---------------------------------------- --------------------------- ,transcriber's ,notes3 ,italics are indicated by the underscore character1 as in word4 ,bold face is indicated by the equal character1 as in word4 ,subscript is indicated by subscript4 ,footnotes have been moved to below the paragraph they refer to4 ,table of contents3 #hd-je changed to #hd-ie4 ,paragraph starting ,uniting ,pieces of ,glass to ,each ,other1 known as ,welding1 or ,soldering3 footnote anchor #a and number #a4 before next paragraph deleted4 ,caption ,,fig4 #ah added to illustration4 ,paragraph directly below ,,fig4 #ah3 comma added 7or better144474 #bnd paragraph under ,,fig4 #ai3 ,,de through ,e changed to ,,de through ,e4 #bnd paragraph under ,,fig4 #cd3 whence it might gradually lead into changed to whence it might gradually leak into4 ,to,c3 several sections added1 so that all named sections are included4 endiometer changed to eudiometer4 ,some minor typographical errors and inconsistencies corrected4 ---------------------------------------- --------------------------- ,,the ,,methods ,,of ,,glass ,,blowing ,,and ,,of ,,working ,,silica ,,by ,,the ,,same ,,author ,with #be ,illustrations4 ,crown #hvo1 #bs4 ,a ,practical ,introduction to ,chemistry4 ,intended to give a practical acquaintance with the ,elementary ,facts and ,principles of ,chemistry4 ,,longmans1 ,,green1 ,,and ,,co4 ,,london1 ,,new ,,york1 ,,bombay1 ,,calcutta1 ,,and ,,madras4 ,the ,methods of ,glass ,blowing ,,and ,,of ,working ,silica in the ,oxy-,gas ,flame ,,for ,,the ,,use ,,of ,,chemical ,,and ,,physical ,,students ,,by ,w4 ,a4 ,,shenstone1 ,f4,r4,s4 ,,formerly ,,lecturer ,,on ,,chemistry ,,in ,,clifton ,,college ,,ninth ,,impression ,,longmans1 ,,green1 ,,and ,,co4 #ci ,,paternoster ,,row1 ,,london ,,fourth ,,avenue #cj,,th ,,street1 ,,new ,,york ,,bombay1 ,,calcutta1 ,,and ,,madras #aiaf ,,preface ,this book consists of a reprint of the third edition of my ,methods of ,glass-blowing1 together with a new chapter in which ,i have described the comparatively new art of working vitreous silica4 ,the individual operations of glass-blowing are much less difficult than is usually supposed1 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 persistent4 ,constructing finished apparatus is often more difficult1 as it may involve the performance of several operations under disadvantageous conditions1 and may demand a little ingenuity on the part of the operator4 ,but ,i think the suggestions in ,chapter ,,iv4 will make this comparatively easy also to those who have mastered the operations described in ,chapter ,,iii4 ,the working of vitreous silica1 though more tedious and expensive than glass-blowing1 is not really more difficult1 and as it seems certain that this new material will soon play a useful part in chemical and physical research1 ,i believe the addition now made to the earlier book will add considerably to its value4 ,as glass is much less expensive to work with than silica1 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 material4 ,therefore1 in writing the new chapter1 ,i have assumed that the reader is already more or less familiar with the rest of the book1 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-pipe4 ,w4 ,a4 ,,shenstone4 ,,clifton ,,college1 ,dec4 #aija4 ,,contents ,,chapter ,i4 ,,glass-,,blower',s ,,apparatus4 ,,page ,introductory--,the ,working-place--,the ,blow-pipe--,the ,bellows--,automatic ,blower--,blow-pipe ,flames1 #a-aa ,,chapter ,,ii4 ,,varieties ,,of ,,glass ,,and ,,their ,,management4 ,characters of good ,glass--,cleaning and ,preparing a ,tube--,presenting ,glass to the ,flame--,methods of working with ,lead and ,soft ,soda ,glass respectively--,management of ,soda ,glass--,annealing--,the ,use of ,combustion ,tube1 #ab-be ,,chapter ,,iii4 ,,cutting ,,and ,,bending ,,glass--,,forming ,,glass ,,apparatus ,,before ,,the ,,blow-,,pipe--,,making ,,and ,,grinding ,,stoppers ,,to ,,apparatus1 ,,etc4 ,cutting ,glass ,tubes--,bending ,glass ,tubes--,rounding and ,bordering the ,ends of ,tubes--,sealing--,choking1 or ,contracting the ,bore of a ,glass ,tube--,widening ,tubes--,piercing ,tubes--,uniting ,pieces of ,glass to ,each ,other1 ,known as ,welding1 or ,soldering--,blowing a ,bulb or ,globe of ,glass--,making and ,grinding ,stoppers1 #bf-ed ,,chapter ,,iv4 ,,making ,,thistle ,,funnels1 ,u-,,tubes1 ,,etc4--,,combining ,,the ,,parts ,,of ,,complicated ,,apparatus--,,mercury1 ,,and ,,other ,,air-,,tight ,,joints--,,vacuum ,,taps--,,safety ,,taps--,,air-,,traps4 ,electrodes--,u-,tubes--,spiral ,tubes--,thistle ,funnels--,closing ,tubes containing ,chemicals--,construction of ,apparatus ,consisting of ,several ,parts--,modes of ,combining the ,parts of ,heavy ,apparatus--,mercury ,joints--,vacuum ,taps--,lubricating ,taps--,air-,traps1 #ee-fi ,,chapter ,v4 ,,graduating ,,and ,,calibrating ,,glass ,,apparatus4 ,to ,graduate ,tubes1 etc4--,to ,divide a ,given ,line into ,equal ,parts--,to ,calibrate ,apparatus--,to ,calibrate ,tubes for ,measuring ,gases--,to ,calibrate the ,tube of a ,thermometer1 #gj-ha ,,chapter ,,vi4 ,,glass ,,tubing4 ,diagrams of ,glass ,tubes1 showing the chief sizes in which they are made1 #hb-hc ,,chapter ,,vii4 ,,vitreous ,,silica ,introductory--,properties of ,vitreous ,silica--,preparing non-splintering ,silica from ,brazil ,pebble--,apparatus--,the ,method of ,making ,silica ,tubes--,precautions--,making ,larger ,tubes and other ,apparatus of ,silica--,quartz ,fibres1 #hd-ie ,,index1 #ig ,,chapter ,i4 ,,glass-,,blower',s ,,apparatus4 ,introductory4--,i shall endeavour to give such an account of the operations required in constructing glass apparatus as will be useful to chemical and other students2 and as this book probably will come into the hands of beginners who are not in a position to secure any further assistance1 ,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 laboratory4 ,i shall not give any particular account of the manufacture of such apparatus as thermometers1 taps1 etc41 because1 being in large demand1 they can be bought so cheaply that time is not profitably spent in making them4 ,but it will be found that what is included will enable any one1 who will devote sufficient time to acquiring the necessary manipulative dexterity1 to prepare such apparatus as test-tubes1 distillation flasks1 apparatus for washing gases1 ozone generating tubes1 etc41 when they are required1 as they often are1 without delay or for special purposes4 ,the amateur probably will not succeed in turning out apparatus so finished in appearance as that of the professional glass-blower until after long practice1 but after a little daily practice for the space of a few weeks1 any one who is fairly skilful in ordinary manipulation1 and who perseveres in the face of failure at first1 will find himself able to make almost all the apparatus he needs for lecture or other experiments1 with a considerable saving in laboratory expenses1 and1 which very often is more important1 without the delay that occurs when one depends upon the professional glass-worker4 ,in the case of those who1 like myself1 work in the provinces1 this latter advantage is a very weighty one4 ,after the description of the instruments used in glass-blowing1 which immediately follows1 the following arrangement of the subject has been adopted4 ,in the first place1 an account of the two chief kinds of glass is given1 and of the peculiarities in the behaviour of each of them before the blow-pipe1 which is followed by a tolerably minute description of the method of performing each of the fundamental operations employed in fashioning glass apparatus4 ,these are not very numerous1 and they should be thoroughly mastered in succession1 preferably upon tubes of both soda and lead glass4 ,then follows1 in ,chapter ,,iv41 an account of the application of these operations to setting up complete apparatus1 full explanations of the construction of two or three typical pieces of apparatus being given as examples1 and also descriptions of the modes of making various pieces of apparatus which in each case present one or more special difficulties in their construction2 together with an account1 which1 ,i think1 will be found valuable1 of some apparatus that has been introduced1 chiefly during recent years1 for experimenting upon gases under reduced pressure1 e4g4 vacuum taps and joints4 ,finally1 in ,chapter ,v41 there is a short account of the methods of graduating and calibrating glass apparatus for use in quantitative experiments4 ,the ,working-place4--,the blow-pipe must be placed in a position perfectly free from draughts4 ,it should not face a window1 nor be in too strong a light1 if that can be avoided1 for a strong light will render the non-luminous flames1 which are used in glass-blowing1 almost invisible1 and seriously inconvenience the operator1 who cannot apply the various parts of the flames to his glass with the degree of certainty that is necessary2 neither can he perceive the condition of the glass so correctly in a strong light1 for though in many operations the glass-worker is guided by feeling rather than by seeing1 yet sight plays a very important part in his proceedings4 ,my own blow-pipe is placed near a window glazed with opaque glass1 which looks southwards1 but is faced by buildings at a short distance4 ,in dull weather the light obtained is good2 but on most days ,i find it advantageous to shade the lower half of the window with a green baize screen4 ,some glass-blowers prefer gaslight to daylight4 ,the form of the table used is unimportant1 provided that it is of a convenient height1 and allows free play to the foot which works the blower underneath it4 ,the blower should be fixed in a convenient position1 or it will get out of control at critical moments4 ,the table1 or that part of it which surrounds the blow-pipe1 should be covered with sheet-iron to protect it from the action of the fragments of hot glass that will fall upon it4 ,the tubes that supply air and gas to the blow-pipe should come from beneath the table1 and may pass through holes cut for the purpose4 ,many glass-blowers prefer to work at a rather high table1 and sit on a rather high stool1 so that they are well above their work4 ,no doubt this gives extra command over the work in hand1 which is often valuable4 ,on the other hand1 it is somewhat fatiguing4 ,for a long spell of labour at work which is not of a novel character nor specially difficult1 ,i am disposed to recommend sitting on a chair or low stool1 at a table of such height as will enable the elbows to rest easily upon it whilst the glass is held in the flame4 ,the precise heights that are desirable for the table and stool1 and the exact position of the blow-pipe1 will depend upon the height and length of arm of the individual workman1 and it must therefore be left to each person to select that which suits him best4 ,a moveable rest made of wood1 for supporting the remote end of a long piece of glass tube a few inches above the table1 whilst the other end is being heated in the flame1 will be found convenient4 ,the ,blow-pipe4--,formerly a lamp1 in which sweet oil or tallow was burnt1 was employed for glass-working1 and such lamps are still occasionally used4 ,thus1 lamps burning oil or tallow were used on board the ,challenger for hermetically sealing up flasks of water collected at various depths to preserve them for subsequent examination4 ,i shall not1 however1 give an account of such a lamp1 for the gas apparatus is so much more convenient for most purposes that it has now practically superseded the oil lamps4 ,fig4 #a shows a gas blow-pipe of exceedingly simple construction1 which can be easily made1 and with which good work can be done4 ,illustration3 ,,fig4 #a4 ,the tube ,a is of brass1 and has a side tube ,b brazed to it1 ten to twelve centimetres from the end ,e1 according to the dimensions of the tube4 ,a tube of glass1 ,,ec1 is fitted into ,a by a cork at ,d4 ,b is connected to a supply of gas by a flexible tube1 ,c is similarly connected to the blower4 ,by means of ,,ce a stream of air can be forced into gas burning at the mouth of the blow-pipe ,g1 and various flames1 with the characters described in a later section1 can be produced with this instrument4 ,for producing the pointed flame 7,fig4 #c1 p4 #i7 the opening ,e of the air-tube should be contracted to the size of a large knitting needle4 ,for producing a flame of large size1 rich in air 7,fig4 #d1 p4 #i71 the internal diameter of ,e may be nearly half as great as that of ,a without disadvantage4 ,this blow-pipe may be fixed in position by the spike ,f1 which will fit into holes in a block of wood or a large cork4 ,several of these holes in various positions should be made in the block1 so that the position of the blow-pipe may be varied easily4 ,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 gas4 ,these taps should be fixed to the table and be connected with the gas and air supplies respectively on one side1 and with the blow-pipe on the other1 by flexible tubes4 ,if blow-pipes of this kind be used1 at least two of them should be provided2 one of small dimensions for working on small tubes and joints1 the other of larger size for operations on larger tubes4 ,it will be convenient to have both of them ready for use at all times1 as it is sometimes necessary to employ large and small flames on the same piece of work in rapid succession4 ,by having several air-tubes of different sizes fitted to each blow-pipe1 a greater variety of work may be done4 ,for the larger blow-pipe1 the internal diameter of ,a may be fifteen to seventeen millimetres4 ,for the smaller instrument1 eleven millimetres for the diameter of ,a would be a useful size4 ,when a slightly greater outlay can be afforded it will be most convenient to purchase the blow-pipe4 ,they can be obtained of compact form1 supported on stands with universal joints giving great freedom of movement1 and with taps for regulating the supplies of gas and air1 at comparatively small cost4 ,as figures of various blow-pipes can be seen in the price-lists of most dealers in apparatus1 they are not given here4 ,their introduction would be of but little service1 for the construction of that which is adopted can be readily ascertained by taking it to pieces4 ,the simplest blow-pipe usually used for glass-working is that of ,herapath4 ,this has two taps to regulate the air and gas supplies respectively1 and will give a considerable variety of flames1 which will be discussed subsequently4 ,an excellent blow-pipe1 made on the same principle as that shown in ,fig4 #a1 but more substantially and with interchangeable jets1 can be obtained from ,messrs4 ,muller of ,holborn for a moderate outlay4 ,another very good blow-pipe is the ,automaton blow-pipe of ,mr4 ,fletcher of ,warrington4 ,in this1 one tap regulates the supply both of air and gas1 which is a great gain when difficult work is in hand4 ,automaton blow-pipes are made of two sizes4 ,i have found that the larger size1 with a powerful bellows1 heats large pieces of lead glass very satisfactorily4 ,on the other hand1 the fine-pointed oxidising flame of the ,herapath blow-pipe is1 perhaps1 the most suitable for working joints of lead glass4 ,therefore a good equipment would be a small ,herapath blow-pipe and a large-sized ,automaton4 ,if only one blow-pipe is purchased it should be either a medium-sized ,herapath1 or the smaller ,automaton1 as those are most useful for general work4 ,mr4 ,fletcher also makes an ingenious combination of two blow-pipes in which the gas and air supplies are regulated by a single lever-handle4 ,this is very convenient1 and gives flames that answer well with tubes made of soft soda glass1 and it is very useful for general work4 ,for use with lead glass the supply of air is rather too small1 and does not enable one to get such good results4 ,this can be easily amended1 however4 ,by slightly increasing the size of the air-tube of the smaller blow-pipe1 and having increased the supply of air to the larger blow-pipe also1 by reducing the external diameter of the end of the innermost tube1 ,i now get medium-sized brush flames and pointed flames with this blow-pipe1 that are equal to any ,i have used for heating lead glass4 ,for small laboratories the inexpensive ,no4 #e ,bunsen burner of ,mr4 ,fletcher1 which is convertible into a blow-pipe1 will be very useful4 ,jets of several sizes to fit the air-tubes of blow-pipes may be obtained with them1 and will serve for regulating the supply of air to the flame4 ,the ,bellows4--,the usual blowing apparatus is some form of foot-blower4 ,these may be obtained fitted to small tables with sheet-iron tops4 ,but a much less expensive apparatus is the large foot-blower made by ,mr4 ,fletcher of ,warrington1 which can be used at an ordinary table or laboratory bench4 ,good foot-blowers can also be obtained from makers of furnace bellows4 ,no part of the glass-blower's equipment exceeds the bellows in importance4 ,the best blower procurable should therefore be adopted4 ,a bellows which1 when used with a large blow-pipe1 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 #ag-ba are followed1 should on no account be received4 ,i am told that at some places1 where the water-supply is at very high pressure1 it is utilised for working blow-pipes by means of the apparatus described below1 and that some glass-workers find it advantageous to use such automatic blowers4 ,but after a little practice1 the effort of working the blower with the foot whilst manipulating the glass is not a source of serious inconvenience4 ,indeed1 as it gives a certain degree of control over the flame without the use of the hands1 the foot-blower is preferable4 ,it is worth while to describe an automatic blower1 however4 ,automatic ,blower 7,fig4 #b74--;,a strong glass tube ,a is welded into a somewhat larger tube ,b so that its end is about #b mm4 from the contraction at ,g4 ,b has a side tube ,c joined to it4 ,the narrow end of ,b is fixed by an india-rubber cork to a strong bottle ,d of two or three litres capacity4 ,the india-rubber cork also carries an exit tube ,e1 and ,d is pierced near its bottom by a small hole at ,f4 ,illustration3 ,,fig4 #b ,in using the apparatus ,a is connected with the water-supply1 and water passing through ,g1 carries air with it into ,d4 ,the water escapes from ,d by the opening at ,f1 and the air is allowed to pass out by the tube ,e1 its passage being regulated by a tap4 ,fresh supplies of air enter ,b by ,c4 ,blow-pipe ,flames--,the ,pointed ,flame4--,if the gas tap of a ,herapath blow-pipe be adjusted so that comparatively little gas can pass1 and if the foot-blower be then worked cautiously1 a long tongue of flame ending in a fine point will be produced 7,fig4 #c74 ,this flame will subsequently be described as the pointed flame4 ,it should be quite free from luminosity1 and as the amount of air necessary for securing a pointed flame is large1 in proportion to the gas1 there is excess of oxygen towards the end ,c4 ,by adjusting the proportions of air and gas1 pointed flames of various dimensions can be obtained with the same blow-pipe4 ,the part of a pointed flame to be used in glass-working is the tip1 or in some cases the space slightly beyond the tip4 ,illustration3 ,,fig4 #c4 ,illustration3 ,,fig4 #d4 ,the ,brush ,flame4--,if a large supply of gas be turned on and a considerable blast of air sent into the flame1 a non-luminous flame of great size will be obtained 7,fig4 #d74 ,in form it somewhat resembles a large camel's hair pencil1 and may conveniently be described as a brush flame4 ,the chief advantage of a large-sized blow-pipe is1 that with it a large brush flame may be produced1 which is often invaluable4 ,by gradually diminishing the supply of gas and air smaller brush flames may be produced4 ,the jet used to supply air to the ,herapath blow-pipe is usually too fine1 and consequently does not permit the passage of sufficient air to produce a brush flame that contains excess of oxygen1 even with the aid of a very powerful blower4 ,my own ,herapath blow-pipe only gives a satisfactory oxidising brush flame when the jet is removed altogether from the end of the air-tube4 ,for producing pointed flames the finer jet of the air-tube must be used1 but when a highly oxidising flame of large size is required it must be removed4 ,the internal diameter of the central air-tube should be nearly half as great as that of the outer or gas-supply tube4 ,fletcher's ,automaton with the large air jet gives a very liberal supply of air1 and produces an excellent oxidising brush flame4 ,in the case of the larger-sized ,automaton a consequence of this is1 however1 that when fitted with the large jet it will not give so good a pointed flame as the ,herapath1 which1 in its turn1 gives an inferior oxidising brush4 ,by fitting finer jets to the air-tube of ,fletcher's apparatus pointed flames can be secured when necessary4 ,the ,smoky ,flame4--,by turning on a very free supply of gas1 and only enough air to give an outward direction to the burning gas1 a smoky flame1 chiefly useful for annealing and for some simple operations on lead glass1 is produced4 ,the ,gimmingham blow-pipe and ,fletcher's combination blow-pipe1 in addition to the above flames1 are also adapted to produce a non-luminous flame1 resembling that of the ,bunsen gas-burner1 which is very convenient for the preliminary heating of the glass1 and also for gradually cooling finished apparatus4 ,it is not necessary to describe the method of using these last-mentioned blow-pipes4 ,with the more complicated of them directions for its use are supplied4 ,mr4 ,madan has suggested the use of oxygen in place of air for producing the oxidising flame required for working lead glass1 and to produce a flame of high temperature for softening tubes of hard1 or combustion1 glass4 ,for the latter purpose the employment of oxygen may be adopted with great advantage4 ,for working lead glass1 however1 it is quite unnecessary if the directions already given are followed4 ,the student's subsequent success will so largely depend upon his acquaintance with the resources of his blow-pipe1 and on the facility with which he can take advantage of them1 that no pains should be spared in the effort to become expert in its management as soon as possible4 ,a few experiments should now be made1 therefore1 upon the adjustment of the flame1 until the student is able to produce and modify any form of flame with promptness and certainty4 ,illustration3 ,,fig4 #e4 ,the remaining apparatus used in glass-working consists of triangular and other files1 charcoal pastils for cutting glass1 pieces of sound charcoal of various diameters with conical ends2 it is convenient to have one end somewhat less pointed than the other 7,fig4 #e74 ,corks of various sizes2 the smallest1 which are most frequently needed1 should be carefully cut with sharpened cork borers from larger corks4 ,besides these there should be provided some freshly distilled turpentine in which camphor has been dissolved1#a fine and coarse emery powder1 and some sheets of cotton-wadding1 an india-rubber blowing-bottle1 glass tubes1 a little white enamel1 and a pair of iron tongs4 #a ,half an ounce of camphor to about six ounces of turpentine will do very well4 ,,chapter ,,ii4 ,,varieties ,,of ,,glass ,,and ,,their ,,management4 ,all the varieties of glass that are ordinarily met with contain silica 7,si,o#b7 associated with metallic oxides4 ,in a true glass there are at least two metallic oxides4 ,the unmixed silicates are not suitable for the purposes of glass4 ,they are not so capable of developing the viscous condition when heated as mixtures--some of them are easily attacked by water1 and many of those which are insoluble are comparatively infusible4 ,there is generally excess of silica in glass1 that is1 more than is necessary to form normal silicates of the metals present4 ,the best proportions of the various constituents have been ascertained by glass-makers1 after long experience2 but the relation of these proportions to each other1 from a chemical point of view1 is not easy to make out4 ,the varieties of glass from which tubes for chemical glass-blowing are made may be placed under three heads1 and are known as#b-- ,soft soda glass4 ,also known as ,french glass4 ,lead glass4 ,also known as ,english glass4 ,hard glass4 #b ,for details of the composition of the various glasses1 some work on glass-making may be consulted4 ,in purchasing glass tubes1 it is well to lay in a considerable stock of tubes made of each of the two first varieties1 and1 if possible1 to obtain them from the manufacturer1 for it frequently happens that pieces of glass from the same batch may be much more readily welded together than pieces of slightly different composition4 ,yet it is not well to lay in too large a stock1 as sometimes it is found that glass deteriorates by prolonged keeping4 ,as it is frequently necessary to make additions1 alterations1 or repairs to purchased apparatus1 it is best to provide supplies both of soft soda glass and lead glass1 for though purchased glass apparatus is frequently made of lead glass1 yet sometimes it is formed from the soda glass1 and as it is a matter of some difficulty to effect a permanent union between soda glass and lead glass1 it is desirable to be provided with tubes of both kinds4 ,many amateurs find that soda glass is in some respects easier to work with than lead glass4 ,but1 on the other hand1 it is somewhat more apt to crack during cooling1 which causes much loss of time and disappointment4 ,also1 perhaps in consequence of its lower conductivity for heat1 it very often breaks under sudden changes of temperature during work4 ,if1 however1 a supply of good soda glass is obtained1 and the directions given in this book in regard to annealing it are thoroughly carried out1 these objections to the use of soda glass will1 to a great extent1 be removed4 ,i find1 however1 that when every precaution has been taken1 apparatus made of soda glass will bear variations of temperature less well than that made of lead glass4 ,therefore1 although the comparatively inexpensive soda glass may be employed for most purposes without distrust1 yet ,i should advise those who propose to confine themselves to one kind of glass1 to take the small extra trouble required in learning to work lead glass4 ,in order to secure glass of good quality1 a few pieces should be obtained as a sample1 and examined by the directions given below4 ,when the larger supply arrives1 a number of pieces1 taken at random1 should be examined before the blow-pipe1 to compare their behaviour with that of the sample pieces1 and each piece should be separately examined in all other respects as described subsequently4 ,hard glass is used for apparatus that is required to withstand great heat4 ,it is difficult to soften1 especially in large pieces4 ,it should only be employed1 therefore1 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 put4 ,what is sold as ,jena combustion tube should be preferred when this is the case4 ,characters of good ,glass4--,glass tubes for glass-blowing should be as free as possible from knots1 air-bubbles1 and stripes4 ,they should be in straight pieces of uniform thickness1 and cylindrical bore4 ,it is not possible to obtain glass tubes of absolutely the same diameter from one end to the other in large quantities1 but the variations should not be considerable4 ,when a sharp transverse scratch is made with a good file on a piece of tube1 and the scratch is touched with a rather fine point of red-hot glass 7this should be lead glass for a lead glass tube1 and soda glass for a tube of soda glass71 the crack which is started should pass round the glass1 so that it may be broken into two pieces with regular ends4 ,if the crack proceeds very irregularly1 and especially if it tends to extend along the tube1 the glass has been badly annealed1 and should not be employed for glass-blowing purposes4 ,it is important that the point of hot glass used shall be very small1 however4 ,even good glass will frequently give an irregular fracture if touched with a large mass of molten glass4 ,finally1 glass tube which is thin and of small diameter should not crack when suddenly brought into a flame4 ,but larger and thicker tubes will not often withstand this treatment4 ,they should not crack1 however1 when they are brought into a flame gradually1 after having been held in the warm air in front of it for a minute or so4 ,good glass does not readily devitrify when held in the blow-pipe flame4 ,as devitrified glass very often may be restored to its vitreous condition by fusion1 devitrification most frequently shows itself round the edges of the heated parts1 and may be recognised by the production of a certain degree of roughness there4 ,it is believed to be due to the separation of certain silicates in the crystallised form4 ,hard glass1 which contains much calcium1 is more apt to devitrify than the more fusible varieties4#c #c ,the presence of silicates of calcium and aluminum are considered to promote a tendency to devitrification in glass2 and glasses of complex composition are more apt to devitrify than the simpler varieties4 ,see ,glass-making1 by ,powell1 ,chance1 and ,harris1 ,chap4 ,,iv4 ,glass tubes are made of various sizes4 ,when purchasing a supply1 it is necessary to be somewhat precise in indicating to the vendor the sizes required4 ,i have therefore placed at the end of the book1 in an appendix1 a table of numbered diagrams4 ,in ordering tubes it will usually only be necessary to give the numbers of the sizes wished for1 and to specify the quantity of each size required4 ,in ordering glass tubes by weight1 it must be remembered that a great many lengths of the smaller sizes1 but very few lengths of the larger sizes1 go to the pound4 ,larger-sized tubes than those on the diagram are also made4 ,in ordering them the external diameter and thickness of glass preferred should be stated4 ,cleaning and ,preparing a ,tube4--,it is frequently much easier to clean the tube from which a piece of apparatus is to be made than to clean the finished apparatus4 ,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 twice1 or1 with small tubes1 to push a bit of wet paper or cotton wool through them4 ,if the dirt cannot be removed in this way1 the interior of the tube should be moistened with a little sulphuric acid in which some bichromate of potassium has been dissolved4 ,in any case1 it must finally be repeatedly rinsed with distilled water1 and dried by cautiously warming it1 and sucking or blowing air through it4 ,in order to avoid heating delicate apparatus which has become damp and needs drying1 the water may be washed out with a few drops of spirit1 which is readily removed at a low temperature4 ,before using a glass tube for an operation in which it will be necessary to blow into it1 one end of it must be contracted1 unless it is already of such a size that it can be held between the lips with perfect ease2 in any case1 its edges must be rounded4 ,for descriptions of these operations1 see page #ce4 ,the other end must be closed4 ,this may be done by means of a cork4 ,presenting ,glass to the ,flame4--,glass tubes must never be brought suddenly into the flame in which they are to be heated4 ,all glass is very likely to crack if so treated4 ,it should in all cases be held for a little while in front of the flame1 rotated constantly in the hot air and moved about1 in order that it may be warmed over a considerable area4 ,when it has become pretty hot by this treatment1 it may be gradually brought nearer to the flame1 and1 finally1 into contact with it1 still with constant rotation and movement1 so as to warm a considerable part of the tube4 ,when the glass has been brought fairly into contact with the flame1 it will be safe to apply the heat at the required part only4 ,care must be taken in these preliminary operations to avoid heating the more fusible glasses sufficiently to soften them4 ,methods of working with ,lead and soft ,soda ,glass respectively4--,when lead glass is heated in the brush flame of the ordinary ,herapath blow-pipe1 or within the point of the pointed flame1 it becomes blackened on its surface1 in consequence of a portion of the lead becoming reduced to the metallic state by the reducing gases in the flame4 ,the same thing will happen in bending a lead glass tube if it is made too hot in a luminous flame4 ,a practical acquaintance with this phenomenon may be acquired by the following experiment3-- ,take a piece of lead glass tube1 bring it gradually from the point of a pointed flame to a position well within the flame1 and observe what happens4 ,when the glass reaches the point ,a 7,fig4 #c71 or thereabouts1 a dark red spot will develop on the glass1 the area of the spot will increase as the glass is brought further in the direction ,a to ,b4 ,if the glass be then removed from the flame and examined1 it will be found that a dark metallic stain covers the area of the dark red spot previously observed4 ,repeat the experiment1 but at the first appearance of the dark spot slowly move the glass in the direction ,a to ,c4 ,the spot will disappear1 and1 if the operation be properly performed1 in its place there will be a characteristically greenish-yellow luminous spot of highly heated glass4 ,in this proceeding the reduced lead of the dark spot has been re-oxidised on passing into the hot gases1 rich in oxygen1 which abound at the point of the flame4 ,if one end of the tube has been previously closed by a piece of cork1 and if air be forced into the tube with the mouth from the open end before the luminous spot has become cool1 the glass will expand4 ,if the experiment be repeated several times1 with pointed flames of various sizes1 the operator will quickly learn how to apply the pointed flame to lead glass so that it may be heated without becoming stained with reduced lead4 ,if the spot of reduced metal produced in the first experiment be next brought into the oxidising flame1 it also may gradually be removed4 ,on occasion1 therefore1 apparatus which has become stained with lead during its production1 may be rendered presentable by suitable treatment in the oxidising flame4 ,the process of re-oxidising a considerable surface in this way after it has cooled down is apt to be very tedious1 however1 and1 especially in the case of thin tubes or bulbs1 often is not practicable4 ,in working with lead glass1 therefore1 any reduction that occurs should be removed by transferring the glass to the oxidising flame at once4 ,small tubes1 and small areas on larger tubes of ,english glass1 may be softened without reduction by means of the pointed oxidising flame2 but it is not easy to heat any considerable area of glass sufficiently with a pointed flame4 ,and though it is possible1 with care1 to employ the hot space immediately in front of the visible end of an ordinary brush flame1 which is rich in air1 yet1 in practice1 it will not be found convenient to heat large masses of lead glass nor tubes of large size1 to a sufficiently high temperature to get the glass into good condition for blowing1 by presenting them to the common brush flame4 ,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 flame1 the difficulty might be overcome by heating it for working in the brush flame1 and subsequently oxidising the reduced lead4 ,it is1 however1 difficult1 as previously stated1 to re-oxidise a large surface of glass which has been seriously reduced by the action of the reducing gases of the flame1 after it has cooled4 ,moreover1 there is this very serious objection1 that if1 as may be necessary1 the action of the reducing flame be prolonged1 the extensive reduction that takes place diminishes the tendency of the glass to acquire the proper degree of viscosity for working it1 the glass becomes difficult to expand by blowing1 seriously roughened on its surface1 and often assumes a very brittle or rotten condition4 ,when it is only required to bend or draw out tubes of lead glass1 they may be softened sufficiently by a smoky flame1 which1 probably owing to its having a comparatively low temperature1 does not so readily reduce the lead as flames of higher temperature4 ,but for making joints1 collecting masses of glass for making bulbs1 and in all cases where it is required that the glass shall be thoroughly softened1 the smoky flame does not give good results4 ,in the glass-works1 where large quantities of ornamental and other glass goods are made of lead or flint glass1 the pots in which the glass is melted are so constructed that the gases of the furnace do not come into contact with the glass2#d and as the intensely-heated sides of the melting-pot maintain a very high temperature within it by radiation1 the workman has a very convenient source of heat to his hand1--he has1 in fact1 only to introduce the object1 or that part of it which is to be softened1 into the mouth of the melting-pot1 and it is quickly heated sufficiently for his purpose1 not only without contact of reducing gases1 but in air4 ,he can therefore easily work upon very large masses of glass4 ,in a special case1 such a source of heat might be devised by the amateur4 ,usually1 however1 the difficulty may be overcome without special apparatus4 ,it is1 in fact1 only necessary to carry out the instructions given below to obtain a considerable brush flame rich in air1 in which the lead glass can be worked1 not only without discoloration1 but with the greatest facility4 #d ,see ,principles of ,glass-making1 p4 #ca4 ,to ,produce an ,oxidising ,brush ,flame4--,the blower used must be powerful1 the air-tube of the blow-pipe must be about half as great in diameter as the outer tube which supplies the gas4 ,the operator must work his bellows so as to supply a strong and steady blast of air1 and the supply of gas must be regulated so that the brush flame produced is free from every sign of incomplete combustion1#e which may be known by its outer zone being only faintly visible in daylight1 and quite free from luminous streaks 7see ,fig4 #d1 p4 #i74 ,when a suitable flame has been produced1 try it by rotating a piece of lead glass at or near the end of the inner blue part of the flame 7,a ,fig4 #d72 the appearance of the glass will quickly indicate reduction4 ,when this occurs move the glass forward to the end of the outer zone ,b1 but keep it sufficiently within the flame to maintain it at a high temperature4 ,if all is right the metallic reduction will quickly disappear1 the glass will become perfectly transparent once more1 and will present the appearance previously observed in the experiments with the pointed flame1 or1 if very hot1 assume a brownish-red appearance4 ,if this does not occur1 the supply of air must be increased or the supply of gas diminished until the proper effects are secured4 #e ,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 glass1 which will occur if the bellows is worked with too much zeal4 ,in working upon lead glass with the highly oxidising brush flame1 it is a good plan to heat it in the reducing part of the flame ,a for thoroughly softening the glass1 and to remove it to the oxidising flame ,b to burn away the reduced metal4 ,in prolonged operations1 in order that reduction may never go too far1 hold the glass alternately in the hot reducing flame and in the oxidising flame4 ,the inferiority of the outer oxidising flame to those portions nearer the inner blue zone for softening the glass1 may perhaps be accounted for by the presence of a larger proportion of unconsumed air in the former1 which being heated at the expense of the hot gases produced by combustion1 thereby lowers the temperature of the flame4 ,at or near ,a 7,fig4 #d7 where the combustion is nearly complete1 but no excess of air exists1 the temperature will naturally be highest4 ,if a very large tube be rotated in the oxidising flame at ,b 7,fig4 #d7 it may happen that the flame is not large enough to surround the tube1 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 condition4 ,this difficulty may be overcome by placing two blow-pipes exactly opposite to each other1 at such a distance that there is an interval of about an inch between the extremities of their flames1 and rotating the tube between the two flames4 ,it may be necessary to provide two blowers for the blow-pipes if they are large4 ,again1 if a very narrow zone of a tube of moderate size is to be heated1 two pointed flames may be similarly arranged with advantage4 ,occasionally more than two flames are made to converge upon one tube in this manner4 ,another method of preventing one side of a tube from cooling down whilst the other is presented to the flame1 is to place a brick at a short distance from the extremity of the flame4 ,the brick checks the loss of heat considerably4 ,a block of beech wood may be used for the same purpose1 the wood ignites and thereby itself becomes a source of heat1 and is even more effective than a brick4 ,fuller details of the management of lead glass under various circumstances will be found in the subsequent descriptions of operations before the blow-pipe4 ,before proceeding to work with soda glass1 the student should not only verify by experiments what has been already said1 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 flame1 varying the proportions of gas and air in every way1 repeating1 and repeating1 his experiments until he can obtain any desired effect with certainty and promptitude4 ,he should practice some of the simpler operations given in ,chapter ,,iii4 in order to impress what he has learned well on his mind4 ,management of ,soda ,glass4--,in working with soda glass the following points must be constantly kept in mind4 ,that as it is much more apt than lead glass to crack when suddenly heated1 great caution must be exercised in bringing it into the flame2 and that in making large joints or in making two joints near each other1 all parts of the tube adjacent to that which1 for the moment1 is being heated1 must be kept hot1 as it is very apt to crack when adjacent parts are unequally heated4 ,this may be effected by stopping work at short intervals and warming the cooler parts of the tube1 or by the use of the brick or block of wood to check radiation1 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 work1 not coming sufficiently into contact to soften the glass1 however1 but near enough to keep it well heated4 ,lastly1 to prevent the finished work from falling to pieces after or during cooling1 the directions given under the head of annealing must be carefully carried out4 ,in very much of his work the glass-blower is guided more by the feel of the glass than by what he sees4 ,the power of feeling glass can only be acquired by practice1 and after a certain amount of preliminary failure4 ,as a rule ,i have observed that beginners are apt to raise their glass to a higher temperature than is necessary1 and that they employ larger flames than are wanted4 ,if glass be made too soft it may fall so completely out of shape as to become unworkable except in very skilful hands4 ,the following rules1 therefore1 should be strictly adhered to4 ,always employ in the first instance the smallest flame that is likely to do the work required4 ,in operations involving blowing out viscous glass1 attempt to blow the glass at low temperatures before higher ones are tried4 ,after a little experience the adoption of the right-sized flame for a given purpose1 and the perception of the best condition of glass for blowing it1 become almost automatic4 ,i may add that glass which is to be bent needs to be much less heated than glass which is to be blown4 ,annealing4--,if apparatus1 the glass of which is very thin and of uniform substance1 be heated1 on removal from the source of heat it will cool equally throughout1 and therefore may often be heated and cooled without any special precautions4 ,if the glass be thick1 and especially if it be of unequal thickness in various parts1 the thinner portions will cool more quickly than those which are more massive2 this will result in the production of tension between the thicker and thinner parts in consequence of inequality in the rates of contraction1 and fractures will occur either spontaneously or upon any sudden shock4 ,thus1 if a hot tube be touched with cold or wet iron1 or slightly scratched with a cold file1 the inequality of the rate of cooling is great1 and it breaks at once4 ,it is therefore necessary to secure that hot glass shall cool as regularly as possible4 ,and this is particularly important in the case of articles made of soda glass4 ,some glass-blowers content themselves with permitting the glass to cool gradually in a smoky flame till it is covered with carbon1 and then leave it to cool upon the table4 ,but under this treatment many joints made of soda glass which are not quite uniform in substance1 but otherwise serviceable1 will break down4 ,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 viscous1 and slowly passed through the cooler parts of the chamber so that it emerges cold at the other end4 ,this method of annealing is not practicable in a small laboratory4 ,but fortunately very good results can be obtained by the following simple device1 viz43-- ,by wrapping the hot apparatus that is to be annealed closely in cotton wool1 and leaving it there till quite cold4 ,the glass should be wrapped up immediately after it is blown into its final shape1 as soon as it is no longer soft enough to give way under slight pressure4 ,and it should be heated as uniformly as possible1 not only at the joint1 but also about the parts adjacent to the joint1 at the moment of surrounding it with the cotton4 ,lead glass appears to cool more regularly than soda glass1 and these precautions may be more safely neglected with apparatus made of lead glass2 but not always4 ,at the date of writing ,i have had several well-blown joints of thick-walled capillary tube to ,no4 #af 7see diagram1 p4 #hb71 break during cooling1 in consequence of circumstances making it dangerous to heat the neighbourhood of the joint so much as was necessary4 ,the black carbonaceous coat formed on hot glass when it is placed in cotton wool may be removed by wiping with methylated spirit1 or1 if it be very closely adherent1 by gently rubbing with fine emery1 moistened with the spirit4 ,cotton wool is rather dangerously inflammable2 it should therefore be kept out of reach of the blow-pipe flame1 and care should be taken that the glass is not placed in contact with it at a sufficiently high temperature to cause its ignition4 ,another method of annealing is to cover the hot glass with hot sand1 and allow it to cool therein4 ,as in the case of lead glass1 so with soda glass4 ,a thorough acquaintance with the effect of the various parts of the flame upon it should be gained before further work is entered upon1 for which purpose an hour or more spent in observing its behaviour in the flame will be fully repaid by increased success subsequently4 ,the ,use of ,combustion ,tube4--,it is often necessary to construct apparatus of what is known as hard glass or combustion tube4 ,it is almost as easy to work combustion tube as to deal with lead and soda glass if the oxy-hydrogen flame be employed4 ,it is not necessary to set up a special apparatus for this purpose2 many of the ordinary blow-pipes can be used with oxygen instead of with air4 ,it is only necessary to connect the air-tube of the blow-pipe with a bottle of compressed oxygen instead of with the bellows4 ,the connecting tube should not be too wide nor too long1 in order to avoid the accumulation in it1 by accident1 of large quantities of explosive mixtures4 ,two precautions are necessary in manipulating hard glass in the oxy-hydrogen flame4 ,the glass must not be overheated4 ,at first one is very apt to go wrong in this direction4 ,the supply of oxygen must not be too great2 a small hissing flame is not what is wanted4 ,if either of these precautions are neglected most glass will devitrify badly4 ,with a little care and experience1 devitrification can be absolutely avoided4 ,ordinary combustion tube can be used1 but ,i find that the glass tube 7,verbrennungsroehr7 made by ,schott ,co4 of ,jena1 which can be obtained through any firm of dealers in apparatus1 is far better than the ordinary tube4 ,by following these instructions1 any one who has learned how to work with lead or soda glass will find it easy to manipulate hard glass4 ,,chapter ,,iii4 ,,cutting ,,and ,,bending ,,glass--,,forming ,,glass ,,apparatus ,,before ,,the ,,blow-,,pipe--,,making ,,and ,,grinding ,,stoppers ,,to ,,apparatus1 ,,etc4 ,in the later pages of this ,chapter it will be assumed that the operations first described have been mastered4 ,the beginner should therefore practise each operation until he finds himself able to perform it with some degree of certainty4 ,generally speaking1 however1 after the failure of two or three attempts to perform any operation1 it is best to give up for a few hours1 and proceed to the work next described1 returning to that upon which you have failed subsequently4 ,if1 unfortunately1 it should happen that the work next in order involves the performance of the operation in which the failure has occurred1 it is best to pass on to some later work which does not demand this particular accomplishment1 or to rest a while1 and re-attack the difficulty when refreshed4 ,cutting ,glass ,tubes4--,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 it1 and on pulling apart the two ends1 it will break clean off4 ,it is important that the file be sharp4 ,in pulling apart the ends the scratch should be held upwards1 and the pull should have a downward direction1 which will tend to open out the scratch4 ,in the case of a large tube1 a scratch will not ensure its breaking clean across4 ,the tube must be filed to some depth1 half-way1 or even all round it4 ,a good way of breaking a tube is to place the file in the table after scratching the glass1 to hold the glass tube above its edge with one hand on each side of the scratch1 and to strike the under side of the tube a sharp blow upon the edge of the file1 directly beneath the scratch4 ,in this way very even fractures of large and moderately thin tubes may be made4 ,it answers particularly well for removing short ends of tube1 not long enough to hold2 the tube is held firmly upon the file1 and a sharp blow given to the short end with a piece of large tube or a key4 ,a file whose faces have been ground till they are nearly smooth1 so as to leave very finely-serrated edges1 will be found useful for cutting glass tubes4 ,such a file should be used almost as a knife is used for cutting a pencil in halves4 ,the simple methods just described are too violent to be applied to delicate apparatus1 too tedious when employed upon the largest tubes1 and very difficult to apply when the tube to be cut is very thin1 or too short to permit the operator to get a good grip of it on either side of the file mark4 ,in such cases1 one or other of the following methods will be useful3-- #a4 ,make a scratch with a file1 and touch it with the end of a very small piece of glass drawn out and heated at the tip to its melting point4 ,it is important that the heated point of glass be very small1 or the fracture is likely to be uneven1 or to spread in several directions4 ,also1 it is best to use hot soda glass for starting cracks in tubes of soda glass1 and lead glass for doing so in lead glass tubes4 ,if the crack does not pass quite round the tube1 you may pull it asunder1 as previously described1 or you may bring the heated piece of glass with which the crack was started to one end of the crack1 and slowly move it 7nearly touching the glass7 in the required direction2 the crack will extend1 following the movements of the hot glass4 ,instead of hot glass1 pastils of charcoal are sometimes employed for this purpose4 ,they continue to burn when once lighted1 and there is no need to re-heat them from time to time4 ,they should be brought as close to the glass as is possible without touching it1 and1 when no longer needed1 should be extinguished by placing the lighted end under sand1 or some other incombustible powder1 for they must not be wetted4 #b4 ,a method much practised by the makers of sheet glass1 and suitable for large objects1 is to wrap a thread of hot glass round the tube1 at once removing it1 and touching any point of the glass which the thread covered with water or a cold iron1 when a crack will be started and will pass round the glass where it was heated by the thread4 #c4 ,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 glass1 then1 the iron being removed1 and a point on the heated glass being at once touched with cold iron as before1 it will break as desired4 ,or a string1 moistened with turpentine1 may be loosely twisted round the tube1 and the turpentine ignited1 afterwards the application of sudden cold to any point on the zone of hot glass will usually start a crack1 which1 if necessary1 may be continued in the usual manner4 ,the last three methods are chiefly useful in dealing with the largest and thickest tubes1 and with bottles4 ,a fairly stout copper wire1 bent into the form of a bow so that it can be applied when hot to a considerable surface of a glass tube1 will be found superior to the point of hot glass or metal usually employed1 for leading cracks in glass tubes4 ,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 tube1 with considerable precision4 ,i am indebted for this suggestion to ,mr4 ,vernon ,boys and ,dr4 ,ebert4 ,bending ,glass ,tubes4--,the blow-pipe flame is not a suitable source of heat for bending tubes1 except in certain cases which will be mentioned in a subsequent paragraph4 ,for small tubes1 and those of moderate size1 a fish-tail burner1 such as is used for purposes of illumination1 will answer best4 ,use a flame from one to two inches in breadth--from ,a to ,a 7,fig4 #f71 according to the size of the tube which is to be bent4 ,if the length of tube that is heated be less than this1 the bend will probably buckle on its concave side4 ,illustration3 ,,fig4 #f4 ,the tube to be heated should be held in the position shown in ,fig4 #f1 supported by the hands on each side4 ,it should be constantly rotated in the flame1 that it may be equally heated on all sides4 ,in the figure the hands are represented above the tube1 with their backs upwards4 ,a tube can be held equally well from below1 the backs of the hands being then directed downwards1 and this1 ,i think1 is the more frequent habit4 ,it is difficult to say which position of the hands is to be preferred4 ,i lately observed how a tube was held by three skilful amateurs and by a professional glass-blower4 ,all the former held the tube with the hands below it4 ,the latter1 however1 held it from above1 as in ,fig4 #f4 ,he1 however1 was working with a rather heavy piece of tube1 and ,i am inclined myself to recommend that position in such cases4 ,during a long spell of work1 the wrist may be rested from time to time by changing the position of the hands4 ,when the tube has softened1 remove it from the flame1 and gently bend it to the desired angle4 ,the side of the tube last exposed to the flame will be slightly hotter1 and therefore softer1 than that which is opposite to it4 ,this hotter side should form the concave side of the bent tube4 ,illustration3 ,,fig4 #g4 ,the exact condition in which the glass is most suitable for bending can only be learned by making a few trials4 ,if it is too soft in consequence of being overheated1 the sides will collapse4 ,if1 in the endeavour to heat the side ,a of ,fig4 #g a little more than ,b1 ,b is insufficiently heated1 the tube will be likely to break on the convex side ,b4 ,if the bent tube be likely to become flattened1 and this cannot always be prevented in bending very thin tubes1 the fault may be avoided by blowing gently into one end of the tube whilst bending it1 for which purpose the other end should be closed beforehand4 ,a tube already flattened may1 to some extent1 be blown into shape after closing one end and re-heating the bent portion1 but it is not easy to give it a really good shape4 ,when making a bend like that in ,fig4 #g1 to secure that the arms of the tube ,c and ,d1 and the curve at ,b1 shall be in one plane1 the tube should be held in a position perpendicular to the body1 and brought into the position shown in the figure during bending1 by which means it will be found easy to secure a good result4 ,lead glass tubes must be removed from the flame before they become hot enough to undergo reduction4 ,if they should become blackened1 however1 the stain may be removed by re-heating in the oxidising flame 7see p4 #ah74 ,when a very sharp bend is to be made1 it is sometimes best to heat a narrow zone of the glass rather highly in the blow-pipe flame1 and to blow the bend into shape at the moment of bending it1 as previously described1 one end having been closed for that purpose beforehand4 ,lead glass should be heated for this purpose in the oxidising flame 7pp4 #ag to #bb74 ,the processes of bending large tubes1 making ,u-tubes and spiral tubes1 are more difficult operations1 and will be explained in ,chap4 ,,iv4 ,rounding and ,bordering the ,ends of ,tubes4--,after cutting a piece of glass tube in two pieces1 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 melt4 ,the oxidising point of a pointed flame may be used for both kinds of glass4 ,the flame will be coloured yellow by soda glass at the moment of melting4 ,this indication of the condition of soda glass should be noted1 for it serves as a criterion of the condition of the glass4 ,the ends of soda glass tubes may also be rounded in the flame of a common ,bunsen's burner4 ,when the end of a tube is to be closed with a cork or stopper1 its mouth should be expanded a little1 or bordered4 ,to do this1 heat the end of the tube by rotating it in the flame till it softens1 then remove it from the flame1 at once introduce the charcoal cone 7,fig4 #e1 p4 #aa71 and rotate it with gentle pressure against the softened glass till the desired effect is produced4 ,in doing this it is very important that the end of the tube shall be uniformly heated1 in order that the enlargement shall be of regular form4 ,if the tube cannot be sufficiently expanded at one operation1 it should be re-heated and the process repeated4 ,borders1 such as are seen on test-tubes1 are made by pressing the softened edge of the tube against a small iron rod4 ,the end of the rod should project over the softened edge of the tube at a slight angle1 and be pressed against it1 passing the rod round the tube1 or rotating the tube under the rod4 ,sealing1 that is closing the ends of tubes1 or other openings1 in glass apparatus4 ,in performing this and all the other operations of glass blowing1 the following points must be constantly kept in mind3-- 7a47 ,that it is rarely safe to blow glass whilst it is still in the flame1 except in certain special cases that will be mentioned subsequently4 ,therefore always remove apparatus from the flame before blowing4 7b47 ,that when heating glass tubes1 unless it is specially desired to heat one portion only1 the tube must be constantly rotated in the flame to ensure that it shall be uniformly heated1 and to prevent the tube or mass of glass from assuming an irregular form4 7c47 ,always blow gently at first1 and slowly increase the force applied till you feel or see the glass giving way4 ,it is a good plan to force the air forward in successive short blasts rather than in one continued stream4 7d47 ,when it is necessary to force air into tubes of fine bore1 such as thermometer tubes1 the mouth must not be used1 for moisture is thereby introduced into the tube1 which it is very difficult to remove again in many cases4 ,all tubes of very small bore should be blown with the aid of an india-rubber blowing-bottle1 such as are used for spray-producers1 ,galton's whistles1 etc4 ,the tube to be blown must be securely fixed to the neck of the bottle1 which is then held in one hand1 and air is forced from it into the tube as it is required4 ,these bottles are frequently of service to the glass-blower--e4g41 when tubes of very fine bore have to be united1 it is necessary to maintain an internal pressure slightly exceeding that of the air throughout the operation1 in order to prevent the viscous glass from running together and closing the tube4 ,an india-rubber blowing-ball is very convenient for this purpose4 ,to seal the end of a glass tube 7,fig4 #h71 adjust the flame so that it will heat a zone of glass about as broad as the diameter of the tube to be sealed 7see ,a1 ,fig4 #h74 ,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 7p4 #bh74 ,bring the tube gradually into the flame1 and heat it with constant rotation1 till the glass softens 7for lead glass the oxidising flame must be used1 as has been already explained74#f ,when the glass begins to thicken1 gently pull asunder the two ends1 taking care not to pull out the softened glass too much1 but to allow the sides to fall together1 as shown at ,a4 ,when this has occurred1 heat the glass at the narrow part till it melts1 and pull asunder the two ends4 ,the closed end should present the appearance shown at ,d4 ,if the glass be drawn out too quickly its thickness will be unduly reduced1 and it will present the appearance shown at ,b4 ,in that case apply a pointed flame at b1 and repeat the previous operation so as to contract the tube as at c1 taking care not to allow the glass to become much increased nor decreased in thickness4 #f ,remember that when the lead glass is heated to the proper temperature it will present an appearance which may be described as a greenish phosphorescence4 ,at higher temperatures it assumes an orange-red appearance4 ,if it loses its transparency and assumes a dull appearance1 it must be moved further into the oxidising parts of the flame4 ,if a considerable mass of glass be left at d1 it may be removed by heating it to redness1 touching it with the pointed end of a cold glass tube1 to which it will adhere1 and by which it may be pulled away4 ,illustration3 ,,fig4 #h4 ,when the end of the tube presents the appearance shown in the diagram ,d1 and the mass of glass at d is small1 the small lump that remains must be removed by heating it till it softens1 and gently blowing with the mouth1 so as to round the end and distribute the glass more regularly1 as shown in ,e4 ,the whole end1 from the dotted line e1 must then be heated with constant rotation in the flame4 ,if this final heating of the end e be done skilfully1 the glass will probably collapse and flatten1 as at ,f4 ,the end must then be gently blown into the form shown at ,g4 ,if a flat end to the tube be desired1 the tube may be left in the condition shown by ,f1 or a thin rounded end may be flattened by pressure on a plate of iron4 ,if a concave end be wished for1 it is only necessary to gently suck air from the tube before the flattened end has become solid4 ,in each case1 immediately after the tube is completed1 it must be closely wrapped in cotton wool and left to cool4 ,with good lead glass this last process1 though advantageous1 is not absolutely necessary2 and as glass cools slowly when enveloped in cotton wool1 this precaution may frequently be neglected in the case of apparatus made from lead glass4 ,illustration3 ,,fig4 #i4 ,in order to draw out tubes for sealing1 close to one end1 and thus to avoid waste of material1 it is a good plan to heat simultaneously the end of the glass tube ,a which is to be sealed1 and one end of a piece of waste tube ,e of about the same diameter1 and when they are fused to bring them together as at ,,dd 7,fig4 #i74 ,e will then serve as a handle in the subsequent operations on ,a4 ,such a rough joint as that at ,d must not be allowed to cool too much during the work in hand1 or ,e and ,a may separate at an inconvenient moment4 ,or the glass at the end of the tube may be pressed together to close the tube1 and the mass of glass may be seized with a pair of tongs and drawn away4 ,choking1 or ,contracting the ,bore of a ,glass ,tube4--,if it be not desired to maintain the uniformity of external dimensions of the tube whilst decreasing the diameter of the bore1 the tube may be heated and drawn out as described in the description of sealing tubes on pp4 #cb-ce4 ,this may be done as shown at ,a or ,b in ,fig4 #h1 according to the use to which the contracted tube is to be put4 ,illustration3 ,,fig4 #aj4 ,greater strength and elegance will be secured by preserving the external diameter of the tube unchanged throughout1 as shown in ,fig4 #aj4 ,for this purpose heat the tube with the pointed flame1 if it be small1 or in the brush flame if it be of large size1 constantly rotating it till the glass softens and the sides show an inclination to fall together1 when this occurs1 push the two ends gently towards ,a4 ,if the tube should become too much thickened at ,a1 the fault may be corrected by removing it from the flame and gently pulling the two ends apart till it is of the proper size4 ,if the bore at the contracted part of the tube should become too much reduced1 it may be enlarged by closing one end of the tube with a small cork1 and blowing gently into the open end after sufficiently heating the contracted part4 ,the tube should be rotated during blowing or the enlargement produced may be irregular4 ,when the external diameter of the tube is to be increased as well as its bore diminished1 press together the ends of a tube heated at the part to be contracted1 as already described1 and regulate the size of the bore by blowing into the tube if at any time it threatens to become too much contracted4 ,widening ,tubes4--,tubes may be moderately expanded at their extremities by means of the charcoal cone 7see ,bordering1 p4 #ca74 ,they may be slightly expanded at any other part by closing one end and gently blowing into the open end of the tube1 after softening the glass at the part to be widened before the blow-pipe4 ,but the best method of obtaining a wide tube with narrow extremities 7,fig4 #aa7 is to join pieces of narrow tube ,,aa to the ends of a piece of wider tube ,b of the desired dimensions4 ,the method of performing this operation is described under welding1 on pp4 #ci-dg4 ,illustration3 ,,fig4 #aa4 ,illustration3 ,,fig4 #ab4 ,piercing ,tubes4--,the glass-blower very frequently requires to make a large or small opening in some part of a tube or other piece of apparatus4 ,this is known as piercing4 ,suppose it is desired to make a small hole at the point a in ,a 7,fig4 #ab74 ,when the tube has been brought to the flame with the usual precautions1 allow the end of the pointed flame to touch it at a till an area corresponding to the desired size of the opening is thoroughly softened4 ,then expand the softened glass by blowing to the form shown at ,b4 ,re-heat a1 blow a small globe as at ,c1 and carefully break the thin glass1 then smooth the rough edges by rotating them in the flame till they form a mouth like that of ,d4 ,instead of leaving the bulb to be broken at the third stage ,c1 it is a good plan to blow more strongly1 so that the bulb becomes very thin and bursts1 the removal of the thin glass is then accompanied by less risk of producing a crack in the thicker parts of the glass4 ,openings may be made in a similar manner in the sides of tubes or in globes1 in fact1 in almost any position on glass apparatus4 ,if another tube is to be attached at the opening1 it is a good plan to proceed to this operation before the tube has cooled down4 ,illustration3 ,,fig4 #ac4 ,the openings obtained by the method above described are too large when platinum wires are to be sealed into them4 ,suppose that it is necessary to pierce the tube ,a of ,fig4 #ac in order to insert a platinum wire at a2 direct the smallest pointed flame that will heat a spot of glass to redness on the point a4 ,when the glass is viscous1 touch it with the end of a platinum wire w1 to which the glass will adhere2 withdraw the wire and the viscous glass will be drawn out into a small tube1 as shown at ,b2 by breaking the end of this tube a small opening will be made4 ,introduce a platinum wire into the opening1 and again allow the flame to play on the glass at that point2 it will melt and close round the wire4 ,before the hot glass has time to cool1 blow gently into the mouth of the tube to produce a slightly curved surface1 then heat the neighbouring parts of the tube till the glass is about to soften1 and let it cool in cotton wool4 ,unless this is done1 ,i find that glass tubes into which platinum wires have been sealed are very apt to break during or after cooling4 ,to ensure that the tube shall be perfectly air-tight1 a small piece of white enamel should be attached to the glass at a before sealing in the wire4 ,uniting ,pieces of ,glass to ,each ,other1 known as ,welding1 or ,soldering4--,the larger and more complicated pieces of glass apparatus are usually made in separate sections1 and completed by joining together the several parts4 ,this is therefore a very important operation1 and should be thoroughly mastered before proceeding to further work4 ,in order to produce secure joints1 the use of tubes made of different kinds of glass must be avoided4 ,soda glass may be joined securely to soda glass1 especially if the tubes belong to the same batch1 and lead glass to lead glass4 ,but1 though by special care a joint between lead glass and soda glass1 if well made1 will often hold together1 yet it is never certain that it will do so4 ,to join two ,tubes of ,equal ,diameters4--,close one end of one of the tubes with a small cork4 ,heat the open end of the closed tube1 and either end of the other tube in a small flame until they are almost melted1 taking care that only the ends of the tubes are heated1 and not to let the glass be thickened2 bring the two ends together with sufficient pressure to make them adhere1 but not sufficient to compress the glass to a thickened ring4 ,before the joint has time to cool too much1 adjust your blow-pipe for a pointed flame1 if you are not already working with that kind of flame1 and allow the point of the flame to play on any spot on the joint till it is heated to redness2 rotate the tube a little so as to heat the glass adjacent to that which is already red-hot1 and repeat this till the whole circumference of the rough joint has been heated4#g ,repeat the operation last described1 but1 when each spot is red-hot1 blow gently into the open end of the tube so as to slightly expand the viscous glass4 ,finally1 rotate the whole joint in the flame till the glass is softened1 and blow gently as before into the open end of the tube1 still rotating it1 in order that the joint may be as symmetrical as possible4 ,if in the last operation the diameter of the joint becomes greater than that of the rest of the tube1 it may be cautiously re-heated and reduced by pulling it out1 or this may be secured by gently pulling apart the two ends1 whilst the operator blows it into its final shape4 #g ,some glass-blowers at once work on the glass as next described1 without this preliminary treatment4 ,i find that some glass1 usually soda glass1 will not always bear the necessary movements without breaking unless first heated all round4 ,illustration3 ,,fig4 #ad4 ,when small tubes1 or tubes of fine bore1 are to be joined1 in order to prevent the fused glass from running together and closing the tube1 it is a good plan to border and enlarge the ends that are to be united1 as at ,a 7,fig4 #ad74 ,some glass-blowers prefer to border all tubes before uniting them4 ,when a narrow tube is to be joined to one that is only slightly wider1 expand the end of the narrow tube till it corresponds in size to the larger tube4 ,if the tube be too narrow to be enlarged by inserting a charcoal cone1 seal one end and pierce it as directed 7on p4 #cg74 ,for joining small thin-walled tubes ,mr4 ,crookes recommends the use of a small ,bunsen flame4 ,in welding pieces of lead glass tube1 take care that the heated glass is perfectly free from reduced lead at the moment when the two ends of viscous glass are brought into contact4 ,illustration3 ,,fig4 #ae4 ,to join ,tubes of ,unequal ,sizes ,end to ,end 7,fig4 #ae74--;,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 tube1 then seal the smaller tube to the contracted end of the larger according to the directions given for joining tubes of equal size4 ,when a good joint has been made1 the tube presents the appearance of ,a1 ,fig4 #ae1 the union being at about bb4 ,next heat the whole tube between the dotted lines aa1 and blow it into the shape of ,b in which the dotted line dd should correspond to the actual line of junction of the two tubes4 ,in making all joints it is important to leave no thick masses of glass about them4 ,if the glass be fairly thin and uniformly distributed1 it is less likely to break during or after annealing under any circumstances1 and especially if it has to bear alternations of temperature4 ,joining a ,tube to the ,side of another ,tube 7,fig4 #af74--,one of the tubes must be pierced as at ,a in ,fig4 #af 7for the method1 see p4 #cg71 and its two ends closed with small pieces of cork4 ,the edges of the opening1 and one end of the other tube1 must then be heated till they melt1 and united by pressing them together4 ,the joint may then be finished as before4 ,illustration3 ,,fig4 #af4 ,a properly blown joint will not present the appearance of ,b 7,fig4 #af71 but rather that of ,c4 ,this is secured by directing the pointed flame upon the glass at aa 7,b7 spot by spot1 and blowing out each spot when it is sufficiently softened4 ,if the tubes are large1 the whole joint should subsequently be heated and blown1 but in the case of small tubes this is of less importance4 ,finally it is to be wrapped whilst hot in cotton wool for the annealing process4 ,if a second tube has to be joined near to the first one1 say at b1 it is well to proceed with it before the joint first made cools down1 and the joint first made1 especially if soda glass be used1 must be held in the flame from time to time during the process of making the second joint to keep it hot2 if this be not done the first joint is very likely to break4 ,a joint previously made may1 however1 be re-heated1 if well made and well annealed4 ,a three-way tube1 like that in ,fig4 #ag1 is made by bending ,a 7,fig4 #af7 to an angle1 and joining ,b to an opening blown on the convex side of the angle2 or1 ,a of ,fig4 #af may be bent as desired after attaching ,b in the ordinary way4 ,illustration3 ,,fig4 #ag4 ,tubes may also be joined to openings made in the sides of globes or flasks2 great care must be taken1 however1 especially if the walls of the globe be thin1 to secure that the tube is well attached to the mouth of the opening when the melted ends are first brought into contact1 for1 with thin glass1 any hole that may be left will probably increase whilst the joint is being blown into shape1 owing to cohesion causing the glass to gather in a thickened ring round an enlargement of the original opening4#h #h ,if such an opening be observed1 it may usually be closed by touching its edges with a fused point of glass at the end of a drawn out tube4 ,in order to unite a tube of soda glass to a tube of lead glass1 the end of the soda glass tube must be carefully covered with a layer of soft arsenic glass4#i ,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 point4 #i ,this can be obtained from ,messrs4 ,powells1 ,whitefriars ,glassworks4 ,to ,seal a ,tube inside a ,larger ,tube or ,bulb4--,suppose that an air-trap 7#c of ,fig4 #ah7 is to be constructed from a small bulb 7,a7 blown on a glass tube 7#a74 ,illustration3 ,,fig4 #ah ,either cut off the tube close to the bulb at ,b1 or better1 remove the end by melting the glass and pulling it away from ,b1 and then pierce ,a at ,b1 ,no4 #b1 by heating the glass there and blowing out a small bulb as described under ,piercing4 ,prepare a tube 7#d7 drawn out at ,e with a bulb blown at ,d4 ,insert ,e into the opening ,b1 press ,d well against the mouth ,b and slowly rotate before the blow-pipe till ,d adheres to ,b4 ,then heat and blow the joint spot by spot as in other cases1 taking care that the glass is blown out on each side of the joint2 lastly1 heat the whole joint between aa1 and blow it into its final shape4 ,these joints are very apt to break after a few minutes or hours if the glass of ,d be much thicker than that of the bulb ,a4 ,they should be wrapped in cotton wool for annealing as soon as possible1 as the rate at which the tube ,e cools is likely to be less rapid than that of the parts of the apparatus which are more freely exposed to the air2 therefore all such internal joints require very careful annealing1 and they should always be made as thin as is consistent with the use to which they are to be put4 ,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 introduced1 and proceeding as in the case of the air-trap just described4 ,ozone generators of the form shown on next page 7,fig4 #ai71 afford an interesting example of the insertion of smaller tubes into larger4 ,on account of the small space that may be left between the inner and outer tubes of an ozone generator1 and of the length of the inner tube1 its construction needs great care4 ,i find the following mode of procedure gives good results4 ,select the pieces of tube for this instrument as free from curvature as possible4 ,for the inner tube1 a tube #ab mm41 or rather more1 in external diameter1 and of rather thin glass1 is drawn out1 as for closing1 until only a very narrow tube remains at ,c1 the end of ,c is closed the area round ,c is carefully blown into shape1 so that by melting off ,c the tube ,a will be left with a well-rounded end4 ,a small bulb of glass is next blown on ,a at ,b4 ,this bulb must be of slightly greater diameter than the contracted end ,e of the larger tube 7,,ii471 so that ,b will just fail to pass through ,e4 ,the length from ,b to ,c must not be made greater than from ,e to ,g on the outside tube4 ,the end at ,c is then to be cut off so as to leave a pin-hole in the end of ,a4 ,illustration3 ,,fig4 #ai4 ,the outer tube 7,,ii471 whose diameter may be #e or #f mm4 greater than that of ,a1 is prepared by sealing a side tube on it at ,f1 after previously contracting the end ,e4 ,for this purpose the end ,e should be closed and rounded1 and then re-heated and blown out till the bulb bursts4 ,to ensure that the diameter of the opening is less than that of the tube1 care must be taken not to re-heat too large an area of the end before blowing it out4 ,it is very important that the cross section at ,e shall be in a plane at right angles to the axis of the tube4 ,wrap a strip of writing paper1 one inch in breadth1 closely round the end of ,a at ,c till the tube and paper will only just pass easily into the mouth ,d of the outer tube1 push the inner tube ,a1 with the paper upon it1 into ,d1 and when the paper is entirely within ,d1 withdraw ,a1 and cautiously push the paper a little further into the outer tube4 ,insert ,a into ,,de through ,e1 so that the bulb ,b is embraced by ,e4 ,close ,d with a cork4 ,ascertain that the paper does not fit sufficiently tightly between the two tubes to prevent the free passage of air1 by blowing into the mouth ,k of ,a4 ,air should escape freely from ,e when this is done4 ,gradually bring the line of contact of ,b and ,e and the surrounding parts of the tube before a pointed flame1 after previously warming them by holding near a larger flame1 and rotate them before the flame so that the glass may soften and adhere4 ,then heat the joint spot by spot as usual4 ,in blowing this joint1 take care that the glass on each side of the actual joint is slightly expanded4 ,it should present the form shown by the dotted lines in ,,iii4 7these are purposely exaggerated1 however74 ,finally1 heat the whole joint between the lines ,,ji till it softens1 and simultaneously blow and draw it into its final shape as seen at ,,iii4 ,the side tube ,f should not be too near the end ,e4 ,if1 however1 it is necessary to have them close together1 the joint ,f must be very carefully annealed when it is made2 it must also be very cautiously warmed up before the construction of the joint at ,h is begun1 and must be kept warm by letting the flame play over it from time to time during the process of making the latter joint4 ,a good joint may be recognised by its freedom from lumps of glass1 its regularity of curve1 and by a sensibly circular line at ,h1 where the two tubes are united4 ,when the joint after annealing has become quite cold1 the pin-hole at ,c on the inner tube may be closed1 after removing the paper support1 by warming the outer tube1 and then directing a fine pointed flame through ,d on to ,c4 ,and the end ,d of the outer tube may be closed in the ordinary manner1 or a narrow tube may be sealed to it4 ,as the end of glass at ,d will be too short to be held by the fingers when hot1 another piece of tube of similar diameter must be attached to it to serve as a handle 7see p4 #ce1 ,fig4 #i74 ,blowing a ,bulb or ,globe of ,glass4--,for this purpose it is very important that the glass tube employed shall be of uniform substance4 ,the size and thickness of the tube to be employed depends partly on the dimensions of the bulb desired1 and partly on the size of neck that is required for the bulb4 ,it is easier to blow large bulbs on large-sized tubes than on those of smaller size4 ,when it is necessary to make a large globe on a small tube1 it can be done1 however1 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 formed4 ,for the purpose of blowing a very large bulb on a small tube1 it is best to unite a wide tube to that which is to serve as the neck1 as it will save some time in collecting the necessary mass of glass from which to form the globe4 ,illustration3 ,,fig4 #bj4 ,to blow a ,bulb at the ,end of a ,tube4--,select a good piece of tube1 say #a4e cm4 in diameter1 and about #cj cm4 long2 draw out one end to a light tail 7a1 ,fig4 #bj7 about #c inches in length4 ,then heat up a short length of the tube at b1 with a small brush flame1 by rotating the glass in the flame1 and gently press it together when soft to thicken it2 blow into it if necessary to preserve the regularity of its figure4 ,repeat this process on the portion of tube nearest to that which has been first thickened1 and so on1 till as much glass has been heated and thickened as you judge will serve to make a bulb of the size desired4 ,you should have a mass of glass somewhat resembling that shown at ,b 7,fig4 #bj71 but probably consisting of the results of more successive operations than are suggested in that diagram4 ,apply the flame as before to the narrower parts cc of ,b1 gently compress and blow until all the small bulbs first made are brought together into a mass still somewhat resembling the enlarged end of ,b1 but more nearly cylindrical1 with the glass as regularly distributed as possible1 and of such length from d to the contracted part that the whole of it may easily be heated simultaneously with the large brush flame of your blow-pipe4 ,take great care in the foregoing operations not to allow the sides of the mass of glass to fall in and run together1 and1 on the other hand1 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 possible4 ,when you are satisfied with the mass of glass you have collected1 melt off the tail a1 and remove the pointed end of glass that remains1 as directed on page #cc4 ,turn on as large a brush flame as is necessary to envelop the whole mass of glass that you have collected1 and heat it with constant rotation1 so that it may gradually run together to the form seen at ,c 7,fig4 #bj71 taking care that it does not get overheated near d1 or the tube which is to form the neck will soften and give way4 ,the position in which the mass of heated glass is to be held will depend upon circumstances2 if the mass of glass be not too great1 it is best to keep it in a nearly horizontal position4 ,if the mass of glass be very large1 it may be necessary to incline the end ,b downwards2 but as that is apt to result in an excess of glass accumulating towards d1 avoid doing so if possible by rotating the glass steadily and rapidly4 ,if at any time the glass shows indications of collapsing1 it must be removed from the flame and gently blown into shape1 during which operation it may be rotated in the perpendicular position2 indeed1 to promote a regular distribution of the glass by allowing it plenty of time to collect1 it is well from time to time to remove the heated mass of glass from the flame1 and slightly expand it by blowing4 ,finally1 when a regular mass of glass1 such as is shown at ,c 7,fig4 #bj7 has been obtained1 remove it from the flame1 and blow it to its final dimensions4 ,a succession of gentle puffs quickly succeeding each other should be employed1 in order that the progress of the bulb may be more easily watched and arrested at the right moment4 ,during the process of blowing1 the hot glass must be steadily rotated4 ,to collect the glass for blowing a bulb of lead glass1 employ the flame described on pp4 #ag-bb for heating lead glass4 ,if the tube be held horizontally whilst the globe is blown1 its form will most nearly approach that of a true globe4 ,if it be held in the perpendicular position1 with the mass of glass depending from it1 the form of the bulb will usually be somewhat elongated4 ,if it be held perpendicularly1 with the mass of glass upwards1 the resulting bulb will be flattened4 ,when a bulb is not of a sufficiently regular form1 it may sometimes be re-made by re-collecting the glass1 and re-blowing it4 ,the greatest care is needed at the earlier stages of re-heating to prevent the glass from collapsing into a formless and unworkable mass4 ,this is to be prevented in all such cases by gently blowing it into shape from time to time whilst gathering the glass4 ,illustration3 ,,fig4 #ba4 ,to blow a ,bulb between two ,points 7,fig #ba74--,select a piece of suitable tube1 seal or cork one end1 gather together a mass of glass at the desired part1 as directed for blowing a bulb at the end of a tube2 when a mass of glass has been collected of sufficient thickness1 blow it into shape from the open end of the tube by a rapid succession of short blasts of air1 till the expanding glass attains the desired dimensions4 ,the tube must be held horizontally1 and must be rotated steadily during the process4 ,by slightly pressing together the glass while blowing1 the bulb will be flattened2 by slightly drawing apart the two ends of the tube1 it will be elongated4 ,a pear-shaped bulb may be obtained by gently re-heating an elongated bulb1 say from a to a1 and drawing it out4 ,it is easiest to perform this operation on a bulb which is rather thick in the glass4 ,if the tubes bb are to be small1 and a globe of considerable size is wanted1 contract a tube as shown in ,fig4 #bb1 taking care that the narrow portions of the tube are about the same axis as the wider portions1 for if this be not the case1 the mouths of the bulb will not be symmetrically placed2 seal at ,c1 cut off the wider tube at ,b1 and make the bulb1 as previously described1 from the glass between ,,aa4 ,if1 as probably will be the case1 the contracted portions of the tube be not very regular1 they may be cut off1 one at a time1 near the bulb1 and replaced by pieces of tube of the size desired4 ,illustration3 ,,fig4 #bb4 ,when a bulb has to be blown upon a very fine tube1 for example upon thermometer tubing1 the mouth should not be employed1 for the moisture introduced by the breath is extremely difficult to remove afterwards4 ,a small india-rubber bottle or reservoir1 such as those which are used in spray-producers1 ,galton's whistles1 etc41 securely attached to the open end of the tube1 should be used4 ,with the help of these bottles bulbs can be blown at the closed ends of fine tubes with ease1 though some care is necessary to produce them of good shape1 as it is difficult to rotate the hot glass properly when working in this way4 ,making and ,grinding ,stoppers4--,apparatus which is to contain chemicals that are likely to be affected by the free admission of air1 needs to have stoppers fitted to it4 ,making a good stopper is a much less tedious process than is commonly supposed4 ,suppose that the tube ,i4 of ,fig4 #bc is to be stoppered at ,a1 it must be slightly enlarged by softening the end and opening it with a pointed cone of charcoal2 or a conical mouth for the stopper may be made by slightly contracting the tube near one end1 as at ,b1 cutting off the cylindrical end of the tube at the dotted line ,c1 and then very slightly expanding the end at ,c with a charcoal cone after its edges have been softened by heat4 ,in either case the conical mouth should be as long and regular as possible4 ,illustration3 ,,fig4 #bc4 ,for the stopper take a piece of rather thick tube1 of such size that it will pass easily1 but not too easily1 into ,a or ,b4 ,expand this tube at ,d1 as shown in ,,ii41 by softening the glass and gently compressing it4 ,the configuration of the enlarged tube as shown at ,d may be obtained by heating and compressing two or more zones of the tube that are adjacent1 one zone being less expanded than the other1 so as to give the sides of the imperfect stopper as nearly as possible the form shown at ,d1 which1 however1 is much less regular than may easily be obtained4 ,seal off the head of the tube at ,h1 and heat the glass till it runs together into a nearly solid mass2 compress this with a pair of iron tongs to the flattened head ,e4 ,in making ,d1 aim at giving it a form which will as nearly as possible correspond to that of the tube into which it is to be ground1 and make it slightly too large1 so that only the lower part at ,d can be introduced into the mouth of ,a or ,b4 ,before it is ground1 the stopper must be heated nearly to its softening-point and annealed4 ,moisten ,d with a solution of camphor in recently distilled turpentine1 and dust the wet surface with finely-ground emery1 then gently grind it into its place till it fits properly4 ,in this operation the tail ,g1 which should fit loosely into the tube ,a1 will be of assistance by preventing ,d from unduly pressing in any direction on ,a in consequence of irregular movements4 ,the stopper should be completely rotated in grinding it4 ,it must not be worked backwards and forwards1 or a well-fitting stopper will not be produced4 ,renew the emery and camphorated turpentine frequently during the earlier part of the grinding2 when the stopper almost fits1 avoid using fresh emery1 but continue to remove the stopper frequently at all stages of the operation4 ,that added at the earlier stages will be reduced to a state of very fine division1 and will therefore leave the stopper and mouth of ,a with smoother surfaces than fresh emery4#aj #aj ,mr4 ,gimmingham recommends giving stoppers a final polish with rotten-stone 7,proceedings of the ,royal ,society1 p4 #cif1 #ahgf74 ,,note4--,the addition of camphor to the turpentine used for grinding glass is very important4 ,notwithstanding its brittle nature1 glass will work under a file moistened with this solution almost as well as the metals4 ,small quantities should be made at a time1 and the solution should be kept in a well-closed vessel1 for after long exposure to the air it is not equally valuable4 ,if the stopper is to fit a tube contracted like ,b1 it must be constructed from a piece of tube that will pass through the contraction at ,b4 ,the tail ,,gf will not do such good service as it does in the case of a tube which has been opened out to receive its stopper1 but it will help to guide the stopper1 and should be retained4 ,when the stopper has been ground into its place1 melt off the tail at ,f4 ,the flame must be applied very cautiously1 as glass which has been ground is particularly apt to crack on heating4 ,to avoid all risk of this1 the tail may simply be cut off1 and its edges filed smooth with a file moistened freely with camphorated turpentine4 ,the stoppers of bottles are not made exactly in the manner described above1 though1 on occasion1 a new stopper may be made for a bottle by following those directions4 ,ill-fitting stoppers1 which are very common1 can be very easily re-ground with emery and camphorated turpentine4 ,,chapter ,,iv4 ,,making ,,thistle ,,funnels1 ,u-,,tubes1 ,,etc4--,,combining ,,the ,,parts ,,of ,,complicated ,,apparatus--,,mercury1 ,,and ,,other ,,air-,,tight ,,joints--,,vacuum ,,taps--,,safety ,,taps--,,air-,,traps4 ,in ,chapter ,,iii4 the simpler operations used in making the separate parts of which apparatus is composed have been described4 ,in this ,chapter finished apparatus will be described1 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 require4 ,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 pressure1 such as safety taps1 air-traps1 vacuum joints1 etc4 ,illustration3 ,,fig4 #bd4 ,electrodes4--,on page #ch 7,fig4 #ac7 is shown a simple form of electrode sealed into a glass tube1 which for many purposes answers very well4 ,but frequently1 in order that there may be less risk of leakage between the glass and the metal1 the latter is covered for a considerable part of its length with solid glass1 which at one extremity is united to the apparatus4 ,in ,fig4 #bd ,w is the metal core of the electrode1 and ,g the glass covering around it4 ,the wire is fused into the glass1 and the glass is then united to the apparatus2 a little white enamel should be applied at one end and combined with the glass by fusion4 ,u-,tubes4--,a ,u-tube is but a particular case of a bent glass tube4 ,it is scarcely possible when bending very large tubes in the manner described on p4 #bi to produce regular curves of sufficient strength4 ,to make a ,u-tube1 or to bend a large tube1 close one end of the tube selected with a cork1 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 collected1 then remove the mass of glass from the flame1 let it cool a little1 and simultaneously draw out the thickened glass1 bend it to the proper form1 and blow the bend into shape from the open end of the tube4 ,small irregularities may be partly corrected afterwards4 ,to make a good ,u-tube of large size1 and of uniform diameter from end to end1 requires much practice1 but to make a tolerably presentable piece of apparatus in which the two limbs are bent round till they are parallel1 without any considerable constriction at the bend1 can be accomplished without much difficulty4#aa #aa ,large tubes may also be bent by rotating a sufficient length of the tube in a large flame till it softens1 and bending in the same manner as in the case of smaller tubes1 and after filling them with sand1 closing one end completely1 and the other so that the sand cannot escape1 though heated air can do so4 ,spiral ,tubes4--,these may be made by twisting a tube gradually softened by heat round a metal cylinder4 ,spiral tubes made of small thin tubes possess considerable elasticity1 and have been used by ,mr4 ,crookes for making air-tight connections between separate pieces of apparatus when a rigid connection would have been unnecessary and inconvenient4 ,by the use of such spiral tubes it is possible to combine comparatively free movement with all the advantages attached to hermetically-sealed joints4 ,to make a flexible spiral tube1 mount a copper cylinder on a screw1 so that the cylinder will travel in the direction of its axis when it is rotated4 ,fix a fine glass tube to the cylinder1 and direct a flame towards the cylinder so as to heat and soften the glass1 which will then bend to the form of the cylinder4 ,gradually rotate the cylinder before the source of heat1 so that fresh portions of tube are successively brought into position1 softened1 and bent4 ,useful spirals may also be made by hand without a cylinder4 ,as each length of tube is bent1 a fresh length may be united to it until the spiral is completed4 ,the fine tubes employed are prepared by heating and drawing out larger tubes4 ,illustration3 ,,fig4 #be4 ,thistle ,funnels 7,fig4 #be74--,seal a moderately thick piece of small glass tube at ,a1 then heat a wide zone of it a little below ,a by rotating it horizontally in the blow-pipe flame till the glass softens1 and expand the glass to a bulb1 as shown at ,b of #a2 during the operation of blowing this bulb1 the end ,a must be directed to the ground4 ,soften the end ,a and a small portion of ,b as before1 and1 holding the tube horizontally from the mouth1 blow out the end ,c as at #b4 ,heat the end of ,c gradually1 till the glass softens and collapses to the dotted line dd1 and at once blow a steady stream of air into the open end of the tube1 rotating it steadily1 till it is about to burst2 finally clean off the thin glass from round the edges of the funnel1 which should have the form shown at #c1 and round them4 ,an inspection of a purchased thistle funnel will generally show that the head ,b has been formed from a larger tube sealed to ,e at f4 ,illustration3 ,,fig4 #bf4 ,closing ,tubes containing ,chemicals for experiments at high temperatures4--,tubes of the hard glass used for organic analyses answer best for this purpose2 the operation of drawing out the end of such a tube is practically identical with what has been described under the head of choking1 p4 #ce4 ,a well-sealed tube presents the appearance of that shown by ,fig4 #bf4 ,in order to secure a thick end to the point of the tube a1 about an inch or so of the tube near the contracted part should be warmed a little1 if it is not already warm1 at the moment of finally sealing it2 the contraction of the air in the tube1 in consequence of the cooling of the warm tube1 will then ensure the glass at a running together to a solid end when it is melted in the flame4 ,if it will be necessary to collect a gas produced during a chemical action from such a tube1 make the contracted end several inches long1 and bend it into the form of a delivery tube4 ,it will then be possible to break the tip of this under a cylinder in a trough of liquid4 ,in order to explain the construction of apparatus consisting of several parts1 it will be sufficient to take as examples1 two very well-known instruments1 and to describe their construction in detail4 ,from what is learned in studying these1 the student will gather the information that is wanted4 ,illustration3 ,,fig4 #bg4 #a4 ,to make ,hofman's ,apparatus for the electrolysis of water 7,fig4 #bg74 ,take two tubes about #ce cm4 in length1 and #ad mm4 in diameter for ,,aa1 join taps ,,tt to the end ,b of each of them1 draw out the other end1 as shown at ,d1 after sheets of platinum foil with wires attached to them#ab have been introduced into the tubes1 and moved by shaking to ,,bb4 ,then allow the platinum wires to pass through the opening ,d left for the purpose1 and seal the glass at ,d round the platinum as at ,e4 ,pierce the tubes at ,,jj1 and join them by a short piece of tube ,k1 about #ad mm4 in diameter1 to which the tube ,t1 carrying the reservoir ,r1 has been previously united4 ,r may be made by blowing a bulb from a larger piece of tube attached to the end of ,t4 ,the mouth ,m of the reservoir being formed from the other end of the wide tube afterwards4 ,one of the taps can be used for blowing through at the later stages4 ,each joint1 especially those at ,,jj1 must be annealed after it is blown4 ,some operators might prefer to join ,,aa by the tube ,k in the first instance1 then to introduce the electrodes at ,e and ,d4 ,in some respects this plan would be rather easier than the other1 but1 on the whole1 it is better to make the joints at ,,jj last in order1 as they are more apt to be broken than the others during the subsequent manipulations4 #ab ,red-hot platinum welds very well4 ,the wire may be joined to the sheet of foil by placing the latter on a small piece of fire-brick1 holding the wire in contact with it at the place where they are to be united1 directing a blow-pipe flame upon them till they are at an intense heat1 and smartly striking the wire with a hammer4 ,the blow should be several times repeated after re-heating the metal4 #b4 ,i have before me the vacuum tube shown by ,fig4 #bh1 in which the dotted lines relate to details of manipulation only4 ,illustration3 ,,fig4 #bh4 ,it is usually possible to detect the parts of which a piece of apparatus has been built up1 for even the best-made joints exhibit evidence of their existence4 ,thus1 although ,i did not make the tube that is before me1 and cannot therefore pretend to say precisely in what order its parts were made and put together1 the evidence which it exhibits of joints at the dotted lines ,a1 ,b1 ,c1 ,d1 ,e1 ,f1 enables me to give a general idea of the processes employed in its construction1 and to explain how a similar tube might be constructed4 ,i should advise proceeding as follows3-- ,join a piece of tube somewhat larger than ,m to its end ,a1 draw out the other end of the larger tube1 and blow a bulb ,l as directed on p4 #dg4 ,then seal the electrode ,r into the bulb ,l 7p4 #ee74 ,blow a similar but larger bulb ,n from a large piece of tube sealed between two tubes of similar size to ,m1 as described at p4 #ej4 ,cut off one of the tubes at ,b1 and join the bulb ,n to ,m at ,b4 ,form the bulb ,q in the same manner as in the case of ,l1 seal into it the electrode ,r1 and add the tube marked by the dotted lines at ,f4 ,seal a narrow tube ,p to the end of a larger tube1 and blow out the tube at the joint till the glass is thin and regular4 ,take a tube ,o1 of similar size to ,m1 slightly longer than ,p1 contract its mouth slightly to meet the wide end of ,p at ,d1 and after loosely supporting ,p inside ,o with a cork1 or otherwise1 close the end ,n of ,o by sealing or corking it1 and join ,p to ,o at ,d4 ,cut off ,o just above ,d at ,e1 and join it to the bulb ,q1 closing either ,o or ,f for the purpose4 ,cut off the end of ,o at ,c parallel to the end of ,p1 and connect ,o to ,n1 using ,f for blowing the joint at ,c4 ,f may be used subsequently for introducing any gas into the tube1 and1 when a vacuum has been established1 may be sealed before the blow-pipe4 ,illustration3 ,,fig4 #bi4 ,modes of combining the ,parts of ,heavy ,apparatus4--,it is often necessary to connect pieces of apparatus which are too heavy to be freely handled before the blow-pipe1 and which1 therefore1 cannot be welded together as described on p4 #ci1 by some more effective method than the ordinary one of connecting by india-rubber tubing4 ,for example1 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 obtained4 ,this1 indeed1 often may be done by welding the apparatus to be exhausted to the air-pump before the blow-pipe4 ,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 necessary1 and that there is some risk of accidental breakages4 ,nevertheless it may be done on occasion1 especially if there be no objection to the use of the flexible spiral tubes already alluded to4 ,when the use of a spiral connecting-tube is not admissible the difficulty is considerably increased4 ,for example1 the author has lately required to attach an ozone generator1 of the form shown by ,fig4 #ai1 which previously had been cemented into a heavy copper jacket1 to a pressure-gauge rigidly fixed to a support1 and of considerable size4 ,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 generator1 a condition which compelled the use of a tube of almost capillary bore1 and of inconsiderable length4 ,at the same time the frailness of such a connection made it necessary to fix the generator and pressure-gauge rigidly to their supports1 in order to avoid the possibility of breakage by slight accidental movements of either of them1 and it was obviously necessary to fix the pieces of apparatus in their final positions before joining them1 lest the fine tube which connected them should be fractured during adjustment4 ,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 also4 ,the desired object was effected as follows4 ,in ,fig4 #bi ,a represents a section of the ozone generator at the point where the tube to connect it to the gauge was fixed4 ,b represents the top of the gauge1 with the side tube ,c1 which was to be connected with that from ,a1 viz4 ,d4 ,the ends of ,c and ,d were expanded as shown at ,d 7by melting them and blowing them out71 so that one of them1 made rather smaller than the other1 could be overlapped by the larger one4 ,a and ,b being rigidly fixed in their final positions1 with ,c and ,d in contact1 as shown in the figure1 all openings in the apparatus were closed1 except one1 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 operator1 and to allow him to observe the operation of joining the tubes at ,d4 ,when everything was in readiness1 a very small-pointed flame from a moveable blow-pipe held in the hand was directed upon the glass at ,d till it melted and the two tubes united4 ,to prevent the fine tube when melted from running into a solid mass of glass1 and so becoming closed1 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 ,c and ,d united4 ,a point of charcoal was kept in readiness to support the softened glass at ,d in case it showed any tendency to fall out of shape4 ,the ,v-tube at ,c served to prevent the subsequent fracture of the joint in consequence of any strain caused by the contraction of the glass in cooling4#ac #ac ,for a method of joining soda glass to lead glass1 see p4 #ha4 ,it is not difficult to connect several pieces of apparatus successively in this manner1 nor is this method only useful in such cases as that just described4 ,pieces of apparatus of great length and weight may be joined in a similar manner1 irrespective of the size of the tubes to be united4 ,the ends to be joined1 prepared as before1 so that one slightly overlaps the other1 must be held firmly in contact by clamps1 and heated in successive portions by a blow-pipe held in the hand of the operator1 each patch of glass being re-heated and gently blown1 after a rough joint has been made4 ,finally1 a larger flame may be used to heat up the whole joint for its final blowing4 ,it is important to place the apparatus so that the operator has free access to it on all sides4 ,a revolving table might be employed4 ,an assistant to work the bellows is necessary4 ,or1 better still1 air may be admitted to the blow-pipe from a large gas-bag placed in some convenient position4 ,but in most cases one or other of the following air-tight joints can be employed1 and will be found to be very convenient3-- ,mercury ,joints4--,the simplest form of mercury joint is shown at ,fig4 #cj4 ,a and ,b are the two tubes which are to be connected4 ,a larger tube or cup ,f is attached to ,a by the india-rubber tube ,e1 and placed on ,a so that the end of ,b may be brought into contact with ,a at ,c1 and connected to it by a well-fitting piece of india-rubber tube ,c4 ,the cup ,e is then brought into the position shown in ,fig4 #cj1 and mercury is introduced till the india-rubber tube at ,c is covered4 ,as mercury and glass do not come into true contact1 however1 such a joint1 though said to give good results in practice1 is not theoretically air-tight1 for air might gradually find its way between the liquid and the glass4 ,by covering the mercury with a little sulphuric acid or glycerine the risk of this occurring may be removed4 ,the same result may be attained by the use of glycerine in place of the mercury in the cup ,f2 but glycerine is less pleasant to work with than mercury4#ad #ad ,if the india-rubber tube ,c be secured by wires1 iron wire1 not copper wire1 should be employed4 ,illustration3 ,,fig4 #cj4 ,when sulphuric acid is to be employed in such a joint1 or when for any other reason the use of an india-rubber tube is undesirable1 the joint may consist of a hollow stopper ,b 7,fig4 #ca71 made of glass tube1 and ground to fit the neck of a thistle funnel ,a4 ,a and ,b are joined respectively to the pieces of apparatus to be connected1 and connection is made by placing ,b in position in the neck of ,a2 the joint is made air-tight by introducing mercury with strong sulphuric acid above it into the cup ,a4 ,the joint may be rendered air-tight by introducing sulphuric acid only into the cup4 ,but this plan must not be adopted if the interior of the apparatus is to be exhausted1 as sulphuric acid is easily forced between the ground glass surfaces by external pressure4 ,mercury1 however1 will not pass between well-ground glass surfaces1 and is therefore to be employed for connecting apparatus which is to be exhausted1 and1 if necessary1 protected by a layer of strong sulphuric acid to completely exclude air4 ,illustration3 ,,fig4 #ca4 ,tubes placed horizontally may be joined by a glycerine or mercury joint such as is shown in ,fig4 #cb4 ,the two tubes ,a and ,b are joined as before by an india-rubber connection ,c1 or one may be ground to fit the other1 and the joint is then enclosed within a larger jacketing-tube ,d1 with a mouth at ,f1 which is filled with glycerine or mercury4 ,d is easily made by drawing out both ends of a piece of tube1 leaving them large enough to pass over the connection at ,c1 however1 and piercing one side at ,f4 ,illustration3 ,,fig4 #cb4 ,vacuum ,taps4--,it is not necessary to enter into a description of the construction of ordinary glass taps1 which can be purchased at very reasonable prices4 ,it may be remarked here1 however1 as a great many of them are very imperfectly ground by the makers1 that they may easily be made air-tight by hand-grinding with camphorated turpentine and fine emery1 finishing with rotten-stone4 ,a well-ground tap1 which is well lubricated1 should be practically air-tight under greatly reduced pressure for a short period2 but when it is necessary to have a tap which absolutely forbids the entrance of air into apparatus1 one of the following may be employed3-- ,illustration3 ,,fig4 #cc4 ,illustration3 ,,fig4 #cd4 7#a47 ,mr4 ,cetti's ,vacuum ,tap 7,fig4 #cd73 ,this tap is cupped at ,a and sealed at ,b1 and the cup ,a is filled with mercury when the tap is in use1 so that if1 for example1 the end ,c be attached to a flask1 and ,d to an apparatus for exhausting the flask1 it will be possible to close the flask by turning off the tap ,e1 and if no air be allowed access through ,d1 the vacuum produced in the flask at ,c cannot be affected by air leaking through the tap at ,a or ,b4 ,a passage ,f must be drilled from the bottom of the plug ,e to meet ,g1 in order that when the plug is in position no residue of air shall be confined within ,b1 whence it might gradually leak into any apparatus connected to it4 ,it is obvious1 however1 that this tap does not protect a flask sealed to ,c from the entrance of air through ,d1 which1 in fact1 is the direction in which air is most likely to effect an entrance4 ,when using one of these taps as part of an apparatus for supplying pure oxygen1 ,i have guarded against this by attaching a trap 7,fig4 #cc7 to the end ,d1 ,c being joined to the delivery tube from the gas-holder4 ,the structure and mode of action of the trap are as follows3-- ,a narrow tube ,g is joined to ,d of ,fig4 #cd1 and terminates in the wide tube ,i1 which is connected above to ,h1 and below to the air-trap ,j4 ,j is connected at ,k1 by a piece of flexible tube1 to a reservoir of mercury1 from which mercury enters the air-trap1 and passing thence to ,i1 can be employed for filling the ,v-trap ,,hlg4 ,the air-trap ,j is in the first instance filled with mercury1 and then serves to intercept any stray bubbles of air that the mercury may carry with it4 ,the particular form of the trap shown at ,,hlg was adopted because with it the arm ,,lg is more readily emptied of mercury than with any other form of trap made of small tube that ,i have tried4 ,it has been used in my apparatus in the following manner3--,h was connected with a vessel to be filled with pure oxygen1 the tap ,e closed1 and the rise of mercury above ,l prevented by a clamp on the flexible tube2 the vessel to be filled and the trap were then exhausted by a ,sprengel pump1 and oxygen allowed to flow into the exhausted space by opening ,e1 the operation of exhausting the tubes and admitting oxygen being repeated as often as necessary4 ,to prevent access of air to ,e on disconnecting the vessel at ,h1 the mercury was allowed to flow into the trap till it reached to ,,mm4 ,e was then closed1 and ,h exposed without danger of air reaching ,e1 the length of the arms of the trap being sufficient to provide against the effects of any changes of temperature and pressure that could occur4 ,a delivery tube may be connected to ,h and filled with mercury1 by closing ,e and raising the mercury reservoir4 ,all air being in that way expelled from the delivery tube1 and the supply of mercury cut off by clamping the tube from the reservoir1 oxygen can be delivered from the tube by opening ,e1 when it will send forward the mercury1 and pass into a tube placed to receive it without any risk of air being derived from the delivery tube4 ,illustration3 ,,fig4 #ce4 7#b47 ,gimmingham's ,vacuum ,tap1#ae shown in ,fig4 #ce1 consists of three parts4 ,a tube ,a is ground to fit the neck of ,b4 ,b is closed at its lower end1 and has a hole d drilled through it2 when ,b is fitted to ,c1 d can be made to coincide with the slit e4 ,when ,a1 ,b1 ,c are fitted together1 if d meet e1 there is communication between any vessels attached to ,a and any other vessel attached to ,c1 entrance of external air being prevented by mercury being placed in the cups of ,c and ,b4 ,the tap may be opened and closed at pleasure by rotating ,b4 #ae ,from ,proceedings of ,royal ,society1 vol4 ,,xxv4 p4 #cif4 ,if ,a has to be removed1 ,c may be converted into a mercury joint pro tem4 by letting a little mercury from the upper cup fall into the tube and cover d1 the tap being closed4 ,this mercury must be removed by a fine pipette in order to use the tap again4 ,it should be noted1 however1 that though external air cannot enter by way of the ground glass joints1 there is no absolute protection against the passage of air between ,a and ,c1 or vessels joined to ,a and ,c1 even when the tap is closed4 ,the passage of air from ,a to ,c depends upon the grinding and lubrication of the joint at ,c4 ,lubricating ,taps4--,for general purposes resin cerate answers very well4 ,in special cases burnt india-rubber1 or a mixture of burnt india-rubber and vaseline will answer well1 or vaseline may be used alone4 ,sulphuric acid and glycerine are too fluid4 ,when a lubricant is wanted that will withstand the action of ether1 the tap may be lubricated by sprinkling phosphorus pentoxide upon it1 and exposing it to air till the oxide becomes gummy4 ,the joint must then be protected from the further action of the air if possible4 ,for example1 if a safety tap be used the cup may be filled with mercury4 ,air-,traps4--,in ,fig4 #cc1 p4 #ff1 an air-trap 7,j7 is shown4 ,an air-trap is a device for preventing the mercury supplied to ,sprengel pumps1 etc41 from carrying air into spaces that are exhausted1 or are for any reason to be kept free from air4 ,figs4 #cf and #cg give examples of air-traps4 ,in the simpler of the two 7,fig4 #cf7 mercury flowing upwards from ,c that may carry bubbles of air with it passes through the bulb ,a1 which is filled with mercury before use4#af ,any air which accompanies the mercury will collect at a1 the mercury will flow on through b4 ,so long as the level of the mercury in ,a is above b1 the trap remains effective4 #af ,this may be done by clamping the tube which supplies mercury below ,c1 exhausting ,a1 and then opening the clamped tube and allowing the mercury to rise4 ,illustration3 ,,fig4 #cf4 ,illustration3 ,,fig4 #cg4 ,in the trap shown by ,fig4 #cg1 the tube d1 which corresponds to b in ,fig4 #cf1 is protected at its end by the cup ,e4 ,e prevents the direct passage of minute bubbles of air through d4 ,this trap1 like the other1 must be filled with mercury before it is used1 and it will then remain effective for some time4 ,,chapter ,v4 ,,graduating ,,and ,,calibrating ,,glass ,,apparatus4 ,although the subjects to which this concluding chapter is devoted do not1 properly speaking1 consist of operations in glass-blowing1 they are so allied to the subject1 and of such great importance1 that ,i think a brief account of them may advantageously be included4 ,graduating ,tubes1 etc4--,it was formerly the custom to graduate the apparatus intended for use in quantitative work into parts of equal capacity2 for example1 into cubic centimetres and fractions of cubic centimetres4 ,for the operations of volumetric analysis by liquids this is still done4 ,but for most purposes it is better to employ a scale of equal divisions by length1 usually of millimetres1 and to determine the relative values of the divisions afterwards1 as described under calibration4 ,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 length1 and indeed1 even for ordinary volumetric work1 no burette should be employed before its accuracy has been verified4 ,an excellent method for graduating glass tubes by hand#ag has been described in ,watts's ,dictionary of ,chemistry1 and elsewhere4 ,another excellent plan1 which ,i have permission to describe1 has been employed by ,professor ,w4 ,ramsay4 ,it will be sufficient if ,i explain its application to the operation of graduating a tube or strip of glass in millimetre divisions4 #ag ,originally suggested by ,bunsen4 ,the apparatus required consists of a standard metre measure1#ah divided into millimetres along each of its edges1 with centimetre divisions between them1 a ruler adapted to the standard metre1 as subsequently explained1 and a style with a fine point for marking waxed surfaces4 #ah ,such measures can be obtained of steel for about fifteen shillings each4 ,they are made by ,mr4 ,chesterman of ,sheffield4 ,they can be obtained also from other makers of philosophical instruments1 at prices depending upon their delicacy4 ,those of the greatest accuracy are somewhat costly4 ,illustration3 ,,fig4 #ch4 ,fig4 #ch represents the standard measure1 and the ruler4 ,at ,,aa are the millimetre divisions on the edges of the measure1 the longer transverse lines at ,,bb are placed at intervals of five millimetres and of centimetres4 ,the ruler is in the form of a right-angled triangle2 it is shown1 by the dotted lines1 in position on the standard metre measure at ,i2 and again1 with its under surface upwards1 in the smaller figure at #b4 ,it consists of a perfectly flat sheet of metal1 about ten centimetres in length from ,c to ,c1 sufficiently thick to be rigid1 and has a ledge1 ,,dd in each figure1 which is pressed against the side of the measure when using it1 to ensure that the successive positions of the edge 7,,ll7 shall be parallel to each other4 ,at ,,gg are two small holes1 into which fit small screws with fine points4 ,these must be in a line parallel to the edge 7,,ll71 so that when the ruler is in position on the scale1 the points of the two screws1 which project slightly1 shall fall into corresponding cuts on the divided scales 7,,aa74 ,to graduate a strip of glass1 or a glass tube 7,,hh71 the surface to be marked must first be coated with wax1 which should be mixed with a little turpentine1 and be applied to the surface of the glass1 previously made warm and dry1 by means of a fine brush1 so as to completely cover it with a thin1 closely-adherent1 and evenly-distributed coat of wax1 which must be allowed to cool4 ,fix ,,hh firmly on a table1 and fix the standard measure by the side of ,,hh4 ,if the thickness of ,,hh be about equal to1 but not greater than that of the standard measure1 this may be done by large drawing-pins4 ,if1 however1 a large tube or thick sheet of glass is to be graduated1 fix it in position by two strips of wood screwed to the table on each side of it4 ,one of these wooden strips1 on which the measure may be placed1 may be about as broad as the standard measure1 and of such thickness that when the measure lies upon it beside the tube to be graduated1 the ruler1 when moved along the measure1 will move freely above the tube1 but will not be elevated more than is necessary to secure free movement4 ,the second strip of wood may be narrower1 and of the same thickness as the broader piece on which the standard measure rests4 ,in any case1 let the standard measure and the object to be graduated be very firmly secured in their places4 ,bring the ruler into position at any desired part of the tube by placing the points of the screws 7,,gg7 in corresponding divisions of the scales 7,,aa74 ,with the style1 which may be a needle mounted in a handle1 make a scratch in the wax along the edge of the ruler at ,f1 move the ruler so that the screws rest in the next divisions1 and repeat the operation till the required number of lines has been ruled4 ,longer marks may be made at intervals of five and ten millimetres4 ,great care must be taken to hold the needle perpendicularly1 and to press it steadily against the edge 7,,ll7 of the ruler in scratching the divisions4#ai ,the length of the lines marking the millimetre divisions should not be too long2 about #a mm4 is a good length4 ,if they are longer than this1 the apparent distance between them is diminished1 and it is less easy to read fractions of millimetres4 ,before removing the scale to etch the glass1 carefully examine it to see that no mistakes have been made4 ,if it is found that any lines have been omitted1 or that long lines have been scratched in the place of short ones1 remelt the wax by means of a heated wire1 and make new marks4 ,finally1 mark the numbers on the scale with a needle-point1 or better1 with a fine steel pen4 #ai ,to avoid variations of the position in which the needle is held when marking the divisions1 the edge 7,,ll7 should not be bevelled2 and an upright support may be placed upon the ruler1 with a ring through which the handle of the needle passes1 thereby securing that the angle formed by the needle and surface of the ruler is constant1 and that equal divisions are marked4 ,the marks on the wax should cut through it4 ,when they are satisfactory1 they may be etched by one of the following processes3-- 7#a47 ,by moistening some cotton wool1 tied to a stick1 with solution of hydrofluoric acid1 and gently rubbing this over the scratched surface for a minute or so2 then washing away the acid with water1 and cleaning off the wax4 ,this is the simplest method1 but the marks made are generally transparent1 and therefore not very easy to read4 ,the simplicity of this method is a great recommendation1 however4 7#b47 ,expose the tube to the fumes of hydrofluoric acid generated from a mixture of powdered fluor-spar and strong sulphuric acid1 in a leaden trough4 ,the marks produced in this way are usually opaque1 and are therefore very visible1 and easily read4 ,after the above detailed account it will only be necessary to give an outline of the other process of graduating tubes4 ,illustration3 ,,fig4 #ci4 ,the standard scale to be copied1 ,a1 which may in this case be another graduated tube1 or even a paper scale1 and the object to be ruled1 ,b1 are securely fixed1 end to end1 a little distance apart1 in a groove made in a board or in the top of a table4 ,a stiff bar of wood1 ,c1 has a point fixed at ,d1 and a knife edge at ,e1 ,d is placed in any division of ,a1 ,c is held firmly at ,e and ,d1 and a cut is made by the knife through the wax on ,b1 the point ,d is then moved into the next division1 and the operation is repeated4 ,to regulate the length and position of the cuts1 ,b is usually held in position by two sheets of brass projecting over the edges of the groove in which it lies2 the metal sheets have notches cut into them at the intervals at which longer marks are to be made4 ,when the scale is completed1 the equality of the divisions in various parts of it may be1 to some extent1 verified as follows3--,adjust a compass so that its points fall into two divisions #e1 #aj1 or #bj mm4 apart4 ,then apply the points of the compass to various parts of the scale4 ,in every part the length of a given number of divisions should be exactly the same4 ,the individual divisions should also be carefully inspected by the eye2 they should be sensibly equal4 ,if badly ruled1 long and short divisions will be found on the scale4 ,very often a long and a short division will be adjacent1 and will be the more easily observed in consequence4 ,to ,divide a ,given ,line into ,equal ,parts4--,occasionally it is necessary to divide a line of given length into x equal parts4 ,for instance1 to divide the stem of a thermometer from the freezing-point to the boiling-point into one hundred degrees4 ,the following outline will explain how a line may be so divided4 ,suppose the line ,,ab 7,fig4 #dj7 is to be divided into nine equal parts4 ,adjust a hinged rule so that the points ,a and ,b coincide with the inside edges of the limbs1 one of them1 ,a1 being at the ninth division 7e4g4 the ninth inch7 of ,,ce4 ,then if lines parallel to ,,ed be drawn from each division of the scale to meet ,,ab1 ,,ab will be divided into nine equal parts4 ,illustration3 ,,fig4 #dj4 ,a very convenient and simple arrangement on this principle for dividing a line into any number of equal parts with considerable accuracy1 is described by ,miss ,s4 ,marks in the ,proceedings of the ,physical ,society1 ,july #ahhe4bj ,one limb of a hinged rule ,d is made to slide upon a plain rule fixed to it2 the plain rule carries needles on its under surface which hold the paper in position4 ,the position of the divided rule and line to be divided being adjusted1 the hinged rule is gently pushed forwards1 as indicated by the arrow in ,fig4 #dj1 till division eight coincides with the line ,,ab4 ,a mark is made at the point of coincidence1 and division seven on the scale is similarly brought to the line ,,ab1 and so on4 ,the inner edge of ,,ec should have the divisions marked upon it1 that their coincidence with ,,ab maybe more accurately noted4 ,the joint ,e must be a very stiff one4 #bj ,since this was printed ,i have observed that the above method is not identical with that described by ,miss ,marks1 but for ordinary purposes ,i do not think it will be found to be inferior4 ,a line drawn of given length or a piece of paper may be divided into any given number of equal parts1 and will then serve as the scale ,a of ,fig4 #ci1 p4 #gd1 the thermometer or other object to be graduated taking the place of ,b4 ,scales carefully divided according to any of the methods described will be fairly accurate if trustworthy instruments have been employed as standards4 ,it will be found possible when observing the volume of a gas over mercury1 or the height of a column of mercury in a tube1 to measure differences of one-sixth to one-eighth of a millimetre with a considerable degree of accuracy4 ,to obtain more delicate measurements a vernier#ba must be employed4 #ba ,for the nature and use of the vernier1 a treatise on ,physics or ,physical ,measurements may be consulted4 ,to ,calibrate ,apparatus4--,the glass tubes of which graduated apparatus is made are1 as already stated1 very rarely truly cylindrical throughout their entire lengths4 ,it follows that the capacities of equal lengths of a tube will usually be unequal1 and therefore it is necessary to ascertain by experiment the true values of equal linear divisions of a tube at various parts of it4 ,a burette may be calibrated by filling it with distilled water1 drawing off portions1 say of #e c4c4 in succession1 into a weighing bottle of known weight1 and weighing them4 ,great care must be taken in reading the level of the liquid at each observation4 ,the best plan is to hold a piece of white paper behind the burette1 and to read from the lower edge of the black line that will be seen4 ,each operation should be repeated two or three times1 and the mean of the results1 which should differ but slightly1 may be taken as the value of the portion of the tube under examination4 ,if the weights of water delivered from equal divisions of the tube are found to be equal1 the burette is an accurate one1 but if1 as is more likely1 different values are obtained1 a table of results should be drawn up in the laboratory book showing the volume of liquid delivered from each portion of the tube examined4 ,and subsequently when the burette is used1 the volumes read from the scale on the burette must be corrected4 ,suppose1 for example1 that a burette delivered the following weights of water from each division of #e c4c4 respectively3-- ,c4,c4 ,grams4 #j to #e gave #d4ij #e #aj #d4ia #aj #ae #d4ib #ae #bj #d4ic #bj #be #d4id #be #cj #d4ie #cj #ce #d4if #ce #dj #d4ig #dj #de #d4ih #de #ej #d4ii and that in two experiments #bj c4c4 and #de c4c4 respectively of a liquid re-agent were employed4 ,the true volumes calculated from the table would be as #ai4ff to #dd4df4 ,if the temperature remained constant throughout the above series of experiments1 and if the temperature selected were #d deg4 ,c41 the weights of water found1 taken in grams1 give the volumes in cubic centimetres1 for one gram of water at #d deg4 ,c4 has a volume of one cubic centimetre4 ,if the temperature at which the experiments were made was other than #d deg4 ,c41 and if great accuracy be desired1 a table of densities must be consulted1 with the help of which the volume of any weight of water at a known temperature can be readily calculated4 ,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 determined1 and also the proportions these bear to the values found for the divisions of the burettes in conjunction with which they will be employed4 ,to ,calibrate ,tubes for ,measuring ,gases4--,prepare a small glass tube sealed at one end and ground at the other to a plate of glass4 ,the tube should hold about as much mercury as will fill #aj mm4 divisions of the graduated tube4 ,fill this tube with mercury1 removing all bubbles of air that adhere to the sides by closing the open end of the tube with the thumb1 and washing them away with a large air-bubble left for the purpose4 ,if any persistently remain1 remove them by means of a fine piece of bone or wood4 ,then completely fill the tube with mercury1 removing any bubbles that may be introduced in the operation1 and remove the excess of mercury by placing the ground-glass plate on the mouth of the tube1 and pressing it so as to force out all excess of mercury between the two surfaces4 ,clean the outside of the tube1 and place it on a small stand 7this may be a small wide-mouthed glass bottle71 with which it has been previously weighed when empty1 and re-weigh4 ,repeat this operation several times4 ,from the mean of the results1 which should differ one from another but very slightly1 the capacity of the tube can be calculated4 ,the purest mercury obtainable should be used4 ,since the density of pure mercury at #j deg4 ,c4 is #ac4eif1 the weight of mercury required to fill the tube at #j deg4 ,c41 taken in grams1 when divided by #ac4eif1 will give the capacity of the tube at #j deg4 ,c4 in cubic centimetres4 ,if the experiment be not made at #j deg4 ,c41 and if a very exact determination of the capacity of the tube be required1 the density of mercury must be corrected for expansion or contraction4 ,having now a vessel of known capacity1 it can be employed for ascertaining the capacities of the divisions of a graduated tube in the following manner3--,the graduated tube is fixed perpendicularly1 mouth upwards1 in a secure position4 ,the small tube of known capacity is filled with mercury as previously described1 and its contents are transferred to the divided tube4 ,the number of divisions which the known volume of mercury occupies is noted after all air-bubbles have been removed4 ,this process is repeated until the divided tube is filled4 ,a table of results is prepared1 showing the number of divisions occupied by each known volume of mercury introduced4 ,in subsequently using the tube the volumes of the gases measured in it must be ascertained from the table of values thus prepared4 ,in observing the level of the mercury1 unless a cathetometer is available1 a slip of mirror should be held behind the mercury close to the tube1 in such a position that the pupil which is visible on the looking-glass is divided into two parts by the surface of the mercury4 ,a correction must be introduced for the error caused by the meniscus of the mercury4 ,as the closed end of the tube was downwards when each measured volume of mercury was introduced1 and as the surface of mercury is convex1 the volume of mercury in the tube when it is filled to any division l 7,fig4 #da7 is represented by ,a of #a4 ,but in subsequently measuring a gas over mercury in the same tube1 when the mercury stands at the same division l1 the volume of the gas will be as represented by ,b of #b1 which is evidently somewhat greater than ,a4 ,this will be seen still more clearly in #c1 where a represents the boundary of the mercury1 and b the boundary of the air1 when the tube is filled to the mark l with mercury or a gas over mercury respectively4 ,illustration3 ,,fig4 #da4 ,it is plain that when the level of the mercury in measuring a gas is read at l1 the volume of the gas is greater than the volume of the mercury recorded1 by twice the difference between the volume ,a of mercury measured1 and that which would fill the tube to the level l1 if its surface were plane4 ,the usual mode of finding the true volume of a gas collected over mercury is as follows3-- ,place the graduated tube mouth upwards1 introduce some mercury1 and1 after removing all bubbles1 note the division at which it stands4 ,then add a few drops of solution of mercuric chloride2 the surface of the mercury will become level1 read and record its new position4 ,then1 in any measurement1 having observed that the mercury stands at n divisions of the tube1 add twice the difference between the two positions of the mercury to n1 and ascertain the volume which corresponds to this reading from the table of capacities4 ,to ,calibrate the ,tube of a ,thermometer4--,detach a thread of mercury from half an inch to one inch in length from the body of the mercury4 ,move it from point to point throughout the length of the tube1 and note its length in each position4 ,if in one part it occupies a length of tube corresponding to eight degrees1 and at another only seven degrees1 then at the former point the value of each division is only seven-eighths of those at the latter position4 ,from the results obtained1 a table of corrections for the thermometer should be prepared4 ,it is sometimes necessary to join soda glass to lead glass4 ,in this case the edge of the lead glass tube may be bordered with white enamel before making the joint4 ,enough enamel must be used to prevent the lead and soda glasses from mingling at any point4 ,the enamel is easily reduced1 and must be heated in the oxidising flame4 ,dr4 ,ebert recommends ,verre d'urane for this purpose4 ,it is supplied by ,herr ,goetze of ,leipzig 7,liebigstrasse74 ,,chapter ,,vi4 ,,glass ,,tubing4 ,the diagrams given below show the sizes and thickness of the glass tubes most frequently required4 ,in ordering1 the numbers of these diagrams may be quoted1 or the exact dimensions desired may be stated4 ,glass tubes are usually sold by weight1 and therefore the weight of tube of each size that is wished for should be indicated1 and also whether it is to be of lead or soda glass4 ,illustration ,illustration ,,chapter ,,vii4 ,,vitreous ,,silica4 ,introductory4--,vitreous ,silica was made in fine threads by ,m4 ,gaudin in #ahci1bb and small tubes of it were made in #ahfi by ,m4 ,a4 ,gautier1 but its remarkable qualities were not really recognised till #ahhi1 when ,professor ,c4 ,v4 ,boys rediscovered the process of making small pieces of apparatus of this substance1 and used the torsion of quartz fibres for measuring small forces4 ,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 workers1 and jointly with ,mr4 ,h4 ,g4 ,lacell1 has produced a variety of apparatus of much larger dimensions than had been attempted previously4 ,at the time of writing we can produce by the processes described in the following pages tubes #a to #a4e cm4 in diameter and about #gej cm4 in length1 globes or flasks capable of containing about #ej cc41 masses of vitreous silica weighing #ajj grams or more1 and a variety of other apparatus4 #bb ,a brief summary of the history of this subject will be found in ,nature1 ,vol4 #fb1 and in the ,proceedings of the ,royal ,institution1 #aija4 ,properties of ,vitreous ,silica4--,for the convenience of those who are not familiar with the literature of this subject1 ,i may commence this chapter with a brief account of the properties and applications of vitreous silica1 as far as they are at present ascertained4 ,vitreous silica is less hard than chalcedony1 but harder than felspar4 ,tubes and rods of it can be cut with a file or with a piece of sharpened and hardened steel1 and can afterwards be broken like similar articles of glass4 ,its conducting power is low1 and ,mr4 ,boys has shown that fine fibres of silica insulate remarkably well1 even in an atmosphere saturated with moisture4 ,the insulating qualities of tubes or rods of large cross sections have not yet been fully tested2 one would expect them to give good results provided that they are kept scrupulously clean4 ,a silica rod which had been much handled would probably insulate no better than one of glass in a similar condition4 ,the density of vitreous silica is very near to that of ordinary amorphous silica4 ,in the case of a small rod not absolutely free from minute bubbles it was found to be #b4ba4 ,vitreous silica is optically inactive1 when homogeneous1 and is highly transparent to ultraviolet radiations4 ,the melting point of vitreous silica cannot be definitely stated4 ,it is plastic over a considerable range of temperature4 ,professor ,callendar has succeeded in measuring the rate of contraction of fine rods in cooling from #abjj deg4 to #aejj deg4 ,c41 so that its plasticity must be very slight below the latter temperature4 ,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 time1 but silica softens to a marked extent at temperatures a little above the melting point of platinum4 ,it has been observed by ,boys1 ,callendar1 and others that fine rods of silica1 and also the so-called quartz fibres1 are apt to become brittle after they have been heated to redness4 ,but ,i have not observed this defect in the case of more massive objects1 such as thick rods or tubes2 and as ,i have repeatedly observed that mere traces of basic matter1 such as may be conveyed by contact with the hand1 seriously injure the surface of silica1 and have found that silica quickly becomes rotten when it is heated to about #ajjj deg4 in contact with an infusible base such as lime1 ,i am disposed to ascribe the above-mentioned phenomenon to chemical rather than to purely physical causes4#bc ,it is certain1 however1 that silica apparatus must never be too strongly heated in contact with basic substances4 ,silica is easily attacked by alkalis and by lime1 less readily by copper oxide1 and still less by iron oxide4 #bc ,in a recent communication ,professor ,callendar tells me that the devitrification commences at the outside and is hastened by particles of foreign matter4 ,the rate of expansion of vitreous silica has been studied by ,h4 le ,chatelier1 and more recently by ,callendar4 ,the former found its mean coefficient of expansion to be #j4jjjjjjg between #j deg4 and #ajjjj deg41#bd and that it contracted when heated above #gjj deg44 #bd ,the silica blocks used were prepared by fusion in an electric furnace2 it is therefore probable that they were not quite pure4 ,professor ,callendar used rods of silica prepared by the author from ,brazil crystal2 these were drawn in the oxy-gas flame and had never been heated in contact with solid foreign matter1 so that they consisted1 presumably1 of very pure silica4 ,his results differ in some respects from those obtained by ,le ,chatelier1 for he finds the mean coefficient of expansion to be only #j4jjjjjjei1 i4e4 about one seventeenth as great as that of platinum4 ,callendar found the rods of silica expanded very regularly up to #ajjj deg4 but less regularly above that temperature4 ,above #abjj deg4 they contracted when heated4 ,the behaviour of vitreous silica under sudden changes of temperature is most remarkable4 ,large masses of it may be plunged suddenly when cold into the oxy-gas flame1 and tubes or rods at a white heat may be thrust into cold water1 or even into liquid air1 with impunity4 ,as a consequence of this1 it is in one respect much more easily worked in the flame than any form of glass4 ,difficult joints can be thrust suddenly into the flame1 or removed from it1 at any stage1 and they may be heated unequally in different parts with impunity4 ,it is safe to say that joints1 etc41 in silica never crack whilst one is making them nor during the subsequent cooling4 ,they may be set aside in an unfinished state and taken up again without any precautions4 ,therefore it is possible for an amateur to construct apparatus in silica which he would be quite unable to produce from glass4 ,the behaviour of vitreous silica with solvents has not yet been fully investigated1 but ,mr4 ,h4 ,g4 ,lacell has this subject in hand4 ,if it behaves like the other forms of anhydrous silica it will withstand the action of all acids except hydrofluoric acid4 ,it is1 of course1 very readily acted upon by solutions of alkalis and alkaline salts4 ,as regards the use of silica in experiments with gases1 it must be remarked that vitreous silica1 like platinum1 is slightly permeable to hydrogen when strongly heated4 ,one consequence of this is that traces of moisture are almost always to be found inside recently-made silica tubes and bulbs1 however carefully we may have dried the air forced into them during the process of construction4 ,owing to the very low coefficient of expansion of silica1 it is not possible to seal platinum wires into silica tubes4 ,nor can platinum be cemented into the silica by means of arsenic enamel1 nor by any of the softer glasses used for such purposes4 ,i have come near to success by using kaolin1 but the results with this material do not afford a real solution of the problem1 though they may perhaps point to a hopeful line of attack4 ,possibly platinum wires might be soldered into the tubes 7see ,laboratory ,arts1 ,r4 ,threlfall71 but this also is uncertain4 ,the process of preparing silica tubes1 etc41 from ,lumps of ,brazil ,crystal may be described conveniently under the following headings4 ,i describe the various processes fully in these pages1 as those who are interested in the matter will probably wish to try every part of the process in the first instance4 ,but ,i may say that in practice ,i think almost every one will find it advantageous to start with purchased silica tubes1 just as a glass-worker starts with a supply of purchased glass tubes4 ,the manufacturer can obtain his oxygen at a lower price than the retail purchaser1 and a workman who gives much time to such work can turn out silica tube so much more quickly than an amateur1 that ,i think it will be found that both time and money can be saved by purchasing the tube4 ,at the same time the beginner will find it worth while to learn and practise each stage of the process at first1 as every part of the work described may be useful in the production of finished apparatus from silica tubes4 ,this being so1 ,i am glad to be able to add that a leading firm of dealers in apparatus#be has commenced making silica goods on a commercial scale1 so that the new material is now available for all those who need it or wish to examine its properties4 #be ,messrs4 ,baird and ,tatlock4 ,preparing non-splintering ,silica from ,brazil ,pebble4--,the best variety of native ,silica is ,brazil ,pebble1 which may be obtained in chips or larger masses4 ,these should be thoroughly cleaned1 heated in boiling water1 and dropped into cold water1 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 hammer4 ,the fragments thus produced must be hand-picked1 and those which are not perfectly free from foreign matter should be rejected4 ,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 water2 this process being repeated1 if necessary1 till the product consists of semi-opaque friable masses1 very much like a white enamel in appearance4 ,after these have been washed with distilled water1 well drained and dried1 they may be brought into the hottest part of an oxy-gas flame safely1 or pressed suddenly against masses of white hot silica without any preliminary heating1 such as is necessary in the case of natural quartz4 ,quartz which has not been submitted to the above preparatory process1 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 material4 ,but after the above treatment1 which really gives little trouble1 all the difficulties which hampered the pioneer workers in silica disappear as if by magic4 ,apparatus4--,very little special apparatus need be provided for working with silica1 but it is absolutely essential to protect the eyes with very dark glasses4 ,these should be so dark as to render it a little difficult to work with them at first4 ,if long spells of work are undertaken1 two pairs of spectacles should be provided1 for the glasses quickly become hot enough to cause great inconvenience and even injury to the eyes4 ,almost any of the available oxy-gas burners may be used1 but they vary considerably in efficiency1 and it is economical to obtain a very efficient burner4 ,the 'blow-through' burners are least satisfactory1 and ,i have long since abandoned the use of them4 ,some of the safety 'mixed-gas jets' have an inconvenient trick of burning-back1 with sharp explosions1 which are highly disconcerting1 if the work be brought too near the nozzle of the burner4 ,i have found the patent burner of ,mr4 ,jackson 7,brin's ,oxygen ,company1 ,manchester7 most satisfactory1 and it offers the advantage that several jets can be combined in a group easily and inexpensively for work on large apparatus4 ,the large roaring flames such as are used1 ,i understand1 for welding steel are very expensive1 and not very efficient for the work here described4 ,the method of making ,silica ,tubes4--,before commencing to make a tube a supply of vitreous silica in rods about one or two millimetres in diameter must be prepared4 ,to make one of these1 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 corners1 press a small fragment of the same material against the melted part till the two adhere and heat it from below upwards1#bf till it becomes clear and vitreous1 add a third fragment in a similar manner1 then a fourth1 and so on till an irregular rod has been formed4 ,finally re-heat this rod in sections and draw it out whilst plastic into rods or coarse threads of the desired dimensions4 ,if one works carefully the forceps do not suffer much4 ,i have had one pair in almost constant use for several years2 they have been used in the training of five beginners and are still practically uninjured4 #bf ,this is to avoid bubbles in the finished glass4 ,the beginner should work with a gauge and regulator on the bottle of oxygen1 and should watch the consumption of oxygen closely4 ,a large expenditure of oxygen does not by any means necessarily imply a corresponding output of silica1 even by one who has mastered the initial difficulties4 ,when a supply of the small rods of vitreous silica has been provided1 bind a few of them round a rod of platinum 7diameter say1 #a mm47 by means of platinum wires at the two ends and heat the silica gradually1 beginning at one end after slightly withdrawing the platinum core from that end1 till a rough tube about four or five centimetres in length has been formed4 ,close one end of this1 expand it1 by blowing1 into a small bulb1 attach a silica rod to the remote end of the bulb1 re-heat the bulb and draw it out into a fine tube4 ,blow a fresh bulb on one end of this and again draw it out1 proceeding in this way till you have a tube about six or eight centimetres in length4 ,all larger tubes and vessels are produced by developing this fine tube suitably4 ,precautions4--,the following points must be carefully kept in mind1 both during the making of the first tube and afterwards3-- 7#a7 ,the hottest spot in the oxy-gas flame is at a point very near the tip of the inner cone of the flame1 and silica can be softened best at this hot spot4 ,the excellence of a burner does not depend on the size of its flame1 so much as on the temperature of its hot spot1 and the success of the worker depends on his skill in bringing his work exactly to this part of the flame4 ,comparatively large masses of silica may be softened in a comparatively small jet if the hot spot is properly utilised4 7#b7 ,silica is very apt to exhibit a phenomenon resembling devitrification during working4 ,it becomes covered with a white incrustation1 which seems to be comparatively rich in alkali4#bg ,this incrustation is very easily removed by re-heating the whitened surface1 provided that the material has been kept scrupulously clean4 ,if the silica has been brought into the flame when dusty1 or even after much contact with the hands of the operator1 its surface is very apt to be permanently injured4 ,too much attention cannot be given to cleanliness by the workman4 #bg ,the rock crystal exhibits a yellow flame when first heated in the oxy-gas flame1 and most samples contain spectroscopic quantities of lithium4 7#c7 ,when a heated tube or bulb of silica is to be expanded by blowing1 it is best not to remove it from the flame1 for if that is done it will lose its plasticity quickly unless it be large4 ,the better plan is to move it slightly from the hot spot into the surrounding parts of the flame at the moment of blowing4 ,it is best to blow the bulb through an india-rubber tube attached to the open end of the silica tube4 ,at first one frequently bursts the bulbs when doing this1 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 lump1 after re-heating it1 by blowing4 ,after a few hours' practice these mishaps gradually become rare4 ,i find it a good plan to interpose a glass tube packed with granulated potash between the mouth and the silica tube4 ,this prevents the interior of the tube from being soiled4 ,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 pressure4 ,it may be mentioned here that a finished tube usually contains a little moisture1 and a recognisable quantity of nitric peroxide4 ,these may be removed by heating the tube and drawing filtered air through it1 but not by washing1 as it is difficult to obtain water which leaves no residue on the silica4 ,making larger tubes and other apparatus of ,silica4--,in order to convert a small bulb of silica into a larger one or into a large tube1 proceed as follows3--,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 figure4 ,then heat the ring and the end of the bulb till it softens1 and expand the end by blowing4 ,if this process is repeated1 the bulb first becomes ovate and then forms a short tube which can be lengthened at will1 but the most convenient way to obtain a very long tube is to make several shorter tubes of the required diameter1 and say #bjj to #bej mm4 in length1 and to join these end to end4 ,it does not answer to add lumps of silica to the end of the bulb1 for the sides of the tube made in this way become too thin1 and blow-holes are constantly formed during the making of them4 ,these can be mended1 it is true1 but they spoil the appearance of the work4 ,illustration ,tubes made in the manner described above are thickened by adding rings of silica and blowing them when hot to spread the silica4 ,if a combination of several jets is employed1 very large tubes can be constructed in this way4 ,one of ,messrs4 ,baird and ,tatlock's workmen lately blew a bulb about #e cm4 in diameter1 and it was clear that he could have converted it into a long cylindrical tube of equal diameter had it been necessary to do so4 ,very thin tubes of #a4e cm4 diameter1 and tubes of considerable thickness and of equal size1 are easily made after some practice1 and fine capilliaries and millimetre tube can be made with about equal readiness4 ,if a very fine tube of even bore is required1 it may be drawn from a small thick cylinder after a little practice4 ,when a tube becomes so large that it cannot be heated uniformly on all sides by rotating it in the flame1 it is convenient to place a sheet of silica in front of the flame a little beyond the object to be heated1 in order that the former may throw back the flame on those parts of the tube which are most remote from the jet4 ,a suitable plate may be made by sticking together small lumps of silica rendered plastic by heat4 ,the silica tubes thus made can be cut and broken like glass1 they can be joined together before the flame1 and they can also be drawn into smaller tubes when softened by heat4 ,in order to make a side connection as in a ,t piece1 a ring of silica should be applied to the tube in the position fixed upon for the joint4 ,this ring must then be slightly expanded1 a new ring added1 and so on1 till a short side tube is formed4 ,to this it is easy to seal a longer tube of the required dimensions4 ,it is thus possible to produce ,geissler tubes1 small distilling flasks1 etc4 ,solid rods of silica are easily made by pressing together the softened ends of the fine rods or threads previously mentioned4 ,such rods and small masses can be ground and polished without annealing them4 ,quartz ,fibres4--,these were introduced into physical work by ,mr4 ,boys in #ahhi4 ,they may be made by attaching a fine rod of vitrified quartz to the tail of a small straw arrow provided with a needle-point2 placing the arrow in position on a cross-bow1 heating the rod of silica till it is thoroughly softened and then letting the arrow fly from the bow1 when it will carry with it an extremely fine thread of silica4 ,a little practice is necessary to ensure success1 but a good operator can produce threads of great tenacity and great uniformity4 ,fuller accounts of the process and of the various properties and uses of quartz fibres will be found in ,mr4 ,boys' lectures 7,roy4 ,inst4 ,proc4 #ahhi1 and ,proc4 ,brit4 ,assn4 #ahij71 and in ,mr4 ,threlfall's ,laboratory ,arts4 ,,index4 ,air-traps1 #fi4 ,annealing1 #bc4 ,apparatus needed for ,glass-working1 #aa4 ,appendix1 #hb4 ,beginners1 ,failures of1 #bb4 ,bellows1 ,position of1 #c4 ---- ,various forms of1 #g4 ,see also ,blower4 ,bending ,glass ,tubes1 #bh4 ,blower1 ,automatic1 #h4 ,blow-pipe1 ,cheap form of1 #d4 ---- ,dimensions of1 #d-e4 ---- ,fletcher's ,automaton1 #f4 ---- ,fletcher's ,compound1 #f4 ---- ,gimmingham's1 #f4 ---- ,herapath's1 #f4 ---- ,jets for the1 #g4 ---- ,use of the1 #h4 ,see also ,flames4 ,blow-pipes1 ,use of several in combination1 #ba4 ,brush ,flame1 #i4 ---- ,oxidising1 #bj4 ,bulbs1 ,methods of blowing1 #dg4 ,calibrating ,apparatus1 #gf-ha4 ,camphorated ,turpentine1 #aa4 ,cetti's ,vacuum ,tap1 #ff4 ,charcoal ,pastils1 #aa4 ,choking or ,contracting the ,bores of ,tubes1 #ce4 ,combining the ,parts of ,complicated ,apparatus1 #fa4 ,combustion ,tube1 how to work it1 #be4 ,contracting the ,bore of a ,tube1 #ce4 ,cotton ,wool for ,annealing1 #bd4 ,cutting ,glass ,tubes1 #bf1 #bg1 #bh4 ,dividing a ,line into ,equal ,parts1 #ge4 ,electrodes1 #ch1 #ee4 ,electrolysis1 ,making ,apparatus for1 #ei4 ,files for ,cutting ,glass1 #bg4 ,flame1 the ,pointed1 #h4 ---- the ,brush1 #i4 ---- the ,oxidising ,brush1 #bj4 ---- the ,smoky1 #aj4 ,fletcher's ,automaton ,blow-pipe1 #f4 ,fletcher's ,compound ,blow-pipe1 #f4 ,funnels1 ,thistle-headed1 #eg4 ,gimmingham's ,blow-pipe1 #f4 ,gimmingham's ,vacuum ,tap1 #fh4 ,glass1 ,annealing1 #bc4 ---- ,devitrification of1 #ae4 ---- ,method of ,working with ,lead1 #ag4 ---- ,method of ,working with ,soda1 #bb4 ---- ,nature of1 #ab4 ---- ,presenting to the ,flame1 #af4 ,glass ,tubes1 ,bending1 #bh4 ---- ,bordering1 #ca4 ---- ,characters of good1 #ad4 ---- ,choking1 #ce4 ---- ,cleaning1 #ae4 ,glass ,tubes1 ,cutting1 #bf1 #bg1 #bh4 ---- ,piercing1 #cg4 ---- ,purchase of1 #ab4 ---- ,sealing1 #cb4 ---- ,sealing ,hermetically1 #eh4 ---- ,sizes of1 #hb4 ---- ,welding or ,soldering1 #ci1 #fb4 ---- ,widening the ,ends of1 #cf4 ,graduating ,apparatus1 #gj4 ,grinding ,stoppers1 #ea4 ,herapath's ,blow-pipe1 #f4 ,hofman's ,apparatus for ,electrolysis1 #ei4 ,inside ,joints1 #dc4 ,jets for ,blow-pipes1 #g4 ,joints1 ,air-tight1 #fd4 ,lead ,glass1 ,method of ,working with1 #ag4 ,lead ,glass1 ,blackening of1 #ag4 ,light1 ,effect of1 in ,working1 #c4 ,line1 to ,divide into ,equal ,parts1 #ge4 ,mercury ,joints1 ,various1 #fd4 ,non-splintering ,silica1 ,preparation of1 from ,quartz1 #hh4 ,ozone ,generator1 ,to ,make an1 #dd4 ,pastils of ,charcoal1 #aa4 ,piercing ,tubes1 etc41 #cg4 ,platinum ,electrodes1 ,sealing in1 #ch1 #ee4 ,pointed ,flame1 the1 #i4 ,quartz ,fibres1 #id4 ,rounding ,ends of ,tubes1 #ca4 ,sealing or ,closing ,openings in ,tubes1 #cb4 ,side-tubes1 ,fixing1 #da4 ,smoky ,flame1 #aj4 ,soda ,glass1 ,method of ,working1 #bb4 ,soldering or ,welding1 #ci1 #fb4 ,spiral ,tubes1 #ef4 ,stoppers1 ,making and ,grinding1 #ea4 ,table for ,glass-blower1 #c4 ,taps1 ,vacuum1 #fe4 ,thistle-headed ,funnels1 #eg4 ,traps1 ,air1 #fi4 ,tube1 ,combustion1 how to work it1 #be4 ,tubes4 ,see ,glass ,tubes4 ---- ,t-1 #da4 ---- ,u-1 #ef4 ,turpentine1 ,camphorated1 for ,grinding1 #aa4 ,u-,tubes1 #ef4 ,vacuum ,taps1 #fe-fh4 ---- ,tube1 ,to ,make a1 #fj4 ,vitreous ,silica1 ,apparatus required for ,making1 #hi4 ---- ,behaviour under sudden changes of ,temperature1 #hg4 ---- ,bulbs1 etc41 ,making ,joints on1 #ic4 ---- ,expansion of1 #hf4 ---- ,hardness of1 #he4 ---- ,insulating ,power of1 #he4 ---- ,melting ,point of1 #he4 ---- ,permeability to ,gases1 #hg4 ---- ,properties of1 #hd4 ---- ,rods1 ,making ,joints on1 #id4 ---- ,tubes1 ,method of ,making1 #ij4 ---- ,tubes1 ,making ,joints on1 #id4 ,welding or ,soldering ,tubes together1 #ci1 #fb4 ,white ,enamel1 ,uses of1 #ci1 #ef4 ,widening the ,ends of ,tubes1 #cf4 ,working-place1 #b4 ,printed by ,t4 and ,a4 ,,constable1 ,printers to ,his ,majesty at the ,edinburgh ,university ,press1 ,scotland