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SHENSTONE, F.R.S. + </title> + <style type="text/css"> + + p {margin-top: .75em; text-align: justify; margin-bottom: .75em;} + h1,h2,h3,h4 {text-align: center; clear: both;} + hr {width: 33%; margin-top: 2em; margin-bottom: 2em; margin-left: auto; margin-right: auto; clear: both;} + + table {margin-left: auto; margin-right: auto;} + + body{margin-left: 10%; margin-right: 10%;} + + .pagenum {position: absolute; left: 92%; font-size: smaller; text-align: right; color: gray;} + + .center {text-align: center;} + .bot {vertical-align: bottom;} + .caption {font-weight: bold; text-align: center; font-size: .9em;} + .chap {font-size: 1.25em; text-align: center; clear: both; font-style: italic; font-weight: bold;} + .figcenter {margin: auto; text-align: center;} + .figleft {float: left; clear: left; margin-left: 0; margin-bottom: 0; margin-top: 0; margin-right: 1em; padding: 0; + text-align: center;} + .figright {float: right; clear: right; margin-left: 1em; margin-bottom: 0; margin-top: 0; margin-right: 0; padding: 0; + text-align: center;} + .footnote {margin-left: 10%; margin-right: 10%; font-size: 0.9em;} + .footnote .label {position: absolute; right: 84%; text-align: right;} + .fnanchor {vertical-align: top; font-size: .8em; text-decoration: none; color: blue;} + .fsize80 {font-size: .8em;} + .fsize125 {font-size: 1.25em;} + .gesp {letter-spacing: .2em; } + hr.c05 {text-align: center; width: 5%; margin: .5em auto .5em auto; color: gray;} + hr.c25 {text-align: center; width: 25%; margin: .5em auto .5em auto; color: gray;} + hr.c40 {text-align: center; width: 40%; margin: .5em auto .5em auto; color: gray;} + hr.l05 {text-align: left; width: 5%; margin: .5em auto .5em 5%; color: gray;} + .just {text-align: justify;} + .leftcenter {text-align: center; margin-left: 5%; margin-right: 80%;} + .right {text-align: right;} + .smcap {font-variant: small-caps;} + .ssfont {font-family: sans-serif; font-size: 1.05em; font-weight: bold; font-style: normal;} + .tab50 {margin-left: 25%; margin-right: 25%;} + .tab60 {margin-left: 20%; margin-right: 20%;} + .tab90 {margin-left: 5%; margin-right: 5%;} + td.ll1 {text-align: left; padding-left: 1em;} + td.rl1 {text-align: right; padding-left: 1em; vertical-align: bottom; width: 15%;} + td.rb1 {text-align: right; padding-right: 1em; padding-left: 1em;} + .tnbox {border: solid 2px; margin-left: 15%; margin-right: 15%; padding: .5em; background: #CCCCB2;} + + </style> + </head> +<body> + + +<pre> + +The Project Gutenberg EBook of The Methods of Glass Blowing and of Working +Silica in the Oxy-Gas Flame, by W. A. Shenstone + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: The Methods of Glass Blowing and of Working Silica in the Oxy-Gas Flame + For the use of chemical and physical students + +Author: W. A. Shenstone + +Release Date: October 6, 2010 [EBook #33941] + +Language: English + +Character set encoding: ISO-8859-1 + +*** START OF THIS PROJECT GUTENBERG EBOOK THE METHODS OF GLASS BLOWING *** + + + + +Produced by Harry Lamé and the Online Distributed +Proofreading Team at http://www.pgdp.net (This file was +produced from images generously made available by The +Internet Archive/American Libraries.) + + + + + + +</pre> + + +<p class='pagenum'><a name="Page_i" id="Page_i">[i]</a></p> + +<h1>THE METHODS OF GLASS BLOWING</h1> +<h3>AND OF</h3> +<h1 class="gesp">WORKING SILICA</h1> +<hr class="c40" /> + +<p class='pagenum'><a name="Page_ii" id="Page_ii">[ii]</a></p> + +<h4>BY THE SAME AUTHOR</h4> +<p class="center"><i>With 25 Illustrations. Crown 8vo, 2s.</i></p> +<p class="center"><b>A Practical Introduction to Chemistry.</b> Intended to<br /> +give a <i>practical</i> acquaintance with the Elementary Facts<br /> +and Principles of Chemistry.</p> +<hr class="c25" /> + +<p class="center"><span class="fsize125">LONGMANS, GREEN, AND CO.</span><br /> +LONDON, NEW YORK, BOMBAY, CALCUTTA, AND MADRAS.</p> +<hr class="c40" /> + +<p class='pagenum'><a name="Page_iii" id="Page_iii">[iii]</a></p> + +<h1>The Methods of Glass Blowing</h1> +<h3>AND OF</h3> +<h1>Working Silica in the Oxy-Gas Flame</h1> + +<p class="center"><i>FOR THE USE OF CHEMICAL AND PHYSICAL <br />STUDENTS</i></p> +<p class="center">BY</p> +<p class="center"><b>W. A. SHENSTONE, F.R.S.</b></p> +<p class="center fsize80">FORMERLY LECTURER ON CHEMISTRY IN CLIFTON COLLEGE</p> +<p class="center fsize80"><i>NINTH IMPRESSION</i></p> + +<hr class="c05" /> + +<p class="center"><span class="gesp">LONGMANS, GREEN, AND C</span>O.<br /> +39 PATERNOSTER ROW, LONDON<br />FOURTH AVENUE & 30TH STREET, NEW YORK<br /> +BOMBAY, CALCUTTA, AND MADRAS<br />1916</p> +<hr class="c40" /> + +<p class='pagenum'><a name="Page_v" id="Page_v">[v]</a></p> + +<h1>PREFACE</h1> + +<p>This book consists of a reprint of the third edition of +my Methods of Glass-blowing, together with a <a href="#Ch_7">new +chapter</a> in which I have described the comparatively +new art of working vitreous silica.</p> + +<p>The individual operations of glass-blowing are much +less difficult than is usually supposed, and considerable +success in the performance of most of them may be +attained by any one who is endowed with average +powers of manipulation and who is moderately persistent. +Constructing finished apparatus is often more +difficult, as it may involve the performance of several +operations under disadvantageous conditions, and may +demand a little ingenuity on the part of the operator. +But I think the suggestions in <a href="#Ch_4">Chapter IV</a>. will +make this comparatively easy also to those who have +mastered the operations described in <a href="#Ch_3">Chapter III</a>.</p> + +<p>The working of vitreous silica, though more tedious +<span class='pagenum'><a name="Page_vi" id="Page_vi">[vi]</a></span>and expensive than glass-blowing, is not really more +difficult, and as it seems certain that this new material +will soon play a useful part in chemical and physical +research, I believe the <a href="#Ch_7">addition</a> now made to the earlier +book will add considerably to its value.</p> + +<p>As glass is much less expensive to work with than +silica, the beginner will find it best to spend a few +days working with the common gas blow-pipe and +glass before he attempts to manipulate the new and +more refractory material. Therefore, in writing the +new chapter, I have assumed that the reader is +already more or less familiar with the rest of the +book, and have given only such instructions and +advice as will be required by one who is already able +to carry out simple work at the blow-pipe.</p> + +<p class="right">W. A. SHENSTONE.</p> + +<p class="leftcenter"><span class="smcap">Clifton College</span>,<br /> +<i>Dec. 1901</i>.</p> + +<p class='pagenum'><a name="Page_vii" id="Page_vii">[vii]</a></p> + +<hr class="c05" /> +<h2><a name="CONTENTS" id="CONTENTS"></a>CONTENTS</h2> + +<table border="0" cellpadding="1" cellspacing="1" summary="ToC" class="tab60"> + +<tr><td class="center" colspan="2"><a href="#Ch_1">CHAPTER I.</a></td></tr> +<tr><td class="center fsize80" colspan="2">GLASS-BLOWER’S APPARATUS.</td></tr> +<tr><td class="right fsize80" colspan="2">PAGE</td></tr> +<tr><td class="just"><a href="#Sec_1_1">Introductory</a>—<a href="#Sec_1_2">The Working-place</a>—<a href="#Sec_1_3">The +Blow-pipe</a>—<a href="#Sec_1_4">The +Bellows</a>—<a href="#Sec_1_5">Automatic Blower</a>—<a href="#Sec_1_6">Blow-pipe Flames</a>,</td><td class="rl1"> +<a href="#Page_1">1</a>-<a href="#Page_11">11</a></td></tr> +<tr><td colspan="2"> </td></tr> + +<tr><td class="center" colspan="2"><a href="#Ch_2">CHAPTER II.</a></td></tr> +<tr><td class="center fsize80" colspan="2">VARIETIES OF GLASS AND THEIR MANAGEMENT.</td></tr> +<tr><td class="just"><a href="#Sec_2_1">Characters of good Glass</a>—<a href="#Sec_2_2">Cleaning and Preparing a +Tube</a>—<a href="#Sec_2_3">Presenting +Glass to the Flame</a>—<a href="#Sec_2_4">Methods of working with +Lead and Soft Soda Glass respectively</a>—<a href="#Sec_2_5">Management of Soda Glass</a>—<a +href="#Sec_2_6">Annealing</a>—<a href="#Sec_2_7">The +Use of Combustion Tube</a>,</td><td class="rl1"><a href="#Page_12">12</a>-<a href="#Page_25">25</a></td></tr> +<tr><td colspan="2"> </td></tr> + +<tr><td class="center" colspan="2"><a href="#Ch_3">CHAPTER III.</a></td></tr> +<tr><td class="center fsize80" colspan="2">CUTTING AND BENDING GLASS—FORMING GLASS APPARATUS +BEFORE THE BLOW-PIPE—MAKING AND GRINDING STOPPERS +TO APPARATUS, ETC.</td></tr> +<tr><td class="just"><a href="#Sec_3_1">Cutting Glass Tubes</a>—<a href="#Sec_3_2">Bending Glass Tubes</a>—<a +href="#Sec_3_3">Rounding and Bordering the Ends of Tubes</a>—<a href="#Sec_3_4">Sealing</a>—<a href="#Sec_3_5">Choking, +or Contracting the Bore of a Glass Tube</a>—<a href="#Sec_3_6">Widening Tubes</a>—<a href="#Sec_3_7">Piercing +Tubes</a>—<a href="#Sec_3_8">Uniting Pieces of Glass to each other, Known as Welding, or Soldering</a>—<a +href="#Sec_3_9">Blowing a Bulb or Globe of Glass</a>—<a href="#Sec_3_10">Making and Grinding Stoppers</a>,</td><td +class="right bot rl1"><a href="#Page_26">26</a>-<a href="#Page_54">54</a></td></tr> +<tr><td colspan="2"> </td></tr> + +<tr><td class="center" colspan="2"><a href="#Ch_4">CHAPTER IV.</a><span class='pagenum'><a name="Page_viii" +id="Page_viii">[viii]</a></span></td></tr> +<tr><td class="center fsize80" colspan="2">MAKING THISTLE FUNNELS, <span class="ssfont">U</span>-TUBES, ETC.—COMBINING THE PARTS +OF COMPLICATED APPARATUS—MERCURY, AND OTHER AIR-TIGHT +JOINTS—VACUUM TAPS—SAFETY TAPS—AIR-TRAPS.</td></tr> +<tr><td class="just"><a href="#Sec_4_1">Electrodes</a>—<a href="#Sec_4_2"><span class="ssfont">U</span>-Tubes</a>—<a +href="#Sec_4_3">Spiral Tubes</a>—<a href="#Sec_4_4">Thistle Funnels</a>—<a href="#Sec_4_5">Closing Tubes containing +Chemicals</a>—<a href="#Sec_4_6">Construction of Apparatus Consisting of Several Parts</a>—<a href="#Sec_4_7">Modes of +Combining the Parts of Heavy Apparatus</a>—<a href="#Sec_4_8">Mercury Joints</a>—<a href="#Sec_4_9">Vacuum Taps</a>—<a +href="#Sec_4_10">Lubricating Taps</a>—<a href="#Sec_4_11">Air-Traps</a>,</td><td class="rl1"><a +href="#Page_55">55</a>-<a href="#Page_69">69</a></td></tr> +<tr><td colspan="2"> </td></tr> + +<tr><td class="center" colspan="2"><a href="#Ch_5">CHAPTER V.</a></td></tr> +<tr><td class="center fsize80" colspan="2">GRADUATING AND CALIBRATING GLASS APPARATUS.</td></tr> +<tr><td class="just"><a href="#Sec_5_1">Graduating Tubes, etc.</a>—<a href="#Sec_5_2">To Divide a Given Line into Equal +Parts</a>—<a href="#Sec_5_3">To Calibrate Apparatus</a>—<a href="#Sec_5_4">To Calibrate Tubes for Measuring +Gases</a>—<a href="#Sec_5_5">To Calibrate the Tube of a Thermometer</a>,</td><td class="rl1"><a +href="#Page_70">70</a>-<a href="#Page_81">81</a></td></tr> +<tr><td colspan="2"> </td></tr> + +<tr><td class="center" colspan="2"><a href="#Ch_6">CHAPTER VI.</a></td></tr> +<tr><td class="center fsize80" colspan="2">GLASS TUBING.</td></tr> +<tr><td class="just"><a href="#Sec_6_1">Diagrams of Glass Tubes, Showing the Chief Sizes in which They +are Made</a>,</td><td class="rl1"><a href="#Page_82">82</a>-<a href="#Page_83">83</a></td></tr> +<tr><td colspan="2"> </td></tr> + +<tr><td class="center" colspan="2"><a href="#Ch_7">CHAPTER VII.</a></td></tr> +<tr><td class="center fsize80" colspan="2">VITREOUS SILICA.</td></tr> +<tr><td class="just"><a href="#Sec_7_1">Introductory</a>—<a href="#Sec_7_2">Properties of Vitreous Silica</a>—<a +href="#Sec_7_3">Preparing non-splintering Silica from Brazil Pebble</a>—<a href="#Sec_7_4">Apparatus</a>—<a +href="#Sec_7_5">The Method of Making Silica Tubes</a>—<a href="#Sec_7_6">Precautions</a>—<a href="#Sec_7_7">Making +Larger Tubes and other Apparatus of Silica</a>—<a href="#Sec_7_8">Quartz Fibres</a>,</td><td class="rl1"><a +href="#Page_84">84</a>-<a href="#Page_95">95</a></td></tr> +<tr><td colspan="2"> </td></tr> + +<tr><td class="smcap"><a href="#Ch_8">Index</a>,</td><td class="rl1"><a href="#Page_97">97</a></td></tr> +<tr><td colspan="2"> </td></tr> +</table> + +<hr class="c05" /><p class='pagenum'><a name="Page_1" id="Page_1">[1]</a></p> +<h2><a name="Ch_1" id="Ch_1"></a>CHAPTER I.</h2> +<p class="chap">GLASS-BLOWER’S APPARATUS.</p> + +<p><a name="Sec_1_1" id="Sec_1_1"></a><span class="ssfont">Introductory.</span>—I shall endeavour to give such an +account of the operations required in constructing glass +apparatus as will be useful to chemical and other students; +and as this book probably will come into the hands of +beginners who are not in a position to secure any further +assistance, I shall include descriptions even of the simple operations +which are usually learned during the first few hours of +practical work in a chemical or physical laboratory. I shall +not give any particular account of the manufacture of such +apparatus as thermometers, taps, etc., because, being in large +demand, they can be bought so cheaply that time is not +profitably spent in making them. But it will be found +that what is included will enable any one, who will devote +sufficient time to acquiring the necessary manipulative +dexterity, to prepare such apparatus as test-tubes, distillation +flasks, apparatus for washing gases, ozone generating +tubes, etc., when they are required, as they often are, without +delay or for special purposes. The amateur probably will +not succeed in turning out apparatus so finished in appearance +as that of the professional glass-blower until after +long practice, but after a little daily practice for the space +of a few weeks, any one who is fairly skilful in ordinary<span class='pagenum'><a name="Page_2" id="Page_2">[2]</a></span> +manipulation, and who perseveres in the face of failure +at first, will find himself able to make almost all the +apparatus he needs for lecture or other experiments, with +a considerable saving in laboratory expenses, and, which +very often is more important, without the delay that occurs +when one depends upon the professional glass-worker. In +the case of those who, like myself, work in the provinces, +this latter advantage is a very weighty one.</p> + +<p>After the description of the instruments used in glass-blowing, +which immediately follows, the following arrangement of +the subject has been adopted. In the first place, an account +of the two chief kinds of glass is given, and of the peculiarities +in the behaviour of each of them before the blow-pipe, which +is followed by a tolerably minute description of the method +of performing each of the fundamental operations employed +in fashioning glass apparatus. These are not very numerous, +and they should be thoroughly mastered in succession, preferably +upon tubes of both soda and lead glass. Then follows, +in <a href="#Ch_4">Chapter IV</a>., an account of the application of these operations +to setting up complete apparatus, full explanations of the construction +of two or three typical pieces of apparatus being +given as examples, and also descriptions of the modes of +making various pieces of apparatus which in each case present +one or more special difficulties in their construction; together +with an account, which, I think, will be found valuable, of +some apparatus that has been introduced, chiefly during +recent years, for experimenting upon gases under reduced +pressure, <i>e.g.</i> vacuum taps and joints. Finally, in Chapter +V., there is a short account of the methods of graduating +and calibrating glass apparatus for use in quantitative +experiments.</p> + +<p><a name="Sec_1_2" id="Sec_1_2"></a><span class="ssfont">The Working-place.</span>—The blow-pipe must be placed in +a position perfectly free from draughts. It should not face<span class='pagenum'><a name="Page_3" id="Page_3">[3]</a></span> +a window, nor be in too strong a light, if that can be avoided, +for a strong light will render the non-luminous flames, which +are used in glass-blowing, almost invisible, and seriously +inconvenience the operator, who cannot apply the various +parts of the flames to his glass with the degree of certainty that +is necessary; neither can he perceive the condition of the glass +so correctly in a strong light, for though in many operations +the glass-worker is guided by feeling rather than by seeing, yet +sight plays a very important part in his proceedings.</p> + +<p>My own blow-pipe is placed near a window glazed with +opaque glass, which looks southwards, but is faced by buildings +at a short distance. In dull weather the light obtained is +good; but on most days I find it advantageous to shade the +lower half of the window with a green baize screen. Some +glass-blowers prefer gaslight to daylight.</p> + +<p>The form of the table used is unimportant, provided that it is +of a convenient height, and allows free play to the foot which +works the blower underneath it. The blower should be +<i>fixed</i> in a convenient position, or it will get out of control at +critical moments. The table, or that part of it which surrounds +the blow-pipe, should be covered with sheet-iron to protect +it from the action of the fragments of hot glass that will fall +upon it. The tubes that supply air and gas to the blow-pipe +should come from beneath the table, and may pass +through holes cut for the purpose.</p> + +<p>Many glass-blowers prefer to work at a rather high table, +and sit on a rather high stool, so that they are well above +their work. No doubt this gives extra command over the +work in hand, which is often valuable. On the other hand, it +is somewhat fatiguing. For a long spell of labour at work +which is not of a novel character nor specially difficult, I am +disposed to recommend sitting on a chair or low stool, at a +table of such height as will enable the elbows to rest easily +upon it whilst the glass is held in the flame. The precise<span class='pagenum'><a name="Page_4" id="Page_4">[4]</a></span> +heights that are desirable for the table and stool, and the +exact position of the blow-pipe, will depend upon the height +and length of arm of the individual workman, and it must +therefore be left to each person to select that which suits him +best. A moveable rest made of wood, for supporting the +remote end of a long piece of glass tube a few inches above +the table, whilst the other end is being heated in the flame, +will be found convenient.</p> + +<p><a name="Sec_1_3" id="Sec_1_3"></a><span class="ssfont">The Blow-pipe.</span>—Formerly a lamp, in which sweet oil or +tallow was burnt, was employed for glass-working, and such +lamps are still occasionally used. Thus, lamps burning oil or +tallow were used on board the <i>Challenger</i> for hermetically +sealing up flasks of water collected at various depths to preserve +them for subsequent examination. I shall not, however, +give an account of such a lamp, for the gas apparatus is so +much more convenient for most purposes that it has now +practically superseded the oil lamps. <a href="#Fig_1">Fig. 1</a> shows a gas +blow-pipe of exceedingly simple construction, which can be +easily made, and with which good work can be done.</p> + +<div class="figleft"><img src="images/illo012sm.png" alt="Blow-pipe" /><a name="Fig_1" id="Fig_1"></a> +<p class="caption"><span class="smcap">Fig. 1.</span></p></div> + +<p>The tube <i>A</i> is of brass, and has a side tube <i>B</i> brazed to it, +ten to twelve centimetres from the end <i>E</i>, according to the +dimensions of the tube. A tube of glass, <i>EC</i>, is fitted into<span class='pagenum'><a name="Page_5" id="Page_5">[5]</a></span> +<i>A</i> by a cork at <i>D</i>. <i>B</i> is connected to a supply of gas by a +flexible tube, <i>C</i> is similarly connected to the blower. By +means of <i>CE</i> a stream of air can be forced into gas burning +at the mouth of the blow-pipe <i>G</i>, and various flames, with +the characters described in a later section, can be produced +with this instrument. For producing the pointed flame +(<a href="#Fig_3">Fig. 3</a>, <a href="#Page_9">p. 9</a>) the opening <i>E</i> of the air-tube should be contracted +to the size of a large knitting needle. For producing +a flame of large size, rich in air (<a href="#Fig_4">Fig. 4</a>, <a href="#Page_9">p. 9</a>), the internal +diameter of <i>E</i> may be nearly half as great as that of <i>A</i> +without disadvantage.</p> + +<p>This blow-pipe may be fixed in position by the spike <i>F</i>, +which will fit into holes in a block of wood or a large cork. +Several of these holes in various positions should be made in +the block, so that the position of the blow-pipe may be varied +easily. Two taps must be provided in convenient positions +near the edge of the table to enable the workman to regulate +the supplies of air and gas. These taps should be fixed to +the table and be connected with the gas and air supplies respectively +on one side, and with the blow-pipe on the other, by +flexible tubes. If blow-pipes of this kind be used, at least +two of them should be provided; one of small dimensions for +working on small tubes and joints, the other of larger size +for operations on larger tubes. It will be convenient to +have both of them ready for use at all times, as it is +sometimes necessary to employ large and small flames on the +same piece of work in rapid succession. By having several +air-tubes of different sizes fitted to each blow-pipe, a greater +variety of work may be done.</p> + +<p>For the larger blow-pipe, the internal diameter of <i>A</i> may +be fifteen to seventeen millimetres.</p> + +<p>For the smaller instrument, eleven millimetres for the +diameter of <i>A</i> would be a useful size.</p> + +<p>When a slightly greater outlay can be afforded it will<span class='pagenum'><a name="Page_6" id="Page_6">[6]</a></span> +be most convenient to purchase the blow-pipe. They can be +obtained of compact form, supported on stands with universal +joints giving great freedom of movement, and with taps for +regulating the supplies of gas and air, at comparatively small +cost.</p> + +<p>As figures of various blow-pipes can be seen in the price-lists +of most dealers in apparatus, they are not given here. +Their introduction would be of but little service, for the +construction of that which is adopted can be readily ascertained +by taking it to pieces. The simplest blow-pipe usually +used for glass-working is that of Herapath. This has two +taps to regulate the air and gas supplies respectively, and will +give a considerable variety of flames, which will be discussed +subsequently.</p> + +<p>An excellent blow-pipe, made on the same principle as +that shown in <a href="#Fig_1">Fig. 1</a>, but more substantially and with +interchangeable jets, can be obtained from Messrs. Muller of +Holborn for a moderate outlay.</p> + +<p>Another very good blow-pipe is the Automaton blow-pipe +of Mr. Fletcher of Warrington. In this, one tap +regulates the supply both of air and gas, which is a great +gain when difficult work is in hand. Automaton blow-pipes +are made of two sizes. I have found that the larger size, +with a powerful bellows, heats large pieces of lead glass +very satisfactorily. On the other hand, the fine-pointed +oxidising flame of the Herapath blow-pipe is, perhaps, the +most suitable for working joints of lead glass. Therefore +a good equipment would be a small Herapath blow-pipe +and a large-sized Automaton. If only one blow-pipe is purchased +it should be either a medium-sized Herapath, or +the smaller Automaton, as those are most useful for general +work.</p> + +<p>Mr. Fletcher also makes an ingenious combination of two +blow-pipes in which the gas and air supplies are regulated by<span class='pagenum'><a name="Page_7" id="Page_7">[7]</a></span> +a single lever-handle. This is very convenient, and gives +flames that answer well with tubes made of soft soda glass, +and it is very useful for general work. For use with lead +glass the supply of air is rather too small, and does not enable +one to get such good results. This can be easily amended, +however. By slightly increasing the size of the air-tube of the +smaller blow-pipe, and having increased the supply of air to +the larger blow-pipe also, by reducing the external diameter of +the end of the innermost tube, I now get medium-sized brush +flames and pointed flames with this blow-pipe, that are equal +to any I have used for heating lead glass.</p> + +<p>For small laboratories the inexpensive No. 5 Bunsen burner +of Mr. Fletcher, which is convertible into a blow-pipe, will be +very useful.</p> + +<p>Jets of several sizes to fit the air-tubes of blow-pipes may +be obtained with them, and will serve for regulating the +supply of air to the flame.</p> + +<p><a name="Sec_1_4" id="Sec_1_4"></a><span class="ssfont">The Bellows.</span>—The usual blowing apparatus is some +form of foot-blower. These may be obtained fitted to +small tables with sheet-iron tops. But a much less expensive +apparatus is the large foot-blower made by Mr. Fletcher of +Warrington, which can be used at an ordinary table or +laboratory bench. Good foot-blowers can also be obtained +from makers of furnace bellows.</p> + +<div class="figright"><img src="images/illo016sm.png" alt="Automatic Blower" /><a name="Fig_2" id="Fig_2"></a> +<p class="caption"><span class="smcap">Fig. 2</span></p></div> + +<p>No part of the glass-blower’s equipment exceeds the bellows +in importance. The best blower procurable should therefore +be adopted. A bellows which, when used with a large blow-pipe, +will not enable you to heat large pieces of lead glass tube +to redness without blackening the glass when the directions +for heating lead glass on pages 17-21 are followed, should on +no account be received. I am told that at some places, where +the water-supply is at very high pressure, it is utilised for +working blow-pipes by means of the apparatus described<span class='pagenum'><a name="Page_8" id="Page_8">[8]</a></span> +below, and that some glass-workers find it advantageous to +use such automatic blowers. But after a little practice, the +effort of working the blower with the foot whilst manipulating +the glass is not a source of serious inconvenience. Indeed, as +it gives a certain degree of control over the flame without the +use of the hands, the foot-blower is preferable. It is worth +while to describe an automatic blower, however.</p> + +<p><a name="Sec_1_5" id="Sec_1_5"></a><span class="ssfont">Automatic Blower</span> (<a href="#Fig_2">Fig. 2</a>).—A strong glass tube +<i>A</i> is welded into a somewhat larger +tube <i>B</i> so that its end is about 2 mm. +from the contraction at <i>G</i>. <i>B</i> has a side +tube <i>C</i> joined to it. The narrow end of <i>B</i> +is fixed by an india-rubber cork to a strong +bottle <i>D</i> of two or three litres capacity. +The india-rubber cork also carries an exit +tube <i>E</i>, and <i>D</i> is pierced near its bottom by +a small hole at <i>F</i>.</p> + +<p>In using the apparatus <i>A</i> is connected +with the water-supply, and water passing +through <i>G</i>, carries air with it into <i>D</i>. The +water escapes from <i>D</i> by the opening at <i>F</i>, +and the air is allowed to pass out by the +tube <i>E</i>, its passage being regulated by a tap. Fresh supplies +of air enter <i>B</i> by <i>C</i>.</p> + +<div class="figleft"><img src="images/illo017asm.png" alt="Fine-pointed Flame" /><a name="Fig_3" id="Fig_3"></a> +<p class="caption"><span class="smcap">Fig. 3.</span></p></div> + +<p><a name="Sec_1_6" id="Sec_1_6"></a><span class="ssfont">Blow-pipe Flames</span>—<i>The Pointed Flame.</i>—If the gas tap +of a Herapath blow-pipe be adjusted so that comparatively +little gas can pass, and if the foot-blower be then worked +cautiously, a long tongue of flame ending in a fine point +will be produced (<a href="#Fig_3">Fig. 3</a>). This flame will subsequently be +described as the <i>pointed flame</i>. It should be quite free from +luminosity, and as the amount of air necessary for securing a<span class='pagenum'><a name="Page_9" id="Page_9">[9]</a></span> +pointed flame is large, in proportion to the gas, there is excess +of oxygen towards the +end <i>C</i>. By adjusting +the proportions of +air and gas, pointed +flames of various +dimensions can be +obtained with the +same blow-pipe. The +part of a pointed +flame to be used in +glass-working is the +tip, or in some cases +the space slightly +beyond the tip.</p> + +<div class="figright"><img src="images/illo017bsm.png" alt="Large Flame" /><a name="Fig_4" id="Fig_4"></a> +<p class="caption"><span class="smcap">Fig. 4.</span></p></div> + +<p><i>The Brush Flame.</i>—If a large supply of gas be turned on and +a considerable blast of air sent into the flame, a non-luminous +flame of great size will be obtained (<a href="#Fig_4">Fig. 4</a>). In form it +somewhat resembles a large camel’s hair pencil, and may<span class='pagenum'><a name="Page_10" id="Page_10">[10]</a></span> +conveniently be described as a <i>brush flame</i>. The chief advantage +of a large-sized blow-pipe is, that with it a large brush flame +may be produced, which is often invaluable. By gradually +diminishing the supply of gas and air smaller brush flames +may be produced.</p> + +<p>The jet used to supply air to the Herapath blow-pipe is +usually too fine, and consequently does not permit the +passage of sufficient air to produce a brush flame that contains +excess of oxygen, even with the aid of a very powerful +blower. My own Herapath blow-pipe only gives a satisfactory +oxidising brush flame when the jet is removed altogether from +the end of the air-tube. For producing pointed flames the finer +jet of the air-tube must be used, but when a highly oxidising +flame of large size is required it must be removed. The +internal diameter of the central air-tube should be nearly half +as great as that of the outer or gas-supply tube. Fletcher’s +Automaton with the large air jet gives a very liberal supply +of air, and produces an excellent oxidising brush flame. In +the case of the larger-sized Automaton a consequence of this +is, however, that when fitted with the large jet it will not give +so good a pointed flame as the Herapath, which, in its turn, +gives an inferior oxidising brush. By fitting finer jets to the +air-tube of Fletcher’s apparatus pointed flames can be secured +when necessary.</p> + +<p><i>The Smoky Flame.</i>—By turning on a very free supply of gas, +and only enough air to give an outward direction to the +burning gas, a smoky flame, chiefly useful for annealing and for +some simple operations on lead glass, is produced.</p> + +<p>The Gimmingham blow-pipe and Fletcher’s combination +blow-pipe, in addition to the above flames, are also adapted +to produce a non-luminous flame, resembling that of the +Bunsen gas-burner, which is very convenient for the preliminary +heating of the glass, and also for gradually cooling +finished apparatus. It is not necessary to describe the method<span class='pagenum'><a name="Page_11" id="Page_11">[11]</a></span> +of using these last-mentioned blow-pipes. With the more +complicated of them directions for its use are supplied.</p> + +<p>Mr. Madan has suggested the use of oxygen in place of air +for producing the oxidising flame required for working lead +glass, and to produce a flame of high temperature for softening +tubes of hard, or combustion, glass. For the latter purpose +the employment of oxygen may be adopted with great advantage. +For working lead glass, however, it is quite unnecessary +if the directions already given are followed.</p> + +<p>The student’s subsequent success will so largely depend upon +his acquaintance with the resources of his blow-pipe, and on +the facility with which he can take advantage of them, that +no pains should be spared in the effort to become expert in +its management as soon as possible. A few experiments +should now be made, therefore, upon the adjustment of the +flame, until the student is able to produce and modify any +form of flame with promptness and certainty.</p> + +<div class="figleft"><img src="images/illo019sm.png" alt="Pointed Charcoal" /><a name="Fig_5" id="Fig_5"></a> +<p class="caption"><span class="smcap">Fig. 5.</span></p></div> + +<p>The remaining apparatus used in glass-working consists of +triangular and other files, charcoal pastils for cutting glass, +pieces of sound charcoal of various diameters with conical +ends; it is convenient to have one end +somewhat less pointed than the other +(<a href="#Fig_5">Fig. 5</a>). Corks of various sizes; the +smallest, which are most frequently +needed, should be carefully cut with +sharpened cork borers from larger corks. Besides these +there should be provided some freshly distilled turpentine in +which camphor has been dissolved,<a name="Fnanchor_1" id="Fnanchor_1"></a><a href="#Fn_1" class="fnanchor">[1]</a> fine and coarse emery +powder, and some sheets of cotton-wadding, an india-rubber +blowing-bottle, glass tubes, a little white enamel, and a pair of +iron tongs.</p> + +<hr class="l05" /> +<p class="footnote"><a name="Fn_1" id="Fn_1"></a><span class="label"><a href="#Fnanchor_1">[1]</a></span>Half +an ounce of camphor to about six ounces of turpentine will do very well.</p> +<hr class="l05" /> + +<hr class="c05" /><p class='pagenum'><a name="Page_12" id="Page_12">[12]</a></p> +<h2><a name="Ch_2" id="Ch_2"></a>CHAPTER II.</h2> +<p class="chap">VARIETIES OF GLASS AND THEIR MANAGEMENT.</p> + +<p>All the varieties of glass that are ordinarily met with contain +silica (SiO<sub>2</sub>) associated with metallic oxides. In a true +glass there are at least two metallic oxides. The unmixed +silicates are not suitable for the purposes of glass. They are +not so capable of developing the viscous condition when heated +as mixtures—some of them are easily attacked by water, and +many of those which are insoluble are comparatively infusible. +There is generally excess of silica in glass, that is, more than +is necessary to form normal silicates of the metals present. +The best proportions of the various constituents have been +ascertained by glass-makers, after long experience; but the +relation of these proportions to each other, from a chemical +point of view, is not easy to make out.</p> + +<p>The varieties of glass from which tubes for chemical glass-blowing +are made may be placed under three heads, and are +known as<a name="Fnanchor_2" id="Fnanchor_2"></a><a href="#Fn_2" class="fnanchor">[2]</a>—</p> + +<table class="tab50" border="0" cellpadding="1" cellspacing="1" summary="Varieties of Glass"> +<tr><td>Soft soda glass.</td><td class="ll1">Also known as French glass.</td></tr> +<tr><td>Lead glass.</td><td class="ll1">Also known as English glass.</td></tr> +<tr><td>Hard glass.</td><td> </td></tr> +</table> + +<p>In purchasing glass tubes, it is well to lay in a considerable<span class='pagenum'><a name="Page_13" id="Page_13">[13]</a></span> +stock of tubes made of each of the two first varieties, +and, if possible, to obtain them from the manufacturer, for it +frequently happens that pieces of glass from the same batch +may be much more readily welded together than pieces of +slightly different composition. Yet it is not well to lay +in too large a stock, as sometimes it is found that glass +deteriorates by prolonged keeping.</p> + +<p>As it is frequently necessary to make additions, alterations, +or repairs to purchased apparatus, it is best to provide +supplies both of soft soda glass and lead glass, for though +purchased glass apparatus is frequently made of lead glass, +yet sometimes it is formed from the soda glass, and as it is a +matter of some difficulty to effect a permanent union between +soda glass and lead glass, it is desirable to be provided with +tubes of both kinds.</p> + +<p>Many amateurs find that soda glass is in some respects +easier to work with than lead glass. But, on the other hand, +it is somewhat more apt to crack during cooling, which causes +much loss of time and disappointment. Also, perhaps in +consequence of its lower conductivity for heat, it very often +breaks under sudden changes of temperature during work. +If, however, a supply of good soda glass is obtained, and the +directions given in this book in regard to annealing it are +thoroughly carried out, these objections to the use of soda glass +will, to a great extent, be removed. I find, however, that when +every precaution has been taken, apparatus made of soda glass +will bear variations of temperature less well than that made of +lead glass. Therefore, although the comparatively inexpensive +soda glass may be employed for most purposes without distrust, +yet I should advise those who propose to confine +themselves to one kind of glass, to take the small extra trouble +required in learning to work lead glass.</p> + +<p>In order to secure glass of good quality, a few pieces should +be obtained as a sample, and examined by the directions<span class='pagenum'><a name="Page_14" id="Page_14">[14]</a></span> +given below. When the larger supply arrives, a number of +pieces, taken at random, should be examined before the blow-pipe, +to compare their behaviour with that of the sample +pieces, and each piece should be separately examined in all +other respects as described subsequently.</p> + +<p>Hard glass is used for apparatus that is required to withstand +great heat. It is difficult to soften, especially in large +pieces. It should only be employed, therefore, when the low +melting points of soda or lead glass would render them unsuitable +for the purpose to which the finished apparatus is to +be put. What is sold as Jena combustion tube should be +preferred when this is the case.</p> + +<p><a name="Sec_2_1" id="Sec_2_1"></a><span class="ssfont">Characters of good Glass.</span>—Glass tubes for glass-blowing +should be as free as possible from knots, air-bubbles, and +stripes. They should be in straight pieces of uniform thickness, +and cylindrical bore. It is not possible to obtain glass +tubes of absolutely the same diameter from one end to the +other in large quantities, but the variations should not be +considerable.</p> + +<p>When a sharp transverse scratch is made with a good file +on a piece of tube, and the scratch is touched with a rather +fine point of red-hot glass (this should be lead glass for a +lead glass tube, and soda glass for a tube of soda glass), the +crack which is started should pass round the glass, so that it +may be broken into two pieces with regular ends. If the +crack proceeds very irregularly, and especially if it tends to +extend along the tube, the glass has been badly annealed, and +should not be employed for glass-blowing purposes. It is +important that the point of hot glass used shall be very +small, however. Even good glass will frequently give an +irregular fracture if touched with a large mass of molten +glass.</p> + +<p>Finally, glass tube which is thin and of small diameter<span class='pagenum'><a name="Page_15" id="Page_15">[15]</a></span> +should not crack when suddenly brought into a flame. But +larger and thicker tubes will not often withstand this treatment. +They should not crack, however, when they are brought +into a flame gradually, after having been held in the warm air +in front of it for a minute or so.</p> + +<p>Good glass does not readily devitrify when held in the blow-pipe +flame. As devitrified glass very often may be restored to +its vitreous condition by fusion, devitrification most frequently +shows itself round the edges of the heated parts, and may be +recognised by the production of a certain degree of roughness +there. It is believed to be due to the separation of certain +silicates in the crystallised form. Hard glass, which contains +much calcium, is more apt to devitrify than the more fusible +varieties.<a name="Fnanchor_3" id="Fnanchor_3"></a><a href="#Fn_3" class="fnanchor">[3]</a></p> + +<p>Glass tubes are made of various sizes. When purchasing a +supply, it is necessary to be somewhat precise in indicating to +the vendor the sizes required. I have therefore placed at +the end of the book, in an appendix, a table of numbered +diagrams. In ordering tubes it will usually only be necessary +to give the numbers of the sizes wished for, and to +specify the quantity of each size required. In ordering glass +tubes by weight, it must be remembered that a great many +lengths of the smaller sizes, but very few lengths of the +larger sizes, go to the pound. Larger-sized tubes than those +on the diagram are also made. In ordering them the +external diameter and thickness of glass preferred should be +stated.</p> + +<p><a name="Sec_2_2" id="Sec_2_2"></a><span class="ssfont">Cleaning and Preparing a Tube.</span>—It is frequently +much easier to clean the tube from which a piece of apparatus<span class='pagenum'><a name="Page_16" id="Page_16">[16]</a></span> +is to be made than to clean the finished apparatus. A simple +method of cleaning a tube is to draw a piece of wet rag which +has been tied to a string through the tube once or twice, or, +with small tubes, to push a bit of wet paper or cotton wool +through them. If the dirt cannot be removed in this way, +the interior of the tube should be moistened with a little sulphuric +acid in which some bichromate of potassium has been +dissolved. In any case, it must finally be repeatedly rinsed +with distilled water, and dried by cautiously warming it, and +sucking or blowing air through it. In order to avoid heating +delicate apparatus which has become damp and needs drying, +the water may be washed out with a few drops of spirit, +which is readily removed at a low temperature.</p> + +<p>Before using a glass tube for an operation in which it will +be necessary to blow into it, one end of it must be contracted, +unless it is already of such a size that it can be held between +the lips with perfect ease; in any case, its edges must +be rounded. For descriptions of these operations, see +<a href="#Page_35">page 35</a>. The other end must be closed. This may be done +by means of a cork.</p> + +<p><a name="Sec_2_3" id="Sec_2_3"></a><span class="ssfont">Presenting Glass to the Flame.</span>—Glass tubes must +never be brought suddenly into the flame in which they +are to be heated. All glass is very likely to crack if so +treated. It should in all cases be held for a little while in +front of the flame, rotated constantly in the hot air and +moved about, in order that it may be warmed over a considerable +area. When it has become pretty hot by this +treatment, it may be gradually brought nearer to the flame, +and, finally, into contact with it, still with constant rotation +and movement, so as to warm a considerable part of the +tube. When the glass has been brought fairly into contact +with the flame, it will be safe to apply the heat at the required +part only. Care must be taken in these preliminary<span class='pagenum'><a name="Page_17" id="Page_17">[17]</a></span> +operations to avoid heating the more fusible glasses sufficiently to +soften them.</p> + +<p><a name="Sec_2_4" id="Sec_2_4"></a><span class="ssfont">Methods of working with Lead and soft Soda +Glass respectively.</span>—When lead glass is heated in the +brush flame of the ordinary Herapath blow-pipe, or within the +point of the pointed flame, it becomes blackened on its surface, +in consequence of a portion of the lead becoming +reduced to the metallic state by the reducing gases in the +flame. The same thing will happen in bending a lead glass +tube if it is made too hot in a luminous flame. A practical +acquaintance with this phenomenon may be acquired by the +following experiment:—</p> + +<p>Take a piece of lead glass tube, bring it gradually from the +point of a pointed flame to a position well within the flame, and +observe what happens. When the glass reaches the point <i>A</i> +(<a href="#Fig_3">Fig. 3</a>), or thereabouts, a dark red spot will develop on the +glass, the area of the spot will increase as the glass is +brought further in the direction <i>A</i> to <i>B</i>. If the glass be then +removed from the flame and examined, it will be found that +a dark metallic stain covers the area of the dark red spot +previously observed. Repeat the experiment, but at the +first appearance of the dark spot slowly move the glass in the +direction <i>A</i> to <i>C</i>. The spot will disappear, and, if the operation +be properly performed, in its place there will be a characteristically +greenish-yellow luminous spot of highly heated +glass. In this proceeding the reduced lead of the dark spot +has been re-oxidised on passing into the hot gases, rich in +oxygen, which abound at the point of the flame. If one end +of the tube has been previously closed by a piece of cork, and if +air be forced into the tube with the mouth from the open end +before the luminous spot has become cool, the glass will expand. +If the experiment be repeated several times, with pointed +flames of various sizes, the operator will quickly learn how to<span class='pagenum'><a name="Page_18" id="Page_18">[18]</a></span> +apply the pointed flame to lead glass so that it may be heated +without becoming stained with reduced lead.</p> + +<p>If the spot of reduced metal produced in the first experiment +be next brought into the oxidising flame, it also may +gradually be removed. On occasion, therefore, apparatus +which has become stained with lead during its production, +may be rendered presentable by suitable treatment in the +oxidising flame. The process of re-oxidising a considerable +surface in this way after it has cooled down is apt +to be very tedious, however, and, especially in the case of +thin tubes or bulbs, often is not practicable. In working +with lead glass, therefore, any reduction that occurs should +be removed by transferring the glass to the oxidising flame +at once.</p> + +<p>Small tubes, and small areas on larger tubes of English +glass, may be softened without reduction by means of the +pointed oxidising flame; but it is not easy to heat any considerable +area of glass sufficiently with a pointed flame. And +though it is possible, with care, to employ the hot space +immediately in front of the visible end of an ordinary brush +flame, which is rich in air, yet, in practice, it will not be +found convenient to heat large masses of lead glass nor tubes +of large size, to a sufficiently high temperature to get the +glass into good condition for blowing, by presenting them +to the common brush flame.</p> + +<p>It may seem that as glass which has become stained with +reduced lead can be subsequently re-oxidised by heating it +with the tip of the pointed flame, the difficulty might be +overcome by heating it for working in the brush flame, and +subsequently oxidising the reduced lead. It is, however, +difficult, as previously stated, to re-oxidise a large surface of +glass which has been seriously reduced by the action of the +reducing gases of the flame, after it has cooled. Moreover, +there is this very serious objection, that if, as may be<span class='pagenum'><a name="Page_19" id="Page_19">[19]</a></span> +necessary, the action of the reducing flame be prolonged, the +extensive reduction that takes place diminishes the tendency +of the glass to acquire the proper degree of viscosity for +working it, the glass becomes difficult to expand by blowing, +seriously roughened on its surface, and often assumes a very +brittle or rotten condition.</p> + +<p>When it is only required to bend or draw out tubes of +lead glass, they may be softened sufficiently by a smoky +flame, which, probably owing to its having a comparatively +low temperature, does not so readily reduce the lead as flames +of higher temperature. But for making joints, collecting +masses of glass for making bulbs, and in all cases where it +is required that the glass shall be thoroughly softened, the +smoky flame does not give good results.</p> + +<p>In the glass-works, where large quantities of ornamental +and other glass goods are made of lead or flint glass, the pots +in which the glass is melted are so constructed that the gases +of the furnace do not come into contact with the glass;<a name="Fnanchor_4" id="Fnanchor_4"></a><a href="#Fn_4" class="fnanchor">[4]</a> +and as the intensely-heated sides of the melting-pot maintain a very +high temperature within it by radiation, the workman has a very +convenient source of heat to his hand,—he has, in fact, only to +introduce the object, or that part of it which is to be softened, +into the mouth of the melting-pot, and it is quickly heated +sufficiently for his purpose, not only without contact of +reducing gases, but in air. He can therefore easily work +upon very large masses of glass. In a special case, such a +source of heat might be devised by the amateur. Usually, +however, the difficulty may be overcome without special +apparatus. It is, in fact, only necessary to carry out the +instructions given below to obtain a considerable brush flame +rich in air, in which the lead glass can be worked, not only +without discoloration, but with the greatest facility.</p> + +<p><span class='pagenum'><a name="Page_20" id="Page_20">[20]</a></span><i>To Produce an Oxidising Brush Flame.</i>—The blower used +must be powerful, the air-tube of the blow-pipe must be +about half as great in diameter as the outer tube which +supplies the gas. The operator must work his bellows so +as to supply a strong and <i>steady</i> blast of air, and the +supply of gas must be regulated so that the brush flame +produced is free from every sign of incomplete combustion,<a name="Fnanchor_5" id="Fnanchor_5"></a><a href="#Fn_5" class="fnanchor">[5]</a> +which may be known by its outer zone being only faintly +visible in daylight, and quite free from luminous streaks +(see <a href="#Fig_4">Fig. 4</a>, <a href="#Page_9">p. 9</a>). When a suitable flame has been produced, +try it by rotating a piece of lead glass at or near the end of the +inner blue part of the flame (<i>A</i> <a href="#Fig_4">Fig. 4</a>); the appearance of +the glass will quickly indicate reduction. When this occurs +move the glass forward to the end of the outer zone <i>B</i>, but +keep it sufficiently within the flame to maintain it at a high +temperature. If all is right the metallic reduction will quickly +disappear, the glass will become perfectly transparent once +more, and will present the appearance previously observed in +the experiments with the pointed flame, or, if very hot, +assume a brownish-red appearance. If this does not occur, +the supply of air must be increased or the supply of gas +diminished until the proper effects are secured.</p> + +<p>In working upon lead glass with the highly oxidising brush +flame, it is a good plan to heat it in the reducing part of the +flame <i>A</i> for thoroughly softening the glass, and to remove it to +the oxidising flame <i>B</i> to burn away the reduced metal. In +prolonged operations, in order that reduction may never +go too far, hold the glass alternately in the hot reducing +flame and in the oxidising flame. The inferiority of the outer +oxidising flame to those portions nearer the inner blue zone for<span class='pagenum'><a name="Page_21" id="Page_21">[21]</a></span> +softening the glass, may perhaps be accounted for by the presence +of a larger proportion of unconsumed air in the former, +which being heated at the expense of the hot gases produced +by combustion, thereby lowers the temperature of the flame. +At or near <i>A</i> (<a href="#Fig_4">Fig. 4</a>) where the combustion is nearly complete, +but no excess of air exists, the temperature will naturally +be highest.</p> + +<p>If a very large tube be rotated in the oxidising flame at +<i>B</i> (<a href="#Fig_4">Fig. 4</a>) it may happen that the flame is not large enough to +surround the tube, and that as it is rotated those parts of it +which are most remote from the flame will cool down too considerably +to allow all parts of the tube to be simultaneously +brought into the desired condition. This difficulty may be +overcome by placing two blow-pipes exactly opposite to +each other, at such a distance that there is an interval of +about an inch between the extremities of their flames, and +rotating the tube between the two flames. It may be +necessary to provide two blowers for the blow-pipes if they +are large.</p> + +<p>Again, if a very narrow zone of a tube of moderate size +is to be heated, two pointed flames may be similarly arranged +with advantage. Occasionally more than two flames are made +to converge upon one tube in this manner.</p> + +<p>Another method of preventing one side of a tube from +cooling down whilst the other is presented to the flame, is to +place a brick at a short distance from the extremity of the +flame. The brick checks the loss of heat considerably. A +block of beech wood may be used for the same purpose, the +wood ignites and thereby itself becomes a source of heat, and +is even more effective than a brick.</p> + +<p>Fuller details of the management of lead glass under various +circumstances will be found in the subsequent descriptions +of operations before the blow-pipe.</p> + +<p>Before proceeding to work with soda glass, the student<span class='pagenum'><a name="Page_22" id="Page_22">[22]</a></span> +should not only verify by experiments what has been already +said, but he should familiarise himself with the action of the +blow-pipe flame on lead glass by trying the glass in every +part of the flame, varying the proportions of gas and air in +every way, repeating, and repeating, his experiments until +he can obtain any desired effect with certainty and promptitude. +He should practice some of the simpler operations +given in Chapter III. in order to impress what he has learned +well on his mind.</p> + +<p><a name="Sec_2_5" id="Sec_2_5"></a><span class="ssfont">Management of Soda Glass.</span>—In working with soda +glass the following points must be constantly kept in mind. +That as it is much more apt than lead glass to crack when +suddenly heated, great caution must be exercised in bringing it +into the flame; and that in making large joints or in making two +joints near each other, all parts of the tube adjacent to that +which, for the moment, is being heated, must be kept hot, as it +is very apt to crack when adjacent parts are unequally heated. +This may be effected by stopping work at short intervals and +warming the cooler parts of the tube, or by the use of the +brick or block of wood to check radiation, or even by placing +a supplementary blow-pipe or Bunsen burner in such a position +that its flame plays upon the more distant parts of the +work, not coming sufficiently into contact to soften the glass, +however, but near enough to keep it well heated. Lastly, to +prevent the finished work from falling to pieces after or during +cooling, the directions given under the head of annealing +must be carefully carried out.</p> + +<p>In very much of his work the glass-blower is guided more +by the <i>feel</i> of the glass than by what he sees. The power of +feeling glass can only be acquired by practice, and after a +certain amount of preliminary failure. As a rule I have +observed that beginners are apt to raise their glass to a higher +temperature than is necessary, and that they employ larger<span class='pagenum'><a name="Page_23" id="Page_23">[23]</a></span> +flames than are wanted. If glass be made too soft it may +fall so completely out of shape as to become unworkable +except in very skilful hands. The following rules, therefore, +should be strictly adhered to. Always employ in the first +instance the smallest flame that is likely to do the work +required. In operations involving <i>blowing out</i> viscous glass, +attempt to blow the glass at low temperatures before higher +ones are tried. After a little experience the adoption of the +right-sized flame for a given purpose, and the perception +of the best condition of glass for blowing it, become almost +automatic.</p> + +<p>I may add that glass which is to be bent needs to be much +less heated than glass which is to be blown.</p> + +<p><a name="Sec_2_6" id="Sec_2_6"></a><span class="ssfont">Annealing.</span>—If apparatus, the glass of which is very thin +and of uniform substance, be heated, on removal from the source +of heat it will cool equally throughout, and therefore may often +be heated and cooled without any special precautions. If the +glass be thick, and especially if it be of unequal thickness +in various parts, the thinner portions will cool more quickly +than those which are more massive; this will result in the +production of tension between the thicker and thinner parts +in consequence of inequality in the rates of contraction, and +fractures will occur either spontaneously or upon any sudden +shock. Thus, if a hot tube be touched with cold or wet +iron, or slightly scratched with a cold file, the inequality of +the rate of cooling is great, and it breaks at once. It is +therefore necessary to secure that hot glass shall cool as +regularly as possible. And this is particularly important in +the case of articles made of soda glass. Some glass-blowers +content themselves with permitting the glass to cool gradually +in a smoky flame till it is covered with carbon, and then leave +it to cool upon the table. But under this treatment many +joints made of soda glass which are not quite uniform in<span class='pagenum'><a name="Page_24" id="Page_24">[24]</a></span> +substance, but otherwise serviceable, will break down. In glass-works +the annealing is done in ovens so arranged that the +glass enters at the hottest end of the oven where it is +uniformly heated to a temperature not much below that at +which it becomes viscous, and slowly passed through the +cooler parts of the chamber so that it emerges cold at the +other end. This method of annealing is not practicable in a +small laboratory. But fortunately very good results can be +obtained by the following simple device, viz.:—</p> + +<p>By wrapping the hot apparatus that is to be annealed +closely in cotton wool, and leaving it there till quite cold. +The glass should be wrapped up immediately after it is +blown into its final shape, as soon as it is no longer soft +enough to give way under slight pressure. And it should +be heated as uniformly as possible, not only at the joint, but +also about the parts adjacent to the joint, at the moment +of surrounding it with the cotton. Lead glass appears to cool +more regularly than soda glass, and these precautions may be +more safely neglected with apparatus made of lead glass; but +not always. At the date of writing I have had several well-blown +joints of thick-walled capillary tube to No. 16 (see +diagram, <a href="#Page_82">p. 82</a>), break during cooling, in consequence of circumstances +making it dangerous to heat the neighbourhood of +the joint so much as was necessary.</p> + +<p>The black carbonaceous coat formed on hot glass when +it is placed in cotton wool may be removed by wiping +with methylated spirit, or, if it be very closely adherent, by +gently rubbing with fine emery, moistened with the spirit.</p> + +<p>Cotton wool is rather dangerously inflammable; it should +therefore be kept out of reach of the blow-pipe flame, and +care should be taken that the glass is not placed in contact with +it at a sufficiently high temperature to cause its ignition.</p> + +<p>Another method of annealing is to cover the hot glass with +hot sand, and allow it to cool therein.</p> + +<p><span class='pagenum'><a name="Page_25" id="Page_25">[25]</a></span>As in the case of lead glass, so with soda glass. A +thorough acquaintance with the effect of the various parts of +the flame upon it should be gained before further work is +entered upon, for which purpose an hour or more spent in +observing its behaviour in the flame will be fully repaid by +increased success subsequently.</p> + +<p><a name="Sec_2_7" id="Sec_2_7"></a><span class="ssfont">The Use of Combustion Tube.</span>—It is often necessary +to construct apparatus of what is known as hard glass or +combustion tube. It is almost as easy to work combustion +tube as to deal with lead and soda glass if the oxy-hydrogen +flame be employed.</p> + +<p>It is not necessary to set up a special apparatus for this +purpose; many of the ordinary blow-pipes can be used with +oxygen instead of with air. It is only necessary to connect the +air-tube of the blow-pipe with a bottle of compressed oxygen +instead of with the bellows. The connecting tube should not +be too wide nor too long, in order to avoid the accumulation +in it, by accident, of large quantities of explosive mixtures.</p> + +<p>Two precautions are necessary in manipulating hard glass +in the oxy-hydrogen flame. The glass must <i>not</i> be overheated. +At first one is very apt to go wrong in this +direction. The supply of oxygen must <i>not</i> be too great; a +small hissing flame is not what is wanted. If either of these +precautions are neglected most glass will devitrify badly. +With a little care and experience, devitrification can be +absolutely avoided. Ordinary combustion tube can be used, +but I find that the glass tube (Verbrennungsröhr) made by +Schott & Co. of Jena, which can be obtained through any firm +of dealers in apparatus, is far better than the ordinary tube.</p> + +<p>By following these instructions, any one who has learned +how to work with lead or soda glass will find it easy to +manipulate hard glass.</p> + +<hr class="l05" /> +<p class="footnote"><a name="Fn_2" id="Fn_2"></a><span class="label"><a href="#Fnanchor_2">[2]</a></span> +For details of the composition of the various glasses, some work on +glass-making may be consulted.</p> + +<p class="footnote"><a name="Fn_3" id="Fn_3"></a><span class="label"><a href="#Fnanchor_3">[3]</a></span> +The presence of silicates of calcium and aluminum are considered to +promote a tendency to devitrification in glass; and glasses of complex +composition are more apt to devitrify than the simpler varieties. See +<i>Glass-making</i>, by Powell, Chance, and Harris, Chap. IV.</p> + +<p class="footnote"><a name="Fn_4" id="Fn_4"></a><span class="label"><a href="#Fnanchor_4">[4]</a></span> +See <i>Principles of Glass-making</i>, p. 31.</p> + +<p class="footnote"><a name="Fn_5" id="Fn_5"></a><span class="label"><a href="#Fnanchor_5">[5]</a></span> +Nevertheless the supply of air must not be so excessive as to reduce +the temperature of the flame sufficiently to prevent the thorough +softening of the glass, which will occur if the bellows is worked with +too much zeal.</p> +<hr class="l05" /> + +<hr class="c05" /><p class='pagenum'><a name="Page_26" id="Page_26">[26]</a></p> +<h2><a name="Ch_3" id="Ch_3"></a>CHAPTER III.</h2> + +<p class="chap">CUTTING AND BENDING GLASS—FORMING GLASS +APPARATUS BEFORE THE BLOW-PIPE—MAKING +AND GRINDING STOPPERS TO APPARATUS, ETC.</p> + +<p>In the later pages of this Chapter it will be assumed that the +operations first described have been mastered. The beginner +should therefore practise each operation until he finds himself +able to perform it with some degree of certainty. Generally +speaking, however, after the failure of two or three attempts +to perform any operation, it is best to give up for a few +hours, and proceed to the work next described, returning to +that upon which you have failed subsequently. If, unfortunately, +it should happen that the work next in order involves +the performance of the operation in which the failure has +occurred, it is best to pass on to some later work which does +not demand this particular accomplishment, or to rest a while, +and re-attack the difficulty when refreshed.</p> + +<p><a name="Sec_3_1" id="Sec_3_1"></a><span class="ssfont">Cutting Glass Tubes.</span>—The simplest method of cutting +a glass tube is to make a sharp scratch with a file across the +glass at the point where it is desired to cut it, and on pulling +apart the two ends, it will break clean off. It is important +that the file be sharp. In pulling apart the ends the +scratch should be held upwards, and the pull should have +a downward direction, which will tend to open out the +scratch. In the case of a large tube, a scratch will not +ensure its breaking clean across. The tube must be filed +to some depth, half-way, or even all round it. A good<span class='pagenum'><a name="Page_27" id="Page_27">[27]</a></span> +way of breaking a tube is to place the file in the table +after scratching the glass, to hold the glass tube above +its edge with one hand on each side of the scratch, and +to strike the under side of the tube a sharp blow upon +the edge of the file, directly beneath the scratch. In this +way very even fractures of large and moderately thin tubes +may be made. It answers particularly well for removing short +ends of tube, not long enough to hold; the tube is held +firmly upon the file, and a sharp blow given to the short end +with a piece of large tube or a key.</p> + +<p>A file whose faces have been ground till they are nearly +smooth, so as to leave very finely-serrated edges, will be +found useful for cutting glass tubes. Such a file should +be used almost as a knife is used for cutting a pencil in +halves.</p> + +<p>The simple methods just described are too violent to be +applied to delicate apparatus, too tedious when employed upon +the largest tubes, and very difficult to apply when the tube to +be cut is very thin, or too short to permit the operator to get +a good grip of it on either side of the file mark. In such +cases, one or other of the following methods will be useful:—</p> + +<p>1. Make a scratch with a file, and touch it with the end of +a <i>very small</i> piece of glass drawn out and heated at the tip +to its melting point. It is important that the heated point of +glass be very small, or the fracture is likely to be uneven, or to +spread in several directions. Also, it is best to use hot soda +glass for starting cracks in tubes of soda glass, and lead glass for +doing so in lead glass tubes. If the crack does not pass quite +round the tube, you may pull it asunder, as previously +described, or you may bring the heated piece of glass with +which the crack was started to one end of the crack, and +slowly move it (nearly touching the glass) in the required +direction; the crack will extend, following the movements of +the hot glass. Instead of hot glass, pastils of charcoal are +sometimes employed for this purpose. They continue to burn<span class='pagenum'><a name="Page_28" id="Page_28">[28]</a></span> +when once lighted, and there is no need to re-heat them from +time to time. They should be brought as close to the glass as +is possible without touching it, and, when no longer needed, +should be extinguished by placing the lighted end under +sand, or some other incombustible powder, for they must not +be wetted.</p> + +<p>2. A method much practised by the makers of sheet glass, +and suitable for large objects, is to wrap a thread of hot +glass round the tube, at once removing it, and touching any +point of the glass which the thread covered with water or a +cold iron, when a crack will be started and will pass round +the glass where it was heated by the thread.</p> + +<p>3. Tubes which are large and slightly conical may have a +ring of red-hot iron passed over them till it comes into contact +with the glass, then, the iron being removed, and a point +on the heated glass being at once touched with cold iron as +before, it will break as desired. Or a string, moistened with +turpentine, may be loosely twisted round the tube, and the +turpentine ignited, afterwards the application of sudden cold +to any point on the zone of hot glass will usually start a crack, +which, if necessary, may be continued in the usual manner. +The last three methods are chiefly useful in dealing with the +largest and thickest tubes, and with bottles.</p> + +<p>A fairly stout copper wire, bent into the form of a bow so +that it can be applied when hot to a considerable surface of a +glass tube, will be found superior to the point of hot glass or +metal usually employed, for leading cracks in glass tubes. +With such a wire a tube can be cut so that the cross section +of the end is at any desired angle to the axis of the tube, with +considerable precision. I am indebted for this suggestion to +Mr. Vernon Boys and Dr. Ebert.</p> + +<div class="figright"><img src="images/illo037sm.jpg" alt="Bending Glass Tube" /><a name="Fig_6" id="Fig_6"></a> +<p class="caption"><span class="smcap">Fig. 6.</span></p></div> + +<p><a name="Sec_3_2" id="Sec_3_2"></a><span class="ssfont">Bending Glass Tubes.</span>—The blow-pipe flame is not a +suitable source of heat for bending tubes, except in certain +cases which will be mentioned in a subsequent paragraph.<span class='pagenum'><a name="Page_29" id="Page_29">[29]</a></span> +For small tubes, and those of moderate size, a fish-tail burner, +such as is used for purposes of illumination, will answer best. +Use a flame from one to two inches in breadth—from <i>A</i> to <i>A</i> +(<a href="#Fig_6">Fig. 6</a>), according to the size of the tube which is to be bent. +If the length of tube that is heated be less than this, the bend +will probably buckle on its concave side.</p> + +<p>The tube to be heated should be held in the position +shown in <a href="#Fig_6">Fig. 6</a>, supported by the hands on each side. It +should be constantly rotated in the flame, that it may be +equally heated on all sides. In the figure the hands are +represented above the tube, with their backs upwards. A +tube can be held equally well from below, the backs of the +hands being then directed downwards, and this, I think, is +the more frequent habit. It is difficult to say which position +of the hands is to be preferred. I lately observed how a +tube was held by three skilful amateurs and by a professional +glass-blower. All the former held the tube with the hands +below it. The latter, however, held it from above, as in +<a href="#Fig_6">Fig. 6</a>. He, however, was working with a rather heavy piece +of tube, and I am inclined myself to recommend that position +in such cases. During a long spell of work, the wrist may be +rested from time to time by changing the position of the +hands.</p> + +<p>When the tube has softened, remove it from the flame, and<span class='pagenum'><a name="Page_30" id="Page_30">[30]</a></span> +gently bend it to the desired angle. The side of the tube +last exposed to the flame will be slightly hotter, and therefore +softer, than that which is opposite to it. This hotter side +should form the concave side of the bent tube.</p> + +<div class="figleft"><img src="images/illo038sm.jpg" alt="Bent Glass Tube" /><a name="Fig_7" id="Fig_7"></a> +<p class="caption"><span class="smcap">Fig. 7.</span></p></div> + +<p>The exact condition in which the glass is most suitable for +bending can only be learned by making a few trials. If it is too +soft in consequence of being overheated, the sides will collapse. +If, in the endeavour to heat the side <i>A</i> of <a href="#Fig_7">Fig. 7</a> a little +more than <i>B</i>, <i>B</i> is insufficiently heated, the tube will be likely +to break on the convex side <i>B</i>. If the bent tube be likely to +become flattened, and this cannot always be prevented in +bending very thin tubes, the fault may be avoided by blowing +gently into one end of the tube whilst bending it, for +which purpose the other end should be closed beforehand. +A tube already flattened may, to some extent, be blown into<span class='pagenum'><a name="Page_31" id="Page_31">[31]</a></span> +shape after closing one end and re-heating the bent portion, +but it is not easy to give it a really good shape.</p> + +<p>When making a bend like that in <a href="#Fig_7">Fig. 7</a>, to secure that +the arms of the tube <i>C</i> and <i>D</i>, and the curve at <i>B</i>, shall be in +one plane, the tube should be held in a position perpendicular +to the body, and brought into the position shown in the +figure during bending, by which means it will be found easy +to secure a good result. Lead glass tubes must be removed +from the flame before they become hot enough to undergo +reduction. If they should become blackened, however, the +stain may be removed by re-heating in the oxidising flame +(see <a href="#Page_18">p. 18</a>).</p> + +<p>When a very sharp bend is to be made, it is sometimes +best to heat a narrow zone of the glass rather highly in the +blow-pipe flame, and to blow the bend into shape at the +moment of bending it, as previously described, one end +having been closed for that purpose beforehand. Lead +glass should be heated for this purpose in the oxidising +flame (<a href="#Page_17">pp. 17</a> to <a href="#Page_22">22</a>).</p> + +<p>The processes of bending large tubes, making <span class="ssfont">U</span>-tubes +and spiral tubes, are more difficult operations, and will be +explained in <a href="#Ch_4">Chap. IV</a>.</p> + +<p><a name="Sec_3_3" id="Sec_3_3"></a><span class="ssfont">Rounding and Bordering the Ends of Tubes.</span>—After +cutting a piece of glass tube in two pieces, the sharp +edges left at its ends should be rounded by holding them in +a flame for a few moments till the glass begins to melt. The +oxidising point of a pointed flame may be used for both kinds +of glass. The flame will be coloured yellow by soda glass at +the moment of melting. This indication of the condition of +soda glass should be noted, for it serves as a criterion of the +condition of the glass. The ends of soda glass tubes may +also be rounded in the flame of a common Bunsen’s burner.</p> + +<p>When the end of a tube is to be closed with a cork or<span class='pagenum'><a name="Page_32" id="Page_32">[32]</a></span> +stopper, its mouth should be expanded a little, or <span class="ssfont">bordered</span>. +To do this, heat the end of the tube by rotating it in +the flame till it softens, then remove it from the flame, at +once introduce the charcoal cone (<a href="#Fig_5">Fig. 5</a>, <a href="#Page_11">p. 11</a>), and rotate +it with gentle pressure against the softened glass till the +desired effect is produced. In doing this it is very important +that the end of the tube shall be uniformly heated, in order +that the enlargement shall be of regular form. If the tube +cannot be sufficiently expanded at one operation, it should be +re-heated and the process repeated.</p> + +<p>Borders, such as are seen on test-tubes, are made by pressing +the softened edge of the tube against a small iron rod. +The end of the rod should project over the softened edge of +the tube at a slight angle, and be pressed against it, passing +the rod round the tube, or rotating the tube under the rod.</p> + +<p><a name="Sec_3_4" id="Sec_3_4"></a><span class="ssfont">Sealing</span>, that is closing the ends of tubes, or other +openings, in glass apparatus.</p> + +<p>In performing this and all the other operations of glass +blowing, the following points must be constantly kept in +mind:—</p> + +<p>(<i>a.</i>) That it is rarely safe to blow glass whilst it is still in the +flame, except in certain special cases that will be mentioned +subsequently. Therefore always remove apparatus from the +flame before blowing.</p> + +<p>(<i>b.</i>) That when heating glass tubes, unless it is specially +desired to heat one portion only, the tube must be constantly +rotated in the flame to ensure that it shall be uniformly +heated, and to prevent the tube or mass of glass from assuming +an irregular form.</p> + +<p>(<i>c.</i>) Always blow gently at first, and slowly increase the +force applied till you feel or see the glass giving way. It is +a good plan to force the air forward in successive short blasts +rather than in one continued stream.</p> + +<div class="figright"><img src="images/illo042sm.png" alt="Sealing End of Tube" /><a name="Fig_8" id="Fig_8"></a> +<p class="caption"><span class="smcap">Fig. 8.</span></p></div> + +<p><span class='pagenum'><a name="Page_33" id="Page_33">[33]</a></span> +(<i>d.</i>) When it is necessary to force air into tubes of fine bore, +such as thermometer tubes, the mouth must not be used, for +moisture is thereby introduced into the tube, which it is +very difficult to remove again in many cases. All tubes of +very small bore should be blown with the aid of an india-rubber +blowing-bottle, such as are used for spray-producers, +Galton’s whistles, etc. The tube to be blown must be +securely fixed to the neck of the bottle, which is then held +in one hand, and air is forced from it into the tube as it is +required. These bottles are frequently of service to the +glass-blower—<i>e.g.</i>, when tubes of very fine bore have to be +united, it is necessary to maintain an internal pressure +slightly exceeding that of the air throughout the operation, +in order to prevent the viscous glass from running together +and closing the tube. An india-rubber blowing-ball is very +convenient for this purpose.</p> + +<p>To seal the end of a glass tube (<a href="#Fig_8">Fig. 8</a>), adjust the flame +so that it will heat a zone of glass about as broad as the +diameter of the tube to be sealed (see <i>A</i>, <a href="#Fig_8">Fig. 8</a>). Hold +the tube on each side of the point where it is to be sealed in +the manner described in the description of bending glass +tubes (<a href="#Page_28">p. 28</a>). Bring the tube gradually into the flame, +and heat it with constant rotation, till the glass softens (for +lead glass the oxidising flame must be used, as has been +already explained).<a name="Fnanchor_6" id="Fnanchor_6"></a><a href="#Fn_6" class="fnanchor">[6]</a> When the glass begins to thicken, +gently pull asunder the two ends, taking care not to pull out +the softened glass too much, but to allow the sides to fall +together, as shown at <i>A</i>. When this has occurred, heat +the glass at the narrow part till it melts, and pull asunder<span class='pagenum'><a name="Page_34" id="Page_34">[34]</a></span> +the two ends. The closed end should present the appearance +shown at <i>D</i>. If the glass be drawn out too quickly its +thickness will be unduly reduced, +and it will present the +appearance shown at <i>B</i>. In +that case apply a pointed +flame at <i>b</i>, and repeat the +previous operation so as to +contract the tube as at <i>c</i>, +taking care not to allow the +glass to become much increased +nor decreased in thickness.</p> + +<p>If a considerable mass of +glass be left at <i>d</i>, it may be +removed by heating it to redness, +touching it with the +pointed end of a cold glass +tube, to which it will adhere, +and by which it may be pulled +away.</p> + +<p>When the end of the tube +presents the appearance shown +in the diagram <i>D</i>, and the +mass of glass at <i>d</i> is small, the +small lump that remains must be removed by heating it till +it softens, and <i>gently</i> blowing with the mouth, so as to round +the end and distribute the glass more regularly, as shown in <i>E</i>. +The whole end, from the dotted line <i>e</i>, must then be heated +with constant rotation in the flame. If this final heating of +the end <i>e</i> be done skilfully, the glass will probably collapse +and flatten, as at <i>F</i>. The end must then be gently blown +into the form shown at <i>G</i>.</p> + +<p>If a flat end to the tube be desired, the tube may be left<span class='pagenum'><a name="Page_35" id="Page_35">[35]</a></span> +in the condition shown by <i>F</i>, or a thin rounded end may be +flattened by pressure on a plate of iron.</p> + +<p>If a concave end be wished for, it is only necessary to gently +suck air from the tube before the flattened end has become +solid.</p> + +<div class="figleft"><img src="images/illo043sm.png" alt="Waste Tube as Handle" /><a name="Fig_9" id="Fig_9"></a> +<p class="caption"><span class="smcap">Fig. 9.</span></p></div> + +<p>In each case, <i>immediately</i> after the tube is completed, it +must be closely wrapped in cotton wool and left to cool. +With good lead glass this last process, though advantageous, +is not absolutely necessary; and as glass cools slowly when +enveloped in cotton wool, this precaution may frequently +be neglected in the case of apparatus made from lead glass.</p> + +<p>In order to draw out tubes +for sealing, close to one end, +and thus to avoid waste of +material, it is a good plan to +heat simultaneously the end +of the glass tube <i>A</i> which is +to be sealed, and one end of a piece of waste tube <i>E</i> of about +the same diameter, and when they are fused to bring them +together as at <i>DD</i> (<a href="#Fig_9">Fig. 9</a>). <i>E</i> will then serve as a handle in +the subsequent operations on <i>A</i>. Such a rough joint as that +at <i>D</i> must not be allowed to cool too much during the work in +hand, or <i>E</i> and <i>A</i> may separate at an inconvenient moment. +Or the glass at the end of the tube may be pressed together +to close the tube, and the mass of glass may be seized with a +pair of tongs and drawn away.</p> + +<p><a name="Sec_3_5" id="Sec_3_5"></a><span class="ssfont">Choking, or Contracting the Bore of a Glass +Tube.</span>—If it be not desired to maintain the uniformity of +external dimensions of the tube whilst decreasing the diameter +of the bore, the tube may be heated and drawn out as described +in the description of sealing tubes on <a href="#Page_32">pp. 32</a>-<a href="#Page_35">35</a>. This may +be done as shown at <i>A</i> or <i>B</i> in <a href="#Fig_8">Fig. 8</a>, according to the use +to which the contracted tube is to be put.</p> + +<div class="figright"><img src="images/illo044sm.png" alt="Unchanged External Diameter" /><a name="Fig_10" id="Fig_10"></a> +<p class="caption"><span class="smcap">Fig. 10.</span></p></div> + +<p><span class='pagenum'><a name="Page_36" id="Page_36">[36]</a></span>Greater strength and elegance will be secured by preserving +the external diameter of the tube unchanged +throughout, as shown in <a href="#Fig_10">Fig. 10</a>. For this purpose heat the +tube with the pointed flame, if it be small, or in the brush +flame if it be of large size, constantly rotating it till the +glass softens and the sides show an inclination to fall together, +when this occurs, push the +two ends gently towards <i>A</i>. +If the tube should become +too much thickened at <i>A</i>, +the fault may be corrected by +removing it from the flame and gently pulling the two ends +apart till it is of the proper size. If the bore at the contracted +part of the tube should become too much reduced, it +may be enlarged by closing one end of the tube with a small +cork, and blowing gently into the open end after sufficiently +heating the contracted part. The tube should be rotated +during blowing or the enlargement produced may be +irregular.</p> + +<div class="figleft"><img src="images/illo045asm.png" alt="Wide Tube with Narrow Extremities" /><a name="Fig_11" id="Fig_11"></a> +<p class="caption"><span class="smcap">Fig. 11.</span></p></div> + +<p>When the external diameter of the tube is to be increased +as well as its bore diminished, press together the ends of a +tube heated at the part to be contracted, as already described, +and regulate the size of the bore by blowing into +the tube if at any time it threatens to become too much +contracted.</p> + +<p><a name="Sec_3_6" id="Sec_3_6"></a><span class="ssfont">Widening Tubes.</span>—Tubes may be moderately expanded +at their extremities by means of the charcoal cone (see <a href="#Sec_3_3">Bordering</a>, +<a href="#Page_31">p. 31</a>). They may be slightly expanded at any other part +by closing one end and gently blowing into the open end of +the tube, after softening the glass at the part to be widened +before the blow-pipe. But the best method of obtaining a +wide tube with narrow extremities (<a href="#Fig_11">Fig. 11</a>) is to join pieces<span class='pagenum'><a name="Page_37" id="Page_37">[37]</a></span> +of narrow tube <i>AA</i> to the ends of a piece of wider tube <i>B</i> of +the desired dimensions. The method of performing this +operation is described under <a href="#Sec_3_8">welding</a>, on <a href="#Page_39">pp. 39</a>-<a href="#Page_47">47</a>.</p> + +<div class="figright"><img src="images/illo045bsm.png" alt="Piercing a Tube" /><a name="Fig_12" id="Fig_12"></a> +<p class="caption"><span class="smcap">Fig. 12.</span></p></div> + +<p><a name="Sec_3_7" id="Sec_3_7"></a><span class="ssfont">Piercing Tubes.</span>—The glass-blower very frequently +requires to make a large or small opening in some part of a +tube or other piece of apparatus. This is known as piercing. +Suppose it is desired to make a small hole at the point <i>a</i> in +<i>A</i> (<a href="#Fig_12">Fig. 12</a>). When the tube has been brought to the flame +with the usual precautions, allow the end of the pointed flame +to touch it at <i>a</i> till an area corresponding to the desired size +of the opening is thoroughly softened. Then expand the +softened glass by blowing to the form shown at <i>B</i>. Re-heat +<i>a</i>, blow a small globe as at <i>C</i>, and carefully break the thin +glass, then smooth the rough edges by rotating them in +the flame till they form a mouth like that of <i>D</i>. Instead of +leaving the bulb to be broken at the third stage <i>C</i>, it is a good +plan to blow more strongly, so that the bulb becomes very +thin and bursts, the removal of the thin glass is then accompanied +by less risk of producing a crack in the thicker parts +of the glass. Openings may be made in a similar manner in +the sides of tubes or in globes, in fact, in almost any position on<span class='pagenum'><a name="Page_38" id="Page_38">[38]</a></span> +glass apparatus. If another tube is to be attached at the +opening, it is a good plan to proceed to this operation before +the tube has cooled down.</p> + +<div class="figleft"><img src="images/illo046sm.png" alt="Inserting Platinum Wire" /><a name="Fig_13" id="Fig_13"></a> +<p class="caption"><span class="smcap">Fig. 13.</span></p></div> + +<p>The openings obtained by the method above described are +too large when platinum wires are to be sealed into them. +Suppose that it is necessary to pierce the tube <i>A</i> of <a href="#Fig_13">Fig. 13</a> +in order to insert a platinum wire at <i>a</i>; direct the smallest +pointed flame that will heat a spot of glass to redness on the +point <i>a</i>. When the glass is viscous, touch it with the end of +a platinum wire <i>w</i>, to which the glass will adhere; withdraw +the wire and the viscous glass will be drawn out into a +small tube, as shown at <i>B</i>; by breaking the end of this +tube a small opening will be made. Introduce a platinum +wire into the opening, and again allow the flame to play on +the glass at that point; it will melt and close round the wire. +Before the hot glass has time to cool, blow gently into the +mouth of the tube to produce a slightly curved surface, +then heat the neighbouring parts of the tube till the glass +is about to soften, and let it cool in cotton wool. Unless +this is done, I find that glass tubes into which platinum +wires have been sealed are very apt to break during or after +cooling.</p> + +<p>To ensure that the tube shall be perfectly air-tight, a small<span class='pagenum'><a name="Page_39" id="Page_39">[39]</a></span> +piece of white enamel should be attached to the glass at <i>a</i> +before sealing in the wire.</p> + +<p><a name="Sec_3_8" id="Sec_3_8"></a><span class="ssfont">Uniting Pieces of Glass to Each Other, known +as Welding, or Soldering.</span>—The larger and more complicated +pieces of glass apparatus are usually made in separate +sections, and completed by joining together the several +parts. This is therefore a very important operation, and +should be thoroughly mastered before proceeding to further +work.</p> + +<p>In order to produce secure joints, the use of tubes made of +different kinds of glass must be avoided. Soda glass may be +joined securely to soda glass, especially if the tubes belong to +the same batch, and lead glass to lead glass. But, though by +special care a joint between lead glass and soda glass, if well +made, will often hold together, yet it is never certain that it +will do so.</p> + +<p><i>To join two Tubes of Equal Diameters.</i>—Close one end of +one of the tubes with a small cork. Heat the open end of +the closed tube, and either end of the other tube in a small +flame until they are almost melted, taking care that only the +ends of the tubes are heated, and not to let the glass be +thickened; bring the two ends together with sufficient pressure +to make them adhere, but not sufficient to compress the +glass to a thickened ring. Before the joint has time to cool too +much, adjust your blow-pipe for a pointed flame, if you are +not already working with that kind of flame, and allow the +point of the flame to play on any spot on the joint till it is +heated to redness; rotate the tube a little so as to heat the +glass adjacent to that which is already red-hot, and repeat this +till the whole circumference of the rough joint has been<span class='pagenum'><a name="Page_40" id="Page_40">[40]</a></span> +heated.<a name="Fnanchor_7" id="Fnanchor_7"></a><a href="#Fn_7" class="fnanchor">[7]</a> Repeat the operation last described, but, when each +spot is red-hot, blow gently into the open end of the tube so +as to slightly expand the viscous glass. Finally, rotate the +whole joint in the flame till the glass is softened, and blow +gently as before into the open end of the tube, still rotating it, +in order that the joint may be as symmetrical as possible. +If in the last operation the diameter of the joint becomes +greater than that of the rest of the tube, it may be cautiously +re-heated and reduced by pulling it out, or this may be secured +by gently pulling apart the two ends, whilst the operator +blows it into its final shape.</p> + +<div class="figright"><img src="images/illo048sm.png" alt="Joining Small Tubes" /><a name="Fig_14" id="Fig_14"></a> +<p class="caption"><span class="smcap">Fig. 14.</span></p></div> + +<p>When small tubes, or tubes of fine bore, are to be +joined, in order to prevent +the fused glass from +running together and +closing the tube, it is a +good plan to border and +enlarge the ends that are +to be united, as at <i>A</i> (<a href="#Fig_14">Fig. 14</a>). Some glass-blowers prefer +to border all tubes before uniting them.</p> + +<p>When a narrow tube is to be joined to one that is only +slightly wider, expand the end of the narrow tube till it +corresponds in size to the larger tube. If the tube be too +narrow to be enlarged by inserting a charcoal cone, seal one +end and pierce it as directed (on <a href="#Page_37">p. 37</a>).</p> + +<p>For joining small thin-walled tubes Mr. Crookes recommends +the use of a small Bunsen flame.</p> + +<div class="figleft"><img src="images/illo049sm.png" alt="Joining Unequal Size Tubes" /><a name="Fig_15" id="Fig_15"></a> +<p class="caption"><span class="smcap">Fig. 15.</span></p></div> + +<p>In welding pieces of lead glass tube, take care that the +heated glass is perfectly free from reduced lead at the<span class='pagenum'><a name="Page_41" id="Page_41">[41]</a></span> +moment when the two ends of viscous glass are brought into +contact.</p> + +<p><i>To join Tubes of Unequal Sizes End to End</i> (<a href="#Fig_15">Fig. 15</a>).—Draw +out the larger tube and cut off the drawn-out end +at the part where its diameter is equal to that of the smaller +tube, then seal the smaller tube to the contracted end of +the larger according to the directions given for joining tubes +of equal size. When a good joint has been made, the tube +presents the appearance of <i>A</i>, <a href="#Fig_15">Fig. 15</a>, the union being at +about <i>bb</i>. Next heat the whole tube between the dotted +lines <i>aa</i>, and blow it into the shape of <i>B</i> in which the dotted +line <i>dd</i> should correspond to the actual line of junction of +the two tubes.</p> + +<p>In making all joints it is important to leave no thick +masses of glass about them. If the glass be fairly thin and +uniformly distributed, it is less likely to break during or after +annealing under any circumstances, and especially if it has to +bear alternations of temperature.</p> + +<p><i>Joining a Tube to the Side of another Tube</i> (<a href="#Fig_16">Fig. 16</a>).—One of +the tubes must be pierced as at <i>A</i> in <a href="#Fig_16">Fig. 16</a> (for the method, +see <a href="#Page_37">p. 37</a>), and its two ends closed with small pieces of cork. +The edges of the opening, and one end of the other tube,<span class='pagenum'><a name="Page_42" id="Page_42">[42]</a></span> +must then be heated till they melt, and united by pressing +them together. The joint may then be finished as before.</p> + +<div class="figright"><img src="images/illo050sm.png" alt="Making T-joint" /><a name="Fig_16" id="Fig_16"></a> +<p class="caption"><span class="smcap">Fig. 16.</span></p></div> + +<p>A properly blown joint will not present the appearance of +<i>B</i> (<a href="#Fig_16">Fig. 16</a>), but rather that of <i>C</i>. This is secured by directing +the pointed flame upon the glass at <i>aa</i> (<i>B</i>) spot by spot, and +blowing out each spot when it is sufficiently softened. If the +tubes are large, the whole joint should subsequently be heated +and blown, but in the case of small tubes this is of less importance. +Finally it is to be wrapped whilst hot in cotton +wool for the annealing process.</p> + +<p>If a second tube has to be joined near to the first one, +say at <i>b</i>, it is well to proceed with it before the joint first +made cools down, and the joint first made, especially if soda +glass be used, must be held in the flame from time to time +during the process of making the second joint to keep it hot; +if this be not done the first joint is very likely to break. A +joint previously made may, however, be re-heated, if well +made and well annealed.</p> + +<p>A three-way tube, like that in <a href="#Fig_17">Fig. 17</a>, is made by bending +<i>A</i> (Fig. 16) to an angle, and joining <i>B</i> to an opening blown +<span class='pagenum'><a name="Page_43" id="Page_43">[43]</a></span> +on the convex side of the angle; or, <i>A</i> of <a href="#Fig_16">Fig. 16</a> may be +bent as desired after attaching <i>B</i> in the ordinary +way.</p> + +<div class="figleft"><img src="images/illo051asm.png" alt="Three-Way Tube" /><a name="Fig_17" id="Fig_17"></a> +<p class="caption"><span class="smcap">Fig. 17.</span></p></div> + +<p>Tubes may also be joined to openings made +in the sides of globes or flasks; great care +must be taken, however, especially if the walls +of the globe be thin, to secure that the tube +is well attached to the mouth of the opening +when the melted ends are first brought into +contact, for, with thin glass, any hole that may +be left will probably increase whilst the joint is being blown +into shape, owing to cohesion causing the glass to gather in a +thickened ring round an enlargement of the original opening.<a name="Fnanchor_8" id="Fnanchor_8"></a><a href="#Fn_8" class="fnanchor">[8]</a></p> + +<p>In order to unite a tube of soda glass to a tube of lead +glass, the end of the soda glass tube must be carefully covered +with a layer of soft arsenic glass.<a name="Fnanchor_9" id="Fnanchor_9"></a><a href="#Fn_9" class="fnanchor">[9]</a> This must be done so +perfectly that when the ends to be united are brought +together the lead and soda glass are separated by the enamel +at every point.</p> + +<p><i>To Seal a Tube inside a Larger Tube or Bulb.</i>—Suppose that +an air-trap (3 of <a href="#Fig_18">Fig. 18</a>) is to be constructed from a small +bulb (<i>A</i>) blown on a glass tube (1).</p> + +<div class="figright"><img src="images/illo051bsm.png" alt="Sealing a Tube Inside a Larger Tube" /><a name="Fig_18" id="Fig_18"></a> +<p class="caption"><span class="smcap">Fig. 18</span></p></div> + +<p>Either cut off the tube close to the bulb at <i>B</i>, or better, +remove the end by melting the glass and pulling it away<span class='pagenum'><a name="Page_44" id="Page_44">[44]</a></span> +from <i>B</i>, and then pierce <i>A</i> at <i>B</i>, No. 2, by heating the glass +there and blowing out a small bulb as described under Piercing.</p> + +<p>Prepare a tube (4) drawn out at <i>E</i> with a bulb blown +at <i>D</i>. Insert <i>E</i> into the opening <i>B</i>, press <i>D</i> well against +the mouth <i>B</i> and slowly rotate before the blow-pipe till <i>D</i> +adheres to <i>B</i>. Then heat and blow the joint spot by spot +as in other cases, taking care that the glass is blown out on +each side of the joint; lastly, heat the whole joint between <i>aa</i>, +and blow it into its final shape.</p> + +<p>These joints are very apt to break after a few minutes or +hours if the glass of <i>D</i> be much thicker than that of the bulb +<i>A</i>. They should be wrapped in cotton wool for annealing +as soon as possible, as the rate at which the tube <i>E</i> cools is +likely to be less rapid than that of the parts of the apparatus +which are more freely exposed to the air; therefore all such +internal joints require very careful annealing, and they should +always be made as thin as is consistent with the use to which +they are to be put.</p> + +<p>Tubes may also be sealed into the ends or sides of larger +tubes by piercing them at the point at which the inserted +tube is to be introduced, and proceeding as in the case of the +air-trap just described.</p> + +<p>Ozone generators of the form shown on next page (<a href="#Fig_19">Fig. 19</a>), +afford an interesting example of the insertion of smaller tubes +into larger.</p> + +<p>On account of the small space that may be left between +the inner and outer tubes of an ozone generator, and of +the length of the inner tube, its construction needs great +care. I find the following mode of procedure gives good +results. Select the pieces of tube for this instrument as free +from curvature as possible. For the inner tube, a tube +12 mm., or rather more, in external diameter, and of rather +thin glass, is drawn out, as for closing, until only a very +narrow tube remains at <i>C</i>, the end of <i>C</i> is closed the area<span class='pagenum'><a name="Page_45" id="Page_45">[45]</a></span> +round <i>C</i> is carefully blown into shape, so that by melting off +<i>C</i> the tube <i>A</i> will be left with a well-rounded end. A small +bulb of glass is next blown on <i>A</i> at <i>B</i>. This bulb must be of +slightly greater diameter than the contracted end <i>E</i> of the +larger tube (II.), so that <i>B</i> will just fail to pass through <i>E</i>. +The length from <i>B</i> to <i>C</i> must not be made greater than +from <i>E</i> to <i>G</i> on the outside tube. The end at <i>C</i> is then to +be cut off so as to leave a pin-hole in the end of <i>A</i>.</p> + +<div class="figleft"><img src="images/illo053sm.png" alt="Ozone Generator" /><a name="Fig_19" id="Fig_19"></a> +<p class="caption"><span class="smcap">Fig. 19.</span></p></div> + +<p>The outer tube (II.), whose diameter may be 5 or 6 mm. +greater than that of <i>A</i>, is prepared by sealing a side tube on +it at <i>F</i>, after previously contracting the end <i>E</i>. For this +purpose the end <i>E</i> should be closed and rounded, and then +re-heated and blown out till the bulb bursts. To ensure that +the diameter of the opening is less than that of the tube, care +must be taken not to re-heat too large an area of the end +before blowing it out. It is very important that the cross<span class='pagenum'><a name="Page_46" id="Page_46">[46]</a></span> +section at <i>E</i> shall be in a plane at right angles to the axis of +the tube.</p> + +<p>Wrap a strip of writing paper, one inch in breadth, closely +round the end of <i>A</i> at <i>C</i> till the tube and paper will only just +pass easily into the mouth <i>D</i> of the outer tube, push the inner +tube <i>A</i>, with the paper upon it, into <i>D</i>, and when the paper is +entirely within <i>D</i>, withdraw <i>A</i>, and cautiously push the paper a +little further into the outer tube. Insert <i>A</i> into <i>DE</i> through +<i>E</i>, so that the bulb <i>B</i> is embraced by <i>E</i>. Close <i>D</i> with a +cork. Ascertain that the paper does not fit sufficiently +tightly between the two tubes to prevent the free passage of +air, by blowing into the mouth <i>K</i> of <i>A</i>. Air should escape +freely from <i>E</i> when this is done. Gradually bring the line of +contact of <i>B</i> and <i>E</i> and the surrounding parts of the tube +before a pointed flame, after previously warming them by holding +near a larger flame, and rotate them before the flame so +that the glass may soften and adhere. Then heat the joint +spot by spot as usual. In blowing this joint, take care that +the glass on each side of the actual joint is slightly expanded. +It should present the form shown by the dotted lines +in III. (these are purposely exaggerated, however). Finally, +heat the whole joint between the lines <i>JI</i> till it softens, and +simultaneously blow and draw it into its final shape as seen +at III.</p> + +<p>The side tube <i>F</i> should not be too near the end <i>E</i>. If, +however, it is necessary to have them close together, the joint +<i>F</i> must be very carefully annealed when it is made; it must +also be very cautiously warmed up before the construction of +the joint at <i>H</i> is begun, and must be kept warm by letting +the flame play over it from time to time during the process +of making the latter joint.</p> + +<p>A good joint may be recognised by its freedom from lumps +of glass, its regularity of curve, and by a sensibly circular +line at <i>H</i>, where the two tubes are united.</p> + +<p><span class='pagenum'><a name="Page_47" id="Page_47">[47]</a></span>When the joint after annealing has become quite cold, the +pin-hole at <i>C</i> on the inner tube may be closed, after removing +the paper support, by warming the outer tube, and then +directing a fine pointed flame through <i>D</i> on to <i>C</i>. And the +end <i>D</i> of the outer tube may be closed in the ordinary +manner, or a narrow tube may be sealed to it. As the end of +glass at <i>D</i> will be too short to be held by the fingers when +hot, another piece of tube of similar diameter must be +attached to it to serve as a handle (see <a href="#Page_35">p. 35</a>, <a href="#Fig_9">Fig. 9</a>).</p> + +<p><a name="Sec_3_9" id="Sec_3_9"></a><span class="ssfont">Blowing a Bulb or Globe of Glass.</span>—For this purpose +it is very important that the glass tube employed shall be of +uniform substance. The size and thickness of the tube to be +employed depends partly on the dimensions of the bulb +desired, and partly on the size of neck that is required for +the bulb. It is easier to blow large bulbs on large-sized +tubes than on those of smaller size. When it is necessary to +make a large globe on a small tube, it can be done, however, +if great care be taken to avoid overheating that part of the +small tube which is nearest to the mass of viscous glass from +which the bulb is to be formed. For the purpose of blowing +a very large bulb on a small tube, it is best to unite a wide +tube to that which is to serve as the neck, as it will save +some time in collecting the necessary mass of glass from +which to form the globe.</p> + +<div class="figright"><img src="images/illo056sm.png" alt="Blowing a Bulb or Globe" /><a name="Fig_20" id="Fig_20"></a> +<p class="caption"><span class="smcap">Fig. 20.</span></p></div> + +<p><i>To blow a Bulb at the End of a Tube.</i>—Select a good piece of +tube, say 1·5 cm. in diameter, and about 30 cm. long; draw +out one end to a light tail (<i>a</i>, <a href="#Fig_20">Fig. 20</a>) about 3 inches in +length. Then heat up a <i>short</i> length of the tube at <i>b</i>, with +a small brush flame, by rotating the glass in the flame, and +gently press it together when soft to thicken it; blow into it +if necessary to preserve the regularity of its figure. Repeat +this process on the portion of tube nearest to that which<span class='pagenum'><a name="Page_48" id="Page_48">[48]</a></span> +has been first thickened, and so on, till as much glass has +been heated and thickened as you judge will serve to make a +bulb of the size desired. You should have a mass of glass +somewhat resembling that shown at <i>B</i> (<a href="#Fig_20">Fig. 20</a>), but probably +consisting of the results of more successive operations +than are suggested in that diagram. Apply the flame as +before to the narrower parts <i>cc</i> of <i>B</i>, gently compress and +blow until all the small bulbs first made are brought together +into a mass still somewhat resembling the enlarged end of <i>B</i>, +but more nearly cylindrical, with the glass as regularly distributed +as possible, and of such length from <i>d</i> to the contracted +part that the whole of it may easily be heated simultaneously +with the large brush flame of your blow-pipe. Take +great care in the foregoing operations not to allow the sides +of the mass of glass to fall in and run together, and, on the +other hand, do not reduce the thickness of the glass needlessly +by blowing it more than is necessary to give the glass as +regular a form as possible. When you are satisfied with the +mass of glass you have collected, melt off the tail <i>a</i>, and<span class='pagenum'><a name="Page_49" id="Page_49">[49]</a></span> +remove the pointed end of glass that remains, as directed on +page 33. Turn on as large a brush flame as is necessary to +envelop the whole mass of glass that you have collected, and +heat it with constant rotation, so that it may gradually run +together to the form seen at <i>C</i> (<a href="#Fig_20">Fig. 20</a>), taking care that it +does not get overheated near <i>d</i>, or the tube which is to form +the neck will soften and give way.</p> + +<p>The position in which the mass of heated glass is to be +held will depend upon circumstances; if the mass of glass +be not too great, it is best to keep it in a nearly horizontal +position. If the mass of glass be very large, it may be necessary +to incline the end <i>B</i> downwards; but as that is apt +to result in an excess of glass accumulating towards <i>d</i>, avoid +doing so if possible by rotating the glass steadily and rapidly. +If at any time the glass shows indications of collapsing, it +must be removed from the flame and gently blown into shape, +during which operation it may be rotated in the perpendicular +position; indeed, to promote a regular distribution of +the glass by allowing it plenty of time to collect, it is well +from time to time to remove the heated mass of glass from +the flame, and slightly expand it by blowing. Finally, when +a regular mass of glass, such as is shown at <i>C</i> (<a href="#Fig_20">Fig. 20</a>) has +been obtained, remove it from the flame, and blow it to its +final dimensions. A succession of gentle puffs <i>quickly</i> succeeding +each other should be employed, in order that the progress +of the bulb may be more easily watched and arrested at the +right moment. During the process of blowing, the hot glass +must be steadily rotated.</p> + +<p>To collect the glass for blowing a bulb of lead glass, employ +the flame described on <a href="#Page_17">pp. 17</a>-<a href="#Page_22">22</a> for heating lead glass.</p> + +<p>If the tube be held horizontally whilst the globe is blown, +its form will most nearly approach that of a true globe. If it +be held in the perpendicular position, with the mass of glass +depending from it, the form of the bulb will usually be<span class='pagenum'><a name="Page_50" id="Page_50">[50]</a></span> +somewhat elongated. If it be held perpendicularly, with the +mass of glass upwards, the resulting bulb will be flattened.</p> + +<p>When a bulb is not of a sufficiently regular form, it may +sometimes be re-made by re-collecting the glass, and re-blowing +it. The greatest care is needed at the earlier stages of re-heating +to prevent the glass from collapsing into a formless +and unworkable mass. This is to be prevented in all such +cases by gently blowing it into shape from time to time +whilst gathering the glass.</p> + +<div class="figleft"><img src="images/illo058sm.png" alt="Blowing a Bulb Between Two Points" /><a name="Fig_21" id="Fig_21"></a> +<p class="caption"><span class="smcap">Fig. 21.</span></p></div> + +<p><i>To blow a Bulb between two Points</i> (<a href="#Fig_21">Fig 21</a>).—Select a piece of +suitable tube, seal or cork one end, gather together a mass of +glass at the desired part, as directed for blowing a bulb at the +end of a tube; when a mass of glass has been collected of +sufficient thickness, blow it +into shape from the open +end of the tube by a rapid +succession of short blasts of +air, till the expanding glass +attains the desired dimensions. +The tube must be +held horizontally, and must be rotated steadily during the +process. By slightly pressing together the glass while +blowing, the bulb will be flattened; by slightly drawing apart +the two ends of the tube, it will be elongated.</p> + +<p>A pear-shaped bulb may be obtained by gently re-heating +an elongated bulb, say from <i>a</i> to <i>a</i>, and drawing it out. It +is easiest to perform this operation on a bulb which is rather +thick in the glass.</p> + +<p>If the tubes <i>bb</i> are to be small, and a globe of considerable +size is wanted, contract a tube as shown in <a href="#Fig_22">Fig. 22</a>, taking +care that the narrow portions of the tube are about the +same axis as the wider portions, for if this be not the case, the +mouths of the bulb will not be symmetrically placed; seal at +<i>C</i>, cut off the wider tube at <i>B</i>, and make the bulb, as<span class='pagenum'><a name="Page_51" id="Page_51">[51]</a></span> +previously described, from the glass between <i>AA</i>. If, as probably +will be the case, the contracted portions of the tube +be not very regular, they may be cut off, one at a time, near +the bulb, and replaced by pieces of tube of the size desired.</p> + +<div class="figright"><img src="images/illo059sm.png" alt="Large Globe from Small Tube" /><a name="Fig_22" id="Fig_22"></a> +<p class="caption"><span class="smcap">Fig. 22.</span></p></div> + +<p>When a bulb has to be blown upon a very fine tube, for example +upon thermometer tubing, the mouth should not be employed, +for the moisture introduced by the breath is extremely +difficult to remove afterwards. A small india-rubber bottle +or reservoir, such as those which are used in spray-producers, +Galton’s whistles, etc., securely attached to the open end of +the tube, should be used. With the help of these bottles bulbs +can be blown at the closed ends of fine tubes with ease, though +some care is necessary to produce them of good shape, as it +is difficult to rotate the hot glass properly when working in +this way.</p> + +<p><a name="Sec_3_10" id="Sec_3_10"></a><span class="ssfont">Making and Grinding Stoppers.</span>—Apparatus which +is to contain chemicals that are likely to be affected by the +free admission of air, needs to have stoppers fitted to it. +Making a good stopper is a much less tedious process than is +commonly supposed.</p> + +<div class="figleft"><img src="images/illo060sm.png" alt="Making Stoppers" /><a name="Fig_23" id="Fig_23"></a> +<p class="caption"><span class="smcap">Fig. 23.</span></p></div> + +<p>Suppose that the tube I. of <a href="#Fig_23">Fig. 23</a> is to be stoppered at <i>A</i>, +it must be slightly enlarged by softening the end and opening +it with a pointed cone of charcoal; or a conical mouth for +the stopper may be made by slightly contracting the tube +near one end, as at <i>B</i>, cutting off the cylindrical end of the +tube at the dotted line <i>C</i>, and then very slightly expanding +the end at <i>C</i> with a charcoal cone after its edges have been<span class='pagenum'><a name="Page_52" id="Page_52">[52]</a></span> +softened by heat. In either case the conical mouth should +be as long and regular as possible.</p> + +<p>For the stopper take a piece of rather thick tube, of +such size that it will pass easily, but not too easily, into <i>A</i> +or <i>B</i>. Expand this tube at <i>D</i>, as shown in II., by softening +the glass and gently compressing it. The configuration of +the enlarged tube as shown at <i>D</i> may be obtained by heating +and compressing two or more zones of the tube that are +adjacent, one zone being less expanded than the other, so as +to give the sides of the imperfect stopper as nearly as possible +the form shown at <i>D</i>, which, however, is much less regular +than may easily be obtained. Seal off the head of the tube +at <i>H</i>, and heat the glass till it runs together into a nearly +solid mass; compress this with a pair of iron tongs to the +flattened head <i>E</i>. In making <i>D</i>, aim at giving it a form +which will as nearly as possible correspond to that of the +tube into which it is to be ground, and make it slightly +too large, so that only the lower part at <i>D</i> can be introduced +into the mouth of <i>A</i> or <i>B</i>. Before it is ground, the +stopper must be heated nearly to its softening-point and +annealed.</p> + +<p>Moisten <i>D</i> with a solution of camphor in recently distilled<span class='pagenum'><a name="Page_53" id="Page_53">[53]</a></span> +turpentine, and dust the wet surface with finely-ground +emery, then gently grind it into its place till it fits properly. +In this operation the tail <i>G</i>, which should fit loosely into +the tube <i>A</i>, will be of assistance by preventing <i>D</i> from +unduly pressing in any direction on <i>A</i> in consequence +of irregular movements. The stopper should be completely +rotated in grinding it. It must not be worked backwards +and forwards, or a well-fitting stopper will not be +produced. Renew the emery and camphorated turpentine +frequently during the earlier part of the grinding; when +the stopper almost fits, avoid using fresh emery, but +continue to remove the stopper frequently at all stages of +the operation. That added at the earlier stages will be reduced +to a state of very fine division, and will therefore leave +the stopper and mouth of <i>A</i> with smoother surfaces than +fresh emery.<a name="Fnanchor_10" id="Fnanchor_10"></a><a href="#Fn_10" class="fnanchor">[10]</a></p> + +<p><span class="smcap">Note.</span>—The addition of camphor to the turpentine used +for grinding glass is very important. Notwithstanding its +brittle nature, glass will work under a file moistened with +this solution almost as well as the metals. Small quantities +should be made at a time, and the solution should be kept +in a well-closed vessel, for after long exposure to the air +it is not equally valuable.</p> + +<p>If the stopper is to fit a tube contracted like <i>B</i>, it must be +constructed from a piece of tube that will pass through the +contraction at <i>B</i>. The tail <i>GF</i> will not do such good +service as it does in the case of a tube which has been opened +out to receive its stopper, but it will help to guide the +stopper, and should be retained.</p> + +<p>When the stopper has been ground into its place, melt off +the tail at <i>F</i>. The flame must be applied very cautiously, as<span class='pagenum'><a name="Page_54" id="Page_54">[54]</a></span> +glass which has been ground is particularly apt to crack on +heating. To avoid all risk of this, the tail may simply be cut +off, and its edges filed smooth with a file moistened freely +with camphorated turpentine.</p> + +<p>The stoppers of bottles are not made exactly in the +manner described above, though, on occasion, a new stopper +may be made for a bottle by following those directions. Ill-fitting +stoppers, which are very common, can be very easily +re-ground with emery and camphorated turpentine.</p> + +<hr class="l05" /> +<p class="footnote"><a name="Fn_6" id="Fn_6"></a><span class="label"><a href="#Fnanchor_6">[6]</a></span> +Remember that when the lead glass is heated to the proper +temperature it will present an appearance which may be described as a +greenish phosphorescence. At higher temperatures it assumes an +orange-red appearance. If it loses its transparency and assumes a dull +appearance, it must be moved further into the oxidising parts of the +flame.</p> + +<p class="footnote"><a name="Fn_7" id="Fn_7"></a><span class="label"><a href="#Fnanchor_7">[7]</a></span> +Some glass-blowers at once work on the glass as next described, +without this preliminary treatment. I find that some glass, usually soda +glass, will not always bear the necessary movements without breaking +unless first heated all round.</p> + +<p class="footnote"><a name="Fn_8" id="Fn_8"></a><span class="label"><a href="#Fnanchor_8">[8]</a></span> +If such an opening be observed, it may usually be closed by touching +its edges with a fused point of glass at the end of a drawn out tube.</p> + +<p class="footnote"><a name="Fn_9" id="Fn_9"></a><span class="label"><a href="#Fnanchor_9">[9]</a></span> +This can be obtained from Messrs. Powells, Whitefriars Glassworks.</p> + +<p class="footnote"><a name="Fn_10" id="Fn_10"></a><span class="label"><a href="#Fnanchor_10">[10]</a></span> +Mr. Gimmingham recommends giving stoppers a final polish with +rotten-stone (<i>Proceedings of the Royal Society</i>, p. 396, 1876).</p> +<hr class="l05" /> + +<hr class="c05" /><p class='pagenum'><a name="Page_55" id="Page_55">[55]</a></p> +<h2><a name="Ch_4" id="Ch_4"></a>CHAPTER IV.</h2> + +<p class="chap">MAKING THISTLE FUNNELS, <span class="ssfont">U</span>-TUBES, ETC.—COMBINING +THE PARTS OF COMPLICATED APPARATUS—MERCURY, +AND OTHER AIR-TIGHT JOINTS—VACUUM +TAPS—SAFETY TAPS—AIR-TRAPS.</p> + +<p>In Chapter III. the simpler operations used in making the +separate parts of which apparatus is composed have been +described. In this Chapter finished apparatus will be +described, and the combination of the separate parts into +the more or less complicated arrangements used in experiments +will be so far explained as to enable the student to +set up such apparatus as he is likely to require. I have +thought it would be useful that I should add a short account +of various contrivances that have come much into use of +late years for experimenting under reduced pressure, such as +safety taps, air-traps, vacuum joints, etc.</p> + +<div class="figright"><img src="images/illo063sm.png" alt="Electrode Sealed in Glass" /><a name="Fig_24" id="Fig_24"></a> +<p class="caption"><span class="smcap">Fig. 24.</span></p></div> + +<p><a name="Sec_4_1" id="Sec_4_1"></a><span class="ssfont">Electrodes.</span>—On <a href="#Page_38">page 38</a> +(<a href="#Fig_13">Fig. 13</a>) is shown a simple +form of electrode sealed into a glass +tube, which for many purposes answers +very well. But frequently, in order +that there may be less risk of leakage +between the glass and the metal, the +latter is covered for a considerable +part of its length with solid glass, which at one extremity is +united to the apparatus. In <a href="#Fig_24">Fig. 24</a> <i>W</i> is the metal core of +the electrode, and <i>G</i> the glass covering around it. The wire<span class='pagenum'><a name="Page_56" id="Page_56">[56]</a></span> +is fused into the glass, and the glass is then united to the +apparatus; a little white enamel should be applied at one +end and combined with the glass by fusion.</p> + +<p><a name="Sec_4_2" id="Sec_4_2"></a><span class="ssfont">U-Tubes.</span>—A <span class="ssfont">U</span>-tube +is but a particular case of a bent glass tube. It is scarcely possible when bending very large +tubes in the manner described on <a href="#Page_29">p. 29</a> to produce regular +curves of sufficient strength.</p> + +<p>To make a <span class="ssfont">U</span>-tube, or to bend a large tube, close one +end of the tube selected with a cork, soften and compress +the glass in the flame at the part where it is to be bent +till a sufficient mass of glass for the bend is collected, then +remove the mass of glass from the flame, let it cool a little, +and simultaneously draw out the thickened glass, bend it to +the proper form, and blow the bend into shape from the open +end of the tube. Small irregularities may be partly corrected +afterwards.</p> + +<p>To make a good <span class="ssfont">U</span>-tube of large size, and of uniform diameter +from end to end, requires much practice, but to make a +tolerably presentable piece of apparatus in which the two +limbs are bent round till they are parallel, without any considerable +constriction at the bend, can be accomplished without +much difficulty.<a name="Fnanchor_11" id="Fnanchor_11"></a><a href="#Fn_11" class="fnanchor">[11]</a></p> + +<p><a name="Sec_4_3" id="Sec_4_3"></a><span class="ssfont">Spiral Tubes.</span>—These may be made by twisting a tube +gradually softened by heat round a metal cylinder. Spiral +tubes made of small thin tubes possess considerable elasticity,<span class='pagenum'><a name="Page_57" id="Page_57">[57]</a></span> +and have been used by Mr. Crookes for making air-tight +connections between separate pieces of apparatus when a +rigid connection would have been unnecessary and inconvenient. +By the use of such spiral tubes it is possible to combine +comparatively free movement with all the advantages +attached to hermetically-sealed joints.</p> + +<p>To make a flexible spiral tube, mount a copper cylinder +on a screw, so that the cylinder will travel in the direction +of its axis when it is rotated. Fix a fine glass tube +to the cylinder, and direct a flame towards the cylinder so +as to heat and soften the glass, which will then bend to the +form of the cylinder. Gradually rotate the cylinder before +the source of heat, so that fresh portions of tube are successively +brought into position, softened, and bent. Useful spirals +may also be made by hand without a cylinder. As each +length of tube is bent, a fresh length may be united to it +until the spiral is completed. The fine tubes employed are +prepared by heating and drawing out larger tubes.</p> + +<div class="figleft"><img src="images/illo065sm.png" alt="Thistle Funnel" /><a name="Fig_25" id="Fig_25"></a> +<p class="caption"><span class="smcap">Fig. 25.</span></p></div> + +<p><a name="Sec_4_4" id="Sec_4_4"></a><span class="ssfont">Thistle Funnels</span> (<a href="#Fig_25">Fig. 25</a>).—Seal +a moderately thick piece of small glass tube at <i>A</i>, then heat a wide zone of it a little +below <i>A</i> by rotating it horizontally in the blow-pipe flame till +the glass softens, and expand the glass to a bulb, as shown<span class='pagenum'><a name="Page_58" id="Page_58">[58]</a></span> +at <i>B</i> of 1; during the operation of blowing this bulb, the end +<i>A</i> must be directed to the ground.</p> + +<p>Soften the end <i>A</i> and a small portion of <i>B</i> as before, and, +holding the tube horizontally from the mouth, blow out +the end <i>C</i> as at 2. Heat the end of <i>C</i> gradually, till the +glass softens and collapses to the dotted line <i>dd</i>, and at once +blow a steady stream of air into the open end of the tube, +rotating it steadily, till it is about to burst; finally clean off +the thin glass from round the edges of the funnel, which +should have the form shown at 3, and round them. An +inspection of a purchased thistle funnel will generally show +that the head <i>B</i> has been formed from a larger tube sealed +to <i>E</i> at <i>f</i>.</p> + +<p><a name="Sec_4_5" id="Sec_4_5"></a><span class="ssfont">Closing Tubes containing Chemicals</span> for experiments +at high temperatures.—Tubes of the hard glass used for organic +analyses answer best for this +purpose; the operation of drawing +out the end of such a tube +is practically identical with +what has been described under +the head of <a href="#Sec_3_5">choking</a>, <a href="#Page_35">p. 35</a>. A +well-sealed tube presents the appearance of that shown by +<a href="#Fig_26">Fig. 26</a>.</p> + +<div class="figright"><img src="images/illo066sm.png" alt="Well-Sealed Tube" /><a name="Fig_26" id="Fig_26"></a> +<p class="caption"><span class="smcap">Fig. 26.</span></p></div> + +<p>In order to secure a thick end to the point of the tube <i>a</i>, +about an inch or so of the tube near the contracted part +should be warmed a little, if it is not already warm, at the +moment of finally sealing it; the contraction of the air in +the tube, in consequence of the cooling of the warm tube, +will then ensure the glass at <i>a</i> running together to a solid end +when it is melted in the flame.</p> + +<p>If it will be necessary to collect a gas produced during a +chemical action from such a tube, make the contracted end +several inches long, and bend it into the form of a delivery<span class='pagenum'><a name="Page_59" id="Page_59">[59]</a></span> +tube. It will then be possible to break the tip of this under +a cylinder in a trough of liquid.</p> + +<p><a name="Sec_4_6" id="Sec_4_6"></a><span class="ssfont">In order to explain the construction of apparatus +consisting of several parts</span>, it will be sufficient +to take as examples, two very well-known +instruments, and to describe their construction +in detail. From what is learned in studying +these, the student will gather the information +that is wanted.</p> + +<div class="figleft"><img src="images/illo067sm.png" alt="Hofmanଁ Apparatus" /><a name="Fig_27" id="Fig_27"></a> +<p class="caption"><span class="smcap">Fig. 27.</span></p></div> + +<p>1. <i>To make Hofman’s Apparatus for the electrolysis +of water</i> (<a href="#Fig_27">Fig. 27</a>).</p> + +<p>Take two tubes about 35 cm. in length, +and 14 mm. in diameter for <i>AA</i>, join taps <i>TT</i> +to the end <i>B</i> of each of them, draw out the +other end, as shown at <i>D</i>, after sheets of +platinum foil with wires attached to them<a name="Fnanchor_12" id="Fnanchor_12"></a><a href="#Fn_12" class="fnanchor">[12]</a> +have been introduced into the tubes, and +moved by shaking to <i>BB</i>. Then allow the +platinum wires to pass through the opening +<i>D</i> left for the purpose, and seal the glass at +<i>D</i> round the platinum as at <i>E</i>. Pierce the +tubes at <i>JJ</i>, and join them by a short piece of +tube <i>K</i>, about 14 mm. in diameter, to which +the tube <i>T</i>, carrying the reservoir <i>R</i>, has +been previously united. <i>R</i> may be made by +blowing a bulb from a larger piece of tube +attached to the end of <i>T</i>. The mouth <i>M</i> of the reservoir<span class='pagenum'><a name="Page_60" id="Page_60">[60]</a></span> +being formed from the other end of the wide tube afterwards. +One of the taps can be used for blowing through +at the later stages. Each joint, especially those at <i>JJ</i>, must +be annealed after it is blown. Some operators might prefer +to join <i>AA</i> by the tube <i>K</i> in the first instance, then to introduce +the electrodes at <i>E</i> and <i>D</i>. In some respects this plan +would be rather easier than the other, but, on the whole, it +is better to make the joints at <i>JJ</i> last in order, as they are +more apt to be broken than the others during the subsequent +manipulations.</p> + +<div class="figright"><img src="images/illo068sm.png" alt="Vacuum Tube" /><a name="Fig_28" id="Fig_28"></a> +<p class="caption"><span class="smcap">Fig. 28.</span></p></div> + +<p>2. I have before me the vacuum tube shown by <a href="#Fig_28">Fig. 28</a>, in +which the dotted lines relate to details of manipulation only.</p> + +<p>It is usually possible to detect the parts of which a piece of +apparatus has been built up, for even the best-made joints +exhibit evidence of their existence. Thus, although I did not +make the tube that is before me, and cannot therefore pretend +to say precisely in what order its parts were made and put +together, the evidence which it exhibits of joints at the dotted +lines <i>A</i>, <i>B</i>, <i>C</i>, <i>D</i>, <i>E</i>, <i>F</i>, enables me to give a general idea of +the processes employed in its construction, and to explain how +a similar tube might be constructed. I should advise proceeding +as follows:—</p> + +<p>Join a piece of tube somewhat larger than <i>M</i> to its +end <i>A</i>, draw out the other end of the larger tube, and blow +a bulb <i>L</i> as directed on <a href="#Page_47">p. 47</a>. Then seal the electrode <i>R</i> +into the bulb <i>L</i> (<a href="#Page_55">p. 55</a>).</p> + +<p>Blow a similar but larger bulb <i>N</i> from a large piece of<span class='pagenum'><a name="Page_61" id="Page_61">[61]</a></span> +tube sealed between two tubes of similar size to <i>M</i>, as +described at <a href="#Page_50">p. 50</a>. Cut off one of the tubes at <i>B</i>, and join +the bulb <i>N</i> to <i>M</i> at <i>B</i>. Form the bulb <i>Q</i> in the same manner +as in the case of <i>L</i>, seal into it the electrode <i>R</i>, and add the +tube marked by the dotted lines at <i>F</i>.</p> + +<p>Seal a narrow tube <i>P</i> to the end of a larger tube, +and blow out the tube at the joint till the glass is thin +and regular. Take a tube <i>O</i>, of similar size to <i>M</i>, slightly +longer than <i>P</i>, contract its mouth slightly to meet the wide +end of <i>P</i> at <i>D</i>, and after loosely supporting <i>P</i> inside <i>O</i> with a +cork, or otherwise, close the end <i>N</i> of <i>O</i> by sealing or corking it, +and join <i>P</i> to <i>O</i> at <i>D</i>. Cut off <i>O</i> just above <i>D</i> at <i>E</i>, and join it +to the bulb <i>Q</i>, closing either <i>O</i> or <i>F</i> for the purpose. Cut off +the end of <i>O</i> at <i>C</i> parallel to the end of <i>P</i>, and connect <i>O</i> to <i>N</i>, +using <i>F</i> for blowing the joint at <i>C</i>. <i>F</i> may be used subsequently +for introducing any gas into the tube, and, when a +vacuum has been established, may be sealed before the blow-pipe.</p> + +<div class="figleft"><img src="images/illo070sm.png" alt="Combining Parts" /><a name="Fig_29" id="Fig_29"></a> +<p class="caption"><span class="smcap">Fig. 29.</span></p></div> + +<p><a name="Sec_4_7" id="Sec_4_7"></a><span class="ssfont">Modes of combining the Parts of Heavy Apparatus.</span>—It +is often necessary to connect pieces of apparatus +which are too heavy to be freely handled before the blow-pipe, +and which, therefore, cannot be welded together as +described on <a href="#Page_39">p. 39</a>, by some more effective method than +the ordinary one of connecting by india-rubber tubing. For +example, apparatus which is to be exhausted by a Sprengel +air-pump must be attached to the pump by a joint as perfectly +air-tight as can be obtained. This, indeed, often may be +done by welding the apparatus to be exhausted to the air-pump +before the blow-pipe. But such a method is open to the +obvious objection that it is very troublesome to connect and +disconnect the parts as often as may be necessary, and that +there is some risk of accidental breakages. Nevertheless it +may be done on occasion, especially if there be no objection to<span class='pagenum'><a name="Page_62" id="Page_62">[62]</a></span> +the use of the flexible spiral tubes already alluded to. When +the use of a spiral connecting-tube is not admissible the difficulty +is considerably increased. For example, the author +has lately required to attach an ozone generator, of the form +shown by <a href="#Fig_19">Fig. 19</a>, which previously had been cemented into a +heavy copper jacket, to a pressure-gauge rigidly fixed to a support, +and of considerable size. The employment of a flexible +spiral connection was prohibited by the fact that it was necessary +that the volume of the connecting-tube should be but a +small fraction of that of the ozone generator, a condition +which compelled the use of a tube of almost capillary bore, +and of inconsiderable length. At the same time the frailness +of such a connection made it necessary to fix the generator and +pressure-gauge rigidly to their supports, in order to avoid the +possibility of breakage by slight accidental movements of +either of them, and it was obviously necessary to fix the +pieces of apparatus in their final positions before joining +them, lest the fine tube which connected them should be +fractured during adjustment. The possibility of a strain +being caused by the contraction that would occur during +the cooling down of the joint last made had to be provided +for also. The desired object was +effected as follows. In <a href="#Fig_29">Fig. 29</a> <i>A</i> represents +a section of the ozone generator at +the point where the tube to connect it +to the gauge was fixed. <i>B</i> represents the +top of the gauge, with the side tube <i>C</i>, +which was to be connected with that +from <i>A</i>, viz. <i>D</i>. The ends of <i>C</i> and +<i>D</i> were expanded as shown at <i>D</i> (by +melting them and blowing them out), +so that one of them, made rather smaller than the other, +could be overlapped by the larger one. <i>A</i> and <i>B</i> being +rigidly fixed in their final positions, with <i>C</i> and <i>D</i> in<span class='pagenum'><a name="Page_63" id="Page_63">[63]</a></span> +contact, as shown in the figure, all openings in the +apparatus were closed, except one, to which was attached +an india-rubber blowing-bottle by means of a tube of +india-rubber long enough to be held in the hand of the +operator, and to allow him to observe the operation of joining +the tubes at <i>D</i>. When everything was in readiness, a very +small-pointed flame from a moveable blow-pipe held in the +hand was directed upon the glass at <i>D</i> till it melted and the +two tubes united. To prevent the fine tube when melted +from running into a solid mass of glass, and so becoming +closed, a slight excess of pressure was maintained inside +the apparatus during the operation by forcing air into it +with the india-rubber blower from the moment at which <i>C</i> +and <i>D</i> united. A point of charcoal was kept in readiness to +support the softened glass at <i>D</i> in case it showed any tendency +to fall out of shape.</p> + +<p>The <span class="ssfont">V</span>-tube at <i>C</i> served to prevent the subsequent fracture +of the joint in consequence of any strain caused by the contraction +of the glass in cooling.<a name="Fnanchor_13" id="Fnanchor_13"></a><a href="#Fn_13" class="fnanchor">[13]</a></p> + +<p>It is not difficult to connect several pieces of apparatus +successively in this manner, nor is this method only useful +in such cases as that just described. Pieces of apparatus of +great length and weight may be joined in a similar manner, +irrespective of the size of the tubes to be united.</p> + +<div class="figright"><img src="images/illo072sm.png" alt="Simplest Mercury Joint" /><a name="Fig_30" id="Fig_30"></a> +<p class="caption"><span class="smcap">Fig. 30.</span></p></div> + +<p>The ends to be joined, prepared as before, so that one +slightly overlaps the other, must be held firmly in contact by +clamps, and heated in successive portions by a blow-pipe held +in the hand of the operator, each patch of glass being +re-heated and gently blown, after a rough joint has been made. +Finally, a larger flame may be used to heat up the whole +joint for its final blowing. It is important to place the +apparatus so that the operator has free access to it on all +sides. A revolving table might be employed. An assistant<span class='pagenum'><a name="Page_64" id="Page_64">[64]</a></span> +to work the bellows is necessary. Or, better still, air may +be admitted to the blow-pipe from a large gas-bag placed in +some convenient position.</p> + +<div class="figleft"><img src="images/illo073asm.png" alt="Glycerine or Mercury Joint" /><a name="Fig_31" id="Fig_31"></a> +<p class="caption"><span class="smcap">Fig. 31.</span></p></div> + +<p>But in most cases one or other of the following air-tight joints +can be employed, and will be found to be very convenient:—</p> + +<p><a name="Sec_4_8" id="Sec_4_8"></a><span class="ssfont">Mercury Joints.</span>—The simplest form of mercury joint is +shown at <a href="#Fig_30">Fig. 30</a>. <i>A</i> and <i>B</i> are the two tubes which are to +be connected. A larger tube or cup <i>F</i> is attached to <i>A</i> by +the india-rubber tube <i>E</i>, and placed on <i>A</i> so that +the end of <i>B</i> may be brought into contact with <i>A</i> +at <i>C</i>, and connected to it by a well-fitting piece +of india-rubber tube <i>C</i>. The cup <i>E</i> is then +brought into the position shown in <a href="#Fig_30">Fig. 30</a>, and +mercury is introduced till the india-rubber tube at +<i>C</i> is covered. As mercury and glass do not come +into true contact, however, such a joint, though +said to give good results in practice, is not +theoretically air-tight, for air <i>might</i> gradually find +its way between the liquid and the glass. By +covering the mercury with a little sulphuric acid +or glycerine the risk of this occurring may be removed. +The same result may be attained by the use of glycerine in +place of the mercury in the cup <i>F</i>; but glycerine is less +pleasant to work with than mercury.<a name="Fnanchor_14" id="Fnanchor_14"></a><a href="#Fn_14" class="fnanchor">[14]</a></p> + +<p>When sulphuric acid is to be employed in such a joint, +or when for any other reason the use of an india-rubber tube +is undesirable, the joint may consist of a hollow stopper <i>B</i> +(<a href="#Fig_31">Fig. 31</a>), made of glass tube, and ground to fit the neck of a +thistle funnel <i>A</i>. <i>A</i> and <i>B</i> are joined respectively to the +pieces of apparatus to be connected, and connection is +made by placing <i>B</i> in position in the neck of <i>A</i>; the +joint is made air-tight by introducing mercury with strong<span class='pagenum'><a name="Page_65" id="Page_65">[65]</a></span> +sulphuric acid above it into the cup <i>A</i>. The joint may be +rendered air-tight by introducing sulphuric acid only into the +cup. But this plan must not be adopted if the +interior of the apparatus is to be exhausted, as +sulphuric acid is easily forced between the ground +glass surfaces by external pressure. Mercury, +however, will not pass between well-ground glass +surfaces, and is therefore to be employed for +connecting apparatus which is to be exhausted, +and, if necessary, protected by a layer of strong +sulphuric acid to completely exclude air.</p> + +<div class="figright"><img src="images/illo073bsm.png" alt="Horizontal Joint" /><a name="Fig_32" id="Fig_32"></a> +<p class="caption"><span class="smcap">Fig. 32.</span></p></div> + +<p>Tubes placed horizontally may be joined by a +glycerine or mercury joint such as is shown in +<a href="#Fig_32">Fig. 32</a>. The two tubes <i>A</i> and <i>B</i> are joined as +before by an india-rubber connection <i>C</i>, or one +may be ground to fit the other, and the joint is +then enclosed within a larger jacketing-tube <i>D</i>, +with a mouth at <i>F</i>, which is filled with glycerine +or mercury. <i>D</i> is easily made by drawing out both ends of +a piece of tube, leaving them large enough to pass over the +connection at <i>C</i>, however, and piercing one side at <i>F</i>.</p> + +<div class="figleft"><img src="images/illo074asm.png" alt="Air-Trap" /><a name="Fig_33" id="Fig_33"></a> +<p class="caption"><span class="smcap">Fig. 33.</span></p></div> + +<p><a name="Sec_4_9" id="Sec_4_9"></a><span class="ssfont">Vacuum Taps.</span>—It is not necessary to enter into a description +of the construction of ordinary glass taps, which can +be purchased at very reasonable prices. It may be remarked +here, however, as a great many of them are very imperfectly +ground by the makers, that they may easily be made air-tight +by hand-grinding with camphorated turpentine and fine emery, +finishing with rotten-stone. A well-ground tap, which is well<span class='pagenum'><a name="Page_66" id="Page_66">[66]</a></span> +lubricated, should be practically air-tight under greatly reduced +pressure for a short period; but when it is necessary +to have a tap which absolutely forbids the entrance of air +into apparatus, one of the following may be employed:—</p> + +<div class="figright"><img src="images/illo074bsm.png" alt="Vacuum Tap" /><a name="Fig_34" id="Fig_34"></a> +<p class="caption"><span class="smcap">Fig. 34.</span></p></div> + +<p>(1.) <i>Mr. Cetti’s Vacuum Tap</i> (<a href="#Fig_34">Fig. 34</a>): This tap is cupped +at <i>A</i> and sealed at <i>B</i>, and the cup <i>A</i> is filled with mercury +when the tap is in use, so that if, for example, the end <i>C</i> +be attached to a flask, and <i>D</i> to an apparatus for exhausting +the flask, it will be possible to close the flask by turning off +the tap <i>E</i>, and if no air be allowed access through <i>D</i>, the +vacuum produced in the flask at <i>C</i> cannot be affected by air +leaking through the tap at <i>A</i> or <i>B</i>.</p> + +<p>A passage <i>F</i> must be drilled from the bottom of the plug +<i>E</i> to meet <i>G</i>, in order that when the plug is in position no +residue of air shall be confined within <i>B</i>, whence it might +gradually leak into any apparatus connected to it.</p> + +<p>It is obvious, however, that this tap does not protect a flask<span class='pagenum'><a name="Page_67" id="Page_67">[67]</a></span> +sealed to <i>C</i> from the entrance of air through <i>D</i>, which, in +fact, is the direction in which air is most likely to effect an +entrance. When using one of these taps as part of an apparatus +for supplying pure oxygen, I have guarded against this +by attaching a trap (<a href="#Fig_33">Fig. 33</a>) to the end <i>D</i>, <i>C</i> being joined to +the delivery tube from the gas-holder. The structure and +mode of action of the trap are as follows:—</p> + +<div class="figleft"><img src="images/illo076sm.png" alt="Gimmingham’s Vacuum Tap" /><a name="Fig_35" id="Fig_35"></a> +<p class="caption"><span class="smcap">Fig. 35.</span></p></div> + +<p>A narrow tube <i>G</i> is joined to <i>D</i> of <a href="#Fig_34">Fig. 34</a>, and terminates +in the wide tube <i>I</i>, which is connected above to <i>H</i>, and +below to the air-trap <i>J</i>. <i>J</i> is connected at <i>K</i>, by a piece +of flexible tube, to a reservoir of mercury, from which mercury +enters the air-trap, and passing thence to <i>I</i>, can be employed +for filling the <span class="ssfont">V</span>-trap <i>HLG</i>. The air-trap <i>J</i> is in the +first instance filled with mercury, and then serves to intercept +any stray bubbles of air that the mercury may carry with it. +The particular form of the trap shown at <i>HLG</i> was adopted +because with it the arm <i>LG</i> is more readily emptied of mercury +than with any other form of trap made of small tube that I +have tried. It has been used in my apparatus in the following +manner:—<i>H</i> was connected with a vessel to be filled with +pure oxygen, the tap <i>E</i> closed, and the rise of mercury above +<i>L</i> prevented by a clamp on the flexible tube; the vessel to be +filled and the trap were then exhausted by a Sprengel pump, +and oxygen allowed to flow into the exhausted space by opening +<i>E</i>, the operation of exhausting the tubes and admitting +oxygen being repeated as often as necessary.</p> + +<p>To prevent access of air to <i>E</i> on disconnecting the vessel +at <i>H</i>, the mercury was allowed to flow into the trap till it +reached to <i>MM</i>. <i>E</i> was then closed, and <i>H</i> exposed without +danger of air reaching <i>E</i>, the length of the arms of the +trap being sufficient to provide against the effects of any +changes of temperature and pressure that could occur.</p> + +<p>A delivery tube may be connected to <i>H</i> and filled with +mercury, by closing <i>E</i> and raising the mercury reservoir. All<span class='pagenum'><a name="Page_68" id="Page_68">[68]</a></span> +air being in that way expelled from the delivery tube, and +the supply of mercury cut off by clamping the tube from the +reservoir, oxygen can be delivered from the tube +by opening <i>E</i>, when it will send forward the +mercury, and pass into a tube placed to receive +it without any risk of air being derived from the +delivery tube.</p> + +<p>(2.) <i>Gimmingham’s Vacuum Tap</i>,<a name="Fnanchor_15" id="Fnanchor_15"></a><a href="#Fn_15" class="fnanchor">[15]</a> shown in +<a href="#Fig_35">Fig. 35</a>, consists of three parts. A tube <i>A</i> is +ground to fit the neck of <i>B</i>. <i>B</i> is closed at +its lower end, and has a hole <i>d</i> drilled through +it; when <i>B</i> is fitted to <i>C</i>, <i>d</i> can be made to +coincide with the slit <i>e</i>. When <i>A</i>, <i>B</i>, <i>C</i> are fitted +together, if <i>d</i> meet <i>e</i>, there is communication +between any vessels attached to <i>A</i> and any +other vessel attached to <i>C</i>, entrance of external +air being prevented by mercury being placed in +the cups of <i>C</i> and <i>B</i>. The tap may be opened +and closed at pleasure by rotating <i>B</i>.</p> + +<div class="figleft"><img src="images/illo077asm.png" alt="Simple Air-Trap" /><a name="Fig_36" id="Fig_36"></a> +<p class="caption"><span class="smcap">Fig. 36.</span></p></div> + +<div class="figright"><img src="images/illo077bsm.png" alt="Less Simple Air-Trap" /><a name="Fig_37" id="Fig_37"></a> +<p class="caption"><span class="smcap">Fig. 37.</span></p></div> + +<p>If <i>A</i> has to be removed, <i>C</i> may be converted +into a mercury joint <i>pro tem.</i> by letting a little +mercury from the upper cup fall into the tube and cover <i>d</i>, +the tap being closed. This mercury must be removed by a +fine pipette in order to use the tap again. It should be +noted, however, that though external air cannot enter by +way of the ground glass joints, there is no absolute protection +against the passage of air between <i>A</i> and <i>C</i>, or vessels joined +to <i>A</i> and <i>C</i>, even when the tap is closed. The passage of +air from <i>A</i> to <i>C</i> depends upon the grinding and lubrication +of the joint at <i>C</i>.</p> + +<p><a name="Sec_4_10" id="Sec_4_10"></a><span class="ssfont">Lubricating Taps.</span>—For general purposes resin cerate +answers very well. In special cases burnt india-rubber, or a<span class='pagenum'><a name="Page_69" id="Page_69">[69]</a></span> +mixture of burnt india-rubber and vaseline will answer well, +or vaseline may be used alone. Sulphuric acid and glycerine +are too fluid. When a lubricant is wanted that will withstand +the action of ether, the tap may be lubricated by sprinkling +phosphorus pentoxide upon it, and exposing it to air till +the oxide becomes gummy. The joint must then be protected +from the further action of the air if possible. For example, +if a safety tap be used the cup may be filled with mercury.</p> + +<p><a name="Sec_4_11" id="Sec_4_11"></a><span class="ssfont">Air-Traps.</span>—In <a href="#Fig_33">Fig. 33</a>, +<a href="#Page_66">p. 66</a>, an air-trap (<i>J</i>) is shown. +An air-trap is a device for preventing the mercury supplied to +Sprengel pumps, etc., from carrying air +into spaces that are exhausted, or are for +any reason to be kept free from air. +Figs. 36 and 37 give examples of air-traps. +In the simpler of the two (<a href="#Fig_36">Fig. +36</a>) mercury flowing upwards from <i>C</i> that +may carry bubbles of air with it passes +through the bulb <i>A</i>, which is <i>filled</i> with +mercury before use.<a name="Fnanchor_16" id="Fnanchor_16"></a><a href="#Fn_16" class="fnanchor">[16]</a> Any air which +accompanies the mercury will collect at <i>a</i>, +the mercury will flow on through <i>b</i>. So +long as the level of the mercury in A +is above <i>b</i>, the trap remains effective.</p> + +<p>In the trap shown by <a href="#Fig_37">Fig. 37</a>, the tube +<i>d</i>, which corresponds to <i>b</i> in <a href="#Fig_36">Fig. 36</a>, is +protected at its end by the cup <i>E</i>. <i>E</i> prevents +the direct passage of minute bubbles +of air through <i>d</i>. This trap, like the other, must be filled +with mercury before it is used, and it will then remain effective +for some time.</p> + +<hr class="l05" /> +<p class="footnote"><a name="Fn_11" id="Fn_11"></a><span class="label"><a href="#Fnanchor_11">[11]</a></span> +Large tubes may also be bent by rotating a sufficient length of the +tube in a large flame till it softens, and bending in the same manner as +in the case of smaller tubes, and after filling them with sand, closing +one end completely, and the other so that the sand cannot escape, though +heated air can do so.</p> + +<p class="footnote"><a name="Fn_12" id="Fn_12"></a><span class="label"><a href="#Fnanchor_12">[12]</a></span> +Red-hot platinum welds very well. The wire may be joined to the +sheet of foil by placing the latter on a small piece of fire-brick, +holding the wire in contact with it at the place where they are to be +united, directing a blow-pipe flame upon them till they are at an +intense heat, and smartly striking the wire with a hammer. The blow +should be several times repeated after re-heating the metal.</p> + +<p class="footnote"><a name="Fn_13" id="Fn_13"></a><span class="label"><a href="#Fnanchor_13">[13]</a></span> +For a method of joining soda glass to lead glass, see <a href="#Page_81">p. 81</a>.</p> + +<p class="footnote"><a name="Fn_14" id="Fn_14"></a><span class="label"><a href="#Fnanchor_14">[14]</a></span> +If the india-rubber tube <i>C</i> be secured by wires, iron wire, not +copper wire, should be employed.</p> + +<p class="footnote"><a name="Fn_15" id="Fn_15"></a><span class="label"><a href="#Fnanchor_15">[15]</a></span> +From <i>Proceedings of Royal Society</i>, vol. <span class="smcap">XXV.</span> p. 396.</p> + +<p class="footnote"><a name="Fn_16" id="Fn_16"></a><span class="label"><a href="#Fnanchor_16">[16]</a></span> +This may be done by clamping the tube which supplies mercury below +<i>C</i>, exhausting <i>A</i>, and then opening the clamped tube and allowing the +mercury to rise.</p> +<hr class="l05" /> + +<hr class="c05" /><p class='pagenum'><a name="Page_70" id="Page_70">[70]</a></p> +<h2><a name="Ch_5" id="Ch_5"></a>CHAPTER V.</h2> + +<p class="chap">GRADUATING AND CALIBRATING GLASS APPARATUS.</p> + +<p>Although the subjects to which this concluding chapter +is devoted do not, properly speaking, consist of operations in +glass-blowing, they are so allied to the subject, and of such +great importance, that I think a brief account of them may +advantageously be included.</p> + +<p><a name="Sec_5_1" id="Sec_5_1"></a><span class="ssfont">Graduating Tubes, etc.</span>—It was formerly the custom +to graduate the apparatus intended for use in quantitative +work into parts of equal capacity; for example, into cubic +centimetres and fractions of cubic centimetres. For the +operations of volumetric analysis by liquids this is still done. +But for most purposes it is better to employ a scale of equal +divisions by length, usually of millimetres, and to determine +the relative values of the divisions afterwards, as +described under calibration. It rarely happens that the +tube of which a burette or eudiometer is made has equal +divisions of its length of exactly equal capacities throughout its +entire length, and indeed, even for ordinary volumetric work, +no burette should be employed before its accuracy has been +verified. An excellent method for graduating glass tubes by +hand<a name="Fnanchor_17" id="Fnanchor_17"></a><a href="#Fn_17" class="fnanchor">[17]</a> +has been described in Watts’s <i>Dictionary of Chemistry</i>, and +elsewhere. Another excellent plan, which I have permission<span class='pagenum'><a name="Page_71" id="Page_71">[71]</a></span> +to describe, has been employed by Professor W. Ramsay. +It will be sufficient if I explain its application to the operation +of graduating a tube or strip of glass in millimetre divisions.</p> + +<p>The apparatus required consists of a standard metre +measure,<a name="Fnanchor_18" id="Fnanchor_18"></a><a href="#Fn_18" class="fnanchor">[18]</a> divided into millimetres along each of its edges, +with centimetre divisions between them, a ruler adapted to +the standard metre, as subsequently explained, and a style +with a fine point for marking waxed surfaces.</p> + +<div class="figleft"><img src="images/illo079sm.png" alt="Standard Measure and Ruler" /><a name="Fig_38" id="Fig_38"></a> +<p class="caption"><span class="smcap">Fig. 38.</span></p></div> + +<p><a href="#Fig_38">Fig. 38</a> represents the standard measure, and the ruler.</p> + +<p><span class='pagenum'><a name="Page_72" id="Page_72">[72]</a></span>At <i>AA</i> are the millimetre divisions on the edges of the +measure, the longer transverse lines at <i>BB</i> are placed at +intervals of five millimetres and of centimetres. The ruler is +in the form of a right-angled triangle; it is shown, by the +dotted lines, in position on the standard metre measure at <i>I</i>; +and again, with its under surface upwards, in the smaller +figure at 2. It consists of a perfectly flat sheet of metal, +about ten centimetres in length from <i>C</i> to <i>C</i>, sufficiently thick +to be rigid, and has a ledge, <i>DD</i> in each figure, which is +pressed against the side of the measure when using it, to +ensure that the successive positions of the edge (<i>LL</i>) shall be +parallel to each other. At <i>GG</i> are two small holes, into +which fit small screws with fine points. These must be in a +line parallel to the edge (<i>LL</i>), so that when the ruler is in +position on the scale, the points of the two screws, which +project slightly, shall fall into corresponding cuts on the +divided scales (<i>AA</i>).</p> + +<p>To graduate a strip of glass, or a glass tube (<i>HH</i>), the surface +to be marked must first be coated with wax, which should +be mixed with a little turpentine, and be applied to the surface +of the glass, previously made <i>warm</i> and <i>dry</i>, by means of +a fine brush, so as to completely cover it with a thin, closely-adherent, +and evenly-distributed coat of wax, which must be +allowed to cool.</p> + +<p>Fix <i>HH</i> firmly on a table, and fix the standard measure by +the side of <i>HH</i>. If the thickness of <i>HH</i> be about equal to, +but not greater than that of the standard measure, this +may be done by large drawing-pins. If, however, a large +tube or thick sheet of glass is to be graduated, fix it in position +by two strips of wood screwed to the table on each side of it. +One of these wooden strips, on which the measure may be +placed, may be about as broad as the standard measure, +and of such thickness that when the measure lies upon it +beside the tube to be graduated, the ruler, when moved along<span class='pagenum'><a name="Page_73" id="Page_73">[73]</a></span> +the measure, will move freely above the tube, but will not +be elevated more than is necessary to secure free movement. +The second strip of wood may be narrower, and of the same +thickness as the broader piece on which the standard +measure rests. In any case, let the standard measure +and the object to be graduated be very firmly secured in +their places. Bring the ruler into position at any desired part +of the tube by placing the points of the screws (<i>GG</i>) in +corresponding divisions of the scales (<i>AA</i>). With the style, +which may be a needle mounted in a handle, make a scratch +in the wax along the edge of the ruler at <i>F</i>, move the ruler so +that the screws rest in the next divisions, and repeat the operation +till the required number of lines has been ruled. Longer +marks may be made at intervals of five and ten millimetres. +Great care must be taken to hold the needle perpendicularly, +and to press it steadily against the edge (<i>LL</i>) of the ruler in +scratching the divisions.<a name="Fnanchor_19" id="Fnanchor_19"></a><a href="#Fn_19" class="fnanchor">[19]</a> The length of the lines marking +the millimetre divisions should not be too long; about 1 mm. +is a good length. If they are longer than this, the <i>apparent</i> +distance between them is diminished, and it is less easy to +read fractions of millimetres. Before removing the scale to +etch the glass, carefully examine it to see that no mistakes +have been made. If it is found that any lines have been +omitted, or that long lines have been scratched in the place +of short ones, remelt the wax by means of a heated wire, and +make new marks. Finally, mark the numbers on the scale +with a needle-point, or better, with a fine steel pen.</p> + +<p>The marks on the wax should cut through it. When they<span class='pagenum'><a name="Page_74" id="Page_74">[74]</a></span> +are satisfactory, they may be etched by one of the following +processes:—</p> + +<p>(1.) By moistening some cotton wool, tied to a stick, +with solution of hydrofluoric acid, and gently rubbing this +over the scratched surface for a minute or so; then washing +away the acid with water, and cleaning off the wax. This is +the simplest method, but the marks made are generally transparent, +and therefore not very easy to read. The simplicity +of this method is a great recommendation, however.</p> + +<p>(2.) Expose the tube to the fumes of hydrofluoric acid generated +from a mixture of powdered fluor-spar and strong +sulphuric acid, in a leaden trough. The marks produced in +this way are usually opaque, and are therefore very visible, +and easily read.</p> + +<p>After the above detailed account it will only be necessary +to give an outline of the other process of graduating tubes.</p> + +<div class="figright"><img src="images/illo082sm.png" alt="Scale of Equal Parts" /><a name="Fig_39" id="Fig_39"></a> +<p class="caption"><span class="smcap">Fig. 39.</span></p></div> + +<p>The standard scale to be copied, <i>A</i>, which may in this +case be another graduated tube, or even a paper scale, and +the object to be ruled, <i>B</i>, are securely fixed, end to end, +a little distance apart, in a groove made in a board or in the +top of a table. A stiff bar of wood, <i>C</i>, has a point fixed +at <i>D</i>, and a knife edge at <i>E</i>, <i>D</i> is placed in any division +of <i>A</i>, <i>C</i> is held firmly at <i>E</i> and <i>D</i>, and a cut is made by the +knife through the wax on <i>B</i>, the point <i>D</i> is then moved +into the next division, and the operation is repeated. To +regulate the length and position of the cuts, <i>B</i> is usually +held in position by two sheets of brass projecting over the +edges of the groove in which it lies; the metal sheets have +notches cut into them at the intervals at which longer marks +are to be made.</p> + +<p><span class='pagenum'><a name="Page_75" id="Page_75">[75]</a></span>When the scale is completed, the equality of the divisions +in various parts of it may be, to some extent, verified as +follows:—Adjust a compass so that its points fall into two +divisions 5, 10, or 20 mm. apart. Then apply the points of +the compass to various parts of the scale. In every part +the length of a given number of divisions should be exactly +the same. The individual divisions should also be carefully +inspected by the eye; they should be sensibly equal. If badly +ruled, long and short divisions will be found on the scale. +Very often a long and a short division will be adjacent, and +will be the more easily observed in consequence.</p> + +<p><a name="Sec_5_2" id="Sec_5_2"></a><span class="ssfont">To Divide a Given Line into Equal Parts.</span>—Occasionally +it is necessary to divide a line of given length +into <i>x</i> equal parts. For instance, to divide the stem of a +thermometer from the freezing-point to the boiling-point into +one hundred degrees.</p> + +<div class="figleft"><img src="images/illo083sm.png" alt="Dividing a Line" /><a name="Fig_40" id="Fig_40"></a> +<p class="caption"><span class="smcap">Fig. 40.</span></p></div> + +<p>The following outline will explain how a line may be +so divided. Suppose the line <i>AB</i> (<a href="#Fig_40">Fig. 40</a>) is to be divided +into nine equal parts. Adjust a hinged rule so that the +points <i>A</i> and <i>B</i> coincide with the inside edges of the limbs, +one of them, <i>A</i>, being at the ninth division (<i>e.g.</i> the ninth +inch) of <i>CE</i>. Then if lines parallel to <i>ED</i> be drawn from +each division of the scale to meet <i>AB</i>, <i>AB</i> will be divided +into nine equal parts.</p> + +<p>A very convenient and simple arrangement on this<span class='pagenum'><a name="Page_76" id="Page_76">[76]</a></span> +principle for dividing a line into any number of equal parts with +considerable accuracy, is described by Miss S. Marks in +the <i>Proceedings of the Physical Society</i>, July 1885.<a name="Fnanchor_20" id="Fnanchor_20"></a><a href="#Fn_20" class="fnanchor">[20]</a> One +limb of a hinged rule <i>D</i> is made to slide upon a plain rule +fixed to it; the plain rule carries needles on its under surface +which hold the paper in position. The position of the +divided rule and line to be divided being adjusted, the hinged +rule is gently pushed forwards, as indicated by the arrow in +<a href="#Fig_40">Fig. 40</a>, till division eight coincides with the line <i>AB</i>. A mark +is made at the point of coincidence, and division seven on the +scale is similarly brought to the line <i>AB</i>, and so on. The +inner edge of <i>EC</i> should have the divisions marked upon it, +that their coincidence with <i>AB</i> maybe more accurately noted. +The joint <i>E</i> must be a very stiff one.</p> + +<p>A line drawn of given length or a piece of paper may be +divided into any given number of equal parts, and will then +serve as the scale <i>A</i> of <a href="#Fig_39">Fig. 39</a>, <a href="#Page_74">p. 74</a>, the thermometer +or other object to be graduated taking the place of <i>B</i>.</p> + +<p>Scales carefully divided according to any of the methods +described will be fairly accurate <i>if trustworthy instruments have +been employed as standards</i>.</p> + +<p>It will be found possible when observing the volume of a gas +over mercury, or the height of a column of mercury in a tube, +to measure differences of one-sixth to one-eighth of a millimetre +with a considerable degree of accuracy. To obtain +more delicate measurements a vernier<a name="Fnanchor_21" id="Fnanchor_21"></a><a href="#Fn_21" class="fnanchor">[21]</a> +must be employed.</p> + +<p><a name="Sec_5_3" id="Sec_5_3"></a><span class="ssfont">To Calibrate Apparatus.</span>—The glass tubes of which +graduated apparatus is made are, as already stated, very<span class='pagenum'><a name="Page_77" id="Page_77">[77]</a></span> +rarely truly cylindrical throughout their entire lengths. It +follows that the capacities of equal lengths of a tube will +usually be unequal, and therefore it is necessary to ascertain +by experiment the true values of equal linear divisions +of a tube at various parts of it.</p> + +<p>A burette may be calibrated by filling it with distilled water, +drawing off portions, say of 5 c.c. in succession, into a weighing +bottle of known weight, and weighing them.</p> + +<p>Great care must be taken in reading the level of the liquid +at each observation. The best plan is to hold a piece of +white paper behind the burette, and to read from the lower +edge of the black line that will be seen. Each operation +should be repeated two or three times, and the mean of the +results, which should differ but slightly, may be taken as the +value of the portion of the tube under examination.</p> + +<p>If the weights of water delivered from equal divisions of the +tube are found to be equal, the burette is an accurate one, +but if, as is more likely, different values are obtained, a table +of results should be drawn up in the laboratory book showing +the volume of liquid delivered from each portion of the tube +examined. And subsequently when the burette is used, the +volumes read from the scale on the burette must be corrected. +Suppose, for example, that a burette delivered the following +weights of water from each division of 5 c.c. respectively:—</p> + +<table class="tab90" border="0" cellpadding="0" cellspacing="0" summary="Example Flow from Burette"> + +<tr> +<td colspan="3" align="center">C.C.</td> +<td colspan="2" class="rb1">Grams.</td> +</tr> + +<tr> +<td class="rb1">0</td> +<td align="center">to</td> +<td class="rb1">5</td> +<td align="center">gave</td> +<td class="rb1">4·90</td> +</tr> + +<tr> +<td class="rb1">5</td> +<td align="center">„</td> +<td class="rb1">10</td> +<td align="center">„</td> +<td class="rb1">4·91</td> +</tr> + +<tr> +<td class="rb1">10</td> +<td align="center">„</td> +<td class="rb1">15</td> +<td align="center">„</td> +<td class="rb1">4·92</td> +</tr> + +<tr> +<td class="rb1">15</td> +<td align="center">„</td> +<td class="rb1">20</td> +<td align="center">„</td> +<td class="rb1">4·93</td> +</tr> + +<tr> +<td class="rb1">20</td> +<td align="center">„</td> +<td class="rb1">25</td> +<td align="center">„</td> +<td class="rb1">4·94</td> +</tr> + +<tr> +<td class="rb1">25</td> +<td align="center">„</td> +<td class="rb1">30</td> +<td align="center">„</td> +<td class="rb1">4·95</td> +</tr> + +<tr> +<td class="rb1">30</td> +<td align="center">„</td> +<td class="rb1">35</td> +<td align="center">„</td> +<td class="rb1">4·96</td> +</tr> + +<tr> +<td class="rb1">35</td> +<td align="center">„</td> +<td class="rb1">40</td> +<td align="center">„</td> +<td class="rb1">4·97</td> +</tr> + +<tr> +<td class="rb1">40</td> +<td align="center">„</td> +<td class="rb1">45</td> +<td align="center">„</td> +<td class="rb1">4·98</td> +</tr> + +<tr> +<td class="rb1">45</td> +<td align="center">„</td> +<td class="rb1">50</td> +<td align="center">„</td> +<td class="rb1">4·99</td> +</tr> + +</table> + +<p><span class='pagenum'><a name="Page_78" id="Page_78">[78]</a></span> +and that in two experiments 20 c.c. and 45 c.c. respectively +of a liquid re-agent were employed. The true +volumes calculated from the table would be as 19·66 to +44·46.</p> + +<p>If the temperature remained constant throughout the above +series of experiments, and if the temperature selected were 4° +C., the weights of water found, taken in grams, give the +volumes in cubic centimetres, for one gram of water at 4° C. +has a volume of one cubic centimetre. If the temperature +at which the experiments were made was other than 4° C., +and if great accuracy be desired, a table of densities must +be consulted, with the help of which the volume of any +weight of water at a known temperature can be readily +calculated.</p> + +<p>Pipettes which are to be used as measuring instruments +should also have the relation one to another of the volumes +of liquid which they deliver determined, and also the proportions +these bear to the values found for the divisions +of the burettes in conjunction with which they will be +employed.</p> + +<p><a name="Sec_5_4" id="Sec_5_4"></a><span class="ssfont">To Calibrate Tubes for Measuring Gases.</span>—Prepare +a small glass tube sealed at one end and ground at the other +to a plate of glass. The tube should hold about as much +mercury as will fill 10 mm. divisions of the graduated tube. +Fill this tube with mercury, removing all bubbles of air +that adhere to the sides by closing the open end of the tube +with the thumb, and washing them away with a large air-bubble +left for the purpose. If any persistently remain, +remove them by means of a fine piece of bone or wood. Then +completely fill the tube with mercury, removing any bubbles +that may be introduced in the operation, and remove the +excess of mercury by placing the ground-glass plate on<span class='pagenum'><a name="Page_79" id="Page_79">[79]</a></span> +the mouth of the tube, and pressing it so as to force out all +excess of mercury between the two surfaces. Clean the outside +of the tube, and place it on a small stand (this may be a +small wide-mouthed glass bottle), with which it has been previously +weighed when empty, and re-weigh. Repeat this +operation several times. From the mean of the results, which +should differ one from another but very slightly, the capacity +of the tube can be calculated.</p> + +<p>The purest mercury obtainable should be used. Since the +density of pure mercury at 0° C. is 13·596, the weight of +mercury required to fill the tube at 0° C., taken in grams, +when divided by 13·596, will give the capacity of the tube at +0° C. in cubic centimetres. If the experiment be not made at +0° C., and if a very exact determination of the capacity of the +tube be required, the density of mercury must be corrected +for expansion or contraction.</p> + +<p>Having now a vessel of known capacity, it can be employed +for ascertaining the capacities of the divisions of a graduated +tube in the following manner:—The graduated tube is fixed +perpendicularly, mouth upwards, in a secure position. The +small tube of known capacity is filled with mercury as +previously described, and its contents are transferred to the +divided tube. The number of divisions which the known +volume of mercury occupies is noted after all air-bubbles have +been removed. This process is repeated until the divided +tube is filled. A table of results is prepared, showing the +number of divisions occupied by each known volume of +mercury introduced.</p> + +<p>In subsequently using the tube the volumes of the gases +measured in it must be ascertained from the table of values +thus prepared.</p> + +<p>In observing the level of the mercury, unless a cathetometer +is available, a slip of mirror should be held behind the +mercury close to the tube, in such a position that the pupil<span class='pagenum'><a name="Page_80" id="Page_80">[80]</a></span> +which is visible on the looking-glass is divided into two parts +by the surface of the mercury.</p> + +<p>A correction must be introduced for the error caused +by the meniscus of the mercury. As the closed end of +the tube was downwards when each measured volume of +mercury was introduced, and as the surface of mercury +is convex, the volume of mercury in the tube when it is +filled to any division <i>l</i> (<a href="#Fig_41">Fig. 41</a>) is represented by <i>A</i> of 1. But +in subsequently measuring a gas over mercury in the same +tube, when the mercury stands at the same division <i>l</i>, the +volume of the gas will be as represented by <i>B</i> of 2, which is +evidently somewhat greater than <i>A</i>. This will be seen still +more clearly in 3, where <i>a</i> represents the boundary of the +mercury, and <i>b</i> the boundary of the air, when the tube is +filled to the mark <i>l</i> with mercury or a gas over mercury +respectively.</p> + +<div class="figleft"><img src="images/illo088sm.png" alt="Correction for Meniscus" /><a name="Fig_41" id="Fig_41"></a> +<p class="caption"><span class="smcap">Fig. 41.</span></p></div> + +<p>It is plain that when the level of the mercury in measuring +a gas is read at <i>l</i>, the volume of the gas is greater than the +volume of the mercury recorded, by twice the difference between +the volume <i>A</i> of mercury measured, and that which +would fill the tube to the level <i>l</i>, if its surface were plane.</p> + +<p>The usual mode of finding the true volume of a gas collected +over mercury is as follows:—</p> + +<p>Place the graduated tube mouth upwards, introduce some +mercury, and, after removing all bubbles, note the division at<span class='pagenum'><a name="Page_81" id="Page_81">[81]</a></span> +which it stands. Then add a few drops of solution of mercuric +chloride; the surface of the mercury will become level, read +and record its new position. Then, in any measurement, +having observed that the mercury stands at <i>n</i> divisions of the +tube, add twice the difference between the two positions of +the mercury to <i>n</i>, and ascertain the volume which corresponds +to this reading from the table of capacities.</p> + +<p><a name="Sec_5_5" id="Sec_5_5"></a><span class="ssfont">To Calibrate the Tube of a Thermometer.</span>—Detach +a thread of mercury from half an inch to one inch in length +from the body of the mercury. Move it from point to point +throughout the length of the tube, and note its length in +each position. If in one part it occupies a length of tube +corresponding to eight degrees, and at another only seven +degrees, then at the former point the value of each division is +only seven-eighths of those at the latter position.</p> + +<p>From the results obtained, a table of corrections for the +thermometer should be prepared.</p> + +<p>It is sometimes necessary to join soda glass to lead glass. +In this case the edge of the lead glass tube may be bordered +with white enamel before making the joint. Enough enamel +must be used to prevent the lead and soda glasses from mingling +at any point. The enamel is easily reduced, and must be +heated in the oxidising flame. Dr. Ebert recommends <i>Verre +d’urane</i> for this purpose. It is supplied by Herr Götze of +Leipzig (Liebigstrasse).</p> + +<hr class="l05" /> +<p class="footnote"><a name="Fn_17" id="Fn_17"></a><span class="label"><a href="#Fnanchor_17">[17]</a></span> +Originally suggested by Bunsen.</p> + +<p class="footnote"><a name="Fn_18" id="Fn_18"></a><span class="label"><a href="#Fnanchor_18">[18]</a></span> +Such measures can be obtained of steel for about <i>fifteen +shillings</i> each. They are made by Mr. Chesterman of Sheffield. They can +be obtained also from other makers of philosophical instruments, at +prices depending upon their delicacy. Those of the greatest accuracy are +somewhat costly.</p> + +<p class="footnote"><a name="Fn_19" id="Fn_19"></a><span class="label"><a href="#Fnanchor_19">[19]</a></span> +To avoid variations of the position in which the needle is held +when marking the divisions, the edge (<i>LL</i>) should not be bevelled; and +an upright support may be placed upon the ruler, with a ring through +which the handle of the needle passes, thereby securing that the angle +formed by the needle and surface of the ruler is constant, and that +equal divisions are marked.</p> + +<p class="footnote"><a name="Fn_20" id="Fn_20"></a><span class="label"><a href="#Fnanchor_20">[20]</a></span> +Since this was printed I have observed that the above method is not +identical with that described by Miss Marks, but for ordinary purposes I +do not think it will be found to be inferior.</p> + +<p class="footnote"><a name="Fn_21" id="Fn_21"></a><span class="label"><a href="#Fnanchor_21">[21]</a></span> +For the nature and use of the vernier, a treatise on Physics or +Physical Measurements may be consulted.</p> +<hr class="l05" /> + +<hr class="c05" /><p class='pagenum'><a name="Page_82" id="Page_82">[82]</a></p> +<h2><a name="Ch_6" id="Ch_6"></a>CHAPTER VI.</h2> + +<p class="chap">GLASS TUBING.</p> + +<p><a name="Sec_6_1" id="Sec_6_1"></a>The diagrams given below show the sizes and thickness of +the glass tubes most frequently required. In ordering, the +numbers of these diagrams may be quoted, or the exact +dimensions desired may be stated.</p> + +<p>Glass tubes are usually sold by weight, and therefore the +weight of tube of each size that is wished for should be +indicated, and also whether it is to be of lead or soda glass.</p> + +<div class="figcenter"><img src="images/illo9091sm.png" alt="Glass Tubing 1" /></div> +<p class='pagenum'><a name="Page_83" id="Page_83">[83]</a></p> + +<hr class="c05" /><p class='pagenum'><a name="Page_84" id="Page_84">[84]</a></p> +<h2><a name="Ch_7" id="Ch_7"></a>CHAPTER VII.</h2> + +<p class="chap">VITREOUS SILICA.</p> + +<p><a name="Sec_7_1" id="Sec_7_1"></a><span class="ssfont">Introductory.</span>—Vitreous Silica was made in fine threads +by M. Gaudin in 1839,<a name="Fnanchor_22" id="Fnanchor_22"></a><a href="#Fn_22" class="fnanchor">[22]</a> and +small tubes of it were made in +1869 by M. A. Gautier, but its remarkable qualities were +not really recognised till 1889, when Professor C. V. Boys +rediscovered the process of making small pieces of apparatus +of this substance, and used the torsion of “quartz fibres” +for measuring small forces. More recently the author of +this book has devised a process for preventing the “splintering” +of quartz which gave so much trouble to the earlier +workers, and jointly with Mr. H. G. Lacell, has produced a +variety of apparatus of much larger dimensions than had +been attempted <b>previously</b>. At the time of writing we can +produce by the processes described in the following pages +tubes 1 to 1·5 cm. in diameter and about 750 cm. in length, +globes or flasks capable of containing about 50 c.c., masses of +vitreous silica weighing 100 grams or more, and a variety +of other apparatus.</p> + +<p><a name="Sec_7_2" id="Sec_7_2"></a><span class="ssfont">Properties of Vitreous Silica.</span>—For the convenience +of those who are not familiar with the literature of this<span class='pagenum'><a name="Page_85" id="Page_85">[85]</a></span> +subject, I may commence this chapter with a brief account +of the properties and applications of vitreous silica, as far as +they are at present ascertained. Vitreous silica is less hard +than chalcedony, but harder than felspar. Tubes and rods +of it can be cut with a file or with a piece of sharpened +and hardened steel, and can afterwards be broken like +similar articles of glass. Its conducting power is low, and +Mr. Boys has shown that fine fibres of silica insulate remarkably +well, even in an atmosphere saturated with moisture. +The insulating qualities of tubes or rods of large cross +sections have not yet been fully tested; one would expect +them to give good results provided that they are kept +scrupulously clean. A silica rod which had been much +handled would probably insulate no better than one of +glass in a similar condition. The density of vitreous silica +is very near to that of ordinary amorphous silica. In the +case of a small rod not absolutely free from minute bubbles +it was found to be 2·21.</p> + +<p>Vitreous silica is optically inactive, when homogeneous, +and is highly transparent to ultraviolet radiations.</p> + +<p>The melting point of vitreous silica cannot be definitely +stated. It is plastic over a considerable range of temperature. +Professor Callendar has succeeded in measuring the rate of +contraction of fine rods in cooling from 1200° to 1500° C., +so that its plasticity must be very slight below the latter +temperature. If a platinum wire embedded in a thick silica +tube be heated from without by an oxy-hydrogen flame the +metal may be melted at temperatures at which the silica tube +will retain its form for a moderate length of time, but silica +softens to a marked extent at temperatures a little above +the melting point of platinum.</p> + +<p>It has been observed by Boys, Callendar, and others that +fine rods of silica, and also the so-called “quartz fibres,” are +apt to become brittle after they have been heated to redness.<span class='pagenum'><a name="Page_86" id="Page_86">[86]</a></span> +But I have not observed this defect in the case of more +massive objects, such as thick rods or tubes; and as I have +repeatedly observed that mere traces of basic matter, such as +may be conveyed by contact with the hand, seriously injure +the surface of silica, and have found that silica quickly +becomes rotten when it is heated to about 1000° in contact +with an infusible base such as lime, I am disposed to ascribe +the above-mentioned phenomenon to chemical rather than to +purely physical causes.<a name="Fnanchor_23" id="Fnanchor_23"></a><a href="#Fn_23" class="fnanchor">[23]</a> It is certain, however, that silica +apparatus must never be too strongly heated in contact +with basic substances. Silica is easily attacked by alkalis +and by lime, less readily by copper oxide, and still less by +iron oxide.</p> + +<p>The rate of expansion of vitreous silica has been studied +by H. le Chatelier, and more recently by Callendar. The +former found its mean coefficient of expansion to be +0·0000007 between 0° and 10000°,<a name="Fnanchor_24" id="Fnanchor_24"></a><a href="#Fn_24" class="fnanchor">[24]</a> +and that it contracted when heated above 700°.</p> + +<p>Professor Callendar used rods of silica prepared by the +author from “Brazil crystal”; these were drawn in the +oxy-gas flame and had never been heated in contact with +solid foreign matter, so that they consisted, presumably, of +very pure silica. His results differ in some respects from +those obtained by Le Chatelier, for he finds the mean coefficient +of expansion to be only 0·00000059, <i>i.e.</i> about one +seventeenth as great as that of platinum. Callendar found +the rods of silica expanded very regularly up to 1000° but +less regularly above that temperature. Above 1200° they +contracted when heated.</p> + +<p><span class='pagenum'><a name="Page_87" id="Page_87">[87]</a></span>The behaviour of vitreous silica under sudden changes +of temperature is most remarkable. Large masses of it +may be plunged suddenly when cold into the oxy-gas flame, +and tubes or rods at a white heat may be thrust into cold +water, or even into liquid air, with impunity. As a consequence +of this, it is in one respect much more easily worked +in the flame than any form of glass. Difficult joints can +be thrust suddenly into the flame, or removed from it, at +any stage, and they may be heated unequally in different +parts with impunity. It is safe to say that joints, etc., in +silica never crack whilst one is making them nor during the +subsequent cooling. They may be set aside in an unfinished +state and taken up again without any precautions. Therefore +it is possible for an amateur to construct apparatus in +silica which he would be quite unable to produce from +glass.</p> + +<p>The behaviour of vitreous silica with solvents has not yet +been fully investigated, but Mr. H. G. Lacell has this subject +in hand. If it behaves like the other forms of anhydrous +silica it will withstand the action of all acids except hydrofluoric +acid. It is, of course, very readily acted upon by +solutions of alkalis and alkaline salts.</p> + +<p>As regards the use of silica in experiments with gases, +it must be remarked that vitreous silica, like platinum, +is slightly permeable to hydrogen when strongly heated. +One consequence of this is that traces of moisture are +almost always to be found inside recently-made silica tubes +and bulbs, however carefully we may have dried the air forced +into them during the process of construction. Owing to the +very low coefficient of expansion of silica, it is not possible +to seal platinum wires into silica tubes. Nor can platinum +be cemented into the silica by means of arsenic enamel, nor +by any of the softer glasses used for such purposes. I have +come near to success by using kaolin, but the results with<span class='pagenum'><a name="Page_88" id="Page_88">[88]</a></span> +this material do not afford a real solution of the problem, +though they may perhaps point to a hopeful line of attack. +Possibly platinum wires might be soldered into the tubes +(see <a href="http://www.gutenberg.org/ebooks/22784"><i>Laboratory Arts</i>, R. Threlfall</a>), but this also is uncertain.</p> + +<hr class="c05" /> + +<p>The process of preparing silica tubes, etc., from Lumps of +Brazil Crystal may be described conveniently under the +following headings. I describe the various processes fully +in these pages, as those who are interested in the matter +will probably wish to try every part of the process in the +first instance. But I may say that in practice I think +almost every one will find it advantageous to start with +purchased silica tubes, just as a glass-worker starts with a +supply of purchased glass tubes. The manufacturer can +obtain his oxygen at a lower price than the retail purchaser, +and a workman who gives much time to such work can turn +out silica tube so much more quickly than an amateur, that I +think it will be found that both time and money can be +saved by purchasing the tube. At the same time the +beginner will find it worth while to learn and practise each +stage of the process at first, as every part of the work +described may be useful in the production of finished +apparatus from silica tubes.</p> + +<p>This being so, I am glad to be able to add that a leading +firm of dealers in apparatus<a name="Fnanchor_25" id="Fnanchor_25"></a><a href="#Fn_25" class="fnanchor">[25]</a> has commenced making silica +goods on a commercial scale, so that the new material is +now available for all those who need it or wish to examine +its properties.</p> + +<p><a name="Sec_7_3" id="Sec_7_3"></a><span class="ssfont">Preparing non-splintering Silica from Brazil +Pebble.</span>—The best variety of native Silica is Brazil Pebble, +which may be obtained in chips or larger masses. These<span class='pagenum'><a name="Page_89" id="Page_89">[89]</a></span> +should be thoroughly cleaned, heated in boiling water, and +dropped into cold water, the treatment being repeated till +the masses have cracked to such an extent that they may +be broken easily by blows from a clean steel pestle or +hammer.</p> + +<p>The fragments thus produced must be hand-picked, and +those which are not perfectly free from foreign matter +should be rejected. The pure and transparent pieces +must then be heated to a yellow-red heat in a covered +platinum dish in a muffle or reverberatory furnace and +quickly plunged into a deep clean vessel containing clean +distilled water; this process being repeated, if necessary, +till the product consists of semi-opaque friable masses, very +much like a white enamel in appearance. After these have +been washed with distilled water, well drained and dried, they +may be brought into the hottest part of an oxy-gas flame +safely, or pressed suddenly against masses of white hot silica +without any preliminary heating, such as is necessary in +the case of natural quartz. Quartz which has not been submitted +to the above preparatory process, splinters on contact +with the flame to such an extent that very few would care to +face the trouble and expense of working with so refractory +a material. But after the above treatment, which really +gives little trouble, all the difficulties which hampered the +pioneer workers in silica disappear as if by magic.</p> + +<p><a name="Sec_7_4" id="Sec_7_4"></a><span class="ssfont">Apparatus.</span>—Very little special apparatus need be provided +for working with silica, but it is absolutely essential to +protect the eyes with very dark glasses. These should be +so dark as to render it a little difficult to work with them +at first. If long spells of work are undertaken, two pairs of +spectacles should be provided, for the glasses quickly become +hot enough to cause great inconvenience and even injury to +the eyes.</p> + +<p><span class='pagenum'><a name="Page_90" id="Page_90">[90]</a></span>Almost any of the available oxy-gas burners may be +used, but they vary considerably in efficiency, and it +is economical to obtain a very efficient burner. The +’blow-through’ burners are least satisfactory, and I have +long since abandoned the use of them. Some of the safety +’mixed-gas jets’ have an inconvenient trick of burning-back, +with sharp explosions, which are highly disconcerting, if the +work be brought too near the nozzle of the burner. I +have found the patent burner of Mr. Jackson (Brin’s Oxygen +Company, Manchester) most satisfactory, and it offers the +advantage that several jets can be combined in a group +easily and inexpensively for work on large apparatus. The +large roaring flames such as are used, I understand, for +welding steel are very expensive, and not very efficient for +the work here described.</p> + +<p><a name="Sec_7_5" id="Sec_7_5"></a><span class="ssfont">The method of making Silica Tubes.</span>—Before commencing +to make a tube a supply of vitreous silica in rods +about one or two millimetres in diameter must be prepared. +To make one of these, hold a fragment of the non-splintering +silica described above in the oxy-gas flame by means of forceps +tipped with platinum so as to melt one of its corners, press +a small fragment of the same material against the melted +part till the two adhere and heat it from below upwards,<a name="Fnanchor_26" id="Fnanchor_26"></a><a href="#Fn_26" class="fnanchor">[26]</a> +till it becomes clear and vitreous, add a third fragment in a +similar manner, then a fourth, and so on till an irregular +rod has been formed. Finally re-heat this rod in sections and +draw it out whilst plastic into rods or coarse threads of +the desired dimensions. If one works carefully the forceps +do not suffer much. I have had one pair in almost constant +use for several years; they have been used in the training of +five beginners and are still practically uninjured.</p> + +<p><span class='pagenum'><a name="Page_91" id="Page_91">[91]</a></span>The beginner should work with a gauge and regulator on +the bottle of oxygen, and should watch the consumption of +oxygen closely. A large expenditure of oxygen does not +by any means necessarily imply a corresponding output of +silica, even by one who has mastered the initial difficulties.</p> + +<p>When a supply of the small rods of vitreous silica has +been provided, bind a few of them round a rod of platinum +(diameter say, 1 mm.) by means of platinum wires at the +two ends and heat the silica gradually, beginning at one end +after slightly withdrawing the platinum core from that end, +till a rough tube about four or five centimetres in length +has been formed. Close one end of this, expand it, by +blowing, into a small bulb, attach a silica rod to the remote +end of the bulb, re-heat the bulb and draw it out into a +fine tube. Blow a fresh bulb on one end of this and again +draw it out, proceeding in this way till you have a tube +about six or eight centimetres in length. All larger tubes +and vessels are produced by developing this fine tube +suitably.</p> + +<p><a name="Sec_7_6" id="Sec_7_6"></a><span class="ssfont">Precautions.</span>—The following points must be carefully +kept in mind, both during the making of the first tube and +afterwards:—</p> + +<p>(1) The hottest spot in the oxy-gas flame is at a point +very near the tip of the inner cone of the flame, and silica +can be softened best at this hot spot. The excellence of a +burner does not depend on the size of its flame, so much as +on the temperature of its “hot spot,” and the success of the +worker depends on his skill in bringing his work exactly to +this part of the flame. Comparatively large masses of silica +may be softened in a comparatively small jet if the hot spot +is properly utilised.</p> + +<p>(2) Silica is very apt to exhibit a phenomenon resembling<span class='pagenum'><a name="Page_92" id="Page_92">[92]</a></span> +devitrification during working. It becomes covered with a +white incrustation, which seems to be comparatively rich in +alkali.<a name="Fnanchor_27" id="Fnanchor_27"></a><a href="#Fn_27" class="fnanchor">[27]</a> This incrustation is very easily removed by re-heating +the whitened surface, provided that the material +has been kept scrupulously clean. If the silica has been +brought into the flame when dusty, or even after much +contact with the hands of the operator, its surface is very +apt to be permanently injured. <i>Too much attention cannot be +given to cleanliness by the workman.</i></p> + +<p>(3) When a heated tube or bulb of silica is to be expanded +by blowing, it is best not to remove it from the flame, for +if that is done it will lose its plasticity quickly unless it be +large. The better plan is to move it slightly from the “hot +spot” into the surrounding parts of the flame at the moment +of blowing.</p> + +<p>It is best to blow the bulb through an india-rubber +tube attached to the open end of the silica tube. At +first one frequently bursts the bulbs when doing this, but +holes are easily repaired by stopping them with plastic silica +applied by the softened end of a fine rod of silica and +expanding the lump, after re-heating it, by blowing. After +a few hours’ practice these mishaps gradually become rare.</p> + +<p>I find it a good plan to interpose a glass tube packed +with granulated potash between the mouth and the silica +tube. This prevents the interior of the tube from being +soiled. The purifying material must not be packed so closely +in the tube as to prevent air from passing freely through it +under a very low pressure.</p> + +<p>It may be mentioned here that a finished tube usually +contains a little moisture, and a recognisable quantity of +nitric peroxide. These may be removed by heating the<span class='pagenum'><a name="Page_93" id="Page_93">[93]</a></span> +tube and drawing filtered air through it, but not by +washing, as it is difficult to obtain water which leaves no +residue on the silica.</p> + +<p><a name="Sec_7_7" id="Sec_7_7"></a><span class="ssfont">Making larger tubes and other apparatus of +Silica.</span>—In order to convert a small bulb of silica into a +larger one or into a large tube, proceed as follows:—Heat +one end of a fine rod of silica and apply it to the bulb +so as to form a ring as shown in the figure. Then +heat the ring and the end of the bulb till it softens, +and expand the end by blowing. If this process +is repeated, the bulb first becomes ovate and +then forms a short tube which can be lengthened +at will, but the most convenient way to obtain a +very long tube is to make several shorter tubes of +the required diameter, and say 200 to 250 mm. in +length, and to join these end to end. It does not +answer to add lumps of silica to the end of the +bulb, for the sides of the tube made in this way +become too thin, and blow-holes are constantly +formed during the making of them. These can +be mended, it is true, but they spoil the appearance +of the work.</p> + +<div class="figright"><img src="images/illo101sm.png" alt="Large Apparatus" /></div> + +<p>Tubes made in the manner described above are +thickened by adding rings of silica and blowing +them when hot to spread the silica. If a combination +of several jets is employed, very large tubes +can be constructed in this way. One of Messrs. Baird and +Tatlock’s workmen lately blew a bulb about 5 cm. in diameter, +and it was clear that he could have converted it into a +long cylindrical tube of equal diameter had it been necessary +to do so.</p> + +<p>Very thin tubes of 1·5 cm. diameter, and tubes of considerable +thickness and of equal size, are easily made after some<span class='pagenum'><a name="Page_94" id="Page_94">[94]</a></span> +practice, and fine capilliaries and millimetre tube can be +made with about equal readiness.</p> + +<p>If a very fine tube of even bore is required, it may be +drawn from a small thick cylinder after a little practice.</p> + +<p>When a tube becomes so large that it cannot be heated +uniformly on all sides by rotating it in the flame, it is convenient +to place a sheet of silica in front of the flame a little +beyond the object to be heated, in order that the former may +throw back the flame on those parts of the tube which are +most remote from the jet. A suitable plate may be made +by sticking together small lumps of silica rendered plastic +by heat.</p> + +<p>The silica tubes thus made can be cut and broken like +glass, they can be joined together before the flame, and they +can also be drawn into smaller tubes when softened by heat.</p> + +<p>In order to make a side connection as in a T piece, a ring +of silica should be applied to the tube in the position fixed +upon for the joint. This ring must then be slightly expanded, +a new ring added, and so on, till a short side tube is formed. +To this it is easy to seal a longer tube of the required dimensions. +It is thus possible to produce Geissler tubes, small +distilling flasks, etc. Solid rods of silica are easily made by +pressing together the softened ends of the fine rods or threads +previously mentioned. Such rods and small masses can be +ground and polished without annealing them.</p> + +<p><a name="Sec_7_8" id="Sec_7_8"></a><span class="ssfont">Quartz Fibres.</span>—These were introduced into physical +work by Mr. Boys in 1889. They may be made by attaching +a fine rod of vitrified quartz to the tail of a small straw +arrow provided with a needle-point; placing the arrow in +position on a cross-bow, heating the rod of silica till it is +thoroughly softened and then letting the arrow fly from the +bow, when it will carry with it an extremely fine thread of +silica. A little practice is necessary to ensure success, but<span class='pagenum'><a name="Page_95" id="Page_95">[95]</a></span> +a good operator can produce threads of great tenacity and +great uniformity. Fuller accounts of the process and of +the various properties and uses of quartz fibres will be +found in Mr. Boys’ lectures (Roy. Inst. Proc. 1889, and +Proc. Brit. Assn. 1890), and in Mr. Threlfall’s Laboratory +Arts.</p> + +<hr class="l05" /> +<p class="footnote"><a name="Fn_22" id="Fn_22"></a><span class="label"><a href="#Fnanchor_22">[22]</a></span> +A brief summary of the history of this subject will be found in +<i>Nature</i>, Vol. 62, and in the Proceedings of the Royal Institution, +1901.</p> + +<p class="footnote"><a name="Fn_23" id="Fn_23"></a><span class="label"><a href="#Fnanchor_23">[23]</a></span> +In a recent communication Professor Callendar tells me that the +devitrification commences at the outside and is hastened by particles of +foreign matter.</p> + +<p class="footnote"><a name="Fn_24" id="Fn_24"></a><span class="label"><a href="#Fnanchor_24">[24]</a></span> +The silica blocks used were prepared by fusion in an electric +furnace; it is therefore probable that they were not quite pure.</p> + +<p class="footnote"><a name="Fn_25" id="Fn_25"></a><span class="label"><a href="#Fnanchor_25">[25]</a></span> +Messrs. Baird and Tatlock.</p> + +<p class="footnote"><a name="Fn_26" id="Fn_26"></a><span class="label"><a href="#Fnanchor_26">[26]</a></span> +This is to avoid bubbles in the finished glass.</p> + +<p class="footnote"><a name="Fn_27" id="Fn_27"></a><span class="label"><a href="#Fnanchor_27">[27]</a></span> +The rock crystal exhibits a yellow flame when first heated in the +oxy-gas flame, and most samples contain spectroscopic quantities of +lithium.</p> +<hr class="l05" /> + +<hr class="c25" /><p><span class='pagenum'><a name="Page_97" id="Page_97">[97]</a></span></p> +<h2><a name="Ch_8" id="Ch_8"></a>INDEX.</h2> + +<table class="tab60" border="0" cellpadding="1" cellspacing="1" summary="Index"> + +<tr> +<td align="left" valign="top">Air-traps,</td> +<td align="right" valign="bottom"><a href="#Page_69">69</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Annealing,</td> +<td align="right" valign="bottom"><a href="#Page_23">23</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Apparatus needed for Glass-working,</td> +<td align="right" valign="bottom"><a href="#Page_11">11</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Appendix,</td> +<td align="right" valign="bottom"><a href="#Page_82">82</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Beginners, Failures of,</td> +<td align="right" valign="bottom"><a href="#Page_22">22</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Bellows, Position of,</td> +<td align="right" valign="bottom"><a href="#Page_3">3</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">—— Various forms of,</td> +<td align="right" valign="bottom"><a href="#Page_7">7</a>.</td> +<td align="left"> <i>See also</i> <a href="#IndSec_1">Blower</a>.</td> +</tr> + +<tr> +<td align="left" valign="top">Bending Glass Tubes,</td> +<td align="right" valign="bottom"><a href="#Page_28">28</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top"><a name="IndSec_1" id="IndSec_1"></a>Blower, Automatic,</td> +<td align="right" valign="bottom"><a href="#Page_8">8</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Blow-pipe, Cheap form of,</td> +<td align="right" valign="bottom"><a href="#Page_4">4</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">—— Dimensions of,</td> +<td align="right" valign="bottom"><a href="#Page_4">4</a>-<a href="#Page_5">5</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">—— Fletcher’s Automaton,</td> +<td align="right" valign="bottom"><a href="#Page_6">6</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">—— Fletcher’s Compound,</td> +<td align="right" valign="bottom"><a href="#Page_6">6</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">—— Gimmingham’s,</td> +<td align="right" valign="bottom"><a href="#Page_6">6</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">—— Herapath’s,</td> +<td align="right" valign="bottom"><a href="#Page_6">6</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">—— Jets for the,</td> +<td align="right" valign="bottom"><a href="#Page_7">7</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">—— Use of the,</td> +<td align="right" valign="bottom"><a href="#Page_8">8</a>.</td> +<td align="left"> <i>See also</i> <a href="#IndSec_2">Flames</a>.</td> +</tr> + +<tr> +<td align="left" valign="top">Blow-pipes, Use of several in combination,</td> +<td align="right" valign="bottom"><a href="#Page_21">21</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Brush Flame,</td> +<td align="right" valign="bottom"><a href="#Page_9">9</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">—— Oxidising,</td> +<td align="right" valign="bottom"><a href="#Page_20">20</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Bulbs, Methods of blowing,</td> +<td align="right" valign="bottom"><a href="#Page_47">47</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Calibrating Apparatus,</td> +<td align="right" valign="bottom"><a href="#Page_76">76</a>-<a href="#Page_81">81</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Camphorated Turpentine,</td> +<td align="right" valign="bottom"><a href="#Page_11">11</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Cetti’s Vacuum Tap,</td> +<td align="right" valign="bottom"><a href="#Page_66">66</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Charcoal Pastils,</td> +<td align="right" valign="bottom"><a href="#Page_11">11</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Choking or Contracting the Bores of Tubes,</td> +<td align="right" valign="bottom"><a href="#Page_35">35</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Combining the Parts of Complicated Apparatus,</td> +<td align="right" valign="bottom"><a href="#Page_61">61</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Combustion Tube, how to work it,</td> +<td align="right" valign="bottom"><a href="#Page_25">25</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Contracting the Bore of a Tube,</td> +<td align="right" valign="bottom"><a href="#Page_35">35</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Cotton Wool for Annealing,</td> +<td align="right" valign="bottom"><a href="#Page_24">24</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Cutting Glass Tubes,</td> +<td align="right" valign="bottom"><a href="#Page_26">26</a>, <a href="#Page_27">27</a>, <a href="#Page_28">28</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Dividing a Line into Equal Parts,</td> +<td align="right" valign="bottom"><a href="#Page_75">75</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Electrodes,</td> +<td align="right" valign="bottom"><a href="#Page_38">38</a>, <a href="#Page_55">55</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Electrolysis, Making Apparatus for,</td> +<td align="right" valign="bottom"><a href="#Page_59">59</a>.</td> +<td> </td> +</tr> + + +<tr> +<td align="left" valign="top">Files for Cutting Glass,</td> +<td align="right" valign="bottom"><a href="#Page_27">27</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top"><a name="IndSec_2" id="IndSec_2"></a>Flame, the Pointed,</td> +<td align="right" valign="bottom"><a href="#Page_8">8</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">—— the Brush,</td> +<td align="right" valign="bottom"><a href="#Page_9">9</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">—— the Oxidising Brush,</td> +<td align="right" valign="bottom"><a href="#Page_20">20</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">—— the Smoky,</td> +<td align="right" valign="bottom"><a href="#Page_10">10</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Fletcher’s Automaton Blow-pipe,</td> +<td align="right" valign="bottom"><a href="#Page_6">6</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Fletcher’s Compound Blow-pipe,</td> +<td align="right" valign="bottom"><a href="#Page_6">6</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Funnels, Thistle-headed,</td> +<td align="right" valign="bottom"><a href="#Page_57">57</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Gimmingham’s Blow-pipe,</td> +<td align="right" valign="bottom"><a href="#Page_6">6</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Gimmingham’s Vacuum Tap,</td> +<td align="right" valign="bottom"><a href="#Page_68">68</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Glass, Annealing,</td> +<td align="right" valign="bottom"><a href="#Page_23">23</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">—— Devitrification of,</td> +<td align="right" valign="bottom"><a href="#Page_15">15</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">—— Method of Working with Lead,</td> +<td align="right" valign="bottom"><a href="#Page_17">17</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">—— Method of Working with Soda,</td> +<td align="right" valign="bottom"><a href="#Page_22">22</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">—— Nature of,</td> +<td align="right" valign="bottom"><a href="#Page_12">12</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">—— Presenting to the Flame,</td> +<td align="right" valign="bottom"><a href="#Page_16">16</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top"><a name="IndSec_3" id="IndSec_3"></a>Glass Tubes, Bending,</td> +<td align="right" valign="bottom"><a href="#Page_28">28</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">—— Bordering,</td> +<td align="right" valign="bottom"><a href="#Page_31">31</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">—— Characters of good,</td> +<td align="right" valign="bottom"><a href="#Page_14">14</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">—— Choking,</td> +<td align="right" valign="bottom"><a href="#Page_35">35</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">—— Cleaning,</td> +<td align="right" valign="bottom"><a href="#Page_15">15</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top"><span class='pagenum'><a name="Page_98" id="Page_98">[98]</a></span>—— Cutting,</td> +<td align="right" valign="bottom"><a href="#Page_26">26</a>, <a href="#Page_27">27</a>, <a href="#Page_28">28</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">—— Piercing,</td> +<td align="right" valign="bottom"><a href="#Page_37">37</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">—— Purchase of,</td> +<td align="right" valign="bottom"><a href="#Page_12">12</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">—— Sealing,</td> +<td align="right" valign="bottom"><a href="#Page_32">32</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">—— Sealing Hermetically,</td> +<td align="right" valign="bottom"><a href="#Page_58">58</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">—— Sizes of,</td> +<td align="right" valign="bottom"><a href="#Page_82">82</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">—— Welding or Soldering,</td> +<td align="right" valign="bottom"><a href="#Page_39">39</a>, <a href="#Page_62">62</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">—— Widening the Ends of,</td> +<td align="right" valign="bottom"><a href="#Page_36">36</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Graduating Apparatus,</td> +<td align="right" valign="bottom"><a href="#Page_70">70</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Grinding Stoppers,</td> +<td align="right" valign="bottom"><a href="#Page_51">51</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Herapath’s Blow-pipe,</td> +<td align="right" valign="bottom"><a href="#Page_6">6</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Hofman’s Apparatus for Electrolysis,</td> +<td align="right" valign="bottom"><a href="#Page_59">59</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Inside Joints,</td> +<td align="right" valign="bottom"><a href="#Page_43">43</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Jets for Blow-pipes,</td> +<td align="right" valign="bottom"><a href="#Page_7">7</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Joints, Air-tight,</td> +<td align="right" valign="bottom"><a href="#Page_64">64</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Lead Glass, Method of Working with,</td> +<td align="right" valign="bottom"><a href="#Page_17">17</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Lead Glass, Blackening of,</td> +<td align="right" valign="bottom"><a href="#Page_17">17</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Light, Effect of, in Working,</td> +<td align="right" valign="bottom"><a href="#Page_3">3</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Line, to Divide into Equal Parts,</td> +<td align="right" valign="bottom"><a href="#Page_75">75</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Mercury Joints, Various,</td> +<td align="right" valign="bottom"><a href="#Page_64">64</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Non-splintering Silica, Preparation of, from Quartz,</td> +<td align="right" valign="bottom"><a href="#Page_88">88</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Ozone Generator, To Make an,</td> +<td align="right" valign="bottom"><a href="#Page_44">44</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Pastils of Charcoal,</td> +<td align="right" valign="bottom"><a href="#Page_11">11</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Piercing Tubes, etc.,</td> +<td align="right" valign="bottom"><a href="#Page_37">37</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Platinum Electrodes, Sealing in,</td> +<td align="right" valign="bottom"><a href="#Page_38">38</a>, <a href="#Page_55">55</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Pointed Flame, the,</td> +<td align="right" valign="bottom"><a href="#Page_9">9</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Quartz Fibres,</td> +<td align="right" valign="bottom"><a href="#Page_94">94</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Rounding Ends of Tubes,</td> +<td align="right" valign="bottom"><a href="#Page_31">31</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Sealing or Closing Openings in Tubes,</td> +<td align="right" valign="bottom"><a href="#Page_32">32</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Side-tubes, Fixing,</td> +<td align="right" valign="bottom"><a href="#Page_41">41</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Smoky Flame,</td> +<td align="right" valign="bottom"><a href="#Page_10">10</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Soda Glass, Method of Working,</td> +<td align="right" valign="bottom"><a href="#Page_22">22</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Soldering or Welding,</td> +<td align="right" valign="bottom"><a href="#Page_39">39</a>, <a href="#Page_62">62</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Spiral Tubes,</td> +<td align="right" valign="bottom"><a href="#Page_56">56</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Stoppers, Making and Grinding,</td> +<td align="right" valign="bottom"><a href="#Page_51">51</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Table for Glass-blower,</td> +<td align="right" valign="bottom"><a href="#Page_3">3</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Taps, Vacuum,</td> +<td align="right" valign="bottom"><a href="#Page_65">65</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Thistle-headed Funnels,</td> +<td align="right" valign="bottom"><a href="#Page_57">57</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Traps, Air,</td> +<td align="right" valign="bottom"><a href="#Page_69">69</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Tube, Combustion, how to work it,</td> +<td align="right" valign="bottom"><a href="#Page_25">25</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Tubes.</td> +<td> </td> +<td><i>See</i> <a href="#IndSec_3">Glass Tubes</a>.</td> +</tr> + +<tr> +<td align="left" valign="top">—— <span class="ssfont">T</span>-,</td> +<td align="right" valign="bottom"><a href="#Page_41">41</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">—— <span class="ssfont">U</span>-,</td> +<td align="right" valign="bottom"><a href="#Page_56">56</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Turpentine, Camphorated, for Grinding,</td> +<td align="right" valign="bottom"><a href="#Page_11">11</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top"><span class="ssfont">U</span>-Tubes,</td> +<td align="right" valign="bottom"><a href="#Page_56">56</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Vacuum Taps,</td> +<td align="right" valign="bottom"><a href="#Page_65">65</a>-<a href="#Page_68">68</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">—— Tube, To Make a,</td> +<td align="right" valign="bottom"><a href="#Page_60">60</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Vitreous Silica, Apparatus required for Making,</td> +<td align="right" valign="bottom"><a href="#Page_89">89</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">—— Behaviour under sudden changes of Temperature,</td> +<td align="right" valign="bottom"><a href="#Page_87">87</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">—— Bulbs, etc., Making Joints on,</td> +<td align="right" valign="bottom"><a href="#Page_93">93</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">—— Expansion of,</td> +<td align="right" valign="bottom"><a href="#Page_86">86</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">—— Hardness of,</td> +<td align="right" valign="bottom"><a href="#Page_85">85</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">—— Insulating Power of,</td> +<td align="right" valign="bottom"><a href="#Page_85">85</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">—— Melting Point of,</td> +<td align="right" valign="bottom"><a href="#Page_85">85</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">—— Permeability to Gases,</td> +<td align="right" valign="bottom"><a href="#Page_87">87</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">—— Properties of,</td> +<td align="right" valign="bottom"><a href="#Page_84">84</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">—— Rods, Making Joints on,</td> +<td align="right" valign="bottom"><a href="#Page_94">94</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">—— Tubes, Method of Making,</td> +<td align="right" valign="bottom"><a href="#Page_90">90</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">—— Tubes, Making Joints on,</td> +<td align="right" valign="bottom"><a href="#Page_94">94</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Welding or Soldering Tubes together,</td> +<td align="right" valign="bottom"><a href="#Page_39">39</a>, <a href="#Page_62">62</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">White Enamel, Uses of,</td> +<td align="right" valign="bottom"><a href="#Page_39">39</a>, <a href="#Page_56">56</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Widening the Ends of Tubes,</td> +<td align="right" valign="bottom"><a href="#Page_36">36</a>.</td> +<td> </td> +</tr> + +<tr> +<td align="left" valign="top">Working-place,</td> +<td align="right" valign="bottom"><a href="#Page_2">2</a>.</td> +<td> </td></tr> + +<tr> +<td colspan="3"> </td> +</tr> + +</table> + +<hr class="c25" /> +<p class="center">Printed by <span class="smcap">T.</span> and <span class="smcap">A. Constable</span>, Printers to His Majesty<br /> +at the Edinburgh University Press, Scotland</p> +<hr class="c25" /> +<p> </p> + +<div class="tnbox"> +<h3>Transciber's Notes:</h3> +<ul> + <li>Some obvious typographical errors and inconsistencies corrected.</li> + <li>Footnotes moved to end of chapter.</li> + <li>Table of Contents: slightly expanded to include all named sections.</li> + <li>Page 39: footnote anchor and number before paragraph removed.</li> + <li>Page 43: Caption <b><span class="smcap">Fig. 18.</span></b> added.</li> + <li>Page 43: comma added: <i>or better, ...</i></li> + <li>Page 46: <i>DE through E</i> changed to <i>DE</i> through <i>E</i>.</li> + <li>Page 66: <i>lead</i> changed to <i>leak</i>.</li> + <li>Page 70: <i>endiometer</i> changed to <i>eudiometer</i>.</li> + <li>Figure 20 (C): added letter <i>d</i> to illustration.</li> +</ul> +</div> + + + + + + + +<pre> + + + + + +End of the Project Gutenberg EBook of The Methods of Glass Blowing and of +Working Silica in the Oxy-Gas Flame, by W. 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