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| author | nfenwick <nfenwick@pglaf.org> | 2025-02-06 22:26:51 -0800 |
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| committer | nfenwick <nfenwick@pglaf.org> | 2025-02-06 22:26:51 -0800 |
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diff --git a/old/54221-h/54221-h.htm b/old/54221-h/54221-h.htm deleted file mode 100644 index 1ea5f57..0000000 --- a/old/54221-h/54221-h.htm +++ /dev/null @@ -1,10420 +0,0 @@ -<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" - "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> -<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 Induction Coils, by H. S. Norrie. - </title> - <link rel="coverpage" href="images/cover.jpg" /> - <style type="text/css"> - -body { - margin-left: 10%; - margin-right: 10%; -} - -/* Headings*/ - -h1 -{ - margin-top: 2em; margin-bottom: 2em; - text-align: center; - font-size: x-large; - font-weight: normal; - line-height: 1.6; -} - - h2,h3{ - text-align: center; - clear: both; - } - h3 {margin-top: 2em;} - -div.chapter {page-break-before: always;} - - -.half-title { - margin-top: 2em; margin-bottom: 2em; - text-align: center; - font-size: x-large; - font-weight: normal; - line-height: 1.6; - } - -/* Paragraphs */ - -p { - margin-top: .75em; - text-align: justify; - margin-bottom: .75em; - } - -.psig {text-align: right; margin-right: 2em;} - -.spaced {margin-top: 3em; margin-bottom: 3em;} -.hang { - text-align: justify; - padding-left: 1.75em; - text-indent: -1.75em; - } -.narrow {min-width: 10em; width: 20em; - max-width: 26em; margin: auto;} - -hr { - width: 33%; - margin-top: 2em; - margin-bottom: 2em; - margin-left: 33.5%; - margin-right: 33.5%; - clear: both; -} - -hr.chap {width: 65%; margin-left: 17.5%; margin-right: 17.5%;} -hr.full {width: 95%; margin-left: 2.5%; margin-right: 2.5%;} -hr.small {width: 25%; margin-left: 37.5%; margin-right: 37.5%; - margin-top: .5em; margin-bottom: .5em;} - -/* Lists */ - -ul.index { list-style-type: none; } -li.ifrst { margin-top: 1em; } -li.indx { margin-top: .5em; - padding-left: 2.5em; - text-indent: -2.5em; } - -/* Tables */ - -table { - margin-left: auto; - margin-right: auto; -} - .tdrb {text-align: right; vertical-align: bottom;} - .tdh { - text-align: justify; - padding-left: 1.75em; - text-indent: -1.75em; - } - .thbr {border-right:1px solid black;} - .tdbr {border-right:1px solid black; text-align: left;} - .chpl {text-align: center; font-size: large;} - .chps {text-align: center; font-size: small;} - .tdba { border: 1px solid black;} - .tdrt {text-align: right; vertical-align: top;} - .tdbtrl {border-right:1px solid black; border-left:1px solid black; - border-top:1px solid black; } - .tdbbrl {border-right:1px solid black; border-left:1px solid black; - border-bottom:1px solid black; } - -.pagenum { /* uncomment the next line for invisible page numbers */ - /* visibility: hidden; */ - position: absolute; - left: 92%; - font-size: smaller; - text-align: right; -} /* page numbers */ - -.ditto {padding-left: 1.5em; padding-right: 1.5em;} - -.gap5 {padding-right: 2.5em;} -.gap10 {padding-right: 10em;} - - -.bbox {border: solid 2px; padding: 1em;} -.center {text-align: center;} - -.smcap {font-variant: small-caps;} - -.u {text-decoration: underline;} - -.xs {font-size: x-small;} -.small {font-size: small;} -.xl {font-size: x-large;} -.xxl {font-size: xx-large;} - - -/* Images */ - -img {border: none; max-width: 100%} -.caption {font-size: smaller; font-weight: bold;} - -.figcenter { - margin: 1em 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; - } - - -/* 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; - white-space: nowrap - } - - -/* Transcriber's notes */ - -.transnote { - background-color: #E6E6FA; - color: black; - font-size:smaller; - padding:0.5em; - margin-bottom:5em; - font-family:sans-serif, serif; - } - - </style> - </head> -<body> - - -<pre> - -The Project Gutenberg EBook of Induction Coils, How to Make, Use, and -Repair Them., by H. S. Norrie - -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/license - - -Title: Induction Coils, How to Make, Use, and Repair Them. - Including Ruhmkorff, Tesla, and medical coils, Roentgen - Radiography, etc. etc. - -Author: H. S. Norrie - -Release Date: February 22, 2017 [EBook #54221] - -Language: English - -Character set encoding: UTF-8 - -*** START OF THIS PROJECT GUTENBERG EBOOK INDUCTION COILS *** - - - - -Produced by Chris Curnow, Les Galloway 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> - -<hr class="chap" /> - -<div class="figcenter"> -<img src="images/i_frontis.jpg" alt="" /> -<div class="caption"><span class="smcap">One of two Ruhmkorff Coils made by Queen & Co. The output with about 650 -Watts of current in the primary was a torrent of sparks 45 inches in length.</span></div> -</div> -<div class="chapter"></div> - -<h1>INDUCTION COILS<br /> - -<span class="smaller">How to Make, Use, and Repair Them</span></h1> - -<p class="center"><small>INCLUDING</small></p> - -<p class="center">RUHMKORFF, TESLA, AND MEDICAL COILS,<br /> -ROENTGEN RADIOGRAPHY, WIRELESS<br /> -TELEGRAPHY, AND PRACTICAL INFORMATION<br /> -ON PRIMARY AND<br /> -SECONDARY BATTERY</p> - -<p class="center spaced"> -<small>BY</small><br /> -H. S. NORRIE<br /> -<small>(NORMAN H. SCHNEIDER)</small></p> - -<p class="center"><i><small>SECOND EDITION, REVISED AND MUCH ENLARGED</small></i></p> - -<div class="figcenter" > -<img src="images/colophon.jpg" alt="Colophon" /> -</div> - - -<p class="center"><small>NEW YORK:</small><br /> -SPON & CHAMBERLAIN, <span class="smcap"><small>12 Cortlandt St.</small></span></p> - -<p class="center"><small>LONDON:</small><br /> -E. & F. N. SPON, Ltd., <span class="smcap"><small>125 Strand</small></span><br /> - -<small>1901</small></p> -<div class="chapter"></div> - -<p class="center spaced xs"> -Entered, according to Act of Congress, in the year 1896<br /> -Re-entered for Copyright in 1901<br /> -By SPON & CHAMBERLAIN<br /> -in the office of the Librarian of Congress, Washington, D. C.</p> - -<p class="center xs">BURR PRINTING HOUSE,<br /> -NEW YORK, N. Y., U. S. A.</p> - - -<hr class="chap" /> -<div class="chapter"></div> - - -<p class="half-title">ERRATA.</p> - - -<p><span class="smcap">Page 55.</span> Should read, "Cords being attached -to binding posts Nos. 1 and 2 are in circuit -with the <i>Secondary</i> Coil only. When at -Nos. 2 and 3 they receive the induced current -or extra current in the <i>Primary</i>."</p> - -<p><span class="smcap">Index.</span> "Tesla coil, descriptive," should -read "Tesla coil, <i>disruptive</i>."</p> - -<hr class="chap" /> - -<p><span class="pagenum" id="Page_iii">iii</span></p> - - - - -<div class="chapter"> -<h2 id="PREFACE_TO_THE_SECOND_EDITION">PREFACE TO THE SECOND EDITION.</h2> -</div> - -<p>The great favor with which the first -edition of this little work has been received -and the steadily growing interest in its -subject, together with many valuable improvements -and researches, may be given -as the reasons for this new edition.</p> - -<p>The book has been thoroughly revised, -partly rewritten, and considerable new matter, -with twenty-six new illustrations, added. -It has been brought up to date as far as electrical -science has gone.</p> - -<p>To detail all that has been done is too -great a task for a preface; we may briefly -mention the following new matter:</p> - -<p>Coils for gas and automobile engines; -medical coils, concise directions for operation -and repairs; new forms of contact -breakers, including electrolytic and mechani<span class="pagenum" id="Page_iv">iv</span>cal; -gas-lighting apparatus; primary and -secondary batteries.</p> - -<p>The chapter on X-Ray Apparatus has -been entirely rewritten, and is thoroughly -practical; and an entire chapter on Wireless -Telegraphy has been added. In a book of -this size it is not feasible to give specific -directions and full dimensions for the manufacture -of all the apparatus described. -Indeed, much of the latter must be adapted -to the particular purpose for which it is to -be utilized. Again, the same amount of -material will not always produce the same -results. A little closer winding, greater -pressure applied to the cooling wax of a -condenser, and the output or capacity of -either is changed.</p> - -<p>Matters purely of design or taste are to -be governed by the creative faculty of the -worker; but such general details and rules -are given as will be sufficient to enable one -possessing ordinary constructive ability to -make his own apparatus.</p> - -<p>The whole process of coil-making does<span class="pagenum" id="Page_v">v</span> -not require high mechanical skill, but chiefly -patience and attention to details; and, perhaps -best of all, but few tools are needed, -all of a simple kind.</p> - -<p>We beg to acknowledge courtesies received -from Messrs. Queen & Co., the -<i>Scientific American</i> for frontispiece and -Fig. 13, Mr. Goldingham's book on Oil -Engines for Fig. 12, and others who have -been of assistance to the author. The best -American and English practice has been -adopted; the American standard gauges and -sizes of wires are used, except where noted.</p> - -<p>A list of works, particularly of value to -the coil worker, will be found following the -index.</p> - -<p class="psig"> -<span class="smcap">H. S. Norrie</span><br /> -(Norman H. Schneider.)</p> -<p><span class="smcap">April,</span> 1901.</p> - -<p><span class="pagenum" id="Page_vi">vi</span></p> -<p><span class="pagenum" id="Page_vii">vii</span></p> -<hr class="chap" /> - - - -<div class="chapter"> -<h2 id="CONTENTS">CONTENTS.</h2> -</div> - -<div class="center small"> -<table border="0" cellpadding="4" cellspacing="0" summary=""> -<tr> - <td class="chpl" colspan="2"><a href="#CHAPTER_I">CHAPTER I</a>.</td> -</tr> -<tr> - <td class="chps" colspan="2">COIL CONSTRUCTION.</td> -</tr> -<tr> - <td class="tdh">Construction of Ruhmkorff Coils. Sizes of - Wires. Winding of Primary and Secondary. Assembling. Connecting - Up. Insulation. Coils in Series. Oil Immersed Coils. "Tesla" Coil. - Disruptive "Tesla" Coil. Coils for Gas Engines. Spark Coils. - Resistance Coils. General Remarks on Coils. The Testing of a Coil - for Polarity. Failure to Work. Medical Coils. Medical Coil with Tube - Regulation. Medical Coil with Interchangeable Secondaries. Bath - Coils</td> - <td class="tdrb">1-64</td> -</tr> - -<tr> - <td class="chpl" colspan="2"><a href="#CHAPTER_II">CHAPTER II</a>.</td> -</tr> -<tr> - <td class="chps" colspan="2">CONTACT BREAKERS.</td> -</tr> - -<tr> -<td class="tdh">Construction of Contact Breakers. Various Forms of -Simple Contact Breakers. The Mercury Vibrator. Polechanging -<span class="pagenum" id="Page_viii">viii</span> -Vibrator. Wehnelt Interrupter. Dessauer Contact Breaker. Steel Ribbon -Interrupter. Contact Breakers in Vacuo. Queen Contact Breaker. -Adjustable Contact Breaker for Medical Coils. The Queen Contact Breaker -for Large Coils, Adjustable Cone Vibrator. Contacts</td> - <td class="tdrb">65-91</td> -</tr> - -<tr> - <td class="chpl" colspan="2"><a href="#CHAPTER_III">CHAPTER III</a>.</td> -</tr> -<tr> - <td class="chps" colspan="2">INSULATIONS AND CEMENTS.</td> -</tr> -<tr> -<td class="tdh">Selection of Insulating Materials. Mineral Oil. -Paraffin Wax. Resin Oils. Beeswax. Shellac Varnishes. Silk. Insulating -Compounds</td> - <td class="tdrb">92-98</td> -</tr> - -<tr> - <td class="chpl" colspan="2"><a href="#CHAPTER_IV">CHAPTER IV</a>.</td> -</tr> -<tr> - <td class="chps" colspan="2">CONDENSERS.</td> -</tr> -<tr> - <td class="tdh">Construction of Condensers. Leyden Jar. -Glass Plate Condenser. Paper Condensers. Series Condenser. Rolled-Up -Condensers. Adjustable Condensers. Application of Condensers</td> - <td class="tdrb">99-119</td> -</tr> - -<tr> - <td class="chpl" colspan="2"><a href="#CHAPTER_V">CHAPTER V</a>.</td> -</tr> -<tr> - <td class="chps" colspan="2">EXPERIMENTS.</td> -</tr> -<tr> -<td class="tdh">Luminous Effects Obtained by Means of a Ruhmkorff Coil. -Materials Used. Spark Experiments. The Luminous Pane. Luminous Designs, -etc.</td> - <td class="tdrb">120-130<span class="pagenum" id="Page_ix">ix</span></td> -</tr> - -<tr> - <td class="chpl" colspan="2"><a href="#CHAPTER_VI">CHAPTER VI</a>.</td> -</tr> -<tr> - <td class="chps" colspan="2">SPECTRUM ANALYSIS.</td> -</tr> -<tr> -<td class="tdh">Color Produced by Burning Different Metals. The -Spectroscope Shown in Connection with the Coil. The Screen. The Color -Spaces in the Solar Spectrum. Color Values</td> - <td class="tdrb">131-139</td> -</tr> - -<tr> - <td class="chpl" colspan="2"><a href="#CHAPTER_VII">CHAPTER VII</a>.</td> -</tr> -<tr> - <td class="chps" colspan="2">CURRENTS IN VACUO.</td> -</tr> -<tr> -<td class="tdh">Different Forms of Mercury Air Pumps. Geissler Tubes. -Discharges in Vacuo. Characteristic Colors of Different Gases in Tubes, -etc.</td> - <td class="tdrb">140-152</td> -</tr> - -<tr> - <td class="chpl" colspan="2"><a href="#CHAPTER_VIII">CHAPTER VIII</a>.</td> -</tr> -<tr> - <td class="chps" colspan="2">ROTATING EFFECTS.</td> -</tr> -<tr> - <td class="tdh">Effects of Discharges in Rotating Tubes. Construction -of Rotating Wheels. Arrangement of Tubes, etc.</td> - <td class="tdrb">153-163</td> -</tr> - -<tr> - <td class="chpl" colspan="2"><a href="#CHAPTER_IX">CHAPTER IX</a>.</td> -</tr> -<tr> - <td class="chps" colspan="2">GAS LIGHTING.</td> -</tr> -<tr> -<td class="tdh">The Application of the Ruhmkorff Coil for Lighting Gas. -Gas Lighting in Series. Gas Lighting in Multiple. Gas Lighting Diagram. -Jump Spark Burner. Automatic Burners</td> - <td class="tdrb">164-177<span class="pagenum" id="Page_x">x</span></td> -</tr> - -<tr> - <td class="chpl" colspan="2"><a href="#CHAPTER_X">CHAPTER X</a>.</td> -</tr> -<tr> - <td class="chps" colspan="2">BATTERIES FOR COILS.</td> -</tr> -<tr> -<td class="tdh">The Selection of Suitable Batteries. Open Circuit -Cells. Closed Circuit Cells. Description of Cells. Formulæ for -Solutions for Different Kinds of Batteries. The Grenet Battery. Fuller -Battery. Gravity Battery. Dun Cell. Gethins Cell. Gordon Battery. New -Standard. Edison-Lalande Cell. Dry Batteries. Dry Cell Construction, -etc.</td> - <td class="tdrb">178-199</td> -</tr> - -<tr> - <td class="chpl" colspan="2"><a href="#CHAPTER_XI">CHAPTER XI</a>.</td> -</tr> -<tr> - <td class="chps" colspan="2">STORAGE OR SECONDARY CELL.</td> -</tr> -<tr> -<td class="tdh">Construction of a Storage Cell. Connecting Up Cells. -Charging Storage Batteries. Diagram for Charging from Dynamo Using -a Rheostat. Diagram for Charging, using Lamp instead of Rheostat. -Charging from. Primary Batteries. Testing Solutions. Setting Up the -Storage Cell. The Harrison Cell. The "U. S." Storage Cell, etc.</td> - <td class="tdrb">200-223</td> -</tr> - -<tr> - <td class="chpl" colspan="2"><a href="#CHAPTER_XII">CHAPTER XII</a>.</td> -</tr> -<tr> - <td class="chps" colspan="2">TESLA AND HERTZ EFFECTS.</td> -</tr> -<tr> -<td class="tdh">Currents of High Frequency. Electric Resonator. The -"Tesla" Effects. Coil Connected to Discharger. High Frequency Currents -in Electro-Therapeutics, etc.</td> - <td class="tdrb">224-234<span class="pagenum" id="Page_xi">xi</span></td> -</tr> - -<tr> - <td class="chpl" colspan="2"><a href="#CHAPTER_XIII">CHAPTER XIII</a>.</td> -</tr> -<tr> - <td class="chps" colspan="2">THE "ROENTGEN" RAYS AND RADIOGRAPHY.</td> -</tr> -<tr> -<td class="tdh">General Arrangement of Connections for Coil and Crookes -Tube for Making X Ray Negatives. The Fluoroscope. Phosphorus Tube. The -Queen Self-Adjusting Crookes Tube. General Remarks, etc.</td> - <td class="tdrb">235-247</td> -</tr> - -<tr> - <td class="chpl" colspan="2"><a href="#CHAPTER_XIV">CHAPTER XIV</a>.</td> -</tr> -<tr> - <td class="chps" colspan="2">WIRELESS TELEGRAPHY.</td> -</tr> -<tr> -<td class="tdh">Arrangements of Simple Circuits of Coil and Coherer for -Receiving and Sending Messages. The Coherer. Carbon Coherer. Coherer -without Filings. Aluminum Coherer. Steel Ball Coherer. The Oscillator. -Clarke's Oscillator. Triple Oscillator. The Coil. Translating Devices. -Air Conductor, etc.</td> - <td class="tdrb">248-265</td> -</tr> - -<tr> - <td class="tdh"><span class="smcap"><a href="#INDEX">Index</a></span></td> - <td class="tdrb">266</td> -</tr> - -<tr> - <td class="tdh"><a href="#BIBLIOGRAPHY">Bibliography</a></td> - <td class="tdrb">270</td> -</tr> -</table></div> - -<hr class="chap" /> - -<p><span class="pagenum" id="Page_xii">xii</span><br /> -<span class="pagenum" id="Page_xiii">xiii</span></p> - - - - -<div class="chapter"> -<h2>CONTENTS OF TABLES.</h2> -</div> -<div class="center small"> -<table border="0" cellpadding="4" cellspacing="0" summary=""> -<tr> - <td class="tdh"></td> - <td class="tdrb"><small>PAGE</small></td> -</tr> -<tr> - <td class="tdh"><span class="smcap">Good Proportions of Core Lengths</span></td> - <td class="tdrb"><a href="#Page_7">7</a></td> -</tr> -<tr> - <td class="tdh"><span class="smcap">Table of "Secondary" Windings</span></td> - <td class="tdrb"><a href="#Page_24">24</a></td> -</tr> -<tr> - <td class="tdh"><span class="smcap">Polarity Tests</span></td> - <td class="tdrb"><a href="#Page_45">45</a></td> -</tr> -<tr> - <td class="tdh"><span class="smcap">Dimensions for Different Spark Lengths</span></td> - <td class="tdrb"><a href="#Page_50">50</a></td> -</tr> -<tr> - <td class="tdh"><span class="smcap">Table Showing Resistances and Feet per Pound of Copper and German Silver Wire</span></td> - <td class="tdrb"><a href="#Page_64">64</a></td> -</tr> -<tr> - <td class="tdh"><span class="smcap">Specific Inductive Capacity</span></td> - <td class="tdrb"><a href="#Page_119">119</a></td> -</tr> -<tr> - <td class="tdh"><span class="smcap">Wave Lengths and Temperatures</span></td> - <td class="tdrb"><a href="#Page_138">138-139</a></td> -</tr> -<tr> - <td class="tdh"><span class="smcap">Table of Relative Costs of Materials</span></td> - <td class="tdrb"><a href="#Page_191">191</a></td> -</tr> -</table></div> -<hr class="chap" /> - -<p><span class="pagenum" id="Page_xiv">xiv</span></p> - - - -<div class="chapter"> -<h2>LIST OF ILLUSTRATIONS.</h2> -</div> -<p class="center"> -<span class="smcap"><small>Frontispiece, The Queen 45″ Spark Coil.</small></span></p> - -<div class="center small"> -<table border="0" cellpadding="4" cellspacing="0" summary=""> -<tr> - <td align="right"><small>FIG</small>.</td> - <td align="right"><small>PAGE</small></td> -</tr> -<tr> - <td align="right"><a href="#fig1">1</a>.</td> - <td align="left">Section of Coil</td> - <td align="right">4</td> -</tr> -<tr> - <td align="right"><a href="#fig2">2</a>.</td> - <td align="left">Insulating Tube Ends</td> - <td align="right">10</td> -</tr> -<tr> - <td align="right"><a href="#fig3">3</a>.</td> - <td align="left">Sectional Winding</td> - <td align="right">11</td> -</tr> -<tr> - <td align="right"><a href="#fig4">4</a>.</td> - <td align="left">Section <span class="ditto">"</span> First Method</td> - <td align="right">12</td> -</tr> -<tr> - <td align="right"><a href="#fig5">5</a>.</td> - <td align="left"> <span class="ditto">"</span><span class="ditto">"</span> Second Method</td> - <td align="right">13</td> -</tr> -<tr> - <td align="right"><a href="#fig6">6</a>.</td> - <td align="left">Proportional Diagram of Coil</td> - <td align="right">15</td> -</tr> -<tr> - <td align="right"><a href="#fig7">7</a>.</td> - <td align="left">Section Winder, End View</td> - <td align="right">17</td> -</tr> -<tr> - <td align="right"><a href="#fig7">8</a>.</td> - <td align="left"> <span class="ditto">"</span><span class="ditto">"</span> Face View</td> - <td align="right">17</td> -</tr> -<tr> - <td align="right"><a href="#fig9">9</a>.</td> - <td align="left">Assembly of Coils</td> - <td align="right">18</td> -</tr> -<tr> - <td align="right"><a href="#fig10">10</a>.</td> - <td align="left">Polechanging Switch</td> - <td align="right">31</td> -</tr> -<tr> - <td align="right"><a href="#fig11">11</a>.</td> - <td align="left">Disruptive Tesla Coil</td> - <td align="right">35</td> -</tr> -<tr> - <td align="right"><a href="#fig12">12</a>.</td> - <td align="left">Spark Coil for Gas Engine</td> - <td align="right">38</td> -</tr> -<tr> - <td align="right"><a href="#fig13">13</a>.</td> - <td align="left">Reproduction of a 32-inch Spark</td> - <td align="right">47</td> -</tr> -<tr> - <td align="right"><a href="#fig14">14</a>.</td> - <td align="left">Simple Medical Coil</td> - <td align="right">53</td> -</tr> -<tr> - <td align="right"><a href="#fig15">15</a>.</td> - <td align="left">Connections for Simple Medical Coil</td> - <td align="right">55</td> -</tr> -<tr> - <td align="right"><a href="#fig16">16</a>.</td> - <td align="left">Interchangeable Medical Coil</td> - <td align="right">56</td> -</tr> -<tr> - <td align="right"><a href="#fig17">17</a>.</td> - <td align="left">Vibrator for Medical Coil</td> - <td align="right">60</td> -</tr> -<tr> - <td align="right"><a href="#fig18">18</a>.</td> - <td align="left">Simple Contact Breaker</td> - <td align="right">65</td> -</tr> -<tr> - <td align="right"><a href="#fig19">19</a>.</td> - <td align="left">Imperfect Form of Contact Breaker</td> - <td align="right">67</td> -</tr> -<tr> - <td align="right"><a href="#fig19">20</a>.</td> - <td align="left">Superior Form of Contact Breaker</td> - <td align="right">67</td> -</tr> -<tr> - <td align="right"><a href="#fig21">21</a>.</td> - <td align="left">Spotteswoode Contact Breaker</td> - <td align="right">69</td> -</tr> -<tr> - <td align="right"><a href="#fig22">22</a>.</td> - <td align="left">Polechanging Contact Breaker</td> - <td align="right">74</td> -</tr> -<tr> - <td align="right"><a href="#fig23">23</a>.</td> - <td align="left">Wehnelt Interrupter</td> - <td align="right">78</td> -</tr> -<tr> - <td align="right"><a href="#fig24">24</a>.</td> - <td align="left">Ribbon Vibrator</td> - <td align="right">81</td> -</tr> -<tr> - <td align="right"><a href="#fig25">25</a>.</td> - <td align="left">Queen Contact Breaker</td> - <td align="right">82<span class="pagenum" id="Page_xv">xv</span></td> -</tr> -<tr> - <td align="right"><a href="#fig26">26</a>.</td> - <td align="left">Adjustable Contact Breaker</td> - <td align="right">86</td> -</tr> -<tr> - <td align="right"><a href="#fig27">27</a>.</td> - <td align="left">Cone Contact Breaker</td> - <td align="right">88</td> -</tr> -<tr> - <td align="right"><a href="#fig28">28</a>.</td> - <td align="left">Coil Head Contact Breaker</td> - <td align="right">89</td> -</tr> -<tr> - <td align="right"><a href="#fig29">29</a>.</td> - <td align="left">Leyden Jar</td> - <td align="right">101</td> -</tr> -<tr> - <td align="right"><a href="#fig30">30</a>.</td> - <td align="left">Plate Condenser</td> - <td align="right">102</td> -</tr> -<tr> - <td align="right"><a href="#fig31">31</a>.</td> - <td align="left">Arrangement of Condenser Plates</td> - <td align="right">104</td> -</tr> -<tr> - <td align="right"><a href="#fig32">32</a>.</td> - <td align="left">Condenser Charging, First Method</td> - <td align="right">110</td> -</tr> -<tr> - <td align="right"><a href="#fig33">33</a>.</td> - <td align="left">Condenser Charging, Second Method</td> - <td align="right">112</td> -</tr> -<tr> - <td align="right"><a href="#fig34">34</a>.</td> - <td align="left">Adjustable Condenser</td> - <td align="right">118</td> -</tr> -<tr> - <td align="right"><a href="#fig35">35</a>.</td> - <td align="left">Spark between Balls</td> - <td align="right">125</td> -</tr> -<tr> - <td align="right"><a href="#fig36">36</a>.</td> - <td align="left">Short Spark between Balls</td> - <td align="right">125</td> -</tr> -<tr> - <td align="right"><a href="#fig37">37</a>.</td> - <td align="left">Sparkling Pane</td> - <td align="right">125</td> -</tr> -<tr> - <td align="right"><a href="#fig38">38</a>.</td> - <td align="left">Luminous Design</td> - <td align="right">128</td> -</tr> -<tr> - <td align="right"><a href="#fig39">39</a>.</td> - <td align="left">Electric Brush</td> - <td align="right">128</td> -</tr> -<tr> - <td align="right"><a href="#fig40">40</a>.</td> - <td align="left">Spectrum—Solar</td> - <td align="right">132</td> -</tr> -<tr> - <td align="right"><a href="#fig41">41</a>.</td> - <td align="left">Spectroscope and Coil</td> - <td align="right">133</td> -</tr> -<tr> - <td align="right"><a href="#fig42">42</a>.</td> - <td align="left">Simple Air Pump</td> - <td align="right">141</td> -</tr> -<tr> - <td align="right"><a href="#fig43">43</a>.</td> - <td align="left">Geissler Air Pump</td> - <td align="right">144</td> -</tr> -<tr> - <td align="right"><a href="#fig43">44</a>.</td> - <td align="left">Sprengel Air Pump</td> - <td align="right">144</td> -</tr> -<tr> - <td align="right"><a href="#fig45">45</a>.</td> - <td align="left">Solution Tube</td> - <td align="right">150</td> -</tr> -<tr> - <td align="right"><a href="#fig46">46</a>.</td> - <td align="left">Fluorescent Bulbs</td> - <td align="right">150</td> -</tr> -<tr> - <td align="right"><a href="#fig47">47</a>.</td> - <td align="left">Ruby Tube—Crookes</td> - <td align="right">150</td> -</tr> -<tr> - <td align="right"><a href="#fig48">48</a>.</td> - <td align="left">Iridio-platinum Tube—Crookes</td> - <td align="right">151</td> -</tr> -<tr> - <td align="right"><a href="#fig49">49</a>.</td> - <td align="left">Revolving Wheel</td> - <td align="right">154</td> -</tr> -<tr> - <td align="right"><a href="#fig50">50</a>.</td> - <td align="left">Tube Holder</td> - <td align="right">157</td> -</tr> -<tr> - <td align="right"><a href="#fig50">51</a>.</td> - <td align="left">Side View of Wheel</td> - <td align="right">157</td> -</tr> -<tr> - <td align="right"><a href="#fig52">52</a>.</td> - <td align="left">Geissler Tubes</td> - <td align="right">160</td> -</tr> -<tr> - <td align="right"><a href="#fig53">53</a>.</td> - <td align="left">Triangle on Disc</td> - <td align="right">161</td> -</tr> -<tr> - <td align="right"><a href="#fig54">54</a>.</td> - <td align="left">Maltese Cross on Disc</td> - <td align="right">161</td> -</tr> -<tr> - <td align="right"><a href="#fig55">55</a>.</td> - <td align="left">Gas Lighting Circuit</td> - <td align="right">165</td> -</tr> -<tr> - <td align="right"><a href="#fig56">56</a>.</td> - <td align="left">Connections for Gas Burners</td> - <td align="right">169</td> -</tr> -<tr> - <td align="right"><a href="#fig57">57</a>.</td> - <td align="left">Bartholdi Automatic Burner</td> - <td align="right">172<span class="pagenum" id="Page_xvi">xvi</span></td> -</tr> -<tr> - <td align="right"><a href="#fig58">58</a>.</td> - <td align="left">Connections for Automatic Burner</td> - <td align="right">174</td> -</tr> -<tr> - <td align="right"><a href="#fig59">59</a>.</td> - <td align="left">The Grenet Cell</td> - <td align="right">180</td> -</tr> -<tr> - <td align="right"><a href="#fig60">60</a>.</td> - <td align="left">The Fuller Cell</td> - <td align="right">184</td> -</tr> -<tr> - <td align="right"><a href="#fig61">61</a>.</td> - <td align="left">The Gethins Cell</td> - <td align="right">193</td> -</tr> -<tr> - <td align="right"><a href="#fig62">62</a>.</td> - <td align="left">Lead Plate for Storage Cell</td> - <td align="right">201</td> -</tr> -<tr> - <td align="right"><a href="#fig62">63</a>.</td> - <td align="left">Wooden Separator</td> - <td align="right">201</td> -</tr> -<tr> - <td align="right"><a href="#fig64">64</a>.</td> - <td align="left">Charging with Rheostat</td> - <td align="right">207</td> -</tr> -<tr> - <td align="right"><a href="#fig65">65</a>.</td> - <td align="left">Charging with Lamps</td> - <td align="right">207</td> -</tr> -<tr> - <td align="right"><a href="#fig66">66</a>.</td> - <td align="left">Harrison Electrodes</td> - <td align="right">211</td> -</tr> -<tr> - <td align="right"><a href="#fig67">67</a>.</td> - <td align="left">Hydrometer</td> - <td align="right">221</td> -</tr> -<tr> - <td align="right"><a href="#fig68">68</a>.</td> - <td align="left">Hertz Resonator</td> - <td align="right">227</td> -</tr> -<tr> - <td align="right"><a href="#fig69">69</a>.</td> - <td align="left">Tesla Circuit</td> - <td align="right">229</td> -</tr> -<tr> - <td align="right"><a href="#fig70">70</a>.</td> - <td align="left">Tesla Cut Out</td> - <td align="right">231</td> -</tr> -<tr> - <td align="right"><a href="#fig71">71</a>.</td> - <td align="left">Tesla Cut Out, Top Plan</td> - <td align="right">232</td> -</tr> -<tr> - <td align="right"><a href="#fig72">72</a>.</td> - <td align="left">Circuit for X Ray Apparatus</td> - <td align="right">237</td> -</tr> -<tr> - <td align="right"><a href="#fig73">73</a>.</td> - <td align="left">Queen's Self-Regulating X Ray Tube</td> - <td align="right">240</td> -</tr> -<tr> - <td align="right"><a href="#fig74">74</a>.</td> - <td align="left">Transmitter for Wireless Telegraphy</td> - <td align="right">250</td> -</tr> -<tr> - <td align="right"><a href="#fig75">75</a>.</td> - <td align="left">Receiver for Wireless Telegraphy</td> - <td align="right">252</td> -</tr> -<tr> - <td align="right"><a href="#fig76">76</a>.</td> - <td align="left">The Branley Coherer</td> - <td align="right">254</td> -</tr> -<tr> - <td align="right"><a href="#fig77">77</a>.</td> - <td align="left">Clarke's Oscillator</td> - <td align="right">259</td> -</tr> -<tr> - <td align="right"><a href="#fig77">78</a>.</td> - <td align="left">Triple Oscillator</td> - <td align="right">259</td> -</tr> -<tr> - <td align="right"><a href="#fig79">79</a>.</td> - <td align="left">Air Wire Insulators</td> - <td align="right">263</td> -</tr> -</table></div> - - - - -<hr class="chap" /> - -<p><span class="pagenum" id="Page_1">1</span></p> - - - - -<div class="chapter"> -<h2 id="CHAPTER_I">CHAPTER I.<br /> - -<small>COIL CONSTRUCTION.</small></h2> -</div> - -<p>In commencing a description of the -Ruhmkorff coil and its uses, a brief mention -of the fundamental laws of induction -directly bearing on its action will assist in -obtaining an intelligent conception of the -proper manner in which it should be constructed -and handled.</p> - -<p>Any variation or cessation of a current -of electricity flowing in one conductor will -induce a momentary current in an adjacent -conductor; and if the second conductor -be an insulated wire coiled around -the first conductor, also a coil of insulated -wire, the effect is heightened. The intensity -of the secondary or induced current -increases with the number of turns of -its conductor, the abruptness and com<span class="pagenum" id="Page_2">2</span>pleteness -of the variation of current in the -first or primary coil, and the proximity of -the coils. And the insertion of a mass of -soft iron within the primary coil by its -consequent magnetization and demagnetization -augments still further the inductive -effect. There are other contributing -causes which cannot be treated of here, -but are of not so much importance as the -foregoing.</p> - -<p>In the Ruhmkorff coil, which is an application -of the above laws, the primary -coil is of large wire and the secondary coil -of extremely fine wire, of a length many -thousand times greater than the wire of -the primary coil. The current is abruptly -broken in the primary circuit by a suitable -device—the contact breaker or rheotome. -The current induced in the secondary at -the make of the circuit is in the opposite -direction to that of the primary coil and -battery, but the current at the break of -the circuit is in the same direction as that -of the primary. The effect of the current<span class="pagenum" id="Page_3">3</span> -at the break of the circuit is more powerful -than that at the make, which latter is -also somewhat neutralized by the opposing -battery current. A condenser or Leyden -jar is connected across the contact -breaker to absorb an <i>extra current</i> induced -in the primary coil by the break of the circuit, -which would tend to prolong the magnetization -of the core beyond the desired -limit.</p> - -<p>The whole apparatus is mounted on a -wood base, having the condenser in a false -bottom for the sake of compactness.</p> - -<p>It is not herein intended to describe all -the minor operations in the construction -of a Ruhmkorff coil. A sufficient description -and review of the main points to be -considered, however, will be given to enable -a person fairly proficient in the use of simple -tools to construct a serviceable instrument.</p> - -<p>The parts and their arrangement in relation -to one another are shown in Fig. 1, -but are not drawn strictly to scale, although -very nearly so.</p> - -<p><span class="pagenum" id="Page_4">4</span></p> - -<div class="figcenter" > <a id="fig1"></a> -<img src="images/i_004.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 1.</span></div> -</div> - -<p><i>C</i> is the core, consisting of a bundle of -soft iron wires as fine as can be obtained. -The greater the subdivision of the core the -quicker will it respond to the magnetizing<span class="pagenum" id="Page_5">5</span> -current in the primary coil, and lose its -magnetism when the current ceases. It -has another advantage, in that the disadvantageous -eddy, or Foucault currents, -are lessened, which fact, however, is of -not enough importance to need extended -consideration.</p> - -<p>Many coil-makers saturate the core with -paraffin or shellac, which is of slight benefit. -This core is wrapped in an insulating -layer of paraffined paper or enclosed in a -rubber shell, there not being any great -necessity to use more than ordinary insulation -between the core and the primary -coil.</p> - -<p>In the majority of induction coils or -"transformers" used in the alternating -current system of electric lighting, the -iron cores form a closed magnetic circuit. -A closed magnetic circuit in a Ruhmkorff -coil could be obtained by extending the -iron core at each end and then bending -and securing the ends together, forming, -as it were, a ring partly inside and partly<span class="pagenum" id="Page_6">6</span> -outside the coil. But although the inductive -effects would be heightened and less -battery power required, the slowness of -the circuit to demagnetize would alone be -detrimental to rapid oscillations of current.</p> - -<p>There would also be a loss from a greater -hysteresis (energy lost in the magnetization -and demagnetization of iron). A -core magnetizes quicker than it demagnetizes, -and the latter is rarely complete; -a certain amount of residual magnetism -remains, hysteresis being strictly due to -this retention of energy (Sprague). Hysteresis -shows itself in heat, but must not -be confounded with Foucault or eddy currents. -The latter are corrected by subdividing -the metal, but the former depends -upon the quality of the metal, and increases -with its length.</p> - -<p>Moreover, a coil with a closed magnetic -circuit requires an independent contact -breaker.</p> - -<p>In most of the alternating currents used -in lighting their rapidity of alternation is<span class="pagenum" id="Page_7">7</span> -but one hundred and twenty-five periods -per second. As in the simple electromagnet, -the proportions of diameter and -length of the primary coil and core will -determine its rapidity of action. A short -fat coil and core will act much quicker -than a long thin one. But on a short fat -coil the outside turns would be too far -removed from the intensest part of the -primary field. A good proportion of core -length is given in the following table:</p> - - -<div class="center small"> -<table border="0" cellpadding="4" cellspacing="0" summary=""> -<tr> - <th>Spark Length <br />of Coil.</th><th>Iron Core.</th> -</tr> -<tr> - <td> ¼</td> - <td align="left"> 4″ × ½″</td> -</tr> -<tr> - <td> ½</td> - <td align="left"> 5″ × - <sup>10</sup>∕<sub>16</sub>″</td> -</tr> -<tr> - <td> 1 </td> - <td align="left"> 7″ × ¾″</td> -</tr> -<tr> - <td> 2 </td> - <td align="left"> 9″ × 1″</td> -</tr> -<tr> - <td> 6 </td> - <td align="left">12″ × 1⅛″</td> -</tr> -<tr> - <td>12 </td> - <td align="left">19″ × 1½″</td> -</tr> -</table></div> - - -<p>The primary coil <i>P</i> consists of two or -not more than three layers of insulated -copper wire of large diameter, being required -to carry a heavy current in a 2-inch -spark coil, probably from 8 to 10 amperes. -In designing the primary coil a great ad<span class="pagenum" id="Page_8">8</span>vantage -arises from using comparatively -few turns but of large wire. Each turn of -wire in the primary has a choking effect -upon its neighbor by what is termed self-induction.</p> - -<p>As the primary coil and core may be -considered as an electro magnet, it may -not be out of place to notice the rule governing -such. Magnetization of an iron -core is mainly dependent upon the ampere -turns of the coil surrounding it—that is, -one ampere carried around the core for -one hundred turns (100 ampere-turns) -would equal in effect ten amperes flowing -through ten turns. Practically speaking, -there would be certain variations to the -rule, for one difficulty would arise in that -the smaller wire used in conveying the -smaller current would fit more compactly -and allow more turns to be nearer the -core, the active effect of the turns always -decreasing with their distance from the -core. And although a large current and -few turns would not have so much self<span class="pagenum" id="Page_9">9</span>-induction, -there would be trouble at the -contact breaker, owing to the large current -it would have to control.</p> - -<p>The most suitable sizes of wire for the -primary coil are: No. 16 B. & S. for -coils up to 1 inch spark; No. 14 B. & S. -up to 4 inches of spark, and No. 12 B. -& S. for a 6-inch spark coil. The coil -should be, say, one-twelfth of the core -length shorter than the core.</p> - -<p><i>I</i> is the insulating tube between the primary -coil and the secondary coil <i>S</i>. Here -great precaution is necessary to prevent -any liability of short circuiting or breaking -through of sparks from the secondary coil. -This danger cannot be underestimated, -and the tube should be either of glass or -hard rubber, free from flaws, varying in -thickness with the dimensions of the coil. -It should extend at least one-tenth of the -total length of the primary coil beyond it -at each end. The end of this tube can be -turned down so as to allow of the hard -rubber reel ends being slipped on and held<span class="pagenum" id="Page_10">10</span> -in position by outside hard rubber rings -(Fig. 2).</p> - -<div class="figcenter" ><a id="fig2"></a> -<img src="images/i_010.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 2.</span></div> -</div> - -<p>The secondary coil consists of many -turns of fine insulated copper wire separated -from the primary coil by the insulating -tube and a liberal amount of insulating -compound at each end. In coils giving -under 1 inch of spark this coil may be -wound in two or more sections.</p> - -<div class="figcenter" ><a id="fig3"></a> -<img src="images/i_011.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 3.</span></div> -</div> - -<p>The usual manner of constructing these<span class="pagenum" id="Page_11">11</span> -sections is to divide up the space on the -insulating tube by means of hard rubber -rings placed at equal distances apart, in -number according to the number of sections -desired (Fig. 3). The space between -each set of rings, or between the coil end -and a ring, is wound with the wire selected, -the filled sections constituting a number -of complete coils, which are finally connected -in series. The sectional method of -winding prevents the liability of the spark -jumping through a short circuit, but<span class="pagenum" id="Page_12">12</span> -heightens its tendency to pass into the primary -coil at the ends, where it must be -therefore specially insulated from it.</p> - -<div class="figcenter" ><a id="fig4"></a> -<img src="images/i_012.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 4.</span></div> -</div> - -<p>In winding these sections there is a -method now generally adopted which has -many good points, although at first it may -seem complicated. The old way of filling -two sections was to wind both in the same<span class="pagenum" id="Page_13">13</span> -direction as full as desired, then join the -outside end of the left-hand coil to the inside -end of the right-hand coil. This -necessitated bringing the outside end -down between two disks, or in a vertical -hole in the sectional divider, and thereby -rendered it liable to spark through into its -own coil. This is shown in Fig. 4, <i>A</i> and -<i>C</i> inside ends, <i>B</i> and <i>D</i> outside ends, the -disk being between <i>B</i> and <i>C</i>.</p> - -<div class="figcenter" ><a id="fig5"></a> -<img src="images/i_013.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 5.</span></div> -</div> - -<p><span class="pagenum" id="Page_14">14</span></p> - -<p>Reference to Fig. 3 shows the new -method, and Fig. 5 shows an enlarged -diagram of sections 2 and 3 of Fig. 3.</p> - -<p>Sections 1 and 3, Fig. 3, are filled with -as many turns as desired; the spool is -then turned end for end, and sections 2 -and 4 are wound, being thus in the opposite -direction of winding to sections 1 -and 3.</p> - -<p>The inside ends of 1 and 2 and 3 and 4 -are soldered together, and the outside -ends of 2 and 3 are also soldered together.</p> - -<p>The outside ends of 1 and 4 serve as terminals -for the coil.</p> - -<p>This method of connection leaves all the -turns so joined that the current circulates -in the same direction through them all, as -will be seen by an examination of the enlarged -diagram, Fig. 5.</p> - -<p>Sprague, in his "Electricity: Its Theory, -Sources, and Application," recommends -that the turns of wire in the secondary -coil shall gradually increase in -number until the middle of the spool is<span class="pagenum" id="Page_15">15</span> -reached, and then decrease to the spool -end, in order that the greatest number of -turns be in the strongest part of the magnetic -field (see Fig. 6). <i>D D D</i> are section -dividers, <i>S</i> secondary windings, <i>P</i> primary -coil. The selection of the size of wire to -be used depends on the requirements as -to the spark. If a short thick spark be -desired, use a thick wire, say No. 34 B. -& S.; if a long thin one, use No. 36 to -No. 40 B. & S.</p> - - -<div class="figcenter" ><a id="fig6"></a> -<img src="images/i_015.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 6.</span></div> -</div> - -<p>Although it is impossible to lay down<span class="pagenum" id="Page_16">16</span> -rules for determining the exact amount of -wire to be used to obtain a certain sized -spark, yet a fair average is to allow -1¼ pounds No. 36 B. & S. per inch spark -for small coils and slightly less for large -ones.</p> - -<p>The most satisfactory and perhaps the -easiest way for large coils is to wind the -secondary in separate coils, made in a -manner similar to that employed in winding -coils for the Thompson reflecting galvanometer. -This method, first described -by Mr. F. C. Alsop in his treatise on -"Induction Coils," is somewhat as follows:</p> - - -<p>A special piece of apparatus (Figs. 7 and -8) is necessary, but presents no great difficulty -in manufacture. A metal disk, <i>D</i>, one-sixth -of an inch thick and 7 inches in diameter, -is mounted on the shaft <i>S</i>. A second -disk is provided with a collar and set -screw, <i>A</i>, in order that it may be adjusted -on the shaft at any desired distance from -the stationary one. When the diameter<span class="pagenum" id="Page_17">17</span> -of the coil to be wound has been decided<span class="pagenum" id="Page_18">18</span> -upon, a wooden collar, <i>W</i>, with a bevelled -surface is slipped on the shaft, it corresponding -in diameter with the desired -diameter of the hole through the centre of -the secondary coil. As these coils are -going to be made as flat -rings and slipped on over -the insulating tube, a remark -here becomes necessary -on this diameter. -Reference to Fig. 9 will -show that it is intended -that the coils near the -reel ends shall fit very -loosely on the tube <i>T</i> -(Fig. 1)—in fact, that -there shall be a clearance of possibly -one-half inch in the extreme end, diminishing -gradually to a fifteenth of an inch in -the centre coils. Therefore it becomes -necessary to provide a number of wooden -rings equal to the desired diameter of the -central hole in the coil. The thickness of<span class="pagenum" id="Page_19">19</span> -the wood determining the width of the individual -coil depends on the selection of -the operator; but the rule may be laid -down that the narrower the coils the better -the insulation of the complete coil will -be on completion.</p> - -<div class="figcenter" ><a id="fig7"></a> -<img src="images/i_017.jpg" alt="" /> -<div class="caption"><span class="smcap gap10">Fig. 7.</span> <span class="smcap">Fig. 8.</span></div> -</div> - -<div class="figleft" ><a id="fig9"></a> -<img src="images/i_018.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 9.</span></div> -</div> - -<p>One-sixteenth of an inch is a very fair -average, and has been generally adopted -by the writer.</p> - -<p>A quantity of paper rings are now cut -out of stout writing paper which has been -soaked in melted paraffin. If a block or -pad of letter paper be soaked in paraffin -and allowed to become cold under pressure, -the ring may be scratched on the surface -of it and the block cut through on a -jig saw. The central apertures of course -will vary in size with their position on the -tube <i>T</i> (Fig. 9).</p> - -<p>The coil winder is now either mounted -in a lathe or fixed in a hand magnet winder -in such manner that it can be steadily and -rapidly rotated. The wire to be wound -comes on spools, which can be so threaded<span class="pagenum" id="Page_20">20</span> -on a piece of metal rod that they turn -readily. A metal dish containing melted -paraffin is provided with a round rod, -preferably of glass, fixed under the paraffin -surface, so that it can rotate freely when -the wire passes under it through the -paraffin. Two paper rings are slipped on -the winder that they may form, as it were, -reel ends for the coil, and if the metal -disks have been warmed it is an easy matter -to lay them flat.</p> - -<p>The end of the wire is then passed -through the paraffin under the glass rod -and through the hole <i>H</i> in the metal disk -for a distance of, say, 6 inches, and held to -the disk outside with a dab of paraffin or -beeswax. Then the winder is rotated -and the space between the paper disks is -filled with wire. The paraffin, being hot, -will adhere to the wire, and cooling as the -wire lays down on the winder, hold the -turns together and at the same time insulate -them from each other. It will not be -possible to lay the wire in even layers, as<span class="pagenum" id="Page_21">21</span> -would be necessary in winding a wider -coil, but the spaces can be filled up, using -ordinary care that no radical irregularity -occurs—that is, that only adjacent layers -are likely to commingle.</p> - -<p>When the space is filled up to the level -of the paper disks and the paraffin is hard, -loosen the set screw, and removing the -outside disk, the coil can be slipped off, or -a slight warming will loosen it. Any -number of these coils can be made, and -there are the advantages in this mode of -construction that a bad coil will not spoil -the whole secondary, and that the wire -can be obtained in comparatively small -quantities.</p> - -<p>As each coil will not be of very high resistance, -the continuity of the wire can be -readily tested by means of a few cells of -battery, connecting one end of the coil to -one pole of the battery, and the other pole -of the battery and coil end touched to the -tongue. If a burning sensation is experienced, -the connection is not broken.<span class="pagenum" id="Page_22">22</span> -Where possible the coils should be measured -as to their resistance on a Wheatstone -bridge.</p> - -<p>When the requisite number of coils has -been prepared, they are assembled in the -following manner (Fig. 9): The coils, having -their aperture diameter graded, are -placed in order, and starting with the one -having the largest hole, it is slipped over -the primary protection tube <i>T</i>, one end -being brought out through a hole in the -reel end drilled vertically or between the -reel end and the coil. A couple of paper -rings are then slipped on the tube, and another -coil placed over them, having its -ends connected as in Fig. 3. This process -is continued until all the coils are in place. -The annular space between the coils and -the tube <i>T</i> (Fig. 9) is filled in with melted -paraffin and the coils gently pressed together, -so as to form a compact mass, -paraffin being poured over the outside of -the whole combination. Before winding -any wire used in this work it must be per<span class="pagenum" id="Page_23">23</span>fectly -dry, which end can be accomplished -by subjecting the whole spool to a short -period of baking in a moderately warm -oven.</p> - -<p>The accompanying table gives the -length of No. 36 silk-covered wire that -will fill a linear space equal to one thickness -of the wire in different-sized rings. -This size wire wound tight will give 125 -turns per linear inch. Therefore on a ring -having a middle aperture of 1½ inches and an -outside diameter of 4 inches, there will be -156 turns, or a total length of 1347 inches. -This is obtained as follows: 1½ inches × -3.1416 = 4.7124 (or 4.712); 4 inches × -3.1416 = 12.5664 (or 12.56); (4.712 + 12.56)∕2 -= mean circumference—viz., 8.635 inches.</p> - -<p>This mean × number of turns in thickness -of ring between the two circumferences—viz., -156 = 1347 inches.</p> -<p><span class="pagenum" id="Page_24">24</span></p> - -<p class="center"><span class="smcap">Table of Secondary Windings.</span></p> -<div class="center small"> -<table border="1" cellpadding="4" cellspacing="0" summary=""> -<tr> - <th align="left"><span class="smcap">No. 36 Silk-Covered Wire. -125 Turns per Linear inch. 13,306 Feet per Pound</span></th> - <th colspan="3">1½″ Aperture Diameter, 4.712″ Aperture Circumference.</th> - <th colspan="3">2″ Aperture Diameter, 6.283″ Aperture Circumference.</th> - <th colspan="3">2½″ Aperture Diameter, 7.854″ Aperture Circumference.</th> -</tr> -<tr> - <td align="left">Outside diameter</td> - <td align="center">4″</td> - <td align="center">5″</td> - <td align="center">6″</td> - <td align="center">4″</td> - <td align="center">5″</td> - <td align="center">6″</td> - <td align="center">5″</td> - <td align="center">6″</td> - <td align="center">7″</td> -</tr> -<tr> - <td align="left">Outside circumference</td> - <td align="center">12.56</td> - <td align="center">15.70</td> - <td align="center">18.84</td> - <td align="center">12.56</td> - <td align="center">15.70</td> - <td align="center">18.84</td> - <td align="center">15.70</td> - <td align="center">18.84</td> - <td align="center">21.99</td> -</tr> -<tr> - <td align="left">Mean circumference</td> - <td align="center">8.635</td> - <td align="center">10.20</td> - <td align="center">11.78</td> - <td align="center">9.421</td> - <td align="center">10.99</td> - <td align="center">12.56</td> - <td align="center">11.78</td> - <td align="center">13.35</td> - <td align="center">14.92</td> -</tr> -<tr> - <td align="left">Turns between circumferences</td> - <td align="center">156</td> - <td align="center">219</td> - <td align="center">282</td> - <td align="center">125</td> - <td align="center">188</td> - <td align="center">250</td> - <td align="center">156</td> - <td align="center">219</td> - <td align="center">282</td> -</tr> -<tr> - <td align="left">Distance between aperture and outside, in inches</td> - <td align="center">1.25</td> - <td align="center">1.75</td> - <td align="center">2.25</td> - <td align="center">1</td> - <td align="center">1.50</td> - <td align="center">2</td> - <td align="center">1.25</td> - <td align="center">1.75</td> - <td align="center">2.25</td> -</tr> -<tr> - <td align="left">Length of wire, in inches</td> - <td align="center">1347</td> - <td align="center">2234</td> - <td align="center">2650</td> - <td align="center">1178</td> - <td align="center">2066</td> - <td align="center">3140</td> - <td align="center">1838</td> - <td align="center">2924</td> - <td align="center">4207</td> -</tr> -</table></div> -<p><span class="pagenum" id="Page_25">25</span></p> - - -<p>To obtain the length of wire necessary -for a ring occupying more than the space -of one turn on the primary insulating tube, -multiply the length before obtained by the -number of turns in the space it occupies. -Thus a flat ring one-tenth of an inch thick -would equal 1347 inches × 12.5.</p> - -<p>This rule is necessarily only approximate, -owing to the way the wires bed on -each other from their cylindrical section. -In actual practice, when the wire is run -through the paraffin bath not more than -50 per cent of the calculated wire will occupy -the space. And the thickness of the -paper rings must also be added when figuring -the total length of the coil. In the -iron-clad transformers or induction coils of -highest efficiency used in the alternating -current electric light system, the rule for -determining the windings of the coils is -based on the ratio of the turns of wire in -the primary to the turns in the secondary, -the electromotive force in the primary, and -the lines of force cut by the windings.</p> - -<p>The secondary ends can be attached to -<span class="pagenum" id="Page_26">26</span>binding posts mounted on the reel ends. -Unless these reel ends be very high and -clear the outside of the coil considerably, -it is better to mount the binding posts on -the top of the hard rubber pillars. A neat -plan is to mount on the top of the coil a -hard rubber plate reaching from reel end -to reel end, and place the binding posts on -that.</p> - -<p>A discharger consists of two sliding -metal rods with insulated handles passing -through pillars attached to the secondary -coil. The inside ends of these rods is provided -with screw threads for the ready -attachment of the balls, points, etc., which -are to be used. The substance to be acted -upon is laid on a rubber or glass table -midway between the rod pillars and -slightly below the level of the rods.</p> - -<p>By hinging the rod pillars, or using a -ball and socket joint, the discharger can -be inclined so as to be better brought near -the substance on the table.</p> - -<p>The next important part of the coil is -<span class="pagenum" id="Page_27">27</span>the contact breaker.</p> - -<p>The armature <i>R</i> is a piece of soft iron -carried at the end of a stiff spring, in about -the middle of which, at <i>B</i>, is riveted a small -platinum disk or stud. The adjusting -screw <i>A</i> has its point also furnished with a -piece of platinum, which is intended to -touch the platinum on the spring when the -latter is in its normal position. The core -<i>C</i> of the coil serves as an electro-magnet. -When the current flows from the battery -(represented by the figure at <i>L</i>) through -the primary coil and armature spring to -the adjusting screw, it causes the armature -to be drawn to the magnetized core, but -thereby draws the platinum disk away -from the adjusting screw. In so doing it -breaks the circuit, the magnet loses its -power, and the elasticity of the spring reasserting -itself, carries the armature back, -thereby reclosing the circuit. This is repeated -many times in a second, the result -being a continual vibration of the spring, -<span class="pagenum" id="Page_28">28</span>and a consequent interruption to the current.</p> - -<p>The condenser or Leyden jar <i>J</i>, connected -as in the diagram to the base of the vibrating -spring at <i>K</i> and to the adjusting screw -wire <i>M</i>, is constructed as follows: On a -sheet of insulated paper is laid a smaller -sheet of tinfoil, one edge of which projects -an inch or so over one end of the paper. -Another sheet of paper covering this carries -a second sheet of tinfoil, one end of -which projects as in the first sheet, but at -the opposite end of the paper. Tinfoil -and paper sheets are laid in this manner -alternately until a sufficient number is attained. -The projecting ends are then -clamped together and the whole pile immersed -in melted paraffin, as will be described -in a subsequent chapter. Wires -are affixed to these clamped ends which -serve to connect the condenser with the -contact breaker. The conventional sign -for a condenser is that used at <i>J</i>, showing -the two series of plates, the insulation or -dielectric, as it is called, being understood.</p> - -<p><span class="pagenum" id="Page_29">29</span>The size of condenser to use with different-sized -coils varies according to the -winding of the primary and the battery -used. A primary coil of few turns would -not necessitate as large a condenser as one -of a large number of turns. At the same -time, a condenser may be made of too -great a capacity, and thereby weaken the -action of the coil.</p> - -<p>The base upon which the coil and its -parts are mounted may be of dried polished -wood. But where the coil is designed -to give large sparks—over 2 -inches—it is an advantage to use hard rubber -one quarter of an inch and upward in -thickness. Glass, were it not for the difficulty -of drilling it and its brittleness, -would be a desirable material for a coil -base in a dry atmosphere. Hard red or -black fibre coated with shellac varnish is -also serviceable, and, moreover, is extremely -easy to work. Slate must never -be used; there is too much liability of iron -veins being found in it, which in such high -<span class="pagenum" id="Page_30">30</span>tension experiments as will be described -would seriously impair the usefulness of -the apparatus. The material selected for -the base must be one that will not absorb -moisture. A paraffined surface collects -moisture up to a certain point in isolated -drops, whereas a glass and even a hard -rubber surface condenses the moisture as -a film, which latter is extremely undesirable. -But unfortunately the fact that a -paraffined surface does not present a -pleasing appearance would probably result -in its rejection. And lastly, by -mounting the coil on hard rubber blocks, -or extending the reel ends to raise the coil -body, a high insulation can be obtained at -the sacrifice perhaps of appearance or -height. From the care taken to insulate -the secondary coil, it may be considered a -superfluous precaution to so carefully select -a base, but practical work with the -instrument at some important crisis will -demonstrate the necessity of extreme care -in the smallest details relating to insulation. -<span class="pagenum" id="Page_31">31</span>It may be well to note here that -hard rubber is acted upon by ozone, and -is thereby impaired as an insulator.</p> - -<div class="figright" ><a id="fig10"></a> -<img src="images/i_031.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 10.</span></div> -</div> - -<p>The base forms the top of a flat box in -which the condenser lies; but there are a -few points worth considering right here. -As the connections of the coil will probably -be under the base, -a sufficient space must -intervene between the -base and the top of the -condenser. It is a good -plan to lay the condenser -at least one half inch below -the top of this box, -and fill up to, say, one -eighth of an inch with -melted paraffin, leaving -the condenser wires projecting for attachment. -The connections of the primary -coil and contact breaker should -by all means be soldered, not simply -wires held under screw nuts. And, -moreover, all wires under the base should -<span class="pagenum" id="Page_32">32</span>be so run that they do not cross one another, -which precaution only requires a -little planning. Then, when the connections -are all made and the base laid on top -of the box, it can be pressed down if the -paraffin be warm, so that the screw heads -and wires mark out their own channels -and cavities in which to lie.</p> - -<p>A commutator or pole-changing switch -is often added to change the polarity of -the battery current. The diagram of connection -is shown in Fig. 10. When the -levers are as in the figure, the circuit is -broken and no current flows through the -coil.</p> - -<h3><span class="smcap">Coils in Series.</span></h3> - -<p>Ruhmkorff coils can be connected in -series, but it is not to be recommended. -When it becomes necessary, however, the -cores should be removed, and one long core -inserted, extending through each primary. -This will bring the time constants of each -primary coil together and prevent the interference -<span class="pagenum" id="Page_33">33</span>otherwise present. The primary -coils and secondary coils are connected in -series by assuming that they are but adjacent -sections of one complete instrument. Of -course, as the resistance of the primary is -raised, the electromotive force of the battery -must be raised also.</p> - -<h3><span class="smcap">Oil Immersed Coil.</span></h3> - -<p>A highly satisfactory induction coil can -be made without much labor and few tools, -and will prove useful in many experiments -which would not warrant a more expensive -instrument.</p> - -<p>Make a bundle of soft iron wires, No. 22 -B W G, for the core, ten inches in length and -one inch or more in diameter. Wrap this -with insulating tape or even ordinary tape -to prevent the primary coil from coming in -contact with the iron. Now, wind on a -primary of two layers No. 14 B & S gauge -cotton-covered copper wire, and insert the -coil into a hard rubber (or glass preferred) -<span class="pagenum" id="Page_34">34</span>tube large enough to hold the coil tight and -to project an inch or so beyond the core -ends.</p> - -<p>A secondary coil of about one pound -No. 36 cotton-covered magnet wire should -now be made on a hard rubber spool, the -hole through centre of this spool must be -at least one inch larger in diameter than the -diameter of the primary cover. This spool -should not exceed four inches in length, and -is to be slipped over the primary coil and -held suspended by blocks of wood in such -a manner that it does not touch the primary -coil or cover. The whole outfit is now -immersed in an earthenware or glass vessel -filled with linseed or heavy paraffin oil. -The contact breaker and condenser will be -mounted independently; the condenser for -the two-inch spark coil will be suitable (see -Table on <a href="#Page_7">page—7</a>).</p> - -<h3><span class="smcap">"Tesla" Coil.</span></h3> - -<p>The coil just described, without contact -breaker or iron core, can be connected up -<span class="pagenum" id="Page_35">35</span>and used in place of a "Tesla coil," which -it resembles. The coils used by Nikola -Tesla are so many and varied that it becomes -a difficult task to describe a mode of construction -which will meet the wants of those -who ask for "Tesla" coils. The <i>American -Electrician</i> gives a description of one -wherein a glass battery jar, 6 inches × -8 inches, is wound with 60 to 80 turns of -No. 18 B & S magnet wire. Into this is -slipped a primary, consisting of 8 to 10 -turns of No. 6 B & S wire, and the whole -combination immersed in a vessel containing -linseed or mineral oil.</p> - -<div class="figcenter" ><a id="fig11"></a> -<img src="images/i_035.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 11.</span></div> -</div> -<p><span class="pagenum" id="Page_36">36</span></p> - -<h3><span class="smcap">Disruptive "Tesla" Coil.</span></h3> - -<p>For Fig. 11 the specification is as follows: -Secondary, 300 turns of No. 30 B & S silk-covered -magnet wire, wound on rubber tube -or rod, and the ends encased in glass or -rubber tubes. This is inserted <i>into</i> the primary, -which consists of two coils, each of -20 turns No. 16 B & S rubber-covered wire, -wound separately on a long rubber tube not -less than ⅛ inch thick. The last tube must -be large enough to be very loose when the -secondary coil is inserted in it, and it must -project at least two inches over each end of -the secondary. A hard rubber division must -be placed between these primary coils. The -four ends of the latter coils are connected -<i>C C</i> to two condensers and <i>D D</i> to two discharger -balls, the secondary wires going to -the exhibitive apparatus. A further description -of these connections is to be found in -<a href="#CHAPTER_XII">Chapter XII</a>., also notes upon the use of the -<span class="pagenum" id="Page_37">37</span>disruptive coil.</p> - -<p> -<i>Coils for Gas Engines.</i></p> - -<p>These are either primary only or primary -and secondary. Two to three pounds of -No. 14 B & S magnet wire are wound on an -iron wire core eight to ten inches in length -by one inch in diameter. The contact is -made and broken in the igniter of the -engine as at the wipe spring of a ratchet gas -burner. Four to eight large cells of dry -battery are used, or eight cells Edison-Lalande—iron-clad -type. Number of cells -varies with size of coil needed, some classes -of engines require a heavier spark than -others to ignite the vapor.</p> - -<p>When a primary and secondary are used, -the primary should be made of two or three -layers No. 14 B & S magnet wire, and a -secondary of one pound No. 34 B & S -magnet wire. There can be an independent -contact breaker or the coil can be made up -similar to a one-half inch spark Ruhmkorff -coil (see Chapter I.).</p> - -<div class="figcenter" ><a id="fig12"></a> -<img src="images/i_038.jpg" alt="" /> -<div class="caption"> <span class="smcap">Fig. 12.</span></div> -</div> - -<p><span class="pagenum" id="Page_38">38</span>The method of connecting up a coil of the -latter description is shown in Fig. 12, which -is self-explanatory. It shows a form of -cam-shaft switch which is operated by the -engine, and which opens and closes the primary -<span class="pagenum" id="Page_39">39</span>circuit of the induction coil, the sparks -from the secondary winding passing between -the points of the igniter in the engine -cylinder. As shown in Fig. 12, the igniter -or ignition plug is similar in operation to a -coil discharger, the two terminals being, -however, insulated from each other by the -use of porcelain. To ensure a good insulation -under the severe working conditions -has been somewhat of a task, but it seems to -have been attained in the types of igniters -known as the Splitdorf and the Roche or -New Standard.</p> - -<p>The Splitdorf gas-engine coil is the result -of much experiment and careful design. It -is built to stand hard usage, and the insulation -used has been adopted only after exhaustive -test. In automobile work, where a -heavy strain is made upon the engine, as in -climbing heavy grades, it has been found -that a stronger spark gives surer results. -This would indicate more battery current -through the coil, and it is a wise precaution -to have a few extra cells attached that can be -<span class="pagenum" id="Page_40">40</span>switched on if necessary.</p> - -<p>In constructing spark coils for gas engines -particular care must be given to the contact -breaker. In most types of gas or oil vapor -engines it is absolutely necessary to have -the spark pass with uniform regularity, and -immediately and surely when required. For -automobiles or where the apparatus is subject -to jar, a heavy iron vibrating armature -would become unreliable by reason of its -inertia and its responding to shock. At -every jolt of the vehicle it would jar and -get out of rhythm, and it certainly seems -preferable to use a mechanical contact apparatus -whenever feasible. In the older type -of gas engine the spark is made by mechanism -breaking contact right in the vapor. -The actual arrangement of these devices is -detailed and illustrated in the later works -on gas and oil engines.</p> - -<h3><span class="smcap">Resistance Coils.</span></h3> - -<p>Although foreign to the title of this book, -<span class="pagenum" id="Page_41">41</span>these coils will be mentioned, being often -necessary as accessories to the operation of -coils, wireless telegraphy, etc. These are -coils of insulated German silver wire, wound -to a specified resistance. The main feature -about those designed for testing is that they -are wound non-inductively—that is, the -wire is wound double in such manner that -the current flows both ways around the -turns, and so neutralizes the inductive action. -In cases where dynamo current is to be -used, as in telegraphs operated from dynamo -current, the coils are wound on tin tubes to -make them fireproof and yet radiate the -heat. As the resistance of German silver -varies very largely, only approximate figures -can be given. The table (<a href="#Page_64">page 64</a>) has -been made up from the best averages obtainable. -The carrying capacity of resistance -coils varies with their construction, the -better they can radiate heat, the more current -<span class="pagenum" id="Page_42">42</span>they can safely carry.</p> - -<h3><span class="smcap">General Remarks on Coils, etc.</span></h3> - -<p>Ruhmkorff induction coils should always -be fitted with a switch to open, close, or -reverse the power circuit, a double throw, -double pole, baby knife switch, mounted on -a separate porcelain base, is very suitable. -Such a switch is open when the handle is -vertical, and it should always be left so when -changing connections, fixing battery, etc. -A large, well-finished coil will have the -secondary wires brought in rubber tubes to -binding posts mounted on hard rubber pillars, -or to binding posts mounted considerably -above the coil cover level. A very neat -mode is shown in the frontispiece on the -large 45-inch spark coil. Here the secondary -wires go to hard rubber pillars, which also -carry adjustable rod dischargers. These -rods are movable towards or away from -each other by means of the large hard rubber -handle to which they are connected by a -simple system of levers. In this coil the -<span class="pagenum" id="Page_43">43</span>secondary is moulded on a flexible tube, -which fits loosely over the primary tube in -order to compensate for changes of temperature -and consequent expansions and contractions. -All well-designed coils should be -so arranged that the primary coil and core -can be readily removed from the secondary, -or <i>vice versa</i>. It is sometimes desirable to -use a different primary. This arrangement -will greatly facilitate any necessary repairs. -It must be always remembered that the -working of a coil depends on the insulation -between primary and secondary. <i>Spare no -pains to have perfect insulation</i>; it is a -hopeless task to reinsulate a broken-down -secondary, although the sectional method -of winding facilitates repairs. In large -winding rooms it is customary to have a -revolution counter connected to the spindle, -so that the number of turns can be seen at -all times. A bicycle cyclometer can be -readily fitted up for this purpose, and will -be found of considerable assistance where -a number of sections are needed, each with -<span class="pagenum" id="Page_44">44</span>a similar number of turns. In the commercial -construction of telephone coils and -magnet spools it is often the rule to specify -only the number of turns of the requisite -size wire, the ampere turns of the coils being -thus regulated.</p> - -<h3><span class="smcap">The Testing of a Coil for Polarity.</span></h3> - -<p>This is often necessary, and may be done -in a variety of ways. When the coil is working, -and sparks be passed between fine wires -mounted on the discharger, the positive wire -tip will be cold, whereas the negative end -will be quite hot. In vacuo, the positive -shows a purple red when the negative glows -with a bluish violet. The decomposition of -water, which consists of oxygen and hydrogen -in the formula H<sub>2</sub>O, is readily accomplished -by the secondary current, and the -greatest volume of gas (hydrogen) will be -evolved at the <i>negative pole</i>. For ready -reference a summary of these facts is given -<span class="pagenum" id="Page_45">45</span>below: -</p> - - -<div class="center small"> -<table border="0" cellpadding="4" cellspacing="0" summary=""> -<tr> - <th class="thbr">Positive</th> - <th>Negative</th> -</tr> -<tr> - <td class="tdbr">Cold wire,</td> - <td align="left">Hot wire,</td> -</tr> -<tr> - <td class="tdbr">Anode,</td> - <td align="left">Cathode,</td> -</tr> -<tr> - <td class="tdbr">+ sign,</td> - <td align="left">- sign,</td> -</tr> -<tr> - <td class="tdbr">Purple red,</td> - <td align="left">Bluish violet,</td> -</tr> -<tr> - <td class="tdbr">Zinc plate,</td> - <td align="left">Carbon plate,</td> -</tr> -<tr> - <td class="tdbr">(Carbon) pole,</td> - <td align="left">Zinc pole,</td> -</tr> -<tr> - <td class="tdbr">Oxygen gas.</td> - <td align="left">Hydrogen gas.</td> -</tr> -</table></div> - - -<p>Although it is customary to use bundles -of fine, soft iron wire for coil cores, very -excellent results have been obtained with -cores made up of soft iron filings. These -filings should be tightly packed in the core -tube and have a soft iron head at the contact -breaker end. Filings demagnetize very -quickly and prevent the formation of destructive -eddy currents, which have been -previously discussed (Chapter I.).</p> - -<p>Modern practice tends towards a lengthening -of the core and primary, in some cases -fully 20 per cent of the core length projects -from each end of the coil. One result must -be as in electromagnets, the longer the core, -the longer it takes to magnetize or demag<span class="pagenum" id="Page_46">46</span>netize. -But even here it is a matter of -individual construction.</p> - -<p>The common practice is to make coils to -be in a horizontal position; there is no reason -why they cannot be made to stand on end. -In fact, this position to an extent takes off -some of the strain on the primary. It is -mostly a matter of choice or convenience.</p> - -<p>As to the possible output of an induction -coil, it depends upon design and construction; -but S. P. Thompson gives the following -law in his work on Electricity and -Magnetism: The electromotive force generated -in the secondary circuit is to that -employed in the primary nearly in the same -proportion as the relative turns of the two -coils.<a id="FNanchor_1_1" href="#Footnote_1_1" class="fnanchor">1</a></p> - -<div class="footnotes"> -<div class="footnote"> - -<p><a id="Footnote_1_1" href="#FNanchor_1_1" class="label">1</a> -We do not attempt to reconcile this quotation with the enormous -estimates of spark potential.</p></div></div> - -<p>In selecting a Ruhmkorff coil, it must be -remembered that the rating in spark length -is subject to question. Supposing two similar -coils be operated, one with a rapid vibrator -and the other with a slow vibrator, -other things being equal, the slow vibrator -will give the greatest spark length. Again,<span class="pagenum" id="Page_47">47</span> -the appearance of the spark is of vast importance. -Although two coils might be -sparking across the same length air-gap, the -one giving the whitest and thickest continuous -succession of sparks is the better. Fig. -13 shows a reproduction from a photograph -of a spark 32 inches long, generated by the -coil shown on the frontispiece.</p> - -<div class="figcenter" ><a id="fig13"></a> -<img src="images/i_047.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 13.</span></div> -</div> - -<p>It is easy to take a coil, and by snapping -the vibrator contacts together a few times a -spark of thin bluish character will jump<span class="pagenum" id="Page_48">48</span> -across a gap, of length far exceeding the -spark gap when vibrator is working at normal -speed. But this spark only passes at -irregular intervals, seemingly gathering -strength for its forced leap. It must not be -considered in rating the coil.</p> - -<p>In winding primary coils it is proposed -to reduce the self-induction or inductance -of its adjacent coils by means of similar -methods used in winding electromagnets. -The primary winding, instead of being composed -of a number of turns of one large -wire, is made up of a multiple winding of -small wires, aggregating the conductivity -of the large wire. This materially reduces -sparking at the contact breaker, and certainly -allows of a closer bedding of wire -nearer the core, also giving a greater percentage -of ampere turns. Another scheme -which uses the Dessauer contact breaker -provides two separate primary windings, -opening one when the other closes. Such -schemes as these come well within the scope -of the experimenter, and it is highly possible<span class="pagenum" id="Page_49">49</span> -that valuable improvements will be made in -coil design during the coming years.</p> - - -<h3><span class="smcap">Failure to Work.</span></h3> - -<p>The following are the commonest causes -of coils not working to their best limit: -Contact breaker contacts dirty, burned, -stuck, too small, not in good parallel relation -face to face of platinum.</p> - -<p>Secondary wires crossed outside coil, -often happens that the secondary is quietly -sparking away into or through some object -touching it, particularly when long wire -connections are run from secondary to place -of desired sparking.</p> - -<p>Condenser too small, burned out, badly -insulated (see other pages on this subject).</p> - -<p>Battery too small—too high internal -resistance or wires leading from battery to -coil too small—for ordinary coil work, distance -of, perhaps, ten feet, use No. 10 to 12 -B & S flexible lamp cord or solid wire. -Ruhmkorff coils require plenty of current -to produce large sparks.</p> - -<p><span class="pagenum" id="Page_50">50</span></p> - - -<div class="center small"> -<table border="1" cellpadding="4" cellspacing="0" summary=""> -<tr> - <th align="center" colspan="6"><span class="smcap">Dimensions for Different Spark Lengths.</span></th> -</tr> -<tr> - <th align="center"> </th> - <th align="center">½ inch</th><th align="center">1 inch</th> - <th align="center">2 inches</th><th align="center">6 inches</th> - <th align="center">12 inches</th> -</tr> -<tr> - <td align="left">Foil sheets</td> - <td align="center">5½ × 4</td> - <td align="center">6 × 4</td> - <td align="center">6 × 6</td> - <td align="center">10 × 5</td> - <td align="center">12 × 8</td> -</tr> -<tr> - <td align="left">Number</td> - <td align="center">40</td> - <td align="center">40</td> - <td align="center">60</td> - <td align="center">60</td> - <td align="center">60</td> -</tr> -<tr> - <td align="left">Paper sheets</td> - <td align="center">6½ × 5</td> - <td align="center">9 × 5</td> - <td align="center">8½ × 7</td> - <td align="center">12 × 7</td> - <td align="center">14 × 10</td> -</tr> -<tr> - <td align="left">Number</td> - <td align="center">60</td> - <td align="center">60</td> - <td align="center">80</td> - <td align="center">80</td> - <td align="center">80</td> -</tr> -<tr> - <td align="left">Core length</td> - <td align="center">5</td> - <td align="center">7</td> - <td align="center">9</td> - <td align="center">12</td> - <td align="center">19</td> -</tr> -<tr> - <td align="left">Core diameter</td> - <td align="center">⅝</td> - <td align="center">¾</td> - <td align="center">1″</td> - <td align="center">1⅛</td> - <td align="center">1½</td> -</tr> -<tr> - <td align="left">Primary size B & S</td> - <td align="center">16</td> - <td align="center">14</td> - <td align="center">14</td> - <td align="center">12</td> - <td align="center">10</td> -</tr> -<tr> - <td align="left">Secondary size B & S.</td> - <td align="center">36</td> - <td align="center">36</td> - <td align="center">36</td> - <td align="center">36</td> - <td align="center">38</td> -</tr> -<tr> - <td align="left">Core wire size B W G.</td> - <td align="center">22</td> - <td align="center">22</td> - <td align="center">22</td> - <td align="center">22</td> - <td align="center">22</td> -</tr> -<tr> - <td align="left">Quantity in pounds<br />of secondary wire</td> - <td align="center">¾</td> - <td align="center">1¼</td> - <td align="center">2½</td> - <td align="center">7</td> - <td align="center">12</td> -</tr> -<tr> - <td align="left">Layers of primary</td> - <td align="center">3</td> - <td align="center">3</td> - <td align="center">2</td> - <td align="center">2</td> - <td align="center">2</td> -</tr> -<tr> - <td align="left">Area of paper, sq. in.</td> - <td align="center">2,000</td> - <td align="center">2,700</td> - <td align="center">4,800</td> - <td align="center">6,600</td> - <td align="center">11,000</td> -</tr> -<tr> - <td align="left">Area of foil, sq. in.</td> - <td align="center">880</td> - <td align="center">960</td> - <td align="center">2,100</td> - <td align="center">3,000</td> - <td align="center">5,760</td> -</tr> -</table></div> - -<p><span class="pagenum" id="Page_51">51</span></p> - -<p>As it is not always convenient to procure -paper and foil in set sizes, the area of -material needed for condensers is also given. -The above table is approximate. It represents -data collected from the best modern -practice. The gauge above given for copper -wire is that of Brown & Sharpe, and is -used throughout these pages.</p> - - -<h3><span class="smcap">Medical Coils.</span></h3> - -<p>The main points of difference between -coils for electrotherapeutics and Ruhmkorff -coils is that the former are devoid of condensers, -are rarely insulated to a high degree, -and are arranged for current strength regulation. -The modes of regulation are many, -briefly the principal are: (<i>a</i>) In coils with -independent circuit breakers, sliding both -core and primary coil out of the secondary -together or independently. (<i>b</i>) Moving a -metal tube over or off the primary coil or -core or both. Many combinations of these -methods are practised. Attempts have been -made to regulate battery current by rheostat,<span class="pagenum" id="Page_52">52</span> -but it is not feasible, except in large stationary -outfits. Cheap medical coils are wound -with bare wire, with layers of thread between -adjacent turns, or even only bedding -the wire turns in paraffined paper. It is not -intended to convey the idea that winding -bare wire coils is a makeshift; far from it. -This method is being very generally adopted -in telephone work. But it requires special -and delicate machinery, and is unsuited to -amateur work, where slight differences of -cost or labor are insignificant. Others for -specific purposes consist of a primary coil -only. The best and most complete made -are so arranged that independent secondary -coils of different sized wires can be used -with the one primary, being readily slipped -on or off as required. There is another -scheme of regulation, where the coil is -wound in sections and these sections cut in -or out by means of a switch, but it is not -desirable.</p> - -<p><span class="pagenum" id="Page_53">53</span></p> - - -<h3><span class="smcap">Medical Coil with Tube Regulation.</span></h3> - -<div class="figcenter" ><a id="fig14"></a> -<img src="images/i_053.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 14.</span></div> -</div> - -<p>Figure 14 shows a coil with tube mode of -regulation. The core <i>C</i> consists of a piece of -iron tube, very thin, 4 inches long by ⅜ inch -diameter, and filled with soft iron wires. -One end of this core is firmly fixed in the -left-hand bobbin head. The object of the -iron tube is to prevent the sliding tube from -catching in the iron wires, otherwise it can -be dispensed with. Over this tube is slipped -a brass tube <i>T</i>, ending in a handle <i>H</i> at the -right-hand end; this must work easily over -the core tube. The spool for the primary is -now made up by fixing the other bobbin head -on a paper or fibre tube and fastening its<span class="pagenum" id="Page_54">54</span> -free end to the left-hand bobbin head, or the -spool can be made in the usual way by -glueing up two spool ends on a fibre or paper -tube and securing the iron core firmly in one -end, allowing room, of course, for the brass -tube to slide in at the right-hand end. The -primary winding is three or four layers of -No. 20 B & S gauge cotton-covered magnet -wire, the ends being brought out for future -connection. Over this is now laid a few -layers of paraffined paper, and ten or twelve -layers of No. 36 B & S cotton-covered -magnet wire is wound on for the secondary -coil.</p> - -<p>The contact breaker <i>R</i> is in no way different -from the simple form described in -Chapter II. Its construction can be readily -seen from the figure.</p> - -<p>A layer of cloth of the kind used in -covering electromagnets is laid on over the -secondary, and the coil is ready to be attached -to the base. The base is seven inches -long by three wide, and has little feet at its -four corners to elevate it from the table and<span class="pagenum" id="Page_55">55</span> -prevent abrasion of the connections underneath.</p> - -<div class="figcenter" ><a id="fig15"></a> -<img src="images/i_055.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 15.</span></div> -</div> - -<p>The connections are as given in Fig. 15. -When in operation, the electrode cords -being attached to binding posts, Nos. 1 and -2 are in circuit with the secondary coil only. -When at Nos. 2 and 3 they receive the -induced current or extra current in the -primary, caused by the break of the battery -circuit (see page 3).</p> - - -<p><span class="smcap">Medical Coil with Interchangeable -Secondaries.</span></p> - -<p>This form of coil is the only one for -practical medical work, and more space will<span class="pagenum" id="Page_56">56</span> -be given to its construction than to the foregoing,<span class="pagenum" id="Page_57">57</span> -which is suited only for limited use.</p> - -<div class="figcenter" ><a id="fig16"></a> -<img src="images/i_056.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 16.</span></div> -</div> - -<p>Fig. 16 shows side elevation of coil on -base. The design can be largely varied, also -it can be used either for a wall board, a -cabinet top, or made to be carried in a case -containing battery, electrodes, etc. <i>S</i> is one -of the secondary coils, of which at least three -should be provided. The dimensions are, of -course, the same—namely, four inches long -by 3½ inches wide over all. The spool ends -are furnished with heel pieces, which slide -under the brass track bar <i>T</i>. This accurately -centres the coil and prevents it from working -loose.</p> - - -<h3><span class="smcap">Windings for Secondary.</span></h3> - -<p>The following windings for removable or -interchangeable secondary coils are those -most in use.</p> - -<p>Coil No. 1. 4500 feet (.375 pound) -No. 36 B & S, approximating 1800 ohms. -This may be led out in three divisions by -means of switch on coil head. First divi<span class="pagenum" id="Page_58">58</span>sion, -4500 feet; second division, 3000 feet; -third division, 1500 feet.</p> - -<p>Coil No. 2. 2400 feet (.6 pound) No. 31 -B & S, about 350 ohms, divided into 2400 -feet, 1500 feet, and 900 feet.</p> - -<p>Coil No. 3. 750 feet (1 pound) No. 22 -B & S in one coil, or two divisions of 500 -and 750 feet, respectively; approximate resistance -of wire, 125 ohms.</p> - -<p>Coil No. 4. It may be necessary to obtain -currents of extremely high tension, in which -case a coil may be prepared of 5000 feet -No. 38 B & S, or No. 40 B & S preferably.</p> - -<p>The finer the wire, the less current and -the most sedative effect; the coarser the -wire, the more current with corresponding -increased painful action.</p> - -<p>The spools, in fact as much of the framework -as possible, should be made of hard -rubber, to which a fine finish can be given, -although mahogany, rosewood, or even -stained oak can be used. On each side of -the right-hand spool heads a flat brass spring -is screwed, making the contact for the sec<span class="pagenum" id="Page_59">59</span>ondary -wires on brass strips screwed on top -of the track rods. These secondary connections -can be made by means of flexible cords -to binding posts, but the sliding contact is -preferable. The primary coil <i>P</i> is firmly -held in the left spool head, and consists of -a core of No. 22 B W G soft iron wires, -insulated and wound with three layers of -No. 20 B & S magnet wire. The outside of -this coil is neatly enclosed in a hard rubber -tube to permit of the secondary coils sliding -freely upon it. It is better, however, for -the secondary coils not to touch the primary -tube. The vibrator, or contact breaker, -should be of the adjustable form shown in -Fig. 17. The adjusting screw for the contact -breaker can be mounted in a brass lug -carried by the spool head.</p> - -<p>Connections of this coil are substantially -the same as those of the first-described -medical coil. This apparatus is well worthy -of elaboration; it should be fitted with a -ribbon vibrator as well as an adjustable -speed slow vibrator, a switch controlling<span class="pagenum" id="Page_60">60</span> -either. A great variety of secondary coils -can be made, those of coarse wire taking -the place of the current from the contact -breaker. The vibrators should be operated -from an independent battery, although in -the last coil described the magnet may be -wound with the same size wire as the primary -and then be in series with it. The -secondary spools can be made of stained -hard wood ends fitted on to fibre tube, which -latter is easily procurable. Particular attention -should always be paid to the spools and -heads; if not properly made, they may come -apart, and a disastrous unravelling of the -wires ensues.</p> - -<div class="figcenter" ><a id="fig17"></a> -<img src="images/i_060.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 17.</span></div> -</div> - -<p><span class="pagenum" id="Page_61">61</span></p> - - -<h3><span class="smcap">Bath Coils.</span></h3> - -<p>A coil much used for electric baths has -a primary winding only, regulated by the -sliding in and out of the iron core, which -necessitates the use of an independent -vibrator, or else by varying the current -strength with a rheostat. The general -directions given before will answer in the -present case, the only data necessary being -the size of wire, which should be about six -to ten layers of No. 20 B & S. The coil -with movable secondaries here comes into -service. Strong currents are needed for -bath work, and any variety of winding can -be used with this make of coil. There are so -many descriptions of bath and small medical -coils in the electrical magazines published -for amateur workers, that it is hardly necessary -here to give more than a mention of -the principal ones.</p> - -<p><span class="pagenum" id="Page_62">62</span></p> - - -<h3><span class="smcap">Hints in Caring for Medical Coils.</span></h3> - -<p>A few remarks on medical coils and their -diseases may not be amiss; often a very little -defect, if remedied in time, will prevent -costly repairs.</p> - -<p>The main care in medical electrical apparatus -is the battery (see Chapter X. for -descriptions of coil batteries and their operation). -Clean, fresh solutions and clean -contacts are essential. Keep zincs well -amalgamated, remove wires from binding -posts, and scrape bright the metal where the -wires make connection; see no fluid is -splashed on contacts, clean all contact -springs periodically. The Edison-Lalande -battery is probably the best for medical use, -but even this requires occasional attention -as to contacts, new zincs, fresh solution, etc.</p> - -<p>Poor adjustment at contact breaker, dirty -or corroded contacts, loose wires, loose -binding posts, corroded binding posts, are -often the only trouble in a coil refusing to -work.</p> - -<p><span class="pagenum" id="Page_63">63</span></p> - -<p>Flexible cords are fruitful of trouble: -the tinsel breaks, and there is no circuit; gets -wet and crosses or causes a leak; cord tips -get loose and alternately open and close a -contact; one minute all is well, next minute -no current can be obtained. Another trouble -in acid batteries is caused by leaving the -zincs in the fluid. It is easy to do it in most -cases, although the ingenuity of the leading -medical electrical apparatus makers to-day -is directed to this point. Cleanliness and -careful inspection of all contacts is well -repaid; carelessness surely brings its evils.</p> - -<p>It is very desirable in medical work to -eliminate the noise attendant upon the working -of the coil vibrator. This jarring or -humming is often in itself a source of irritation -to a nervous patient. The sound can be -deadened in various ways, for instance, by -placing over the vibrator a temporary wood -cover, lined with felt, resting upon a soft -rubber gasket; or in any other manner that -may suggest itself to the operator.</p> - -<p><span class="pagenum" id="Page_64">64</span></p> - -<p class="center"><span class="smcap">Table Showing Resistances and Feet Per Pound -of Copper and German Silver Wires.</span></p> - - - -<div class="center small"> -<table border="1" cellpadding="6" cellspacing="0" summary=""> -<tr><th rowspan="3">Gauge,<br />Browne<br />&<br /> Sharpe.</th> -<th rowspan="3">Diameter.</th> -<th rowspan="3">Feet<br />per lb.</th> -<th><span class="smcap">Copper.</span></th> -<th><span class="smcap">German<br />Silver.</span></th> -</tr> -<tr> -<th rowspan="2">Ohms<br />per 1,000 ft.</th> -<th>ONLY<br /> APPROXIMATE</th> -</tr> -<tr><th>Ohms<br />per 1,000 ft.</th> -</tr> -<tr> - <td align="right"> 8</td> - <td align="right">.1285 </td> - <td align="right">20</td> - <td align="right">.62881</td> - <td align="right">11.77</td> -</tr> -<tr> - <td align="right"> 9</td> - <td align="right">.1144 </td> - <td align="right">25</td> - <td align="right">.79281</td> - <td align="right">11.83</td> -</tr> -<tr> - <td align="right"> 10</td> - <td align="right">.1019 </td> - <td align="right">32</td> - <td align="right">1 </td> - <td align="right">18.72</td> -</tr> -<tr> - <td align="right"> 11</td> - <td align="right">.09074</td> - <td align="right">40</td> - <td align="right">1.2607 </td> - <td align="right">25.59</td> -</tr> -<tr> - <td align="right"> 12</td> - <td align="right">.08081</td> - <td align="right">51</td> - <td align="right">1.5898 </td> - <td align="right">29.75</td> -</tr> -<tr> - <td align="right"> 13</td> - <td align="right">.07196</td> - <td align="right">64</td> - <td align="right">1.995 </td> - <td align="right">37.51</td> -</tr> -<tr> - <td align="right"> 14</td> - <td align="right">.06408</td> - <td align="right">81</td> - <td align="right">2.504 </td> - <td align="right">47.30</td> -</tr> -<tr> - <td align="right"> 15</td> - <td align="right">.05707</td> - <td align="right">102</td> - <td align="right">3.172 </td> - <td align="right">59.65</td> -</tr> -<tr> - <td align="right"> 16</td> - <td align="right">.05082</td> - <td align="right">129</td> - <td align="right">4.001 </td> - <td align="right">75.22</td> -</tr> -<tr> - <td align="right"> 17</td> - <td align="right">.04525</td> - <td align="right">162</td> - <td align="right">5.04 </td> - <td align="right">94.84</td> -</tr> -<tr> - <td align="right"> 18</td> - <td align="right">.0403 </td> - <td align="right">204</td> - <td align="right">6.36 </td> - <td align="right">119.61</td> -</tr> -<tr> - <td align="right"> 19</td> - <td align="right">.03539</td> - <td align="right">264</td> - <td align="right">8.25 </td> - <td align="right">155.10</td> -</tr> -<tr> - <td align="right"> 20</td> - <td align="right">.03196</td> - <td align="right">325</td> - <td align="right">10.12 </td> - <td align="right">190.18</td> -</tr> -<tr> - <td align="right"> 21</td> - <td align="right">.02846</td> - <td align="right">409</td> - <td align="right">12.76 </td> - <td align="right">239.81</td> -</tr> -<tr> - <td align="right"> 22</td> - <td align="right">.02535</td> - <td align="right">517</td> - <td align="right">16.25 </td> - <td align="right">302.38</td> -</tr> -<tr> - <td align="right"> 23</td> - <td align="right">.02257</td> - <td align="right">660</td> - <td align="right">20.30 </td> - <td align="right">381.33</td> -</tr> -<tr> - <td align="right"> 24</td> - <td align="right">.0201 </td> - <td align="right">823</td> - <td align="right">25.60 </td> - <td align="right">480.83</td> -</tr> -<tr> - <td align="right"> 25</td> - <td align="right">.0179 </td> - <td align="right">1039</td> - <td align="right">32.20 </td> - <td align="right">606.31</td> -</tr> -<tr> - <td align="right"> 26</td> - <td align="right">.01594</td> - <td align="right">1310</td> - <td align="right">40.70 </td> - <td align="right">764.59</td> -</tr> -<tr> - <td align="right"> 27</td> - <td align="right">.01419</td> - <td align="right">1650</td> - <td align="right">51.30 </td> - <td align="right">964.13</td> -</tr> -<tr> - <td align="right"> 28</td> - <td align="right">.01264</td> - <td align="right">2082</td> - <td align="right">64.80 </td> - <td align="right">1215.76</td> -</tr> -<tr> - <td align="right"> 29</td> - <td align="right">.01126</td> - <td align="right">2623</td> - <td align="right">81.60 </td> - <td align="right">1533.06</td> -</tr> -<tr> - <td align="right"> 30</td> - <td align="right">.01002</td> - <td align="right">3311</td> - <td align="left"> 103</td> - <td align="right">1933.03</td> -</tr> -<tr> - <td align="right"> 31</td> - <td align="right">.00893</td> - <td align="right">4165</td> - <td align="left"> 130</td> - <td align="right">2437.23</td> -</tr> -<tr> - <td align="right"> 32</td> - <td align="right">.00795</td> - <td align="right">5263</td> - <td align="left"> 164</td> - <td align="right">3073.77</td> -</tr> -<tr> - <td align="right"> 33</td> - <td align="right">.00708</td> - <td align="right">6636</td> - <td align="left"> 206</td> - <td align="right">3875.61</td> -</tr> -<tr> - <td align="right"> 34</td> - <td align="right">.0063 </td> - <td align="right">8381</td> - <td align="left"> 260</td> - <td align="right">4888.49</td> -</tr> -<tr> - <td align="right"> 35</td> - <td align="right">.00561</td> - <td align="right">10560</td> - <td align="left"> 328</td> - <td align="right">6163.97</td> -</tr> -<tr> - <td align="right"> 36</td> - <td align="right">.005 </td> - <td align="right">13306</td> - <td align="left"> 414</td> - <td align="right">7770.81</td> -</tr> -</table></div> - -<hr class="chap" /> - -<p><span class="pagenum" id="Page_65">65</span></p> - - - - -<div class="chapter"> -<h2 id="CHAPTER_II">CHAPTER II.<br /> - -<small>CONTACT BREAKERS.</small></h2> -</div> -<div class="figright" ><a id="fig18"></a> -<img src="images/i_065.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 18.</span></div> -</div> - -<p>The simple form of contact breaker already -described is useful up to a certain -point, but it has -disadvantages. -Its rate of vibration -is only variable -through narrow -limits, and it -is not suitable for -very heavy currents. -But as it -stands it has done -long service, and -will be used probably -wherever -the requirements from it are not exacting. -The most desirable form of this<span class="pagenum" id="Page_66">66</span> -simple spring break is shown in Fig. -18. <i>R</i> is the soft iron armature; <i>S</i>, the -spring; <i>C</i>, check-nut which holds the adjusting -screw <i>A</i> from becoming loose; <i>T</i>, a -second adjusting screw used to tighten -the spring and so raise its rate of vibration; -<i>K</i> is the base to which one wire of -the coil is attached; <i>L</i>, base of adjusting -device to which battery wire runs at <i>I</i>. -Where tightening screw T passes through -the pillar of the adjusting screw, the hole -therein is bushed with rubber to prevent -accidental contact. Both <i>A</i> and <i>T</i> are provided -with insulating heads of rubber or -ivory. At <i>B</i> are the platinum contacts, -which should be fully ⅛ inch in diameter.</p> - -<p>One serious defect in the action of the -simple spring vibrator (Fig. 19) is the -tendency of the spring to vibrate, as it -were, sinusoidally. This causes an irregularity -in the rate of the vibrations, which -affects the discharge of the coil very considerably. -By far the better plan is to use -a very short thick spring riveted to an<span class="pagenum" id="Page_67">67</span> -arm carrying the armature at its end (Fig. -20). <i>R</i> is the armature, <i>S</i> the piece of -spring, and <i>K</i> the point of attachment to -the base. The actual width of the portion -of the spring which vibrates—the hinge -portion, it might be called—should not be -over ⅛ inch.</p> - -<div class="figcenter" ><a id="fig19"></a> -<img src="images/i_067.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 19.</span> <span class="smcap">Fig. 20.</span></div> -</div> - -<p>The rate of motion is high; but an -erroneous notion has been taken of its -performance by many persons in the -knowledge of the writer. The rate of -vibration is <i>not</i> wholly dependent on the<span class="pagenum" id="Page_68">68</span> -size, or, rather, smallness of its spring; -the arm and armature considerably alter -this, although they are not pliable, by reason -of their mass and the momentum consequent -on their mass.</p> - -<p>A word here on the size of the armature. -It should be somewhat larger than -the face of the electro-magnet core, and -should be thick—that is, in a circular -form—say one half its diameter. Of -course this does not apply to the steel -lever armature before mentioned. It is -impossible to lay down arbitrary rules -where the conditions are not determined, -but a very small amount of experimenting -will demonstrate the correct lines on -which to build.</p> - -<p>When in action, all rapid rheotomes -give out a definite musical note whereby -the rate of vibration can be determined. -Reference to any work on acoustics will -show a table of the number of vibrations -necessary to produce any stated musical -note. The foregoing style of rheotome<span class="pagenum" id="Page_69">69</span> -forms the basis of very nearly all those -which are in use. The shorter and stouter -a spring the more rapidly will it vibrate, -and <i>vice-versa</i>. Carrying out this rule, -we can manufacture an instrument which -will give as high as 2500 vibrations per -second (Fig. 21).</p> - -<div class="figcenter" ><a id="fig21"></a> -<img src="images/i_069.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 21.</span></div> -</div> - -<p>The armature <i>A</i> is a piece of flat hard -steel bar ¼ × ½ inch, held rigidly on the -metal support <i>S</i> and just clearing the up<span class="pagenum" id="Page_70">70</span>per -surfaces of the magnet cores <i>C</i>. The -adjusting screw <i>P</i> should be provided with -an arm, <i>B B</i>, whereby the rotation of it can -be delicately varied. This screw must -also be firmly held or the high speed of -the armature will jar it loose. A check-nut -on each side of the frame carrying it -should be provided in every case. The -necessary platinum contact can be hammered -into a hole drilled before the armature -is hardened. The proper place for -this contact is about one fourth of the total -length of the armature from its support, -although in the simple contact breaker it can -be placed at the distance of one third if desired. -The reason is that the concussion -of the adjusting screw dampens the free -vibration, and the amplitude thereof is lessened -in addition to the counter vibrations -of the screw disturbing the regular vibrationary -series.</p> - -<p>Owing to the fact that the amplitude of -the armature vibration is so small, a very -delicate adjustment is necessary. The ad<span class="pagenum" id="Page_71">71</span>justing -screw can be placed nearer the -free end, but for the reasons given it is not -to be desired. The metal bridge should -be a solid casting, and the armature -clamped by more than one screw.</p> - -<p>The mercury vibrator, which is applied -to almost every large coil, is as follows:</p> - -<p>A pivoted arm carries on one end a -soft iron armature, which is attracted by -the coil core. The other end is provided -with a platinum point adjustable by a set -screw. This platinum point dips into a -mercury cup—a glass cup containing mercury, -with a thin layer of spirits of turpentine. -The object of the spirits of turpentine, -which is a non-conductor, is to help -choke off the spark which would ensue -whenever the platinum point was raised -from the mercury.</p> - -<p>A form of contact breaker which will -admit of great variation of speed, and -which is adapted to carry large currents, -is the wheel-break, constructed in the following -manner:</p> - -<p><span class="pagenum" id="Page_72">72</span></p> - -<p>A brass or copper disk 3 inches or more -in diameter and upward of ½ inch thick -has its periphery divided by a number of -saw cuts, which divisions are often filled -in with plugs of hard rubber or fibre. -This disk is mounted on a shaft, which latter -is either the shaft of an electro-motor, -or is provided with a pulley by which it -can be rapidly rotated. A strip of spring -copper on each side of the disk presses -upon the toothed surface, one strip being -connected to the coil and the other to the -battery or other current source. It will -now be seen that when the disk rotates the -slits or pieces of hard rubber cause the -break in the circuit through the brushes or -copper strips, the rapidity of the breaks -depending upon the rate of rotation of the -disk, and the number of slits in the wheel.</p> - -<p>The slits or rubber pieces should be one-half -the width of the intervening brass, -but must be at least one sixteenth of an -inch in width, especially where a high -voltage is used in the primary coil.</p> - -<p><span class="pagenum" id="Page_73">73</span></p> - -<p>The shaft of the machine may serve as -one point of connection in place of one of -the copper brushes; but in this event -either a wide journal must be used, or else -some conducting substance, as plumbago, -replace the lubricating oil in the bearings.</p> - - -<h3><span class="smcap">Pole Changing Breaker.</span></h3> - -<p>Fig. 22 shows a diagram of a pole -changing contact breaker which will allow -of rapid alternations of current. It is operated -by an electric motor by preference, -although any motive power can be applied -to it.</p> - -<div class="figcenter" ><a id="fig22"></a> -<img src="images/i_074.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 22.</span></div> -</div> - -<p><i>W a W b</i> are two brass wheels, the peripheries -of which are broken by the insertion -of insulating blocks <i>I I</i>, shown black -in the sketch. <i>S S</i> are the shafts on which -the wheels are mounted, the two wheels -being necessarily insulated from each -other. 1, 2, 3, 4 are four brushes of copper -pressing on the rim of the wheel and -leading in the current from the battery <i>B</i>.<span class="pagenum" id="Page_74">74</span> -The primary coil is attached to the brass<span class="pagenum" id="Page_75">75</span> -body of the wheel or to the shafts. When -the wheel is in the position shown, the coil -and battery are on an open circuit; but on -the wheel commencing to revolve, the -brushes 1 and 2 bear on the brass, and the -current flows from the positive pole of the -battery to 2 through the wheel <i>W a</i> to the -coil <i>P</i>, up through wheel <i>W b</i> and out at -1 back to the battery. The next position -of the brushes 1 and 2 will be on the insulations, -and 3 and 4 will come into action. -Then the positive current will reach <i>W b</i> -by means of brush 3, and after traversing -the primary coil and wheel <i>W a</i>, emerge at -4 to the battery, thus reversing the current -through <i>P</i> as many times as there are sets -of segments, which latter can be multiplied -according to requirements. The -main point to be considered after that of -good connections is that the brushes 1 and -3 and 2 and 4 do not at any time touch -any part of the brass wheel at the same -time, as this would short circuit the bat<span class="pagenum" id="Page_76">76</span>tery. -This is avoided by making the insulating -space longer than the brass surface, -and adjusting the brushes as in the sketch, -that each pair of them is a fraction further -apart than the length of the brass tooth.</p> - -<p>Accordingly, a wheel may be constructed -with many segments and rotated at a -high speed and rapid reversals of current -produced, the uses of which are manifold.</p> - -<p>As will be described in the notes on the -Tesla effects, an electro-magnet, the poles -of which are brought near the sparking -point of the contact breaker, will help wipe -out the spark, and so assist the suddenness -of the break.</p> - -<p>An extremely successful expedient in -operating contact breakers is to employ a -high-pressure air blast directed point blank -against the contact point. The effect of -this air blast when the contact is made is -of course null, but on the platinum surfaces -becoming separated, the high air -pressure produced forms a path of extremely -high resistance, and tends to blow<span class="pagenum" id="Page_77">77</span> -off the spark as soon as it is generated. -The stream of air should issue from an insulated -nozzle of glass or rubber, and should -not contain moisture.</p> - - -<h3><span class="smcap">Wehnelt Interrupter.</span></h3> - -<p>One of the most important inventions in -coil work is the electrolytic interrupter of -Wehnelt. Briefly, the apparatus consists of -a vessel containing a solution of acid, into -which dip two electrodes connected in series -with the source of power and the primary of -the coil. Upon passing a current through -the combination the fluid becomes agitated -at the electrodes and a rapid make and break -of the current ensues (Fig. 23).</p> - -<div class="figcenter" ><a id="fig23"></a> -<img src="images/i_078.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 23.</span></div> -</div> - -<p>It requires considerable electromotive -force for operation, a minimum of 40 volts -being desirable. Its rapidity of action varies -up to and at times exceeding 4000 interruptions -per second. A Wehnelt interrupter -can be made as follows: Procure a glass jar -<i>J</i> holding about one quart or a little less, also<span class="pagenum" id="Page_78">78</span> -a cover for same <i>C</i>, a piece of sheet lead <i>L</i> -large enough to fit loosely across the jar and -yet not touch the bottom, eight inches of -one-quarter-inch glass tube <i>M</i>, a few inches -of No. 20 platinum wire <i>P</i>, and two ounces -of mercury. Heat the end of the glass tube -in a gas flame, and bend an inch or less at -a right angle; at the same time seal in the -platinum wire by means of a blowpipe, so -that the tip just projects from the bent end<span class="pagenum" id="Page_79">79</span> -of the tube. This sealing can be accomplished -readily by one unused to working -glass, but almost any philosophical instrument -maker will have it done at small cost. -Holes being bored through the cover, the -lead plate and the glass tube are fitted in, the -platinum point almost touching the lead. -Adjustment is, however, easy, as the tube, -being turned, will retract or advance the -platinum point from or towards the lead -electrode. Nearly fill the jar with a solution -composed of one part sulphuric acid to -eight parts water, and fill up the glass tube -with mercury. The connections can then -be made by means of a clamp on the lead -and a wire dipping into the mercury. Connect -the lead plate <i>L</i> to one pole of the -battery or source of energy, and the platinum-mercury -electrode <i>F</i> to one post of -primary. The other side of battery and coil -being closed, the apparatus will begin to -work. No condenser is needed with this -interrupter.</p> - -<p><span class="pagenum" id="Page_80">80</span></p> - - -<h3><span class="smcap">Dessauer Contact Breaker.</span></h3> - -<p>This is a modification of the spring -hammer-head type, but has a platinum contact -on both sides of the spring. It thus -obtains double vibrations, but is liable to -stick. The elasticity of the spring normally -prevents the circuit remaining closed on the -forward movement of the hammer head, but -this combination requires attention.</p> - - -<h3><span class="smcap">Steel Ribbon Interrupter.</span></h3> - -<p>For light currents and rapid vibrations, -such as are employed in electrotherapy, the -steel ribbon interrupter is suitable. It consists -of a steel ribbon <i>V</i> one-half inch wide -by six or eight inches long and the thickness -of a stout visiting-card. Near the end is -riveted a platinum contact. One end of the -ribbon is held by a brass upright <i>R</i>, to which -connection is made to circuit; the other end -is riveted to a threaded rod, which passes -through a brass pillar, and is held by a<span class="pagenum" id="Page_81">81</span> -thumb-screw and check nut <i>S</i>. Turning the -thumb-screw either way tightens or loosens -the ribbon and so raises or lowers the rate -of vibration (Fig. 24).</p> - - -<h3><span class="smcap">Contact Breakers in Vacuo.</span></h3> - -<p>Contact breakers in vacuo, as applied to -Ruhmkorff coils, are by no means of recent -date. Poggendorff made use of such prior -to 1859, and noted the diminished sparking -at the contact breaker and increased effect -in the secondary circuit.</p> - -<div class="figcenter" ><a id="fig24"></a> -<img src="images/i_081.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 24.</span></div> -</div> - -<div class="figcenter" ><a id="fig25"></a> -<img src="images/i_082.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 25.</span></div> -</div> - -<p>Mr. D. McFarlan Moore, whose experi<span class="pagenum" id="Page_82">82</span>ments -in vacuum tube lighting have proven -so interesting, was granted patents upon -various forms of contact breakers, in which<span class="pagenum" id="Page_83">83</span> -the chief merit was that the contacts were -broken in a vacuum. The sparking was -almost eliminated, and the suddenness of -the break of contact so accentuated as to -materially improve the output of an induction -coil. A perusal of his patents, copies -of which may be procured through almost -any bookseller, will prove profitable to the -coil constructor.</p> - - -<h3><span class="smcap">Queen Contact Breaker.</span></h3> - -<p>The most important advantage of this -arrangement is the abrupt break, owing to -a collar in the vibrator striking a movable -contact while at full speed. Reference to -Fig. 25 will show that the movable platinum -contact is carried on a small vertical spring -behind the vibrator spring, and projects -through a collar on the vibrator spring. -When the contact is made, the movement of -the vibrator is not arrested, but continues at -its full amplitude, thus allowing a long -"make." The vibrator is kept moving at<span class="pagenum" id="Page_84">84</span> -a constant amplitude by means of the small -coil shown in the illustration, which is in -shunt with the main circuit. In the old -forms there has always been a liability of -the platinum contacts sticking (or welding -together). In the new form, as the break is -made when the vibrator is in the middle of -its swing, the sudden blow with the entire -momentum of the iron hammer head is -always sufficient to break the platinums -apart. This form of contact breaker is very -efficient on electric-light circuits, and operates -with the utmost regularity.</p> - - -<h3><span class="smcap">The Queen Contact Breaker for Large -Coils.</span></h3> - -<p>This is a device where the actual break -is made in alcohol between large studs of -platinum nearly one-quarter inch in diameter. -The bottom contact can be raised or -lowered by means of an adjusting screw. -The top contact is secured into the bottom -end of a rod passing down a guide tube into<span class="pagenum" id="Page_85">85</span> -the alcohol to meet the lower contact. By -means of an electric motor and a cam -motion, the top contact and plunger are made -to work up and down in the alcohol, thus -making and breaking the current flow. One -of the commendable features of this contact -breaker is that the platinum studs are caused -to revolve while in operation, thus presenting -new faces to each other after each blow. -The apparatus is not adapted for rapid -action, but for the handling of heavy currents.</p> - - -<p><span class="smcap">Adjustable Contact Breaker for -Medical Coils.</span></p> - -<p>An adjustable contact breaker for medical -coils is shown in Fig. 26. <i>M M</i> are the -magnet coils, <i>A</i> is the armature, carrying -a platinum contact, which vibrates against -the adjusting screw <i>P</i>. The armature is -pivoted at <i>J</i>, but is held at a distance from -the magnets by the springs <i>S S</i>. The other -end of the armature carries a ball <i>B</i>, which<span class="pagenum" id="Page_86">86</span> -can be slid up and down on the rod and set -at any point by a set-screw. When the ball -is at the end of the armature rod most -remote from the magnets, the vibrations are -slowest; when moved towards the magnets, -the vibrations become more rapid. Adjustment -of the two springs <i>S S</i> at <i>R R</i> enables -the contact breaker to operate on varying -current strength, and also tends to lessen -the jerkiness of gravity contact breakers. -A flat spring, however, can be substituted<span class="pagenum" id="Page_87">87</span> -for the spiral springs, in which case the pivot -would be dispensed with and the spring -riveted, as in the hammer form of vibrator. -The illustration shows this arranged for -a wall board, but it can readily be adapted -for table work.</p> - -<div class="figcenter" ><a id="fig26"></a> -<img src="images/i_086.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 26.</span></div> -</div> - -<h3><span class="smcap">Adjustable Cone Vibrator.</span></h3> - -<p>Fig. 27 shows a form of contact breaker -much used in portable medical coils for slow -speeds. It consists of a cone of iron <i>H</i>, -mounted on the vibrator spring, and furnished -with adjustable contact spring and -screw <i>A</i>. Its amplitude of vibration is -limited by the two pins mounted on the -disc, between which the cone vibrates. The -disc is turned by hand, thus moving the -pins, and so varying the travel of the cone <i>H</i> -to and from the core <i>C</i>. It does not give -good results from the fact that the rhythmical -movements are disturbed every time -the cone strikes against the pins, also at the -contact spring striking the contact screw.<span class="pagenum" id="Page_88">88</span> -As we showed before, a really satisfactory -contact breaker should have a spring, which -allows of no sinusoidal movement. Where -a pivoted armature is governed by a spiral -spring, the result is a series of steady, -rhythmical shocks, provided the adjustments -are satisfactory.</p> - -<div class="figcenter" ><a id="fig27"></a> -<img src="images/i_088.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 27.</span></div> -</div> - - -<h3><span class="smcap">Coil Head Contact Breaker.</span></h3> - -<p>Fig. 28 shows the details of a contact -breaker to be attached to the coil head direct.<span class="pagenum" id="Page_89">89</span> -It is often used on very small coils, which, -together with a miniature dry cell, is slipped -into a pocket case. An important detail in -small coils is to use a contact breaker of sufficient -size. Most of them are not large -enough to stand ordinary usage, the adjusting -screw is not of sufficient diameter and -the thread soon strips. There is no reason -why the adjusting screw, its platinum tip, -and the pillar or lug which holds it should -not be solidly built, it would certainly require -less adjustment. Either single or -double check-nuts can be fitted to the adjust<span class="pagenum" id="Page_90">90</span>ment -screws of nearly all the forms of contact -breakers described.</p> - -<div class="figcenter" ><a id="fig28"></a> -<img src="images/i_089.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 28.</span></div> -</div> - -<h3><span class="smcap">Contacts.</span></h3> - -<p>It is absolutely essential that the <i>diameter</i> -of contacts for all contact breakers should -be as large as possible and their faces filed -truly parallel to enable them to easily carry -all the current required. One of the main -causes of failure of coil is burning of the -platinum point and platinum burr, the current -being then materially reduced. Large -sparks at point of rupture are often indications -that the condenser is not working -properly—perhaps has broken down or is -not large enough. The contacts will sometimes -fuse together; at any rate, the excessive -sparking is an evidence of waste as -much as in a dynamo generator.</p> - -<p>The adjustable method of arranging condensers -(see Chapter IV.) is here of great -value, but it is easy to attach more condenser<span class="pagenum" id="Page_91">91</span> -sections to the contact screw pillar and -vibrator pillar and notice result. In the construction -of Ruhmkorff coils it is a good plan -to make all connections possible on the coil -base, instead of inside the condenser chamber. -This is done either by means of rubber-covered -wires or neat strips of brass, screwed -down on the base from points of connection, -and, of course, carefully bent over or well -insulated from all other leads which they -have to cross.</p> - -<p>The best makers of induction coils construct -their instruments so that they can be -readily taken apart with as little detachment -of connections as possible.</p> - -<hr class="chap" /> - -<p><span class="pagenum" id="Page_92">92</span></p> - - - - -<div class="chapter"> -<h2 id="CHAPTER_III">CHAPTER III.<br /> - -<small>INSULATIONS AND CEMENTS.</small></h2> -</div> - -<p>In selecting an insulating compound for -apparatus designed to be under the influence -of high tension currents, a glance at -some of the peculiarities of such currents -will not be out of place. Mineral oil is -used in many of the converters employed -to transform the high voltage currents on -the mains of the alternating electric-light -systems to the comparatively low voltage -used at the points of consumption. Professor -Elihu Thomson, in a series of experiments, -noticed some interesting facts -in the sparking distances of high potentials -in oils.</p> - -<p>He found that discharges of low frequencies, -as 125 alternations per second, -were capable of puncturing mineral oils at<span class="pagenum" id="Page_93">93</span> -one third to one half the thickness of an -air layer sufficient to just resist punctures -by the same discharge; but with frequencies -of 50,000 to 100,000 per second, an oil -thickness of one thirtieth to one sixtieth -was a sufficient barrier.</p> - -<p>At a frequency of 125 per second, a half-inch -spark in the air penetrated one third -to one fourth inch of oil; but at frequencies -of 50,000 to 100,000 per second, a -layer of oil one fourth of an inch successfully -resisted the passage of a spark which -freely passed through 8 inches of air.</p> - -<p>The effect of drying an oil improved its -insulating qualities. (Tesla uses boiled-out -linseed-oil.)</p> - -<p>He also noted that pointed electrodes -could be brought nearer together under -oil than balls without allowing a discharge. -Flat plates allowed of still greater sparking -distances. Tesla notes that oil through -which sparks have passed must be discarded, -probably owing to particles of carbon -being formed.</p> - -<p><span class="pagenum" id="Page_94">94</span></p> - -<p>Paraffin wax has a higher resistance than -oil, providing it has not been heated over -135° C. It will stand alternate heating up -to 100° C. and cooling, being of lower resistance -when hot than when cold. But -a serious permanent deterioration takes -place when it has been heated over 100°C.; -its color, from the normal pure white, -changes to a yellowish tint when its insulation -is impaired. Paraffin also undergoes -a deterioration when heated for a -long time even at 100° C., and should -never be used for fine work when it is at -all yellow. It is always best to melt it in -a hot-water bath, not permitting, however, -any steam or moisture to come near -it. In this climate (United States) it is -not so necessary to mix in any tallow to -obviate brittleness, the average temperature -of most workshops being sufficiently -high to keep it from becoming brittle.</p> - -<p>Resin oils do not suffer permanent injury -from being heated, as does paraffin, -but their insulating properties diminish<span class="pagenum" id="Page_95">95</span> -much more rapidly on becoming even -warm, the initial resistance of resin oils -being lower than that of paraffin.</p> - -<p>Paraffin has a fault—its tendency to absorb -a slight degree of moisture. It has -been found in telephone and telegraph -cables saturated with paraffin that this is a -very important cause of their deterioration. -In Ruhmkorff coils, however, which -are intended for operation in enclosed -places free from damp atmospheres, the -absorption of moisture would be probably -reduced to its minimum.</p> - -<p>There is one substance which, were it not -for its cost, would be far preferable to -paraffin for coil work, and that is beeswax. -Its cost, however, is generally five -times that of paraffin, even when purchased -in quantities. It never becomes brittle -enough to be damaged in careful handling, -its melting point is low, and it does not -absorb moisture. But it must be unquestionably -pure and clear.</p> - -<p>In foreign practice a variety of resinous<span class="pagenum" id="Page_96">96</span> -mixtures are used to insulate the turns of -the wire in Ruhmkorff coils.</p> - -<p>Equal parts of resin and beeswax used -hot, paraffin, resin and tallow, and shellac -and resin are employed.</p> - -<p>Shellac—that is, the yellow lac—is -much used as a varnish for electrical instruments, -being dissolved in alcohol to -saturation. For dynamo armatures and -similar apparatus the shellac varnish is of -great service, and many good compounds -of shellac, such as insullac and armalac, -have been prepared for ready use. But -(excluding beeswax) for our purposes paraffin -stands pre-eminently at the head of -the list.</p> - -<p>In using shellac varnish, in high tension -work more particularly, care must be -taken that the moisture has entirely evaporated. -Although a piece of shellacked apparatus -may appear perfectly dry, yet -when the current is allowed to flow unlooked-for -results may appear—it takes -hours in a dry atmosphere for shellac var<span class="pagenum" id="Page_97">97</span>nish -to dry. Baking the apparatus in a -warm oven is a necessary expedient -whenever feasible, care being taken not -to burn or decompose the shellac. The -proportions most generally used are 1 -ounce shellac to 5 ounces alcohol. Stand -the vessel containing the mixture in -a warm place, and shake it frequently; -filtration improves the varnish somewhat.</p> - -<p>A ready and efficient varnish for silk is -prepared by mixing 6 ounces of boiled linseed-oil -and 2 ounces of rectified spirits of -turpentine. For paper, 1 part of Canada -balsam and 2 parts of spirits of turpentine -dissolved in a warm place and filtered before -being used. A good insulating cement -for Leyden jars and insulating stands is -prepared from sulphur, 100 parts; tallow, 2 -parts, and resin, 2 parts, melted together -until of the consistence of syrup, and sufficient -powdered glass added to make a -paste. To be heated when applied, this -will resist most acids. The resin and<span class="pagenum" id="Page_98">98</span> -beeswax compound is handy when making -experimental mercurial air pumps of glass -tubes, as it has a fair tenacity, is not too -brittle, and is easily used.</p> - -<hr class="chap" /> - -<p><span class="pagenum" id="Page_99">99</span></p> - - - - -<div class="chapter"> -<h2 id="CHAPTER_IV">CHAPTER IV.<br /> - -<small>CONDENSERS.</small></h2> -</div> - -<p>A condenser is an apparatus whereby -a charge of electrical energy may be temporarily -stored, the amount of energy it -will hold determining its "capacity." -The capacity of a condenser is measured -in micro-farads, the commercial unit representing -one millionth of a farad. A -farad equals the capacity of a body raised -to the potential of one volt by a charge of -one ampere for one second at one volt—<i>i.e.</i> -= one coulomb.</p> - -<p>The measurement of the capacity of a -condenser is accomplished by the use of a -ballistic galvanometer. The latter instrument -has a bell-shaped magnet suspended -in a coil of fine wire. When a momentary -current is passed through this coil the<span class="pagenum" id="Page_100">100</span> -magnet hardly commences to rotate until -the current has practically ceased. A -beam of light is reflected from a mirror -fixed to the magnet on to a scale. The degree -of deflection is compared with that -obtained by the discharge of a condenser -of known capacity, and the capacity of the -condenser being measured is deduced by a -simple rule. The farad, which is the unit -of capacity requiring a condenser of an -immense size, is replaced by a commercial -unit, the micro-farad—that is, one millionth -of a farad.</p> - -<p>The original form of the condenser was -the Leyden jar, which owes its name from -the town of Leyden in Europe.</p> - -<div class="figleft" ><a id="fig29"></a> -<img src="images/i_101.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 29.</span></div> -</div> - - -<p>The Leyden jar is made as follows (Fig. -29): A clean uncracked glass jar with a -wide mouth is coated on the inside and -outside with tinfoil; sometimes loose tinfoil -is filled inside, the tinfoil, however, -not reaching more than two thirds of the -jar's length from the bottom. A cork is -fitted, and through the middle of it a wire<span class="pagenum" id="Page_101">101</span> -is passed touching the inside coating of -tinfoil and terminating in a metal sphere -outside. A simple Leyden -jar can be made in a -few moments by half filling -a glass bottle with -water and wetting the -lower half of the outside; -a wire run through the -cork into the water finishes -the job. But this -is at least only a makeshift, -although a fair -amount of current has -been collected from a -leather engine belt in -motion in one thus made.</p> - -<p>A condenser can be easily made as follows -(Fig. 30):</p> - -<div class="figright" ><a id="fig30"></a> -<img src="images/i_102.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 30.</span></div> -</div> -<p>Procure a clear glass plate, <i>G</i>, free from -flaws, 11 inches square by 3/3<sup>3</sup>∕<sub>32</sub> inch thick. -Give this a good coating of shellac varnish -all over, sides and edges. Cut out of -smooth tinfoil two sheets, <i>T</i>, 8 inches square,<span class="pagenum" id="Page_102">102</span> -and round off the corners with a pair of -shears. There must be no sharp corners, -projections, or angles to -induce leakage. Lay -the glass plate on a -sheet of paper, and mark -its outline thereon with -a pencil; then remove it -and substitute a sheet of -the tinfoil, and mark that. This will enable -you to centre the foil. Give one side -of the glass plate another coat of varnish, -and so lay it on the paper that its outline -coincides with the pencil outline. When -the varnish has partly dried take a sheet -of the trimmed foil, and by observing the -pencilled marks you can lay it on the varnished -plate exactly in the centre. Lay -down the top edge first along this line, and -carefully deposit the remainder of the foil -in place. Next, with a flat brush full of -varnish go over the plate, pressing out any -air bubbles, and ensuring both a flat and a -well-varnished surface. When this is dry,<span class="pagenum" id="Page_103">103</span> -turn over the plate and repeat the operation -on the other side.</p> - -<p>If desired, a metal hemisphere of at least -an inch in diameter may be attached with -varnish, first scraping the foil to make a -contact. The whole plate can be swung in -a cradle of two silk threads, laid on a glass -tumbler, or mounted on end in a shellacked -block of wood.</p> - -<p>A strip of tinfoil, <i>S</i>, attached at the corner -can be used as a connector. The -plates must be joined in the following -manner when two or more are used in -conjunction, and a quantity of current is -desired. They should be placed so the -connecting strips project alternately from -each side (Fig. 31), and all on each side -joined so as to leave two terminals, one to -the 1, 3, 5 plates, the other to the 2, 4, 6 -plates, and so on, which, when joined, will -have the same effect as would result from -the use of two large plates of the same -total area. The nearer the plates are together -the greater capacity they will have,<span class="pagenum" id="Page_104">104</span> -always supposing the insulation is good, -the insulation being known as the dielectric. -Another good -method, when a high -quality of glass can be -procured, is to lay the -tinfoil on the plates -without varnish, piling -one on top of the other, -tinfoil and glass alternately, -and clamping the -whole securely, laying a piece of cloth top -and bottom to avoid cracking the glass from -the pressure. This must be kept from -moisture; a strip of paraffined paper stuck -along the edges and extra paraffin run on -will answer very well.</p> - -<div class="figright" ><a id="fig31"></a> -<img src="images/i_104.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 31.</span></div> -</div> - -<p>In constructing these glass condensers, -they must be designed to correspond with -the coil with which they are to be charged. -In the foregoing description we have allowed -a margin of 1½ inches of glass -around the foil coatings. This will make -3 inches as the maximum distance between<span class="pagenum" id="Page_105">105</span> -the coatings. Although a 2-inch spark -from the coil would not jump this interval, -a certain discharge will take place, and the -less this occurs, the more serviceable the -condenser will be. Therefore a greater -margin should be allowed for a longer -spark than 2 inches.</p> - -<p>In the commercial condenser for telephone -and telegraph use, paraffin and -paper are substituted for glass, as will be -described later. Heavy paraffin oil gives -excellent results, but its fluidity is disadvantageous.</p> - -<p>There is no valid reason why paraffin -could not be used on the glass plate condensers, -care being observed that it is free -from dirt and metallic chips. In fact, the -space between the glass plates of the multiplate -condenser may be filled in with -paraffin, and thereby exclude the air. Only -a condenser so built up is not convenient -to take apart for experimental purposes.</p> - -<p>The foregoing description of a glass in<span class="pagenum" id="Page_106">106</span>sulated -condenser was written with the -assumption that a good quality of glass be -used. But the ordinary window glass is -generally useless, and paraffined paper is -preferable. The quality of glass known as -"hard flint glass" is best, the superior -qualities being imported from Europe. -This latter is used in the manufacture of -the standard Leyden jar for lecture purposes.</p> - -<p>Were it not for its cost, the finest dielectric -we could use would be sheet mica. -Unfortunately sheet mica over 3 inches -square is expensive, and becomes rapidly -more so as it becomes larger.</p> - -<p>Standard condensers for testing are -made with mica carefully selected, and retain -the charge for the maximum length of -time. The built-up mica condenser is -immersed in molten paraffin until the same -has permeated the sheets, and then the -complete mass is put under a pressure -until the paraffin is well set.</p> - -<p><span class="pagenum" id="Page_107">107</span></p> - - -<h3><span class="smcap">Paper Condenser.</span></h3> - -<p>The paper used in the manufacture of -the commercial form is a special thin, -tough linen paper carefully selected, sheet -by sheet, to avoid pin-holes or flaws, and -kept in an oven until used to ensure absolute -dryness.</p> - -<p>When this cannot be procured, use thin -unsized writing paper of a good quality, -well dried, and absolutely clean. As an -example of the necessity of cleanliness, -a light lead-pencil mark would serve -to conduct the current entirely from a -charged sheet to wherever it terminated, -and if suitably located, utterly destroy -the usefulness of the apparatus. Ink, -which most generally contains iron, will -cause trouble, and although some cheap -foreign condensers are built up of old -ledger pages, yet their efficiency is very -uncertain.</p> - -<p>The paper used in commercial condensers -is from four to seven thousandths -of an inch in thickness.</p> - -<p><span class="pagenum" id="Page_108">108</span></p> - - -<h3><span class="smcap">Series.</span></h3> - -<p>The smaller the amount of surface the -less will be the capacity, but the quicker -the discharge. The apparatus heretofore -mentioned has had the alternate plates -connected together in two series, presenting -a large surface and rendering a large -amount of current. A condenser so made -will have a low voltage or potential, but is -not so liable to leakage as one made to -render a high potential. The multiple -condenser of a large capacity will hardly -discharge and spark over an air gap requiring -a contact of the two electrodes. -But a smaller one, consisting only of a -single pair of small plates, will spark -across quite a considerable air gap.</p> - -<p>A number of charged condensers may -be put in series, and the resultant potential -thereby increased. Cut a number of -pieces of paper of the desired size, say 6 -inches square, and a number of sheets of -foil 3 inches square. Round off the corners -of the foil and build up first a sheet<span class="pagenum" id="Page_109">109</span> -of paper, then a sheet of foil in its centre, -then another paper and another foil sheet, -and so on. There is to be no connection -from sheet to sheet, only the inductive -action of one on its neighbor. The foil -must be considerably smaller than the -paper in this construction, owing to the -greater tendency to discharge round the -edges of the sheets, owing to the greater -potential of the current.</p> - -<p>When the requisite number of sheets -have been built up, leave a sheet of foil top -and bottom for connection, tie between -two pieces of stout card or board, and immerse -in the molten paraffin. When thoroughly -soaked, remove and put under -pressure until cold. It will be found undesirable -to make these with more than a -dozen pairs of sheets, but to make a number -of blocks of that number for ready -service.</p> - -<div class="figcenter" ><a id="fig32"></a> -<img src="images/i_110.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 32.</span></div> -</div> - -<p>Fig. 32 shows the arrangement of the -apparatus to charge a Leyden jar, the -plate form being connected in a similar<span class="pagenum" id="Page_110">110</span> -manner. The jar is stood upon an insulating -support—a dry tumbler will answer—with -the ball <i>B</i> connected to one pole of -the coil. From the outside tinfoil coating<span class="pagenum" id="Page_111">111</span> -<i>T</i> a wire runs to the discharger <i>D D</i>, which -is in circuit with the secondary coil, <i>S</i>. -The discharger balls <i>D D</i> are carefully approximated -until the spark just passes, this -latter point being of great importance. -Were the discharger balls too near the -spark would probably pierce the dielectric -of the condenser, therefore the balls should -be carefully <i>brought near</i> to each other -until the exact distance is found. Even if -the insulation of the condenser were not -pierced, yet a path would probably be -opened through which some succeeding -discharge would pass, and ruin the instrument.</p> - -<p>Another method of charging is to leave -an air gap at <i>B</i>; then there is not much -liability of the condenser discharging back -through the coil—an undesirable event, as -it would most likely perforate the insulation -of the coil.</p> - -<div class="figcenter" ><a id="fig33"></a> -<img src="images/i_112.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 33.</span></div> -</div> - -<p>In designing or using any apparatus intended -to hold a charge of high potential, it -must be kept in mind how readily points or<span class="pagenum" id="Page_112">112</span> -sharp edges serve to allow the current to<span class="pagenum" id="Page_113">113</span> -pass off—we might almost say evaporate. -Given two bodies, one a globe and the -other a rectangular block, each well insulated -from the earth or any other large -body, and the globe would be found to -hold its charge long after the block had -dissipated all trace of the charge given to -it. Therefore round off every edge and -angle, projection or point.</p> - -<p>In making handles, supports, or any -work requiring an intervening high insulation, -hard rubber is preferable to glass -where there is liability to moisture. When -the apparatus is as shown in Fig. 33, the -condenser is alternately charged and discharged -with a loud noise, the vivid sparks -passing across the discharger balls <i>D D</i> -possessing great deflagratory powers.</p> - -<p>In experimenting with a Ruhmkorff coil -it is not advisable to leave the instrument -working while the secondary terminals are -beyond sparking distance, as there is a -great strain on the secondary insulation.<span class="pagenum" id="Page_114">114</span> -Nor is it wise to use only one electrode in -an experiment, unless the other is connected -to some apparatus of an approximate capacity -to that at the other, for the foregoing -reason.</p> - - -<h3><span class="smcap">Rolled-Up Condensers.</span></h3> - -<p>Now that the condenser has become so -important a factor in telephone work, many -schemes for cheapening and facilitating -their manufacture have been devised. One -in particular merits description, the "rolled-up" -condenser having come largely into -use. The tin-foil is supplied in rolls containing -many yards of foil of the requisite width -for the condenser to be made. Likewise rolls -of paper are provided, exceeding in width, -however, those of tin-foil. These rolls are -arranged upon horizontal spindles in front -of an empty spindle, or mandrel, upon which -the condenser is to be formed. A few turns -of the paper ribbon are made around the -mandrel, then the foil is brought forward<span class="pagenum" id="Page_115">115</span> -and a few turns made, then follows a turn of -paper ribbon and another of foil, and finally -a paper layer; and the mandrel being rotated, -the alternate layers of foil and paper are -laid on and rolled around each other on the -mandrel until the requisite quantity is obtained. -It then becomes an easy matter to -cut the paper ends so no contact is possible -between the layers of foil. The whole thing -is slipped off the mandrel, secured by a -rubber band or two, placed in a hot paraffin -bath, and left to become saturated while -still warm and before the paraffin has time -to harden; the cylinder is put under a press -and squeezed flat, driving out excess paraffin, -and leaving the condenser in a convenient -shape to handle. Connections are then made -to the foil leaves, and a case of wood or -metal completes the work.</p> - -<p>There is no reason why aluminum foil or -lead foil, or, in fact, any thin sheet metal -should not be used in condensers. In telephone -work, paper covered with gilt paint -was tried, and worked fairly well, but was<span class="pagenum" id="Page_116">116</span> -ultimately rejected in favor of tin-foil. In -some cases, when it is desired to construct -a condenser for high potential work, the -oil-tank apparatus can be used. This is -readily made of any desired dimensions, as -follows: Procure a square glass jar, such -as is made for storage batteries, a few pieces -of sheet metal cut to fit loosely in the jar, -some glass rods and sufficient clean "transformer -oil" or heavy paraffin oil to nearly -fill the jar. The sheets of metal can then be -hung from the glass rods into the jar, being -separated one-half inch, and the oil poured -in. Two plates, about 8 inches by 6 inches, -will hang nicely into a type D<sup>3</sup> Chloride -Battery jar, which is 7⅞ inches long by 9½ -inches high by 3¼ inches wide. Altering the -relative distances between the plates will -give considerable adjustment to this simple -condenser, or, if desired, more plates may be -inserted and connected up, as in the tin-foil -condensers. This type can be made portable, -but it is not to be recommended unless no<span class="pagenum" id="Page_117">117</span> -objection is had to emptying and refilling -the jar with oil.</p> - - -<h3><span class="smcap">Adjustable Condensers.</span></h3> - -<p>In operating large coils, it is convenient -to be able to vary the capacity of the condenser -on the primary circuit. To make -an adjustable condenser presents no more -difficulty than a non-adjustable one, simply -more labor. For example, the large condenser -used with the 6-inch spark coil might -be divided into four sections, containing -2000 square inches, 500 square inches, 300 -square inches, and 200 square inches of -surface (see Fig. 34). Wires leading from -the ends of the foil sheets <i>C C</i> are to be -brought to the brass plates <i>G G</i>. The brass -rods <i>B B</i> are connected by binding posts to -the coil, each strip being well insulated from -its neighbor. Any combination is possible -by the insertion of brass plugs in holes -drilled between the strips. The plugs must -be fully large enough to make good contact -on each of the two strips between which<span class="pagenum" id="Page_118">118</span> -they are inserted, and should be turned -taper. With the largest coils the condenser -and contact breaker are generally mounted -separately, and are fully adjustable.</p> - -<div class="figcenter" ><a id="fig34"></a> -<img src="images/i_118.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 34.</span></div> -</div> - -<p><span class="pagenum" id="Page_119">119</span></p> -<div class="center small"> -<table border="0" cellpadding="4" cellspacing="0" summary=""> -<tr><th colspan="2"><span class="smcap">Specific Inductive Capacity.</span></th></tr> -<tr> - <td align="left">Dry air</td> - <td align="left">1.000</td> -</tr> -<tr> - <td align="left">Sulphur</td> - <td align="left">2.590</td> -</tr> -<tr> - <td align="left">Hard rubber</td> - <td align="left">2.290</td> -</tr> -<tr> - <td align="left">Paraffin</td> - <td align="left">1.996</td> -</tr> -<tr> - <td align="left">Shellac</td> - <td align="left">2.750</td> -</tr> -<tr> - <td align="left">Kerosene</td> - <td align="left">2.225</td> -</tr> -<tr> - <td align="left">Paraffin oil</td> - <td align="left">2.710</td> -</tr> -<tr> - <td align="left">Castor oil</td> - <td align="left">4.962</td> -</tr> -<tr> - <td align="left">Olive oil</td> - <td align="left">3.575</td> -</tr> -</table></div> - -<p>Condensers made with dielectric of high -inductive capacity (insulation being equal) -will retain greater charge than those made -with dielectrics of low inductive capacity. -Thus, one made with shellac would be nearly -half as great again as with paraffin.</p> - -<p>Capacity of a condenser increases with -area of foil surface, with diminished distance -between foil plates and with increase -of insulation.</p> - -<hr class="chap" /> - -<p><span class="pagenum" id="Page_120">120</span></p> - - - - -<div class="chapter"> -<h2 id="CHAPTER_V">CHAPTER V.<br /> - -<small>EXPERIMENTS.</small></h2> -</div> - -<p>The luminous effects that can be obtained -by means of a Ruhmkorff coil are -exceedingly beautiful and instructive. -The simplest experiment of this nature is -the production of the spark consequent on -the approximation of the electrodes attached -to the secondary coil. This spark -can be varied in both length, intensity, or -shape by the form and nature of the substances -between which it is permitted to -pass. Attach to each end of the discharger -a fine steel needle, and bring them -together until the spark jumps from one -to the other. A long thin snapping spark -will pass, which, however, appears to be -trying to take any but a straight path -across the air gap. The peculiar crooked<span class="pagenum" id="Page_121">121</span>ness -of this, as in a lightning flash, is credited -to the fact of particles of matter floating -in the air conducting the current better -than the pure air. The curious odor -noticed in these discharges, as, in fact, in -the working of all high-tension apparatus, -is ozone—O<sub>3</sub>, triatomic oxygen. This gas, -so noticeable after a thunderstorm, has a -powerful effect on the mucous membranes -of the throat and nasal passages, and must -be inhaled with caution. It is being used -by the medical profession for the destruction -of germs and for general therapeutic -service.</p> - -<p>Substitute pieces of fine iron wire for -the needles, and bring the ends together -about one quarter the distance through -which the normal spark will pass. The -spark will be found to have changed its -appearance, now being thick and redder, -or, rather, of a deep yellow, and to possess -vast heating qualities.</p> - -<p>The iron wire will melt at one electrode, -and if the other be examined it will be per<span class="pagenum" id="Page_122">122</span>ceived -that it has not even become warm. -The cold wire will be the one connected -to the positive pole of the coil.</p> - -<p>Connecting the poles together with a -piece of very fine iron wire will result in -the deflagration of the wire in a vivid -light.</p> - -<p>The short thick spark is termed the -calorific spark, and believed to possess its -yellow color from the combustion of the -sodium in the air. This spark will easily -ignite a piece of paper held in its path.</p> - -<p>Take a sheet of hard rubber and breathe -on its surface; lay a wire from each pole of -the secondary to points on the sheet, about -twice as far apart as the spark would pass -over in the air. The electric current will -strive to complete its circuit; streams of -violet light forming a perfect network will -issue from each pole, until, provided the -rubber is sufficiently damp, they will unite -in a spark far exceeding its normal length -in the air. It is curious to watch how the -streams branch out from these two points,<span class="pagenum" id="Page_123">123</span> -and how persistently they strive to meet -each other. Scatter some finely powdered -carbon on this sheet (crushed lead-pencil -or electric light carbon is good material). -The points may now be removed to still -further distant places, and yet the current -will work across. Each particle of carbon -seems to be provided with innumerable -scintillating diamonds, so sparkling is this -effect.</p> - -<p>Hard rubber is not absolutely necessary -for these experiments; glass will do, but -the black background of the rubber intensifies -the luminosity of the discharges. -Take a teaspoonful of powdered carbon -and scatter it between the points on the -rubber, so that the spark can find a ready -path, evidenced by but little visible light. -It will be seen that this powder is blown -away from one electrode after a few minutes, -leaving the latter in the centre of a -clear space, but at the other electrode not -much disturbed.</p> - -<p>Bring the points so close to one another<span class="pagenum" id="Page_124">124</span> -that the spark becomes short and fat; soon -the carbon will commence to burn, forming -a veritable arc light. Take two pointed -lead-pencils and wrap a few turns of wire -from the electrodes round the blunt ends -of them; bring the pointed ends together, -and an arc will soon be established; but -at various points where the wire is wrapped -the current will burn through the wood, -and a number of incandescent points will -ensue.</p> - -<p>In these experiments on the rubber sheet -it will be noticed that the spark acts as it -does in the air, inasmuch as it does not take -a direct path, but jumps in an irregular -track from point to point.</p> - -<p>If two small metal balls be substituted -(Fig. 35) for the points between which the -sparks be passing, it will be noted that the -sparks do not pass through so great an air -gap as before, or even as rapidly.</p> - -<p>The spark between two balls is much -noisier than that passing between points, -and if the balls be of about 1 inch in<span class="pagenum" id="Page_125">125</span> -diameter, a curious effect ensues on the -passage of the current (Fig. 36). This -effect has been likened to a stream of -water issuing from a horizontal nozzle into -a cavity when the nozzle is moved up and -down slowly in the space of a few inches.</p> - -<div class="figleft" ><a id="fig35"></a> -<img src="images/i_125.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 35.</span></div> -</div> -<div class="figright" ><a id="fig36"></a> -<img src="images/i_125b.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 36.</span></div> -</div> - -<h3><span class="smcap">The Luminous Pane.</span></h3> - -<div class="figright" ><a id="fig37"></a> -<img src="images/i_125c.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 37.</span></div> -</div> -<p>This easily made exhibit (Fig. 37) is one -that is susceptible of quite a number of applications. -In its simple -form it is but an enlarged -version of the rubber -sheet scattered with carbon -dust. The old way -to make it was to take -a plate of glass and cement -on one face of it a sheet of tinfoil, -using shellac varnish preferably. When -dry, the tinfoil was scored across and<span class="pagenum" id="Page_126">126</span> -across in such manner as to divide it up -into little squares or diamonds. When -the current was applied to each end of the -plate, the spark divided into innumerable -little ones; between each bit of tinfoil and -its neighbors there would be many little -sparks, and the effect was very pretty, -somewhat as was described before when -the carbon dust was strewn between the -electrodes. It is more easily and quickly -prepared by giving a sheet of glass a coating -of shellac varnish, and then sparingly -dusting any powdered conductor over its -surface, using perhaps carbon dust or -filings of metal. By cutting out a stencil -from a piece of thin card and laying it over -the sparkling plate, the design shows out -very strikingly, and various designs in stencils -can be prepared, different powdered -conductors giving different colored sparks.</p> - -<p>A long glass tube moistened inside with -mucilage or shellac varnish and then having -some conducting dust shaken through -will also give quite a pleasing effect.</p> - -<p><span class="pagenum" id="Page_127">127</span></p> - - -<h3><span class="smcap">Luminous Designs.</span></h3> - -<p>Coat one side of a glass plate with tinfoil, -leaving an attached strip for connection. -Shellac a piece of paper of a size corresponding -to the design to be rendered -luminous. When the shellac has dried so -far as to become "tacky," lay a sheet of -foil on it and press it down evenly all over.</p> - -<p>Then draw on the paper a design that -can be readily cut out. Use a pair of scissors -or a very sharp knife. If the latter, -lay the sheet on a piece of glass; but -there is a greater tendency to tear the design -when a knife is used if an unpractised -hand wields it.</p> - -<p>This design may either be stuck on to -the plain side of the glass plate with varnish -or simply laid on (Fig. 38). Connect -one secondary wire to the foil coating of -the plate and the other to the design. -This must be shown in the dark, and the -luminosity will not be strikingly apparent -until the eyes become accustomed to the<span class="pagenum" id="Page_128">128</span> -darkness—that is, when the room has -been previously lighted.</p> - -<p>One of the most beautiful and easily obtained -phenomena of the high-tension discharge -is the "electric brush" (Fig. 39). -This occurs when the secondary electrodes -of the coil are too far apart to allow of the -free passage of the spark, and can only be -seen at its best in a perfectly dark place. -The ball tips before mentioned show this -brush very plainly, or two sheets of tinfoil -in circuit hung far enough apart to prevent -vivid sparking will cause this so-called -"silent" discharge. This latter arrangement -should not be used for over fifteen -minutes, as the ozone which is liberated in -large quantities will affect those persons in -the vicinity.</p> - -<div class="figleft" ><a id="fig38"></a> -<img src="images/i_128.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 38.</span></div> -</div> -<div class="figright" ><a id="fig39"></a> -<img src="images/i_128b.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 39.</span></div> -</div> - -<p><span class="pagenum" id="Page_129">129</span></p> - -<p>In fact, when a rapid vibrator is being -used with the coil, the leading wires from -the secondary terminals present this brush -appearance, the curious threads of light -resembling luminous hairs waving in the -air. The more rapid the vibrations the -more prominent the brush effect, as will -be seen in the Tesla coils. The positive -ball of the discharger shows the brush as -a spreading mass of luminous threads -reaching out toward the negative ball, -which latter resembles a star, as in the -figure.</p> - -<p>The intensely disruptive power of the -long spark is readily shown by its power -to perforate substances, but great care -must be taken that the secondary wires of -a coil are led away from the body of the -coil. A good plan is to hang two silk -cords or stout threads from the ceiling, to -which the secondary wires may be attached -and kept in sight when experimenting -at any distance from the coil.</p> - -<p>To pierce a piece of thin glass, take two<span class="pagenum" id="Page_130">130</span> -lumps of paraffin about the size of a walnut, -and, warming them and the glass -sheet, stick them on opposite sides of -the glass facing each other. Then warm -the ends of the two pointed wires and -thrust them into the lumps of paraffin, that -they terminate on the glass surface directly -opposite each other. On connecting -these to the secondary coil a few impulses -to the contact breaker will start an electric -discharge sufficient to pierce the glass -if the thickness be proportioned to the -power of the apparatus. The great -Spottiswood coil pierced a block of glass -6 inches in thickness.</p> - -<p>There is, however, a certain element of -danger to the secondary insulation in performing -this experiment.</p> - -<hr class="chap" /> - -<p><span class="pagenum" id="Page_131">131</span></p> - - - - -<div class="chapter"> -<h2 id="CHAPTER_VI">CHAPTER VI.<br /> - -<small>SPECTRUM ANALYSIS.</small></h2> -</div> - -<p>If a metal or the salt of a metal be -burned in a flame it imparts to the flame a -distinctive color; table salt thrown into -the fire burns with a yellowish flame, denoting -the presence of sodium, and a -greenish tint, indicating the combustion -of chlorine. Violet flames accompany the -burning of the salts of potassium, and -barium burns green. Lithium and strontium -give a red hue. But to be ordinarily -perceptible, the salts require for the most -part to be present in considerable quantities. -By the use of the spectroscope, -however, extremely small proportions of -these metals and salts can be readily detected -and classified.</p> - -<div class="figcenter" ><a id="fig40"></a> -<img src="images/i_132.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 40.</span></div> -</div> - -<p>If a beam of light be transmitted<span class="pagenum" id="Page_132">132</span> -through a prism of glass the rays are decomposed, -and what is known as a spectrum -is formed (Fig. 40). The most generally -observed spectrum is the rainbow. -When the light from a flame in which is -burning some suitable substance be transmitted -through the prism, the color which -predominates in the flame will predominate -in its spectrum. The combination of -a prism and tubes for observing these -effects is a spectroscope (Fig. 41). The -short fat spark from the Ruhmkorff coil is -most useful in this work. The electrodes<span class="pagenum" id="Page_133">133</span> -are provided with a portion of the substance -to be examined, and the spark is -passed and viewed through the spectroscope.</p> - -<div class="figcenter" ><a id="fig41"></a> -<img src="images/i_133.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 41.</span></div> -</div> - -<p>The spectroscope is shown in connection -with the coil in Fig. 41. <i>A</i> is the<span class="pagenum" id="Page_134">134</span> -aperture in the screen through which the -rays from the metal burning at the discharger -balls <i>D D</i> passes. The lens at <i>L</i> -is used to view these rays after they have -been decomposed by the prism <i>P</i>, which, -as well as the lens, can be rotated. <i>I</i> is -the coil, <i>P P</i> the primary and <i>S S</i> the secondary -wires, <i>C</i> being a condenser bridged -across the circuit.</p> - -<p>The screen should be pierced by a very -narrow aperture, <i>A</i>, and be placed at a -considerable distance from the prism <i>P</i>, -that the rays issuing through the aperture -may not strike the prism until they have -widely diverged and become separated -from each other. The aperture is practically -formed of perfectly parallel knife -edges, forming a slit not exceeding one -hundredth of an inch in width.</p> - -<p>The colored spaces in the solar spectrum -do not occupy an equal extent of -area; the violet is the most extended, the -orange the least. The proportion is in -three hundred parts: Violet, 80; green,<span class="pagenum" id="Page_135">135</span> -60; yellow, 48; red, 45; indigo, 40; -orange, 27.</p> - -<p>The solar rays exhibit on careful examination -dark lines crossing the spectrum at -right angles to the order of the colors, and -always occupying the same relative positions. -These are called Fraunhofer's -lines.</p> - -<p>If, however, the spectra of metals, -gases, and other elements be examined -they will be found to present certain characteristic -<i>bright</i> lines, the body of the spectrum -being often feeble or entirely dark. -The spectrum of hydrogen gives two very -bright lines of red and orange.</p> - -<p>An extremely minute quantity of an element -is necessary to give distinct lines. -Sodium gives a single or double line of -yellow light in a position agreeing with -that of the orange rays in the solar spectrum.</p> - -<p>Potassium gives a red line in the red -end and a violet line in the violet end of -the solar spectrum. Strontium presents<span class="pagenum" id="Page_136">136</span> -eight bright lines; calcium gives mainly -one broad green band and one bright -orange band.</p> - -<p>In practical work with the spectroscope -a solar spectrum is often arranged that it -can be used as a comparison with the spectrum -being investigated, one spectrum -being formed above the other, and the observation -made as to which lines coincide. -Iron gives nearly sixty bright lines coinciding -with the same number of dark lines -of the solar spectrum.</p> - -<p>The violet rays of the solar spectrum -are the rays which possess the maximum -chemical action, the yellow the maximum -light effect, the red the maximum heating -effect. Beyond the violet band of the -spectrum exist certain rays termed the invisible -rays or ultra-violet rays, which in -themselves are not luminous. Their vibratory -rate is higher and their wave length -shorter than the violet rays, according to -the most generally accepted theory of -light. These rays, when passed through<span class="pagenum" id="Page_137">137</span> -certain substances, suffer a change and become -visible in a luminous state of the substance, -which luminosity is termed fluorescence.</p> - -<p>The bright yellow line of sodium in the -orange rays is found in nearly all spectra, -owing to its extensive diffusion in the atmosphere.</p> - -<p>Tesla has succeeded in producing electric -waves of length approximating to -those of white light, which appear to have -very little heat. The ideal light is that -which shows no heat and does not liberate -noxious gases in the air, and were it not for -its feeble luminosity, the light of the electric -spark passing through a carbonic acid vacuum -would approximate this most nearly.</p> - -<p>The present mode of obtaining light—that -of raising to a high temperature some -substance or collection of particles—seems -certainly somewhat antiquated. The following -notes may be of interest and assistance -in researches bearing on the lighting -question.</p> - -<p><span class="pagenum" id="Page_138">138</span></p> - -<p>Solid bodies, when heated, show a red -glow in daylight at an elevation of temperature -corresponding to 1000° Fahr.</p> - - - -<div class="center small"> -<table border="0" cellpadding="4" cellspacing="0" summary=""> -<tr><th><small>Temperature,<br /> degrees F.</small></th><th colspan="2"><small>Color of <br /> Substance. </small></th></tr> -<tr> - <td>1000</td> - <td> </td> - <td align="left">Red.</td> -</tr> -<tr> - <td>1200</td> - <td></td> - <td align="left">Orange.</td> -</tr> -<tr> - <td>1300</td> - <td></td> - <td align="left">Yellow.</td> -</tr> -<tr> - <td>1500</td> - <td></td> - <td align="left">Blue.</td> -</tr> -<tr> - <td>1700</td> - <td></td> - <td align="left">Indigo.</td> -</tr> -<tr> - <td>2000</td> - <td></td> - <td align="left">Violet.</td> -</tr> -<tr> - <td>2130</td> - <td></td> - <td align="left">All colors—<i>i.e.</i>, white.</td> -</tr> -</table></div> - -<p>The number of vibrations per second -necessary for the production of light, and -the velocity of light being determined, the -calculation of the wave lengths of the colored -rays becomes possible.</p> - -<p>The following table (Sprague) shows -this in ten-millionths of a millimetre (a -millimetre = .039 inch) measured in the -dark lines of the solar spectrum, from red -to violet:</p> - - - -<div class="center small"> -<table border="0" cellpadding="4" cellspacing="0" summary=""> -<tr> - <td align="left">Orange =</td> - <td align="left">6.88</td> -</tr> -<tr> - <td align="left">Orange, Higher = </td> - <td align="left">6.56<span class="pagenum" id="Page_139">139</span></td> -</tr> -<tr> - <td align="left">Yellow =</td> - <td align="left">5.89</td> -</tr> -<tr> - <td align="left">Green =</td> - <td align="left">5.26</td> -</tr> -<tr> - <td align="left">Blue =</td> - <td align="left">4.84</td> -</tr> -<tr> - <td align="left">Blue, Higher =</td> - <td align="left">4.29</td> -</tr> -<tr> - <td align="left">Violet =</td> - <td align="left">3.93</td> -</tr> -</table></div> - - -<hr class="chap" /> - -<p><span class="pagenum" id="Page_140">140</span></p> - - - - -<div class="chapter"> -<h2 id="CHAPTER_VII">CHAPTER VII.<br /> - -<small>CURRENTS IN VACUO.</small></h2> -</div> - -<p>Notwithstanding it requires an intensely -high potential to enable the current -to jump an air gap of 1 inch, the -same potential will produce a luminous -discharge through exhausted glass tubes -aggregating 8 feet or even more.</p> - -<p>But the exhaustion can be carried so far -that there is no apparent discharge; and, -on the contrary, air at as high a pressure -as 600 pounds per square inch will resist -the passage of the spark over an extremely -short space. If the tubes be filled with -various gases and then partially exhausted, -the length of tube through which the -luminous discharge will pass varies with -the gas, becoming shorter in the following<span class="pagenum" id="Page_141">141</span> -order: Hydrogen, nitrogen, air, oxygen, -and carbonic acid—the shortest.</p> - -<div class="figright" ><a id="fig42"></a> -<img src="images/i_141.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 42.</span></div> -</div> -<p>Before detailing some -of the more striking phenomena -connected with -high-tension discharges in -vacuo, a description of -a few forms of simple mercurial -air pumps will be -serviceable.</p> - -<p>Fig. 42: If a glass tube, -<i>F</i>, stopped at one end, 3 -feet long or over, be filled -with mercury and the -open end immersed in a -vessel of mercury, <i>T</i>, the -column of metal in the -tube will sink until it attains -a height, <i>M</i>, of about -30 inches, varying according -to the condition of the atmosphere.</p> - -<p>The space between the mercury column -and the top of the tube will be a fairly -good vacuum. This fact was noted many<span class="pagenum" id="Page_142">142</span> -years ago, and the gradual evolution of -the mercurial air-pump based on this result -can be followed in the articles on the -mercurial air-pump by Silvanus P. Thompson, -read before the Society of Arts, England, -some years ago.</p> - -<p>Geissler, the first manufacturer of the -"Geissler" or vacuum tube for electrical -research, seeing the inconvenience of the -above-described operation and the meagre -results obtained, invented the pump called -by his name (Fig. 43).</p> - -<p><i>F E</i> is a stout glass tube some 3 feet -long, having a bulb, <i>B</i>, at its upper extremity, -and a rubber tube, <i>S</i>, attached to the -curved end. A reservoir of mercury, <i>R</i>, -connects with this rubber tube, and a special -glass tap is fixed in the upper end of -the glass tube at <i>E</i>, beyond which tap -being the point of attachment for the object -to be exhausted. The operation is as -follows: On turning the tap a part of the -way it allows a passage between the tube -<i>F E</i> and the atmosphere. The reservoir<span class="pagenum" id="Page_143">143</span> -<i>R</i> is then raised until the mercury flows -into the bulb and up the tube to the tap. -The tap is then turned a fraction, and the -communication with the air is shut off and -opened between the object to be exhausted -and the tube <i>F E</i>. The reservoir is -then lowered and the mercury falls, drawing -down the air from the object into the -tube. The tap is then turned as in the -first place, and the reservoir <i>R</i> raised, -when the air drawn into the tube is forced -out by the rising column of metal. This -operation being repeated many times, -withdraws nearly all the air from the object—in -fact, makes a fairly good vacuum. -This pump has been much modified from -the simple form described.</p> - -<p>The form of pump most used in the -United States lamp factories is based on -the application of the piston-like action of -a quantity of mercury dropping down a -tube. This is known as the Sprengel -pump, after the inventor.</p> - -<div class="figcenter"><a id="fig43"></a> -<img src="images/i_144.jpg" alt="" /> -<div class="caption"><span class="smcap gap10">Fig. 43.</span> <span class="smcap">Fig. 44.</span></div> -</div> -<p>Fig. 44: <i>F</i> is a stout glass tube about<span class="pagenum" id="Page_144">144</span> -40 inches long by one-twelfth of an inch<span class="pagenum" id="Page_145">145</span> -internal diameter, carrying the reservoir -funnel <i>R</i> at the top, a piece of soft rubber -tubing, <i>S</i>, nipped by a pinch-cock being -interposed to admit of the regulation of -the mercurial drops. The lower end of -this "fall tube," as it is called, is immersed -in mercury contained in a suitable -vessel, <i>V</i>, a branch tube being blown or -cemented into the fall tube to admit of the -connection of the object to be exhausted -at <i>E</i>. <i>S</i> is another piece of rubber tubing -with a pinch-cock regulation. The point -<i>H</i> is the normal barometric height of the -mercury—about 30 inches. On attaching -a bulb, for example, at <i>E</i>, and regulating -the pinch-cock at the top of the fall tube <i>F</i>, -a succession of drops of mercury falls -down the tube, each drop acting as a piston -to drive the air before it, sucking the -same from the bulb, and forcing it down -through the tube and vessel out into the -atmosphere.</p> - -<p>On its first being set into operation, the<span class="pagenum" id="Page_146">146</span> -cushions of air between the drops silence -their fall; but as a higher degree of rarefaction -occurs, the air cushions become -insufficient, and the drops fall with a sharp -click on the top of the barometric column.</p> - -<p>One great disadvantage in this form of -pump is the tendency to fracture of the -glass tube that is manifested by the concussion -of the drops of mercury at the -barometric height. However, this has to -a certain extent been obviated in later -forms of this useful and efficient pump.</p> - -<p>For many electrical experiments, the -simple exhaust tube (Fig. 42) mentioned -at the beginning of the article will be found -very satisfactory. The top end need not -necessarily be sealed off with glass, a cork -having a wire, <i>W</i>, run through for connection -being driven in, and a coat of paraffin -or one of the cements mentioned in a later -chapter be laid on.</p> - -<p>The second electrical connection is made -by a wire dipping in the tumbler of mercury.</p> - -<p><span class="pagenum" id="Page_147">147</span></p> - - -<h3><span class="smcap">Discharges in Vacuo.</span></h3> - -<p>In a simple glass tube having two wires -carrying balls inserted through its ends, -from which the air has been partially exhausted, -the study of the changes shown -by the passage of the spark is extremely -interesting. Before the commencement -of exhaustion no luminous effect can be -discerned; at a low degree of exhaustion -a luminosity appears between the ends of -the wires, the negative pole being surrounded -by a violet glow and a larger -pear-shaped red discharge from the positive. -An interval near the negative electrode -is in darkness, widening as the exhaustion -progresses. When the degree of -exhaustion is very high, a series of arches -concentric with the positive ball appear -and become broader and more distinct as -the rarefaction progresses. The arches or -bands are called striæ, and are most distinct -when the tube is made in the form of -a narrow cylinder, with a bulb at each end.<span class="pagenum" id="Page_148">148</span> -Carbonic acid gas vacua give the best results. -If the finger be placed on the bulb -at either end a luminous spot appears, and -by using a very rapid contact breaker in -the primary circuit, the luminous discharges -become highly sensitive, being -diverted from their regular path on the -approach of the hand, a magnet, or a -grounded wire. An extended treatment -of these phenomena would be out of place -here, but can be found in nearly all comprehensive -works on electricity.</p> - -<p>If an incandescent-lamp bulb be held in -the hand and one end be brought near to -a terminal of the coil, a beautiful bluish -light appears.<a id="FNanchor_2_2" href="#Footnote_2_2" class="fnanchor">2</a> The carbon filament, if -long, and not held by its loop, becomes -electrified and oscillates, often giving out -a clear, high, bell-like sound as it strikes -the glass. Particles of carbon deposited -on the glass during the burning of the -lamp, shown in daylight as a blackening -deposit, generally show little sparks, like -stars scattered over the inside of the globe.</p> - -<div class="footnotes"> -<div class="footnote"> - -<p><a id="Footnote_2_2" href="#FNanchor_2_2" class="label">2</a> -This depends on the degree of exhaustion.</p></div></div> - -<p><span class="pagenum" id="Page_149">149</span></p> - -<p>A vacuum tube will phosphoresce if -held in the hand near a secondary terminal, -or even if laid on the table near the -coil, and will light quite brilliantly if one -end be held against a terminal. This latter -method, however, is generally inconvenient, -as a certain amount of physical -pain ensues from the discharge into the -skin.</p> - -<p>Different gases in the tubes give characteristic -colors. In carbonic acid gas the -whitish green hue prevails; in hydrogen, -white and red; in nitrogen, orange yellow. -The characteristic spectra are given -by the gases in the tubes, and can be -readily examined in the spectroscope. -But there is sometimes a slight variation -in these colors, dependent upon changes in -the current.</p> - -<p>In many Geissler tubes, a portion of the -bulbs is made of uranium glass. On the -passage of the spark in the tube this glass -glows with a magnificent emerald green -hue. Other tubes are constructed with<span class="pagenum" id="Page_150">150</span> -an outside enveloping glass tube fitted -with a corked orifice into which can be -poured different solutions.</p> - -<div class="figcenter" ><a id="fig45"></a> -<img src="images/i_150a.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 45.</span></div> -</div> - -<div class="figcenter" ><a id="fig46"></a> -<img src="images/i_150b.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 46.</span></div> -</div> - -<div class="figcenter" ><a id="fig47"></a> -<img src="images/i_150c.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 47.</span></div> -</div> - -<p>Fig. 45 shows a solution tube to be filled -with solution of sulphate of quinine, etc.</p> - -<p>Fig. 46 shows three exhausted tubes arranged -in series.</p> - -<p><span class="pagenum" id="Page_151">151</span></p> - -<p><i>A</i> is of uranium glass, and glows dark -green; <i>B</i> of English glass, showing a blue -hue, and <i>C</i> of soft German glass, glowing -with a bright apple-green -tint.</p> - -<div class="figright" ><a id="fig48"></a> -<img src="images/i_151.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 48.</span></div> -</div> - -<p>Crystals of nitrate -of calcium, nitrate -of silver, benzoic -acid, tungstate of -calcium, lithia benzoate, -sodium salicylate, -zinc sulphide, -and acetate of zinc -fluoresce.</p> - -<p>Fig. 47 is a highly -exhausted tube, having -at its lowest part -a few pieces of ruby. -When the secondary -current is turned on -at <i>P</i> and <i>N</i> the rubies -shine with a brilliant rich red, as if they -were glowing hot.</p> - -<p>Fig. 48 shows the tube to exhibit the<span class="pagenum" id="Page_152">152</span> -effect resulting from focussing the electric -rays on a piece of iridio-platinum at <i>B</i>.</p> - -<p>The cup <i>A</i> forms the negative pole; the -metal disk <i>C</i>, the positive.</p> - -<p>On increasing the intensity of the spark, -the metal at <i>B</i> glows with extreme brilliancy, -and melts if the intensity be carried -too far.</p> - -<hr class="chap" /> - -<p><span class="pagenum" id="Page_153">153</span></p> - - - - -<div class="chapter"> -<h2 id="CHAPTER_VIII">CHAPTER VIII.<br /> - -<small>ROTATING EFFECTS.</small></h2> -</div> - -<p>Although the luminous discharges in -the exhausted tubes are extremely beautiful, -yet the effect is indescribably enhanced -when the tubes are rotated. Gassiot's star -was the name given to the earliest exhibit -of a rotating tube carrying a luminous discharge, -owing to the curious phenomenon -ensuing from the interruptions of the spark. -As the human retina is only capable of retaining -an impression for a fraction of a -second, and as the tube is only momentarily -luminous during the passage of the -spark, the effect of the revolving tube is -that of a series of such arranged as the -radii of a circle, the number apparent, -being governed by the rapidity of rotation -and the rate of interruption of the current.</p> - -<p><span class="pagenum" id="Page_154">154</span></p> - -<div class="figcenter" ><a id="fig49"></a> -<img src="images/i_154.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 49.</span></div> -</div> - -<p>Fig. 49 represents a form of rotating -wheel which is easily made, and yet susceptible -of many novel and attractive -effects. Such a wheel, placed in a store -window, would undoubtedly attract many -persons by the beautiful variations of col<span class="pagenum" id="Page_155">155</span>ored -figures which it presents while in -motion. And once a crowd is collected -and its attention attracted to one spot, the -capabilities of advertising the goods on -sale are apparent.</p> - -<p>A pasteboard or light wooden disk <i>D</i>, -3 feet in diameter or over, is mounted on -a shaft, <i>S</i>, operated by an electric motor -or such power as may be attainable. Upon -its surface are mounted the tube-holders -<i>T T T T</i>, connected, as shown, by wires -leading from the secondary of the Ruhmkorff -coil. Starting at the shaft <i>S</i>, the circuit -runs to the first tube-holder, where -the continuity of the wire is broken to -allow of the attachment of the vacuum -tube. From the first tube-holder the wire -runs in turn to each of the other three -tube-holders, terminating at <i>R</i>, where it -passes through a hole to a metal ring on -the back of the disk shown by the dotted -circle. This ring and the shaft are in connection -with the secondary coil, by reason -of its electrodes being attached to two<span class="pagenum" id="Page_156">156</span> -brushes or strips of metal pressing, one on -the ring, the other on the shaft; or the -bearing in which the shaft turns may displace -one of the brushes. <i>W W</i> are two -counterbalance weights, that the wheel -may run smoothly and be not affected by -the irregular distribution of the tubes or -its surface. <i>E E</i> are elastic bands, looped -over the wire and through rings in the -disk, that the wires may not be liable to -touch or short circuit.</p> - -<p>At Fig. 50 is an enlarged view of a tube-holder, -although, as it is meant only as a -diagram, considerable variation of design -is permissible. The springs at <i>H H</i>, to -which the wires run, being bent back, the -metal pins <i>P P</i> may be thrust through the -rings on the ends of the tube, and the elasticity -and pressure of the spring will hold -it in place and make the necessary contact. -A wooden block, <i>B</i>, secured to the -face of the disk, is provided with a thumb-screw, -<i>S</i>, securing the tube-holder to it, -by means of which the tube-holders may<span class="pagenum" id="Page_157">157</span> -be turned a trifle upon their axes and so -vary the effect of the wheel.</p> - -<div class="figcenter" ><a id="fig50"></a> -<img src="images/i_157.jpg" alt="" /> -<div class="caption"><span class="smcap gap10">Fig. 50.</span> <span class="smcap">Fig. 51.</span></div> -</div> - -<p>Fig. 51 is a side view of the wheel, showing -one manner of mounting the disk and<span class="pagenum" id="Page_158">158</span> -its connections. The same figures apply -to the parts as in the preceding figure. -<i>M N</i> are the wires leading to the coil, <i>P</i> is -a pulley on the shaft whereby the rotary -power may be applied. The wires on the -face of the disk are not shown, as they -would impair the clearness of the diagram -unnecessarily.</p> - -<p>The greatest danger in the operation of -such a piece of apparatus will be the tendency -of the high tension spark to wander -where it is not wanted, and to take short -but forbidden paths back to the coil. However, -care and perhaps experiment will -prove the remedy. It will be noticed by -reference to Fig. 49 that a circle has been -drawn almost bisecting two of the tube-holders. -This circle represents a circle of -danger, and where a thin material has been -used for the disk, the disk may very well -be reinforced by a piece of stouter card -cemented on its face.</p> - -<p>The disk, whether of wood or of pasteboard, -must have a liberal coating of in<span class="pagenum" id="Page_159">159</span>sulation, -either shellac varnish, paraffin, -or beeswax, and be absolutely free from -unnecessary holes. Moreover, the ring <i>R</i> -must be of such a distance from the support -<i>F</i>, if the latter be metal, as will preclude -any jumping of the spark. A Ruhmkorff -coil giving upward of three quarters -of an inch of spark will be large enough -to operate a wheel carrying four 8-inch -tubes.</p> - -<p>The wheel may be set back in a window -and surrounded by dark fabrics, or built -in, as it were, in a cave of such. The -judicious use of pieces of looking-glass scattered -on the sides of the cave, in such -manner as to reflect the light of the tubes, -will enhance the effect. There is no danger -of fire where ordinary care is used, as -the <i>long</i> spark necessary to the production -of the luminosity will hardly ignite anything -but gas, unless specially arranged to -do so.</p> - -<p>Fig. 52 is a triangle formed of three -Geissler tubes, and intended for rotation<span class="pagenum" id="Page_160">160</span> -as a whole. <i>M M</i> are two pieces of mica -or glass, to prevent any possibility of the -spark jumping and short circuiting, in -which event the tubes would fail to light.</p> - -<div class="figcenter" ><a id="fig52"></a> -<img src="images/i_160.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 52.</span></div> -</div> - -<p>This triangle is shown diagrammatically -at <i>A B C</i>, Fig. 53, mounted on an insulated -rotating disk. Before commencement of -rotation, and upon the current being turned -on to the tubes, a simple triangle will result, -but at a certain stage of rotation the -Maltese cross shown is formed. A still -higher rate of rotation will produce the<span class="pagenum" id="Page_161">161</span> -double star, Fig. 54, and as the rotation and -rate of vibration of the coil contact-breaker -is varied, an apparently endless succession -of stars or triangles appears to grow out -into view.</p> - -<div class="figleft" ><a id="fig53"></a> -<img src="images/i_161a.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 53.</span></div> -</div> -<div class="figright" ><a id="fig54"></a> -<img src="images/i_161b.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 54.</span></div> -</div> - -<p>Although Figs. 53 and 54 serve to illustrate -a triangle of tubes and its variations, -a very pretty and simple effect can -be obtained with it as follows: Three -strips of looking-glass are cut and scratched -across their silvered surface, as described -for the luminous pane, Fig. 37. The current -then being allowed to pass, and the -wheel being rotated, the triangle acts as<span class="pagenum" id="Page_162">162</span> -in the preceding paragraphs, multiplying -and forming figures, which are extremely -interesting to watch.</p> - -<p>While treating on the subject of store-window -attractions, a few suggestions on -a display of stationary Geissler tubes may -be made. Starting with the assumption -that the platform on which the goods -would be displayed is of wood, a very -small amount of preparation is necessary. -The platform is covered with a dark material -free from gloss, such as canton flannel, -on which the tubes are laid in any fancy -pattern, or may be scattered haphazard. -Fine bare wire (No. 36 B. & S. is not any -too small) is run from tube to tube, using -care that it does not touch itself in such -manner as to short circuit the current. -There is not much necessity to cover the -wires, unless the rate of vibration of the -contact be so rapid as to show the brush -discharge from the wire strands. In a -jewelry store the cylindrical portions of -the tubes may be covered with strips of<span class="pagenum" id="Page_163">163</span> -dark cloth, concealing all but the bulbs. -The Uranium bulbs will resemble emeralds; -the yellow bulbs, topaz; and the blue, -turquoise—certainly a very striking collection -of gems. A few diamond-shaped -pieces of the foil-coated glass scratched -across, by the whiteness of the tiny sparks -will aid to set off the whole. The outfit is -not expensive: a coil giving a one half inch -spark will light from four to six tubes to -great brilliancy. Cloths with metallic -threads woven in them must not be used, -nor any of the metallic powders known in -the trade as "glitters."</p> - -<hr class="chap" /> - -<p><span class="pagenum" id="Page_164">164</span></p> - - - - -<div class="chapter"> -<h2 id="CHAPTER_IX">CHAPTER IX.<br /> - -<small>GAS LIGHTING.</small></h2> -</div> - -<p>When it is desired to light clusters of -gas jets situated in inaccessible places, or -a number of them simultaneously, this -method finds ready application. It operates -in the division of a long spark among -a number of burners, the gas being turned -on at the main and the primary circuit of a -Ruhmkorff coil closed and opened until the -succession of sparks ignites the gas, Fig. 55. -There are various commercial forms of -these burners, prominent among which is -the "Smith jump spark" burner.</p> - -<div class="figcenter" ><a id="fig55"></a> -<img src="images/i_165.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 55.</span></div> -</div> - -<p>A lava tip is provided with a mica or -isinglass flange midway between the tip -and the lower end of the burner. This -flange isolates the electrodes from any possibility -of the spark straying away to the<span class="pagenum" id="Page_165">165</span> -metallic pillar in which the burner is inserted. -The multiple lava tip burner is intended -for use where a very short burner is -needed, also for flash rings multiple lights. -Here the tips are placed close enough together -to ignite by contagion. In this -case one of the common tips is removed -from the ring and a multiple lava tip substituted. -It is customary to allow sixteen -burners to one inch of spark. Any num<span class="pagenum" id="Page_166">166</span>ber -of series can be operated alternately -by means of a suitable switch.</p> - -<p>The wire used to connect the burners is -generally bare copper, and as small in -diameter as will sustain its own weight -without injury, the amount of the current -being infinitesimal. It is supported on -porcelain or glass knobs screwed to the -wall or ceiling, being carefully planned to -avoid any metallic substances to which -the spark might be tempted to escape. In -wiring chandeliers, the wire is run through -glass tubes wherever there is any liability -of its coming near the metal pipes. There -is a very great danger of this jumping of -the spark where it is not wanted, and the -utmost care must be taken in planning the -course the wires shall take. Even a damp -wall will cause trouble or a gilt cornice, -although the latter may be entirely insulated -from the ground. The switch -bases for the groups of circuits must be of -hard rubber, and the switch points and -levers be placed so far apart that there is<span class="pagenum" id="Page_167">167</span> -no liability of the spark jumping, which -it certainly will do if it gets a chance. -Ordinary insulated wires are ineffectually -protected by the rubber compounds used. -Glass, mica, and better still, a large air -gap are the only insulations that will serve, -for the tremendous potential or voltage of -the current must be carefully considered -whenever insulation is necessary. The coil -is better provided with a spring key in the -primary circuit than a vibrator, it gives -better control of the circuit and probably -a larger and better spark.</p> - - -<h3><span class="smcap">Gas Lighting in Multiple.</span></h3> - -<p>The spark which occurs at the contact -breaker of a Ruhmkorff coil is held in check -by the condenser; were no condenser used, -it would possess considerable powers of -combustion. Using a large primary coil -and a few cells of open circuit battery, this -spark is made to pass across the path of -a gas jet, which it instantly ignites. The<span class="pagenum" id="Page_168">168</span> -contact breaker consists of a platinum point, -fixed on the gas tip, and a German silver -spring, carried on a lever, which latter is -pulled across the tip so as to make and break -the circuit at the burner orifice. Some -burners are provided with a ratchet arrangement, -by which pulling the lever once turns -on and lights the gas, pulling again turns -it off; others require the gas to be turned -on first.</p> - -<div class="figcenter" ><a id="fig56"></a> -<img src="images/i_169.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 56.</span></div> -</div> - -<p>Reference to Fig. 56 will show the -connections to two burners <i>P P</i> and an -automatic burner <i>A</i>, to be described later. -The coil <i>C</i> is a core of soft iron, about -¾ inch diameter and eight to ten inches long, -wound with from two to four pounds of -magnet wire, Nos. 12 or 14 B & S. One -side of the battery goes to ground or to the -gas pipe, thus forming the return circuit. -The wiring on the fixtures is done with -No. 20 to 24 B & S gas fixture wire, insulated -with four windings of silk or cotton. -This is fastened to the lacquered brass work -by means of thick shellac varnish, it being<span class="pagenum" id="Page_169">169</span> -tied on first with thread, which can readily -be removed when shellac is dry and hard. -The wire is held on the insulated collar of -the burner by a small nut and screw, and<span class="pagenum" id="Page_170">170</span> -great care must be taken to ensure no -grounding. The setting up of a gas-lighting -outfit is extremely simple, but it often fails -for want of care. There must be the best -possible insulation between wire and metal -work.</p> - - -<h3><span class="smcap">Automatic Burners.</span></h3> - -<p>There are several forms of these burners, -but the principle of all is the same. A gas -burner protrudes from the top of a brass -case which encloses the actuating mechanism. -This mechanism consists of two -electromagnets, the armature of one opening -a valve and allowing the gas to flow, at -the same time vibrating a platinum-tipped -rod, which produces a series of sparks at the -burner tip. These sparks ignite the gas, and -a second magnet is provided to shut off the -flow of gas, thus extinguishing the light. -Some devices use one electromagnet for -both lighting or extinguishing, but the -majority are with double magnets. The<span class="pagenum" id="Page_171">171</span> -circuit is worked from a push button situated -at any desired location, and having a -white and black button, one for lighting -and the other for extinguishing. The principal -automatic burners are the Holtzer, the -Boston, and the Bartholdi, between which -there lies little choice, so admirably are they -constructed.</p> - - -<h3><span class="smcap">Bartholdi Automatic Burner.</span></h3> - -<p>Instead of a rotating stop-cock, as in -other automatics, a gravity valve is employed -in the Bartholdi, which is held to its -seat by the weight of the armature and -connecting stem, as shown in Fig. 57. When -the gas is turned off the valve rests upon -its seat, as indicated in the cut. By a closure -of the electric circuit at the turn-on button, -two of the helices <i>M P</i> are energized, causing -the armature <i>J</i> to be lifted, thus, by -means of the stem <i>H</i>, raising the valve <i>G</i> -from its seat into the dotted position, and -opening the gas way so that the gas may<span class="pagenum" id="Page_172">172</span> -issue to the tip, as shown by the arrows. -At the same time, the top of the valve strikes -against the end of the lever <i>W</i>, causing the -circuit to be broken at the spark points <i>T U</i>, -resulting in a continuous sparking as long -as the finger presses the button. The magnet<span class="pagenum" id="Page_173">173</span> -when raising the armature has also twisted -or partially revolved it, so as to bring the -notch <i>d</i> in the armature over the end of the -hook <i>e</i>, as shown in dotted lines. When -the circuit is broken by lifting the finger -from the button the notch falls into the -hook and the valve is locked open.</p> - -<div class="figcenter" ><a id="fig57"></a> -<img src="images/i_172.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 57.</span></div> -</div> -<p>To extinguish the flame the turn-off -button is pressed, when a second magnet -(not shown in cut) lifts the armature -and twists it in the opposite direction, so -that when the circuit is broken the armature -falls free to its normal position, closing the -valve.</p> - -<div class="figcenter" ><a id="fig58"></a> -<img src="images/i_174.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 58.</span></div> -</div> - -<p>In wiring up an automatic burner it is -necessary to run two wires to it, one from -the white button and another from black -button on push plate <i>S</i>. Reference to Fig. 58 -will make this clear. Most burners are -provided with two binding posts inside the -brass case, and the wires are run through -a rubber-bushed hole in the base. If the -push has already been set in position and -wired up, as per Fig. 58, have the buttons<span class="pagenum" id="Page_174">174</span> -pressed alternately, when on touching the -binding posts on automatic with the wires, -the lighting or extinguishing connection is<span class="pagenum" id="Page_175">175</span> -easily selected. The lighting armature in -most automatic burners buzzes violently, -while the extinguishing one only strikes once -on contact being made. Fig. 58 shows how -to connect up two pushes to one automatic, -one push, perhaps, being located downstairs -and the other upstairs in the case of a -hall lamp. In setting up these burners care -must be taken not to bend contacts or -alter adjustment, and absolute precaution -is necessary that no crosses or weakly insulated -places are in circuit. After burning -for some time it often happens that the -burner refuses to light, only buzzing feebly -or not at all. If feebly, the trouble is in -battery, which should consist of, at least, -four or six cells of open circuit battery with -low internal resistance, such as Samson-Law -carbon cylinder, or for occasional use large, -dry cells.</p> - -<p>If no click is heard on pressing white -button, examine all connections; if still no -trouble is found, examine the platinum -break. The platinum tip may be bent<span class="pagenum" id="Page_176">176</span> -by the continual hammering against the -platinum tip on vibrating rod, preventing -contact on collar, or that soot has formed -there. These are the commonest maladies -of automatic burners, and can be easily -remedied by readjusting platinum tip and -cleaning. Contacts here must be clean. In -general wiring use waterproof office wire or, -better still, rubber-covered wire; for fixtures -use the fixture wire before described. When -shellacking the wire to the fixture don't -attempt to connect up batteries until the -shellac is dry and hard, say for half a day. -Electric gas-lighting is fruitful of trouble -if the work is not well done. Another cause -of trouble may arise from a dirty burner not -allowing the gas to strike near the contact -(clean the burner), or the collar carrying -contact may have shifted, perhaps short-circuited; -it should be insulated with a thin -strip of asbestos. Although white lead at -the joints makes a fairly good contact, some -persons prefer to use tin-foil, a piece of foil -being worked around screw thread and the<span class="pagenum" id="Page_177">177</span> -burner screwed on; it prevents leaks as well -as lead if well done, and makes better contact. -As a short circuit on the wires will -cause all the burners to fail, many devices -have been invented to open the circuit upon -such an occurrence. These will be found described -in the catalogues of electrical stores; -they do not come within the province of this -book for description.</p> - -<hr class="chap" /> - -<p><span class="pagenum" id="Page_178">178</span></p> - - - - -<div class="chapter"> -<h2 id="CHAPTER_X">CHAPTER X.<br /> - -<small>BATTERIES FOR COILS.</small></h2> -</div> - -<p>In selecting a battery to operate the -coil, one is needed which will supply a -large steady current for a considerable -period. Although the primary circuit is -opened and closed rapidly, yet the class -known as open circuit cells is not suitable, -even though they have a low internal resistance, -and thereby render a large current. -Such cells are only suitable for the -uses for which they are mostly designed, -bell-ringing or annunciator work. There -is one case, however, where an open circuit -cell may be used with an induction -coil, and that is in gas lighting as previously -described; but here a dozen or so -impulses of current are generally sufficient, -followed by long periods of rest. For the<span class="pagenum" id="Page_179">179</span> -latter work the cells in common use are -the Samson, Champion, and Monarch, all -of which are of low internal resistance and -great recuperative power.</p> - -<p>The reason that such cells will not work -for long periods, is that they polarize. -This latter action takes place in these open -circuit cells, which are of the Leclanché -type as follows: A positive plate of zinc -is immersed in a solution of ammonium -chloride (or salammoniac), and a negative -plate of carbon and peroxide of manganese, -contained either in a porous cup or -compressed into a block also stands in the -solution. Care is taken that these two -plates do not touch each other. When the -outside circuit is closed the zinc combines -with the chlorine of the solution liberating -free hydrogen and ammonia. The hydrogen -appears at the negative plate, where -it is acted upon by the oxygen of the peroxide -of manganese to form water.</p> - -<p>But when the circuit is of too low resistance, -the oxidizing action of the peroxide<span class="pagenum" id="Page_180">180</span> -of manganese is not rapid enough, and a -film of hydrogen, which is a poor conductor, -forms over the negative plate, increasing -the internal resistance of the cell and -setting up local action. -In the best class of these -open circuit cells, this -hydrogen is absorbed -after a rest, and the battery -recuperates and is -ready for work again. -The circuit of the Ruhmkorff -coil is low, and -this polarization always -occurs a few minutes -after the contact-breaker -is started.</p> - -<div class="figleft" ><a id="fig59"></a> -<img src="images/i_180.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 59.</span></div> -</div> - -<p>In the class of closed -circuit cells, chosen for -the present purpose, the Grenet or bottle -bichromate is one of the handiest -for occasional use. A glass bottle-shaped -jar, <i>J</i>, Fig. 59, is provided with a hard -rubber cap, <i>G</i>, on which are mounted the<span class="pagenum" id="Page_181">181</span> -binding posts <i>A B</i>. To the underside of -this cap are attached two carbon plates -<i>C C</i>, which reach nearly to the bottom of -the jar, being connected together on the -cap by a varnished copper strip, the latter -being in turn connected to one binding -post. Through the centre of the cap -passes a brass rod, <i>R</i>, having attached to -its lower end a piece of sheet zinc, <i>Z</i>, well -amalgamated with mercury. This process -of amalgamation consists in cleaning the -zinc, then rubbing its surface with a rag -dipped in dilute sulphuric acid, and pouring -a few drops of mercury on the wet -zinc. The mercury will spread readily -over the zinc, provided it has been well -cleaned, and if properly done should give -the zinc plate a bright, shining appearance.</p> - -<p>When the cell is not in use, the zinc is -drawn up into the neck of the bottle and -clamped by a set screw against the brass -rod. A copper spring pressing on the rod -serves to carry the current to the second -binding post.</p> - -<p><span class="pagenum" id="Page_182">182</span></p> - -<p>This cell originated in France, whence -its name, but a cheaper form is now made -in the United States known as the Novelty -Grenet. The shape of the jar is somewhat -different, and the carbon is moulded, -whereas the French carbon is sawed from -the carbon deposited in the gas retort; -but the American form is practically of as -great utility as the French, and the cost -recommends it.</p> - -<p>The bichromate solutions are affected by -light, and deteriorate less it kept in stoneware -jugs. The Grenet battery can very -well be fitted into a neat wood case, which -will serve the further purpose of preventing -chance knocks from fracturing the -glass jar.</p> - -<p>Carbons which are used in batteries containing -the foregoing solution should be -well washed in warm water whenever the -solution is changed, and especially when -it is intended to put the battery out of -active service. When the solution acquires -a decidedly green hue it should be re<span class="pagenum" id="Page_183">183</span>placed -with fresh. The electromotive -force of this cell varies from 1.90 to 2 -volts, and the amperage is dependent on -the size of the plates, running from 5 amperes -upward.</p> - -<p>The glass jar is filled up to the commencement -of the neck with a solution of -bichromate of potash or sodium, called -electropoion fluid, and prepared as follows: -To 1 gallon of water add 1 pound -of bichromate of sodium, mixing in a stoneware -vessel. When dissolved add 3 pounds -of sulphuric acid in a thin stream, stirring -slowly. As the mixture heats on the introduction -of the acid, care must be used -to pour in the latter slowly. This solution -should not be used until quite cold.</p> - -<p>The sodium salt is preferable to the -potassium, owing to its not forming the -crystals of chrome alum, and also on account -of its lower cost and greater solubility, -the latter being four times greater -than that of the potassium salt. The commercial -acid used should contain at least<span class="pagenum" id="Page_184">184</span> -90 per cent pure acid and should be free -from impurities. On filling the battery -use utmost care not to splash the solution -on any of the metal work, or it will cause -corrosion. Although the salts in the solution -will most likely make a stain, the corrosive -action of the acid can be arrested -if the solution be -splashed on the -clothes by the prompt -application of ammonia -solution.</p> - -<div class="figleft" ><a id="fig60"></a> -<img src="images/i_184.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 60.</span></div> -</div> - -<p>The "Fuller" cell, -Fig. 60, which is another -type of the bichromate -cell, is one -from which a steady -current can be obtained for a longer interval -than from the Grenet, but the current -is less. The electromotive force is -the same, but the current is only 3 amperes, -except in certain modifications.</p> - -<p>In the porous cup is a cone-shaped zinc -having a stout copper wire cast in. This<span class="pagenum" id="Page_185">185</span> -wire is occasionally covered with rubber -insulation, but, as a rule, is bare. The -porous cup is of unglazed porcelain, thick, -but very porous. This sets in the glass -jar, a wooden cover fitting <i>loosely</i> over the -whole to exclude dust. Through this -cover passes the wire leading from the -zinc, and also the carbon plate carrying a -machine screw and check nuts for connection. -The cover is dipped in melted paraffin, -as is also the upper end of the carbon -and the rim of the glass jar. This is to -prevent the creeping of the salts in the -solutions and the corrosion of the brass -work.</p> - -<p>Into the porous cup is poured a solution -composed of 18 parts by weight of common -salt and 72 parts by weight of water. -Electropoion fluid is held by the glass jar, -the two solutions reaching a level of two -thirds the height of the jar. One ounce -of mercury is added to the porous cup -solution to ensure the complete and continuous -amalgamation of the zinc. The<span class="pagenum" id="Page_186">186</span> -salt can be more readily dissolved in warm -water, but <i>all</i> solutions must be used <i>cold</i>. -It is not always necessary to renew the -solutions when the battery fails to give -out its accustomed strength, but several -ounces of water can be substituted for a -similar amount of fluid in the porous cup. -Stir the solution by moving the zinc up -and down, and a temporary improvement -will be noticed.</p> - -<p>To obtain a greater current from this -cell, use a larger zinc, such as a well-amalgamated -zinc plate, and add a teaspoonful -of sulphuric acid to clean water for the -porous cup solution. Additional carbon -plates connected together and placed -round the porous cup will lower the resistance -of the cell and increase the current, -and also tend to keep down the polarization.</p> - -<p>A new form of this battery was described -by M. Morisot a short time ago.</p> - -<p>The positive pole is of retort carbon in -the outer cell in a depolarizing mixture<span class="pagenum" id="Page_187">187</span> -made of 1 part sulphuric acid, 3 parts saturated -solution bichromate of potash, crystals -of the latter salt being suspended in -the cell to keep up the saturation. A porous -cup contains a solution of caustic soda. -The zinc is in a second porous cup placed -within the first, which holds a caustic soda -solution of greater density. The electromotive -force is 2½ volts when the cell is -first placed in circuit, and will remain at -2.4 for some hours. The internal resistance -is low, but varies with the thickness -of the porous cups. This cell is not suitable -for any but use for a few hours at one -time.</p> - -<p>The Dun cell has a negative electrode of -a carbon porous cup filled with broken -carbon. The zinc is in the form of a heavy -ring, and hangs at the top of the solution -in the outer jar. Permanganate of potash -crystals are placed in the porous cup, and -the entire cell filled with a solution of caustic -potash 1 part to water 5 parts. The -voltage is 1.8, and the internal resist<span class="pagenum" id="Page_188">188</span>ance -being low the resultant current is -large.</p> - -<p>A cell with an electrode of aluminum in -a solution of caustic potash and carbon in -strong nitric acid in porous cup is claimed -to have an electromotive force of 2.8, but -the nitric acid is not a desirable acid to -handle.</p> - -<p>Metallic magnesium in a salammoniac -solution with a copper plate in a hydrochloric -acid and sulphate of copper mixture -is of high voltage, nearly 3 volts -being obtained, and the current is large, -but it is a new combination and has not as -yet stood the test of time.</p> - -<p>There are other formulæ for solutions to -be used in Fuller or Grenet cells which -may be useful to the experimenter. -Trouvé's is as follows: Water, 36 parts; -bichromate of potash, 3 parts; sulphuric -acid, 15 parts, all by weight. Bottone's: -Chromic acid, 6 parts; water, 20 parts; -chlorate of potassium (increases electromotive -force), ⅓ part; sulphuric acid, 3<span class="pagenum" id="Page_189">189</span>½ -parts, all by weight. A convenient "red -salt" or "electric sand": Sulphate of -soda, 14 parts; sulphuric acid, 68 parts; -bichromate of potash, 29 parts; soda dissolved -in heated acid, and potash stirred -in slowly. When cold can be broken up -and prepared when required by dissolving -in five times its weight of water.</p> - -<p>The chromic acid used in Bottone's solution -is very soluble in water, it being possible -to dissolve five or six times the -amount in the same quantity of water as -of bichromate of potash. The simple solution -of chromic acid is 1 pound to 1 pint -of water, to which is added 6 ounces of -sulphuric acid.</p> - -<p>When it becomes necessary to cut zinc -plates, it may be readily done by making a -deep scratch on the surface, filling the -scratch first with dilute sulphuric acid, -and then with mercury. The mercury -will quickly eat into the metal, and the -plate may be easily broken across or cut -with a saw. Zinc plates can be bent into<span class="pagenum" id="Page_190">190</span> -shape by the application of heat. Hold -the plate in front of a hot fire until it cannot -be touched by the bare hand: it will -be found that it has softened so that it can -be bent around a suitable wooden form. -As zinc plates are most attacked at the -surface of the acid solution, it is advisable -to coat the extreme upper portion of them -with varnish or paraffin. Rolled zinc is -always preferable to cast, especially so -when immersed in acid solutions.</p> - -<p>To avoid confusion, it may be stated -here that it is the rule to speak of the zinc -element as the positive plate and the negative -electrode or pole, and the carbon <i>vice -versa</i>. The portion of the element immersed -in the solution is the plate, the part -outside, the pole or electrode. In diagrams -and also in formulæ positive is -shown by a + (plus) sign and negative by -a-(minus) sign.</p> - -<p>The relation of cost of the materials most -used is shown in the subjoined table, which -cost, however, varies with the market:</p> - -<p><span class="pagenum" id="Page_191">191</span></p> - - -<div class="center small"> -<table border="0" cellpadding="4" cellspacing="0" summary=""> -<tr> - <td align="left">Sulphuric acid, chemically pure</td> - <td align="left">18</td> -</tr> -<tr> - <td align="left"><span class="ditto">"</span><span class="ditto">"</span>commercial</td> - <td align="left">1.5</td> -</tr> -<tr> - <td align="left">Muriatic<span class="ditto">"</span></td> - <td align="left">1.12</td> -</tr> -<tr> - <td align="left">Nitric <span class="ditto">"</span></td> - <td align="left">3.5</td> -</tr> -<tr> - <td align="left">Electropoion fluid</td> - <td align="left">2</td> -</tr> -<tr> - <td align="left">Bichromate of potash</td> - <td align="left">10.5</td> -</tr> -<tr> - <td align="left"><span class="ditto">"</span><span class="ditto">"</span>soda</td> - <td align="left">8.5</td> -</tr> -<tr> - <td align="left">Caustic soda</td> - <td align="left">9</td> -</tr> -<tr> - <td align="left">Salammoniac</td> - <td align="left">7</td> -</tr> -<tr> - <td align="left">Chromic acid</td> - <td align="left">19</td> -</tr> -<tr> - <td align="left">Blue vitriol</td> - <td align="left">4</td> -</tr> -<tr> - <td align="left">Litharge</td> - <td align="left">5.75</td> -</tr> -<tr> - <td align="left">Mercury bisulphate</td> - <td align="left">94</td> -</tr> -<tr> - <td align="left">Paraffin</td> - <td align="left">9</td> -</tr> -<tr> - <td align="left">Beeswax</td> - <td align="left">35 to 45</td> -</tr> -<tr> - <td align="left">Shellac varnish</td> - <td align="left">87</td> -</tr> -<tr> - <td align="left">Tinfoil</td> - <td align="left">35</td> -</tr> -</table></div> - - -<h3><span class="smcap">Gravity Battery.</span></h3> - -<p>A cheap modification of the Daniell cell. -A glass jar has at the bottom a copper -plate consisting of 4 to 6 leaves of thin -sheet copper, set on their edges in a starlike -shape, a copper wire being attached -to the copper rivet which holds the leaves -together. A mass of crystals of sulphate -of copper is filled in and laid on the top of<span class="pagenum" id="Page_192">192</span> -the copper electrode an inch or so above -its top. The negative plate is a variously -shaped plate of cast zinc hung from the -edge of the jar and reaching about 2 inches -from the top into the fluid. Water is -poured in until it covers the zinc, and the -battery is complete. The sulphate of copper -deposits its metallic copper on the -copper leaves and liberates sulphuric acid, -which rises and attacks the zinc, setting -free sulphate of zinc. The sulphate of -zinc solution being of greater density remains -near the bottom, and the sulphate -of zinc solution stays near the zinc. When -the cell is left too long on an open circuit -the two solutions tend to mix, and copper -is deposited on the zinc. The sulphate of -zinc finally saturates the top solution, -which has to be partly drawn off and replaced -by fresh water and crystals of sulphate -of copper dropped into the jar to -take the place of that which has been decomposed. -Electromotive force 1 volt, -current from <sup>3</sup>∕<sub>10</sub> to <sup>5</sup>∕<sub>10</sub> of an ampere. The<span class="pagenum" id="Page_193">193</span> -practical working of this cell will be treated -of later on in these pages.</p> - -<div class="figright" ><a id="fig61"></a> -<img src="images/i_193.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 61.</span></div> -</div> - -<p>The Gethins (Fig. 61) and the Hussey -bluestone cells both have the zincs standing -in porous cups (shown by dotted lines), -which in turn are supported -half-way down the -jar, generally resting on -the copper strip acting as -a porous partition between -the fluids. The -zinc stands in a solution -of zinc sulphate, or a weak -sulphuric acid solution. -The internal resistance is -low, and the current large, -being from 1 to 5 amperes. -These cells are the -ideal bluestone cells for charging storage -batteries requiring very little attention. -The special Gethins cell shown in the figure -has the copper made with a collar, -which encircles the porous cup, and thereby -lowers the internal resistance of the<span class="pagenum" id="Page_194">194</span> -battery. The voltage not being over 1 volt, -however, renders these cells hardly suitable -for direct connection. Five cells connected -in multiple would give all of 10 amperes of -current, and 1 volt, and a number of these -multiple groups could be connected in series -for a higher voltage.</p> - - -<h3><span class="smcap">Gordon Battery</span></h3> - -<p>is similar in operation to the Edison-Lalande, -but differs in details of construction. The -zinc is a heavy ring suspended outside, but -not touching a perforated tin cylinder closed -at the bottom, containing the oxide of copper -in flakes. Its internal resistance is slightly -higher than the Edison-Lalande cell, otherwise -there is little choice. The 6 × 8 size -is excellent for coil work, giving 250 actual -ampere hours and remaining on open circuit -for long periods without deterioration.</p> - -<p><span class="pagenum" id="Page_195">195</span></p> - - -<h3><span class="smcap">Edison-Lalande Cell.</span></h3> - -<p>This is a practical form of the old -Lalande-Chaperon cell, and gives a steady, -large current, being of low internal resistance, -but is of low electromotive force, being -less than .70 volt on closed circuit of medium -resistance. Being of low internal resistance, -however, its output is large—three cells of -the type <i>S</i>; internal resistance, 0.025 ohm. -Capacity, 300 ampere hours, will about equal -one cell type E 5 of the Chloride Storage -Battery. The elements of this cell consist -of positive plates of amalgamated zinc, suspended -on each side of negative plates of -the black oxide of copper in an electrolyte -solution of caustic potash. In action the -decomposition of water forms an oxide of -zinc from the positive element, which with -the potash in combination leaves a soluble -salt of zinc and potash. The hydrogen of -the water acts on the oxide plates to form -metallic copper, thus really reducing, instead -of increasing, the internal resistance of<span class="pagenum" id="Page_196">196</span> -the cell. A layer of heavy paraffin oil is -poured on top of the solution to prevent the -action of air.</p> - - -<h3><span class="smcap">New Standard</span>,</h3> - -<p>or Roche dry cell. This cell possesses -remarkable recuperative powers and low -internal resistance. Made in many sizes, the -best suited for medical coils is No. 2; dimensions, -5<sup>7</sup>∕<sub>8</sub> × 2<sup>7</sup>∕<sub>16</sub> inches. For heavier work -the No. 5, 6 × 2<sup>9</sup>∕<sub>16</sub> inches, and known as -the Navy Standard, is recommended. A -convenient size for portable medical coils is -No. 3, 3¾ × 1⅞ inches, taking up very little -room, yet giving a large output. Two of -these latter cells enclosed in the coil case -will give with a suitably wound primary -(No. 18 to 20 B & S) as strong a current -as can be used in electrotherapy. For -Ruhmkorff coils cells Nos. 6 and 7 (6 × 3 -inches and 7 × 3 inches) furnish a most -desirable battery for all work not needing -the constant operation of the contact breaker,<span class="pagenum" id="Page_197">197</span> -such as wireless telegraphy, gas-lighting, -etc. They will do service on X-ray work, -but the writer prefers a storage cell or the -copper oxide types. The E. M. F. of the -above cells is one and six-tenths volts, and -current from 9 amperes to the No. 7 size, -which gives 24 amperes on short circuit.</p> - - -<h3><span class="smcap">Dry-Cell Construction.</span></h3> - -<p>As a matter of practice, there is no really -dry cell; all so-called cells contain liquid -held in suspension, and their output is -limited to the amount of fluid. One of this -type can easily be made in the following -manner: A containing jar is made up of -first-quality sheet zinc, the edges being -joined by a turned seam and then soldered, -the bottom of zinc being also soldered in. -In soldering here, as actually in all such -operations, be <i>absolutely sure</i> the edges of -the metal are clean. The jar is partially filled -with the following composition: Oxide of -zinc, 1 part; sal ammoniac, 1 part; plaster<span class="pagenum" id="Page_198">198</span> -of paris, 3 parts; chloride of zinc, 1 part; -water, 2 parts, all by weight; or sal ammoniac, -1 part; chloride of calcium, 5 parts; -calcined magnesia, 5 parts; water, 2 parts, -or enough water to make a thin paste. A -brass binding post is soldered to the zinc -case and a carbon plate having a binding -post is inserted in the centre of the cell, care -being taken that it does not touch the zinc. -A small disc of wood laid in the bottom of -the cell will prevent contact at the bottom. -Molten pitch or a composition of pitch and -rosin in the proportion of 6 to 1 is poured -on top, so as to seal the cell. As gas is -generated in the cell, a safety valve should -be provided, either a piece of porous cane -or a short length of hard rubber tube, inside -of which have been placed a few strands of -woollen thread. This class of cell is so -cheap and so many forms are available for -choice that it is rarely desirable to make -one's own. They will not do for steady -current, but only for intermittent work. The -large sizes being of low internal resistance,<span class="pagenum" id="Page_199">199</span> -can be used for signalling in wireless telegraphy, -where it is not possible to use wet -(or free fluid) cells. The principal dry cells -on the market are the Mesco, the O. K., the -Nungesser, and the Samson semi-dry cell.</p> - -<hr class="chap" /> - -<p><span class="pagenum" id="Page_200">200</span></p> - - - - -<div class="chapter"> -<h2 id="CHAPTER_XI">CHAPTER XI.<br /> - -<small>STORAGE OR SECONDARY CELL.</small></h2> -</div> - -<p>The development of the storage or secondary -cell has been one of the most important -electrical advances of the century. -For purposes of experiment or work, where -a large or steady current is required from -compact and readily tended apparatus, -the storage cell proves its utility. The -simplest form was that used by the early -experimenters, and as it is easy to make, -a form of it may very well be described.</p> - - -<div class="figcenter" ><a id="fig62"></a> -<img src="images/i_201.jpg" alt="" /> -<div class="caption"><span class="smcap gap10">Fig. 62.</span> <span class="smcap">Fig. 63.</span></div> -</div> - -<p>From a sheet of lead ⅛ inch thick two or -more pieces are cut of the requisite size, -say, 5 inches square. In making these -plates, they should be cut so as to leave a -strip 1 inch wide and 3 inches long, projecting -from one corner, <i>A</i> (Fig. 62), for -the purpose of connection. This is for<span class="pagenum" id="Page_201">201</span> -the reason that the fumes of the sulphuric -acid solution would quickly corrode any -wires or screws in the plates, and also to -give a better connection. The number of -plates cut must be an odd one, as it is -general to make the two outside plates of -the same polarity—viz., negative. These -plates are then scored with a steel point -across and across on both sides to perhaps -a depth of <sup>1</sup>∕<sub>64</sub> of an inch. This scoring is -not absolutely necessary; it somewhat -hastens the formation of the plates. The<span class="pagenum" id="Page_202">202</span> -plates are then laid face to face, being -separated by pieces of wood, rubber, or, -still better, by a piece of grooved wood, -Fig. 63 having a thin piece of asbestos on -each side. These grooves are to carry off -the gas, and should run up and down the -board, as in the figure. The wood is ⅛ of -an inch thick or thereabouts, and preferably -perforated with holes ¼ of an inch or -larger. When laid together, a few strong -rubber bands hold the plates from coming -apart. To prevent lateral motion, a few -rubber pins may be thrust through the -plates. The alternate strips are to be connected -together in two series, as in a condenser, -and the complete series placed in -a jar containing a mixture of seven parts -of water to one of sulphuric acid. The -terminal of the strips connected to the -smallest number of plates is to be marked -<i>P</i> or +, for positive.</p> - -<p>This terminal is now to be connected to -a charging current (not over 1 ampere), as -described in the directions for charging<span class="pagenum" id="Page_203">203</span> -batteries, for eight hours, and then discharged -at a rate not over 1 ampere for -six hours. Then the connections are to -be reversed and the cell charged backward, -as it were, and discharged. This -has to be repeated for a long period, perhaps -a month, before the cell is in good -condition; on the final charge it is to be -connected positive to positive of charging -source. This operation is called "forming," -and the result is to change the metallic -lead of the positive plate into red-brown -peroxide of lead, and the lead negative -plates into spongy lead.</p> - -<p>In modern commercial cells this operation -is no longer pursued, the plates are -variously constructed of lead frameworks -holding plugs of litharge or lead oxide, -which is "formed" with great facility. -For many purposes other than operating -Ruhmkorff coils, a few simple cells made, -as described, are handy to have and easy -to make. In sealing the cells up for portability, -care must always be taken to leave<span class="pagenum" id="Page_204">204</span> -a small hole in the cover for the escape of -the sulphurous acid gas.</p> - - -<h3><span class="smcap">Charging Storage Batteries.</span></h3> - -<p>Although the charging of a storage or -secondary battery is by no means a difficult -operation, yet it requires care, and -one unaccustomed to the work will meet -many slight difficulties which may seriously -affect the results. Pre-eminently the -best charging source is a direct current, -constant potential electric-light circuit. -The amount of current required varies according -to the type and make of the cell, -but we will select one of a capacity of 50 -ampere hours for illustration.</p> - -<p>By 50 ampere hours is meant a delivery -of 1 ampere per hour for fifty hours, or a -rate of discharge equal to the above, as -2 amperes per hour for twenty-five hours. -In practice a secondary cell will not be -found to act exactly as above, the total -amount of current decreasing as the discharge -is greater. Each cell is constructed<span class="pagenum" id="Page_205">205</span> -to discharge at a certain rate, above which -it is not safe to go. Five amperes per -hour is a suitable rate for a fifty-hour cell, -and should not be greatly exceeded. The -Chloride type, however, is one which can -be discharged at a higher rate than normal -without any serious results, the latter -being generally a bulging or "buckling," -as it is called, of the plates whereby they -short circuit or fall apart. The voltage of -the charging source should be at least 10 -per cent over that of the battery when -fully charged. The voltage of a cell of -storage battery varies from about 2.3 at -commencement of discharge to 1.7, at -which latter voltage discharge must be -stopped and charging recommenced.</p> - -<p>Fig. 64 shows the connections to charge -a storage battery from an electric-light circuit. -The latter must be direct current -and of low tension. The circuit from the -negative lead runs to the rheostat handle -<i>R</i>, thence through as many coils as are in -circuit (varied by moving the handle over<span class="pagenum" id="Page_206">206</span> -the contact pieces in connection with the -resistance coils). The positive of the cell is -connected to the positive main.</p> - -<p>In connecting storage cells to the mains -the utmost care must be taken that the terminals -are correctly attached. It happens in -isolated plants that some change is made in -the wiring or the switchboard, which reverses -the current without warning being -given to the battery charger. It is the -safest way to test the polarity of the terminals -of <i>both</i> battery and mains each time -charging is commenced. For polarity tests -see Chapter I. It is immaterial on which -side of the battery the rheostat or similar -device is placed.</p> - -<div class="figcenter" ><a id="fig64"></a> -<img src="images/i_207a.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 64.</span></div> -</div> - -<div class="figcenter" ><a id="fig65"></a> -<img src="images/i_207b.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 65.</span></div> -</div> - -<p>Fig. 65 shows the employment of lamps -instead of the rheostat. The lamps <i>L L</i> -regulate the current flow by the manner -in which the circuit is arranged. If only -one lamp be turned on, the current necessary -for only one lamp circulates through<span class="pagenum" id="Page_207">207</span> -the battery. Each additional lighted lamp<span class="pagenum" id="Page_208">208</span> -adds to the current by decreasing the resistance -of the circuit. <i>S</i> is a switch which -must always be left open when the dynamos -are to be stopped.</p> - - -<h3><span class="smcap">Charging from Primary Battery.</span></h3> - -<p>In many instances an electric-light circuit -is not available for charging purposes, -in which event recourse must be made to -a primary battery. The one most suited -for the work is the modified Daniell, or -copper and zinc combination in solutions -of sulphate of copper (bluestone) and sulphate -of zinc respectively.</p> - -<p>There are many good forms of this cell -on the market, chief of which are the simple -gravity, the Gethins, and the Hussey, -which have been previously described. -An example will now be described of the -operations necessary with the gravity cell, -charging one 50-ampere hour storage cell. -At least six cells of gravity will be required, -as the voltage of each cell is never<span class="pagenum" id="Page_209">209</span> -over 1 volt, and is dependent on the resistance -in the external circuit falling as the -resistance is lowered. Place the six clean -glass jars on a firm foundation, where there -is no liability of shaking and no dust likely -to settle. Unfold the copper strips into -the form of a star, bending the corners for -half an inch so as to give an anchorage in -the bluestone. Place them into the bottom -of the jars and pour in water enough -to cover them at least 3 inches below the -surface. Now carefully drop in 4 pounds -of clean bluestone, which will fill in the -angles between the copper wings, at the -same time holding the element down to -the bottom of the jar. Hang the zincs -from the top edge of the jar, and fill up -with water to 1 inch from the top. The -addition of 5 ounces of sulphate of zinc -per cell will render the cells immediately -available, and for the further hastening of -the chemical action, the copper wire from -each copper may be inserted in the binding -post-hole of the zinc belonging to its<span class="pagenum" id="Page_210">210</span> -own cell and screwed tight for a few -hours; or the cells may be connected together -in series, and the wire from the last -copper be screwed to the zinc of the first, -thus putting the whole series on short circuit. -The only advantage of the first -method being a saving of time when a -number of cells is being set up. This saving -of time is often of consequence, as the -longer the newly set-up cell is on open -circuit, the more copper will be deposited -on the zinc, which is highly undesirable. -This is shown by the blackening of the -zinc as soon as it is put in the solution, -which blackening it is hard to prevent entirely. -When the cell is working satisfactorily -it will show a clearly defined line -between the colorless solution above and -the deep blue solution beneath.</p> - -<p>Gravity cells should never be moved. -If no sulphate of zinc is available, half a -teaspoonful of sulphuric acid may be -poured in over the zinc, which will tend -to form the sulphate of zinc. Without<span class="pagenum" id="Page_211">211</span> -any of these helps the cell will take at -least twenty-four hours on a short circuit -before it will give its normal current. This -current should be from <sup>4</sup>∕<sub>10</sub> to <sup>5</sup>∕<sub>10</sub> of an -ampere. Five cells set up by the writer -varied after the addition of the -zinc sulphate from 200 milli-amperes -(thousandths of an ampere) -to 300 milli-amperes, although -they were apparently -all set up alike; but after twelve -hours' short circuiting they all -gave a fairly uniform current of -from 470 to 500 milli-amperes.</p> - -<div class="figright" ><a id="fig66"></a> -<img src="images/i_211.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 66.</span></div> -</div> -<p>From time to time on storage -battery work, say, every week, -the specific gravity of the top -solution must be tested with a -hydrometer (see Fig. 66), which -should be put into the solution and allowed -to come to rest. The indicated number at -the level of the liquid should be 25°. If -the number is higher some solution should -be drawn off and clear water added, until<span class="pagenum" id="Page_212">212</span> -the hydrometer settles down to 25° or -thereabouts. The inside of the glass jar -for 1 inch from the top may be greased to -prevent the salts of zinc creeping over the -edge, or half an inch of heavy paraffin oil -be poured on the top to prevent evaporation -and creeping. When the zinc gets -very much coated with the dark deposit it -must be taken out and scraped and washed. -When the bluestone needs replenishing, -drop in carefully and be sure none lodges -on the zinc element.</p> - - -<h3><span class="smcap">Setting up the Storage Cell.</span></h3> - -<p>Each manufacturer of storage cells issues -specific directions for the charging of his -own make, but generally the method is as -follows: The acid solution is prepared by -mixing one volume of sulphuric acid to -from four to seven volumes of water, according -to the make of the cell. The sulphuric -acid should have a specific gravity -of 1.82 and be chemically pure. <i>The acid -must always be poured into the water, and<span class="pagenum" id="Page_213">213</span> -slowly, stirring all the time, then set aside -for the mixture to cool.</i> It is best to mix -the solution in a separate earthenware vessel, -and when two or more cells are to be -set up, to mix all the solution at one time, -to ensure the same strength, unless a -hydrometer is used to determine this.</p> - -<p>A good method to ascertain the exact -quantity of solution required is to place -the elements in the jar and cover 1 inch -deep at least with water, then remove the -elements and pour off the volume of water -corresponding to the proportion of acid -to be added, and lastly pouring the remaining -water into the mixing vessel, prepare -the solution, or electrolyte, as it is called. -New elements should be wetted with pure -water before being immersed in the solution. -An ordinary charge of the electrolyte -requires from six to ten hours to cool -thoroughly, as considerable heat is evolved -in the mixing.</p> - -<p>Having now prepared the storage battery -solution and set up the primary cells,<span class="pagenum" id="Page_214">214</span> -the charging can be proceeded with. The -current must be turned on the storage cell -immediately the elements are placed in -the acid. Connect the wire from the zinc -of the primary battery to the negative of -the storage cell and the copper wire to -the positive. As the current from a gravity -cell is but small, it will take quite a -time to charge a storage cell of 50 ampere -hours' capacity fully; it is a good scheme -to get the cell charged up from a dynamo -source, and use the gravity cells to keep -it charged; but this cannot always be -done, and the gravity battery will do the -work in time. As the best storage cells -render but 90 per cent of the current put -into them, they must be charged over the -number of hours for which they are required -to deliver current.</p> - -<p>When the cell is fully charged the solution -will become milky and give off gas -freely. This gas in large quantities is detrimental -to health, and on no account -should a storage cell be <i>charged</i> in a sleep<span class="pagenum" id="Page_215">215</span>ing -apartment. It affects the throat and -lungs, and renders them susceptible to -take cold under suitable circumstances. -The average voltage of storage cells, when -tested with the charging current on, is 2.4 -volts, and the lowest they should be allowed -to reach is 1.9 volts, unless otherwise -specified by the manufacturers.</p> - -<p>Cells in poor condition are liable to form -a <i>white</i> deposit of sulphate of lead, this -fault being known as "sulphating." This -trouble requires much careful nursing, -and the cells must be charged for a long -time at a very low rate until the plates of -the positive element regain their normal -gray color. Chips of straw or excelsior, -etc., falling in between the plates will carbonize -and cause trouble.</p> - -<p>Most portable cells are sealed, but all -cells can be easily sealed with paraffin wax -for amateur use. Cover the elements fully -½ inch above the normal height of the electrolyte -with water before pouring in the -electrolyte. Melt some paraffin in an<span class="pagenum" id="Page_216">216</span> -earthenware jar and pour it on top of the -water, about the middle of the surface, -when it will spread, and care having been -taken to have the jar sides dry, will cake -solid and form a good seal. Then bore a -hole with a brace and bit or some such -tool through the wax and pour out the -water. The cell can then be set up as -usual, the hole being only partly closed to -allow of the escape of the generated gas. -A glass or rubber tube can be sealed into -the hole in the wax, and makes a more -finished job.</p> - -<p>While on the subject of primary batteries -for charging storage cells, a few remarks -on their electromotive force may -not be amiss. Although the specifications -issued by the manufacturers specify an excess -charging voltage of 10 per cent over -the total voltage of the storage cells, this -does not apply to primary cells in its entirety. -The voltage of five gravity cells -in series would aggregate 5 volts, and the -voltage of one storage cell but 2 volts, but<span class="pagenum" id="Page_217">217</span> -there would not be 5 volts available to force -the charging current through the latter. In -the first place there is the counter electromotive -force of the storage cell working -against the gravity battery. Simple subtraction -would show only 3 volts excess in -favor of the primary electromotive force; -but the working voltage of a galvanic cell -varies according to external resistance of -the cell and the external resistance of the -circuit. When the internal resistance is -high, as in the gravity cell, and the circuit -resistance is low, in this case being the -storage cell, the available electromotive -force of the primary is low also.</p> - -<p>In many cases it is desired to operate a -Ruhmkorff coil from an electric-light main -direct. This can readily be done if the circuit -be of the constant potential class—that -is, one constructed to furnish current -for incandescent lamps in multiple. With -the direct current, such as the Edison, all -that is necessary is either to interpose a -rheostat, as in Fig. 64, or to use the lamps,<span class="pagenum" id="Page_218">218</span> -as in Fig. 65. The manner of connecting -up is the same as if the storage cell B be -replaced by the coil. Using the formula -<i>C</i> = <i>E</i>/<i>R</i>, for example, if the circuit be at -110 volts and the coil require 10 amperes, -a resistance of 11 ohms will be required. -Or using the lamps in the diagram, Fig. -65, about 20 lamps are to be put in circuit. -If the current be an alternating one, -the contact-breaker will have to be screwed -down or short circuited.</p> - - -<h3><span class="smcap">The "U. S." Storage Cell.</span></h3> - -<p>This cell is of the lead-zinc type, being -the practical form of the Reynier cell. It -is to be recommended for working Ruhmkorff -coils, its output weight for weight -being far in excess of the lead-lead types. -This cell is readily portable and easy of -operation, the zinc electrode being the only -one needing renewal, and that at very infrequent -intervals.</p> - -<p><span class="pagenum" id="Page_219">219</span></p> - -<p>The lead electrode consists of plates of -peroxide clamped together, and presents -quite a large surface. The zinc in most -types is of the circular sheet form, and -encloses the lead block, being kept amalgamated -by mercury lying in the bottom of -the cell. The E. M. F. on open circuit is -about 2.5 volts, which is higher than any -lead-lead combination. On closed-circuit -work this drops to from 2.35 volts downwards. -During action, when a large amount -of current is being drawn from the cell, a -white sulphate appears, but this disappears -upon the cell being recharged or even left -to rest. Bubbles of gas, which sometimes -form under the peroxide block, should be -removed by gently tilting the cell or hitting -the table or shelf upon which it stands a -smart blow. The large type No. 3 is suitable -for X-ray work, and a still larger cell is -made, which is preferable for heavy or -continuous discharges of current.</p> - -<p><span class="pagenum" id="Page_220">220</span></p> - - -<h3><span class="smcap">Harrison Cell.</span></h3> - -<p>The No. 1 cell recently put upon the -market has given excellent results for open -circuit work. It consists of a negative element -with lead peroxide as a depolarizer. -The positive element is self-amalgamating -zinc, which is free from local action. The -electrolyte is dilute pure sulphuric acid. -The potential is high, being 2.5 volts, and -the internal resistance is 0.14 ohm. This -cell belongs to a group which is midway -between primary and storage, or secondary -cells. Its construction is similar to the lead-zinc -secondary cell, in place of which it may -be used, it being easy to recharge an exhausted -cell by passing a weak current -through it in reverse direction, thus recharging -the peroxide of lead grid and renewing -the zinc and electrolyte.</p> - -<p>The large size, or type No. 3, which the -manufacturers are producing, differs from -the No. 1 cell in that it has a larger negative<span class="pagenum" id="Page_221">221</span> -element, or grid, and has two zincs, instead -of one; consequently, it has a lower internal -resistance—0.07 ohm—and a higher discharge -rate with a capacity of 150 ampere -hours. The potential is 2.5 volts. It is -suitable for coil work or for sparking gas -engines, and for ease of manipulation and -convenience is to be highly recommended.</p> - -<div class="figcenter" ><a id="fig67"></a> -<img src="images/i_221.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 67.</span></div> -</div> - -<p>The elements are shown in Fig. 67, lead -grid <i>L</i>, which is filled in with paste of -peroxide of lead, and which neither buckles -nor disintegrates. The zinc <i>Z</i>, however,<span class="pagenum" id="Page_222">222</span> -possesses a novel feature. A cavity is cast -in the zinc element and filled with an amalgam -of mercury, the copper electrode passing -through this amalgam into the solid zinc, as -shown in the cut. As the action of the -battery proceeds, this amalgam forces its -way into the pores of the element and keeps -up so good an amalgamation of both copper -rod and zinc that zincs can be used up to -a point when the rising internal resistance -makes it economy to throw them away, and -absolutely no perceptible local action takes -place in the cell upon continued open circuit. -A preparation is furnished if desired, which -forms a jelly of the electrolyte, making the -cell readily portable. Like all of these combinations, -its electromotive force exceeds -two volts, and its internal resistance is low -enough to advise its employment in coil -work.</p> - -<p>When a storage battery is to remain unused -for a long time it must first be fully -charged, and then every week or so the charging -current passed through it until it bubbles.<span class="pagenum" id="Page_223">223</span> -Where it is to be laid away for a long period -of time, and weekly charging is not feasible, -the following operations are necessary: -First, fully charge battery, remove electrolyte, -and replace by water immediately. -Discharge at normal rate until voltage runs -down to 1.7 per cell. Gradually decrease -resistance until battery is almost on short -circuit. Let it stand for a day, then pour -off the water, and keep elements in a dry, -clean place.</p> - -<hr class="chap" /> - -<p><span class="pagenum" id="Page_224">224</span></p> - - - - -<div class="chapter"> -<h2 id="CHAPTER_XII">CHAPTER XII.<br /> - -<small>TESLA AND HERTZ EFFECTS.</small></h2> -</div> - -<p>The currents of high frequency used by -Tesla in his researches are produced by -electrical rather than mechanical means. -The alternating current dynamo used by -him renders a current of 10,000 alternations -per second, but the actual current -necessary to the performance of the luminous -effects has a frequency of millions of -oscillations per second, produced by the -discharge of Leyden jars or condensers.</p> - -<p>Dr. Oliver J. Lodge, in his "Modern -Views of Electricity," shows that the discharge -of the Leyden jar is in general oscillatory, -the apparently single and momentary -spark, when analyzed in a very rapidly -rotating mirror, is shown to consist of a -series of alternating flashes, rapidly suc<span class="pagenum" id="Page_225">225</span>ceeding -one another and lasting individually -less than one hundred thousandth of -a second. The capacity of the condenser -and inertia of the circuit regulate the -rapidity of these oscillations. A 1 microfarad -condenser discharging through a -coil of large self-induction, such as one -having an iron core, may oscillate only a -few hundred times per second. On the -other hand, a Leyden jar of the 1 pint size -discharging through a short circuit will -set up oscillations, perhaps ten million per -second; and a still smaller jar would give -oscillations away up in the billions. But -these small jars are quickly discharged, -and require a constant replenishing.</p> - -<p>The discharge actually consists of a principal -discharge in one direction, and then -several reflex actions back and forth, becoming -feebler until their cessation. In -their vibration they generate waves in the -surrounding medium, similar in many respects -to sound waves, but of infinitely -higher velocity. Their length depends on<span class="pagenum" id="Page_226">226</span> -the rate of vibration of the source and -their velocity. The microfarad discharge -before mentioned will have a wave length -of perhaps 1200 miles, the small jar not -over 70 feet; and yet the true light wave -has only an average length of one fifty -thousandth of 1 inch. These waves travel -into space until they either die out from -exhaustion or are absorbed by some suitable -body; but they possess the quality of -resonance in a degree like those of sound. -Two tuning forks of the same pitch will -influence one another—that is, one on -being vibrated will start the other in vibration, -even at a considerable distance, but -the electric waves far surpass them in this -respect.</p> - -<div class="figcenter" ><a id="fig68"></a> -<img src="images/i_227.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 68.</span></div> -</div> - -<p>Dr. Hertz made the first practical experiments -in this direction with his electric -resonator (Fig. 68). This apparatus -consisted of a 3-inch spark induction coil, -<i>I</i>, the secondary wires <i>S S</i> being connected -to the copper rods <i>R R</i>, provided with -metal balls <i>B B</i>, nearly 11 inches in diam<span class="pagenum" id="Page_227">227</span>eter. -The discharging balls <i>D D</i> were approximated -until a satisfactory discharge -passed between them. A large wire ring -having a spark gap in its circuit was so -influenced by the resonance as to show -minute sparks passing across this gap even -when the ring was situated in a distant -room. In many experiments with a rapidly -vibrating induction coil current, a -sparking has been noticed in metallic objects -in the same room, in one instance it<span class="pagenum" id="Page_228">228</span> -being discovered in the metallic designs -on a wall-paper.</p> - - -<h3><span class="smcap">The "Tesla" Effects.</span></h3> - -<p>In exploring the comparatively new field -opened up by Professor Crookes, Nikola -Tesla has stimulated research into the mysteries -of high tension and frequency currents -and their effects. In the majority of -his experiments Tesla uses alternating currents -generated by machinery of his own -design, but in a large number of cases his -effects can be duplicated with an induction -coil suitably energized. In the latter case -the apparatus consists of a battery, a -Ruhmkorff coil, two condensers, and a -second specially constructed induction or -disruptive coil, with some few subsidiary -implements. The contact-breaker or rheotome -must be one giving interruptions of -very rapid sequence.</p> - -<div class="figcenter" ><a id="fig69"></a> -<img src="images/i_229.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 69.</span></div> -</div> - -<p>Fig. 69 shows a diagram of the Tesla -arrangement with a Ruhmkorff coil. The -terminals of the secondary coil of the<span class="pagenum" id="Page_229">229</span> -Ruhmkorff coil <i>I</i> terminate at the condensers<span class="pagenum" id="Page_230">230</span> -<i>C C</i>. Bridged across the wires -before they reach the condensers is the -discharger <i>D</i>. The second terminals of -the condensers are led through the split -primary of the disruptive coil, terminating -at the points <i>B B</i> of the second discharger. -The secondary of the disruptive coil is -either outside or inside the primary coil. -The condensers are of special design, being -small, but of high insulation. They each -consist of two plates of metal a few inches -square immersed in oil and arranged so -they can be brought nearer together or -further apart, as necessary. Within limits, -the smaller these plates are the more -frequent will be the oscillations of their -discharge. They also fulfil another purpose, -they help nullify the high self-induction -of the secondary coil by adding capacity -to it.</p> - -<div class="figcenter" ><a id="fig70"></a> -<img src="images/i_231.jpg" alt="" /> -<div class="caption"> <span class="smcap">Fig. 70.</span></div> -</div> - -<p>The discharger tips are preferably metal -balls under 1 inch in diameter. Tesla uses -various forms of dischargers, but for ex<span class="pagenum" id="Page_231">231</span>perimental -purposes the two metal balls -will answer. They are adjusted when the -whole apparatus is working according to -the results desired. The mica plates serve -to establish an air current up through the -gap, making the discharge more abrupt, an -air blast being also used at times for the -furtherance of this object. The device -(Fig. 70) consists of an electro-magnet, <i>C</i>,<span class="pagenum" id="Page_232">232</span> -set with its poles <i>P</i> across the air gap, -helping to wipe out the spark, as in a well-known -form of lightning arrester. This -form, described by Tesla, has the pole -pieces <i>P</i> shielded by mica plates <i>M</i>, to prevent -the sparks jumping into the magnets. -Fig. 70 is an elevation and Fig. 71 a plan -of this device.</p> - -<div class="figcenter" ><a id="fig71"></a> -<img src="images/i_232.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 71.</span></div> -</div> - -<p>The resonance effects obtained during<span class="pagenum" id="Page_233">233</span> -the operation of a Tesla coil are very -marked, and their study may lead to the -solution of the problems of communication -between distant points without the use of -other conducting media than the atmosphere. -But the main use to which the -Tesla currents have been put is that of artificial -illumination. These currents have -enabled experimenters to obtain a high -luminosity in vacua by the aid of only one -conducting wire—in fact, in some cases -without the utilization of any conductor -than the air. An ordinary incandescent -lamp connected to one terminal of the coil -will show in a fair degree some of the luminescent -phenomena. The brush effects -from the terminals of the secondary coil -are extremely marked and interesting; -but to detail the experiments that can be -performed with the Tesla disruptive coil -would be an impossibility here. Reference -is recommended to the published -works of Nikola Tesla, which happily are -readily procurable.</p> - -<p><span class="pagenum" id="Page_234">234</span></p> - -<p>These currents of high frequency have -of late been turned to account in electrotherapeutics, -principally for the stimulation -they exert on the nutritive process. -They also exert a very great influence on -the vasomotor centres, as is evidenced by -the reddening of the skin and exudation -of perspiration. This result is readily obtainable -by placing the patient in connection -with one electrode on an insulating -stool, and terminating the other electrode -at a large metal plate situated a few feet -distant; or the patient may be surrounded -by a coil of wire in connection with the -coil of sufficient diameter, however, to -prevent contact.</p> - -<hr class="chap" /> - -<p><span class="pagenum" id="Page_235">235</span></p> - - - - -<div class="chapter"> -<h2 id="CHAPTER_XIII">CHAPTER XIII.<br /> - -<small>THE "ROENTGEN" RAYS AND RADIOGRAPHY.</small></h2> -</div> - -<p>Although the remarkable discovery -that it was possible by electrical means to -depict an image of an object on a photographic -sensitized plate, despite the intervention -of solid bodies, was first given to -the world at large by Professor Roentgen, -yet he was undoubtedly led to the results -by consideration of the works of previous -experimenters in electrical discharges -through vacua.</p> - -<p>It is not intended here to trace the previous -work of Professor Crookes, the inventor -of the radiometer, which is actuated -by the heat rays of light, nor of -Hertz, who found that gold leaf was transparent -to rays emanating from certain<span class="pagenum" id="Page_236">236</span> -vacuum tubes carrying a luminous electrical -discharge. It is mainly the purpose of -these pages to give directions for practical -work, and not deal in theories, interesting -though they be. At the beginning of X-ray -investigation many claims were made which -have since been disproven, but the fundamental -operations remain the same. A -Crookes tube of special design is energized -from a coil or similar electrical distributor, -and by means of the resultant rays otherwise -opaque objects appear partially transparent, -their shadows being cast upon the -screen of a fluoroscope, or these shadows -are allowed to act upon a sensitized photographic -plate, and subsequent development -reveals outlines or shadowgraphs. The -general arrangement of apparatus is shown -in Fig. 72. <i>C</i> is a Ruhmkorff coil, giving -not less than 2 inches of spark; <i>B</i> the battery -operating same; <i>T</i> the modified form of -Crookes tube used most generally; <i>X</i> the -object under observation; <i>F</i> the fluoroscope -or the sensitized photographic plate. The<span class="pagenum" id="Page_238">238</span> -usual precautions are taken to avoid the -leakage of current from the secondary wires, -the tube <i>T</i> being best mounted in a wooden -stand (Fig. 72), and the wire connections -brought to it as direct as possible. No -condenser, stand, etc., are shown in drawing, -to avoid unnecessary complication.</p> - -<div class="figcenter" ><a id="fig72"></a> -<img src="images/i_237.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 72.</span></div> -</div> -<p><span class="pagenum" id="Page_237">237</span></p> - - -<h3><span class="smcap">The Fluoroscope.</span></h3> - -<p>This is a funnel-shaped cardboard box -with an opening at the smaller end for the -eyes and a piece of card across the larger -end. The inside surface of this card is -covered with crystals of barium platino -cyanide, the most satisfactory fluorescent -substance obtainable. The earlier fluoroscopes -were made with tungstate of calcium, -but the above salt has proven far more -satisfactory. The operation of the fluoroscope -is simple. It is held in the hand by a -convenient handle, the open end pressed -close to the eyes, so as to exclude outside<span class="pagenum" id="Page_239">239</span> -light, and with the hand or other object held -against the outside of the big end, or screen, -it is directed towards the Crookes tube. -The screen then appears to glow with a -bluish light, and the shadow of the object -is distinctly seen on the screen. Different -adjustments of the coil give results which -will be treated upon later.</p> - - -<h3><span class="smcap">Phosphorus Tube.</span></h3> - -<p>Messrs. Siemens and Halske manufactured -a tube which allowed of a slight -variation of vacuum by using the vapor of -phosphorus. An auxiliary tube containing -phosphorus was added to the main tube, and -upon heat being applied to it by means of -a lamp, vapor is given off, which materially -reduces the vacuum of the main tube. When -the opposite result is desired part of the -current is diverted through the auxiliary -tube, and the vapor is caused to solidify itself -upon the walls of the tube.</p> - -<p><span class="pagenum" id="Page_240">240</span></p> - -<div class="figcenter" ><a id="fig73"></a> -<img src="images/i_240.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 73.</span></div> -</div> -<p><span class="pagenum" id="Page_241">241</span></p> - - -<h3><span class="smcap">The Crookes Tube.</span></h3> - -<p>The most satisfactory tube for X-ray -work is one where the vacuum is readily -adjustable. Reference to Fig. 73 shows the -Queen form. A small bulb, containing a -chemical which gives off vapor when heated -and reabsorbs it when cooled, is directly -connected to the main tube and surrounded -by an auxiliary tube, which is exhausted to -a low vacuum. In the auxiliary tube the -cathode is opposite to the above-mentioned -bulb, so that any discharge through it will -heat the bulb by the bombardment of the -cathode rays. The cathode is connected to -a spark point, which can be adjusted to any -distance from the cathode of the main tube. -The anode of the small tube is directly connected -to that of the main tube. When the -tube is put into operation the vacuum and, -consequently, the resistance of the main tube -being high, the current preferably passes -by the spark point and auxiliary tube, heat<span class="pagenum" id="Page_242">242</span>ing -the chemical for a few seconds until -sufficient vapor has been driven into the -main tube to permit the current to pass -through the latter. After this only an occasional -spark will jump across the gap to -counteract the tendency of the reabsorption -of the vapor and consequent raising in -resistance of the main tube.</p> - -<p>This device presents easy means of adjusting -the vacuum in the main tube. With the -spark point at a considerable distance from -cathode the vacuum will be high. When the -spark gap is short the vacuum will become -low. The main bulb is about 4½ inches in -diameter, and at the place where the X-rays -pass only <sup>1</sup>∕<sub>64</sub> of an inch in thickness. The -cathode is of aluminum, the anode of platinum. -In starting this tube, it is best to -make the spark gap about one inch in width. -When connected up and working properly -the main bulb will be filled with a green -striated luminosity between anode and -cathode, and the tip of the chemical bulb -will have the shadow of the little platinum<span class="pagenum" id="Page_243">243</span> -tip thrown upon it. The green light is not -always brilliant; at times it is quite weak, -but yet does its work well. A brilliant green -light is often one of the signs of wrong -connection, and particularly so when the -little shadow on the chemical bulb is absent. -Never run these or any other tubes backwards, -but be sure the current is flowing -in correct direction at first operation.</p> - -<p>Other forms of Crookes tubes differ only -in form, or are devoid of adjustment, and -the connections of coil, tube, etc., are the -same.</p> - - -<h3><span class="smcap">General Remarks.</span></h3> - -<p>A high vacuum gives greater penetrative -power than a low vacuum. Where the -operator has not an adjustable tube it is -imperative that he have at least two tubes, -one high and one low. It is the contrasts -which render the X-ray practical, and these -contrasts are largely governed by the -vacuum. In locating a metallic substance -in the human body a high vacuum tube<span class="pagenum" id="Page_244">244</span> -would be needed, that the bones and dense -tissue be rendered more transparent. On -the other hand, to make a radiograph of the -bones, a lower vacuum is necessary in order -to get a contrast between the bones and the -tissues. In general, a high vacuum is best -for fluoroscope work and a low vacuum for -making pictures on a photographic plate. -Short exposures in radiography are obtained -by powerful rays and consequently by coils -operating at considerable energy. In extended -examinations or where a subject is -under the X-rays for more than a minute -or so, a screen should be interposed between -the subject and the tube to avoid the burning -effect which is often noticeable. This screen -consists of a piece of cardboard well covered -with gold leaf, and should be grounded—that -is, a connection be run from the gold -surface to a water-pipe or other ground -connection. Sheet lead is an efficient screen -to the rays, and, if desired, a lead screen can -be made, partially enclosing the apparatus, -to protect the operator. But it must be large<span class="pagenum" id="Page_245">245</span> -enough and far enough distant from the -coil and tube to avoid any possibility of -leakage of current or even inductive influence. -In operating X-ray machines never -attempt to alter connections or make adjustments -other than at coil platinum screw or -Crookes tube spark gap without first shutting -off current. Remember that a very -unpleasant shock can be easily obtained from -touching the apparatus with only one hand. -It is often advisable to remove one's watch, -particularly when using Ruhmkorff coils of -large size.</p> - -<p>The tube may be worked until it shows -a slight redness in the centre of the platinum, -but care must then be taken not to increase -current, or the platinum will melt. Never -allow the tube to come in contact with any -object other than its stand and connections -while working, and be sure the wires from -secondary do not come near tube until they -reach places of attachment, or they may -spark through glass and ruin the tube.</p> - -<p>In making radiographs on sensitized<span class="pagenum" id="Page_246">246</span> -plates the unused plates should be kept at -a considerable distance from the coil while -working. Better still if they are in another -room. Plates for X-ray work are made by -most photographic supply dealers; in fact, -almost any good brand of sensitized plates -or even films will answer. When making -a radiograph, the plate can either be left in -the holder or well wrapped in black paper, -but current should never be turned on coil -before the plate and subject are in position. -In photographing the chest, neck, etc., the -plate can be strapped on to the part; but the -subject must remain absolutely still. The -time of exposure varies considerably with the -size of coil, thickness of object, etc. Radiographs -of the hand have been taken by -simply laying the hand on top of the plateholder -and operating tube for 100 seconds. -But, as a rule, longer exposures are necessary. -Most radiographs will generally -require that the plate be "intensified" and -a developer used that gives great detail, such -as metol quinol, etc. At any rate, great care<span class="pagenum" id="Page_247">247</span> -should be exercised in developing the plate, -as many a good radiograph has been spoiled -by undue haste.</p> - -<hr class="chap" /> - -<p><span class="pagenum" id="Page_248">248</span></p> - - - - -<div class="chapter"> -<h2 id="CHAPTER_XIV">CHAPTER XIV.<br /> - -<small>WIRELESS TELEGRAPHY.</small></h2> -</div> - -<p>In Chapter XII. we showed how Dr. -Hertz caused electric waves to pass through -space and become visible by sparks across -an air gap in a wire ring situated at a distance -from the source of energy. The -apparatus used, and termed an electric -resonator, is in principle similar to that of -the wireless telegraph. The minute sparks -instead of idly passing across the air gap -are made to traverse a "coherer" (to be -afterwards more fully described). This -"coherer" substantially consists of a resistance, -preferably metal filings placed in series, -with a battery and relay. Normally, the -resistance is so adjusted that the battery -current is not strong enough to operate the<span class="pagenum" id="Page_249">249</span> -relay. A wire is led from one side of this -coherer up into the air to intercept the -Hertzian waves, the other side of the coherer -is put to earth, or "grounded." When a -wave strikes the air wire it sends a current -through the coherer to ground (as before it -sent a spark across the air gap), and this -wave acts on the filings in its passage -through them; in effect, to lower their resistance, -so that the current is increased through -the relay circuit and the relay armature is -attracted to its magnet. The relay makes -contact in the usual manner at the platinum -points, and in its turn causes the local -circuit, sounder, bell, or pen register to -record the wave (or signal). After each -wave the filings are in such state that to -restore them to their former high resistance -it is necessary to give the coherer a smart -tap. This is generally accomplished automatically -by means of an arm extending -from the sounder lever, which strikes against -the coherer each time the sounder armature -is moved.</p> - -<p><span class="pagenum" id="Page_250">250</span></p> - -<div class="figcenter" ><a id="fig74"></a> -<img src="images/i_250.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 74.</span></div> -</div> -<p><span class="pagenum" id="Page_251">251</span></p> - -<p>Figures 74 and 75 are diagrams of a -simple circuit, Fig. 74 being the transmitting -apparatus and Fig. 75 the receiving apparatus.</p> - -<p>In Fig. 74 <i>P P</i> and <i>S S</i> are the primary -and secondary of a Ruhmkorff coil, <i>D</i> two -brass balls on the discharger, <i>B</i> the battery, -<i>K</i> a key, in place of the usual contact -breaker, which is either absent or screwed -down; <i>V</i> a wire leading from one arm of -the discharger up into the air, of a height -varying with the results desired; <i>G</i> a ground -plate in connection with the other discharger -arm.</p> - -<p>The coil condenser is left out of the diagram -for sake of clearness; but, of course, -is necessary to the operation of the apparatus.</p> - -<p>In Fig. 75, <i>C</i> is the coherer, also called -the Branly tube, or radio conductor; <i>S</i> -a telegraph sounder, or electric bell; <i>R</i> a -relay; <i>R B</i> and <i>L B</i> the relay battery and -local battery, respectively; <i>G</i> a ground connection; -<i>M</i> a resistance, or choke coil, and<span class="pagenum" id="Page_252">252</span> -<i>V</i> a vertical wire, as in the transmitter; in<span class="pagenum" id="Page_253">253</span> -fact, in the station set the same vertical wire -answers for both transmitter and receiver.</p> - -<div class="figcenter" ><a id="fig75"></a> -<img src="images/i_252.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 75.</span></div> -</div> - -<p>The coil to be used may be from two -inches of spark upwards, dependent upon -the distance the signals have to travel. The -relay battery may be two cells of dry battery, -the local battery as much as is desired to -operate the bell, sounder, or pen register -receiving the signals. Presuming the apparatus -set up and adjusted, and designating -the transmitter as Station A and the receiver -as Station B, the operation will be as follows: -A pressure and release of key <i>K</i> sends -an impulse of current through the primary -<i>P</i>, inducing a current in <i>S</i>, which manifests -itself by a spark between the discharger balls -at <i>D</i>. An electric wave is released, which, -starting from <i>V</i>, Station A, meets in its -passage <i>V</i> of Station B. Travelling along -this wire to the ground, it finds two paths—through -<i>C</i> or <i>R</i>. As the choke coil deters it -from passing through the relay, it finds -passage through <i>C</i> and so to ground.</p> - -<p><span class="pagenum" id="Page_254">254</span></p> - - -<h3><span class="smcap">The Coherer.</span></h3> - -<p>Many forms of this apparatus are in use, -but as yet no definite design can be recommended -for specific purposes. The most -general mode of construction is that of the -Branley Coherer, as shown in Fig. 76.</p> - -<div class="figcenter" ><a id="fig76"></a> -<img src="images/i_254.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 76.</span></div> -</div> - -<p>It consists of a glass tube, 2 inches long -by ¼ inch inside diameter, furnished with -well-fitted metal plugs at each end, to which -connections are made. These plugs can be -slid in and out of tube for adjustment, the -gap between them being loosely filled with<span class="pagenum" id="Page_255">255</span> -fine metal filings. The metal used varies, -according to the operator's preference, the -most generally adopted being pure nickel -for both plugs and filings. Another mode -of construction for purely experimental use -is to merely cork the ends of the tube and -pass the wires through these corks into the -filings, ensuring, however, good contact -between wires and filings. Marconi's favorite -form is a glass tube two inches long with -silver plugs, each one-quarter inch long, in -each end, intervening space being partially -filled with a mixture of nickel and silver -filings. These plugs are then adjusted to -as close as one-twenty-fifth of an inch, and -the whole apparatus exhausted of air either -by means of a leading-in tube or by placing -coherer in a vessel from which the air can -be drawn. As a rule, coherers containing -air become less sensitive after continued -use.</p> - -<p><span class="pagenum" id="Page_256">256</span></p> - - -<h3><span class="smcap">Carbon Coherer.</span></h3> - -<p>Pointed carbon rods can be inserted in -the tube instead of metal, and carbon dust -substituted for the metal filings; but this -form is suitable only for special purposes. -It is very delicate in its action, but somewhat -uncertain.</p> - - -<h3><span class="smcap">Coherer without Filings.</span></h3> - -<p>Were it not for reasons, such as difficulty -of decoherence, the metal filings might be -dispensed with and two rods of metal placed -in light contact. The construction of the -coherer reminds one very much of the microphone, -a satisfactory coherer having been -made out of the old "nail microphone," four -wire nails being placed crossing one another -in the battery circuit, in one case acting as -a sound transmitter, whence the name; in -the other as a coherer.</p> - -<p><span class="pagenum" id="Page_257">257</span></p> - - -<h3><span class="smcap">Aluminium Coherer.</span></h3> - -<p>Aluminium, a metal which has steadily -grown into favor, and which is now readily -obtainable, can be made to serve in the -present apparatus in place of nickel both as -to electrodes and filings. It is advisable, -however, to use aluminium electrodes of -slightly larger diameter than those of other -metals.</p> - - -<h3><span class="smcap">Steel Ball Coherer.</span></h3> - -<p>A recent writer has recommended the use -of balls of steel, such as are used in ball -bearings, such, however, not to exceed -⅜ inch diameter. Such a coherer would take -the form of an upright glass tube, with -electrodes exerting pressure on a series of -four or more steel balls. Decoherence here -becomes difficult, and mention is but made -of it to show the variety of forms which -this important little article may assume.</p> - -<p>Coherers are adjusted by advancing or<span class="pagenum" id="Page_258">258</span> -receding the electrodes, altering the quantity -of the filings, etc. There exists but little -difficulty in operating coherers; considerable -latitude is permissible as to adjustment, size, -character, etc. There does not seem so much -difficulty in obtaining sensitiveness as in -guarding against external electrical disturbances. -Wings or vanes of thin sheet metal -are sometimes attached to the metal ends or -electrodes of the coherer for purposes of -adjustment, their size and capacity being -determined by experiment. It is best that -they present no sharp angles, but be of a disc, -or spherical, form, the better not to dissipate -energy.</p> - - -<h3><span class="smcap">The Oscillator.</span></h3> - -<p>This is the name given the contrivance at -the ends of the discharger, <i>D</i> being the point -at which the electrical oscillations, or waves, -are radiated.</p> - -<p><span class="pagenum" id="Page_259">259</span></p> - - -<h3><span class="smcap">Clarke's Oscillator.</span></h3> - -<p>This consists of two brass spheres, generally -3 inches in diameter, and mounted on -a stand or sometimes on top of the induction -coil. The distance between the balls is -readily adjustable by either attaching the -balls on the ends of two sliding rods, or -causing the balls themselves to slide on the -rods (Fig. 77).</p> - -<div class="figcenter" ><a id="fig77"></a> -<img src="images/i_259.jpg" alt="" /> -<div class="caption"><span class="smcap gap10">Fig. 77.</span> <span class="smcap">Fig. 78.</span></div> -</div> - - -<h3><span class="smcap">Triple Oscillator.</span></h3> - -<p>Here three balls are used, two outside ones -connected to the circuit, being one-half inch<span class="pagenum" id="Page_260">260</span> -diameter, and the middle one, isolated from -all connection, of three inches in diameter. -This form is best mounted on a separate -stand, the balls either being on glass or hard -rubber legs (Fig. 78). Connecting wires -from the secondary of the coil must in all -cases be run with the greatest precautions -against crosses, as directed in Chapter V.</p> - -<p>It is possible to make many different -designs in oscillators. Some experimenters -use the simple Clarke form, others prefer -the triple balls; yet, again, others vary the -sizes and the relative sizes of the balls. One -form of oscillator prescribes the balls to be -immersed in oil or vaseline. Such methods -all have their adherents. Even the plain -points of an induction coil discharger will -serve for short-distance work.</p> - -<p>Oscillators are adjusted by altering their -proximity to one another, and should have -care given to keep the spheres bright. It is -easy to alter capacity of an oscillator by -connecting its spheres to other insulated -spheres.</p> - -<p><span class="pagenum" id="Page_261">261</span></p> - - -<h3><span class="smcap">The Coil.</span></h3> - -<p>The coil for wireless telegraphy does not -differ from the regular Ruhmkorff, except -that in place of the contact breaker a signal -or Morse telegraph key is substituted. Of -course, the contact breaker can be made to -perform the same duty by retracting the -adjusting screw out of reach of the platinum -on spring, and then operating the hammer -and spring in same manner as key.</p> - - -<h3><span class="smcap">Translating Devices.</span></h3> - -<p>Under this head are included relay -sounder, bell, or register, which are at receiving -set. They do not differ from the -regular telegraphic apparatus. The sounder -may be of the Western Union pattern, -wound to 4 ohms; the relay also Western -Union pattern, and wound to 150 or 250 -ohms, as best suits the individual case.</p> - -<p>In order to protect the receiver from the -action of the transmitter belonging to the<span class="pagenum" id="Page_262">262</span> -same set of instruments, particularly when -powerful waves are generated, it has been -found at times necessary to enclose the -receiver in a metal case. Marconi has patents -on such devices, particularly on a -movable shutter in the case, which opens -when the transmitter is not in operation. -Edouard Branly placed his receiving set in -a metal case with a vertical slit eight inches -by one-tenth of an inch.</p> - - -<h3><span class="smcap">Air Conductor.</span></h3> - -<p>The vertical wire extending from the -coherer up into the air must be insulated -from all other objects in the best possible -manner. A bare copper wire of No. 14 -B & S gauge can be suspended from porcelain -insulating knobs, which in turn can be -strung from each other by means of stout -silk cord or even wire. There is a special -form of insulator used in electric construction -work, and known as a circuit breaker, -which will answer and which is easy of<span class="pagenum" id="Page_263">263</span> -attachment; reference to Fig. 79 will show -manner of using.</p> - -<div class="figleft" ><a id="fig79"></a> -<img src="images/i_263.jpg" alt="" /> -<div class="caption"><span class="smcap">Fig. 79.</span></div> -</div> -<p>Temporary grounds can be made to water -pipes, but it is better to use regular -telephone copper ground-plates sunk -deep in moist earth.</p> - -<p>At South Foreland, England, a -mast has been erected, 150 feet in -height for transmission across Channel, -a distance of nearly thirty miles. -At Notre Dame University, Illinois, -Professor Green used a wire 150 feet -in length, suspended from top of a -high church tower, but was unable -to transmit much over three miles, -owing, presumably, to fact that the -intervening country was well supplied -with overhead wires, which -probably intercepted the waves.</p> - -<p>It has been claimed that earthed or -grounded air wires are necessary, but -balls or similar "capacities" are not of service -on the top of the wire. A theory has been -advanced that the currents do not pass from<span class="pagenum" id="Page_264">264</span> -air wire tip to air wire tip, but are conducted -by the varying strata of the earth. No -general confirmation is obtainable, however, -and the experimental reader will find a wide -field for research in this direction. Marconi, -on the other hand, has accomplished much -with zinc cylinders under six feet high, <i>not -grounded in any respect</i>, indeed, and he also -finds it impossible to assume a proportion -between distance of effect and height of air -wire. The following investigations and -experiments are of interest in this connection:</p> - -<p>At a meeting of the Institution of Electrical -Engineers, in December, 1898, Dr. -Oliver Lodge showed that there must be -a certain relative position between the receiving -and transmitting circuits.</p> - -<p>He placed on one side of a room a box, -containing a battery, bell, relay, and coherer -properly connected up. On the other side -he had an induction coil and pair of parallel -discharger rods, with a spark gap to transmit -waves across the room. When the rods<span class="pagenum" id="Page_265">265</span> -of the receiver and transmitter were placed -parallel to each other the receiving bell was -operated; when the receiving rods of the -transmitter were at right angles to those of -the receiver the bell either failed to work, -or weakened very considerably. He also -told of an experiment made to determine the -influence of different methods of grounding -the apparatus. He found that when the -apparatus was connected by a wire laid on -the ground, there was the required response -at the receiving station; but when the two -stations were situated each side of a lake, -and the ground wires immersed in the -water, the receiving instrument failed to -work. It seemed to him that the conductivity -and power absorption of ether wave energy -by water was too great to allow of the -transmission of Hertz waves. This would -seem to bear out the results obtained by -Marconi in dispensing with ground wires.</p> - -<hr class="chap" /> - -<p><span class="pagenum" id="Page_266">266</span></p> - - - - -<div class="chapter"> -<h2 id="INDEX">INDEX.</h2> -</div> - -<div class="index"> -<ul class="index"> -<li class="ifrst">A</li> - -<li class="indx">Acid, Chromic, <a href='#Page_189'>189</a>.</li> - -<li class="indx"><span class="ditto">"</span> Sulphuric, <a href='#Page_212'>212</a>.</li> - -<li class="indx">Air pump, Geissler, <a href='#Page_142'>142</a>.</li> - -<li class="indx"><span class="ditto">"</span> <span class="ditto">"</span> Simple, <a href='#Page_141'>141</a>.</li> - -<li class="indx"><span class="ditto">"</span> <span class="ditto">"</span> Sprengel, <a href='#Page_143'>143</a>.</li> - -<li class="indx"><span class="ditto">"</span> blast, <a href='#Page_76'>76</a>.</li> - -<li class="indx"><span class="ditto">"</span> wire, <a href='#Page_262'>262</a>.</li> - -<li class="indx">Amalgamation, <a href='#Page_180'>180</a>.</li> - -<li class="indx">Assembly of coil, <a href='#Page_22'>22</a>.</li> - -<li class="indx">Attraction, Window, 154, <a href='#Page_163'>163</a>.</li> - -<li class="indx">Automobile coil, <a href='#Page_40'>40</a>.</li> - -<li class="indx">Automatic burners, <a href='#Page_170'>170</a>.</li> - -<li class="indx">Automatic burners, Adjustment, <a href='#Page_176'>176</a>.</li> - - -<li class="ifrst">B</li> - -<li class="indx">Ballistic galvanometer, <a href='#Page_99'>99</a>.</li> - -<li class="indx">Barium platino cyanide, <a href='#Page_238'>238</a>.</li> - -<li class="indx">Base for coil, <a href='#Page_30'>30</a>.</li> - -<li class="indx">Bath coil, <a href='#Page_61'>61</a>.</li> - -<li class="indx">Battery, Bichromate, <a href='#Page_180'>180</a>.</li> - -<li class="indx"><span class="ditto">"</span> Champion, <a href='#Page_179'>179</a>.</li> - -<li class="indx"><span class="ditto">"</span> Daniell, <a href='#Page_191'>191</a>.</li> - -<li class="indx"><span class="ditto">"</span> Dun, <a href='#Page_187'>187</a>.</li> - -<li class="indx"><span class="ditto">"</span> Edison-Lalande, <a href='#Page_195'>195</a>.</li> - -<li class="indx"><span class="ditto">"</span> Fuller, <a href='#Page_184'>184</a>.</li> - -<li class="indx"><span class="ditto">"</span> Gas-lighting, <a href='#Page_179'>179</a>.</li> - -<li class="indx"><span class="ditto">"</span> Gethins, <a href='#Page_193'>193</a>.</li> - -<li class="indx"><span class="ditto">"</span> Gordon, <a href='#Page_194'>194</a>.</li> - -<li class="indx"><span class="ditto">"</span> Gravity, <a href='#Page_191'>191</a>.</li> - -<li class="indx"><span class="ditto">"</span> Grenet, <a href='#Page_180'>180</a>.</li> - -<li class="indx"><span class="ditto">"</span> Harrison, <a href='#Page_219'>219</a>.</li> - -<li class="indx"><span class="ditto">"</span> Monarch, <a href='#Page_179'>179</a>.</li> - -<li class="indx"><span class="ditto">"</span> Morisot, <a href='#Page_188'>188</a>.</li> - -<li class="indx"><span class="ditto">"</span> Novelty, <a href='#Page_182'>182</a>.</li> - -<li class="indx"><span class="ditto">"</span> Open circuit, <a href='#Page_178'>178</a>.</li> - -<li class="indx"><span class="ditto">"</span> Polarization, <a href='#Page_179'>179</a>.</li> - -<li class="indx"><span class="ditto">"</span> Samson, <a href='#Page_179'>179</a>.</li> - -<li class="indx"><span class="ditto">"</span> solutions, <a href='#Page_185'>185</a>, <a href='#Page_188'>188</a>, <a href='#Page_189'>189</a>.</li> - -<li class="indx"><span class="ditto">"</span> Standard dry, <a href='#Page_196'>196</a>.</li> - -<li class="indx"><span class="ditto">"</span> Storage, <a href='#Page_200'>200</a>.</li> - -<li class="indx"><span class="ditto">"</span> Storage, to charge, <a href='#Page_208'>208</a>.</li> - -<li class="indx"><span class="ditto">"</span> Storage, to make, <a href='#Page_101'>101</a>.</li> - -<li class="indx"><span class="ditto">"</span> Storage, to seal, <a href='#Page_215'>215</a>.</li> - -<li class="indx"><span class="ditto">"</span> U. S. storage, <a href='#Page_218'>218</a>.</li> - -<li class="indx">Beeswax, <a href='#Page_95'>95</a>.</li> - -<li class="indx">Brush, Electric, <a href='#Page_128'>128</a>.</li> - - -<li class="ifrst">C</li> - -<li class="indx">Capacity of condenser, <a href='#Page_100'>100</a>.</li> - -<li class="indx">Carbons for battery, <a href='#Page_182'>182</a>.</li> - -<li class="indx">Cements, <a href='#Page_97'>97</a>.</li> - -<li class="indx">Charging condenser, <a href='#Page_110'>110</a>.</li> - -<li class="indx">Chromic acid, <a href='#Page_189'>189</a>.</li> - -<li class="indx">Closed magnetic circuit, <a href='#Page_6'>6</a>.</li> - -<li class="indx">Coherer, Aluminium, <a href='#Page_251'>251</a>.</li> - -<li class="indx"><span class="ditto">"</span> Branly, <a href='#Page_254'>254</a>.</li> - -<li class="indx"><span class="ditto">"</span> Carbon, <a href='#Page_256'>256</a>.</li> - -<li class="indx"><span class="ditto">"</span> Steel ball, <a href='#Page_258'>258</a>.</li> - -<li class="indx">Coil, Failure to work, <a href='#Page_49'>49</a>.</li> - -<li class="indx"><span class="ditto">"</span> for gas engine, <a href='#Page_37'>37</a>.</li> - -<li class="indx"><span class="pagenum" id="Page_267">267</span><span class="ditto">"</span> general remarks, <a href='#Page_42'>42</a>.</li> - -<li class="indx"><span class="ditto">"</span> in series, <a href='#Page_32'>32</a>.</li> - -<li class="indx"><span class="ditto">"</span> Medical, <a href='#Page_51'>51</a>.</li> - -<li class="indx"><span class="ditto">"</span> Oil immersed, <a href='#Page_33'>33</a>.</li> - -<li class="indx"><span class="ditto">"</span> Output of, <a href='#Page_46'>46</a>.</li> - -<li class="indx"><span class="ditto">"</span> Primary, <a href='#Page_7'>7</a>.</li> - -<li class="indx"><span class="ditto">"</span> Resistance, <a href='#Page_40'>40</a>.</li> - -<li class="indx"><span class="ditto">"</span> Secondary, <a href='#Page_10'>10</a>.</li> - -<li class="indx"><span class="ditto">"</span> Table of dimensions, <a href='#Page_50'>50</a>.</li> - -<li class="indx"><span class="ditto">"</span> Tesla, <a href='#Page_35'>35</a>.</li> - -<li class="indx"><span class="ditto">"</span> Testing, <a href='#Page_44'>44</a>.</li> - -<li class="indx"><span class="ditto">"</span> To select, <a href='#Page_46'>46</a>.</li> - -<li class="indx"><span class="ditto">"</span> Winding, <a href='#Page_20'>20</a>.</li> - -<li class="indx">Condensers, Aluminium, <a href='#Page_115'>115</a>.</li> - -<li class="indx"><span class="ditto">"</span> Adjustable, <a href='#Page_117'>117</a>.</li> - -<li class="indx"><span class="ditto">"</span> Charging, <a href='#Page_110'>110</a>.</li> - -<li class="indx"><span class="ditto">"</span> capacity, 100, <a href='#Page_119'>119</a>.</li> - -<li class="indx"><span class="ditto">"</span> Discharge of, <a href='#Page_225'>225</a>.</li> - -<li class="indx"><span class="ditto">"</span> Glass, <a href='#Page_101'>101</a>.</li> - -<li class="indx"><span class="ditto">"</span> Mica, <a href='#Page_108'>108</a>.</li> - -<li class="indx"><span class="ditto">"</span> Oil, <a href='#Page_116'>116</a>.</li> - -<li class="indx"><span class="ditto">"</span> Paper, 105, <a href='#Page_107'>107</a>.</li> - -<li class="indx"><span class="ditto">"</span> Rolled up, <a href='#Page_115'>115</a>.</li> - -<li class="indx"><span class="ditto">"</span> Series, <a href='#Page_108'>108</a>.</li> - -<li class="indx">Cone vibrator, <a href='#Page_88'>88</a>.</li> - -<li class="indx">Contact breaker, <a href='#Page_26'>26</a>.</li> - -<li class="indx"><span class="ditto">"</span> <span class="ditto">"</span> Adjustable medical, <a href='#Page_85'>85</a>.</li> - -<li class="indx"><span class="ditto">"</span> <span class="ditto">"</span> Adjustable cone, <a href='#Page_88'>88</a>.</li> - -<li class="indx"><span class="ditto">"</span> <span class="ditto">"</span> Dessauer, <a href='#Page_80'>80</a>.</li> - -<li class="indx"><span class="ditto">"</span> <span class="ditto">"</span> Electrolytic, <a href='#Page_77'>77</a>.</li> - -<li class="indx"><span class="ditto">"</span> <span class="ditto">"</span> Highspeed, <a href='#Page_69'>69</a>.</li> - -<li class="indx"><span class="ditto">"</span> <span class="ditto">"</span> in vacuo, <a href='#Page_81'>81</a>.</li> - -<li class="indx"><span class="ditto">"</span> <span class="ditto">"</span> Polechanging, <a href='#Page_73'>73</a>.</li> - -<li class="indx"><span class="ditto">"</span> <span class="ditto">"</span> Queen, <a href='#Page_83'>83</a>.</li> - -<li class="indx"><span class="ditto">"</span> <span class="ditto">"</span> Queen, large form, <a href='#Page_84'>84</a>.</li> - -<li class="indx"><span class="ditto">"</span> <span class="ditto">"</span> Steel ribbon, <a href='#Page_80'>80</a>.</li> - -<li class="indx">Contacts, Care of, <a href='#Page_90'>90</a>.</li> - -<li class="indx">Core, <a href='#Page_4'>4</a>.</li> - -<li class="indx"><span class="ditto">"</span> Iron filing, <a href='#Page_46'>46</a>.</li> - -<li class="indx">Crookes tube, <a href='#Page_241'>241</a>.</li> - - -<li class="ifrst">D</li> - -<li class="indx">Dessauer contact breaker, <a href='#Page_80'>80</a>.</li> - -<li class="indx">Dielectric, <a href='#Page_104'>104</a>.</li> - -<li class="indx">Discharger, <a href='#Page_26'>26</a>.</li> - -<li class="indx">Dry cell, <a href='#Page_196'>196</a>.</li> - -<li class="indx">Dun cell, <a href='#Page_187'>187</a>.</li> - - -<li class="ifrst">E</li> - -<li class="indx">Eddy currents, <a href='#Page_6'>6</a>.</li> - -<li class="indx">Edison-Lalande cell, <a href='#Page_195'>195</a>.</li> - -<li class="indx">Electric sand, <a href='#Page_189'>189</a>.</li> - -<li class="indx">Electrode, <a href='#Page_190'>190</a>.</li> - -<li class="indx">Electrolyte, <a href='#Page_213'>213</a>.</li> - -<li class="indx">Electrolytic interrupter, <a href='#Page_77'>77</a>.</li> - -<li class="indx">Ends for coil, <a href='#Page_25'>25</a>.</li> - -<li class="indx">Extra current, <a href='#Page_3'>3</a>.</li> - - -<li class="ifrst">F</li> - -<li class="indx">Farad, <a href='#Page_100'>100</a>.</li> - -<li class="indx">Fluoroscope, <a href='#Page_239'>239</a>.</li> - -<li class="indx">Fluorescence, <a href='#Page_137'>137</a>.</li> - -<li class="indx">Foucault currents, <a href='#Page_6'>6</a>.</li> - -<li class="indx">Frauenhofer lines, <a href='#Page_135'>135</a>.</li> - -<li class="indx">Frontispiece, Notes on, <a href='#Page_42'>42</a>, <a href='#Page_47'>47</a>.</li> - - -<li class="ifrst">G</li> - -<li class="indx">Galvanometer, <a href='#Page_99'>99</a>.</li> - -<li class="indx">Gas burners, <a href='#Page_170'>170</a>.</li> - -<li class="indx"><span class="pagenum" id="Page_268">268</span><span class="ditto">"</span> engine coil, <a href='#Page_39'>39</a>.</li> - -<li class="indx"><span class="ditto">"</span> from water, <a href='#Page_44'>44</a>.</li> - -<li class="indx"><span class="ditto">"</span> lighting, <a href='#Page_164'>164</a>.</li> - -<li class="indx">Gassiot star, <a href='#Page_153'>153</a>.</li> - -<li class="indx">Geissler tube, <a href='#Page_159'>159</a>.</li> - -<li class="indx">Glass, To pierce, <a href='#Page_130'>130</a>.</li> - -<li class="indx">Gordon battery, <a href='#Page_194'>194</a>.</li> - - -<li class="ifrst">H</li> - -<li class="indx">Harrison cell, <a href='#Page_219'>219</a>.</li> - -<li class="indx">Hertz resonator, <a href='#Page_226'>226</a>.</li> - -<li class="indx">Hydrometer, <a href='#Page_211'>211</a>.</li> - -<li class="indx">Hysteresis, <a href='#Page_6'>6</a>.</li> - - -<li class="ifrst">I</li> - -<li class="indx">Induction, <a href='#Page_1'>1</a>.</li> - -<li class="indx"><span class="ditto">"</span> Self, <a href='#Page_8'>8</a>.</li> - -<li class="indx">Insulations, <a href='#Page_97'>97</a>.</li> - - -<li class="ifrst">L</li> - -<li class="indx">Leyden jars, <a href='#Page_99'>99</a>.</li> - -<li class="indx">Lighting gas, <a href='#Page_164'>164</a>.</li> - - -<li class="ifrst">M</li> - -<li class="indx">Magnetic circuit, Closed, <a href='#Page_6'>6</a>.</li> - -<li class="indx">Medical coils, <a href='#Page_51'>51</a>.</li> - -<li class="indx"><span class="ditto">"</span> <span class="ditto">"</span> Care of, <a href='#Page_62'>62</a>.</li> - -<li class="indx">Mercury contact breaker, <a href='#Page_71'>71</a>.</li> - -<li class="indx">Mica condenser, <a href='#Page_61'>61</a>.</li> - - -<li class="ifrst">N</li> - -<li class="indx">Noise of contact breaker, <a href='#Page_63'>63</a>.</li> - - -<li class="ifrst">O</li> - -<li class="indx">Oil, Capacity of, <a href='#Page_119'>119</a>.</li> - -<li class="indx"><span class="ditto">"</span> Coil immersion, <a href='#Page_33'>33</a>.</li> - -<li class="indx"><span class="ditto">"</span> for oscillator, <a href='#Page_260'>260</a>.</li> - -<li class="indx"><span class="ditto">"</span> Linseed, <a href='#Page_93'>93</a>.</li> - -<li class="indx"><span class="ditto">"</span> Resin, <a href='#Page_96'>96</a>.</li> - -<li class="indx"><span class="ditto">"</span> Spark through, <a href='#Page_95'>95</a>.</li> - -<li class="indx">Oscillator, <a href='#Page_258'>258</a>.</li> - -<li class="indx"><span class="ditto">"</span> Clarkes, <a href='#Page_259'>259</a>.</li> - -<li class="indx"><span class="ditto">"</span> Triple, <a href='#Page_259'>259</a>.</li> - -<li class="indx">Output of coil, <a href='#Page_46'>46</a>.</li> - - -<li class="ifrst">P</li> - -<li class="indx">Paper condenser, <a href='#Page_107'>107</a>.</li> - -<li class="indx">Paraffin, <a href='#Page_94'>94</a>.</li> - -<li class="indx">Phosphorus tube, <a href='#Page_239'>239</a>.</li> - -<li class="indx">Photography, X-Ray, <a href='#Page_245'>245</a>.</li> - -<li class="indx">Pocket coil, <a href='#Page_89'>89</a>.</li> - -<li class="indx">Polarity tests, <a href='#Page_45'>45</a>.</li> - -<li class="indx">Pole, <a href='#Page_190'>190</a>.</li> - -<li class="indx">Polechanging switch, <a href='#Page_32'>32</a>.</li> - -<li class="indx">Polechanging contact breaker, <a href='#Page_73'>73</a>.</li> - -<li class="indx">Primary coil, <a href='#Page_7'>7</a>.</li> - - -<li class="ifrst">Q</li> - -<li class="indx">Queen contact breaker, <a href='#Page_83'>83</a>.</li> - -<li class="indx"><span class="ditto">"</span> Crookes tube, <a href='#Page_241'>241</a>.</li> - - -<li class="ifrst">R</li> - -<li class="indx">Radiography, <a href='#Page_245'>245</a>.</li> - -<li class="indx">Reel ends, <a href='#Page_25'>25</a>.</li> - -<li class="indx">Resistance coils, <a href='#Page_40'>40</a>.</li> - -<li class="indx">Resonance, Electric, <a href='#Page_226'>226</a>.</li> - -<li class="indx">Resonator, Hertz, <a href='#Page_226'>226</a>.</li> - -<li class="indx">Rheotome, <a href='#Page_2'>2</a>.</li> - -<li class="indx">Roentgen Ray apparatus, <a href='#Page_236'>236</a>.</li> - -<li class="indx">Rotating wheel, <a href='#Page_154'>154</a>.</li> - - -<li class="ifrst">S</li> - -<li class="indx">Series, Coils in, <a href='#Page_32'>32</a>.</li> - -<li class="indx">Selection of coil, <a href='#Page_46'>46</a>.</li> - -<li class="indx">Shellac, <a href='#Page_96'>96</a>.</li> - -<li class="indx">Signs, Battery, <a href='#Page_190'>190</a>.</li> - -<li class="indx">Soda, Bichromate of, <a href='#Page_183'>183</a>.</li> - -<li class="indx">Spark, Electric, <a href='#Page_120'>120</a>.</li> - -<li class="indx"><span class="pagenum" id="Page_269">269</span><span class="ditto">"</span> Choice of, <a href='#Page_47'>47</a>.</li> - -<li class="indx">Spectroscope, <a href='#Page_132'>132</a>.</li> - -<li class="indx">Spectrum, Solar, <a href='#Page_132'>132</a>.</li> - -<li class="indx">Standard dry cell, <a href='#Page_196'>196</a>.</li> - -<li class="indx">Sulphating, <a href='#Page_215'>215</a>.</li> - -<li class="indx">Switch, Polechanging, <a href='#Page_32'>32</a>.</li> - - -<li class="ifrst">T</li> - -<li class="indx">Table of cost, <a href='#Page_191'>191</a>.</li> - -<li class="indx">Tesla coil, <a href='#Page_35'>35</a>.</li> - -<li class="indx"><span class="ditto">"</span> <span class="ditto">"</span> disruptive, <a href='#Page_36'>36</a>.</li> - -<li class="indx">Testing polarity, <a href='#Page_46'>46</a>.</li> - -<li class="indx">Transformer, <a href='#Page_5'>5</a>.</li> - -<li class="indx">Tube, Insulating, <a href='#Page_9'>9</a>.</li> - - -<li class="ifrst">U</li> - -<li class="indx">U. S. storage cell, <a href='#Page_218'>218</a>.</li> - - -<li class="ifrst">V</li> - -<li class="indx">Vacuum, Adjusting, <a href='#Page_242'>242</a>.</li> - -<li class="indx"><span class="ditto">"</span> Choice of, <a href='#Page_243'>243</a>.</li> - -<li class="indx"><span class="ditto">"</span> Contact breaker, <a href='#Page_81'>81</a>.</li> - -<li class="indx"><span class="ditto">"</span> To procure, <a href='#Page_141'>141</a>.</li> - -<li class="indx"><span class="ditto">"</span> pumps, <a href='#Page_140'>140</a>.</li> - - -<li class="ifrst">W</li> - -<li class="indx">Water, Decomposition of, <a href='#Page_44'>44</a>.</li> - -<li class="indx">Wax, <a href='#Page_95'>95</a>.</li> - -<li class="indx">Wehnelt interrupter, <a href='#Page_77'>77</a>.</li> - -<li class="indx">Wheel, Rotating, <a href='#Page_154'>154</a>.</li> - -<li class="indx">Winder, Coil, <a href='#Page_16'>16</a>.</li> - -<li class="indx">Winding coils, <a href='#Page_20'>20</a>.</li> - -<li class="indx"><span class="ditto">"</span> Secondary, 10, <a href='#Page_14'>14</a>.</li> - -<li class="indx"><span class="ditto">"</span> Sectional, <a href='#Page_11'>11</a>.</li> - -<li class="indx">Wire for secondary coil, <a href='#Page_24'>24</a>.</li> - -<li class="indx"><span class="ditto">"</span> " primary coil, <a href='#Page_9'>9</a>.</li> - -<li class="indx">Wires, Air, <a href='#Page_262'>262</a>.</li> - -<li class="indx">Wireless telegraphy, <a href='#Page_248'>248</a>.</li> - -<li class="indx">Wireless telegraphy circuit, <a href='#Page_250'>250</a>.</li> - - -<li class="ifrst">X</li> - -<li class="indx">X-Ray apparatus, <a href='#Page_236'>236</a>.</li> - -<li class="indx"><span class="ditto">"</span> Remarks, <a href='#Page_243'>243</a>.</li> - -<li class="indx"><span class="ditto">"</span> photographs, <a href='#Page_246'>246</a>.</li> -</ul></div> - -<hr class="chap" /> - -<p><span class="pagenum" id="Page_270">270</span></p> - - - - -<div class="chapter"> -<h2 id="BIBLIOGRAPHY">BIBLIOGRAPHY</h2> -</div> - -<p class="center"><i>GENERAL REFERENCE</i></p> - -<div class="hang"> - -<p>Electricity, Its Theory, Sources and Applications, -<small>by <span class="smcap">John T. Sprague</span>. 3rd edition.</small></p> - -<p>Induction Coils and Coil Making,<small> by <span class="smcap">F. C. Allsop</span>.</small></p> - -<p>The Construction of Large Induction Coils, -<small>a Workshop Handbook, by <span class="smcap">A. Thare</span>. Illustrated.</small></p> - -<p>A Manual of Electricity,<small> by <span class="smcap">H. M. Noad</span>, Ph.D. -London, 1859. (<i>Scarce.</i>)</small></p> - -<p>Practical Electrics.</p> - -<p>Sloane's Electrical Dictionary.</p> - -<p>Houston's Electrical Dictionary.</p> - -<p>Electricity and Magnetism,<small> by <span class="smcap">Prof. Silvanus P. -Thompson</span>.</small></p> - - -<p class="center"><i>BATTERIES</i></p> - -<p>Small Accumulators and How to Make Them,<small> by -<span class="smcap">P. Marshall</span></small>.</p> - -<p>Primary Batteries, <small>by <span class="smcap">H. S. Carhart</span></small>.</p> - -<p>Practical Electrics.</p> - -<p>Electric Batteries, How to Make Them,<small> by <span class="smcap">P. -Marshall</span>.</small></p> - - -<p class="center"><i>WIRELESS TELEGRAPHY</i></p> - -<p>A History of Wireless Telegraphy, <small>by <span class="smcap">J. J. Fahie</span></small>.</p> - -<p>Improvements in Magnetic Space Telegraphy, -Telegraphing by Magnetic Induction, and -Aetheric Telegraphy, <small>by <span class="smcap">Sir W. H. Preece</span>, -<span class="smcap">S. Evershed</span>, and <span class="smcap">Oliver Lodge</span></small>.</p> - -<p>Science Abstracts, Physics and Electrical Engineering.</p> - -<p>The Model Engineer and Amateur Electrician.</p> -</div> -<hr class="chap" /> -<div class="chapter"></div> - -<div class="narrow"> -<p class="center xxl">Queen Instruments</p> - - -<p><span class="xl u">Induction Coils</span> capable of producing thick, -heavy sparks from 60" to -¼" in length. Made in 15 -different styles for either direct or alternating currents -of any voltage.</p> - -<p><span class="xl u">X Ray Tubes</span> which have an automatic -vacuum regulating device -by means of which rays of -penetrating power can be obtained. Our tubes have -large, clear bulbs with a great current capacity and -sharp definition.</p> - -<p><span class="xl">Fluoroscopes</span> of Platino Barium Cyanide -or Calcium Tungstate with -removable screens. Permanent -and brilliant.</p> - -<p><span class="xl u">Accessories</span>—such as <b>Tube Stands</b>, <b>Independent -Vibrators</b>, <b>Wehnelt -Interrupters</b>, <b>Localization Apparatus</b>, -<b>Protecting Screens</b>, <b>Radiographic Table</b>, <b>X Ray -Plates</b>, <b>Storage Batteries</b>, <b>Motor Transformers</b>, <b>Archives of -the Roentgen Ray</b>—everything to make X Ray Work -simple and successful.</p> - - -<p class="center"><big>Electrical Testing Instruments, Meters, -Photometric Apparatus</big></p> - - -<p class="center"><span class="xl">Queen & Co.</span> (Incorporated)<br /> - -J. G. GRAY, President</p> - -<p> -1010 Chestnut Street<br /> -Philadelphia, Pa.</p> -<p>59 Fifth Avenue<br /> -New York</p> - -<hr class="chap" /> -<div class="chapter"></div> - -<table border="0" cellpadding="4" cellspacing="1" summary=""> -<tr> - <td class="tdba"> - <span class="u"><big>The</big></span><br /> - <span class="xxl"> American <br /> - Inventor. </span></td> - <td class="tdba"> - <small>PUBLISHED AT<br /> - 1302<br /> - F. Street, N. W.<br /> - Washington, D. C.<br /> - The first and fifteenth<br /> - of every<br /> - month.</small></td> -</tr> - -<tr> - <td class= "tdbtrl" colspan="2"> - <div class="small"> - - <p class="center">Is the recognized medium between<br /> - Capital and Industry.</p> - - <p><span class="u">It reaches</span></p> - - <div class="center"> - <table border="0" cellpadding="4" cellspacing="0" summary=""> - <tr> - <td align="left">THE MANUFACTURER,</td> - <td align="left">THE ARCHITECT,</td> - </tr> - <tr> - <td align="left">THE CAPITALIST,</td> - <td align="left">THE CONTRACTOR,</td> - </tr> - <tr> - <td align="left">THE PROMOTOR,</td> - <td align="left">THE INVENTOR,</td> - </tr> - </table></div></div> - </td> -</tr> - -<tr> -<td class="tdbbrl" colspan="2"> - <p class="center small">THE PEOPLE WHO HAVE MONEY TO SPEND.<br /> - THE PEOPLE WHO SPEND IT.</p> - - <p class="hang xs">Subscription price $1.00 a year ($2.00 foreign), and agents - wanted on liberal commission in all sections of the country - and Europe. Send for sample copy. Advertising rates, as - per published card, furnished on application.</p></td> -</tr> -<tr> - <td class="tdba" colspan="2"> - Address<br /> - The American Inventor,<br /> - 1302 F. St., N.W., Washington, D.C., U.S.A.</td> -</tr> -</table> - -<hr class="chap" /> -<div class="chapter"></div> - - -<p class="center">The <span class="smcap xl">Gas-Engine Handbook</span></p> - -<p class="center"><b>By E. W. ROBERTS, M.E.</b></p> - -<p class="center small">has established itself as a standard of reference in</p> - -<p class="center">GAS ENGINERY.</p> -<div class="small"> -<p class="center"><b>2,000 Copies sold in one year.</b></p> - - -<p>The book contains 234 pages of just the kind of -information you have been looking for on gas engines. -It explains their principles of operation their -faults and the remedies which apply, how to run -them, how to design them and how to make a complete -test. All rules and formulas are simple and -easily understood by the average mechanic.</p> - -<p>"All the most essential information connected -with the gas or gasoline engine."—<i>American Machinist.</i></p> - -<p>"The only practical book of its kind."—<i>Engineering -and Mining Journal.</i></p> - -<p>"Eminently practical in character."—<i>American -Electrician.</i></p> - -<p>"Just the kind of information the buyer and the -user of a gas engine wants and finds most difficult to -obtain."—<i>Mines and Minerals.</i></p> - -<p>"It discusses almost every phase of the subject."—<i>The -Engineer.</i></p> - -<p>"All of the essentials of construction and operation -are to be found in it."—<i>The Automobile Review.</i></p> - -<p>The book is published in handy pocket size 3½ × 5½ -inches and is handsomely bound in flexible leather.</p> - -<p class="center"><b>Sent prepaid to any address for $1.50</b></p></div> - - -<p class="center"><big>The Gas Engine Publishing Co</big>.</p> - -<p class="center"><small>ALSO PUBLISHERS OF</small></p> - -<p class="center">THE GAS ENGINE MAGAZINE,</p> - -<p class="center"> -<span class="gap10">330 West Ninth St.,</span> CINCINNATI, O. -</p> - - -<hr class="chap" /> -<div class="chapter"></div> - - -<div class="bbox"> -<p class="center"><span class="xl">No. 1. Harrison Cell</span></p> - -<p class="center">THE MOST POWERFUL OPEN CIRCUIT -CELL MADE.</p> - - -<div class="center"> -<table border="0" cellpadding="4" cellspacing="0" summary=""> -<tr> - <td>E. M. F.</td> - <td rowspan="8"><img src="images/i_274.jpg" alt="The Cell" /></td> -<td>Capacity</td> -</tr> -<tr> - <td>2.5</td> - <td>40</td> -</tr> -<tr> - <td>Volts.</td> - <td>Ampere</td> -</tr> -<tr> - <td></td> - <td>Hours.</td> -</tr> -<tr> - <td></td> - <td></td> -</tr> -<tr> - <td>No</td> - <td>No</td> -</tr> -<tr> - <td>Local</td> - <td>Creeping</td> -</tr> -<tr> - <td>Action.</td> - <td>Salts.</td> -</tr> -</table></div> - -<p>Highly recommended for all kinds of open circuit work -such as telephones, gas engines, bells, auto gas lighting, -and for medical outfits. Guaranteed to do all that is -claimed for it.</p> - - -<p class="center"> -<big>HARRISON BROS. & CO., Incorporated</big>.<br /> -<span class="gap5">PHILADELPHIA.</span> <span class="gap5">CHICAGO.</span> NEW YORK.<br /> -<small>J. H. LEHMAN,<br /> -<span class="gap5">Manager of Electrical Department,</span> 102 Times Building, New York.</small></p> -</div> - -<hr class="chap" /> -<div class="chapter"></div> - - -<p class="center"><span class="u"><big>Mesco Dry Battery</big></span></p> - -<div class="figleft" > -<img src="images/i_275a.jpg" alt="The battery" /> -</div> -<p><big>OVER 1,000,000 -SOLD ANNUALLY</big></p> -<div class="small"> -<p>Can be purchased in all cities -and most towns in the United -States of Electric Supply dealers. -Price low as worthless dry batteries. -We are the largest manufacturers -of general electric supplies -in this country. Catalogue issued -yearly.</p> - -<p>Manhattan Electrical -Supply Co.==========</p> - -<p>32 Cortlandt Street, New York</p></div> -<hr class="full" /> - -<p class="center"><big>TO OUR READERS</big></p> - -<p class="hang"><i>ARE YOU IN THE MARKET FOR</i><br /> -COILS, X-RAY TUBES, BATTERIES, OR -ANY ELECTRICAL APPARATUS?</p> - -<p class="hang"><i>IF SO</i><br /> -Send to our advertisers for their catalogues -and prices before buying.</p> -<hr class="full" /> - - -<div class="center"> -<table border="0" cellpadding="4" cellspacing="0" summary=""> -<tr> - <td align="left">X-Ray Coils</td> -<td align="center" rowspan="4"><img src="images/i_275.jpg" alt="A coil" /></td> -</tr> -<tr> - <td align="left"> Telephone Coils</td> -</tr> -<tr> - <td align="left">Medical Coils</td> -</tr> -<tr> - <td align="left"> Spark Coils</td> -</tr> -</table></div> - -<p class="center"><small>MAGNET WINDING OF EVERY DESCRIPTION</small><br /> - -C. F. SPLITDORF, 17-27 Vandewater St., New York</p> - -<hr class="chap" /> -<p class="center"> -<big>New Standard Oil, Gas and Gasoline<br /> -Engine Outfit</big> <small>Consisting of</small> ... -</p> -<div class="small"> -<div class="center"> -<table border="0" cellpadding="4" cellspacing="0" summary=""> -<tr> - <td align="left">New Standard</td> - <td align="left"> "Autogas" Dry Battery,</td> - <td align="right">$5.00</td> -</tr> -<tr> - <td align="left"> " "</td> - <td align="left">Jump Spark Coil,</td> - <td align="right">12.00</td> -</tr> -<tr> - <td align="left"> " "</td> - <td align="left">Insulated Cam-Contact Key,</td> - <td align="right">3.50</td> -</tr> -<tr> - <td align="left"> " "</td> - <td align="left">Double Porcelain Insulated Ignition Plug,</td> - <td align="right">6.00</td> -</tr> -</table></div> - -<p class="center"><small>If you are interested write for descriptive pamphlet</small>.</p> - -<p class="center">WILLIAM ROCHE, Inventor and Sole Mfr., 42 VESEY ST., NEW YORK CITY</p> - -<p class="center"><small>We also manufacture other good and useful appliances to be operated with dry cells</small>.</p> -</div> -<hr class="full" /> -<p class="center"><span class="xl"><i>GOOD BOOKS</i></span></p> - -<div class="hang"> - -<p><b>The French Polishers Manual</b>, <small>full directions for polishing -by a French Polisher. 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Halliday. 79 pages, illustrated, -8vo, cloth,</td> - -<td class="tdrb">1.00‡</td> -</tr> - -<tr> - <td class="tdh"><b>Electric Bells.</b>—A treatise on the construction -of electric bells, indicators and similar apparatus. -By F. C. Allsop. 131 pages, 177 -illustrations, 12mo, cloth,</td> - -<td class="tdrb">1.25</td> -</tr> - -<tr> - <td class="tdh"><b>Electric Bells.</b>—Practical electric bell fitting. -A treatise on the fitting up and maintenance -of electric bells and all their necessary apparatus. -By F. C. Allsop. 170 pages, -186 illustrations, 12mo, cloth,</td> - -<td class="tdrb">1.25</td> -</tr> - -<tr> - <td class="tdh"><b>Electrical Notes.</b>—Practical electrical notes -and definitions, for the use of engineering -students and practical men. By W. Perren -Maycock, E.E. 286 pages, illustrated, -32mo, cloth,</td> - -<td class="tdrb">.75</td> -</tr> - -<tr> - <td class="tdh"><b>Electricity.</b>—Comparisons between the different -systems of distributing electricity. By -Prof. Henry Robinson. 8vo, paper,</td> - -<td class="tdrb">.80</td> -</tr> - -<tr> - <td class="tdh"><b>Galvanometer.</b>—A series of lectures on the -galvanometer and its uses, delivered by -Prof. E. L. Nicols, and used by him in his -class at Cornell University. 112 pages, 76 -illustrations, 8vo, paper,</td> - -<td class="tdrb">1.00</td> -</tr> - -<tr> - <td class="tdh"><b>Induction Coils</b>, and coil making. A treatise -on the construction and working of shock, -medical, and spark coils. By F. C. Allsop. -172 Pages, 124 illustrations, 12mo, cloth,</td> - -<td class="tdrb">1.25</td> -</tr> - -<tr> - <td class="tdh"><b>Measurements.</b>—A systematic treatise on electrical -measurements. By H. C. Parker. -120 pages, 96 illustrations, 8vo, cloth,</td> - -<td class="tdrb">1.00‡</td> -</tr> - -<tr> - <td class="tdh"><b>Phonograph.</b>—The phonograph and how to -construct it, and a chapter on sound, with -full set of working drawings. 12mo, cloth,</td> - -<td class="tdrb">2.00</td> -</tr> - -<tr> - <td class="tdh"><b>Transformer.</b>—History of the transformer, -translated from the German. By F. Uppenborn. -60 pages, 31 illustrations, 12mo,</td> - -<td class="tdrb">.75</td> -</tr> - -<tr> - <td class="tdh"><b>Transformer.</b>—Transformer design, a treatise -on their design, construction and use. By -G. Adams. In the work the author has -avoided as much as possible all historical -matter and unnecessary mathematical problems, -and has confined himself to practical -experience. The work contains much information -that will prove of value to the -draughtsman, designer and electrical student. -Second edition. 75 pages, 34 illustrations, -12mo, cloth,</td> - -<td class="tdrb">1.50‡</td> -</tr> - -<tr> - <td class="tdh"><b>Telephones, etc.</b>—Their construction and fitting. -A practical treatise on the fitting-up -and maintenance of telephones and the -auxiliary apparatus. By F. C. Allsop. 5th -edition, 184 pages, 13 folding plates and 124 -illustrations, 12mo, cloth,</td> - -<td class="tdrb">1.25</td> -</tr> - -<tr> - <td class="tdh"><b>Magnets</b> and electric currents. An elementary -treatise for the use of electricians and beginners. -By J. A. Fleming, M.A., D.Sc., -F.R.S., 408 pages, illustrated, 12mo, cloth,</td> - -<td class="tdrb">3.00</td> -</tr> -</table></div> -<hr class="chap" /> -<div class="chapter"></div> - - -<p class="center"><span class="xxl">Workshop Receipts.</span></p> - -<p class="center"><small>THE MOST COMPLETE</small></p> - -<p class="center"><big>Technical Cyclopedia in 5 Vols.</big></p> -<hr class="small" /> -<div class="small"> -<p><b><big>First Series.</big> Principal Contents.</b>—Bronzes, Cements, -Dyeing, Electro-metallurgy, -Enamels, Etchings, Fireworks, Fluxes, Fulminates, Gilding, -Gums, Japanning, Lacquers, Marble Working, Nitro-Glycerine, -Photography, Pottery, Varnishes. 420 pages, 103 illus., -cloth, $2.00.</p> - -<p><b><big>Second Series.</big> Principal Contents.</b>—Acidimetry, -Albumen, Alcohol, Alkaloids, -Bitters, Bleaching, Boiler Incrustations, Cleansing, -Confectionery, Copying, Disinfectants, Essences, Extracts, -Fire-proofing, Glycerine, Gut, Iodine, Ivory Substitutes, -Leather, Matches, Pigments, Paint, Paper, Parchment. 485 -pages, 16 illus., cloth, $2.00.</p> - -<p><b><big>Third Series.</big> Principal Contents.</b>—Alloys, Aluminium, -Antimony, Copper, Electrics, -Enamels, Glass, Gold, Iron, Steel, Liquors, Lead, Lubricants, -Magnesium, Manganese, Mercury, Mica, Nickel, -Platinum, Silver, Slag, Tin, Uranium, Zinc. 480 pages, 183 -illus., cloth, $2.00.</p> - -<p><b><big>Fourth Series.</big> Principal Contents.</b>—Water-proofing, -Packing, Stowing, -Embalming, Preserving, Leather Polishes, Cooling Air and -Water, Pumps and Siphons, Dessicating, Distilling, Emulsifying, -Evaporating, Filtering, Percolating, Macerating, -Electrotyping, Stereotyping, Book-binding, Straw-plaiting, -Musical Instruments, Clock and Watch Mending, Photography. -443 pages, 243 illus., cloth, $2.00.</p> - -<p><b><big>Fifth Series.</big> Principal Contents.</b>—Diamond Cutting, -Laboratory Apparatus, Filtering, -Magic Lanterns, Metal Work, Percolation, Illuminating -Agents, Tobacco Pipes, Taps, Tying and Splicing Tackle, -Repairing Books, Netting, Walking Sticks, Boat-Building. -440 pages, 373 illus., cloth, $2.00.</p> -</div> - -<p class="center"><b>EACH SERIES has its own Contents -and Index and is complete in itself.</b></p> - -<hr class="chap" /> -<div class="chapter"></div> - - -<p class="center xl">Cleaning and Scouring</p> - -<p class="center"><small>A MANUAL FOR</small></p> - -<p class="center"><big>DYERS AND LAUNDRESSES</big></p> - -<p class="center"><small>And for Domestic Use.</small></p> - -<p class="center"><i>BY S. CHRISTOPHER.</i></p> -<hr class="small" /> - -<p class="center">CONTENTS.</p> - -<div class="hang small"> - -<p><span class="smcap">Dresses.</span>—Silk, Satin, Irish Poplin and Tabinet, Llama, Alpaca, -Printed Muslin and Pique, Pique and Colored Muslin.</p> - -<p><span class="smcap">Shawls and Scarves.</span>—China Crape, Brocaded or Printed -Silk, and Woolen.</p> - -<p><span class="smcap">Silk Handkerchiefs, Ribbons, Mantles, Fancy Waistcoats, -and Lace. Gloves.</span>—Kid, Washleather.</p> - -<p><span class="smcap">Feathers.</span>—White, Colored; to purify—for Beds, &c.</p> - -<p><span class="smcap">Bonnets.</span>—Chip, Straw, and Leghorn. <span class="smcap">Ancient Tapestry.</span></p> - -<p><span class="smcap">Curtains, Bed Furniture, &c.</span>—Chintz, Damask, Worsted-and-cotton -Damask, French Damask—Silk-and-worsted -Moreen, Tabaret or Tabbarea, Satin, Tammy Lining, -Fringes—Bullion and worsted, Lace and Gimp—Bullion.</p> - -<p><span class="smcap">Table Covers.</span>—Silk-and-worsted, Cotton-and-worsted, and -Printed Cloth.</p> - -<p><span class="smcap">Carpets.</span>—Dry Cleaning, thorough Cleaning.</p> - -<p><span class="smcap">Hearthrugs, Sheepskin Rugs and Mats.</span></p> - -<p><span class="smcap">To Remove Various Stains from Linen and Cotton.</span>—Fruit -Stains, Grease Spots, Ink Stains, Marking Ink, Mildew, -Paint or Varnish, Wine Stains.</p> - -<p><span class="smcap">Recipes for general Domestic Use.</span>—Oilcloth, Paint, -Floors, Marble, Iron and Steel, Brass or Copper, Silver -Plate, Furniture, Gilt Frames, Ivory Ornaments, Mirrors, -Wall-paper, Stone Steps.</p> - -<p><span class="smcap">Definitions, &c.</span>—Boards, &c., for French Cleaning, Camphine, -Common Sour, Drying, Frame, French Board, Hot -Stove, Irons, Parchment Size, Pegs, Puncher, Size, Soap, -Starch, To Handle, To Sheet-up, Water.</p> - -<p class="center"><b>Price 20 cents, post-paid.</b></p></div> -<hr class="chap" /> -<div class="chapter"></div> - - -<p class="center xs"><small>THEORETICAL AND PRACTICAL</small></p> - -<p class="center xl">Ammonia Refrigeration</p> - -<p class="center"><i>A Work of Reference for Engineers and others Employed in the -Management of Ice and Refrigeration Machinery.</i></p> - -<p class="center">By ILTYD I. REDWOOD</p> - -<div class="small"> -<p class="center">CONTENTS</p> - -<p>B. T. U. Mechanical Equivalent of a Unit of Heat. -Specific Heat. Latent Heat. Theory of Refrigeration. -Freezing, by Compressed Air. Ammonia. Characteristics -of Ammonia. The Compressor. Stuffing-Boxes. -Lubrication. Suction and Discharge Valves. -Separator. Condenser-Worm, Receiver. Refrigerator -or Brine Tank. Size of Pipe and Area of Cooling -Surface. Charging the Plant with Ammonia. Jacket-Water, -for Compressor, for Separator. Quantity of -Condensing Water Necessary. Loss due to Heating -of Condensed Ammonia. Cause of Variation in Excess -Pressure. Use of Condensing Pressure in Determining -Loss of Ammonia by Leakage. Cooling Directly -by Ammonia. Freezing Point of Brine. Making -Brine. Specific Heat of Brine. Regulation of -Brine Temperature. Indirect Effect of Condensing -Water on Brine Temperature. Directions for Determining -Refrigerating Efficiency. Equivalent of a Ton -of Ice. Compressor Measurement of Ammonia Circulated. -Loss of Well-Jacketed Compressors. Loss in -Double-Acting Compressors. Distribution of Mercury -Wells. Examination of Working Parts. Indicator -Diagrams. Ammonia Figures—Effectual Displacement. -Volume of Gas. Ammonia Circulated per -Twenty-Four Hours. Refrigerating Efficiency. Brine -Figures-Gallons Circulated. Pounds Circulated. Degrees -Cooled. Total Degrees Extracted. Loss due to -Heating of Ammonia Gas. Loss due to Heating of -Liquid Ammonia. Calculation of the Maximum Capacity -of a Machine. Preparation of Anhydrous Ammonia. -Construction of Apparatus, etc., etc.</p> - - -<p class="center"><b>150 pages, 15 illustrations, cloth, $1.00.</b></p> -</div> -<hr class="chap" /> -<div class="chapter"></div> - -<p class="center xxl">LUBRICANTS,</p> - -<p class="center xl">OILS AND GREASES</p> - -<p class="center xs">Treated Theoretically and Giving Practical Information -Regarding Their</p> - -<p class="center"><big>COMPOSITION, USES AND MANUFACTURE</big></p> - -<p class="center">BY ILTYD I. REDWOOD</p> -<hr class="small" /> - -<p class="center">CONTENTS</p> - -<div class="hang small"> - -<p><span class="smcap">Introduction.</span>—Lubricants.</p> - -<p><span class="smcap">Theoretical.</span>—Chapter I. Mineral Oils: American -and Russian; Hydrocarbons. Chapter II. Fatty -Oils: Glycerides; Vegetable Oils; Fish Oils. -Chapter III. Mineral Lubricants: Graphite; -Plumbago. Chapter IV. Greases: Compounded; -"Set" or Axle; "Boiled" or Cup. Chapter V. -Tests of Oils: Mineral Oils. Fatty Oils.</p> - -<p><span class="smcap">Manufacture.</span>—Chapter VI. Mineral Oil Lubricants: -Compounded Oils; Debloomed Oils. -Chapter VII. Greases: Compounded Greases; -"Set" or Axle Greases; Boiled Greases; Engine -Greases. Appendix. The Action of Oils on -Various Metals. Index.</p> - -<p><span class="smcap">Tables.</span>—I. Viscosity and Specific Gravity. II. -Atomic Weights. III. Origin, Tests, Etc., of -Oils. IV. Action of Oils on Metals.</p> - -<p><span class="smcap">List of Plates.</span>—I.—I. I. Redwood's Improved -Set Measuring Apparatus. II. Section Grease -Kettle. III. Diagram of the Action of Oils on -Different Kinds of Metals.</p> -</div> - -<p class="center"><small><b>8vo, cloth, $1.50.</b></small></p> - -<hr class="chap" /> -<div class="chapter"></div> - -<p class="center">PRACTICAL HANDBOOK ON</p> - -<p class="center xxl">Gas Engines</p> - -<p class="center">With Instructions for Care and Working of the Same.<br /> - -<i>BY G. LIECKFELD, C.E.</i><br /> - -<small>Translated with permission of the Author by<br /> -<i>GEORGE RICHMOND, M.E.</i></small><br /> - -WITH A CHAPTER ON OIL ENGINES</p> - -<hr class="small" /> -<p class="center">CONTENTS</p> -<div class="small"> -<p>Choosing and installing a gas engine. The construction -of good gas engines. Examination as to -workmanship, running, economy. Reliability and -durability of gas engines. Proper erection of a -gas engine. Foundation. Arrangement for gas pipes. -Rubber bag. Locking devices. Exhaust pipes. Air -pipes. Setting up gas engines. Brakes and their -use in ascertaining the power of gas engines. Arrangement -of a brake test. Distribution of heat in a -gas engine. Attendance on gas engines. General -remarks. Gas engine oil. Cylinder lubricators. -Rules as to starting and stopping a gas engine. The -cleaning of a gas engine. General observations and -specific examination for defects. The engine refuses -to work. Non-starting of the engine. Too much -pressure on the gas. Water in the exhaust pot. -Difficulty in starting the engine. Irregular running. -Loss of power. Weak gas mixtures. Late ignition. -Cracks in air inlet. Back firing. Knocking and -pounding inside of engine. Dangers and precautionary -measure in handling gas engines. Precautions -when opening gas valves, removing piston from -cylinder, examining with light openings of gas -engines. Dangers in starting, cleaning, putting on -belts. <b>Oil Engines.</b> Gas engines with producer gas. -Gasoline and oil engines. Concluding remarks.</p> - - -<p class="center"><b>120 pages, illustrated, 12mo, cloth, $1.00.</b></p> -</div> -<hr class="chap" /> -<div class="chapter"></div> - - -<p class="center"><big>The Best and Cheapest in the Market</big></p> -<hr class="small" /> -<p class="center xxl">ALGEBRA SELF-TAUGHT</p> - -<p class="center"><small>FOR THE USE OF</small><br /> - -Mechanics, Young Engineers and Home Students</p> -<hr class="small" /> -<p class="center"><i>BY W. PAGET HIGGS, M.A., D.Sc.</i></p> -<hr class="small" /> -<p class="center">FOURTH EDITION</p> -<hr class="small" /> - -<p class="center">CONTENTS</p> -<div class="small"> -<p>Symbols and the signs of operation. The equation -and the unknown quantity. Positive and negative -quantities. Multiplication, involution, exponents, -negative exponents, roots, and the use of exponents -as logarithms. Logarithms. Tables of logarithms -and proportional parts. Transportation of systems -of logarithms. Common uses of common logarithms. -Compound multiplication and the binomial theorem. -Division, fractions and ratio. Rules for division. -Rules for fractions. Continued proportion, the series -and the summation of the series. Examples. Geometrical -means. Limit of series. Equations. Appendix. -Index. 104 pages, 12mo, cloth, 60c.</p> -<hr class="small" /> - -<p><i>See also</i> <b>Algebraic Signs</b>, Spons' Dictionary of -Engineering, No. 2. 40 cts.</p> - -<p><i>See also</i> <b>Calculus</b>, Supplement to Spons' Dictionary, -No. 5. 75 cts.</p> -</div> -<hr class="chap" /> -<div class="chapter"></div> - - -<p class="center">THE</p> - -<p class="center xxl">FIREMAN'S GUIDE</p> - -<p class="center">A Handbook on the Care of Boilers</p> - -<p class="center"><i>BY KARL P. DAHLSTROM, M.E.</i></p> - -<hr class="small" /> -<p class="center">CONTENTS OF CHAPTERS</p> -<div class="small"> -<p><b>I. Firing and Economy of Fuel.</b>—Precautions -before and after starting the fire, care of the fire, -proper firing, draft, smoke, progress of firing, fuel on -the grate, cleaning out, cleaning grate bars and ash -pan, dampers, firing into two or more furnaces, dry -fuel, loss of heat.</p> - -<p><b>II. Feed and Water Line.</b>—Feeding, the water -line, false water line, defective feeding apparatus, -formation of scale, gauge cocks, glass gauge, the -float, safety plug, alarm whistle.</p> - -<p><b>III. Low Water and Foaming or Priming.</b>—Precautions -when water is low, foaming, priming.</p> - -<p><b>IV. Steam Pressure.</b>—Steam gauge, safety valves.</p> - -<p><b>V. Cleaning and Blowing Out.</b>—Cleaning the -boiler, to examine the state of the boiler, blowing -out, refilling the boiler.</p> - -<p><b>VI. General Directions.</b>—How to prevent accidents, -repairs, the care of the boiler when not in use, -testing boilers, trimming and cleaning outside. -Summary of rules. Index.</p> - - -<p class="center">8vo, cloth, 50 cents.</p> -</div> - -<hr class="chap" /> -<div class="chapter"></div> - -<p class="center xl">THE CORLISS ENGINE.</p> - -<p class="center"><span class="smcap"><small>By John T. Henthorn.</small></span></p> - -<p class="center">AND</p> - -<p class="center"><big>MANAGEMENT OF THE CORLISS ENGINE.</big></p> - -<p class="center"><span class="smcap"><small>By Charles D. Thurber.</small></span></p> - -<p class="center"><i><small>Uniform in One Volume. Cloth Cover; Price, $1.00.</small></i></p> - -<hr class="small" /> -<p class="center">Table of Contents.</p> -<div class="small"> -<p><span class="smcap">Chapter I.</span>—Introductory and Historical; Steam Jacketing. -<span class="smcap">Chapter II.</span>—Indicator Cards. <span class="smcap">Chapter III.</span>—Indicator -Cards continued; the Governor. <span class="smcap">Chapter IV.</span>—Valve -Gear and Eccentric; Valve Setting. <span class="smcap">Chapter V.</span>—Valve -Setting continued, with diagrams of same; Table -for laps of Steam Valve. <span class="smcap">Chapter VI.</span>—Valve Setting -continued. <span class="smcap">Chapter VII.</span>—Lubrication with diagrams -for same. <span class="smcap">Chapter VIII.</span>—Discussion of the Air Pump -and its Management. <span class="smcap">Chapter IX.</span>—Care of Main Driving -Gears; best Lubricator for same. <span class="smcap">Chapter X.</span>—Heating -of Mills by Exhaust Steam. <span class="smcap">Chapter XI.</span>—Engine -Foundations; diagrams and templets for same. <span class="smcap">Chapter -XII.</span>—Foundations continued; Materials for same, etc.</p> - -<hr class="small" /> -<p class="center">Third Edition, with an Appendix.</p> -</div> - -<hr class="chap" /> -<div class="chapter"></div> - - -<p class="center">HOW TO RUN</p> - -<p class="center xxl">Engines and Boilers</p> - -<p class="center"><small>Practical Instruction for Young Engineers and -Steam Users.</small></p> - -<p class="center"><i>BY EGBERT POMEROY WATSON</i></p> -<hr class="small" /> -<p class="center">REVISED AND ENLARGED</p> -<hr class="small" /> -<div class="small"> -<p class="center"><b>Synopsis of Contents</b></p> - -<p>Cleaning the boiler, removing scale, scale preventers, -oil in boilers, braces and stays, mud drums -and feed pipes, boiler fittings, grate bars and tubes, -bridge walls, the slide valve, throttling engine, the -piston, testing the slide valve with relation to the -ports, defects of the slide valve, lap and lead, the -pressure on a slide valve, stem connections to the -valve, valves off their seats, valve stem guides, governors, -running with the sun, eccentrics and connections, -the crank pin, brass boxes, bearings on pins, -adjustment of bearings, the valve and gearing, setting -eccentrics, the actual operation, return crank -motion, pounding, the connections, lining up engines, -making joints, condensing engines, Torricelli's -vacuum, proof of atmospheric pressure, pumps, no -power in a vacuum, supporting a water column by -the atmosphere, starting a new plant, the highest -qualities demanded.</p> - -<p>Water tube boilers, fire tube boilers, why water -tube boilers steam rapidly, torpedo boat boilers, -management of water tube boilers, economy and -maintenance of water tube boilers.</p> - -<p class="center"><b>150 pages, illustrated, 16mo, cloth, $1.00</b></p> -</div> - -<hr class="chap" /> -<div class="chapter"></div> - -<p class="center"><span class="u">GOOD AMERICAN PRACTICE.</span></p> - -<p class="center">AN</p> - -<p class="center">ELEMENTARY TEXT BOOK</p> - -<p class="center">ON</p> - -<p class="center"> -<span class="xxl">S</span><span class="u xl">TEAM</span> <span class="xl">E</span><span class="u"><big>NGINES</big> AND</span><br /> -<span class="xl">B</span><span class="u"><big>OILERS</big></span><br /> -</p> - -<p class="center">By J. H. KINEALY, M.E.</p> -<div class="small"> -<p>A first class <b>American</b> Book for young Engineers -and all those wishing to take a higher position.</p> - - -<p class="center">CONTENTS OF CHAPTERS.</p> - -<p>1. Elementary Thermodynamics. 2. Theory of the -Steam Engine. 3, Types and details of Engines. 4. -Admission of Steam by Valve. 5. Valve diagrams. -6. Indicator and indicator cards. 7. Compound Engines -and condensers. 8. Heat and combustion of -fuel. 9. Boilers, types, fittings, etc. 10. Chimneys. -<span class="smcap">Appendix.</span> Care of Boilers, Tables, Numerous Problems -with answers.</p> - -<p><b>Third</b> edition, (1901), thoroughly revised to date -and considerably enlarged.</p> - - -<p class="center">259 pages, 108 illustrations, size 9¼ × 6¼.<br /> - -Cloth, $2.00‡</p> -</div> - -<hr class="chap" /> -<div class="chapter"></div> - - -<p class="center"><span class="xl">THE SLIDE VALVE</span><br /> - -<big>SIMPLY EXPLAINED</big><br /> - -<span class="smcap">By</span> W. J. TENNANT, Asso. M.I.M.E.</p> - -<p class="center"><small>REVISED AND MUCH ENLARGED</small><br /> - -<span class="smcap">By</span> J. H. KINEALY, D.E.</p> -<hr class="small" /> - - -<div class="center small"> -<table border="0" cellpadding="4" cellspacing="0" summary=""> -<tr><th colspan="2">CONTENTS OF CHAPTERS:</th></tr> -<tr> - <td class="tdrt">I.</td> - <td class="hang">The Simple Slide.</td> -</tr> - -<tr> - <td class="tdrt">II.</td> - <td class="hang">The Eccentric a Crank. Special Model to<br /> -Give Quantitative Results.</td> -</tr> -<tr> - <td class="tdrt">III.</td> - <td class="hang">Advance of the Eccentric.</td> -</tr> -<tr> - <td class="tdrt">IV.</td> - <td class="hang">Dead Centre. Order of Cranks. Cushioning</td> -</tr> - -<tr> - <td class="tdrt">V.</td> - <td class="hang">Expansion—Inside and Outside Lap and -Lead; Advance Affected Thereby. Compression.</td> -</tr> -<tr> - <td class="tdrt">VI.</td> - <td class="hang">Double-Ported and Piston Valves.</td> -</tr> -<tr> - <td class="tdrt">VII.</td> - <td class="hang">The Effect of Alterations to Valve and -Eccentric.</td> -</tr> -<tr> - <td class="tdrt">VIII.</td> - <td class="hang">Note on Link Motions.</td> -</tr> -<tr> - <td class="tdrt">IX.</td> - <td class="hang">Note on Very Early Cut-Off, and on Reversing -Gears in General.</td> -</tr> -</table></div> - -<p class="center"> -<small><i>88 Pages.</i> <i>41 Illustrations.</i> <i>12mo, Cloth, $1.00.</i></small> -</p> -<hr class="full" /> - -<p class="center">QUICK AND EASY METHODS</p> - -<p class="center"><small>OF</small></p> - -<p class="center"><span class="xl smcap">Calculating<br /> - -With the Slide Rule</span></p> - -<p class="center"><small><span class="smcap">A Simple Explanation of the Theory and -Use of the Slide Rule, Logarithms, Etc.</span></small></p> - -<p class="center"><small><i>With numerous examples worked out.</i></small></p> - -<p class="center"><span class="smcap">By</span> R. G. BLAINE, M.E.</p> -<hr class="small" /> -<p class="center"><small>A most reliable, practical and valuable work for the engineer.</small></p> -<hr class="small" /> -<p class="center"> -<small><i>144 Pages.</i> <i>Illustrated.</i> <i>12mo, Cloth, $1.00</i></small> -</p> -<hr class="chap" /> -<div class="chapter"></div> - - -<p class="center"><i>The Design and Construction</i><br /> - -<small>OF</small><br /> - -<span class="xl">OIL ENGINES</span></p> - -<p class="center"><small><i>With full directions for</i></small></p> - -<p class="center"><b>Erecting, Testing, Installing, Running and -Repairing.</b></p> - -<p class="center xs">Including descriptions of American and English<br /> - -<big>KEROSENE OIL ENGINES</big>.</p> -<hr class="small" /> -<p class="center"><b>By A. H. GOLDINGHAM, M.E.</b></p> -<hr class="small" /> - -<p class="center"><i>Synopsis of Contents of Chapters</i>:</p> -<div class="small"> -<p>1. Introductory, Classification, Vaporizers, Spraying -and Ignition Devices, etc. 2. Design and -Construction, Cylinders, Cranks, Shafts, Pistons, -Connecting Rods, Fly-Wheels, Air and Exhaust -Cams, Valves, etc., Bearings, Engine Frames, Valve -Mechanisms, Gearing, Oil Supply, Different Kinds of -Engines, etc. 3. Testing the Engine, Faults and -Remedies, etc. 4. Cooling Water Tanks, Exhaust -Silencers, Starters. 5. Oil Engine Driving Dynamo, -Various Systems. 6. Oil Engine Driving Air Compressors. -Water Pump, etc. 7. Full Instructions for -Running Oil Engines. 8. Hints on Repairing. 9. -Description of the Various English and American -Oil Engines.</p> - - -<p class="center"><b>Fully Illustrated, 12mo. Cloth, $2.00‡</b></p> -</div> -<hr class="chap" /> -<div class="chapter"></div> - - -<p class="center"><span class="xxl"> -S</span><span class="u xl gap5">PONS'</span><span class="xxl">$2.</span><span class="xl u">50</span></p> - -<p class="center xl">MECHANIC'S OWN BOOK,</p> - -<p class="center"><big>A PRACTICAL MANUAL</big>.</p> - - -<p class="center"><span class="smcap">Principal Contents.</span></p> - -<div class="hang small"> - -<p>Mechanical Drawing. (13 pages).</p> - -<p>Casting and Founding. (31 pages).</p> - -<p>Forging and Finishing. (56 pages).</p> - -<p>Soldering. (26 pages).</p> - -<p>Sheet-Metal Working. (10 pages).</p> - -<p>Carpentry, Woods, Tools etc. (224 pages).</p> - -<p>Cabinet Making. (36 pages).</p> - -<p>Carving and Fretwork. (13 pages).</p> - -<p>Upholstery. (6 pages).</p> - -<p>Painting, Graining and Marbling. (28 pages).</p> - -<p>Staining, and Gilding. (16 pages).</p> - -<p>Polishing. Varnishing. (26 pages).</p> - -<p>Mechanical Movements. (56 pages).</p> - -<p>Turning and Lathe work. (30 pages).</p> - -<p>Masonry, Stonework, Brickwork, Concrete, etc. (45 -pages).</p> - -<p>Plastering, Whitewashing, Paperhanging. (13 pages).</p> - -<p>Roofing, Glazing. (14 pages).</p> - -<p>Bell hanging, Gas fitting. (8 pages).</p> - -<p>Lighting, Ventilation, Warming. (21 pages).</p> - -<p>Foundations, Roads and Bridges, Banks, Hedges, -Ditches and Drains, Water Supply and Sanitation. -House Construction, etc. Size of book 6¾ in. by 8¾.</p></div> - - -<p class="center"><small><b>702 pages, half extra gilt and 1420 illustrations.</b></small></p> -<hr class="chap" /> -<div class="chapter"></div> - - -<p class="center">NEW<br /> - -<span class="xl">EDITION "DE LUXE"</span><br /> - -<small>ON HEAVY PLATE PAPER</small></p> - -<div class="figcenter"> -<img src="images/i_294.jpg" alt="" /> -</div> - -<p class="center small">A SYSTEM OF<br /> - -EASY LETTERING.<br /> -BY<br /> -J. H. CROMWELL.</p> - - - -<p class="center"><b>ITS GOOD POINTS.</b></p> -<div class="small"> -<p>Very easy to learn.</p> - -<p>A rapid method to become a good letterer with a -little practice.</p> - -<p>Very easy to lay out a line of words in <span class="smcap">Strict -Proportion</span>, whether it be on a fence 500 yards long -or on a drawing only a few inches across.</p> - -<p>Good for draughtsmen who prefer neat lettering, -yet something out of the ordinary.</p> - -<p>It contains 26 pages of alphabets whose modifications -are almost limitless.</p> - -<p>One of the cheapest in the market.</p></div> - -<p class="xs">This little book will be appreciated by draughtsmen who wish to -use plain letters (and yet somewhat different from the ordinary run of -letters) for the titles on drawings. The book will also be valuable -and useful to any one who has had no practice in lettering, as the -easy method given for forming the letters will enable a person to -form the letters correctly, and with a little practice to do so quickly.—<i>American -Machinist.</i></p> - - -<p class="center"><small><b>Oblong, 8vo, cloth, 50 cents</b></small></p> - -<hr class="chap" /> -<div class="chapter"></div> - -<p class="center"><big>EVERYONE'S GUIDE</big><br /> -TO<br /> - -<span class="xl">PHOTOGRAPHY</span></p> -<p class="center">CONTAINING<br /> - -<span class="xs">INSTRUCTIONS FOR MAKING YOUR OWN APPLIANCES AND<br /> -SIMPLE PRACTICAL DIRECTIONS FOR EVERY BRANCH<br /> -OF PHOTOGRAPHIC WORK.</span></p> - -<p class="center"><small>BY</small><br /> -E. J. WALL, F.R.P.S.<br /> -<span class="xs">Author of <i>The Dictionary of Photography</i>, etc., etc.</span></p> - -<p class="center"><small>SECOND EDITION</small></p> - -<div class="figcenter"> -<img src="images/colophon.jpg" alt="Colophon" /> -</div> - -<p class="center"><span class="smcap"><small>New York</small></span>:<br /> -SPON & CHAMBERLAIN,<br /> -<span class="smcap"><small>12 Cortlandt Street</small></span>.<br /> -<br /> -<small>1892</small><br /> -</p> - -<hr class="chap" /> -<div class="chapter"></div> - -<p class="center xl">CROSS SECTION PAPER.</p> -<hr class="small" /> - -<p class="center">THE HANDY SKETCHING PAD.</p> - -<p><small>Printed on one side, in blue ink, all the lines being -of equal thickness, with useful tables. Size 8 × 10 -inches. Price, 25c. each. Per dozen pads, $2.50.</small></p> - -<p class="center">THE HANDY SKETCHING BOOK.</p> - -<p><small>Made from this paper but printed on both sides. -Size of book 5 × 8 inches, stiff board covers. Price, -25c. each; per dozen books, $2.50.</small></p> -<hr class="small" /> - -<p class="center">SCALE EIGHT TO ONE INCH.</p> - -<p><small>A large sheet with heavy inch lines and half inch -lines, printed in blue ink. Size of sheet, 17 × 22 inches. -Per quire (24 sheets), 75c.</small></p> -<hr class="small" /> - -<p class="center">SCALE TEN TO ONE INCH.</p> - -<p><small>Size 17 x 22 inches, printed in blue ink, with heavy -inch lines and half inch lines. Per quire (24 sheets), 75c.</small></p> - -<p class="center">THE ELECTRICIAN'S SKETCHING PAD.</p> - -<p><small>Size 8 × 10. Scale 10 to 1 in. Price 25c. each. Per -dozen, $2.50.</small></p> - -<p class="center">THE ELECTRICIAN'S SKETCHING BOOK.</p> - -<p><small>Made from this paper. Scale 10 to 1 inch. Size of -book 5 × 8 inches, with stiff board covers. Price, 25c. -each; per dozen, $2.50.</small></p> - - -<p class="center"><small>Any quantity mailed to any part of the world on receipt -of price.<br /> - -Or Books and Pads Assorted, per dozen, $2.50</small></p> - -<p class="center"><small>This paper is <i>not ruled</i>. Try it and you will find it<br /> -GOOD, ACCURATE AND CHEAP.</small></p> - -<p class="center"> -<big>SPON & CHAMBERLAIN,</big> <small>12 Cortlandt St</small>.,<br /> -NEW YORK.<br /> -</p> - -<hr class="chap" /> -<div class="chapter"></div> - -<p class="center"><big><b>Manual of Instruction in</b></big></p> - -<p class="center"><span class="xxl"><b>Hard Soldering</b></span></p> - -<p class="center"><small>WITH AN APPENDIX ON THE</small><br /> - -<big><b>Repair of Bicycle Frames</b></big></p> - -<p class="center"><b>Notes on Alloys and a Chapter on Soft Soldering</b></p> - -<p class="center"><i>BY HARVEY ROWELL</i></p> - -<div class="small"> -<p>The flame, lamp, charcoal, mats, blow-pipes, -wash-bottle, binding wire, chemicals, borax, spelter, -silver solder, gold solder, oxidation of metals, fluxes, -anti-oxidisers, oxidation of cases, the cone, oxidising -flame, reducing flame, heat transmission, conduction, -capacity of metals, radiation, application, the work -table, the joint, applying solder, applying heat, the -use of the blow-pipe, joints, making a ferrule, to repair -a spoon, to repair a watch case, hard soldering -with a forge or hearth, hard soldering with tongs, -preserving thin edges, silversmith's pickle, restoring -color to gold, chromic acid, to mend steel springs, -sweating metals together, retaining work in position, -making joints, applying heat, preventing the loss of -heat, effect of sulphur lead and zinc, to preserve -precious stones, annealing and hardening, burnt iron, -to hard solder after soft solder. Tables of—specific -gravity, tenacity, fusibility, alloys.</p> - - -<p class="center"><b>66 pages, illustrated, cloth, 75 cents.</b></p></div> - -<hr class="small" /> - -<p class="xs">For Soldering Receipts, Cements and Lutes, Pastes, Glues -and such like, <i>see</i> <span class="smcap">Workshop Receipts</span>.</p> - -<hr class="chap" /> -<div class="chapter"></div> - - -<p class="center xl">SMALL ACCUMULATORS</p> -<div class="small"> -<p class="center">How Made and Used</p> - -<p class="center"><i>A Practical Handbook for Students and Young -Electricians</i></p> - -<p class="center"><i>EDITED BY PERCIVAL MARSHALL, A.I.M.E.</i></p> - - -<p class="center">Contents of Chapters</p> - -<p>I.—The Theory of the Accumulator.</p> - -<p>II.—How to make a 4-Volt Pocket Accumulator.</p> - -<p>III.—How to make a 32-Ampere-Hour Accumulator.</p> - -<p>IV.—Types of Small Accumulators.</p> - -<p>V.—How to Charge and Use Accumulators.</p> - -<p>VI.—Applications of Small Accumulators, Electrical Novelties, -etc. Useful Receipts. Glossary of Technical Terms.</p> - -<p class="center"><b>80 pages, 40 illustrations, 12mo, cloth, 50c.</b></p> -</div> - -<hr class="full" /> - -<p class="center xl">THE MAGNETO-TELEPHONE<br /> - -<small>ITS CONSTRUCTION,</small></p> - -<p class="center">Fitting Up and Adaptability to Every-Day Use</p> - -<p class="center"><i>BY NORMAN HUGHES</i></p> - - -<p class="center">CONTENTS OF CHAPTERS</p> -<div class="small"> -<p>Some electrical considerations: I.—Introductory. II.—Construction. -III.—Lines, Indoor Lines. IV.—Signalling -Apparatus. V.—Batteries. Open Circuit Batteries. Closed -Circuit Batteries. VI.—Practical Operations. Circuit with -Magneto Bells and Lightning Arresters. How to Test the -Line. Push-Button Magneto Circuit. Two Stations with -Battery Bells. VII.—Battery Telephone. Battery Telephone -Circuit. Three Instruments on one Line. VIII.—General -remarks. Index.</p> - -<p class="center"><b>80 pages, 23 illustrations, 12mo, cloth, $1.00. In paper, 50c.</b></p> -</div> - -<hr class="chap" /> -<div class="chapter"></div> - -<p class="center"><span class="u">EVERYBODY'S BOOK ON ELECTRICITY</span><br /> - -<span class="xl">PRACTICAL ELECTRICS</span></p> - -<p class="center">A UNIVERSAL HANDY-BOOK<br /> - -ON<br /> - -EVERYDAY ELECTRICAL MATTERS</p> - -<hr class="small" /> - -<p class="center">FIFTH EDITION</p> - -<hr class="small" /> -<div class="small"> -<p class="center">CONTENTS:</p> - -<p><i>Alarms.</i>—Doors and Windows; Cisterns; Low Water in -Boilers; Time Signals; Clocks. <i>Batteries.</i>—Making; Cells; -Bichromate; Bunsen; Callan's; Copper-oxide; Cruikshank's; -Daniel's; Granule carbon; Groves; Insulite; Leclanché; -Lime Chromate; Silver Chloride; Smee; Thermo-electric. -<i>Bells.</i>—Annunciator System; Double System; and Telephone; -Making; Magnet for; Bobbins or Coils; Trembling; Single -Stroke; Continuous Ringing. <i>Connections.</i> <i>Carbons.</i> <i>Coils.</i>—Induction; -Primary; Secondary; Contact-breakers; Resistance. -<i>Intensity</i> Coils.—Reel; Primary; Secondary; Core; -Contact-breaker; Condenser; Pedestal; Commutator; Connections. -<i>Dynamo-electric Machines.</i>—Field-Magnets; Pole-pieces; -Field-magnet Coils; Armature Cores and Coils; -Commutator Collectors and Brushes; Relation of size to -efficiency; Methods of exciting Field-Magnets; Magneto-Dynamos; -Separately excited Dynamos; Shunt Dynamos; -Field-Magnets; Armatures; Collectors; Brush Dynamo; -Alternate Currents. <i>Fire Risks.</i>—Wires; Lamps; Danger to -persons. <i>Measuring.</i>—Non-Registering Instruments; Registering -Instruments. <i>Microphones.</i> <i>Motors.</i> <i>Phonographs.</i> -<i>Photophones.</i> <i>Storage.</i> <i>Telephones.</i>—Forms; Circuits and -Calls; Transmitter and Switch; Switch for Simplex; etc., etc.</p> - -<p class="center"> -<b>135 PAGES. 126 ILLUSTRATIONS. 8VO.<br /> -Cloth, 75 cents</b> -</p></div> - -<hr class="chap" /> -<div class="chapter"></div> -<p class="center"><b>VEST POCKET SERIES.<br /> - -<small>ACTUAL SIZE</small></b>.</p> - -<div class="figcenter" > -<img src="images/i_300a.jpg" alt="Spons' Engineers Tables" /> -</div> -<p class="center xs">Bound in roan, round corners, gilt edges in celluloid case, 50c.</p> - -<div class="figcenter" > -<img src="images/i_300.jpg" alt="Thompson's Electric Tables and Memoranda" /> -</div> -<p class="center xs">Bound in roan, round corners, gilt edges, in celluloid case, 50c.<br /> - - -<i>Copies mailed post-paid on receipt of price.</i></p> -</div> - -<div class="transnote"> -<h3>Transcriber's Notes</h3> - -<p>The Errata have been implemented.</p> - -<p>Obvious typographical errors have been silently corrected. All other -spelling, hyphenation and punctuation remains unchanged.</p> - -<p>The highly varied decorative typography of the book catalogue has -not been reproduced but every effort has been made to maintain the -general appearance and effect of the original.</p> -</div> - - - - - - - - -<pre> - - - - - -End of the Project Gutenberg EBook of Induction Coils, How to Make, Use, and -Repair Them., by H. S. 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