indiarubber tubing, as recommended) that leakage +may be taking place between these wires and some +portion of the metal work of the base or frame. This +must be carefully examined, and if any point of contact +be observed, a little piece of Prout's elastic glue, +previously heated, must be inserted at the suspected +places. With regard to the binding screws, if they +stand on the wooden base, their insulation (unless the +base be very damp indeed) will be sufficiently good; +but if the base is entirely metallic, then ebonite or +boxwood washers must be used to insulate them from +contact with the base-plate. With regard to the contact +spring block and the platinum screw pillar, it is <i>permissible</i> +that one or the other should not be insulated +from the base or frame; but one or the other <i>must</i> be +insulated by means of ebonite or other insulating washers. +Personally, I prefer to insulate both; but in many really +good bells only the platinum screw pillar is thus insulated. +Any such leakage can be immediately detected +by holding one pole of a powerful battery against the +suspected binding-screw, or block, or pillar, and while +in this position, drawing the other pole across some bare +iron portion of the frame or metal base. Sparks will +appear if there is any leakage.</p> + +<div class="figright" style="width: 192px;"> +<a name="FIG_32" id="FIG_32"></a> +<img src="images/i_097.png" width="192" height="400" alt="Fig. 32." title="Bell action enclosed in case" /> +<p class="caption">Fig. 32.</p> +</div> + +<p>The fourth defect—that is, warpage or shrinkage of the +base—can only occur in badly-made bells, in which the<!-- Page 88 --><span class="pagenum"><a name="Page_88" id="Page_88">[Pg 88]</a></span> +entire base is of wood. A cursory examination will +show whether the board is warped or swollen, or whether +it has shrunk. Warping or swelling will throw the +electro-magnet too far from the armature, or "set" the +pillar out of place; shrinkage, on the contrary, will bring +the parts too close together and jamb the magnets, the +armature, and the contact pillar into an unworkable +position.</p> + + +<p><a name="SEC_45" id="SEC_45"></a>§ 45. Before quitting the subject of the defects of +bells, it may not be out of place to mention that no bell +that is set to do real work should be fitted up without a +cover or case. The dust which is sure to accumulate, +not to speak of damp and fumes, etc., will certainly +militate against good contacts and good action if this +important point be neglected. The cover or case +generally takes the form of a shallow box, as shown +at <a href="#FIG_32">Fig. 32</a>, and may be made from ¼-in. teak, mahogany, +or walnut, dovetailed together and well +polished. It is fastened to the base in +the same manner as the sides of a +Dutch clock, by means of studs, hooks +and eyes. At the bottom of the box +is cut a slot, of sufficient width and +length to admit the play of the hammer +shank.</p> + +<p>In the annexed table is given a +general idea of the proportion which +should be observed in the construction of +bells of different sizes. It must be noted +that if the bells are to be used at long distances from the<!-- Page 89 --><span class="pagenum"><a name="Page_89" id="Page_89">[Pg 89]</a></span> +battery, rather more of a finer gauge of wire must be +employed to wind the magnets than that herein recommended, +unless, indeed, <i>relays</i> be used in conjunction +with the bells.</p> + + +<p><a name="SEC_46" id="SEC_46"></a>§ 46.—</p> + +<p class="center"><span class="smcap">Table</span></p> + +<p class="center">Showing proportions to be observed in the different +parts of electric bells.</p> + +<div class="center"> +<table border="0" cellpadding="4" cellspacing="0" summary=""> +<tr><th align="left">Diameter of Bell.</th><th align="left">Length of Magnet Cores.</th><th align="left">Diameter of Magnet Cores.</th><th align="left">Length of Bobbin.</th><th align="left">Diameter of Bobbin Head.</th><th align="center">B. W. G. of Wire on Bobbin.</th></tr> +<tr><td align="left" class="in1">2½''</td><td align="left">2''</td><td align="left" class="in1">5/16''</td><td align="left">1¾''</td><td align="left" class="in1">¾''</td><td align="center">24</td></tr> +<tr><td align="left" class="in1">3</td><td align="left">2¼</td><td align="left" class="in1">⅜</td><td align="left">2</td><td align="left" class="in1">⅞</td><td align="center">24</td></tr> +<tr><td align="left" class="in1">3½</td><td align="left">2½</td><td align="left" class="in1">7/16</td><td align="left">2¼</td><td align="left">1</td><td align="center">22</td></tr> +<tr><td align="left" class="in1">4</td><td align="left">2¾</td><td align="left" class="in1">½</td><td align="left">2½</td><td align="left">1⅛</td><td align="center">22</td></tr> +<tr><td align="left" class="in1">4½</td><td align="left">3</td><td align="left" class="in1">9/16</td><td align="left">2¾</td><td align="left">1¼</td><td align="center">20</td></tr> +<tr><td align="left" class="in1">5</td><td align="left">3¼</td><td align="left" class="in1">⅝</td><td align="left">3</td><td align="left">1⅜</td><td align="center">18</td></tr> +<tr><td align="left" class="in1">5½</td><td align="left">3½</td><td align="left" class="in1">11/16</td><td align="left">3¼</td><td align="left">1½</td><td align="center">16</td></tr> +<tr><td align="left" class="in1">6</td><td align="left">3¾</td><td align="left" class="in1">¾</td><td align="left">3½</td><td align="left">1⅝</td><td align="center">16</td></tr> +<tr><td align="left" class="in1">6½</td><td align="left">4</td><td align="left" class="in1">13/16</td><td align="left">3¾</td><td align="left">1¾</td><td align="center">16</td></tr> +<tr><td align="left" class="in1">7</td><td align="left">4¼</td><td align="left" class="in1">⅞</td><td align="left">4</td><td align="left">1⅞</td><td align="center">16</td></tr> +<tr><td align="left" class="in1">7½</td><td align="left">4½</td><td align="left" class="in1">15/16</td><td align="left">4¼</td><td align="left">2</td><td align="center">14</td></tr> +<tr><td align="left" class="in1">8</td><td align="left">4¾</td><td align="left">1</td><td align="left">4½</td><td align="left">2⅛</td><td align="center">14</td></tr> +<tr><td align="left" class="in1">8½</td><td align="left">5</td><td align="left">1-1/16</td><td align="left">4¾</td><td align="left">2¼</td><td align="center">14</td></tr> +<tr><td align="left" class="in1">9</td><td align="left">5¼</td><td align="left">1⅛</td><td align="left">5</td><td align="left">2⅜</td><td align="center">14</td></tr> +<tr><td align="left" class="in1">9½</td><td align="left">5½</td><td align="left">1-3/16</td><td align="left">5¼</td><td align="left">2½</td><td align="center">14</td></tr> +<tr><td align="left">10</td><td align="left">5¾</td><td align="left">1¼</td><td align="left">5½</td><td align="left">2⅝</td><td align="center">14</td></tr> +<tr><td align="left">10½</td><td align="left">6</td><td align="left">1-5/16</td><td align="left">5¾</td><td align="left">2¾</td><td align="center">12</td></tr> +<tr><td align="left">11</td><td align="left">6¼</td><td align="left">1⅜</td><td align="left">6</td><td align="left">2⅞</td><td align="center">12</td></tr> +<tr><td align="left">11½</td><td align="left">6½</td><td align="left">1-7/16</td><td align="left">6¼</td><td align="left">3</td><td align="center">10</td></tr> +<tr><td align="left">12</td><td align="left">6¾</td><td align="left">1½</td><td align="left">6½</td><td align="left">3⅛</td><td align="center">10</td></tr> +</table></div> + +<hr /> + +<p><!-- Page 90 --><span class="pagenum"><a name="Page_90" id="Page_90">[Pg 90]</a></span></p> + +<div class="figright" style="width: 339px;"> +<a name="FIG_33A" id="FIG_33A"></a> +<img src="images/i_099a.png" width="339" height="400" alt="Fig. 33 A." title="Ordinary trembling bell (A)" /> +<p class="caption">Fig. 33 A.</p> +</div> + + +<p><a name="SEC_47" id="SEC_47"></a>§ 47. We can now glance at several modifications in +the shape and mode of action of electric bells and their +congeners. Taking Figs. <a href="#FIG_33A">33 <span class="smcap">A</span></a> and <a href="#FIG_33B"><span class="smcap">B</span></a> as our typical +forms of trembling bell, the first notable modification +is one by means of which the bell is made to give a +single stroke only, for each contact with the battery. +This form, which is known as the "single stroke bell," +lends itself to those cases in which it may be required +to transmit preconcerted signals; as also where it is +desired to place many bells in one circuit. <a href="#FIG_34">Fig. 34</a> +illustrates the construction of the single stroke bell. +It differs from the trembling bell in the mode in which +the electro-magnet is connected up to the binding +screws. In the trembling bell, <a href="#FIG_33A">Fig. 33</a>, the circuit is +completed through the platinum screw pillar, to the +binding screw marked <span class="smcap">Z</span>, hence the circuit is rapidly made<!-- Page 91 --><span class="pagenum"><a name="Page_91" id="Page_91">[Pg 91]</a></span> +and broken as long as by any means contact is made +with the battery, and the binding screws <span class="smcap">L</span> and <span class="smcap">Z</span>. But +in the single stroke bell, <a href="#FIG_34">Fig. 34</a>, the wires from the +electro-magnet are connected directly to the two binding +screws <span class="smcap">L</span> and <span class="smcap">Z</span>, so that when contact is made with +the battery, the armature is drawn to the poles of the +electro-magnet, and kept there +so long as the battery current +passes. By this means, only +one stroke or blow is given to +the bell for each contact of the +battery. Of course, directly +the connection with the battery +is broken, the spring which +carries the armature and clapper +flies back ready to be +again attracted, should connection +again be made with +the battery. To regulate the +distance of the armature from +the poles of the electro-magnets, +a set screw <span class="smcap">Q</span> takes +the place of the platinum screw +in the ordinary form, while to +prevent the hammer remaining in contact with the bell +(which would produce a dull thud and stop the clear +ring of the bell), a stop (<i>g</i>) is set near the end of the +armature, or two studs are fixed on the tips of the poles +of the electro-magnets. The mode of adjusting this +kind of bell, so as to obtain the best effect, differs a<!-- Page 92 --><span class="pagenum"><a name="Page_92" id="Page_92">[Pg 92]</a></span> +little from that employed in the case of the trembling +bell. The armature must be pressed towards the poles +of the electro-magnets, until it rests against the stop +or studs. A piece of wood or cork may be placed +between the armature and the set screw <span class="smcap">Q</span>, to retain +the armature in this position, while the rod carrying the +hammer or clapper is being bent (if required) until +the hammer just clears the bell. If it touches the bell, +a thud instead of a ring is the result; if it is set off too +far, the ring will be too weak. The armature can now +be released, by removing the wood or cork, and the set +screw <span class="smcap">Q</span> driven forwards or backwards until the best +effect is produced when tested with the battery. The +tension of the armature spring must be carefully looked +to in these single stroke bells. If it is too strong, the +blow will be weak; if too weak, the hammer trembles, +so that a clear single stroke is not obtainable, as the +spring <i>chatters</i>.</p> + +<div class="figcenter" style="width: 284px;"> +<a name="FIG_33B" id="FIG_33B"></a> +<img src="images/i_099b.png" width="284" height="400" alt="Fig. 34." title="Ordinary trembling bell (B)" /> +<p class="caption">Fig. 33 B.</p> +</div> + +<hr /> + +<div class="figcenter" style="width: 209px;"> +<a name="FIG_34" id="FIG_34"></a> +<img src="images/i_100.png" width="209" height="400" alt="Fig. 34." title="Single stroke bell" /> +<p class="caption">Fig. 34.</p> +</div> + + +<p><a name="SEC_48" id="SEC_48"></a>§ 48. <i>The continuous ringing bell</i> is the modification +which next demands our attention. In this, the ringing +action, when once started by the push,<a name="FNanchor_12_12" id="FNanchor_12_12"></a><a href="#Footnote_12_12" class="fnanchor">[12]</a> or other contact +maker, having been touched, continues either until the +battery is exhausted, or until it is stopped by the +person in charge. The great use of this arrangement<!-- Page 93 --><span class="pagenum"><a name="Page_93" id="Page_93">[Pg 93]</a></span> +is self-evident in cases of burglar alarms, watchman's +alarms, etc., as the continuous ringing gives notice that +the "call" has not received attention. The continuous +ringing bell differs but little from the ordinary trembling +bell. The chief difference lies in the addition of an +automatic device whereby contact is kept up with the +battery, even after the "push" contact has ceased. As +it is desirable for the person in charge to be able to +stop the ringing at will, without proceeding to the place +where the "push" stands, so it is not usual to make +the continuous ringing arrangement dependent on the +"push," though, of course, this could be done, by +causing it to engage in a catch, which would keep up +the contact, when once made. Continuous ringing bells +may be conveniently divided into two classes; viz., +1st, those in which a device is attached to the framework +of the bell; which device, when once upset by the +first stroke of the bell, places the bell in direct communication +with the battery independent of the "push" +or usual contact; and 2ndly, those in which a separate +device is used, for the same purpose. This latter +arrangement admits of the use of an ordinary trembling +bell.</p> + +<div class="figcenter" style="width: 230px;"> +<a name="FIG_35" id="FIG_35"></a> +<img src="images/i_103.png" width="230" height="400" alt="Fig. 35." title="Continuous ringing bell" /> +<p class="caption">Fig. 35.</p> +</div> + +<hr /> + +<div class="figcenter" style="width: 328px;"> +<a name="FIG_36" id="FIG_36"></a> +<img src="images/i_104.png" width="328" height="400" alt="Fig. 36." title="Release action" /> +<p class="caption">Fig. 36.</p> +</div> + +<p><a href="#FIG_35">Fig. 35</a> illustrates the action of bells of the first +class. In the first place it will be noticed that there +are three binding screws instead of two, as in the +ordinary pattern, one marked <span class="smcap">C</span> connected as usual +with the carbon element of the battery; another +marked <span class="smcap">L</span>, which connects with line wire, and a third, +<span class="smcap">Z</span>, connected by means of a branch wire (shunt wire),<!-- Page 94 --><span class="pagenum"><a name="Page_94" id="Page_94">[Pg 94]</a></span> +proceeding from the zinc of the battery. It will be +seen, that if the battery current is by means of the +push caused to flow through the coils of the electro-magnets, +the armature is attracted as usual by them, +and in moving towards them, releases and lets fall the +lever contact, which, resting on the contact screw, +completes the circuit between <span class="smcap">Z</span> and <span class="smcap">C</span>, so that the +bell is in direct communication with its battery, +independently of the push. Hence the bell continues +ringing, until the lever is replaced. This can be<!-- Page 95 --><span class="pagenum"><a name="Page_95" id="Page_95">[Pg 95]</a></span> +done, either by pulling a check string (like a bell-pull) +attached to an eye in the lever, or by means of a +press-button and counter-spring; as shown in <a href="#FIG_36">Fig. 36</a>, +<span class="smcap">A</span> and <span class="smcap">B</span>.</p> + +<div class="figright" style="width: 170px;"> +<a name="FIG_37" id="FIG_37"></a> +<img src="images/i_105.png" width="170" height="400" alt="Fig. 37." title="Continuous ringing with relay" /> +<p class="caption">Fig. 37.</p> +</div> + +<p>In continuous ringing bells of the second class, a +detent similar to that shown at <a href="#FIG_35">Fig. 35</a> <span class="smcap">D</span> is used, but +this, instead of being actuated by the electro-magnet +belonging to the bell itself, is controlled by a separate +and entirely independent electro-magnet, which, as it +may be wound with many coils of fine wire, and have +a specially light spring for the armature, can be made +very sensitive. This second electro-magnet, which<!-- Page 96 --><span class="pagenum"><a name="Page_96" id="Page_96">[Pg 96]</a></span> +serves only to make contact with a battery, is known +as a <i>Relay</i>, and is extensively employed in many cases +where it is desired to put one or more batteries into, +or out of circuit, from a distance. The relay may be +looked upon as an automatic hand, which can be made +to repeat at a distant point contacts made or broken +by hand at a nearer one. <a href="#FIG_37">Fig. 37</a> shows this arrange<!-- Page 97 --><span class="pagenum"><a name="Page_97" id="Page_97">[Pg 97]</a></span>ment, +attached to the same base board as the bell itself. +On contact being made with the push, the current +enters at <span class="smcap">C</span>, circulates round the cores of the relay, thus +converting it into a magnet. The armature <i>a</i> is thereby +pulled to the magnet, and in so doing releases the detent +lever, which falls on the contact screw, thus at one +and the same time breaking the circuit through the +relay, and making the circuit through the bell magnets +<span class="smcap">B B´</span>, back to the battery by <span class="smcap">Z</span>. A second modification +of this mode of causing an ordinary bell to ring continuously +is shown at <a href="#FIG_38">Fig. 38</a>, the peculiar form of<!-- Page 98 --><span class="pagenum"><a name="Page_98" id="Page_98">[Pg 98]</a></span> +relay used therewith being illustrated at <a href="#FIG_39">Fig. 39</a>. +Here, the relay is placed on a separate base board of +its own, and could, if necessary, be thrown out of +circuit altogether, by means of a <i>switch</i>,<a name="FNanchor_13_13" id="FNanchor_13_13"></a><a href="#Footnote_13_13" class="fnanchor">[13]</a> so that the +bell can be used as an ordinary bell or continuous +action at will. It will be noticed that the relay has +in this sketch only one core. But the delicacy of the +action is not impaired thereby, as the armature, by +means of the steel spring <i>s</i>, is made to form part and +parcel of the magnet, so that it becomes magnetised +as well as the core, and is attracted with more force +than it would be, if it were magnetically insulated. +The battery current enters by the wires <span class="smcap">C</span> and <span class="smcap">W</span>, passes +round the coils of the electro-magnet, and returns by <span class="smcap">Z</span>. +In so doing it energises the electro-magnet <span class="smcap">E</span>, which +immediately attracts its armature <span class="smcap">A</span>. The forward +movement of the armature <span class="smcap">A</span>, releases the pivoted +arm <span class="smcap">L</span>, to which is attached a platinum-tipped contact +prong <span class="smcap">P</span>. This, it will be noticed, is in metallic connection +with the pillar <span class="smcap">P'</span>, and with the base, and, +therefore, through the wire <span class="smcap">W</span>, with the battery. When +the arm <span class="smcap">L</span> falls, the contact prong completes the circuit +to the bell, through the insulated pillar <span class="smcap">X</span>. The relay +is thus thrown out of the circuit at the same time +that the bell is thrown in. A device similar to those +illustrated at <a href="#FIG_36">Fig. 36</a> can be employed to reset the +arm <span class="smcap">L</span>.</p> + +<div class="figcenter" style="width: 400px;"> +<a name="FIG_38" id="FIG_38"></a> +<img src="images/i_106a.png" width="400" height="146" alt="Fig. 38." title="Continuous ringing action with indicator" /> +<p class="caption">Fig. 38.</p> +</div> + +<hr /> + +<div class="figcenter" style="width: 400px;"> +<a name="FIG_39" id="FIG_39"></a> +<img src="images/i_106b.png" width="400" height="226" alt="Fig. 39." title="Relay and detent lever for indicator" /> +<p class="caption">Fig. 39.</p> +</div> + +<hr /> + +<div class="figcenter" style="width: 600px;"> +<a name="FIG_40" id="FIG_40"></a> +<img src="images/i_108.png" width="600" height="214" alt="Fig. 40." title="Callow's attachment" /> +<p class="caption">Fig. 40.</p> +</div> + +<p>A rather more complicated arrangement for continuous +bell ringing is shown at <a href="#FIG_40">Fig. 40</a>. It is known<!-- Page 99 --><span class="pagenum"><a name="Page_99" id="Page_99">[Pg 99]</a></span> +as Callow's, and is peculiarly adapted to ringing several +bells from one attachment, etc. Owing to the relay +in this form being wound with two sets of wires, it +takes a little more battery power; but this disadvantage +is compensated by its many good points. +The following description, taken from F. C. Allsop's +papers in the <i>English Mechanic</i>, will render the working +of Callow's attachment perfectly clear. "When the +button of the push <span class="smcap">P</span> is pressed, the current in +the main circuit flows from the positive pole <span class="smcap">C</span> of the +battery <span class="smcap">D</span> through the relay coil <i>a</i>, and thence by +the wire <i>d</i> and push <span class="smcap">P</span>, to the zinc of the battery. +This attracts the armature <span class="smcap">A</span> of the relay <span class="smcap">R</span>, closing the +local bell circuit, the current flowing from <span class="smcap">C</span> of the +battery to armature <span class="smcap">A</span> of the relay <span class="smcap">R</span>, through contact +post <i>p</i>, terminal <span class="smcap">L</span> of the bell, through bell to terminal +<span class="smcap">Z</span>, and thence by the wire <i>g</i> to the zinc of the battery. +Part of the current also flows along the wire from the +bell terminal <span class="smcap">L</span> through the relay coil <i>b</i> and switch <span class="smcap">W</span>, +to terminal <span class="smcap">Z</span> of the bell, thus keeping the armature<!-- Page 100 --><span class="pagenum"><a name="Page_100" id="Page_100">[Pg 100]</a></span> +of the relay down, after the main circuit (through the +push) has been broken; the bell continuing to ring +until the shunt circuit is broken by moving the arm +of the switch <span class="smcap">W</span> over to the opposite (or non-contact) +side. The bell can also be stopped by short circuiting +the relay, which can be effected by an ordinary push. +It will be seen that more than one bell can be rung +from the same attachment, and the bell can, by moving +the arm of the switch <span class="smcap">W</span>, be made continuous ringing +or not, at will. If the arm of the switch is moved +over to the opposite side to which it is shown in the +figure, the shunt circuit of the bell through the relay +is broken, and the bell will ring only so long as the +button of the push is kept in. This continuous arrangement +is very convenient for front doors, etc., where +trouble is experienced in securing immediate attention +to the summons. Instead of being taken to the switch, +as in <a href="#FIG_40">Fig. 40</a>, the two wires are taken to a contact piece +fixed on the side of the door frame, and so arranged +that when the door is opened, it either short circuits +or breaks the shunt circuit: thus when the push is +pressed, the bell rings until the door is opened, the +continual ringing of the bell insuring prompt attention."</p> + +<div class="figright" style="width: 220px;"> +<a name="FIG_40A" id="FIG_40A"></a> +<img src="images/i_110.png" width="220" height="400" alt="Fig. 40 A." title="Thorpe's arrangement" /> +<p class="caption">Fig. 40 A.</p> +</div> + +<p>Mr. H. Thorpe, of 59, Theobald's Road, London, has +devised a very ingenious arrangement for the continuous +ringing of one or more bells for a stated period of +time. This is shown at <a href="#FIG_40A">Fig. 40 <span class="smcap">A</span></a>. It is set in action +by pulling the ring outside the bottom of the core. +The bell or bells then start ringing, as contact is<!-- Page 101 --><span class="pagenum"><a name="Page_101" id="Page_101">[Pg 101]</a></span> +established and kept up. The novelty lies in the fact +that the duration of the contact, and consequently of +the ringing, can be accurately timed from 5 seconds +to 30 seconds, by merely inserting a pin at different +holes in the rod, as shown. After +the bells have rung the required +time the instrument automatically +resets itself.</p> + + +<p><a name="SEC_49" id="SEC_49"></a>§ 49. The modifications we are +now about to consider, differ from +the ordinary bell, either in the +shape or material of the bell +itself, the relative disposition of +the parts, or some structural +detail; but not upon the introduction +of any new principle. +The most striking is certainly the +Jensen bell, which is shown in +section at <a href="#FIG_41">Fig. 41</a>.</p> + +<hr /> + +<div class="figcenter" style="width: 332px;"> +<a name="FIG_41" id="FIG_41"></a> +<img src="images/i_111.png" width="332" height="400" alt="Fig. 41." title="Jensen bell, section" /> +<p class="caption">Fig. 41.</p> +</div> + +<p>According to Mr. Jensen's system of electric bells, +the bell may take any desired form, that of the ordinary +church bell being preferred, and the electro-magnetic +apparatus is placed entirely inside the bell itself. To +attain this end the electro-magnetic apparatus must +be compact in form. A single electro-magnet has pole +pieces at each end opposite to which an armature is +suspended from a pivot and balanced by the hammer +of the bell. At the back of the armature there may be +a make and break arrangement, whereby a continuous +succession of strokes is effected, or this may be omitted,<!-- Page 102 --><span class="pagenum"><a name="Page_102" id="Page_102">[Pg 102]</a></span> +in which case a single stroke is given when the contact +with the battery is made, or both may be effected by +separate wires, make contact with one wire, and a single +stroke is struck; make it with the other and the current +passes through the make and break and a succession +of strokes is heard. When the contact-breaker is used, +it is so arranged that a slight rub is caused at every +stroke, so keeping the contact clean. The flexible +break, with the ingenious wiping contact, is a great +improvement over the ordinary screw, which often +becomes disarranged.</p> + +<p>The form of the magnet is such that a considerable<!-- Page 103 --><span class="pagenum"><a name="Page_103" id="Page_103">[Pg 103]</a></span> +degree of magnetic force is caused by a comparatively +small battery power. The electro-magnetic apparatus +being within the bell the latter forms a very effective +and handsome shield for the former. Not only can the +bell shield the electro-magnet from wet but the whole +of the conducting wires as well.</p> + +<p>The bell may be screwed to a tube through which +passes the conducting wire, which makes contact with +an insulated metallic piece in the centre of the top +of the bell. Both the wire and the contact piece are as +completely shielded from the weather as if within the +bell itself.</p> + +<div class="figcenter" style="width: 327px;"> +<a name="FIG_42" id="FIG_42"></a> +<img src="images/i_113.png" width="327" height="400" alt="Fig. 42." title="Jensen bell, exterior" /> +<p class="caption">Fig. 42.</p> +</div> + +<p>The great point of departure is the discarding of +the unsightly magnet box, and the hemispherical bell +(<i>see</i> <a href="#FIG_32">Fig. 32</a>), and substituting a bell of the Church +type (see <a href="#FIG_42">Fig. 42</a>), and placing inside it an electro-magnet +specially arranged. The inventors use a single +solenoidal magnet of a peculiar construction, by which +the armature is attracted by both poles simultaneously. +By this means less than half the usual quantity of wire +is required, thus reducing the external resistance of the +circuit one half. Moreover the armature, besides being +magnetised by induction, as acted on in the ordinary +method of making electric bells, is by Messrs. Jensen's +plan directly polarised by being in actual magnetic +contact by the connection of the gimbal (which is one +piece with the armature) with the core iron of their +magnet. It is thus induced to perform the largest +amount of work with the smallest electro-motive force. +Instead of the armature and clapper being in a<!-- Page 105 --><span class="pagenum"><a name="Page_105" id="Page_105">[Pg 105]</a></span><!-- Page 104 --><span class="pagenum"><a name="Page_104" id="Page_104">[Pg 104]</a></span> +straight line attached to a rigid spring, which necessitates +a considerable attractive power to primarily give it +momentum, in the Jensen Bell the armature and +hammer are in the form of an inverted U, and being +perfectly balanced from the point of suspension, the +lines of force from a comparatively small magnetic +field suffice to set this improved form of armature into +instant regular vibration. By using a flexible break +and make arrangement instead of the usual armature +spring and set screw (at best of most uncertain action), +it is found that a much better result is attained, and +by this device the armature can be set much nearer +the poles of the magnet with sufficient traverse of the +hammer. This is in strict accordance with the law +of inverse squares, which holds that the force exerted +between two magnetic poles is inversely proportionate +to the square of the distance between them, or, in other +words, that magnets increase proportionately in their +power of attraction as they decrease in the square of +the distance. It will now be seen why these bells +require so little battery power to ring them: firstly, +the armature and hammer are so perfectly balanced +as to offer but little resistance; secondly, the external +resistance to the current is reduced; and thirdly, the +best possible use is made of the electro-magnetic force +at disposal.</p> + + +<p><a name="SEC_50" id="SEC_50"></a>§ 50. The next modification which demands attention +is the so-called "Circular bell." This differs from the +ordinary form only in having the action entirely covered +by the dome. Except, perhaps, in point of appearance,<!-- Page 106 --><span class="pagenum"><a name="Page_106" id="Page_106">[Pg 106]</a></span> +this presents no advantages to that. The bells known +as "Mining bells" resemble somewhat in outward appearance +the circular bell; but in these mining bells the +action is all enclosed in strong, square teak cases, to protect +the movement, as far as possible, from the effects of +the damp. All the parts are, for the same reason, made +very large and strong; the armature is pivoted instead +of being supported on a spring, the hammer shank +being long, and furnished with a heavy bob. The +domes or bells are from 6 inches to 12 inches in diameter, +and are generally fitted with <i>single stroke</i> +movement, so as to enable them to be used for signalling. +The hammer shank, with its bob, and the +dome, which stands in the centre of the case, are the +only parts left uncovered, as may be seen on reference +to Figs. <a href="#FIG_43A">43 <span class="smcap">A</span></a> and <a href="#FIG_43B"><span class="smcap">B</span></a>, where the exterior and interior of +such a bell are shown.</p> + +<div class="figcenter" style="width: 400px;"> +<a name="FIG_43A" id="FIG_43A"></a> +<img src="images/i_115a.png" width="400" height="299" alt="Fig. 43 A." title="Circular bell" /> +<p class="caption">Fig. 43 A.</p> +</div> + +<hr /> + +<div class="figcenter" style="width: 400px;"> +<a name="FIG_43B" id="FIG_43B"></a> +<img src="images/i_115b.png" width="400" height="345" alt="Fig. 43 B." title="Mining bell" /> +<p class="caption">Fig. 43 B.</p> +</div> + +<hr /> + +<div class="figcenter" style="width: 400px;"> +<a name="FIG_44" id="FIG_44"></a> +<img src="images/i_116.png" width="400" height="362" alt="Fig. 44." title="Electric trumpet (Binswanger's)" /> +<p class="caption">Fig. 44.</p> +</div> + + +<p><a name="SEC_51" id="SEC_51"></a>§ 51. In the "Electric Trumpet," introduced by +Messrs. Binswanger, of the General Electric Company, +we have a very novel and effective arrangement of<!-- Page 107 --><span class="pagenum"><a name="Page_107" id="Page_107">[Pg 107]</a></span> +the parts of an electric bell and telephone together. +This instrument, along with its battery, line and push, +is illustrated at <a href="#FIG_44">Fig. 44</a>, where <span class="smcap">A</span> is a hollow brass +cylinder, in which is placed an ordinary electro-magnet +similar to <a href="#FIG_20">Figs. 20</a> or <a href="#FIG_20A">20 <span class="smcap">A</span></a>. At the front end, near <span class="smcap">B</span>, is +affixed by its edges a thin disc of sheet iron, precisely +as in the Bell telephone,<a name="FNanchor_14_14" id="FNanchor_14_14"></a><a href="#Footnote_14_14" class="fnanchor">[14]</a> and over against it, at <span class="smcap">B</span>, is an +insulated contact screw, as in the ordinary trembling +bell. On the disc of sheet iron, at the spot where the +screw touches, is soldered a speck of platinum. The +wires from the electro-magnet are connected, one to the +upper binding screw, the other to the brass case of the +instrument itself, which is in metallic communication<!-- Page 108 --><span class="pagenum"><a name="Page_108" id="Page_108">[Pg 108]</a></span> +with the sheet iron disc. The return wire from the contact +screw is shown attached to the insulated piece, and +is fastened to another binding screw (not visible) on the +base board. When contact is made with the battery, +through the press or push, the magnet becomes energised, +and pulls the iron disc or diaphragm towards it, +causing it to buckle inwards. In doing this, contact is +broken with the screw <span class="smcap">B</span>; consequently the diaphragm +again straightens out, as the magnet no longer pulls it. +Again contact is made; when of course the same round +of performances is continuously repeated. As the plate +or diaphragm vibrates many hundreds of times per +second, it sets up a distinctly musical and loud sound +wave, not unlike the note of a cornet-a-piston, or a loud +harmonium reed. With a number of these "trumpets," +each diaphragm being duly tuned to its proper pitch, it +would be possible to construct a novel musical instrument, +working solely by electricity. The "pushes" +need only take the form of pianoforte keys to render +the instrument within the grasp of any pianoforte or +organ player.</p> + + +<p><a name="SEC_52" id="SEC_52"></a>§ 52. Sometimes the gong or "dome" of the ordinary +bell is replaced by a coil spring, as in the American +clocks; sometimes quaint forms are given to the parts +covering the "movement," so as to imitate the head of +an owl, etc. But bells with these changes in outward +form will not present any difficulty, either in fixing or in +management, to those who have mastered the structural +and working details given in this chapter.</p> + +<div class="footnote"><p><a name="Footnote_10_10" id="Footnote_10_10"></a><a href="#FNanchor_10_10"><span class="label">[10]</span></a> "Amateur Work."</p></div> + +<div class="footnote"><p><a name="Footnote_11_11" id="Footnote_11_11"></a><a href="#FNanchor_11_11"><span class="label">[11]</span></a> <i>Insula</i> in Latin means an island, hence an electrified body is said to +be insulated when surrounded by non-conductors, as an island by the sea.</p></div> + +<div class="footnote"><p><a name="Footnote_12_12" id="Footnote_12_12"></a><a href="#FNanchor_12_12"><span class="label">[12]</span></a> A "push," of which several forms will hereafter be described and +figured, consists essentially in a spring carrying a stud, standing directly +over, but not touching, another stud, fixed to a base. The lower stud is +connected to one terminal of battery, the spring is connected to the bell. +When the spring is pressed down, the two studs come into contact, the +current flows, and the bell rings.</p></div> + +<div class="footnote"><p><a name="Footnote_13_13" id="Footnote_13_13"></a><a href="#FNanchor_13_13"><span class="label">[13]</span></a> Described at <a href="#SEC_61">§ 61</a>.</p></div> + +<div class="footnote"><p><a name="Footnote_14_14" id="Footnote_14_14"></a><a href="#FNanchor_14_14"><span class="label">[14]</span></a> See "Electrical Instrument Making for Amateurs." Whittaker & Co. +Second edition.</p></div> + + + +<hr class="long" /> +<p><!-- Page 109 --><span class="pagenum"><a name="Page_109" id="Page_109">[Pg 109]</a></span></p> +<h2><a name="CHAPTER_IV" id="CHAPTER_IV"></a>CHAPTER IV. +<br /> +ON CONTACTS, PUSHES, SWITCHES, KEYS, ALARMS, +AND RELAYS.</h2> + + +<p><a name="SEC_53" id="SEC_53"></a>§ 53. All the appliances which have hitherto been +described, would be utterly useless for the purposes intended, +had we not at hand some means of easily, +certainly and rapidly completing and breaking the +circuit between the bell or bells, on the one hand, and +the battery on the other. This necessary piece of +apparatus, which is simply a contact maker, receives +different names, dependent on its application. When it +is intended to be actuated directly by hand, it is known +as a "push," a "pressel," or "pull," according to the +mode in which the contact is made. At <a href="#FIG_45">Fig. 45</a>, <span class="smcap">A</span>, <span class="smcap">B</span>, <span class="smcap">C</span>, +<span class="smcap">D</span>, and <span class="smcap">E</span>, show the outward forms of various "pushes," +in wood and china, as sent out by the leading makers. +(The ones figured are from Messrs. Binswanger & Co.) +At <span class="smcap">F</span> is a sectional view of one of these pushes, and <span class="smcap">G</span> +shows the interior when the cover has been removed. +From these two latter illustrations it will be easily understood +that the "push" consists essentially in two pieces of<!-- Page 110 --><span class="pagenum"><a name="Page_110" id="Page_110">[Pg 110]</a></span> +metal one or both of which are springs, and one of which +is connected with one of the wires from the battery, +while the other is attached to the wire proceeding to the +bell. When the button is pressed the upper spring +comes into contact with the lower metal spring or plate. +The circuit is now complete; hence the bell rings. But +as soon as the finger is removed from the stud or button +of the "push," the spring returns to its old place, contact +being thereby broken when the bell ceases to ring, +unless it be fitted with a continuous ringing arrangement +(see <a href="#SEC_48">§ 48</a>). In fastening the leading wires to these<!-- Page 111 --><span class="pagenum"><a name="Page_111" id="Page_111">[Pg 111]</a></span> +pushes, care must be taken that the ends of the wires be +scraped, and sand papered quite clean and bright, bent +into a loop which must be inserted under the head of the +screw that holds the wire to the spring pieces; the +screws being then tightened up carefully to ensure +a good grip and contact with the wires.</p> + +<div class="figcenter" style="width: 600px;"> +<a name="FIG_45" id="FIG_45"></a> +<img src="images/i_119.png" width="600" height="501" alt="Fig. 45." title="Various forms of pushes" /> +<p class="caption">Fig. 45.</p> +</div> + +<hr /> + +<div class="figright" style="width: 250px;"> +<a name="FIG_46" id="FIG_46"></a> +<img src="images/i_120.png" width="250" height="400" alt="Fig. 46." title="Pressel" /> +<p class="caption">Fig. 46.</p> +</div> + + +<p><a name="SEC_54" id="SEC_54"></a>§ 54. A "pressel" (<a href="#FIG_46">Fig. 46</a>) is simply a push which +instead of being made a fixture by being fastened in the +wall or door, is attached to a +metallic wired line, so that it is +generally made to resemble somewhat +in outward appearance the +knob or tassel of the bell-pull of the +last generation, the interior arrangement +is precisely similar to that of +the push; that is to say, the pressel +consists in a pear-shaped or acorn-shaped +hollow wooden box, with a +projecting knob or button below. +This button is attached to a spring, +the tension of which keeps the +knob protruding from the end of the box, and at the +same time prevents contacts with the second spring at +the bottom of the box. Two insulated wires, one from +the battery, the other from the bell, are connected to +separate screws at the top of the pressel. One of these +screws connects with the lower spring, the other with +the upper.</p> + +<hr /> + +<div class="figcenter" style="width: 400px;"> +<a name="FIG_47" id="FIG_47"></a> +<img src="images/i_121.png" width="400" height="293" alt="Fig. 47." title="Pull" /> +<p class="caption">Fig. 47.</p> +</div> + +<hr /> + +<div class="figright" style="width: 127px;"> +<a name="FIG_48" id="FIG_48"></a> +<img src="images/i_122.png" width="127" height="400" alt="Fig. 48." title="Bedroom pull" /> +<p class="caption">Fig. 48.</p> +</div> + +<p><a name="SEC_55" id="SEC_55"></a>§ 55. The "pull" (<a href="#FIG_47">Fig. 47</a>), as its name implies, +makes contact and rings the bell on being pulled. The<!-- Page 112 --><span class="pagenum"><a name="Page_112" id="Page_112">[Pg 112]</a></span> +knob has a rather long shank bar, around which is coiled +a pretty stiff spring. At the farther extremity is an +ebonite or boxwood collar ending in a rather wider +metal ring. The wires from the bell and battery are +connected respectively to two flat springs, <i>a a'</i>, by +the screws <i>b b'</i>. When the knob is pulled, the metal +collar touches both springs, and the circuit is completed. +Closely allied to the "pull" is a form of bedroom contact, +which combines pear-push or pressel and pull in one +device. This will be readily understood on reference +to <a href="#FIG_48">Fig. 48</a>. Another form of bedroom pull, with +ordinary rope and tassel, consists in a box containing a +jointed metal lever, standing over a stud, from which it +is kept out of contact by a counter spring. To the projecting +end of the lever is attached the bell rope. When +this is pulled the lever touches the stud, contact is made, +and the bell rings. This is clearly shown in <a href="#FIG_49A">Fig. 49 <span class="smcap">A</span></a>. In +all these contacts, except the door pull (<a href="#FIG_47">Fig. 47</a>) where +the friction of the action of pulling keeps the surfaces<!-- Page 113 --><span class="pagenum"><a name="Page_113" id="Page_113">[Pg 113]</a></span> +bright, the points of contact should be tipped with platinum. +Another form of contact to be let in the floor +of the dining-room, within easy reach of the foot of the +carver, or other persons at the head of the table, is +shown at <a href="#FIG_49B">Fig. 49 <span class="smcap">B</span></a>.</p> + +<div class="figcenter" style="width: 395px;"> +<a name="FIG_49A" id="FIG_49A"></a> +<img src="images/i_123a.png" width="395" height="400" alt="Fig. 49 A." title="Bedroom pull Another form" /> +<p class="caption">Fig. 49 A.</p> +</div> + +<hr /> + +<div class="figcenter" style="width: 400px;"> +<a name="FIG_49B" id="FIG_49B"></a> +<img src="images/i_123b.png" width="400" height="76" alt="Fig. 49 B." title="Floor contact, ball form" /> +<p class="caption">Fig. 49 B.</p> +</div> + +<p>Mr. Mackenzie has introduced a +very ingenious contrivance whereby +the ringer may know whether the bell +at the distant end has rung. This is +effected by inclosing in the push a +device similar to that shown at <a href="#FIG_43A">Fig. +43 <span class="smcap">A</span></a>. That is to say, an electro-magnet +wound with wire, and surmounted +by a thin iron disc, is placed +in circuit with the line wires. The +ringing of the bell rapidly magnetises +and demagnetises the electro-magnet, +and causes a humming sound, which +clearly indicates whether the bell is +ringing or not. As this device can +be made very small, compact, and +not liable to derangement, it is of +easy application.</p> + + +<div class="figright" style="width: 120px;"> +<a name="FIG_50" id="FIG_50"></a> +<img src="images/i_124a.png" width="120" height="400" alt="Fig. 50." title="Burglar alarm" /> +<p class="caption">Fig. 50.</p> +</div> + +<p><a name="SEC_56" id="SEC_56"></a>§ 56. The next form of contact +to which our attention must be +directed, is that known as the <i>burglar alarm</i>, with +its variant of door-contacts, sash-contacts, till-contacts, +etc.</p> + +<p>The "burglar's pest" (as the contrivance we illustrate +is called) is one of the most useful applications of<!-- Page 114 --><span class="pagenum"><a name="Page_114" id="Page_114">[Pg 114]</a></span> +electricity for the protection of property against thieves. +It consists usually, first, of a brass plate (<a href="#FIG_50">Fig. 50</a>), upon +which a platinum contact piece is fixed, and second, of +a spring made of hardened brass or steel insulated from +the plate; or of a cylindrical box with a spiral spring +inside (see <a href="#FIG_51">Fig. 51</a>). It is so arranged that as long as +the stud is kept pressed in, the platinum points of contact +are kept apart; this is the position when fixed in +the rebate of a closed door or window; but as soon as +opened, the stud passes outward through the hole, and +the points of contact come together and complete the +circuit of the wires in connection with the bell. The +bell is best to be a continuous ringing one. It may be<!-- Page 115 --><span class="pagenum"><a name="Page_115" id="Page_115">[Pg 115]</a></span> +fixed in the master's bedroom, or outside the premises +in the street.</p> + +<div class="figcenter" style="width: 376px;"> +<a name="FIG_51" id="FIG_51"></a> +<img src="images/i_124b.png" width="376" height="400" alt="Fig. 51." title="Burglar alarm Another form" /> +<p class="caption">Fig. 51.</p> +</div> + +<div class="figright" style="width: 223px;"> +<a name="FIG_52" id="FIG_52"></a> +<img src="images/i_124c.png" width="223" height="400" alt="Fig. 52." title="Floor contact" /> +<p class="caption">Fig. 52.</p> +</div> + +<p>Legge's Window Blind contact is an arrangement by +which the blind is secured at the bottom by attaching it +to a hook or button. A slight pressure against the +blind (caused by anyone trying to enter after having +broken a window) sets the electric bell in motion +unknown to the intruder.</p> + +<p>A form of floor contact, which may be placed under a +light mat or carpet, illustrated at <a href="#FIG_52">Fig. 52</a>, serves to +give notice if anyone be waiting at the door, or stepping +into places which are desired to be kept private. All these +arrangements, to be serviceable, should be connected +with continuous ringing bells (see <a href="#SEC_48">§ 48</a>). Wherever it +is likely that these arrangements may stand a long time<!-- Page 116 --><span class="pagenum"><a name="Page_116" id="Page_116">[Pg 116]</a></span> +without being called into play, it is better to employ +some form of contact in which a <i>rubbing</i> action (which +tends to clean the surfaces and then make a good contact) +is brought into play, rather than a merely <i>dotting</i> +action. For this reason, spring contacts in which the +springs connected with the wires are kept apart by an +insulating wedge (shown at <a href="#FIG_53">Fig. 53</a>) as long as the +door or window are kept closed, are preferred. In the +case of windows, strips of brass let into the frame on +each side of the sash, are thrown into contact by the +springs <i>a</i> and <i>a'</i> in the sash itself, as shown at <a href="#FIG_54">Fig. 54</a>. +For shop doors and others, where a short contact only +is required, and this only when the door is opened, a +contact such as shown at <a href="#FIG_55">Fig. 55</a> is well adapted. It +consists, as will be seen, in a peculiarly shaped pivoted +trigger <i>a</i>, which is lifted forwards when the door is +opened, so that it makes contact with the spring <i>b</i>. +Owing to the curved shape of the arm of the<!-- Page 117 --><span class="pagenum"><a name="Page_117" id="Page_117">[Pg 117]</a></span> +trigger, the contact is not repeated when the door is +closed.</p> + +<div class="figcenter" style="width: 260px;"> +<a name="FIG_53" id="FIG_53"></a> +<img src="images/i_125.png" width="260" height="400" alt="Fig. 53." title="Door contact" /> +<p class="caption">Fig. 53.</p> +</div> + +<hr /> + +<div class="figcenter" style="width: 365px;"> +<a name="FIG_54" id="FIG_54"></a> +<img src="images/i_126a.png" width="365" height="400" alt="Fig. 54." title="Sash contact" /> +<p class="caption">Fig. 54.</p> +</div> + +<hr /> + +<div class="figcenter" style="width: 400px;"> +<a name="FIG_55" id="FIG_55"></a> +<img src="images/i_126b.png" width="400" height="119" alt="Fig. 55." title="Shop door contact" /> +<p class="caption">Fig. 55.</p> +</div> + + +<p><a name="SEC_57" id="SEC_57"></a>§ 57. In all forms of burglar or thief alarms, the +ordinary system of having the circuit broken, until contact +is made by the intruder involuntarily making contact +at some point, presents one great disadvantage; and +that is, that if "<i>notre ami l'ennemi</i>," viz., the thief or +burglar, be anything of an electrician (and alas! to what +base uses may not even science be perverted) he will +begin by cutting all suspicious-looking wires before he<!-- Page 118 --><span class="pagenum"><a name="Page_118" id="Page_118">[Pg 118]</a></span> +attempts to set about any serious work. This disadvantage +may be entirely overcome by the adoption of a +simple modification, known as the "closed circuit +system" of bell ringing. For this the bells, etc., are +continuously in contact with the batteries, but owing +to the peculiar connections, do not ring unless the +circuit is broken. To render the working of such a +system clear to my readers, I quote the description +given in the <i>English Mechanic</i>, by one of our leading +electricians:—</p> + +<p>Writing on the subject of Closed Circuit Bell-ringing, +Mr. Perren Maycock says:—"This is principally adopted +for alarm purposes. Its superiority over the open circuit +system lies in the fact that notice is given on opening +(breaking) the circuit, which is the reverse to the +usual practice. In the ordinary method it becomes +necessary to have a contact maker, differing in form for +various purposes and situations, which, along with the +leading wires, must be artfully concealed. All this +entails great expense; besides which one can never be +sure that the contacts and wires are in proper order +without actually trying each one. On the other hand, +with the "closed circuit" system, one has merely to +place the wire in any convenient position, it being better +<i>seen</i> than <i>hidden</i>. The very fact that alarm is given on +breaking the contact renders the method applicable in +circumstances and under conditions which would render +the "open" method difficult and expensive, if not impossible. +One can always be certain that everything is +in order. The modern burglar, electrically educated<!-- Page 119 --><span class="pagenum"><a name="Page_119" id="Page_119">[Pg 119]</a></span> +as regards common practise in such matters, would +naturally make a point of cutting all wires that fall +in his path. From these and other obvious considerations, +it is evident how simple and yet how perfect +a means of protection such a system provides. I +will now proceed to explain the manner of application. +The bell used differs from the ordinary, only in the +arrangement of its external connections.</p> + +<div class="figcenter" style="width: 400px;"> +<a name="FIG_56A" id="FIG_56A"></a> +<img src="images/i_128a.png" width="400" height="367" alt="Fig. 56 A." title="Closed circuit system, single" /> +<p class="caption">Fig. 56 A.</p> +</div> + +<p><a href="#FIG_56A">Fig. 56 <span class="smcap">A</span></a> represents a single-alarm circuit. When +contact is broken externally, there is a closed circuit +in which are the battery and bell magnet coils.<!-- Page 120 --><span class="pagenum"><a name="Page_120" id="Page_120">[Pg 120]</a></span> +Consequently the armature is drawn away from the +contact stud, close up to the electro-magnet, and is +held so. When a break occurs, the armature flies back, +completes the local circuit, and rings so long as the +external circuit remains broken. There is a switch for +use when the alarm is not required.</p> + +<div class="figcenter" style="width: 600px;"> +<a name="FIG_56B" id="FIG_56B"></a> +<img src="images/i_128b.png" width="600" height="229" alt="Fig. 56 B." title="Closed circuit system, double" /> +<p class="caption">Fig. 56 B.</p> +</div> + +<hr /> + +<div class="figcenter" style="width: 600px;"> +<a name="FIG_57" id="FIG_57"></a> +<img src="images/i_129.png" width="600" height="395" alt="Fig. 57." title="Modified gravity, Daniell" /> +<p class="caption">Fig. 57.</p> +</div> + +<p><a href="#FIG_56B">Fig. 56 <span class="smcap">B</span></a> represents a case in which notice is given at +two places. By insulating a key as shown, reply signalling +can be carried on between the points at which the +bells are placed. A special gravity Daniell modification +(<a href="#SEC_25">§ 25</a>) is used for this class of work (<a href="#FIG_57">Fig. 57</a>): a narrow +lead cylinder, about 2" in diameter, watertight except +at the bottom, where it opens out into an inverted cone, +the surface of which is pierced with holes. This stands +immersed in dilute sulphuric acid. A saturated solution +of copper sulphate is next carefully introduced, so as to +displace the acid upwards. Crystals of sulphate of<!-- Page 121 --><span class="pagenum"><a name="Page_121" id="Page_121">[Pg 121]</a></span> +copper are introduced into the open end at the top of +cylinder, to fill the perforated portion at the bottom. +From the wooden cover of cell a thick flat ring of amalgamated +zinc hangs suspended in the dilute acid. Care +should be taken not to introduce the zinc till the two +solutions have become well separated. During action +this becomes coppered, while in contact with the sulphate +of copper, but it is not attacked by the acid. It is, +however, preferable to <i>paint</i> that portion of the lead, +which is surrounded by the acid. The height of the +cell is about 14."</p> + +<p>It will be readily understood that if this latter system +be employed, special contacts, +which break contact when the +pressure is removed, must be +employed for the door or window +contacts. A simple form is shown +at <a href="#FIG_58">Fig. 58</a>.</p> + +<p>Contacts similar to Figs. <a href="#FIG_50">50</a>, <a href="#FIG_53">53</a> and <a href="#FIG_54">54</a>, may be fitted +on tills or drawers.</p> + +<div class="figcenter" style="width: 400px;"> +<a name="FIG_58" id="FIG_58"></a> +<img src="images/i_130.png" width="400" height="227" alt="Fig. 58." title="Contact for closed circuit" /> +<p class="caption">Fig. 58.</p> +</div> + + +<div class="figright" style="width: 124px;"> +<a name="FIG_59" id="FIG_59"></a> +<img src="images/i_131.png" width="124" height="400" alt="Fig. 59." title="Thermometer alarm" /> +<p class="caption">Fig. 59.</p> +</div> + +<p><a name="SEC_58" id="SEC_58"></a>§ 58. Another useful application of "contact" is for +the notification of any rise or fall of temperature beyond +certain fixed limits. The devices used for this purpose +are known as "fire alarms," "frost alarms," and "thermometer +alarms." The thermometer alarm is at once +the most effective and trustworthy of the forms known, +as, besides its delicacy, it has the advantage of being able +to give notice of low, as well as of abnormally high temperature. +The form usually given to the electric alarm +thermometer, is well shown at <a href="#FIG_59">Fig. 59</a>. It consists in an<!-- Page 122 --><span class="pagenum"><a name="Page_122" id="Page_122">[Pg 122]</a></span> +ordinary thermometer with a wire projecting into the tube +to a certain point, say 100 degrees. The mercury in +the bulb being also connected with another wire. When +the temperature is within the usual +climatic range, the mercury does not +reach the upper wire. If by reason of +fire or any other abnormal heat, the +temperature rises beyond that to which +the instrument is set, the mercury rises +and touches the upper wire, contact +is thus established, and the bell rings.</p> + +<p>By giving the thermometer the shape +of a letter U, it is possible to notify also +a fall below a certain degree, as well as +a rise beyond a certain fixed point. +These thermometers are specially used +by nurserymen and others, to warn +them of the too great lowering of +temperature, or <i>vice versâ</i>, in the +houses under their charge.</p> + +<p>Other forms of fire alarms are shown +at Fig. <a href="#FIG_60">60</a> and <a href="#FIG_61">61</a>. If a strip be built +up of two thin layers of dissimilar +metals riveted together, as the two +metals do not expand at the same +rate, the strip will bend to the <i>right</i> +if heated, and to the <i>left</i> if cooled. +In the instrument shown at <a href="#FIG_60">Fig. 60</a>, the application of +heat causes the flexible strip carrying the contact screw, +to bend over till it touches the lower stop, when, of<!-- Page 123 --><span class="pagenum"><a name="Page_123" id="Page_123">[Pg 123]</a></span> +course, the bell rings. If two stops are employed instead +of the lower one only, the bell will ring when a low +temperature is reached, which causes the strip to bend +in the opposite direction.</p> + +<div class="figcenter" style="width: 400px;"> +<a name="FIG_60" id="FIG_60"></a> +<img src="images/i_132a.png" width="400" height="84" alt="Fig. 60." title="Fire alarm" /> +<p class="caption">Fig. 60.</p> +</div> + +<hr /> + +<div class="figcenter" style="width: 394px;"> +<a name="FIG_61" id="FIG_61"></a> +<img src="images/i_132b.png" width="394" height="400" alt="Fig. 61." title="Fire alarm Another form and (below) in action" /> +<p class="caption">Fig. 61.</p> +</div> + +<p>At <a href="#FIG_61">Fig. 61</a> is illustrated a novel form, in which the +expansion of air causes contact to be made. It consists +in an air chamber hermetically closed by a corrugated +metal plate I, similar to that used in the aneroid barometers. +When the temperature rises to a certain point, +the expansion of the air in the chamber brings the<!-- Page 124 --><span class="pagenum"><a name="Page_124" id="Page_124">[Pg 124]</a></span> +metallic plate into contact with the screw, as shown below. +This closes the circuit and rings the bell in the usual +manner. In all these fire or thermometer alarms, the +exact degree of heat at which the bell shall ring, can be +pretty accurately adjusted by means of the contact +screws.</p> + + +<p><a name="SEC_59" id="SEC_59"></a>§ 59. Closely allied to these forms of contacts are +the devices whereby an ordinary clock or watch can be +made to arouse the over-drowsy sleeper by the ringing +of an electric bell, which in this case should be of the +continuous type. All these depend in their action upon +some arrangement whereby when the hour hand of the +clock or watch arrives at a certain given point in its +travel, it makes contact between the battery and bell. +In general the contact piece is attached bodily to the +clock, but in the very ingenious arrangement illustrated +at <a href="#FIG_62">Fig. 62</a> (devised by Messrs. Binswanger) the contacts +are attached to an outer case, and as the case of the +watch itself forms one point of contact, any watch that +will slip in the case, may be set to ring the bell.</p> + +<div class="figcenter" style="width: 317px;"> +<a name="FIG_62" id="FIG_62"></a> +<img src="images/i_134.png" width="317" height="400" alt="Fig. 62." title="Binswanger's "watch alarm" contact" /> +<p class="caption">Fig. 62.</p> +</div> + +<hr /> + +<div class="figcenter" style="width: 278px;"> +<a name="FIG_63" id="FIG_63"></a> +<img src="images/i_135.png" width="278" height="400" alt="Fig. 63." title="Watchman's electric tell-tale clock" /> +<p class="caption">Fig. 63.</p> +</div> + +<p>Messrs. Gent, of Leicester, have also perfected an +electric watchman's clock, which records the number of +places the watchman in charge has visited or missed on +his rounds. This we illustrate at <a href="#FIG_63">Fig. 63</a>. We quote +Messrs. Gent's own words, in the following description:—</p> + +<p>"It consists of an eight-day clock, to which is attached +a disc or table revolving upon a vertical axis and driven +by the mechanism of the clock. The disc is covered +with a sheet of paper, attached to it by a binding screw<!-- Page 125 --><span class="pagenum"><a name="Page_125" id="Page_125">[Pg 125]</a></span> +so that it can be removed when used and a clean sheet +substituted for it. Each sheet of paper is divided longitudinally +into hours and, if necessary, parts of hours, and +crosswise into as many divisions as there are places to +be visited by the watchman—any number from one to +twenty. Each division has a corresponding marker, +which indicates, by the impression it makes upon the +paper, the time the watchman visits the place connected +with that marker. Wires are carried from the terminals +of the clock, one to the battery, and one to each press-button +fixed at the points intended to be visited by the +watchman; another wire is carried from each press-button +to the other end of the battery. The action is +very simple: when the button is pressed in the current<!-- Page 126 --><span class="pagenum"><a name="Page_126" id="Page_126">[Pg 126]</a></span> +passes through a coil carrying an armature and contact +breaker with a point at the end of a long arm; a +hammer-like motion is given to the pointer, and a distinct +perforation made in the card. It is usual to have +the press-button in a box locked up, of which the watchman +only has the key.</p> + +<p>"The clock may be in the office or bedroom of the<!-- Page 127 --><span class="pagenum"><a name="Page_127" id="Page_127">[Pg 127]</a></span> +manager or head of the establishment, who can thus, +from time to time, satisfy himself of the watchman's +vigilance. The record should be examined in the morning, +and replaced by a clean sheet of card.</p> + +<p>"This clock received the special mention of Her +Majesty's Commissioners in Lunacy, and has been +adopted by some of the largest asylums in the country.</p> + +<p>"We have recently made an important improvement by +adding a relay for every marker, thus enabling a local +battery of greater power to be used for actuating the +markers. This has made no alteration in the appearance +of the clock, as the relays are contained within the +cornice at the top of the clock case."</p> + + +<p><a name="SEC_60" id="SEC_60"></a>§ 60. By means of a float, it is possible to give notice +of the height of water in a tank, a reservoir, or even of +the state of the tide. In these cases all that is needed is +a float with an arm, having a suitable contact attached, +so that when the water rises to the level of the float and +lifts it, it causes the contact piece to complete the circuit +through a set screw. Or the float may be attached to +an arm having a certain play in both directions, <i>i.e.</i>, up +and down, within which no contact is made, as the +arm has a contact piece on either side, which can touch +either an upper or a lower contact screw, according +to whether the tide is low or high, or whether the lock +or tank is nearly empty or too full.</p> + +<div class="figcenter" style="width: 373px;"> +<a name="FIG_64" id="FIG_64"></a> +<img src="images/i_137.png" width="373" height="400" alt="Fig. 64." title="Lever switch, two-way" /> +<p class="caption">Fig. 64.</p> +</div> + + +<p><a name="SEC_61" id="SEC_61"></a>§ 61. Sometimes it is convenient to be able to ring +an ordinary trembling bell continuously, as when a +master wishes to wake a member of his family or a +servant; or again, to cut a given bell or bells out of<!-- Page 128 --><span class="pagenum"><a name="Page_128" id="Page_128">[Pg 128]</a></span> +circuit altogether. The arrangements by which this can +be effected, are known as "switches." Of switches there +are two kinds, namely, <i>plugswitches</i> or <i>interruptors</i>, and +<i>lever switches</i>. The former consists essentially in two +stout plates of brass affixed to a base board of any insulating +material. These brass plates are set parallel to +each other, a short distance apart, and the centre of the +facing edge is hollowed out to take a brass taper plug. +A binding or other screw is fixed to each brass plate, to +connect up to the leading wires. +When the plug is in its socket, +the circuit between the two +plates (and consequently between +the battery and bell, etc.) is +complete; when the plug is out, +the contact is broken. This +form of switch is subject to +work out of order, owing to the +fact that the taper plug +gradually widens the hole, so +that the contact becomes uncertain or defective altogether. +By far the better form of switch is the lever switch, as +shown at <a href="#FIG_64">Fig. 64</a>. This consists in a movable metal +lever or arm, which is held by a strong spring in contact +with the upper binding screw. It can be made to slide +over to the right or left of the centre, at its lower or free +end, as far as the binding screws or studs shown, which +act at once as stops and point of connection to wires. +When the arm or lever is in the centre no contact is +made but if it be pushed over to the right, it slides on a<!-- Page 129 --><span class="pagenum"><a name="Page_129" id="Page_129">[Pg 129]</a></span> +brass strip let into and lying flush with the base. +Contact is thus made between the upper binding +screw and the left-hand screw. If there is another +brass strip on the left-hand side (as shown in the +figure), contact may be made with another bell, +etc., by sliding the arm to the left; or again, if +no metal strip be placed on the left side the contact +may be broken by pushing the arm towards the left-hand +stud.</p> + + +<p><a name="SEC_62" id="SEC_62"></a>§ 62. A <i>key</i> is another form of contact, by means of +which a long or short completion of circuit can be made +by simply tapping on the knob. It is particularly useful +when it is desired to transmit signals, either by +ringing or otherwise. It consists, as may be seen at +<a href="#FIG_65">Fig. 65</a>, of a lever or arm of brass, pivoted at its centre, +furnished with a spring which keeps the portion under +the knob out of contact with the stud in the front of +the base-board. As both the stud and the lever are +connected to binding screws communicating with the +battery and bell, etc., it is evident that on depressing +the key the circuit with the bell will be completed for a +longer or shorter period, varying with the duration of +the depression. Hence, either by using preconcerted +signals of short and long rings to signify certain common +words, such as a long ring for <i>No</i>, and a short one for +<i>Yes</i>, or by an adaptation of the ordinary Morse code, +intelligible conversation can be kept up between house +and stable, etc., etc., by means of a key and a bell. As +Mr. Edwinson has given much time to the elucidation +of this system of bell signalling, I cannot do better<!-- Page 130 --><span class="pagenum"><a name="Page_130" id="Page_130">[Pg 130]</a></span> +than quote his instructions, as given in <i>Amateur +Work</i>:—</p> + +<p>"For this purpose preconcerted signals have been +agreed upon or invented as required, and these have +been found to be irksome and difficult to remember, +because constructed without any reference to a +definite plan. We may, however, reduce bell signals +to a definite system, and use this system or code as +a means to carry on conversation at a distance as +intelligently as it can be done by a pair of telegraph +instruments. In fact, the Morse telegraph code can be +easily adopted for use with electric bells of the vibrating +or trembling type, and its alphabet, as appended +below, easily learnt. The letters of the alphabet are +represented by long strokes and short strokes on the +bell, as here shown.—</p> + + + +<div class="center"> +<table border="0" cellpadding="4" cellspacing="0" summary="Morse telegraph code"> +<tr><td align="left">A</td><td align="left">– — </td></tr> +<tr><td align="left">B</td><td align="left">— – – – </td></tr> +<tr><td align="left">C</td><td align="left">— – — – </td></tr> +<tr><td align="left">D</td><td align="left">— – – </td></tr> +<tr><td align="left">E</td><td align="left">– </td></tr> +<tr><td align="left">F</td><td align="left">– – — – </td></tr> +<tr><td align="left">G</td><td align="left">— — – </td></tr> +<tr><td align="left">H</td><td align="left">– – – – </td></tr> +<tr><td align="left">I</td><td align="left">– – </td></tr> +<tr><td align="left">J</td><td align="left">– — — — </td></tr> +<tr><td align="left">K</td><td align="left">— – — </td></tr> +<tr><td align="left">L</td><td align="left">– — – – </td></tr> +<tr><td align="left">M</td><td align="left">— —</td></tr> +<tr><td align="left">N</td><td align="left">— – </td></tr> +<tr><td align="left">O</td><td align="left">— — — </td></tr> +<tr><td align="left">P</td><td align="left">– — — – </td></tr> +<tr><td align="left">Q</td><td align="left">— — – – – </td></tr> +<tr><td align="left">R</td><td align="left">– — – </td></tr> +<tr><td align="left">S</td><td align="left">– – – </td></tr> +<tr><td align="left">T</td><td align="left">— </td></tr> +<tr><td align="left">U</td><td align="left">– – — </td></tr> +<tr><td align="left">V</td><td align="left">– – – — </td></tr> +<tr><td align="left">W</td><td align="left">– — —</td></tr> +<tr><td align="left">X</td><td align="left">— – – — </td></tr> +<tr><td align="left">Y</td><td align="left">— – — —</td></tr> +<tr><td align="left">Z</td><td align="left">— — – – </td></tr> +<tr><td align="left">Ch</td><td align="left">— — —</td></tr> +<tr><td align="left">Ä (æ)</td><td align="left">– — – — </td></tr> +<tr><td align="left">Ö (œ)</td><td align="left">— — — – </td></tr> +<tr><td align="left">Ü (ue)</td><td align="left">– – — —</td></tr> +<tr><td align="left">1</td><td align="left">– — — —</td></tr> +<tr><td align="left">2</td><td align="left">– – — — — </td></tr> +<tr><td align="left">3</td><td align="left">– – – — —</td></tr> +<tr><td align="left">4</td><td align="left">– – – – — </td></tr> +<tr><td align="left">5</td><td align="left">– – – – – </td></tr> +<tr><td align="left">6</td><td align="left">— – – – – </td></tr> +<tr><td align="left">7</td><td align="left">— — – – – </td></tr> +<tr><td align="left">8</td><td align="left">— — — – – </td></tr> +<tr><td align="left">9</td><td align="left">— — — – </td></tr> +<tr><td align="left">0</td><td align="left">— — — — </td></tr> +</table></div> + + +<p>"It will be noticed that the strokes to represent a letter +do not in any case exceed four, and that all the figures +are represented by five strokes of varying length to each<!-- Page 131 --><span class="pagenum"><a name="Page_131" id="Page_131">[Pg 131]</a></span> +figure. Stops, and other marks of punctuation, are +represented by six strokes, which are in their combination +representations of two or three letters respectively, +as shown below:—</p> + + + +<div class="center"> +<table border="0" cellpadding="4" cellspacing="0" summary="Morse telegraph punctuation marks"> +<tr><td align="left">Comma</td><td align="left">(,)</td><td align="center">by</td><td align="left">A A A</td><td align="center">or</td><td align="left">– — – — – —</td></tr> +<tr><td align="left">Full stop</td><td align="left">(.)</td><td align="center">"</td><td align="left">I I I</td><td align="center">"</td><td align="left">– – – – – –</td></tr> +<tr><td align="left">Interrogation</td><td align="left">(?)</td><td align="center">"</td><td align="left">U D</td><td align="center">"</td><td align="left">– – — — – – </td></tr> +<tr><td align="left">Hyphen</td><td align="left">(-)</td><td align="center">"</td><td align="left">B A</td><td align="center">"</td><td align="left">— – – – – — </td></tr> +<tr><td align="left">Apostrophe</td><td align="left">(')</td><td align="center">"</td><td align="left">W G</td><td align="center">"</td><td align="left">– — — — — – </td></tr> +<tr><td align="left">Inverted commas</td><td align="left">(")</td><td align="center">"</td><td align="left">A F</td><td align="center">"</td><td align="left">– — – – — –</td></tr> +<tr><td align="left">Parenthesis</td><td align="left">( )</td><td align="center">"</td><td align="left">K K</td><td align="center">"</td><td align="left">— – — — – —</td></tr> +<tr><td align="left">Semi-colon</td><td align="left">(;)</td><td align="center">"</td><td align="left">K Ch</td><td align="center">"</td><td align="left">– — — — — —</td></tr> +<tr><td align="left">Surprise</td><td align="left">(!)</td><td align="center">"</td><td align="left">N Ch</td><td align="center">"</td><td align="left">— – — — — —</td></tr> +<tr><td align="left">Colon</td><td align="left">(:)</td><td align="center">"</td><td align="left">I Ch</td><td align="center">"</td><td align="left">– – — — — — </td></tr> +</table></div> + + +<p>"In sending signals to indicate stops, no regard must +be had to the letters which they represent; these are only +given as aids to memory, and are not to be represented +separately on the bell. Bell signals must be given with a +certain amount of regularity as to time; indeed, to +carry on a conversation in this way it is necessary to be +as punctilious in time as when playing a piece of music +on a piano, if the signals are to be understood. The dots of +the signal should therefore be represented in time by +<i>one</i>, and the dashes by <i>two</i>, whilst the spaces between +words and figures where a stop does not intervene should +be represented by a pause equal to that taken by a person +counting <i>three</i>, the space between a word and a stop +being of the same duration. To make this more clear<!-- Page 132 --><span class="pagenum"><a name="Page_132" id="Page_132">[Pg 132]</a></span> +I give an example. The mistress signals to her coachman:—</p> + + + +<div class="center"> +<table border="0" cellpadding="4" cellspacing="0" summary="display of Morse code message"> +<tr><td align="center" class="br">G</td><td align="center" class="br">E</td><td align="center" class="br">T</td><td align="center" class="br"> </td><td align="center" class="br">T</td><td align="center" class="br">H</td><td align="center" class="br">E</td></tr> +<tr><td align="center" class="br">— — –</td><td align="center" class="br">–</td><td align="center" class="br">—</td><td align="center" class="br"> </td><td align="center" class="br">—</td><td align="center" class="br">– – – –</td><td align="center" class="br">–</td></tr> +<tr><td align="center" class="br">2 2 1</td><td align="center" class="br">1</td><td align="center" class="br">2</td><td align="center" class="br">3</td><td align="center" class="br">2</td><td align="center" class="br">1 1 1 1</td><td align="center" class="br">1</td><td align="center">3</td></tr> +</table></div> + + + +<div class="center"> +<table border="0" cellpadding="4" cellspacing="0" summary=""> +<tr><td> </td></tr> +<tr><td align="center" class="br">C</td><td align="center" class="br">A</td><td align="center" class="br">R</td><td align="center" class="br">R</td><td align="center" class="br">I</td><td align="center" class="br">A</td><td align="center" class="br">G</td><td align="center" class="br">E</td></tr> +<tr><td align="center" class="br">— – — –</td><td align="center" class="br">– —</td><td align="center" class="br">– — –</td><td align="center" class="br">– — –</td><td align="center" class="br">– –</td><td align="center" class="br">– —</td><td align="center" class="br">— — –</td><td align="center" class="br">–</td></tr> +<tr><td align="center" class="br">2 1 2 1</td><td align="center" class="br">1 2</td><td align="center" class="br">1 2 1</td><td align="center" class="br">1 2 1</td><td align="center" class="br">1 1</td><td align="center" class="br">1 2</td><td align="center" class="br">2 2 1</td><td align="center" class="br">1</td><td align="center">3</td></tr> +</table></div> + + + +<div class="center"> +<table border="0" cellpadding="4" cellspacing="0" summary=""> +<tr><td> </td></tr> +<tr><td align="center" class="br">R</td><td align="center" class="br">E</td><td align="center" class="br">A</td><td align="center" class="br">D</td><td align="center">Y</td></tr> +<tr><td align="center" class="br">– — –</td><td align="center" class="br">–</td><td align="center" class="br">– —</td><td align="center" class="br">— – –</td><td align="center">— – — —</td></tr> +<tr><td align="center" class="br">1 2 1</td><td align="center" class="br">1</td><td align="center" class="br">1 2</td><td align="center" class="br">2 1 1</td><td align="center">2 1 2 2</td></tr> +</table></div> + + +<p>"The coachman replies:—</p> + +<div class="center"> +<table border="0" cellpadding="4" cellspacing="0" summary=""> +<tr><td> </td></tr> +<tr><td align="center" class="br">R</td><td align="center" class="br">E</td><td align="center" class="br">A</td><td align="center" class="br">D</td><td align="center">Y</td></tr> +<tr><td align="center" class="br">– — –</td><td align="center" class="br">–</td><td align="center" class="br">– —</td><td align="center" class="br">— – –</td><td align="center">— – — —</td></tr> +<tr><td align="center" class="br">1 2 1</td><td align="center" class="br">1</td><td align="center" class="br">1 2</td><td align="center" class="br">2 1 1</td><td align="center">2 1 2 2</td></tr> +</table></div> + +<p>"When the mistress is ready she signals:—</p> + + + +<div class="center"> +<table border="0" cellpadding="4" cellspacing="0" summary=""> +<tr><td align="center" class="br">B</td><td align="center" class="br">R</td><td align="center" class="br">I</td><td align="center" class="br">N</td><td align="center" class="br">G</td><td align="center" class="br"> </td><td align="center" class="br">T</td><td align="center" class="br">H</td><td align="center" class="br">E</td></tr> +<tr><td align="center" class="br">— – – –</td><td align="center" class="br">– — –</td><td align="center" class="br">– –</td><td align="center" class="br">— –</td><td align="center" class="br">— — –</td><td align="center" class="br"> </td><td align="center" class="br">—</td><td align="center" class="br">– – – –</td><td align="center" class="br">–</td></tr> +<tr><td align="center" class="br">2 1 1 1</td><td align="center" class="br">1 2 1</td><td align="center" class="br">1 1</td><td align="center" class="br">2 1</td><td align="center" class="br">2 2 1</td><td align="center" class="br">3</td><td align="center" class="br">2</td><td align="center" class="br">1 1 1 1</td><td align="center" class="br">1</td><td align="center">3</td></tr> +</table></div> + + +<div class="center"> +<table border="0" cellpadding="4" cellspacing="0" summary=""> +<tr><td> </td></tr> +<tr><td align="center" class="br">C</td><td align="center" class="br">A</td><td align="center" class="br">R</td><td align="center" class="br">R</td><td align="center" class="br">I</td><td align="center" class="br">A</td><td align="center" class="br">G</td><td align="center" class="br">E</td></tr> +<tr><td align="center" class="br">— – — –</td><td align="center" class="br">– —</td><td align="center" class="br">– — –</td><td align="center" class="br">– — –</td><td align="center" class="br">– –</td><td align="center" class="br">– —</td><td align="center" class="br">— — –</td><td align="center" class="br">–</td></tr> +<tr><td align="center" class="br">2 1 2 1</td><td align="center" class="br">1 2</td><td align="center" class="br">1 2 1</td><td align="center" class="br">1 2 1</td><td align="center" class="br">1 1</td><td align="center" class="br">1 2</td><td align="center" class="br">2 2 1</td><td align="center" class="br">1</td></tr> +</table></div> + +<p>"And the coachman replies with a single long ring to +signify that he understands. It will be found convenient +to have an answering signal from the receiving +end of the line to each word separately. This must be +sent in the pause after each word, and consists of the +short signal E – when the word is understood, or the +double short signal I – – when the word is not understood. +A negative reply to a question may be given by the<!-- Page 133 --><span class="pagenum"><a name="Page_133" id="Page_133">[Pg 133]</a></span> +signal for N — –, and an affirmative by the signal for +Æ – — – —; other abbreviations may be devised and +used where desired. The code having been committed +to memory, it will be quite easy to transpose the words +and send messages in cypher when we wish to make a +confidential communication; or the bells may be muffled +under a thick cloak, and thus, whilst the measured +beats are heard by the person for whom the signal is +intended, others outside the room will not be annoyed +by them."</p> + +<div class="figcenter" style="width: 400px;"> +<a name="FIG_65" id="FIG_65"></a> +<img src="images/i_142.png" width="400" height="240" alt="Fig. 65." title="Morse key, double contact" /> +<p class="caption">Fig. 65.</p> +</div> + + +<p><a name="SEC_63" id="SEC_63"></a>§ 63. At <a href="#SEC_48">§ 48</a>, we +noticed that a device +known as a <i>Relay</i> is a +convenient, if not an +essential mode of working +continuous ringing +bells. Here we will +direct our attention to +its structural arrangement, +and to its adaptations. Let us suppose that we had +to ring a bell at a considerable distance, so far indeed that +a single battery would not energise the electro-magnets +of an ordinary bell, sufficiently to produce a distinct +ring. It is evident that if we could signal, ever so +feebly, to an attendant at the other end of the line to +make contact with another battery at the distant end +of the line to <i>his</i> bell, by means, say, of a key similar +to that shown at <a href="#FIG_65">Fig. 65</a>, we should get a clear ring, +since this second battery, being close to the bell, would +send plenty of current to energise the bell's magnets.<!-- Page 134 --><span class="pagenum"><a name="Page_134" id="Page_134">[Pg 134]</a></span> +But this would require a person constantly in attendance. +Now the <i>relay</i> does this automatically; it <i>relays</i> +another battery in the circuit. The manner in which +it effects this will be rendered clear, on examination of +<a href="#FIG_66">Fig. 66</a>. Here we have an armature <span class="smcap">A</span> attached to a +light spring, which can play between an insulated stop +<span class="smcap">C</span>, and a contact screw <span class="smcap">B</span>. The play of this armature +can be regulated to a nicety by turning the screws +<span class="smcap">B</span> or <span class="smcap">C</span>. These two screws are both borne by a double +bent arm (of metal) affixed +to the pillar <span class="smcap">D</span>. This pillar +is separated from the rest of +the frame by an insulating +collar or washer of ebonite, +so that no current can +pass from <span class="smcap">E</span> to <span class="smcap">D</span>, unless the +armature be pulled down +so as to make contact with +the contact screw <span class="smcap">B</span>. Just +under the armature, stands +the electro-magnet <span class="smcap">G</span>, which when energised can and does +pull down the armature <span class="smcap">A</span>. It will be readily understood +that if we connect the wires from the electro-magnet <span class="smcap">G</span>, +to the wires proceeding from the battery and push (or +other form of contact) at the distant station, the electro-magnet, +being wound with a large quantity of fine +wire, will become sufficiently magnetized to pull the +armature down through the small space intervening +between <span class="smcap">C</span> and <span class="smcap">B</span>; so that if the screws <span class="smcap">D</span> and <span class="smcap">E</span> are +connected respectively to the free terminals of a<!-- Page 135 --><span class="pagenum"><a name="Page_135" id="Page_135">[Pg 135]</a></span> +battery and bell coupled together at the nearer station, +this second battery will be thrown into circuit with the +bell, and cause it to ring as well and as exactly as if the +most skilful and most trustworthy assistant were in +communication with the distant signaller. Every tap, +every release of the contact, (be it push, key, or switch) +made at the distant end, will be faithfully reproduced at +the nearer end, by the motion of the armature A. For +this reason we may use a comparatively weak battery to +work the relay, which in its turn brings a more powerful +and <i>local</i> battery into play, for doing whatever +work is required. In cases where a number of calls +are required to be made simultaneously from one +centre, as in the case of calling assistance from several +fire engine stations at once, a relay is fixed at each +station, each connected with its own local battery and +bell. The current from the sending station passes +direct through all the relays, connecting all the local +batteries and bells at the same time. This is perhaps +the best way of ringing any number of bells from one +push or contact, at a distant point. Ordinary trembling +bells, unless fitted with an appropriate contrivance, +cannot well be rung if connected up in <i>series</i>. This is +owing to the fact that the clappers of the bells do not +all break or make contact at the same time, so that +intermittent ringing and interruptions take place. With +single stroke bells, this is not the case, as the pulling +down of the armature does not break the contact.</p> + +<div class="figcenter" style="width: 400px;"> +<a name="FIG_66" id="FIG_66"></a> +<img src="images/i_143.png" width="400" height="352" alt="Fig. 66." title="Relay" /> +<p class="caption">Fig. 66.</p> +</div> + +<hr /> + +<div class="figcenter" style="width: 370px;"> +<a name="FIG_67" id="FIG_67"></a> +<img src="images/i_146.png" width="370" height="400" alt="Fig. 67." title="Indicator, drop" /> +<p class="caption">Fig. 67.</p> +</div> + +<hr /> + +<div class="figcenter" style="width: 367px;"> +<a name="FIG_68" id="FIG_68"></a> +<img src="images/i_147.png" width="367" height="400" alt="Fig. 68." title="Indicator, Semaphore" /> +<p class="caption">Fig. 68.</p> +</div> + + +<p><a name="SEC_64" id="SEC_64"></a>§ 64. We now have to consider those contrivances +by means of which it is possible for an attendant to<!-- Page 136 --><span class="pagenum"><a name="Page_136" id="Page_136">[Pg 136]</a></span> +know when a single bell is actuated by a number of +pushes in different rooms, etc., from whence the signal +emanates. These contrivances are known as <i>indicators</i>. +Indicators may be conveniently divided into 3 classes, +viz.:—1st, indicators with <i>mechanical</i> replacements; +2nd, those with electrical replacements; and 3rdly, those +which are self replacing. Of the former class we may +mention two typical forms, namely, the ordinary "fall +back" indicator, and the drop indicator. All indicators +depend in their action on the sudden magnetisation of an +electro-magnet by the same current that works the +electric bell at the time the call is sent. To understand +the way in which this may be effected, let the +reader turn to the illustration of the Relay (<a href="#FIG_66">Fig. 66</a>), +and let him suppose that the pillar <span class="smcap">D</span>, with its accompanying +rectangle <span class="smcap">B C</span>, were removed, leaving only +the electro-magnet <span class="smcap">G</span>, with its frame and armature <span class="smcap">A</span>. +If this armature holds up a light tablet or card, on which +is marked the number of the room, it is evident that +any downward motion of the armature, such as would +occur if the electro-magnet were energised by a current +passing around it, would let the tablet fall, so as to +become visible through a hole cut in the frame containing +this contrivance. It is also equally evident +that the card or tablet would require replacing by hand, +after having once fallen, to render it capable of again +notifying a call. <a href="#FIG_67">Fig. 67</a> shows the working parts of +one of these "drop" indicators, as sent out by Messrs. +Binswanger. In another modification, known as +Thorpe's "Semaphore Indicator," we have a most<!-- Page 137 --><span class="pagenum"><a name="Page_137" id="Page_137">[Pg 137]</a></span> +ingenious application of the same principle in a very +compact form. In this (<a href="#FIG_68">Fig. 68</a>), the electro-magnet +is placed directly behind a disc-shaped iron armature, on +which is painted or marked the number of the room +etc. (in this case 4); this armature is attached by a springy +shank to the drop bar, shown to the left of the electro-magnet. +In front of the armature is a light metal +disc, also pivoted on the drop bar. This engages in a +catch above, when pushed up so as to cover the +number. When pushed up, the +spring of the armature retains +it in its place so that the +number is hidden. When the +current passes around the +electro-magnet, the armature is +pulled toward it, and thus frees +the covering disc, which therefore +falls, and displays the +number. The ordinary form +of "fall back" indicator (a +misnomer, by the way, since the indicator falls forwards) +is well illustrated at <a href="#FIG_69">Fig 69</a>. Here we have an +ordinary electro-magnet <span class="smcap">A</span>, with its wires <i>w</i> <i>w'</i> standing +over an armature <span class="smcap">B</span> attached to a spring <span class="smcap">C</span>, which bears +on its lower extremity, a toothed projection which +serves to hold up the short arm of the bent lever <span class="smcap">D</span>, +which supports the number plate <span class="smcap">E</span>. When the electro-magnet +<span class="smcap">A</span> is energised by the current, it pulls up the +armature <span class="smcap">B</span>, which releases the detent <span class="smcap">D</span> from the +tooth <span class="smcap">C</span>; the number plate therefore falls forwards, as<!-- Page 138 --><span class="pagenum"><a name="Page_138" id="Page_138">[Pg 138]</a></span> +shown by the dotted lines, and shows itself at the +aperture <span class="smcap">E´</span>, which is in front of the indicator frame. +To replace the number out of sight, the attendant +pushes back the plate <span class="smcap">E</span>, till it again engages the +bent lever <span class="smcap">D</span> in the tooth <span class="smcap">C</span>. This replacement of the +number plate, which the attendant in charge is obliged +to perform, gives +rise to confusion, +if through carelessness +it is not effected +at once, as two or +more numbers may +be left showing at +one time. For this +reason, indicators +which require no +extraneous assistance +to replace +them, are preferred +by many. Indicators +with electrical +replacements meet +in part the necessities +of the case. This form of indicator consists usually +of a permanent bar magnet pivoted near its centre, +so that it can hang vertically between the two poles +of an electro-magnet placed at its lower extremity. +The upper extremity carries the number plate, which +shows through the aperture in the frame. This bar +magnet is made a trifle heavier at the upper end, so<!-- Page 139 --><span class="pagenum"><a name="Page_139" id="Page_139">[Pg 139]</a></span> +that it must rest against either the one or other pole +of the electro-magnet below. If the <i>north</i> pole of the +bar magnet rests against the <i>right</i> hand pole of the +electro-magnet when the number does not show, we +can cause the bar magnet to cross over to the other +pole, and display the number by sending a current +through the electro-magnet in such a direction as to +make its right hand pole a north pole, and its left +hand a south pole. This +is because the two north +poles will repel each other, +while the south will attract +the north. On being once +tilted over, the bar magnet +cannot return to its former +position, until the person +who used the bell sends a +current in the opposite +direction (which he can do +by means of a reversing +switch), when the poles of +the electro-magnet being +reversed, the bar magnet will be pulled back into +its original position. Indicators of this class, owing +to the fact that their replacement depends on the +<i>polarity</i> of the bar magnet, are also known as "polarised +indicators."</p> + +<div class="figcenter" style="width: 293px;"> +<a name="FIG_69" id="FIG_69"></a> +<img src="images/i_148.png" width="293" height="400" alt="Fig. 69." title="Indicator, Fall back" /> +<p class="caption">Fig. 69.</p> +</div> + +<hr /> + + +<div class="figright" style="width: 297px;"> +<a name="FIG_70" id="FIG_70"></a> +<img src="images/i_149.png" width="297" height="400" alt="Fig. 70." title="Indicator, Pendulum" /> +<p class="caption">Fig. 70.</p> +</div> + +<p><a name="SEC_65" id="SEC_65"></a>§ 65. For general efficiency and trustworthiness, the +<i>pendulum indicator</i>; as shown at <a href="#FIG_70">Fig. 70</a>, is unsurpassed. +It consists of an electro-magnet with prolongation<!-- Page 140 --><span class="pagenum"><a name="Page_140" id="Page_140">[Pg 140]</a></span> +at the free end on which is delicately pivoted a soft +iron armature. From the centre of this armature +hangs, pendulum fashion, a light brass rod carrying +a vane of fluted silver glass, or a card with a number on +it, as may be found most convenient. This vane or card +hangs just before the aperture in the indicator frame. +Stops are usually placed on each side of the pendulum +rod to limit the swing. When the electro-magnet is +magnetised by the passage of the current, the armature +is pulled suddenly on one side, and +then the pendulum swings backwards +and forwards in front of the aperture +for some minutes before it comes to +rest. When fitted with silver fluted +glass, the motion of the vane is clearly +visible even in badly lighted places. +As the pendulum, after performing +several oscillations, comes to rest by +itself in front of the aperture, this +indicator requires no setting. Messrs. +Binswanger fit these indicators with double core +magnets, and have a patented adjustment for regulating +the duration of the swings of the pendulum, which +may be made to swing for two or three minutes when +the circuit is completed by pressing the push; it then +returns to its normal position, thus saving the servant +the trouble of replacing the "drop."</p> + +<p>Messrs. Gent, of Leicester, have also patented a device +in connection with this form of indicator, which we +give in the patentee's own words:—"The objection so<!-- Page 141 --><span class="pagenum"><a name="Page_141" id="Page_141">[Pg 141]</a></span> +frequently urged against the use of Electric Bells, that +the servants cannot be depended upon to perform the +operation of replacing the signals, cannot any longer +apply, for the pendulum signals require no attention +whatever. It consists of an electro-magnet having forks +standing up in which V openings are made. An armature +of soft iron, with a piece of thin steel projecting +at each end lies suspended at the bottom of the V +opening, a brass stem carrying the signal card is +screwed into the armature, the action being, that when +a current is allowed to pass through the electro-magnet +the armature with the pendulum is drawn towards it +and held there until the current ceases to pass, when it +instantly looses its hold of the armature, which swings +away and continues to oscillate for two or three minutes, +so that if the servant happens to be out of the way, it +may be seen on her return which pendulum has been +set in motion. The Pendulum Indicator we have +recently patented is entirely self-contained. The magnet +has its projecting poles riveted into the brass base which +carries the flag. The flag is constructed as <a href="#FIG_70">Fig. 70</a>, but +swings in closed bearings, which prevents its jerking out +of its place, and enables us to send it out in position +ready for use. It will be seen this <i>patented</i> improvement +makes all screws and plates as formerly used for securing +the parts unnecessary. It will be seen at once that this +is simplicity itself, and has nothing about it which may +by any possibility be put out of order, either by warping +or shrinking of the case or carelessness of attendants."</p> + +<div class="figcenter" style="width: 600px;"> +<a name="FIG_71" id="FIG_71"></a> +<img src="images/i_151.png" width="600" height="409" alt="Fig. 71." title="Indicator, Coupled up" /> +<p class="caption">Fig. 71.</p> +</div> + +<p>There is only one point that needs further notice<!-- Page 142 --><span class="pagenum"><a name="Page_142" id="Page_142">[Pg 142]</a></span> +with regard to these pendulum indicators, and that is, +that since the rapid break and make contact of the +ringing bell interferes somewhat with the proper action +of the indicator magnet, it is always advisable to work +the indicator by means of a relay (fixed in the same +frame) and a <i>local</i> battery. This is shown in <a href="#FIG_71">Fig. 71</a>, +where a second pair of wires attached to <span class="smcap">C</span> and <span class="smcap">C</span>, to the +extreme right of the indicator frame, are brought from +the same battery to work the indicator and contained +relay. It is not advisable, however, with the pendulum +indicator, to use the same battery for the indicator; the +relay should throw a local battery into the indicator +circuit. In <a href="#FIG_71">Fig. 71</a> six pushes are shown to the left of +the indicator frame. These, of course, are supposed to +be in as many different rooms.<!-- Page 143 --><span class="pagenum"><a name="Page_143" id="Page_143">[Pg 143]</a></span></p> + +<div class="figright" style="width: 336px;"> +<a name="FIG_72" id="FIG_72"></a> +<img src="images/i_152.png" width="336" height="400" alt="Fig. 72." title="Indicator, Gent's tripolar" /> +<p class="caption">Fig. 72.</p> +</div> + +<p>We close this chapter with an engraving of a very +compact and neat form of drop indicator devised by +Messrs. Gent, and called by them a "Tripolar Indicator." +It consists, as the name implies, of a single magnet, +having one end of the iron core as one pole, the other +end extending on each side like a V, +forming, as it were, three poles. Though +but one bobbin is used, the effect is very +powerful. There are no springs or other +complications, so that the arrangement +is adapted for ship use, as are also those +represented at Figs. <a href="#FIG_67">67</a> and <a href="#FIG_68">68</a>. Pendulum +and fall-back indicators, as well as polarised +indicators, owing to the delicacy of the adjustments, are +unfitted for use on board ship, or in the cabs of lifts, +where the sudden jolts and jerks are sure to move the +indicators, and falsify the indications. The tripolar +indicator is illustrated at <a href="#FIG_72">Fig. 72</a>.</p> + + + +<hr class="long" /> +<p><!-- Page 144 --><span class="pagenum"><a name="Page_144" id="Page_144">[Pg 144]</a></span></p> +<h2><a name="CHAPTER_V" id="CHAPTER_V"></a>CHAPTER V. +<br /> +ON WIRING, CONNECTING UP, AND LOCALISING FAULTS.</h2> + + +<p><a name="SEC_66" id="SEC_66"></a>§ 66. However good may be the bells, indicators, +batteries, etc., used in an electric bell installation, if the +<i>wiring</i> be in any wise faulty, the system will surely be +continually breaking down, and giving rise to dissatisfaction. +It is therefore of the highest importance that +the workman, if he value his good name, should pay the +greatest attention to ensure that this part of his work +be well and thoroughly done. This is all the more +necessary, since while the bells, batteries, relays, pushes, +etc., are easily got at for examination and repair, the +wires, when once laid, are not so easily examined, and +it entails a great deal of trouble to pull up floor boards, +to remove skirtings etc., in order to be able to overhaul +and replace defective wires or joints. The first consideration +of course, is the kind and size of wire fitted +to carry the current for indoor and outdoor work. Now +this must evidently depend on three points. 1st, The +amount of current (in ampères) required to ring the bell. +2nd, The battery power it is intended to employ. 3rd, +The distance to which the lines are to be carried. From<!-- Page 145 --><span class="pagenum"><a name="Page_145" id="Page_145">[Pg 145]</a></span> +practical experience I have found that it is just possible +to ring a 2½" bell with ½ an ampère of current. Let +us consider what this would allow us to use, in the +way of batteries and wire, to ring such a bell. The +electro-motive force of a single Leclanchè cell is, as we +have seen at <a href="#SEC_38">§ 38</a>, about 1·6 volt, and the internal +resistance of the quart size, about 1·1 ohm. No. 20 +gauge copper wire has a resistance of about 1·2 ohm to +the pound, and in a pound (of the cotton covered wire) +there are about 60 yards. Supposing we were to use +60 yards of this wire, we should have a wire resistance +of 1·2 ohm, an internal resistance of 1·1 ohm, and a +bell resistance of about 0·1 of an ohm, altogether +about 2·4 ohms. Since the E.M.F. of the cell is 1·6 +volt, we must divide this by the total resistance to +get the amount of current passing. That is to +say:—</p> + + + +<div class="center"> +<table border="0" cellpadding="4" cellspacing="0" summary=""> +<tr><td align="center">Ohms.</td><td align="center">Volts.</td><td align="center">Ampères.</td></tr> +<tr><td align="center">2·4)</td><td align="center">1·60</td><td align="center">(0·66,</td></tr> +</table></div> + + +<p>or about 2/3 of an ampère; just a little over what +is absolutely necessary to ring the bell. Now this +would allow nothing for the deterioration in the +battery, and the increased resistance in the pushes, +joints, etc. We may safely say, therefore, that no +copper wire, of less diameter than No. 18 gauge (48/1000 +of an inch diameter) should be used in wiring up house +bells, except only in very short circuits of two or three +yards, with one single bell in circuit; and as the +difference in price between No. 18 and No. 20 is very<!-- Page 146 --><span class="pagenum"><a name="Page_146" id="Page_146">[Pg 146]</a></span> +trifling, I should strongly recommend the bell-fitter to +adhere to No. 18, as his smallest standard size. It +would also be well to so proportion the size and arrangement +of the batteries and wires, that, at the time of +setting up, a current of at least one ampère should flow +through the entire circuit. This will allow margin for +the weakening of the battery, which takes place after +it has been for some months in use. As a guide as to +what resistance a given length of copper wire introduces +into any circuit in which it may be employed, I subjoin +the following table of the Birmingham wire gauge, +diameter in 1,000ths of an inch, yards per lb., and +resistance in ohms per lb. or 100 yards, of the wires +which the fitter is likely to be called upon to +employ:—</p> + +<p>Table of Resistance and lengths per lbs. + & 100 yards of cotton covered copper wires.</p> + + +<div class="center"> +<table border="0" cellpadding="4" cellspacing="0" summary=""> +<tr><th align="right">Birmingham <br />Wire Gauge.</th><th align="right">Diameter in <br />1000th of an inch.</th><th align="center">Yards per lb.</th><th align="center">Ohms. per lb.</th><th align="center">Ohms. per 100 yards.</th></tr> +<tr><td align="right">No. 12</td><td align="right">100</td><td align="right">9</td><td align="center">0·0342</td><td align="center">0·0038</td></tr> +<tr><td align="right">14</td><td align="right">80</td><td align="right">15</td><td align="center">0·0850</td><td align="center">0·0094</td></tr> +<tr><td align="right">16</td><td align="right">62</td><td align="right">24</td><td align="center">0·2239</td><td align="center">0·0249</td></tr> +<tr><td align="right">18</td><td align="right">48</td><td align="right">41</td><td align="center">0·6900</td><td align="center">0·0766</td></tr> +<tr><td align="right">20</td><td align="right">41</td><td align="right">59</td><td align="center">1·2100</td><td align="center">0·1333</td></tr> +<tr><td align="right">22</td><td align="right">32</td><td align="right">109</td><td align="center">3·1000</td><td align="center">0·3444</td></tr> +</table></div> + + +<p><a name="SEC_67" id="SEC_67"></a>§ 67. Whatever gauge wire be selected, it must be +carefully insulated, to avoid all chance contact with nails, +staples, metal pipes or other wires. The best insulation +for wires employed indoors is gutta-percha, surrounded +with a coating of cotton wound over it, except only in +cases when the atmosphere is excessively dry. In these,<!-- Page 147 --><span class="pagenum"><a name="Page_147" id="Page_147">[Pg 147]</a></span> +as the gutta-percha is apt to crack, india-rubber as the +inner coating is preferable. If No. 18 wire be used, +the thickness of the entire insulating coating should +be thick enough to bring it up to No. 10 gauge, say +a little over 1/10th inch in diameter. There is one point +that will be found very important in practice, and that +is to have the cotton covering on the wires <i>leading</i> to +the bells of a different colour from that on the <i>return</i> +wires; in other words, the wires starting from the zinc +poles of the battery to the bells, indicators, relays, etc., +should be of a different colour from that leading from +the carbon poles to the bells, etc. Attention to this +apparently trifling matter, will save an infinite amount +of trouble in connecting up, repairing, or adding on fresh +branch circuits. For outdoor work, wire of the same +gauge (No. 18) may generally be used, but it must be +covered to the thickness of 1/10" with pure gutta-percha, +and over this must be wound tape served with Stockholm +tar. Wires of this description, either with or +without the tarred tape covering, may be obtained from +all the leading electricians' sundriesmen. Many firms +use copper wire <i>tinned</i> previous to being insulated. This +tinning serves two good purposes, 1st, the copper wire +does not verdigris so easily; 2ndly, it is more easily +soldered. On the other hand, a tinned wire is always a +little harder, and presents a little higher resistance. +Whenever wires are to be joined together, the ends to +be joined must be carefully divested of their covering +for a length of about three inches, the copper carefully +cleaned by scraping and sand-papering, twisted tightly<!-- Page 148 --><span class="pagenum"><a name="Page_148" id="Page_148">[Pg 148]</a></span> +and evenly together, as shown in <a href="#FIG_73">Fig. 73 A</a>, and soldered +with ordinary soft solder (without spirits), and a little +resin or composite candle as a flux. A heavy plumber's +soldering iron, or even a tinman's bit, is not well adapted +for this purpose, and the blowpipe is even worse, as the +great heat melts and spoils the gutta-percha covering. +The best form of bit, is one made out of a stout piece +of round copper wire ¼" thick with a nick filed in its +upper surface for the wire to lie in (see <a href="#FIG_73">Fig. 73 <span class="smcap">B</span></a>). This +may be fastened into a wooden handle, and when required +heated over the flame of a spirit lamp. When the soldering +has been neatly effected, the waste ends <i>a</i> and <i>b</i> of the +wire should be cut off flush. The wire must then be carefully +covered with warm Prout's elastic or softened gutta-percha, +heated and kneaded round the wire with the +fingers (moistened so as not to stick) until the joint is of +the same size as the rest of the covered wire. As a +further precaution, the joints should be wrapped with +a layer of tarred tape. Let me strongly dissuade<!-- Page 149 --><span class="pagenum"><a name="Page_149" id="Page_149">[Pg 149]</a></span> +the fitter from ever being contented with a simply +twisted joint. Although this may and does act +while the surfaces are still clean, yet the copper soon +oxidises, and a poor non-conducting joint is the final +result.</p> + +<p>"That'll do" will not do for electric bell-fitting.</p> + +<div class="figcenter" style="width: 400px;"> +<a name="FIG_73" id="FIG_73"></a> +<img src="images/i_157.png" width="400" height="128" alt="Fig. 73." title="Soldering iron and wires" /> +<p class="caption">Fig. 73.</p> +</div> + + +<p><a name="SEC_68" id="SEC_68"></a>§ 68. Whenever possible, the wiring of a house, etc., +for bell work, should be done as soon as the walls are +up and the roof is on. The shortest and straightest convenient +route from bell to battery, etc., should always +be chosen where practicable to facilitate drawing the +wire through and to avoid the loss of current which +the resistance of long lengths of wire inevitably entails. +The wires should be run in light zinc tubes nailed to +the wall.</p> + +<div class="figright" style="width: 279px;"> +<a name="FIG_74" id="FIG_74"></a> +<img src="images/i_160.png" width="279" height="400" alt="Fig. 74." title="Push, interior of" /> +<p class="caption">Fig. 74.</p> +</div> + + +<p>In joining up several lengths of tubing, the end of +one piece of tube should be opened out <i>considerably</i> of +a trumpet shape for the other piece to slip in; and the +end of this latter should also be <i>slightly</i> opened out, +so as not to catch in the covering of any wire drawn +through it. The greatest care must be exercised in +drawing the wires through the tubes or otherwise, that +the covering be not abraded, or else leakage at this point +may take place. In cases where tubes already exist, as +in replacing old crank bells by the electric bells, the +new wires can be drawn through the tubes, by tying +the ends of the new wire to the old wire, and carefully +pulling this out, when it brings the new wire with it. +Or if the tubes are already empty, some straight stout +wire may be run through the tubes, to which the new<!-- Page 150 --><span class="pagenum"><a name="Page_150" id="Page_150">[Pg 150]</a></span> +wires may be attached, and then drawn through, using, +of course, every possible precaution to avoid the abrasion +of the insulating covering of the wire, which would +surely entail leakage and loss of current. All the old +fittings, cranks, levers, etc., must be removed, and the +holes left, carefully filled with dowels or plaster. In +those cases where it is quite impossible to lay the wires +in zinc or wooden tubes (as in putting up wires in furnished +rooms already papered, etc.), the wires may be +run along the walls, and suspended by staples driven in +the least noticeable places; but in no case should the two +wires (go and return) lie under the same staple, for fear +of a short circuit. It must be borne in mind that each +complete circuit will require at least two wires, viz., +the one leading from the battery to the bell, and the +other back from the bell to the battery; and these +until connection is made between them by means of +the "contact" (pull, push, or key) must be perfectly +insulated from each other. In these cases, as far as +possible, the wires should be laid in slots cut in the +joists under the floor boards, or, better still, as tending +to weaken the joists less, small holes may be bored in +the joists and the wires passed through them; or +again, the wires may be led along the skirting board, +along the side of the doorpost, etc., and when the sight +of the wires is objectionable, covered with a light ornamental +wood casing. When the wires have been laid and +the position of the "pushes," etc., decided upon, the <i>blocks</i> +to which these are to be fastened must be bedded in +the plaster. These blocks may be either square or circular<!-- Page 151 --><span class="pagenum"><a name="Page_151" id="Page_151">[Pg 151]</a></span> +pieces of elm, about 3 inches across, and 1 inch thick, +bevelled off smaller above, so as to be easily and firmly +set in the plaster. They may be fastened to the brickwork +by two or three brads, at such a height to lie level +with the finished plaster. There must of course be a +hole in the centre of the block, through which the wires +can pass to the push. When the block has been fixed +in place, the zinc tube, if it does not come quite up to +the block, should have its orifice stopped +with a little paper, to prevent any +plaster, etc., getting into the tube. A +little care in setting the block will avoid +the necessity of this makeshift. A long +nail or screw driven into the block will +serve to mark its place, and save time +in hunting for it after the plastering has +been done. When the blocks have been +put in their places, and the plastering, +papering, etc., done, the wires are drawn through the +bottom hole of the push (after the lid or cover has been +taken off), <a href="#FIG_74">Fig. 74</a>, and a very small piece of the covering +of the wire having been removed from each wire, and +brightened by sand papering, one piece is passed round +the shank of the screw connected with the lower spring, +shown to the <i>right</i> in <a href="#FIG_74">Fig. 74</a>, and the other round the +shank of the screw connected to the upper spring, shown +to the <i>left</i> in the Fig. The screws must be loosened to +enable the operator to pass the wire under their heads. +The screws must then be tightened up to clench the wire +quite firmly. In doing this, we must guard against three<!-- Page 152 --><span class="pagenum"><a name="Page_152" id="Page_152">[Pg 152]</a></span> +things. Firstly, in pulling the wire through the block, +not to pull so tightly as to cut the covering against the +edge of the zinc tube. Secondly, not to uncover too +much of the wire, so as to make contact between the +wires themselves either at the back of the push, or +at any other part of the push itself. Thirdly, to +secure good contact under the screws, by having the +ends of the wires quite clean, and tightly screwed +down.</p> + +<p><a name="SEC_69" id="SEC_69"></a>§ 69. In all cases where the wires have to be taken +out of doors, such as is necessitated by communication +from house to outhouses, stables, greenhouses, etc., over +head lines (No. 18 gauge, gutta-percha tape and tar +covering) should be used. Where overhead lines are +not admissible, either as being eyesores, or otherwise, +the wires may be laid in square wooden casings of this +section <span title="box section with opening to above">┗━┛</span>, the open part of which must be covered by a +strip of wood laid over it. The wood must have been +previously creosoted, in the same manner as railway +sleepers. This mode admits of easy examination. Iron +pipes must, however, be used if the lines have to pass +under roads, etc., where there is any heavy traffic. And +it must be borne in mind that however carefully the iron +pipes, etc., be cemented at the joints, to make them +watertight, there will always be more electrical leakage +in underground lines than in overhead ones. In certain +rare cases it may be needful to use <i>iron</i> wires for this +purpose instead of copper; in this case, as iron is six or +seven times a worse conductor than copper, a much heavier +wire must be employed to get the same effect. In other<!-- Page 153 --><span class="pagenum"><a name="Page_153" id="Page_153">[Pg 153]</a></span> +words, where iron wire is used, its section must be not +less than seven times that of the copper wire which it +replaces.</p> + + +<p><a name="SEC_70" id="SEC_70"></a>§ 70. It is always preferable, where great distance +(and, consequently, greater expense) do not preclude it, +to use wire for the leading as well as for the returning +circuit. Still, where for any reason this is not practicable, +it is perfectly admissible and possible to make a +good return circuit through the <i>earth</i>, that is to make +the damp soil carry the return current (see <a href="#SEC_37">§ 37</a>). As +recommended at the section just quoted, this earth circuit +must have at each extremity a mass of some good +conductor plunged into the moist ground. In <i>towns</i>, +where there are plenty of water mains and gas mains, this +is a matter of no difficulty, the only point being to +ensure <i>good</i> contact with these masses of metal. In +other places a hole must be dug into the ground until +the point of constant moisture is reached; in this must +be placed a sheet of lead or copper, not less than five +square feet surface, to which the <i>earth</i> wires are soldered, +the hole then filled in with ordinary coke, well rammed +down to within about six inches of the surface, and then +covered up with soil well trodden down. In making +contact with water or gas pipes, care must be taken to +see that these are <i>main</i> pipes, so that they <i>do</i> lead to +earth, and not to a cistern or meter only, as, if there are +any white or red lead joints the circuit will be defective. +To secure a good contact with an iron pipe, bare it, file +its surface clean, rub it over with a bit of blue stone +(sulphate of copper) dipped in water; wipe it quite<!-- Page 154 --><span class="pagenum"><a name="Page_154" id="Page_154">[Pg 154]</a></span> +dry, bind it tightly and evenly round with some bare +copper wire (also well cleaned), No. 16 gauge. Bring +the two ends of the wire together, and twist them up +tightly for a length of three or four inches. Now heat a +large soldering bit, put some resin on the copper wire, +and solder the wire, binding firmly down to the iron +pipe. Do likewise to the projecting twist of wire, and +to this twist solder the end of the <i>return</i> wire. On no +account should the two opposite <i>earth</i> wires be soldered +to water mains and gas mains at the same time, since it +has been found that the different conditions in which +these pipes find themselves is sufficient to set up a current +which might seriously interfere with the working +of the battery proper. Sometimes there is no means of +getting a good <i>earth</i> except through the gas main: in +this case we must be careful to get to the street side of +the meter, for the red lead joints will prevent good conductivity +being obtained. In out of the way country +places, if it is possible to get at the metal pipe leading +to the well of a pump, a very good "earth" can be obtained +by soldering the wires to that pipe, in the same +manner as directed in the case of the water main. The +operator should in no case be contented with a merely +twisted joint, for the mere contact of the two metals +(copper and iron) sets up in the moist earth or air a +little electric circuit of its own, and this speedily rusts +through and destroys the wires. The following suggestions, +by Messrs. Gent, on the subject of wiring, are so +good, that we feel that we shall be doing real service to +the reader to quote them here in full:<!-- Page 155 --><span class="pagenum"><a name="Page_155" id="Page_155">[Pg 155]</a></span>—</p> + +<p>"1st.—The description of wire to be used. It is of +the utmost importance that all wires used for electric +bell purposes be of pure copper and thoroughly well +insulated. The materials mostly employed for insulating +purposes are indiarubber, gutta-percha, or cotton +saturated with paraffin. For ordinary indoor work, in +dry places, and for connecting doors and windows with +burglar alarms, or for signalling in case of fire, indiarubber +and cotton covered wires answer well; but for +connecting long distances, part or all underground, or +along walls, or in damp cellars or buildings, gutta-percha +covered wire is required, but it should be fixed +where it will not be exposed to heat or the sun, or in +very dry places, as the covering so exposed will perish, +crack, and in time fall off. This may be, to some extent, +prevented by its being covered with cotton; but +we recommend for warm or exposed positions a specially-prepared +wire, in which rubber and compound form +the insulating materials, the outside being braided or +taped.</p> + +<p>"For ordinary house work, we refer to lay a wire of +No. 18 or 20 copper, covered to No. 14 or 11 with gutta-percha, +and an outer covering of cotton, which we called +the 'battery' wire, this being the wire which conveys +the current from the battery to every push, etc., no +matter how many or in what position. The reason for +selecting this kind is, that with the gutta-percha wires +the joints may be more perfectly covered and made +secure against damp. This is of the utmost importance +in the case of '<i>battery wires</i>,' as the current is always<!-- Page 156 --><span class="pagenum"><a name="Page_156" id="Page_156">[Pg 156]</a></span> +present and ready to take advantage of any defect +in the insulation to escape to an adjoining wire, or to +'<i>earth</i>,' and so cause a continuous waste of current. +The wires leading from the pushes to the signalling +apparatus or bell we call the 'line' wires. In these, +and the rest of the house wires, the perfect covering of +the joints is important. For <i>line wires</i> we usually prefer +No. 18 or 20 copper, covered with indiarubber, and an +outer coating of cotton, well varnished. In joining the +'<i>battery wires</i>,' the place where the junction is to be +made must be carefully uncovered for the distance of +about an inch; the ends of the wire to be joined, well +cleaned, and tightly twisted together; with the flame of +a spirit lamp or candle the joint must be then heated +sufficiently to melt fine solder in strips when held upon +it, having first put a little powdered resin on the joint +as a flux; the solder should be seen to run well and adhere +firmly to the copper wire. A piece of gutta-percha +should then be taken and placed upon the joint while +warm, and with the aid of the spirit lamp and wet +fingers, moulded round until a firm and perfect covering +has been formed. <i>On no account use spirits</i> in soldering. +With the <i>line wire</i>, it is best, as far as possible, to convey +it all the way from the push to the signal box or bell in +<i>one continuous</i> length. Of course, when two or more +pushes are required to the same wire, a junction is unavoidable. +The same process of joining and covering, +as given for the battery wire, applies to the line wire. +Where many wires are to be brought down to one position, +a large tube may be buried in the wall, or a wood<!-- Page 157 --><span class="pagenum"><a name="Page_157" id="Page_157">[Pg 157]</a></span> +casing fixed flush with the plaster, with a removable +front. The latter plan is easiest for fixing and for making +alterations and additions. For stapling the wires, in no +case should the wires be left naked. When they pass +along a damp wall, it is best to fix a board and <i>loosely</i> +staple them. <i>In no case allow more than one wire to lie +under the same staple</i>, and do not let the staples touch +one another. In many cases, electric bells have been an +incessant annoyance and complete failure, through driving +the staples <i>tight up to the wires</i>, and several wires to +the same staple,—this must not be done on any account. +A number of wires may be twisted into a cable, +and run through a short piece of gutta-percha tube, and +fastened with ordinary gas hooks where it is an advantage +to do so. In running the wires, avoid hot water +pipes, and do not take them along the same way as +plumber pipes. Underground wires must be laid between +pieces of wood, or in a gas or drain pipe, and not +exposed in the bare earth without protection, as sharp +pieces of stone are apt to penetrate the covering and +cause a loss; in fact, in this, as in every part of fixing +wires, the best wire and the best protection is by far the +cheapest in the end. The copper wire in this case +should not be less than No. 16 <span class="smcap">B.W.G.</span>, covered with gutta-percha, +to No. 9 or 10 <span class="smcap">B.W.G.</span>, and preferably an outer +covering of tape or braid well tarred. Outside wire, +when run along walls and exposed to the weather, +should be covered with rubber and compound, and varnished +or tarred on an outer covering of tape or braid. +Hooks or staples must be well galvanised to prevent<!-- Page 158 --><span class="pagenum"><a name="Page_158" id="Page_158">[Pg 158]</a></span> +rusting, and fixed loosely. If the wire is contained +within an iron pipe, a lighter insulation may be used: +<i>but the pipe must be watertight</i>. In a new building, +wires must be contained within zinc or copper bell tubes. +A ⅜ inch tube will hold two wires comfortably. The tubes +should be fixed to terminate in the same positions in the +rooms as ordinary crank bell levers,—that is, about three +feet from the floor. At the side of the fireplace a block +of wood should be fixed in the wall before any plaster +is put on, and the end of the tube should terminate in +the centre of the same. A large nail or screw may be +put in to mark the place, so that the end of the tube +may be found easily when the plastering is finished. Bend +the tube slightly forward at the end, and insert a short +peg of wood to prevent dirt getting into the tube. Do +the same at the side of, or over the bed in bedroom. If +the tubes are kept clean, the wires may be easily drawn +up or down as the case may require. The best way is +to get a length of ordinary copper bell wire, No. 16, +sufficient to pass through the tube, and having stretched +it, pass it through and out at the other end. Here have +your coils of insulated wire, viz., one battery wire, which +is branched off to every push, and one line wire, which +has to go direct to the indicator or bells, and having +removed a short portion of the insulation from the end +of each, they are tied to the bare copper wire and drawn +through. This is repeated wherever a push is to be fixed +throughout the building. In making connection with +binding screws or metal of any kind, it is of the utmost +importance that everything should be <i>perfectly clean</i><!-- Page 159 --><span class="pagenum"><a name="Page_159" id="Page_159">[Pg 159]</a></span>. +<i>Joints</i> in wire, whether tinned or untinned, <i>must be +soldered and covered</i>. We cannot impress this too earnestly +on fixers. Never bury wires in plaster unprotected, +and in houses in course of erection, the <i>tubes</i> only +should be fixed until the plastering is finished, the wires +to be run in at the same time that the other work is +completed."</p> + +<div class="figcenter" style="width: 400px;"> +<a name="FIG_75" id="FIG_75"></a> +<img src="images/i_168.png" width="400" height="116" alt="Fig. 75." title="Bell, battery and push" /> +<p class="caption">Fig. 75.</p> +</div> + + +<p><a name="SEC_71" id="SEC_71"></a>§ 71. The wires having been laid by any of the +methods indicated in the preceding five sections, the +fixer is now in a position to <i>connect up</i>. No two houses +or offices will admit of this being done in <i>exactly</i> the +same way; but in the following sections most of the +possible cases are described +and illustrated, +and the intelligent fixer +will find no difficulty, +when he has once +grasped the principle, in making those trifling modifications +which the particular requirements may render +necessary. The first and simplest form, which engages +our attention, is that of a <i>single bell, battery, and push</i>, +connected by wire only. This is illustrated at <a href="#FIG_75">Fig. 75</a>. +Here we see that the bell is connected by means of one +of the wires to the zinc pole of the battery, the push or +other contact being connected to the carbon pole of the +same battery. A second wire unites the other screw +of the push or contact with the second binding screw +of the bell. There is no complete circuit until the +push is pressed, when the current circulates from +the carbon or positive pole of the battery, through the<!-- Page 160 --><span class="pagenum"><a name="Page_160" id="Page_160">[Pg 160]</a></span> +contact springs of the push, along the wire to the bell, +and then back again through the under wire to the zinc +or negative pole of the battery.<a name="FNanchor_15_15" id="FNanchor_15_15"></a><a href="#Footnote_15_15" class="fnanchor">[15]</a> It must be clearly +understood that the exact position of battery, bell, and +push is quite immaterial. What is essential is, that the +relative connections between battery, bell, and push be +maintained unaltered. <a href="#FIG_76">Fig. 76</a> shows the next simplest +case, viz., that in which a single bell and push are worked +by a single cell through an "earth" return (see <a href="#SEC_70">§ 70</a>). +Here the current is made to pass from the carbon pole +of the battery to the +push, thence along the +line wire to the bell. +After passing through +the bell, it goes to the +right-hand earth-plate +<span class="smcap">E</span>, passing through the +soil till it reaches the +left-hand earth-plate <span class="smcap">E</span>, thence back to the zinc pole +of the battery. It is of no consequence to the +working of the bell whether the battery be placed +between the push and the left-hand earth-plate, or +between the bell and the right-hand earth-plate; indeed, +some operators prefer to keep the battery as near to the +bell as possible. At <a href="#FIG_77">Fig. 77</a> is shown the mode by +which a single battery and single bell can be made to +ring from two (or more) pushes situated in different +rooms. Here it is evident that, whichever of the two<!-- Page 161 --><span class="pagenum"><a name="Page_161" id="Page_161">[Pg 161]</a></span> +pushes be pressed, the current finds its way to the bell +by the upper wire, and back home again through the +lower wire; and, even if both pushes are down at once, +the bell rings just the same, for both pushes lead from +the same pole of +the battery (the +carbon) to the same +wire (the line wire).</p> + +<div class="figcenter" style="width: 400px;"> +<a name="FIG_76" id="FIG_76"></a> +<img src="images/i_169.png" width="400" height="228" alt="Fig. 76." title="Bell, battery and push And earth return" /> +<p class="caption">Fig. 76.</p> +</div> + +<hr /> + +<div class="figcenter" style="width: 400px;"> +<a name="FIG_77" id="FIG_77"></a> +<img src="images/i_170a.png" width="400" height="113" alt="Fig. 77." title="Bell, and two pushes" /> +<p class="caption">Fig. 77.</p> +</div> + +<p>In <a href="#FIG_78">Fig. 78</a>, we +have a slight modification +of the same arrangement, a front-door <i>pull</i> +contact being inserted in the circuit; and here, in view +of the probably increased resistance of longer distance, +<i>two</i> cells are supposed to be employed instead of <i>one</i>, +and these are coupled up in series (<a href="#SEC_40">§ 40</a>), in order +to overcome this +increased resistance.</p> + +<div class="figcenter" style="width: 400px;"> +<a name="FIG_78" id="FIG_78"></a> +<img src="images/i_170b.png" width="400" height="268" alt="Fig. 78." title="Bell, two pushes and one pull" /> +<p class="caption">Fig. 78.</p> +</div> + +<p>The next case +which may occur is +where it is desired to +ring two or more +bells from one push. +There are two +manners of doing +this. The first mode +is to make the current divide itself between the two bells, +which are then said to be "<i>in parallel</i>." This mode is well +illustrated both at Figs. <a href="#FIG_79">79</a> and <a href="#FIG_80">80</a>. As in these cases +the current has to divide itself among the bells, larger +cells must be used, to provide for the larger demand; or<!-- Page 162 --><span class="pagenum"><a name="Page_162" id="Page_162">[Pg 162]</a></span> +several cells may be coupled up in parallel (<a href="#SEC_40">§ 40</a>). At +<a href="#FIG_79">Fig. 79</a> is shown the arrangement for two adjoining +rooms; at <a href="#FIG_80">Fig. 80</a>, that to be adopted when the rooms +are at some distance apart. If, as shown at <a href="#FIG_81">Fig. 81</a>, a +switch similar to that figured in the cut <a href="#FIG_64">Fig. 64</a> be +inserted at the +point where the +line wires converge +to meet the push, +it is possible for +the person using +the push to ring both bells at once, or to ring either the +right-hand or the left-hand bell at will, according to +whether he turns the arm of the switch-lever on to +the right-hand or left-hand contact plate.</p> + +<div class="figcenter" style="width: 400px;"> +<a name="FIG_79" id="FIG_79"></a> +<img src="images/i_171a.png" width="400" height="115" alt="Fig. 79." title="Two bells in parallel" /> +<p class="caption">Fig. 79.</p> +</div> + +<hr /> + +<div class="figcenter" style="width: 400px;"> +<a name="FIG_80" id="FIG_80"></a> +<img src="images/i_171b.png" width="400" height="259" alt="Fig. 80." title="Two bells in parallel Another mode" /> +<p class="caption">Fig. 80.</p> +</div> + +<hr /> + +<div class="figcenter" style="width: 400px;"> +<a name="FIG_81" id="FIG_81"></a> +<img src="images/i_172a.png" width="400" height="270" alt="Fig. 81." title="Two bells in parallel with two-way switch" /> +<p class="caption">Fig. 81.</p> +</div> + +<p>The second mode of ringing two or more bells from +one push is that of +connecting one bell +to the other, the right-hand +binding screw +of the one to the left-hand +binding screw +of the next, and so +on, and then connecting +up the whole +series of bells to +the push and battery, as if they were a single +bell. This mode of disposing the bells is called the +<i>series</i> arrangement. As we have already noticed +at <a href="#SEC_63">§ 63</a>, owing to the difference in the times at which<!-- Page 163 --><span class="pagenum"><a name="Page_163" id="Page_163">[Pg 163]</a></span> +the different contact springs of the various bells +make contact, this mode is not very satisfactory. If the +bells are single stroke +bells, they work very +well in series; but, to +get trembling bells to +work in series, it is +best to adopt the form +of bell recommended +by Mr. F. C. Allsop. +He says: "Perhaps +the best plan is to use +the form of bell shown at <a href="#FIG_82">Fig. 82</a>, which, as will be seen +from the figure, governs its vibrations, not by breaking +the circuit, but by shunting its coils. On the current flowing +round the electro-magnet, the armature is attracted, +and the spring makes contact with the lower screw.<!-- Page 164 --><span class="pagenum"><a name="Page_164" id="Page_164">[Pg 164]</a></span> +There now exists a path of practically no resistance from +end to end. The current is therefore diverted from +the magnet coils, and passes by the +armature and lower screw to the next +bell, the armature falling back against +the top screw, and repeating the previous +operation so long as the circuit +is closed. Thus, no matter how many +bells there be in the series, the circuit +is never broken. This form of bell, +however, does not ring so energetically +as the ordinary form, with a corresponding +amount of battery power."</p> + +<div class="figcenter" style="width: 329px;"> +<a name="FIG_82" id="FIG_82"></a> +<img src="images/i_172b.png" width="329" height="400" alt="Fig. 82." title="Series coupler" /> +<p class="caption">Fig. 82.</p> +</div> + +<hr /> + +<div class="figcenter" style="width: 600px;"> +<a name="FIG_83" id="FIG_83"></a> +<img src="images/i_173.png" width="600" height="157" alt="Fig. 83." title="Bell with local battery and relay" /> +<p class="caption">Fig. 83.</p> +</div> + +<p><a href="#FIG_83">Fig. 83</a> illustrates the mode in which +a bell, at a long distance, must be +coupled up to work with a local battery +and relay. The relay is not shown +separately, but is supposed to be +enclosed in the bell case. Here, on +pressing the push at the external left-hand +corner, the battery current +passes into the relay at the distant +station, and out at the right-hand +earth-plate <span class="smcap">E</span> returning to the left-hand +earth-plate <span class="smcap">E</span>. In doing this, it throws +in circuit (just as long as the push +is held down) the right-hand local +battery, so that the bell rings by the +current sent by the local battery, the more delicate relay +working by the current sent from the distant battery.<!-- Page 165 --><span class="pagenum"><a name="Page_165" id="Page_165">[Pg 165]</a></span></p> + +<div class="figcenter" style="width: 400px;"> +<a name="FIG_84" id="FIG_84"></a> +<img src="images/i_174a.png" width="400" height="269" alt="Fig. 84." title="Continuous ringing bell with wire return" /> +<p class="caption">Fig. 84.</p> +</div> + +<hr /> + +<div class="figcenter" style="width: 600px;"> +<a name="FIG_85" id="FIG_85"></a> +<img src="images/i_174b.png" width="600" height="170" alt="Fig. 85." title="Bells with Morse keys for signalling" /> +<p class="caption">Fig. 85.</p> +</div> + + <p>At <a href="#FIG_84">Fig. 84</a>, we have illustrated the mode of connecting +up a continuous ringing bell, with a wire return. Of +course, if the distance is great, or a +roadway, etc., intervene, an overhead +line and an earth plate may replace +the lines shown therein, or both lines +may be buried. It is possible, by +using a Morse key (<a href="#FIG_65">Fig. 65</a>) constructed +so as to make contact in one +direction when <i>not</i> pressed down, +and in the other <i>when</i> pressed down, +to signal from either end of a circuit, +using only one line wire and one +return. The mode of connecting up +for this purpose is shown at <a href="#FIG_85">Fig. 85</a>. +At each end we have a battery and +bell, with a double contact Morse key +as shown, the Morse key at each end +being connected through the intervention of the line wire +through the central stud. The batteries and bells at each<!-- Page 166 --><span class="pagenum"><a name="Page_166" id="Page_166">[Pg 166]</a></span> +station are connected to earth plates, as shown. Suppose +now we depress the Morse key at the right-hand station. +Since by so doing, we lift the back end of the lever, we +throw our own bell out of circuit, but make contact +between our battery and the line wire. Therefore the +current traverses the line wire, enters in the left-hand +Morse key, and, since this is not depressed, can, and +does, pass into the bell, which therefore rings, then +descends to the left-hand earth-plate, returning along +the ground to the +battery from whence +it started at the +right-hand <span class="smcap">E</span>. If, on +the contrary, the <i>left</i>-hand +Morse key be +depressed, while the +right-hand key is not +being manipulated, +the current traverses +in the opposite +direction, and the right-hand bell rings. Instead of +Morse keys, <i>double contact</i> pushes (that is, pushes +making contact in one direction when <i>not</i> pressed, and +in the opposite <i>when</i> pressed) may advantageously +be employed. This latter arrangement is shown at +<a href="#FIG_86">Fig. 86</a>.</p> + +<div class="figcenter" style="width: 400px;"> +<a name="FIG_86" id="FIG_86"></a> +<img src="images/i_175.png" width="400" height="267" alt="Fig. 86." title="Bells with double contact pushes for signalling" /> +<p class="caption">Fig. 86.</p> +</div> + +<p>It is also possible, as shown at <a href="#FIG_87">Fig. 87</a>, to send signals +from two stations, using but one battery (which, if the +distance is great, should be of a proportionate number +of cells), two bells, and two ordinary pushes. Three<!-- Page 167 --><span class="pagenum"><a name="Page_167" id="Page_167">[Pg 167]</a></span> +wires, besides the earth-plate or return wire, are required +in this case. The whole of the wires, +except the <i>return</i>, must be carefully +insulated. Suppose in this case we +press the right-hand button. The +current flows from the battery along +the lower wire through this right-hand +push and returns to the distant bell +along the top wire, down the left-hand +dotted wire back to the battery, since +it cannot enter by the left-hand press, +which, not being pushed, makes no +contact. The left-hand bell therefore +rings. If, on the other hand, the left-hand +push be pressed, the current +from the carbon of the battery passes +through the left-hand push, traverses +the central line wire, passes into the +bell, rings it, and descends to the right-hand +earth plate <span class="smcap">E</span>, traverses the earth +circuit till it reaches the left-hand +earth plate <span class="smcap">E</span>, whence it returns to +the zinc pole of the battery by the +lower dotted line.</p> + +<div class="figcenter" style="width: 600px;"> +<a name="FIG_87" id="FIG_87"></a> +<img src="images/i_176.png" width="600" height="153" alt="Fig. 87." title="Bells with double contact with one battery only" /> +<p class="caption">Fig. 87.</p> +</div> + +<p><a href="#FIG_88">Fig. 88</a> shows how the same result +(signalling in both directions) may +be attained, using only two wires, +with earth return, and two Morse +keys. The direction of the current is shown by +the arrows. Both wires must be insulated and<!-- Page 168 --><span class="pagenum"><a name="Page_168" id="Page_168">[Pg 168]</a></span> +either carried overhead or underground, buried in +tubes. <a href="#FIG_89">Fig. 89</a> shows the proper +mode of connecting the entire system +of bells, pushes, etc., running through +a building. The dotted lines are the +wires starting from the two poles +of the battery (which should consist +of more cells in proportion as there +is more work to do), the plain lines +being the wires between the pushes +and the bell and signalling box. In +this illustration a door-pull is shown +to the extreme left. Pendulum +indicators are usually connected up +as shown in this figure, except that +the bell is generally enclosed in the +indicator case. The wire, therefore, +has to be carried from the left-hand +screw of the indicator case direct to +the upper dotted line, which is the +wire returning to the zinc pole of +the battery. N.B.—When the wires +from the press-buttons are connected +with the binding-screw, of the top of +or inside of the indicator case, the +insulating material of the wires, at +the point where connection is to be +made, must be removed, and the +wires <i>carefully cleaned</i> and <i>tightly clamped down</i>.</p> + +<div class="figcenter" style="width: 600px;"> +<a name="FIG_88" id="FIG_88"></a> +<img src="images/i_177.png" width="600" height="162" alt="Fig. 88." title="Two-way signalling with one battery only" /> +<p class="caption">Fig. 88.</p> +</div> + +<hr /> + +<div class="figcenter" style="width: 600px;"> +<a name="FIG_89" id="FIG_89"></a> +<img src="images/i_178.png" width="600" height="204" alt="Fig. 89." title="Complete installation of bells, batteries, pushes, etc." /> +<p class="caption">Fig. 89.</p> +</div> + +<p>When it is desired to connect separate bells to ring<!-- Page 169 --><span class="pagenum"><a name="Page_169" id="Page_169">[Pg 169]</a></span> +in other parts of the building, the quickest way is to +take a branch wire out of the nearest <i>battery wire</i> (the +wire coming from the carbon +pole), and carry it to the push +or pull, from thence to the bell, +and from the bell back to the +zinc of the battery.</p> + + +<p><a name="SEC_72" id="SEC_72"></a>§ 72. We should advise the +fixer always to draw out a little +sketch of the arrangement he +intends to adopt in carrying out +any plan, as any means of saving +useless lengths of wire, etc., will +then easily be seen. In doing +this, instead of making full +sketches of batteries, he may use +the conventional signs <span title="battery symbol (thick and thin vertical lines)">▍▏</span> for each +cell of the battery, the thick +stroke meaning the carbon, the +thin one the zinc. Pushes may +be represented by (·), earth-plates +by [<span class="smcap">E</span>] and pulls, switches, +&c., as shown in the annexed +cut, <a href="#FIG_90">Fig. 90</a>, which illustrates a +mode of connecting up a lodge +with a house, continuous bells +being used, in such a way that +the lodge bell can be made to +ring from the lodge pull, the house bell ringing or not, +according to the way the switch (shown at top left-hand<!-- Page 170 --><span class="pagenum"><a name="Page_170" id="Page_170">[Pg 170]</a></span> +corner) is set. As it is set in the engraving, only the +lodge bell rings.</p> + +<div class="figcenter" style="width: 600px;"> +<a name="FIG_90" id="FIG_90"></a> +<img src="images/i_179.png" width="600" height="348" alt="Fig. 90." title="Mode of getting out plan or design" /> +<p class="caption">Fig. 90.</p> +</div> + + +<p><a name="SEC_73" id="SEC_73"></a>§ 73. There are still two cases of electric bell and +signal fitting, to which attention must be directed. +The first is in the case of <i>ships</i>. Here all the connections +can be made exactly as in a house, the only exception +to be made being that the indicators must not be of +the <i>pendulum</i>, or other easily displaced type; but either +of the form shown at <a href="#FIG_67">Fig. 67</a> or <a href="#FIG_68">68</a>, in which the electro-magnet +has to lift a latch to release the fall or drop, +against a pretty stiff spring. Besides being thus firmly +locking, so as not to be affected by the ship's motion, all +the wood work should be soaked in melted paraffin wax, +the iron work japanned, and the brass work well +lacquered, to protect all parts from damp. The second +case requiring notice is that of <i>lifts</i>. Every well-appointed +lift should be fitted with electric bells and<!-- Page 171 --><span class="pagenum"><a name="Page_171" id="Page_171">[Pg 171]</a></span> +indicators. In the cab of the lift itself should be placed +an electric bell, with as many double contact pushes and +indicators as there are floors to be communicated with. +At the top and at the bottom of the left shaft, as near +to the landing side as possible, must be set two stout +wooden blocks (oak, elm, or other non-perishable wood). +From top to bottom of the shaft must then be stretched, in +the same manner as a pianoforte is strung, on stout metal +pins, with threading holes and square heads, as many +No. 12 or 14 bare copper wires as there are floors or +landings, and two more for the battery and return wire +respectively. Care must be taken that these wires are strung +perfectly parallel, and that they are stretched quite taut, +but not strained, otherwise they will surely break. To the +top of the cab, and in connection in the usual manner +by wires with the bell and indicator (which, as in the case +of ships, must be of the locking type, lest the jolts of the +cab disturb their action) must be attached a number of +spoonbill springs, which press against the naked wires +running down the shaft. The shape of these springs +(which should be of brass) at the part where they press +against the bare wires, is similar to that of the spoon +break of a bicycle. Some operators use rollers at the +end of the spring instead of spoonbills, but these latter +<i>rub</i> the wires and keep up good contact, while the rollers +slip over the wires and do not keep them clean. By +means of these springs, the current from the batteries, +which are best placed either at the top of the lift itself, +or in one of the adjacent rooms (never at the bottom of +the shaft, owing to the damp which always reigns there),<!-- Page 172 --><span class="pagenum"><a name="Page_172" id="Page_172">[Pg 172]</a></span> +can be taken off and directed where it is desired, precisely +as if the batteries were in the cab itself. It is +usual (though not obligatory) to use the two wires <i>furthest</i> +from the landing as the go and return battery wires, +and from these, through the other wires, all desired +communication with the landings can be effected. To +obtain this end, it will be necessary to furnish every landing +with a double contact push and bell, and each bell +and push must be connected up to the shaft wires in the +following mode:—</p> + +<p>A wire must be led from the <i>lower</i> contact spring of +the double contact push, to the <i>main battery carbon wire</i> +in the shaft. A second wire is led from the <i>upper contact +stop</i> of the double contact push to the bell, and thence +to the <i>main battery zinc wire</i> on the shaft. Lastly, a +third wire is taken from the <i>upper contact spring</i> of the +push and connected to that particular wire in the shaft +which by means of the spoonbill springs connects the +particular push and indicator in the cab, destined to +correspond with it. It will be seen that with the exception +of using the rubbing spoonbill springs and return +wires in the shaft, this arrangement is similar to that +illustrated at <a href="#FIG_87">Fig. 87</a>.</p> + +<div class="figcenter" style="width: 267px;"> +<a name="FIG_91" id="FIG_91"></a> +<img src="images/i_182.png" width="267" height="400" alt="Fig. 91." title="Lift fitted with bells" /> +<p class="caption">Fig. 91.</p> +</div> + +<p>A glance at <a href="#FIG_91">Fig. 91</a> will render the whole system of +wiring and connecting up with lifts and landing, perfectly +clear. In connecting the branch lines to the main +bare copper wires in the shaft, in order that the spoonbill +springs should not interfere with them, they (the +ends of the branch wires) must be bent at right angles, +like a letter L, and the upright portion soldered neatly<!-- Page 173 --><span class="pagenum"><a name="Page_173" id="Page_173">[Pg 173]</a></span> +to the <i>back</i> of the shaft wire. Any solder which may +flow over to the <i>front</i> of the wire must be carefully +scraped off to prevent any bumps affecting the smooth +working of the contact springs. It will be evident on +examination of <a href="#FIG_91">Fig. 91</a>, that if any of the pushes on the +landings be pressed, the circuit is completed between +the battery at the top, through the two battery wires<!-- Page 174 --><span class="pagenum"><a name="Page_174" id="Page_174">[Pg 174]</a></span> +to the bell and one of the indicators to the cab, and, on +the other hand, that if a push be pressed in the cab, a +corresponding bell on the landing will be rung, precisely +as in <a href="#FIG_87">Fig. 87</a>.</p> + +<p>Some fitters employ a many-stranded cable to convey +the current to and from the battery to the cab and landing, +instead of the system of stretched wires herein recommended; +but this practice cannot be advocated, as +the continual bending and +unbending of this cable, +repeated so frequently every +day, soon breaks the leading +wires contained in the cable.</p> + + +<div class="figright" style="width: 319px;"> +<a name="FIG_92" id="FIG_92"></a> +<img src="images/i_183.png" width="319" height="400" alt="Fig. 92." title="Magneto bell: generator" /> +<p class="caption">Fig. 92.</p> +</div> + +<p><a name="SEC_74" id="SEC_74"></a>§ 74. In many cases where +a "call" bell alone is required, +the battery may be entirely +dispensed with, and a small +dynamo (<a href="#SEC_15">§ 15</a>) employed instead. +The entire apparatus +is then known as the +"magneto-bell," and consists +essentially of two parts, viz., the generator, <a href="#FIG_92">Fig. 92</a>, +and the bell, <a href="#FIG_93">Fig. 93</a>. The <i>generator</i> or <i>inductor</i> consists +of an armature, which by means of a projecting +handle and train of wheels can be revolved rapidly +between the poles of a powerful magnet; the whole being +enclosed in a box. The current produced by the revolution +of the armature is led to the two binding screws +at the top of the box. By means of two wires, or one +wire and an earth circuit, the current is led to the<!-- Page 175 --><span class="pagenum"><a name="Page_175" id="Page_175">[Pg 175]</a></span> +receiver or bell case, <a href="#FIG_93">Fig. 93</a>. Here, there are usually +two bells, placed very near one another, and the armature +attached to the bell clapper is so arranged between the +poles of the double-bell magnets, that it strikes alternately +the one and the other, so that a clear ringing is +kept up as long as the handle is being turned at the +generator.</p> + +<div class="figcenter" style="width: 400px;"> +<a name="FIG_93" id="FIG_93"></a> +<img src="images/i_184.png" width="400" height="391" alt="Fig. 93." title="Magneto bell: Receiver" /> +<p class="caption">Fig. 93.</p> +</div> + +<hr /> + +<div class="figcenter" style="width: 340px;"> +<a name="FIG_94" id="FIG_94"></a> +<img src="images/i_185a.png" width="340" height="400" alt="Fig. 94." title="Magneto bell: Combined" /> +<p class="caption">Fig. 94.</p> +</div> + +<p>If a <i>combined</i> generator and bell be fitted at each +end of a line, it becomes possible to communicate both +ways; one terminal of each +instrument must be connected +to the line, and the other terminal +on each to earth. A combined +generator and bell is shown at +<a href="#FIG_94">Fig. 94</a>. These instruments are +always ready for use, require no +battery or press-buttons. The +generator, <a href="#FIG_92">Fig. 92</a>, will ring seven +bells simultaneously, if required, +so powerful is the current set up; and by using a switch +any number of bells, placed in different positions, can +be rung, by carrying a separate wire from the switch +to the bell.</p> + +<div class="figcenter" style="width: 309px;"> +<a name="FIG_95" id="FIG_95"></a> +<img src="images/i_185b.png" width="309" height="400" alt="Fig. 95." title="Detector or galvanometer" /> +<p class="caption">Fig. 95.</p> +</div> + + +<p><a name="SEC_75" id="SEC_75"></a>§ 75. Our work would not be complete unless we +pointed out the means necessary to detect faults in our +work. In order to localise faults, two things are requisite: +first, a means of knowing whether the battery itself is +working properly, that is to say, giving the due <i>amount</i> +of current of the right <i>pressure</i>, or E.M.F.; secondly, a +means of detecting whether there is leakage, or loss of<!-- Page 176 --><span class="pagenum"><a name="Page_176" id="Page_176">[Pg 176]</a></span> +current, or break of circuit in our lines. Fortunately, +the means of ascertaining these data can be all combined +in one instrument, known as a linesman's galvanometer +or detector, of which we give an +illustration at <a href="#FIG_95">Fig. 95</a>. It will be remembered +(<a href="#SEC_10">§ 10</a>) that if a current be +passed over or under a poised magnetic +needle, parallel to it, the needle is +immediately deflected out of the +parallel line, and swings round to the +right or left of the current, according to +the <i>direction</i> of the current; likewise +that the needle is deflected farther from the original +position as the current becomes stronger. The deflections, +however, are not proportionate +to the strength of the +current, being fairly so up to +about 25 to 30 degrees of arc +out of the original position, but +being very much less than +proportionate to the current +strength as the needle gets +farther from the line of current; +so that a current of infinite +strength would be required to +send the needle up to 90°. On +this principle the detector is +constructed. It consists of a lozenge-shaped magnetic +needle, suspended vertically on a light spindle, carrying at +one end a pointer, which indicates on a card, or metal dial,<!-- Page 177 --><span class="pagenum"><a name="Page_177" id="Page_177">[Pg 177]</a></span> +the deflection of the needle. Behind the dial is arranged +a flat upright coil of wire (or two coils in many cases) +parallel to the needle, along which the current to be +tested can be sent. The needle lies between the front +and back of the flat coil. The whole is enclosed in a +neat wooden box, with glazed front to show the dial, +and binding screws to connect up to the enclosed coil or +coils. If the coil surrounding the needle be of a few +turns of coarse wire, since it opposes little resistance to +the passage of the current, it will serve to detect the +presence of large <i>quantities</i> of electricity (many ampères) +at a low pressure; this is called a <i>quantity</i> coil. If, on +the other hand, the coil be one of fine wire, in many +convolutions, as it requires more <i>pressure</i>, or E.M.F., +or "intensity" to force the current through the fine +high-resistance wire, the instrument becomes one +fitted to measure the voltage or <i>pressure</i> of the +current, and the coil is known as the "intensity." +If both coils are inserted in the case, so that either can +be used at will, the instrument is capable of measuring +either the quantity of electricity passing, or the pressure +at which it is sent, and is then known as a quantity and +intensity detector. No two galvanometers give exactly +the same deflection for the same amount of current, or +the same pressure; the fitter will therefore do well to +run out a little table (which he will soon learn by heart) +of the deflection <i>his</i> instrument gives with 1, 2, 3, 4, 5 +and 6 Leclanché's <i>coupled in parallel</i>, when connected +with the quantity coil. He will find the smaller sizes +give less current than the larger ones. In testing the<!-- Page 178 --><span class="pagenum"><a name="Page_178" id="Page_178">[Pg 178]</a></span> +deflections given by the intensity coil, he must remember +to couple his cells <i>in series</i>, as he will get no increase +in <i>tension</i> or <i>pressure</i> by coupling up in parallel. In +either case the cells should be new, and freshly set up, +say, within 24 hours. As some of my readers may like +to try their skill at constructing such a detector, I transcribe +the directions given in "Amateur work" by Mr. +Edwinson:—</p> + + +<p><a name="SEC_76" id="SEC_76"></a>§ 76. "Such an instrument, suitable for detecting the +currents in an electric bell circuit, may be made up at the +cost of a few shillings for material, and by the exercise of +a little constructive ability. We shall need, first of all, a +magnetised needle; this can be made out of a piece of +watch spring. Procure a piece of watch spring two +inches long, soften it by heating it to redness, and +allowing it to cool gradually in a bed of hot ashes; +then file it up to the form of a long lozenge, drill a +small hole in the centre to receive the spindle or pivot, +see that the needle is quite straight, then harden it by +heating it again to a bright red and plunging it at once into +cold water. It now has to be magnetised. To do this, +rub it on a permanent horse-shoe, or other magnet, +until it will attract an ordinary sewing needle strongly, +or wrap it up in several turns of insulated line wire, and +send many jerky charges of electricity from a strong +battery through the wire. When it has been well magnetised, +mount it on a spindle of fine hard wire, and +secure it by a drop of solder. We will next turn our +attention to the case, bobbin, or chamber in which the +needle has to work. This may be made out of card<!-- Page 179 --><span class="pagenum"><a name="Page_179" id="Page_179">[Pg 179]</a></span>board +entirely, or the end pieces may be made of ivory +or ebonite, or it may be made out of thin sheet brass; +for our purpose we will choose cardboard. Procure a +piece of stout cardboard 4¾ inches long by 2 inches +wide, double it to the form of a Tãndstickor match-box, +and pierce it in exactly opposite sides, and in the +centre of those sides with holes for the needle spindle. +Now cut another piece of stout, stiff cardboard 2¾ inches +long by ¾ inch wide, and cut a slit with a sharp knife +to exactly fit the ends of the case or body already prepared. +The spindle holes must now be bushed with +short lengths of hard brass or glass bugles, or tubing, +made to allow the spindle free movement, and these +secured in position by a little melted shellac, sealing-wax, +or glue. The needle must now be placed in the +case, the long end of the spindle first, then the short +end in its bearing; then, whilst the case with the needle +enclosed is held between the finger and thumb of the +left hand, we secure the joint with a little glue or with +melted sealing-wax. The end-pieces are now to be put +on, glued, or sealed in position, and set aside to get firm, +whilst we turn our attention to other parts. The case, +5 inches by 4 inches by 2 inches in depth, may be +improvised out of an old cigar-box, but is best made of +thin mahogany or teak, nicely polished on the outside, +and fitted with a cover sliding in a groove, or hinged to +form the back of the instrument. The binding screws +should be of the pattern known as the telegraph pattern, +fitted with nuts, shown at <a href="#FIG_27">Fig. 27</a>. A small brass +handle to be fitted to the top of the instrument,<!-- Page 180 --><span class="pagenum"><a name="Page_180" id="Page_180">[Pg 180]</a></span> +will also be handy. A circular piece of smooth +cardboard 3¼ inches in diameter, with a graduated +arc, marked as shown in <a href="#FIG_95">Fig. 95</a>, will serve the purpose +of a dial, and a piece of thin brass, bent to the form of +┏━┓, will be required as a needle guard. The face +of the dial may be a circular piece of glass, held in a +brass ogee, or a hole the size of the dial may be cut in +a piece of thin wood; this, glazed on the inside with a +square of glass, may be made to form the front of the +instrument over the dial. An indicating needle will also +be required for an outside needle; this is usually +made of watch spring, and nicely blued; but it may +be made of brass or any other metal, one made of +aluminium being probably the best on account of its +lightness. It must be pierced with a hole exactly in +the centre, so as to balance it as the beam of scales +should be balanced, and should one end be heavier than +the other it must be filed until they are equal.</p> + +<p>We will now turn our attention to the coil.</p> + +<p>Procure sixpennyworth of No. 36 silk-covered copper +wire and wind three layers of it very evenly on the coil +case or bobbin, being careful in passing the needle +spindle not to pinch it or throw it out of truth. When +this has been wound on, it will be found that one end of +the wire points to the left and the other end to the right. +These are destined to be connected to the under side of +the binding screws shown on the top of <a href="#FIG_95">Fig. 95</a>. We +therefore secure them to their respective sides with a +touch of sealing wax, and leave enough wire free at the +ends to reach the binding screws—say, about 6 inches.<!-- Page 181 --><span class="pagenum"><a name="Page_181" id="Page_181">[Pg 181]</a></span> +It is handy to have an additional coil for testing strong +currents, and as this may be combined in one instrument +at a trifle additional cost, we will get some line wire +(No. 22) and wind six or eight turns of it around the +coil outside the other wire; one end of this wire will be +attached to an additional binding screw placed between +the others, and the other end to left binding screw +shown. The coil thus prepared may now be mounted +in position. Pierce the board dial and the wood at its +back with a hole large enough for the needle spindle to +pass through from the back to the centre of the dial. +See that the thick end of the inside needle hangs downwards, +then place the coil in the position it is intended +to occupy, and note how far the needle spindle protrudes +on the face of the dial. If this is too long, nip +off the end and file it up taper and smooth until it will +work freely in a hole in the needle guard, with all parts +in their proper places. This being satisfactory, secure +the coil in its place by sealing wax, or, better still, by +two thin straps of brass, held by screws at each end, +placed across the coil. Now clean the free ends of the +coil wires, insert them under the nuts of the binding +screws, fix the indicating needle on the end of the spindle +outside, and see that it hangs in a vertical position with +the inside needle when the instrument is standing on a +level surface. Secure it in this position, screw on the +needle guard, fasten on the glass face, and the instrument +will be complete.</p> + + +<p><a name="SEC_77" id="SEC_77"></a>§ 77. Provided thus with an efficient detector, the +fitter may proceed to test his work. In cases of <!-- Page 182 --><span class="pagenum"><a name="Page_182" id="Page_182">[Pg 182]</a></span> +<i>new installations</i>, take the wire off the carbon binding screw +of the battery and attach it to one screw of the galvanometer +(on the intensity coil side), next attach a piece +of wire from the other binding screw of the galvanometer +(the central one) so as to place the galvanometer +in circuit. <i>There should be no movement of the needle</i>, +and in proportion to the deflection of the needle, so will +the loss or waste be. If loss is going on, every means +must be used to remedy it. It is of the utmost importance +to the effective working of the battery and bells +that not the <i>slightest leakage</i> or <i>local action</i> should be +allowed to remain. However slight such loss may be, +it will eventually ruin the battery. Let damp places be +sought out, and the wires removed from near them. Bad +or injured coverings must also be looked for, such as +may have been caused by roughly drawing the wires +across angular walls, treading on them, or driving staples +too tightly over them. Two or more staples may be +touching, or two or more wires carelessly allowed to lie +under one staple. The wire may have been bared in +some places in passing over the sharp edges of the zinc +tube. The backs of the pushes should be examined to see +if too much wire has been bared, and is touching another +wire at the back of the push-case itself. Or the same +thing may be taking place at the junction with the +relays or at the indicator cases. Should the defect not +be at any of these places, the indicator should next be +examined, and wire by wire detached (not cut) until the +particular wire in which the loss is going on has been +found. This wire should then be traced until the defect<!-- Page 183 --><span class="pagenum"><a name="Page_183" id="Page_183">[Pg 183]</a></span> +has been discovered. In testing underground wires for +a loss or break, it will be necessary first to uncouple the +<i>distant</i> end, then to disconnect the other end from the +instruments, and attach the wire going underground to +the screw of the galvanometer. A piece of wire must +then be taken from the other screw of the detector to +the carbon end of the battery, and a second wire from +the zinc end of the battery to the earth plate or other +connection. Proceeding to that part of the wire where +the injury is suspected, the wire is taken up, and a temporary +earth connection having been made (water main, +gas pipe, etc.), and by means of a sharp knife connected +with this latter, the covering of the suspected wire +penetrated through to the wire, so as to make a good +connection between this suspected wire and the temporary +earth plates. If, when this is done, the needle +is deflected fully, the injury is farther away from the +testing end, and other trials must be made farther on, +until the spot is discovered. Wherever the covering of +the wire has been pierced for testing, it must be carefully +recovered, finished off with Prout's elastic glue, or +gutta-percha, and made quite sound. The connections +with the earth plates very frequently give trouble, the +wires corrode or become detached from the iron pipes +etc., and then the circuit is broken.</p> + + +<p><a name="SEC_78" id="SEC_78"></a>§ 78. When the fitter is called to localise defects +which may have occurred in an installation which has +been put up some time, before proceeding to work +let him ask questions as to what kind of defect there +is, and when and where it evinces itself. If all the<!-- Page 184 --><span class="pagenum"><a name="Page_184" id="Page_184">[Pg 184]</a></span> +bells have broken down, and will not ring, either the +battery or the main go and return wires are at fault. +Let him proceed to the battery, examine the binding +screws and connected wires for corrosion. If they are +all right, let the batteries themselves be tested to see +if they are giving the right amount of current. This +should be done with the quantity coil of the detector. +Should the battery be faulty, it will be well to renew the +zincs and recharge the battery, if the porous cell be still +in good condition; if not, new cells should be substituted +for the old ones. Should the battery be all right, and +still none of the bells ring, a break or bad contact, +or short circuit in the main wires near the battery +may be the cause of the mischief. If some bell rings +continuously, there must be a short circuit in the push +or pushes somewhere; the upper spring of one of the +pushes may have got bent, or have otherwise caught +in the lower spring. <i>Pulls</i> are very subject to this +defect. By violent manipulations on the part of +mischievous butcher or baker boys, the return spring +may be broken, or so far weakened as not to return +the pull into the "off" position. If, the batteries being +in good order, any bell rings feebly, there is either +leakage along its line, or else bad contact in the push +or in the connections of the wires to and from the +push. There should be platinum contacts at the ends +of the push springs; if there are not, the springs may +have worked dirty at the points of contact, hence the +poor current and poor ringing. It is seldom that the +bells themselves, unless, indeed, of the lowest quality,<!-- Page 185 --><span class="pagenum"><a name="Page_185" id="Page_185">[Pg 185]</a></span> +give any serious trouble. Still the set screw may have +shaken loose (which must then be adjusted and tightened +up), or the platinum speck has got solder on its +face and therefore got oxidised. This may be scraped +carefully with a penknife until bright. Or, purposely +or inadvertently, no platinum is on the speck at all, +only the solder. A piece of platinum foil should be +soldered on the spot, if this is so. Or again (and this +only in very bad bells), the electro-magnets being of +hard iron, may have retained a certain amount +of <i>permanent magnetism</i>, and pull the armature into +permanent contact with itself. This can be remedied +by sticking a thin piece of paper (stamp paper will do) +over the poles of the magnet, between them and the +armature. In no case should the fitter <i>cut</i> or <i>draw up</i> +out of tubes, etc., any wire or wires, without having first +ascertained that the fault is in that wire; for, however +carefully joints are made, it is rare that the jointed +places are so thoroughly insulated as they were before +the cutting and subsequent joining were undertaken. +To avoid as much as possible cutting uselessly, let +every binding screw be examined and tightened up, +and every length of wire, which it is possible to get at, +be tested for continuity before any "slashing" at the +wires, or furious onslaughts on the indicator be consummated.</p> + +<p>In conclusion, I beg to record my thanks for the very +generous assistance which I have received in the compilation +of the foregoing pages from the electrical +firms of Messrs. Blakey Emmot, Binswanger, Gent, +Judson, Jensen, and Thorpe.</p> + + +<div class="footnote"><p><a name="Footnote_15_15" id="Footnote_15_15"></a><a href="#FNanchor_15_15"><span class="label">[15]</span></a> It must be borne in mind that the negative element is that to which +the positive pole is attached, and <i>vice versâ</i> (see ss. 8 and 9).</p></div> + + + +<hr class="long" /> +<p><!-- Page 186 --><span class="pagenum"><a name="Page_186" id="Page_186">[Pg 186]</a></span></p> +<h2><a name="ADDENDUM" id="ADDENDUM"></a>ADDENDUM. +<br /> +<span class="smcap">The Gassner Battery.</span></h2> + + +<p>Since the compilation of the foregoing pages, a <i>dry +battery</i>, known by the above name, has found great +favour with electric-bell fitters. Its peculiarity consists +in the zinc element forming the outside cell. In this is +placed the carbon, which is separated from the zinc by +a thick paste or jelly made of gypsum and oxide of +zinc. The cell can be placed in any position, works as +well on its side as upright, is not subject to creeping, +has an E.M.F. of about 1·5 volt, with an internal resistance +of only 0·25 ohm in the round form, and 0·6 in +the flat form. The Gassner dry battery polarizes much +less quickly than the ordinary Leclanché. The only +defects at present noticeable, are the flimsy connections, +and the fact that the outer cases being <i>metal</i> must be +carefully guarded from touching one another. This +can be effected by enclosing in a partitioned <i>wooden box</i>.<!-- Page 187 --><span class="pagenum"><a name="Page_187" id="Page_187">[Pg 187]</a></span></p> + + + +<hr class="long" /> +<h2><a name="INDEX" id="INDEX"></a>INDEX.</h2> + + + +<p>A.</p> +<ul> +<li>Acid, Chromic, <a href="#Page_33">33</a>, <a href="#Page_46">46</a></li> +<li class="indent1">Hydrobromic, <a href="#Page_20">20</a></li> +<li class="indent1">Hydrochloric, <a href="#Page_20">20</a></li> +<li class="indent1">Hydriodic, <a href="#Page_20">20</a></li> +<li class="indent1">Nitric, <a href="#Page_20">20</a></li> +<li class="indent1">Sulphuric, <a href="#Page_20">20</a></li> +<li>Action in Bichromate, <a href="#Page_47">47</a></li> +<li class="indent1">Dotting, <a href="#Page_116">116</a></li> +<li class="indent1">of electric bell, <a href="#Page_81">81</a></li> +<li class="indent1">Leclanché, <a href="#Page_35">35</a></li> +<li class="indent1">Relay, <a href="#Page_134">134</a></li> +<li class="indent1">Rubbing, <a href="#Page_116">116</a></li> +<li class="indent1">of zinc on acids, <a href="#Page_21">21</a></li> +<li>Agglomerate block, <a href="#Page_38">38</a></li> +<li class="indent1">Cell, <a href="#Page_38">38</a></li> +<li class="indent1">Compo, <a href="#Page_38">38</a></li> +<li>Alarms, Burglar, <a href="#Page_113">113</a></li> +<li class="indent1">Fire, <a href="#Page_123">123</a></li> +<li class="indent1">Frost, <a href="#Page_121">121</a></li> +<li class="indent1">Thermometer, <a href="#Page_122">122</a></li> +<li class="indent1">Thief, <a href="#Page_113">113</a></li> +<li class="indent1">Watch, <a href="#Page_124">124</a></li> +<li>Amber, <a href="#Page_1">1</a></li> +<li>Ampère, <a href="#Page_55">55</a></li> +<li>Ampère's law, <a href="#Page_11">11</a></li> +<li>Annealing iron, <a href="#Page_13">13</a></li> +<li>Arrangement of bells for lifts, <a href="#Page_171">171</a></li> +<li class="indent1">Ships, <a href="#Page_170">170</a></li> +<li>Attraction, <a href="#Page_3">3</a></li> +</ul> + +<p>B.</p> +<ul> +<li>Batteries, <a href="#Page_18">18</a></li> +<li>Battery agglomerate, <a href="#Page_39">39</a></li> +<li>Battery, Bichromate, <a href="#Page_48">48</a></li> +<li class="indent1">Bunsen, <a href="#Page_33">33</a></li> +<li class="indent1">Chromic acid, <a href="#Page_46">46</a></li> +<li class="indent1">Daniell's, <a href="#Page_29">29</a></li> +<li class="indent1">Gassner (addendum), <a href="#Page_186">186</a></li> +<li class="indent1">Gent's, <a href="#Page_44">44</a></li> +<li class="indent1">Gravity, <a href="#Page_31">31</a></li> +<li class="indent1">Modified, <a href="#Page_120">120</a></li> +<li class="indent1">Grenet, <a href="#Page_46">46</a></li> +<li class="indent1">Grove, <a href="#Page_33">33</a></li> +<li class="indent1">Judson's, <a href="#Page_41">41</a></li> +<li class="indent1">Leclanché, <a href="#Page_33">33</a></li> +<li class="indent1">Reversed, <a href="#Page_46">46</a></li> +<li class="indent1">Minotto, <a href="#Page_31">31</a></li> +<li class="indent1">Smee's, <a href="#Page_27">27</a></li> +<li class="indent1">Walker's, <a href="#Page_27">27</a></li> +<li>Bell action, case for, <a href="#Page_88">88</a></li> +<li>Blocks, wooden, <a href="#Page_150">150</a></li> +<li>Bobbins, electric bell, <a href="#Page_67">67</a></li> +<li>Box for batteries, <a href="#Page_43">43</a></li> +<li>Brushes, dynamo, <a href="#Page_17">17</a></li> +</ul> + + +<p>C.</p> +<ul> +<li>Cable, many stranded, <a href="#Page_174">174</a></li> +<li>Case for bell action, <a href="#Page_88">88</a></li> +<li>Cells in parallel, <a href="#Page_57">57</a></li> +<li class="indent1">series, <a href="#Page_53">53</a></li> +<li>Charging fluid, recipes, <a href="#Page_48">48</a></li> +<li class="indent1">Fuller, <a href="#Page_49">49</a></li> +<li>Circuits, closed, <a href="#Page_52">52</a>, <a href="#Page_118">118</a></li> +<li class="indent1">Of bells complete in house, <a href="#Page_168">168</a></li> +<li class="indent1">For signalling, <a href="#Page_167">167</a></li> +<li class="indent1">In both directions, <a href="#Page_168">168</a><!-- Page 188 --><span class="pagenum"><a name="Page_188" id="Page_188">[Pg 188]</a></span></li> +<li>Circuits of bells with Morse key, <a href="#Page_165">165</a></li> +<li class="indent1">In parallel, <a href="#Page_161">161</a></li> +<li class="indent1">Series, <a href="#Page_162">162</a></li> +<li class="indent1">With relay, <a href="#Page_164">164</a></li> +<li class="indent1">Single bell and wire, <a href="#Page_159">159</a></li> +<li class="indent1">Earth, <a href="#Page_160">160</a></li> +<li class="indent1">Two pushes, <a href="#Page_161">161</a></li> +<li class="indent1">Push and pull, <a href="#Page_161">161</a></li> +<li class="indent1">Open, <a href="#Page_52">52</a></li> +<li>Closed circuit system, <a href="#Page_118">118</a></li> +<li>Code for signalling, <a href="#Page_130">130</a></li> +<li>Coil spring, <a href="#Page_108">108</a></li> +<li>Conductors, <a href="#Page_3">3</a></li> +<li>Connecting up, <a href="#Page_144">144</a>, <a href="#Page_159">159</a></li> +<li>Contacts, burglar alarm, <a href="#Page_113">113</a></li> +<li class="indent1">Door, <a href="#Page_116">116</a></li> +<li class="indent1">Drawer, <a href="#Page_121">121</a></li> +<li class="indent1">Floor, <a href="#Page_113">113</a></li> +<li class="indent1">For closed circuits, <a href="#Page_121">121</a></li> +<li class="indent1">Mackenzie's humming, <a href="#Page_113">113</a></li> +<li class="indent1">Shop door, <a href="#Page_116">116</a></li> +<li class="indent1">Till, <a href="#Page_121">121</a></li> +<li class="indent1">Watch alarm, <a href="#Page_124">124</a></li> +<li class="indent1">Window sash, <a href="#Page_116">116</a></li> +<li>Corrugated carbons, <a href="#Page_41">41</a></li> +<li>Creeping in cells, <a href="#Page_43">43</a></li> +<li class="indent1">To remedy, <a href="#Page_44">44</a></li> +<li>Callow's attachment, <a href="#Page_99">99</a></li> +<li>Current, <a href="#Page_54">54</a></li> +<li class="indent1">To ring bell, <a href="#Page_145">145</a></li> +</ul> + + +<p>D.</p> +<ul> +<li>Daniell's cell, <a href="#Page_29">29</a></li> +<li class="indent1">Action in, <a href="#Page_29">29</a></li> +<li>Deflection of needle, <a href="#Page_9">9</a>, <a href="#Page_11">11</a></li> +<li>Detector or galvanometer, to make, <a href="#Page_178">178</a></li> +<li>Detent lever, <a href="#Page_94">94</a></li> +<li>Door contact, <a href="#Page_116">116</a></li> +<li>Dotting action, <a href="#Page_116">116</a></li> +<li>Drawing out plans, <a href="#Page_169">169</a></li> +<li>Dynamo, <a href="#Page_15">15</a></li> +<li class="indent1">Armature, <a href="#Page_16">16</a></li> +<li class="indent1">Brushes, <a href="#Page_17">17</a></li> +<li class="indent1">Commutator, <a href="#Page_17">17</a></li> +<li>Dynamo, Cumulative effects, <a href="#Page_7">17</a></li> +<li class="indent1">Field magnets, <a href="#Page_16">16</a></li> +</ul> + +<p>E.</p> +<ul> +<li>Earth, <a href="#Page_52">52</a></li> +<li class="indent1">Plate, <a href="#Page_53">53</a></li> +<li class="indent1">Return, <a href="#Page_153">153</a></li> +<li>Electric bell, action of, <a href="#Page_81">81</a></li> +<li class="indent1">Armature, <a href="#Page_74">74</a></li> +<li class="indent1">Base, <a href="#Page_61">61</a></li> +<li class="indent1">Bobbins, <a href="#Page_67">67</a></li> +<li class="indent1">Contact screw, <a href="#Page_75">75</a></li> +<li class="indent1">Continuous, <a href="#Page_92">92</a></li> +<li class="indent1">Circular bell, <a href="#Page_106">106</a></li> +<li class="indent1">Gong, <a href="#Page_77">77</a></li> +<li class="indent1">How to make, <a href="#Page_60">60</a></li> +<li class="indent1">In lifts, <a href="#Page_171">171</a></li> +<li class="indent1">Ships, <a href="#Page_170">170</a></li> +<li class="indent1">Jensen's, <a href="#Page_101">101</a></li> +<li class="indent1">Joining E. M. wire, <a href="#Page_73">73</a></li> +<li class="indent1">Magnets, <a href="#Page_63">63</a></li> +<li class="indent1">Magneto, <a href="#Page_174">174</a></li> +<li class="indent1">Mining, <a href="#Page_106">106</a></li> +<li class="indent1">Paraffining, <a href="#Page_69">69</a></li> +<li class="indent1">Platinum tip, <a href="#Page_76">76</a></li> +<li class="indent1">Putting together, <a href="#Page_78">78</a></li> +<li class="indent1">Single stroke, <a href="#Page_91">91</a></li> +<li class="indent1">Spring, <a href="#Page_74">74</a></li> +<li class="indent1">Thorpe's, <a href="#Page_100">100</a></li> +<li class="indent1">Trembling, <a href="#Page_81">81</a>, <a href="#Page_90">90</a></li> +<li class="indent1">Winding wire on, <a href="#Page_71">71</a></li> +<li class="indent1">Wire for, <a href="#Page_69">69</a></li> +<li class="indent1">Trumpet, <a href="#Page_107">107</a></li> +<li>Electricity, sources of, <a href="#Page_2">2</a></li> +<li>Electrodes, <a href="#Page_26">26</a></li> +<li>Electro-motive force, <a href="#Page_51">51</a></li> +<li>Electron, <a href="#Page_1">1</a></li> +<li>E.M.F., <a href="#Page_51">51</a></li> +<li>Excitation, <a href="#Page_6">6</a></li> +</ul> + +<p>F.</p> +<ul> +<li>Faults to detect, <a href="#Page_182">182</a></li> +<li>Fire alarms, <a href="#Page_123">123</a></li> +<li>Floor contacts, <a href="#Page_113">113</a><!-- Page 189 --><span class="pagenum"><a name="Page_189" id="Page_189">[Pg 189]</a></span></li> +<li>Frost alarms, <a href="#Page_121">121</a></li> +<li>Fuller charging, <a href="#Page_49">49</a></li> +</ul> + +<p>G.</p> +<ul> +<li>Galvanometer, <a href="#Page_176">176</a></li> +<li>Gas evolved, <a href="#Page_18">18</a></li> +<li>Gassner battery (addendum), <a href="#Page_186">186</a></li> +<li>Generator (magneto), <a href="#Page_174">174</a></li> +<li>Gent's battery, <a href="#Page_44">44</a></li> +<li>Glue, Prout's elastic, <a href="#Page_148">148</a></li> +<li>Graphite, <a href="#Page_27">27</a></li> +<li>Gravity battery, <a href="#Page_31">31</a></li> +<li class="indent1">Daniell battery, <a href="#Page_31">31</a></li> +<li class="indent1">Modified, <a href="#Page_120">120</a></li> +<li>Grenet battery, <a href="#Page_46">46</a></li> +<li>Grove battery, <a href="#Page_33">33</a></li> +<li>Gutta-percha, <a href="#Page_148">148</a></li> +</ul> + +<p>I.</p> +<ul> +<li>Indicator, <a href="#Page_135">135</a></li> +<li class="indent1">Automatic, <a href="#Page_138">138</a></li> +<li class="indent1">Drop, <a href="#Page_136">136</a></li> +<li class="indent1">Electric replacement, <a href="#Page_136">136</a></li> +<li class="indent1">Gent's, <a href="#Page_140">140</a></li> +<li class="indent1">Tripolar, <a href="#Page_143">143</a></li> +<li class="indent1">Mechanical replacement, <a href="#Page_136">136</a></li> +<li class="indent1">Mode of coupling up, <a href="#Page_142">142</a></li> +<li class="indent1">Pendulum, <a href="#Page_139">139</a></li> +<li class="indent1">Polarised, <a href="#Page_139">139</a></li> +<li class="indent1">Self replacing, <a href="#Page_136">136</a></li> +<li class="indent1">Semaphore, <a href="#Page_136">136</a></li> +<li>Inductor, <a href="#Page_174">174</a></li> +<li>Insulation, <a href="#Page_68">68</a></li> +<li>Insulators, <a href="#Page_4">4</a></li> +<li>Internal resistance, <a href="#Page_56">56</a></li> +<li>Interior of push, <a href="#Page_151">151</a></li> +<li>Iron, importance of soft, <a href="#Page_65">65</a></li> +<li class="indent1">Yoke, <a href="#Page_66">66</a></li> +</ul> + +<p>J.</p> +<ul> +<li>Jensen's bell, <a href="#Page_101">101</a></li> +<li>Joining wires to push, <a href="#Page_151">151</a></li> +<li>Judson's cell, <a href="#Page_41">41</a></li> +</ul> + +<p>K.</p> +<ul> +<li>Key, Morse, <a href="#Page_129">129</a></li> +</ul> + +<p>L.</p> +<ul> +<li>Leakage, <a href="#Page_52">52</a></li> +<li>Leclanché cell, <a href="#Page_33">33</a></li> +<li class="indent1">reversed, <a href="#Page_46">46</a></li> +<li>Legge's contact, <a href="#Page_115">115</a></li> +<li>Lever switches, <a href="#Page_128">128</a></li> +<li>Lifts, bells for, <a href="#Page_171">171</a></li> +<li>Localising faults, <a href="#Page_144">144</a>, <a href="#Page_175">175</a></li> +<li>Lodge bell, <a href="#Page_169">169</a></li> +</ul> + +<p>M.</p> +<ul> +<li>Magnetic field, <a href="#Page_14">14</a></li> +<li>Magneto bells, <a href="#Page_175">175</a></li> +<li class="indent1">Electric machines, <a href="#Page_14">14</a>, <a href="#Page_15">15</a></li> +<li>Magnets, <a href="#Page_13">13</a></li> +<li>Magnets producing electricity, <a href="#Page_14">14</a></li> +<li>Magnetisation of iron, <a href="#Page_12">12</a></li> +<li class="indent1">Steel, <a href="#Page_13">13</a></li> +<li>Manganese oxide, <a href="#Page_33">33</a></li> +<li>Minotto cell, <a href="#Page_31">31</a></li> +<li>Modified gravity battery, <a href="#Page_120">120</a></li> +<li>Morse key, <a href="#Page_129">129</a></li> +<li>Musical instrument, novel, <a href="#Page_108">108</a></li> +</ul> + +<p>N.</p> +<ul> +<li>Negative electricity, <a href="#Page_7">7</a></li> +<li>Non-conductors, <a href="#Page_3">3</a></li> +<li>Novel musical instrument, <a href="#Page_108">108</a></li> +</ul> + +<p>O.</p> +<ul> +<li>Ohm, <a href="#Page_55">55</a></li> +<li>Ohm's law, <a href="#Page_55">55</a></li> +<li>Open circuit, <a href="#Page_52">52</a></li> +<li>Overhead lines, <a href="#Page_152">152</a></li> +</ul> + +<p>P.</p> +<ul> +<li>Paraffin, <a href="#Page_69">69</a>, <a href="#Page_170">170</a></li> +<li>Percha, gutta, <a href="#Page_148">148</a></li> +<li>Plans, drawing out, <a href="#Page_169">169</a></li> +<li><!-- Page 190 --><span class="pagenum"><a name="Page_190" id="Page_190">[Pg 190]</a></span> +Platinum, riveting, <a href="#Page_76">76</a></li> +<li>Platinum, use of, <a href="#Page_76">76</a></li> +<li>Plug switches, <a href="#Page_128">128</a></li> +<li>Polarisation, <a href="#Page_26">26</a></li> +<li>Positive electricity, <a href="#Page_7">7</a></li> +<li>Proportions of bell parts, table of, <a href="#Page_89">89</a></li> +<li>Pressels, <a href="#Page_111">111</a></li> +<li>Prout's elastic glue, <a href="#Page_148">148</a></li> +<li>Pulls, <a href="#Page_111">111</a></li> +<li>Push, <a href="#Page_92">92</a>, <a href="#Page_151">151</a>, <a href="#Page_109">109</a></li> +<li class="indent1">Interior of, <a href="#Page_151">151</a></li> +<li class="indent1">Joining wires to, <a href="#Page_151">151</a></li> +</ul> + +<p>R.</p> +<ul> +<li>Relay, <a href="#Page_96">96</a>, <a href="#Page_133">133</a></li> +<li class="indent1">Action of, <a href="#Page_134">134</a></li> +<li>Repulsion, <a href="#Page_3">3</a></li> +<li>Resinous electricity, <a href="#Page_7">7</a></li> +<li>Resistance of wire, table of, <a href="#Page_146">146</a></li> +<li>Return current, <a href="#Page_153">153</a></li> +<li>Riveting platinum, <a href="#Page_76">76</a></li> +<li>Rubbing action, <a href="#Page_116">116</a></li> +</ul> + +<p>S.</p> +<ul> +<li>Ships, bells for, <a href="#Page_170">170</a></li> +<li>Shop door contact, <a href="#Page_116">116</a></li> +<li>Signalling by bells, <a href="#Page_130">130</a></li> +<li class="indent1">Code, <a href="#Page_130">130</a></li> +<li>Silver platinised, <a href="#Page_27">27</a></li> +<li>Single cell, <a href="#Page_9">9</a></li> +<li>Sizes of Leclanché's, <a href="#Page_42">42</a></li> +<li>Smee's cell, <a href="#Page_27">27</a></li> +<li>Spring coil, <a href="#Page_108">108</a></li> +<li>Standard size of wires, <a href="#Page_146">146</a></li> +<li>Switches, lever, <a href="#Page_128">128</a></li> +<li class="indent1">Plug, <a href="#Page_128">128</a></li> +</ul> + +<p>T.</p> +<ul> +<li>Table of batteries, E.M.F. and R., <a href="#Page_58">58</a></li> +<li class="indent1">Conductors and insulators, <a href="#Page_4">4</a>, <a href="#Page_68">68</a></li> +<li class="indent1">Metals in acid, <a href="#Page_8">8</a></li> +<li>Table of Proportions of bell parts, <a href="#Page_89">89</a></li> +<li class="indent1">Wire resistance, etc., <a href="#Page_146">146</a></li> +<li>Testing new work, <a href="#Page_182">182</a></li> +<li class="indent1">Old, <a href="#Page_183">183</a></li> +<li>Thermometer alarms, <a href="#Page_122">122</a></li> +<li>Thorpe's Ball, <a href="#Page_100">100</a></li> +</ul> + +<p>U.</p> +<ul> +<li>Use of platinum, <a href="#Page_76">76</a></li> +</ul> + +<p>V.</p> +<ul> +<li>Vitreous electricity, <a href="#Page_7">7</a></li> +<li>Volt, <a href="#Page_53">53</a></li> +</ul> + +<p>W.</p> +<ul> +<li>Walker's cell, <a href="#Page_27">27</a></li> +<li>Watchman's clock, <a href="#Page_124">124</a></li> +<li>Water level indicator, <a href="#Page_127">127</a></li> +<li>Washer, insulating, <a href="#Page_77">77</a></li> +<li>Window sash contact, <a href="#Page_116">116</a></li> +<li>Wiping contact, <a href="#Page_102">102</a></li> +<li>Wire covering, <a href="#Page_147">147</a></li> +<li class="indent1">In iron pipes, <a href="#Page_152">152</a></li> +<li class="indent1">In wooden boxes, <a href="#Page_152">152</a></li> +<li class="indent1">Iron, <a href="#Page_152">152</a></li> +<li class="indent1">Joining, <a href="#Page_148">148</a></li> +<li class="indent1">To push, <a href="#Page_151">151</a></li> +<li class="indent1">Laying in tubes, <a href="#Page_149">149</a></li> +<li class="indent1">Leading, <a href="#Page_147">147</a>, <a href="#Page_150">150</a></li> +<li class="indent1">Overhead, <a href="#Page_152">152</a></li> +<li class="indent1">Resistance, table of, <a href="#Page_146">146</a></li> +<li class="indent1">Return, <a href="#Page_147">147</a>, <a href="#Page_150">150</a></li> +<li class="indent1">Soldering iron, <a href="#Page_148">148</a></li> +<li class="indent1">Tinned, <a href="#Page_147">147</a></li> +<li class="indent1">Underground, <a href="#Page_152">152</a></li> +<li>Wiring, general instructions, <a href="#Page_155">155</a></li> +<li class="indent1">Up, <a href="#Page_144">144</a></li> +</ul> + +<p>Z.</p> +<ul> +<li>Zinc, amalgamated, <a href="#Page_22">22</a></li> +<li class="indent1">Blacking, <a href="#Page_45">45</a></li> +<li class="indent1">Consumption, <a href="#Page_21">21</a></li> +<li class="indent1">Commercial, <a href="#Page_19">19</a></li> +<li class="indent1">Pure, <a href="#Page_19">19</a></li> +</ul> + + +<p class="center">WILLIAM RIDER AND SON, PRINTERS, LONDON.</p> + +<hr style="width: 45%;" /> + +<p class="center"> +<i>Small crown 8vo, cloth.</i>     <i>With many Illustrations.</i><br /> +</p> + +<h3>WHITTAKER'S LIBRARY OF ARTS, SCIENCES, +MANUFACTURES AND INDUSTRIES.</h3> + + +<div class="blockquot"><p>MANAGEMENT OF ACCUMULATORS AND +PRIVATE ELECTRIC LIGHT INSTALLATIONS.</p> + +<p>A Practical Handbook by Sir <span class="smcap">David Salomons</span>, Bart., M. A.</p> + +<p>4th Edition, Revised and Enlarged, with 32 Illustrations. Cloth 3s.</p> + +<p>"To say that this book is the best of its kind would be a poor compliment, as +it is practically the only work on accumulators that has been written."—<i>Electrical +Review.</i></p></div> + +<div class="blockquot"><p>ELECTRICAL INSTRUMENT-MAKING FOR +AMATEURS. A Practical Handbook. By <span class="smcap">S. R. Bottone</span>, +Author of "The Dynamo," &c. With 60 Illustrations. Second +Edition. Cloth 3s.</p></div> + +<div class="blockquot"><p>ELECTRIC BELLS. By <span class="smcap">S. R. Bottone</span>. With +numerous Illustrations.</p></div> + + +<p class="center"><span class="smcap">In Preparation.</span></p> + +<div class="blockquot"><p>THE PROTECTION OF BUILDINGS FROM +LIGHTNING. A Treatise on the Theory of Lightning Conductors +from a Modern Point of View. Being the substance of +two lectures delivered before the Society of Arts in March, 1888. +By <span class="smcap">Oliver J. Lodge</span>, LL.D., D.Sc, F.R.S., Professor of Physics +in University College, Liverpool.</p> + +<p>Published with various amplifications and additions, with the +approval of the Society of Arts.</p></div> + +<div class="blockquot"><p>ELECTRICAL INFLUENCE MACHINES: +Containing a full account of their historical development, their +modern Forms, and their Practical Construction. By <span class="smcap">J. Gray</span>, +B.Sc.</p></div> + +<div class="blockquot"><p>ELECTRICAL ENGINEERING IN OUR +WORKSHOPS. A Practical Handbook. By <span class="smcap">Sydney F. +Walker</span>.</p></div> + +<p> +<span style="margin-left: 30em;">[<i>Ready Shortly</i></span><br /> +</p> + + +<div class="trans-note"> +<h4><a name="Transcribers_Notes" id="Transcribers_Notes"></a>Transcriber's Notes</h4> + +<p>Page <a href="#Page_12">12</a>: changed "guage" to "gauge" ( ... cotton-covered copper +wire, say No. 20 gauge ...)</p> + +<p>Page <a href="#Page_35">35</a>: changed "change" to "charge" ( ... losing at the same +time its electrical charge ...)</p> + +<p>Page <a href="#Page_55">55</a>: changed "guage" to "gauge" ( ... 1 foot of No. +41 gauge pure copper wire ...)</p> + +<p>Page <a href="#Page_64">64</a>: changed "exaet" to "exact" ( ... of the exact +diameter of the turned ends of the cores ...)</p> + +<p>Page <a href="#Page_73">73</a>: moved comma "Rivetting, is" to "Rivetting is," +(Rivetting, is perhaps, the best mode ...)</p> + +<p>Page <a href="#Page_81">81</a>: added hyphen ( ... along the short +length of wire to the right-hand binding-screw ...)</p> + +<p>Page <a href="#Page_83">83</a>: changed "head" to "heads" ( ... the possible defects of +electric bells may be classed under four heads: ...)</p> + +<p>Page <a href="#Page_92">92</a>: changed "its" to "it" ( ... until it rests against the stop +or studs.)</p> + +<p>Page <a href="#Page_102">102</a>: changed "contract-breaker" to "contact-breaker" +(When the contact-breaker is used, ...)</p> + +<p>Page <a href="#Page_103">103</a>: changed "instead" to "Instead" (Instead of the armature and clapper ...)</p> + +<p>Page <a href="#Page_132">132</a>: in the Morse code for "BRING THE", the code for "H" has been +corrected from two dots to four dots.</p> + +<p>Page <a href="#Page_136">136</a>: changed "eletro-magnet" to "electro-magnet" ( ... if the electro-magnet were energised ...)</p> + +<p>Page <a href="#Page_137">137</a>: changed "idicator" to "indicator" (since the indicator falls forwards)</p> + +<p>Page <a href="#Page_146">146</a>: changed "arrangment" to "arrangement" (the size and arrangement +of the batteries and wires)</p> + +<p>Page <a href="#Page_146">146</a>: added comma "nails," ( ... chance contact with nails, +staples, metal pipes or other wires ...)</p> + +<p>Page <a href="#Page_179">179</a>: changed "carboard" to "cardboard" ( ... for our purpose we will choose cardboard.)</p> + +<p>Page <a href="#Page_179">179</a>: changed "Tanstickor" to "Tãndstickor" ( ... double it to the form of a Tãndstickor match-box, ...)</p> + +<p>Page <a href="#Page_185">185</a>: suspected typo (unchanged) "Emmot" should perhaps be +"Emmott" (... the electrical firms of Messrs. Blakey Emmot, ...)</p> + +<p>Page <a href="#Page_186">186</a>: changed "Leclanchè" to "Leclanché" ( ... polarizes much +less quickly than the ordinary Leclanché.)</p> + +<p>Page <a href="#Page_187">187</a>: changed two instances of "Ampére" to "Ampère" in the index (Ampère, 55 / Ampère's law, 11)</p> +</div> + + + + + + + +<pre> + + + + + +End of Project Gutenberg's Electric Bells and All About Them, by S. R. 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