,libraries47 ,a ,,handbook ,,of ,,laboratory ,,glass-,,blowing ,to my ,friends ,eric ,reid and ,sidney ,wilkinson ,a ,handbook of ,laboratory ,glass-,blowing ,,by ,,bernard ,d4 ,,bolas ,,with ,,numerous ,,diagrams ,,in ,,the ,,text ,,by ,,naomi ,,bolas ,illustration ,,london ,,george ,,routledge ,,sons1 ,,ltd ,,new ,,york3 ,e4 ,p4 ,,dutton ,,co4 #aiba ,,contents ,,chap4 ,,page ,i4 ,introduction and ,preliminary ,remarks--,general ,principles to be observed in ,glass ,working--,choice of ,apparatus--,tools and ,appliances--,glass #a ,,ii4 ,easy ,examples of ,laboratory ,glass-,blowing--,cutting and ,sealing ,tubes1 ,tubes for ,high ,temperature ,experiments--,thermometer-,bulbs1 ,bulbs of ,special ,glass1 ,pipettes1 ,absorption-,bulbs or ,washing ,bulbs--,joining ,tubes1 ,branches1 ,exhaustion-,branches1 ,branches of ,dissimilar ,glass1 ,blowing ,bulbs1 ,a ,thistle ,funnel1 ,cracking and ,breaking ,glass1 ,leading and ,direction of ,cracks--,use of ,glass ,rod or ,strips of ,window-,glass1 ,joining ,rod1 ,feet and ,supports--,gripping ,devices for use in ,corrosive ,solutions--,the ,building up of ,special ,forms from ,solid ,glass #aj ,,iii4 ,internal ,seals1 ,air-,traps1 ,spray ,arresters1 ,filter-,pumps--,sprays1 ,condensers2 plain1 double surface1 and spherical--,soxhlet ,tubes and ,fat ,extraction ,apparatus--,vacuum ,tubes1 ,electrode ,work1 ,enclosed ,thermometers1 ,alarm ,thermometers 444 ,recording ,thermometers1 ,spinning ,glass #cb ,,iv4 ,glass1 its ,composition and ,characteristics--,annealing--,drilling1 ,grinding1 and ,shaping ,glass by methods other than ,fusion--,stopcocks--,marking ,glass--,calibration and ,graduation of ,apparatus--,thermometers--,exhaustion of ,apparatus--,joining ,glass and ,metal--,silvering ,glass #ee ,v4 ,extemporised ,glass-,blowing ,apparatus--,the use of ,oil or other ,fuels--,making ,small ,rods and ,tubes from ,glass ,scraps--,the ,examination of ,manufactured ,apparatus with a view to ,discovering the ,methods used in ,manufacture--,summary of ,conditions necessary for ,successful ,glass-,blowing #hj ,index #aje ,,preface ,to cover the whole field of glass-blowing in a small handbook would be impossible4 ,to attempt even a complete outline of the methods used in making commercial apparatus would involve more than could be undertaken without omitting the essential details of manipulation that a novice needs4 ,i have1 therefore1 confined myself as far as possible to such work as will find practical application in the laboratory and will1 ,i hope1 prove of value to those whose interests lie therein4 ,the method of treatment and somewhat disjointed style of writing have been chosen solely with the view to economy of space without the undue sacrifice of clearness4 ,,bernard ,d4 ,,bolas4 ,handbook of ,laboratory ,glass-,blowing ,,chapter ,i ,introduction and ,preliminary ,remarks--,general ,principles to be observed in ,glass ,working--,choice of ,apparatus--,tools and ,appliances--,glass4 ,glass-blowing is neither very easy nor very difficult2 there are operations so easy that the youngest laboratory boy should be able to repeat them successfully after once having been shown the way1 there are operations so difficult that years are needed to train eye and hand and judgment to carry them out2 but the greater number of scientific needs lie between these two extremes4 ,yet a surprisingly large number of scientific workers fail even to join a glass tube or make a ,t piece that will not crack spontaneously1 and the fault is rather one of understanding than of lack of ability to carry out the necessary manipulation4 ,in following the scheme of instruction adopted in this handbook1 it will be well for the student to pay particular attention to the reason given for each detail of the desirable procedure1 and1 as far as may be1 to memorise it4 ,once having mastered the underlying reason1 he can evolve schemes of manipulation to suit his own particular needs1 although1 as a rule1 those given in the following pages will be found to embody the result of many years' experience4 ,there is a wide choice of apparatus1 from a simple mouth-blowpipe and a candle flame to a power-driven blower and a multiple-jet heating device4 ,all are useful1 and all have their special applications1 but1 for the present1 we will consider the ordinary types of bellows and blowpipes1 such as one usually finds in a chemical or physical laboratory4 ,the usual1 or ,herepath1 type of gas blowpipe consists of an outer tube through which coal gas can be passed and an inner tube through which a stream of air may be blown4 ,such a blowpipe is shown in section by ,fig4 #a4 ,it is desirable to have the three centring screws as shown1 in order to adjust the position of the air jet and obtain a well-shaped flame1 but these screws are sometimes omitted4 ,fig4 #a1 a and b show the effects of defective centring of the air jet1 c shows the effect of dirt or roughness in the inside of the air jet1 d shows a satisfactory flame4 ,illustration3 ,fig #a ,for many purposes1 it is an advantage to have what is sometimes known as a quick-change blowpipe2 that is one in which jets of varying size may be brought into position without stopping the work for more than a fraction of a second4 ,such a device is made by ,messrs4 ,letcher1 and is shown by e1 and in section by f ,fig4 #a4 ,it is only necessary to rotate the desired jet into position in order to connect it with both gas and air supplies4 ,a small bye-pass ignites the gas1 and adjustment of gas and air may be made by a partial rotation of the cylinder which carries the jets4 ,for specially heavy work1 where it is needed to heat a large mass of glass1 a multiple blowpipe jet of the pattern invented by my father1 ,thomas ,bolas1 as the result of a suggestion derived from a study of the jet used in ,griffin's gas furnace1 is of considerable value4 ,this jet consists of a block of metal in which are drilled seven holes1 one being central and the other six arranged in a close circle around the central hole4 ,to each of these holes is a communication way leading to the gas supply1 and an air jet is arranged centrally in each4 ,each hole has also an extension tube fitted into it1 the whole effect being that of seven blowpipes4 ,in order to provide a final adjustment for the flame1 a perforated plate having seven holes which correspond in size and position to the outer tubes is arranged to slide on parallel guides in front of these outer tubes4 ,illustration3 ,fig4 #b ,the next piece of apparatus for consideration is the bellows1 of which there are three or more types on the market1 although all consist of two essential parts1 the blower or bellows proper and the wind chamber or reservoir4 ,two patterns are shown in ,fig4 #b2 a1 is the form which is commonly used by jewellers and metal workers to supply the air blast necessary for heating small furnaces4 ,such a bellows may be obtained at almost any jewellers' supply dealer in ,clerkenwell1 but it not infrequently happens that the spring in the wind chamber is too strong for glass-blowing1 and hence the air supply tends to vary in pressure4 ,this can be improved by fitting a weaker spring1 but an easier way and one that usually gives fairly satisfactory results1 is to place an ordinary screw-clip on the rubber tube leading from the bellows to the blowpipe1 and to tighten this until an even blast is obtained4 ,another form of bellows1 made by ,messrs4 ,fletcher and ,co41 and common in most laboratories1 is shown by b2 the wind chamber consists of a disc of india-rubber clamped under a circular frame or tied on to a circular rim4 ,this form is shown by ,fig4 #b1 b4 ,the third form1 and one which my own experience has caused me to prefer to any other1 is cylindrical1 and stands inside the pedestal of the blowpipe-table4 ,a blowpipe-table of this description is made by ,enfer of ,paris4 ,there is no need1 however1 to purchase an expensive table for laboratory use4 ,all the work described in this book can quite well be done with a simple foot bellows and a quick-change blowpipe4 ,nearly all of it can be done with a single jet blowpipe1 such as that described first1 or even with the still simpler apparatus mentioned on page #hd1 but ,i do not advise the beginner to practise with quite so simple a form at first1 and for that reason have postponed a description of it until the last chapter4 ,glass-blowers' tools and appliances are many and various1 quite a number of them are better rejected than used1 but there are a few essentials4 ,these are1--file1 glass-knife1 small turn-pin1 large turn-pin1 carbon cones1 carbon plate1 rubber tube of small diameter1 various sizes of corks1 and an asbestos heat reflector4 ,for ordinary work1 an annealing oven is not necessary1 but one is described on page #fj in connection with the special cases where annealing is desirable4 ,fig4 #c illustrates the tools and appliances4 a is an end view of the desirable form of file1 and shows the best method of grinding the edges in order to obtain a highly satisfactory tool4 b is a glass knife1 shown both in perspective and end view1 it is made of glass-hard steel and should be sharpened on a rough stone1 such as a scythe-stone1 in order to give a slightly irregular edge4 c is a small turn-pin which may be made by flattening and filing the end of a six-inch nail4 d is the large turn-pin and consists of a polished iron spike1 about five inches long and a quarter of an inch diameter at its largest part4 ,this should be mounted in a wooden handle4 e and f are carbon cones4 ,a thin rubber tube is also useful2 it may be attached to the work and serve as a blowing tube1 thus obviating the necessity of moving the work to the mouth when internal air pressure is to be applied4 ,in order to avoid undue repetition1 the uses of these tools and appliances will be described as they occur4 ,illustration3 ,fig4 #c ,glass1 as usually supplied by chemical apparatus dealers is of the composition known as soda-glass4 ,they also supply hard or combustion glass1 but this is only used for special purposes1 as it is too infusible for convenient working in the ordinary blowpipe flame4 ,soda-glass consists primarily of silicate of sodium with smaller quantities of silicate of aluminum and potassium4 ,its exact composition varies4 ,it is not blackened1 as lead glass is1 by exposure to the reducing gases which are present in the blue cone of a blowpipe flame1 and hence is easier for a beginner to work without producing discolouration4 ,further notes on glasses will be found on page #ee1 but for ordinary purposes soda-glass will probably be used4 ,,chapter ,,ii ,easy ,examples of ,laboratory ,glass-,blowing--,cutting and ,sealing ,tubes for ,various ,purposes2 ,test-,tubes1 ,pressure-,tubes1 ,tubes for ,high ,temperature ,experiments--,thermometer-,bulbs1 ,bulbs of ,special ,glass1 ,pipettes1 ,absorption-,bulbs or ,washing-,bulbs--,joining ,tubes2 ,branches1 ,exhaustion-,branches1 ,branches of ,dissimilar ,glass--,blowing ,bulbs2 ,a ,thistle ,funnel2 ,cracking and ,breaking ,glass2 ,leading and ,direction of ,cracks--,use of ,glass ,rod or ,strips of ,window-,glass2 ,joining ,rod1 ,feet and ,supports--,gripping ,devices for use in ,corrosive ,solutions--,the ,building ,up of ,special ,forms from ,solid ,glass4 ,perhaps the most common need of the glass-blower whose work is connected with that of the laboratory is for a sealed tube2 and the sealing of a tube is an excellent preliminary exercise in glass-blowing4 ,we will assume that the student has adjusted the blowpipe to give a flame similar to that shown in d1 ,fig4 #a1 and that he has learned to maintain a steady blast of air with the bellows2 further1 we will assume that the tube he wishes to seal is of moderate size1 say not more than half an inch in diameter and with walls of from one-tenth to one-fifth of an inch thick4 ,illustration3 ,fig4 #d ,a convenient length of tube for the first trial is about one foot2 this should be cut off from the longer piece1 in which it is usually supplied1 as follows3--lay the tube on a flat surface and make a deep cut with the edge of a file4 ,do not saw the file to and fro over the glass4 ,if the file edge has been ground as shown in a1 ,fig4 #c1 such a procedure will be quite unnecessary and only involve undue wear2 one movement with sufficient pressure to make the file bite will give a deep cut4 ,now rotate the tube through about one-eighth of a turn and make another cut in continuation of the first4 ,take the tube in the hands1 as shown in a1 ,fig4 #d1 and apply pressure with the thumbs1 at the same time straining at the ends4 ,the tube should break easily4 ,if it does not1 do not strain too hard1 as it may shatter and cause serious injuries to the hands1 but repeat the operation with the file and so deepen the original cuts4 ,in holding a tube for breaking1 it is important to place the hands as shown in sketch1 as this method is least likely to cause shattering and also minimises the risk of injury even if the tube should shatter4 ,to cut a large tube1 or one having very thick walls1 it is better to avoid straining altogether and to break by applying a small bead of intensely heated glass to the file cut4 ,if the walls are very thin1 a glass-blower's knife should be used instead of a file4 ,the tube and glass-blower's knife should be held in the hand1 and the tube rotated against the edge of the knife2 this will not produce a deep cut1 but is less likely to break the tube4 ,a bead of hot glass should be used to complete the work4 ,the next operation is to heat the glass tube in the middle2 this must be done gradually and evenly2 that is to say the tube must be rotated during heating and held some considerable distance in front of the flame at first2 otherwise the outer surface of the glass will expand before the interior is affected and the tube will break4 ,from two to five minutes1 heating at a distance of about eight inches in front of the flame will be found sufficient in most cases1 and another minute should be taken in bringing the tube into the flame4 ,gradual heating is important1 but even heating is still more important and this can only be obtained by uniform and steady rotation4 ,until the student can rotate a tube steadily without thinking about it1 real progress in glass-blowing is impossible4 ,when the tube is in the flame it must be held just in front of the blue cone and rotated until the glass is soft enough to permit the ends to be drawn apart4 ,continue to separate the ends and1 at the same time1 move the tube very slightly along its own axis1 so that the flame tends to play a little more on the thicker part than on the drawn-out portion4 ,if this is done carefully1 the drawn-out portion can be separated off1 leaving only a slight bleb on the portion it is desired to seal4 ,this is illustrated by b1 ,fig4 #d4 ,to convert the seal at b1 ,fig4 #d41 into the ordinary form of test-tube seal1 it is only necessary to heat the bleb a little more strongly1 blow gently into the tube until the thick portion is slightly expanded1 re-heat the whole of the rounded end until it is beginning to collapse1 and give a final shaping by careful blowing after it has commenced to cool4 ,in each case the glass must be removed from the flame before blowing4 ,the finished seal is shown by c1 ,fig4 #d4 ,if desired1 the open end may now be finished by heating and rotating the soft glass against the large turn-pin1 as illustrated in d1 but the turn-pin must not be allowed to become too hot1 as if this happens it will stick to the glass4 ,after turning out the end1 the lip of glass must be heated to redness and allowed to cool without coming in contact with anything2 otherwise it will be in a condition of strain and liable to crack spontaneously4 ,the finished test-tube is shown by e4 ,when it is necessary to seal a substance inside a glass tube1 the bottom of the tube is first closed1 as explained above1 and allowed to cool2 the substance1 if a solid1 is now introduced1 but should not come to within less than two inches of the point where the second seal is to be made4 ,if the substance is a liquid it can more conveniently be introduced at a later stage4 ,now bring the tube into the blowpipe flame gradually1 and rotate it1 while heating1 at the place where it is to be closed4 ,allow the glass to soften and commence to run together until the diameter of the tube is reduced to about half its original size4 ,remove from the flame and draw the ends apart1 this should give a long1 thick extension as shown by f1 ,fig4 #d4 ,if any liquid is to be introduced1 it may now be done by inserting a thin rubber or other tube through the opening and running the liquid in4 ,a glass tube should be used with caution for introducing the liquid1 as any hard substance will tend to scratch the inside of the glass and cause cracking4 ,the final closure is made by melting the drawn-out extension in the blowpipe flame2 the finished seal being shown by g1 ,fig4 #d4 ,if the sealed tube has to stand internal pressure1 it is desirable to allow the glass to thicken somewhat more before drawing out1 and the bottom seal should also be made thicker4 ,for such a tube1 and especially when it has to stand heating1 as in a ,carius determination of chlorine1 each seal should be cooled very slowly by rotating it in a gas flame until the surface is covered with a thick layer of soot1 and it should then be placed aside in a position where the hot glass will not come in contact with anything1 and where it will be screened from all draughts4 ,joining ,tube4--,we will now consider the various forms of join in glass tubing which are met with in the laboratory4 ,first1 as being easiest1 we will deal with the end-to-end joining of two tubes of similar glass4 a1 b1 and c1 ,fig4 #e1 illustrate this4 ,one end of one of the tubes should be closed1 a lip should be turned out on each of the ends to be joined1 and both lips heated simultaneously until the glass is thoroughly soft4 ,now bring the lips together gently1 until they are in contact at all points and there are no places at which air can escape2 remove from the flame1 and blow slowly and very cautiously until the joint is expanded as shown in b1 ,fig4 #e4 ,reheat in the flame until the glass has run down to rather less than the original diameter of the tube1 and give a final shaping by re-blowing4 ,the chief factors of success in making such a join are1 thorough heating of the glass before bringing the two tubes together1 and avoidance of hard or sudden blowing when expanding the joint4 ,the finished work is shown by c1 ,fig4 #e4 ,illustration3 ,fig4 #e ,to join a small glass tube to the end of a large one1 the large tube should first be sealed1 a small spot on the extreme end of the seal heated1 and air pressure used to expand the heated spot as shown in d4 ,this expanded spot is then re-heated and blown out until it bursts as shown in e1 the thin fragments of glass are removed and the end of the small tube turned out as shown in f4 ,after this the procedure is similar to that used in jointing two tubes of equal size4 ,when these two forms of joint have been mastered1 a ,t piece will present but little difficulty4 ,it is made in three stages as shown in ,fig4 #e1 and the procedure is similar to that used in joining a large and small tube4 ,care should be taken to avoid softening the top of the ,t too much1 or the glass will bend and distort the finished work2 although a slight bend can be rectified by re-heating and bending back4 ,local re-heating is often useful in giving the joint its final shape4 ,an exhaustion branch is often made by a totally different method4 ,this method is shown by g1 h1 and i1 ,fig4 #e2 g is the tube on which the branch is to be made4 ,the end of a rod of similar glass should be heated until a mass of thoroughly liquid glass has collected1 as shown1 and at the same time a spot should be heated on that part of the tube where it is desired to make the branch4 ,the mass of hot glass on the rod is now brought in contact with the heated spot on the tube and expanded by blowing as shown by h4 ,the air pressure in the tube is still maintained while the rod is drawn away as shown by i4 ,this will give a hollow branch which may be cut off at any desired point1 and is then ready for connection to the vacuum pump4 ,if the rod used is of a dissimilar glass1 the branch should be blown much thinner4 ,such a branch will often serve as a useful basis for joining two tubes of different composition1 as the ordinary type of branch is more liable to crack when made with two glasses having different coefficients of expansion4 ,blowing ,bulbs4--,a bulb may be blown on a closed tube such as that shown by c1 ,fig4 #e1 by rotating it in the blowpipe flame until the end is softened1 removing it from the flame and blowing cautiously4 ,it is desirable to continue the rotation during blowing4 ,in the case of a very small tube1 it is sufficient to melt the end without previous sealing1 rotate it in the flame until enough glass has collected1 remove from the flame and blow while keeping the tube in rotation4 ,thermometer ,bulbs4--,if the thermometer is to be filled with mercury1 it is desirable to use a rubber bulb for blowing1 as moisture is liable to condense inside the tube when the mouth is used1 and this moisture will cause the mercury thread to break4 ,in any case1 a slight pressure should be maintained inside the thermometer tube while it is in the flame2 otherwise the fine capillary tube will close and it will be very difficult to expand the heated glass into a bulb4 ,large ,bulbs4--,when a large bulb is needed on a small or medium sized tube1 it is often necessary to provide more glass than would be obtained if the bulb were blown in the ordinary way4 ,one method is to expand the tube in successive stages along its axis1 as shown by a1 ,fig4 #f4 ,these expanded portions are then re-heated1 so that they run together into one hollow mass from which the bulb is blown2 b and c1 illustrate this4 ,another method1 and one which is useful for very large bulbs1 is to fuse on a length of large1 thick-walled1 tubing4 ,the heat reflector1 g1 ,fig4 #c1 should be used1 if necessary1 when making large bulbs4 ,it consists of a sheet of asbestos mounted in a foot1 and is used by being placed close to the mass of glass on the side away from the blowpipe flame while the glass is being heated4 ,illustration3 ,fig4 #f ,bulbs of ,dissimilar ,glass4--,these may be made by the second method given under ,large ,bulbs1 but the joint should be blown as thin as possible4 ,further instructions in the use of unlike glasses are given on page #id4 ,a ,bulb in the ,middle of a ,tube4--,unless the bulb is to be quite small1 it will be necessary to join in a piece of thick glass tubing1 or to draw the thin tube out from a larger piece1 thus leaving a thick mass in the middle as shown by d1 ,fig4 #f4 ,this mass of glass should now be rotated in the blowpipe flame until it is quite soft and on the point of running together4 ,considerable practice will be necessary before the two ends of the tube can be rotated at the same speed and without wobbling1 but this power must be acquired4 ,when the glass is thoroughly hot1 remove from the flame1 hold in a horizontal position1 and expand by blowing4 ,it is essential to continue the rotation while this is done4 ,should one part of the bulb tend to expand more than the other1 turn the expanded part to the bottom1 pause for about a second1 both in rotating and blowing1 in order that the lower portion may be cooled by ascending air-currents2 then continue blowing and turning as before4 ,absorption ,bulbs or ,washing ,bulbs4--,these are made by an elaboration of the processes given in the last paragraph1 g1 h1 and i1 ,fig4 #f1 illustrate this4 ,a ,thistle ,funnel4--,this is made by blowing a fairly thick-walled bulb on a glass tube1 bursting a hole by heating and blowing1 and enlarging the burst-out part by heating and rotating against a turn-pin4 ,bending ,glass ,tube4--,small tubing may be bent in a flat flame gas burner and offers no special difficulty4 ,large or thin-walled tubing should be heated in the blowpipe flame and a slight bend made2 another zone of the tube1 just touching the first bend1 should now be heated and another slight bend made4 ,in this way it is possible to avoid flattening and a bend having any required angle can gradually be produced4 ,a final shaping of the bend may be made by heating in a large blowpipe flame and expanding slightly by air pressure4 ,glass ,spirals4--,if a tube is heated by means of a long1 flat-flame burner1 the softened tube may be wound on to an iron mandrel which has previously been covered with asbestos4 ,the mandrel should be made slightly conical in order to facilitate withdrawal4 ,it is desirable to heat the surface of the asbestos almost to redness by means of a second burner1 and thus avoid undue chilling of the glass and the consequent production of internal strain4 ,illustration3 ,fig4 #g ,a ,thermo-,regulator for ,gas4--,fig4 #g1 a-e1 shows an easily constructed thermo-regulator4 ,the mercury reservoir1 a1 and the upper part1 b1 are made by joining two larger pieces of tubing on to the capillary4 ,the gas inlet passes through a rubber stopper1 in order to allow of adjustment for depth of insertion1 and the bye-pass branches1 d and e1 are connected by a piece of rubber tubing which can be compressed by means of a screw clip1 thus providing a means of regulating the bye-pass4 ,use of ,glass ,rod4--,apart from its most common laboratory use for stirring2 glass rod may be used in building up such articles as insulating feet for electrical apparatus or acid-resisting cages for chemical purposes4 ,such a cage is shown by f1 g and h1 ,fig4 #g4 ,further1 by an elaboration of the method of making an exhaustion branch1 given on page #ah1 blown articles may also be constructed from rod4 ,note the added parts of e1 ,fig4 #i4 ,a ,simple ,foot4--,the form of foot shown by ,fig4 #g1 k1 is easy to make and has many uses4 ,first join a glass rod to a length of glass tubing as shown 7the joint should be expanded slightly by blowing71 cut off the tube and heat the piece remaining on the rod until it can be turned out as shown by i4 ,this should be done with the large turn-pin1 and care should be taken not to heat the supporting rod too strongly1 otherwise the piece of tube will become bent and distorted2 it is better to commence by heating the edge of the piece of tube and turn out a lip1 then extend the heating by degrees and turn out more and more until the foot looks like that shown by i4 ,we now need to make three projections of glass rod4 ,these are produced as follows3--,heat the end of the glass rod until a thoroughly melted mass of glass has accumulated 7the rod must be rotated while this is being done1 otherwise the glass will drop off72 when sufficient melted glass has been obtained1 the edge of the turned-out foot should be heated to dull redness over about one-third of its circumference1 and the melted glass on the rod should be drawn along the heated portion until both are so completely in contact as to form one mass of semi-fluid glass4 ,the rod should now be drawn away slowly1 and1 finally1 separated by melting off1 thus producing a flat projection4 ,a repetition of the process will give the other two projections1 and the finished foot may be adjusted to stand upright by heating the projections slightly and standing it on the carbon plate mentioned on page #g4 ,after the foot is adjusted it should be annealed slightly by heating to just below the softening point of the glass and then rotating in a smoky gas flame until it is covered with a deposit of carbon1 after which it should be allowed to cool in a place free from draughts and where the hot glass will not come in contact with anything4 ,the finished foot is shown by k1 ,fig4 #g4 ,building up from ,glass ,rod4--,a glass skeleton-work can be constructed from rod without much difficulty1 and is sometimes useful as a container for a substance which has to be treated with acid1 or for similar purposes4 ,the method is almost sufficiently explained by the illustration in ,fig4 #g2 f shows the initial stage1 g the method of construction of the net-work1 and h the finished container4 ,it is convenient to introduce the substance at the stage indicated by g4 ,the important points to observe in making this contrivance are that the glass rod must be kept hot by working while it is actually in the flame1 and that the skeleton must be made as thin as possible with the avoidance of heavy masses of glass at any place4 ,if these details are neglected it will be almost certain to crack4 ,stirrers4--,these are usually made from glass rod1 and no special instructions are necessary for their construction1 except that the glass should be in a thoroughly fused condition before making any joins and the finished join should be annealed slightly by covering with a deposit of soot1 as explained on page #af4 ,the flat ends shown in a1 ,fig4 #h1 are made by squeezing the soft glass rod between two pieces of carbon1 and should be re-heated to dull redness after shaping4 ,fig4 #h also shows various forms of stirrer4 ,in order to carry out stirring operations in the presence of a gas or mixture of gases other than air1 some form of gland or seal may be necessary where the stirrer passes through the bearing in which it runs4 ,a flask to which is fitted a stirrer and gas seal is shown in section by b1 ,fig4 #h4 ,the liquid used in this seal may be mercury1 petroleum1 or any other that the experimental conditions indicate4 ,illustration3 ,fig4 #h ,if the bearing for a stirrer is made of glass tube1 it is desirable to lubricate rather freely2 otherwise heat will be produced by the friction of the stirrer and the tube will probably crack4 ,such lubrication may be supplied by turning out the top of the bearing tube and filling the turned-out portion with petroleum jelly mixed with a small quantity of finely ground or1 better1 colloidal graphite1 and the bearing should also be lubricated with the same composition4 ,care should be taken not to employ so soft a lubricant or so large an excess as to cause it to run down the stirrer into the liquid which is being stirred4 ,leading a ,crack4--,it sometimes happens that a large bulb or specially thin-walled tube has to be divided4 ,in such a case it is scarcely practicable to use the method recommended for small tubes on page #ab1 but it is quite easy to lead a crack in any desired direction4 ,a convenient starting point is a file cut2 this is touched with hot glass until a crack is initiated4 ,a small flame or a bead of hot glass is now used to heat the article at a point about a quarter of an inch from the end of the crack and in whatever direction it has to be led4 ,the crack will now extend towards the source of heat1 which should be moved farther away as the crack advances4 ,in this manner a crack may be caused to take any desired path and can be led round a large bulb4 ,cutting ,glass with the ,diamond4--,slips of window-glass can be used in place of glass rod for some purposes1 and as cutting them involves the use of the glaziers' diamond or a wheel-cutter1 they may well be mentioned under this heading4 ,in cutting a sheet of glass with the diamond1 one needs a flat surface on which to rest the glass1 and a rule against which to guide the diamond4 ,the diamond should be held in an almost vertical position1 and drawn over the surface of the glass with slight pressure4 ,while this is being done the angle of the diamond should be changed by bringing the top of the handle forward until the sound changes from one of scratching to a clear singing note4 ,when this happens the diamond is cutting4 ,a few trials will teach the student the correct angle for the diamond with which he works1 and the glass1 if properly cut1 will break easily4 ,if the cut fails it is better to turn the glass over and make a corresponding cut on the other side rather than make any attempt to improve the original cut4 ,the diamond is seldom used for cutting small glass tubes4 ,the use of the wheel-cutter calls for no special mention as it will cut at any angle1 although the pressure required is somewhat greater than that needed by most diamonds4 ,,chapter ,,iii ,internal ,seals1 ,air-,traps1 ,spray ,arresters1 ,filter-,pumps--,sprays1 ,condensers2 ,plain1 ,double ,surface1 and ,spherical--,soxhlet ,tubes and ,fat ,extraction ,apparatus--,vacuum ,tubes1 ,electrode ,work1 ,enclosed ,thermometers1 ,alarm ,thermometers1 ,recording ,thermometers1 ,spinning ,glass4 ,internal ,seals4--,it is convenient to class those cases in which a glass tube passes through the wall of another tube or bulb under the heading of ,internal ,seals4 ,these are met with in barometers1 spray arresters1 and filter pumps1 in condensers and some forms of vacuum tube4 ,the two principal methods of making such seals will be considered first and their special application afterwards4 ,an ,air ,trap on a ,barometer ,tube4--,this involves the use of the first method1 and is perhaps the simplest example that can be given4 ,fig4 #i1 a1 a#a and a#b1 show the stages by which this form of internal seal is made4 ,for the first trials1 it is well to work with fairly thick-walled tubing1 which should be cut into two pieces1 each being about eight inches long4 ,illustration3 ,fig4 #i ,first seal the end of one tube as described on page #ac1 heat the sealed end and expand to a thick walled bulb4 ,fuse the end of the other tube1 attach a piece of glass rod to serve as a handle1 and draw out2 cut off the drawn-out portion3 leaving an end like a4 ,now heat a small spot at the end of the bulb1 blow1 burst out1 and remove the thin fragments of glass4 ,heat a zone on the other tube at the point where the drawn-out portion commences and expand as shown by a#a4 ,the next stage is to join the tubes4 ,heat the ragged edges of the burst-out portion until they are thoroughly rounded4 ,at the same time heat the drawn-out tube to just below softening point4 ,then1 while the rounded edges of the burst-out portion are still soft1 insert the other tube2 rotate the join in the blowpipe flame until it is quite soft1 and expand by blowing4 ,if necessary1 re-heat and expand again4 ,the finished seal1 which should be slightly annealed by smoking in a sooty flame1 is shown by a#b4 ,a ,spray ,arrester4--,this is made by the second method1 in which the piece of tube which projects inside the bulb is fused in position first and the outer tube is then joined on4 ,the various stages of making are illustrated by b1 b#a and b#b1 ,fig4 #i4 ,a bulb is blown between two tubes by the method given on page #bb1 the larger tube is then cut off and the small piece of tube introduced into the bulb after having been shaped as shown in by b1 ,fig4 #i4 ,the opening in the bulb is sealed as shown by b#a4 ,the sealed part is now heated and the bulb inclined downwards until the inner tube comes in contact with the seal and is fused in position4 ,this operation requires some practice in order to prevent the inner tube either falling through the soft glass or becoming unsymmetrical4 ,the end of the bulb1 where the inner tube comes in contact with it1 is now perforated by heating and blowing1 thus giving the form shown by b#b1 and the outer tube is joined on4 ,the finished spray arrester is shown by b#c4 ,practice alone will give the power to produce a symmetrical and stable piece of work4 ,two ,forms of ,filter ,pump4--,that illustrated by d1 ,fig4 #i1 is made by the method explained under ,an ,air ,trap on a ,barometer ,tube4 ,that illustrated by c is made by the method explained under ,a ,spray ,arrester4 ,no new manipulation is involved1 and the construction should be clear from a study of the drawings4 ,multiple and ,branched ,internal ,seals4--,a fuller consideration of these will be found on page #ci1 but one general principle may well be borne in mind2 that1 as far as is possible1 a tube having both ends fastened inside another tube or bulb should be curved or have a spiral or bulb at some point in its length1 otherwise any expansion or contraction will put great strain on the joints4 ,sprays4--,a spray which is easy to make1 easy to adjust1 and easy to clean after use is shown by e1 ,fig4 #i4 ,the opening on the top of the bulb is made by melting on a bead of glass1 expanding1 bursting1 and fusing the ragged edges4 ,the two branches which form the spray producing junction are made by the method used for an exhaustion branch and described on page #ah4 ,a spray which can be introduced through the neck of a bottle is shown by h1 ,fig4 #i4 ,the various stages in making this are illustrated by f1 and g4 ,if the inner tube is made by drawing out from a larger piece of glass so that two supporting pieces are left on each side of the place where it is intended to make the final bend1 that bend can be made in a flat-flame gas burner without causing the inner tube to come in contact with the walls of the outer tube4 ,care must be taken when joining on the side piece that the inner tube is not heated enough to fuse it4 ,the small hole in the side of the outer tube is produced by heating and bursting4 ,a ,liebig's ,condenser4--,this consists of a straight glass tube passing through an outer cooling jacket4 ,in practice it is better to make the jacket as a separate piece1 and to effect a water-tight junction by means of two short rubber tubes4 ,it may1 however1 be made with two internal seals of the class described under ,a ,spray ,arrester4 ,there is much less risk of these seals cracking if the inner tube is made in the form of a spiral or has a number of bulbs blown on it in order to give a certain amount of elasticity4 ,a ,double-,surface ,condenser4--,fig4 #aj shows a condenser of this nature which is supplied by ,messrs4 ,baird and ,tatlock4 ,it may be built up in stages as shown by a1 b1 and c1 but the work involved requires considerable skill1 and the majority of laboratory workers will find it cheaper to buy than to make4 ,illustration3 ,fig4 #aj ,a ,spherical ,condenser4--,such a condenser as that shown by f1 ,fig #aj1 involves a method which may find application in a number of cases4 ,the outer bulb is blown from a thick piece of tubing which has been inserted in a smaller piece 7see d1 ,fig4 #f72 then the inner bulb by similar method4 ,it is now necessary to introduce the smaller bulb into the larger1 and for this purpose the larger bulb must be cut into halves4 ,a small but deep cut is made with the file or glass-blowers' knife in the middle of the larger bulb1 and at right angles to the axis of the tube on which it is blown4 ,a minute bead of intensely heated glass is now brought in contact with the cut in order to start a crack4 ,this crack may now be led round the bulb as described on page #cj4 ,if the work is carried out with care1 it is possible to obtain the bulb in two halves as shown by d1 and these two halves will correspond so exactly that when the cut edges are placed in contact they will be almost air-tight4 ,the two tubes from the smaller bulb should be cut to such a length that they will just rest inside the larger1 and the ends should be expanded4 ,place the inner bulb in position and fit the two halves of the outer bulb together1 taking great care not to chip the edges4 ,if the length of the tubes on the inner bulb has been adjusted properly1 the inner bulb will be supported in position by their contact with the tubes on the outer bulb4 ,now rotate the cracked portion of the outer bulb in front of a blowpipe flame and press the halves together very gently as the glass softens4 ,expand slightly by blowing if necessary4 ,if a small pin-hole develops at the joint it is sometimes possible to close this with a bead of hot glass2 but if the bulb has been cut properly there should be no pin-holes formed4 ,the condenser is finished by joining on the side tubes and sealing the inner tube through by the methods already given4 ,in order to blow bulbs large enough to make a useful condenser1 it will be convenient to employ the multiple-jet blowpipe described on page #d4 ,a ,soxhlet-,tube or ,extraction ,apparatus4--,this involves the construction of a re-entrant join where the syphon flows into the lower tube4 ,it is of considerable value as an exercise and the complete apparatus is easy to make4 ,a large tube is sealed at the bottom and the top is lipped1 as in making a test-tube4 ,a smaller tube is then joined on by a method similar to that given on page #ah1 but without making a perforation in the bottom of the large tube4 ,heating and expanding by air pressure1 first through the large tube1 then through the smaller tube and then again through the large tube1 will give a satisfactory finish to this part of the work4 ,illustration3 ,fig4 #aa ,the syphon tube is now joined on to the large tube as shown by a1 ,fig4 #aa1 care being taken to seal the other end of the syphon tube before joining4 ,the details of the final and re-entrant joint of the syphon tube are shown at the lower part of a4 ,this join is made by expanding the sealed end of the syphon tube into a small1 thick-walled bulb1 and the bottom of this bulb is burst out by local heating and blowing2 the fragments of glass are removed and the edges made smooth by melting4 ,a similar operation is carried out on the side of the tube to which the syphon tube is to be joined4 ,this stage is shown by a4 ,now heat the syphon tube at the upper bend until it is flexible1 and press the bulb at its end into the opening on the side of the other tube4 ,hold the glass thus until the syphon is no longer flexible4 ,the final join is made by heating the two contacting surfaces1 if necessary pressing the edges in contact with the end of a turn-pin1 fusing together and expanding4 ,the finished apparatus is shown by c4 ,electrodes4--,a thin platinum wire may be sealed into a capillary tube without any special precautions being necessary4 ,the capillary tube may be drawn out from the side of a larger tube by heating a spot on the glass1 touching with a glass rod and drawing the rod away2 or the exhaustion branch described on page #ah may be used for the introduction of an electrode4 ,it is convenient sometimes to carry out the exhaustion through the same tube that will afterwards serve for the electrode4 ,the electrode wire is laid inside the branch before connecting to the exhaustion pump4 ,when exhaustion is completed the tube is heated until the soft glass flows round the platinum and makes the seal air-tight4 ,the branch is now cut off close to the seal on the pump side1 a loop is made in the projecting end of the platinum wire1 and the seal is finished by melting the cut-off end4 ,platinum is usually employed for such work1 but if care is taken to avoid oxidation it is not impossible to make fairly satisfactory seals with clean iron or nickel wire4 ,hard rods of fine graphite1 such as are used in some pencils1 may also be sealed into glass1 but it seems probable that air would diffuse through the graphite in the course of time4 ,another method for the introduction of an electrode is illustrated by d1 e1 f and g1 ,fig4 #aa4 ,in this case the bulb or thin-walled tube into which the electrode is to be sealed is perforated by a quick stab with an intensely heated wire--preferably of platinum--which is then withdrawn before the glass has had time to harden1 and thus a minute circular hole is made4 ,the electrode is coated with a layer of similar glass1 or of the specially made enamel which is sold for this purpose1 inserted into the bulb or tube by any convenient opening1 and adjusted by careful shaking until the platinum wire projects through the small hole4 ,the bulb or tube is then fused to the coating of the electrode and the whole spot expanded slightly by blowing4 ,the appearance of the finished seal is shown by g4 ,it is well to anneal slightly by smoking4 ,thermometers4--,apart from the notes on page #bj with respect to the blowing of a suitable bulb on capillary tubing there is little to say in connection with the glass working needed in making a plain thermometer4 ,the size desirable for the bulb will be determined by the bore of the capillary tube1 the coefficient of expansion of the liquid used for filling1 and the range of temperature for which the thermometer is intended4 ,filling may be carried out as follows3--,fit a small funnel to the open end of the capillary by means of a rubber tube1 and pour into the funnel rather more than enough of the liquid to be used than is required to fill the bulb4 ,mercury or alcohol will be used in practice1 most probably4 ,warm the bulb until a few air bubbles have escaped through the liquid and then allow to cool4 ,this will suck a certain amount of liquid into the bulb4 ,now heat the bulb again1 and at the same time heat the capillary tube over a second burner4 ,the liquid will boil and sweep out the residual air1 but it is necessary to heat the capillary tube as well in order to prevent condensation4 ,allow the bulb and tube to cool1 then repeat the heating once more4 ,by this time the bulb and tube should be free from air1 and cooling should give a completely filled thermometer4 ,remove the funnel and heat the thermometer to a few degrees above the maximum temperature for which it is to be used2 the mercury or other filling liquid will overflow from the top1 and1 as the temperature falls1 will recede1 thus allowing the end of the capillary to be drawn out4 ,reheat again until the liquid rises to the top of the tube1 then seal by means of the blowpipe flame4 ,the thermometer is now finished except for graduation2 this is dealt with on page #ge4 ,an ,alarm ,thermometer4--,a thermometer which will complete an electric circuit when a certain temperature is reached may be made by sealing an electrode in the bulb and introducing a wire into the top1 which in this case is not sealed4 ,naturally1 this thermometer will be filled with mercury4 ,there is considerable difficulty in filling such a bulb without causing it to crack4 ,several elaborations of this form are made1 in which electrodes are sealed through the walls of the capillary tube1 thus making it possible to detect electrically the variation of temperature when it exceeds any given limits4 ,an ,enclosed or ,floating ,thermometer4--,the construction of this type of thermometer is shown by h and i1 ,fig #aa4 ,it is made in the following stages3--,a bulb is blown on the drawn-out end of a thin-walled tube as shown by h4 ,a small bulb is blown on the end of a capillary tube1 burst1 and turned out to form a lip which will rest in the drawn-out part of the thin-walled tube but is just too large to enter the bulb4 ,the capillary tube is introduced and sealed in position1 care being taken to expand the joint a little4 ,the thermometer is filled and the top of the capillary tube closed by the use of a small blowpipe flame4 ,a paper scale having the necessary graduations is inserted1 and the top of the outer tube is closed as shown by i4 ,a ,maximum and ,minimum ,thermometer4--,if a small dumb-bell-shaped rod of glass or metal is introduced into the capillary tube of a horizontally placed1 mercury-filled thermometer in such a position that the rising mercury column will come in contact with it1 the rod will be pushed forward4 ,when the mercury falls again the rod will be left behind and thus indicate the maximum temperature attained4 ,if a similar dumb-bell-shaped rod is introduced into an alcohol-filled thermometer and pushed down until it is within the alcohol column1 it will be drawn down by surface tension as the column falls2 but the rising column will flow passed it without causing any displacement2 thus the minimum temperature will be recorded4 ,six's combined maximum and minimum thermometer is shown by b1 ,fig4 #aa4 ,in this case both maximum and minimum records are obtained from a mercury column1 although the thermometer bulb is filled with alcohol4 ,it is an advantage to make the dumb-bell-shaped rods of iron1 as the thermometer can then be reset by the use of a small magnet1 another advantage consequent on the use of metal being that the rods can be easily adjusted1 by slight bending1 so as to remain stationary in the tubes when the thermometer is hanging vertically1 and yet to move with sufficient freedom to yield to the pressure of the recording column4 ,the thermometer may be filled by the following method3--,when the straight tube has been made the first dumb-bell is introduced and shaken down well towards the lower bulb1 the tube is now bent to its final shape and the whole thermometer filled with alcohol as described on page #dd4 ,now heat the thermometer to a little above the maximum temperature that it is intended to record1 and pour clean mercury into the open bulb while holding the thermometer vertically4 ,allow to cool1 and the mercury will be sucked down4 ,the second dumb-bell is now introduced1 sufficient alcohol being allowed to remain in the open bulb to about half fill it1 and the alcohol in this bulb is boiled to expel air4 ,the tube through which the bulb was filled in now sealed4 ,clinical ,thermometers4--,the clinical thermometer is a maximum thermometer of a different type4 ,in this case there is a constriction of the bore at a point just above the bulb4 ,when the mercury in the bulb commences to contract1 the mercury column breaks at the constriction and remains stationary in the tube1 thus showing the maximum temperature to which it has risen4 ,vacuum ,tubes4--,there are so many forms of these that it is scarcely practicable or desirable to give detailed instructions for making them2 but an application of the various methods of glass-working which have already been explained should enable the student to construct most of the simpler varieties4 ,an interesting vacuum tube is made which has no electrodes1 but contains a quantity of mercury4 ,when the tube is rocked so as to cause friction between the mercury and the glass sufficient charge is produced to cause the tube to glow4 ,a ,sprengel ,pump4--,this1 in its simplest form1 is illustrated by a1 ,fig4 #ab4 ,such a form1 although highly satisfactory in action1 needs constant watching while in action1 as should the mercury funnel become empty air will enter the exhausted vessel4 ,obviously1 the fall-tube must be made not less than thirty inches long2 the measurement being taken from the junction of the exhaustion branch with the fall-tube to the top of the turned-up end4 ,illustration3 ,fig4 #ab ,a ,macleod ,pump4--,one form of this is illustrated by b1 ,fig4 #ab4 ,it has the advantage that the mercury reservoir may be allowed to become empty without affecting the vacuum in the vessel being exhausted4 ,spinning ,glass4--,by the use of suitable appliances1 it is quite possible to draw out a continuous thread of glass1 which is so thin as to have almost the flexibility and apparent softness of woollen fibre2 a mass of such threads constitutes the glass wool of commerce4 ,the appliances necessary are3--a blowpipe capable of giving a well-formed flame of about six or eight inches in length1 a wheel of from eighteen inches to three feet in diameter and having a flat rim of about three inches wide1 and a device for rotating the wheel at a speed of about three hundred revolutions per minute4 ,a very satisfactory arrangement may be made from an old bicycle2 the back wheel having the tyre removed and a flat rim of tin fastened on in its place4 ,the chain drive should be retained1 but one of the cranks removed and a handle substituted for the remaining pedal4 ,the whole device is shown by ,fig4 #ac4 ,illustration3 ,fig4 #ac ,the procedure in spinning glass is as follows3--,first melt the end of a glass rod and obtain a large mass of thoroughly softened glass1 now spin the wheel at such a speed that its own momentum will keep it spinning for several seconds4 ,touch the end of the melted rod with another piece of glass and1 without withdrawing the original rod from the blowpipe flame1 draw out a thread of molten glass and twist it round the spinning wheel4 ,if this is done properly1 the thread of glass will grip on the flat rim1 and by continuing to turn the wheel by hand it is possible to draw out a continuous thread from the melted rod1 which must be advanced in the blowpipe flame as it is drawn on the wheel4 ,if the rod is not advanced sufficiently the thread will melt off1 if it is advanced too much1 so as to heat the thick part and allow the glass to become too cool at the point of drawing out1 then the thread will become too thick1 but it is easy after a little practice to obtain the right conditions4 ,practice is necessary also in order to find the right speed for the wheel4 ,when sufficient glass has been spun1 the whole hank of thin thread may be removed by drawing the thumb-nail across the wheel at any point on its flat rim1 thus breaking the threads1 and allowing the hank to open4 ,brushes for ,use with ,strong ,acids4--,glass wool1 if of fine enough texture to be highly flexible1 can be used to make acid-resisting brushes4 ,a convenient method for mounting the spun glass is to melt the ends of the threads together into a bead1 and then to fuse the bead on to a rod2 thus giving a brush4 ,if a pointed brush is necessary1 the point may be ground on an ordinary grindstone or carborundum wheel by pressing the loose end of the spun glass against the grinding wheel with a thin piece of cardboard4 ,when using brushes of this description1 it is well to bear in mind the fact that there is always a liability of a few threads of glass breaking off during use4 ,,chapter ,,iv ,glass1 ,its ,composition and ,characteristics4 ,annealing4 ,drilling1 ,grinding1 and ,shaping ,glass by methods other than ,fusion4 ,stopcocks4 ,marking ,glass4 ,calibration and ,graduation of ,apparatus4 ,thermometers4 ,exhaustion of ,apparatus4 ,joining ,glass and ,metal4 ,silvering ,glass4 ,there are three kinds of glass rod and tubing which are easily obtainable2 these are soda-glass1 which is that usually supplied by chemical apparatus dealers when no particular glass is specified2 combustion-glass1 which is supplied for work requiring a glass that does not so easily soften or fuse as soda-glass2 and lead-glass1 which is less common4 ,there are also resistance-glass1 made for use where very slight solubility in water or other solutions is desirable1 and a number of other special glasses2 but of these soda-glass1 combustion-glass1 lead-glass1 and resistance-glass are the most important to the glass-blower whose work is connected with laboratory needs4 ,soda-,glass4--,consists chiefly of sodium silicate1 but contains smaller quantities of aluminum silicate1 and often of calcium silicate2 there may also be traces of several other compounds4 ,the ordinary soda-glass tubing melts easily in the blowpipe flame1 it has not a long intermediate or viscous stage during fusion1 but becomes highly fluid rather suddenly2 it does not blacken in the reducing flame4 ,bad soda-glass or that which has been kept for many years1 tends to devitrify when worked4 ,that is to say the glass becomes more or less crystalline and infusible while it is in the flame2 and in this case it is often impossible to do good work with that particular sample of glass2 although the devitrification may sometimes be remedied by heating the devitrified glass to a higher temperature4 ,the presence of aluminum compounds appears to have some influence on the tendency of the glass to resist devitrification4 ,soda-glass1 as a rule1 is more liable to crack by sudden heating than lead-glass1 and articles made from soda-glass often tend to crack spontaneously if badly made or1 in the case of heavier and thicker articles1 if insufficiently annealed4 ,combustion-,glass4--,is usually a glass containing more calcium silicate and potassium silicate than the ordinary soft soda-glass4 ,it is much less fusible than ordinary soda-glass1 and passes through a longer intermediate or viscous stage when heated4 ,such a glass is not very suitable for use with the blowpipe owing to the difficulty experienced in obtaining a sufficiently high temperature4 ,if1 however1 a certain amount of oxygen is mixed with the air used in producing the blowpipe flame this difficulty is minimised4 ,resistance-,glass4--,may contain zinc1 magnesium1 and other substances4 ,as a rule it is harder than ordinary soda-glass1 and less suitable for working in the blowpipe flame4 ,it should have very little tendency to dissolve in water1 and hence is used when traces of alkali or silicates would prove injurious in the solutions for which the glass vessels are to be used4 ,lead-,glass4--,this1 or flint glass as it is often called from the fact that silica in the form of crushed and calcined flint was often used in making the ,english lead-glasses1 contains a considerable proportion of lead silicate4 ,such a glass has1 usually1 a particularly bright appearance1 a high refractive index1 and is specially suitable for the production of the heavy cut-glass ware4 ,lead-glass tubing is easy to work in the blowpipe flame1 melts easily1 but does not become fluid quite so suddenly as most soda-glasses2 articles made from it are remarkably stable and free from tendency to spontaneous cracking1 although1 as is essential for all the heavy or glass-house work1 the massive articles need annealing in the oven4 ,the two chief disadvantages of lead-glass for laboratory work are that it is blackened by the reducing gases if held too near to the blue cone of the blowpipe flame1 and that it is rather easily attacked by chemical reagents2 thus ammonium sulphide will cause blackening4 ,the effect of the reducing flame on lead is not altogether a disadvantage1 however2 because a little care in adjusting the blowpipe and a little care in holding the glass in the right position will enable the student to work lead-glass without producing the faintest trace of blackening4 ,this1 in addition to being a valuable exercise in manipulation1 will teach him to keep his blowpipe in good order1 and prove a useful aid in his early efforts to judge as to the condition of the flame4 ,it prevents discouragement if the student does his preliminary work with the soda-glass1 but he should certainly make experiments with lead-glass as soon as he has acquired reasonable dexterity with soda-glass4 ,annealing4--,annealing is a process by which any condition of strain which has been set up in a glass article1 either by rapid cooling of one part while another part still remains hot1 or by the application of mechanical stress after cooling is relieved4 ,annealing is carried out by subjecting the article to a temperature just below the softening point of the glass1 maintaining that temperature until the whole article has become heated through the thicker part1 and then reducing the temperature very gradually2 thus avoiding any marked cooling of the thinner and outer parts first4 ,for thin glass apparatus of the lamp-blown or blowpipe-made variety in which there are no marked difference of thickness1 such as joins on tubes1 ordinary seals1 bulbs1 etc41 there is little need for annealing2 and even those having rather marked changes of thickness1 such as filter pumps1 can be annealed sufficiently by taking care that the last step in making is heating to just below visible redness in the blowpipe flame and then rotating in a sooty gas flame until covered with a deposit of carbon4 ,the article should then be allowed to cool in a place free from draughts and where the hot glass will not come in contact with anything4 ,a few of the blowpipe-made articles1 such1 for example1 as glass stopcocks1 need more careful annealing1 and for this purpose a small sheet-iron oven which can be heated to dull redness over a collection of gas burners will serve4 ,better still1 a small clay muffle can be used4 ,in either case1 the article to be annealed should be laid on a clean1 smooth1 fireclay surface1 the temperature should be maintained at a very dull red for two or three hours and then reduced steadily until the oven is cold4 ,this cooling should take anything from three to twelve hours1 according to the nature of the article to be annealed4 ,a thick article1 or one having great irregularities in thickness will need much longer annealing than one thinner or more regular4 ,as a rule1 soda-glass will need more annealing than lead-glass4 ,drilling ,glass4--,small holes may be drilled in glass by means of a rod of hard steel which has been broken off1 thus giving a more or less irregular and crystalline end4 ,there are several conditions necessary to enable the drilling of small holes to be carried out successfully3--the first of these is that the drill should be driven at a high speed4 ,this may be done by means of a geared hand-drill such as the ,american pattern drill1 although a somewhat higher speed than this will give is even more satisfactory4 ,the second condition is that the pressure on the drill is neither too light nor too heavy2 this is conveniently regulated by hand4 ,the third condition is that the drill be prevented from straying over the surface of the glass2 for this purpose a small metal guide is useful4 ,the fourth condition is that a suitable lubricant be used2 a strong solution of camphor in oil of turpentine is perhaps the most suitable4 ,for commercial work1 a diamond drill is often used1 but this is scarcely necessary for the occasional work of a laboratory4 ,larger ,holes in ,glass4--,the method of drilling with a hard steel rod is not highly satisfactory for anything but small holes4 ,when a larger hole1 say one of an eighth of an inch or more1 is needed it is better to use a copper or brass tube4 ,this tube may be held in an ,american hand-drill1 but a mixture of carborundum or emery and water is supplied to the rotating end4 ,tube or drill must be lifted at frequent intervals in order to allow a fresh supply of the grinding material to reach the end4 ,in this case1 also1 a guide is quite essential in the early stages of drilling2 otherwise the end of the tube will stray4 ,the speed of cutting may be increased slightly by making a number of radial slots in the end of the tube2 these serve to hold a supply of the grinding material4 ,grinding ,lenses4--,this is scarcely within the scope of a book on glass-blowing for laboratory purposes1 but it may be said that the lens may be ground by means of a permutating mould of hard lead or type-metal4 ,the rough shaping is done with coarse carborundum or emery1 and successive stages are carried on with finer and finer material4 ,the last polishing is by the use of jewellers' rouge on the mould1 now lined with a fine textile4 ,filing ,glass4--,if a new file1 thoroughly lubricated with a solution of camphor in oil of turpentine1 is used1 there is but little difficulty in filing the softer glasses4 ,a slow movement of the file1 without excessive pressure but without allowing the file to slip1 is desirable4 ,after a time the cutting edges of the file teeth will wear down and it will be necessary to replace the file by another4 ,grinding ,stoppers4--,this is1 perhaps1 the most common form of grinding that the laboratory worker will need to perform1 and for that reason1 rather full details of the procedure are desirable4 ,a very crude form of ground-in stopper may be made by drawing out the neck and the mass of glass which is intended to form the stopper to approximately corresponding angles1 wetting the surfaces with a mixture of the abrasive material and water1 and grinding the stopper in by hand4 ,frequent lifting of the stopper is necessary during grinding1 in order to allow fresh supplies of abrasive material to reach the contacts4 ,when an approximate fit is obtained1 the coarse abrasive should be washed off1 care being taken that the washing is complete1 and a finer abrasive substituted4 ,after a while1 this is replaced in its turn by a still finer grinding material4 ,such a method of grinding may give a satisfactory stoppering if the angles of the plug and socket correspond very closely before grinding is commenced2 but if there is a wide difference in the original angles1 then no amount of grinding by this method will produce a good result4 ,the reason for this is that the plug will become so worn in the preliminary grinding as to assume the form of a highly truncated cone2 the socket will assume a reverse form1 and the end result will be a loose-fitting plug and socket4 ,satisfactory grinding may be carried out by the use of copper or type-metal cones for the preliminary shaping4 ,such cones should be mounted on a mandrel which will fit into the chuck of the ,american hand-drill and turned on the lathe to the desirable angle for stoppering4 ,a number of these cones will be necessary4 ,a number of similar moulds1 that is to say blocks of type-metal or hard lead in which is a hole corresponding in size and angle to the plug desired1 should be made also4 ,these must be rotated1 either in the lathe or by other means1 and are used for the preliminary shaping of the plug4 ,if but few plugs are to be ground it is unnecessary to provide a means of rotating the moulds1 as the plug may be held in the hand and ground into the mould in a manner similar to that used in the first method of stoppering4 ,illustration3 ,fig4 #ad ,when the socket and plug have been ground1 by the successive use of cones and moulds1 to the desired angle1 so that they correspond almost exactly1 the plug is given its final fitting into the socket by grinding-in with a fine abrasive1 in the manner first described4 ,stopcocks4--,although it would be more strictly in keeping with the form of this book to divide the making of stopcocks into two parts2 shaping by heat and grinding1 we will consider the whole operation here1 and take for our example a simple stopcock such as that illustrated by ,fig4 #ad4 ,the blank1 f1 that is the socket before grinding1 is made by drawing out a piece of fairly thick-walled tubing into the form shown by a4 ,two zones on this tube are then heated by means of a small1 pointed flame1 and the tube is compressed along its axis1 thus producing two raised rings as shown by b4 ,two zones1 slightly towards the outer sides of these two raised rings are heated and the tube is drawn while air pressure is maintained within4 ,this produces two thin-walled bulbs or extensions similar to those shown by c4 ,one of these extensions is now broken off by means of a sharp blow with the edge of a file or other piece of metal1 and the edges of the broken glass are rounded in the flame4 ,the other extension is left to serve as a handle4 ,we have now a piece of glass like that shown by d4 ,now heat a spot on the side of this1 medially between the raised rings1 until the glass is on the point of becoming deformed1 and bring the intensely heated end of a smaller tube in contact with the heated spot4 ,without disturbing the relative positions of the two tubes1 press the smaller tube down on a thin steel wire1 so that the wire passes along the tube and enters the soft glass2 thus forming a projection inside the sockets as shown by e4 ,the wire must be withdrawn1 again immediately4 ,when the wire has been withdrawn1 heat the place where it entered to dull redness1 in order to relieve any strain2 break off the thin extension1 which up to the present has served as a handle1 round off the broken edges in the flame1 and join on and indent a similar piece of small tubing to the opposite side of the socket2 the socket at this stage being shown by f4 ,the blank for the socket is now completed1 but it must be heated to dull redness in order to relieve strain and be placed in an annealing oven1 where it should be annealed for some hours4 ,the blank for the plug offers no special difficulty2 it is made by heating a glass rod and compressing it axially until a mass having the form shown by g1 ,fig4 #ad1 is produced2 the end of this is heated intensely and brought in contact with the rather less heated side of a glass tube which has been drawn to the shape desired for the handle2 when contact is made a slight air pressure is maintained in the glass tube1 thus producing a hollow join4 ,the ends of the tube are sealed and the bottom of the plug is drawn off1 thus giving the finished blank as shown by h4 ,this blank is now held in a pair of asbestos-covered tongs1 heated to dull redness all over1 and transferred to the annealing oven4 ,when cold1 the socket is ground out by the second method given under ,grinding ,stoppers2 that is to say1 by means of type-metal or copper cone1 and the plug is ground to fit in a corresponding mould4 ,when the fit is almost perfect1 the transverse hole is drilled in the plug1 and the final finishing is made with fine abrasive powder4 ,great care must be taken in the final grinding that there is no accumulation of abrasive material in the transverse hole of the plug2 if this is allowed to occur there will be a ring ground out of the socket where the holes move1 and the tightness of the finished stopcock will be lost4 ,marking ,glass4--,as a preliminary to a consideration of the methods of graduating and calibrating glass apparatus1 it is convenient to consider the various methods which are available for marking glass4 ,among these are1 the writing diamond1 the carborundum or abrasive pencil1 the cutting-wheel1 and etching by means of hydrofluoric acid4 ,each produces a different class of marking and each is worthy of independent consideration4 ,the ,writing ,diamond4--,this is the name given to a small irregular fragment of bort which is usually mounted in a thin brass rod4 ,such a diamond1 if properly selected1 has none of the characteristics of a cutting diamond2 although one occasionally finds so-called writing diamonds which will produce a definite cut4 ,these should be rejected4 ,the writing diamond is used in much the same way as a pencil1 but is held more perpendicularly to the object1 and a certain amount of pressure is necessary4 ,the mark produced is a thin scratch which1 although fairly definite1 lacks breadth1 and this is a disadvantage where the marking has to be read at a distance4 ,this disadvantage may to some extent be overcome by making a number of parallel scratches4 ,the ,abrasive ,pencil4--,a rod of carborundum composition may be ground or filed to a point1 and this forms a very useful pencil for general work4 ,the marking produced is rather less definite than that produced by a writing diamond1 but has the advantage of being broader4 ,the ,cutting ,wheel4--,cutting in this case is scarcely the ideal expression1 it should rather be grinding1 but cutting is more commonly used4 ,exceedingly good graduations may be made by the edge of a small1 thin1 abrasive wheel which is mounted on the end of a small mandrel and driven by a flexible shaft from an electric motor or any other convenient source of power4 ,the depth of the mark can be controlled1 and very light pressure will suffice4 ,etching4--,this is often the quickest and easiest way of marking glass apparatus4 ,the object to be marked should first be warmed and coated very thoroughly with a thin film of paraffin wax4 ,when cold1 the marking is made through the paraffin wax by means of a needle point1 and the object is then exposed to the action of hydrofluoric acid4 ,if a shallow but clearly visible marking is desired1 it is well to use the vapour of the acid2 this may be done by bending up a sheet-lead trough on which the object can rest with the marked surface downwards4 ,a little of the commercial hydrofluoric acid1 or a mixture of a fluoride and sulphuric acid1 is distributed over the bottom of the trough1 and the whole arrangement is allowed to stand for about an hour4 ,the object is washed thoroughly and the paraffin wax removed1 either by melting and wiping off or by the use of a solvent1 and the marking is finished4 ,if a deep marking is desired1 in order that it may afterwards be filled with some pigment1 a better result is obtained by the use of liquid commercial hydrofluoric acid1 which is a solution of hydrogen fluoride in water4 ,the acid is mopped on to the object after the markings have been made on the paraffin wax film1 and allowed to remain in contact for a few minutes4 ,it is advantageous to repeat the mopping-on process at intervals during the etching4 ,in all cases where hydrofluoric acid is used1 or stored1 it is of great importance to keep it well away from any optical instruments1 as the most minute trace of vapour in the air will produce a highly destructive corrosion of any glass surfaces4 ,methods of ,calibration4--,in the case of apparatus for volumetric work1 this is usually carried out by weighing1 although some of the smaller subdivisions are often made by measurement4 ,when the subdivisions are made in this way it is of importance to see that the walls of the tube or vessel to be calibrated are parallel4 ,great errors arise in some of the commercial apparatus from neglect of this precaution4 ,a convenient method of testing for parallelism1 in the case of a wide tube1 is to close one end and to weigh in successive quantities of mercury4 ,an observation of the length occupied by each successive quantity will indicate any change in the bore4 ,in the case of capillary tubes1 it is convenient to introduce an unweighed quantity of mercury1 measure its length accurately1 and then to move it along the tube in stages1 either by tilting the tube or by the application of air pressure4 ,a measurement of the length at each stage will indicate whether the bore is approximately parallel or not4 ,neither of these methods is to be relied on without a careful examination of the tube1 as it may happen that there are local irregularities in the bore which compensate for each other1 and do not1 therefore1 affect the volume of a given length4 ,obviously1 the smaller the quantity of mercury with which the test is carried out and the greater the number of observations made1 the less risk will there be of such an error4 ,a liquid1 such as water or alcohol1 which wets the glass is not suitable for such a test1 unless special precautions are taken4 ,when1 however1 a pipette or burette has to be calibrated to deliver a certain volume of water1 the final calibration must be made with this liquid4 ,thus1 the burette would first be calibrated by weighing in definite quantities of mercury of say #ac4ed grammes 7#a cc at #ae;,c471 each of the #a cc divisions should be marked by some temporary marking4 ,the burette is now filled with a solution of potassium bichromate and sulphuric acid and allowed to soak for some time2 the bichromate is washed out and distilled water is put in4 ,successive quantities of water are run out of the jet1 a fixed time being allowed for draining1 and the weights of the quantities delivered are noted4 ,this procedure will give the necessary data for altering the marking so that it may correspond to #a cc delivered4 ,each #a cc division is now divided into tenths by the method described below4 ,a final verification of the markings should be made when the subdivision is completed4 ,subdivision of ,graduations4--,mark out the spaces to be subdivided on a sheet of paper4 ,take a reliable ruler on which any convenient length is divided into the desired number and place it across the lines at such an angle that the limits noted on the rule exactly bridge the gap4 ,now draw parallel lines through the markings4 ,copying a ,scale4--,when a scale has been prepared on paper and it is necessary to copy that scale on the waxed-glass surface for etching1 a convenient method is to employ a long wooden bar having a sharp needle passing through it at either end4 ,the scale and object to be marked are fastened in line with one another1 and the caliper bar is used from step to step4 ,the mark is made by moving the bar through a minute portion of a circle1 which provided that the bar is two or three feet in length1 will not introduce any perceptible error in a scale of say a quarter of an inch in width4 ,the arrangement is shown by ,fig4 #ae4 ,illustration3 ,fig4 #ae ,graduating a ,thermometer4--,assuming that the thermometer has been made of carefully selected tubing in which the bore is parallel and free from any small irregularities1 we have only to fix the freezing point and boiling point4 ,the intervening space may then be divided into #ajj 7if the thermometer is to be ,centigrade7 or #ahj 7if ,fahrenheit74 ,this division may be carried out by the method given under ,subdivisions of ,graduations4 ,a thermometer should not be calibrated until some weeks after making1 as the glass bulb tends to contract4 ,joining ,glass and ,metal4--,it sometimes happens that one needs to make a more permanent and less flexible joint between a glass and metal tube than can be obtained by means of a rubber tube4 ,to this end1 any one of three slightly different methods may be employed4 ,in the method of ,chatelier one first coats the glass with platinum or silver1 which may be done by moistening the glass with platinum chloride or silver nitrate and then heating to redness2 a layer of copper is then deposited electrolytically on the treated surface of the glass1 and soldering is carried out in the usual manner4 ,mc,kelvy and ,taylor call attention to two other methods in the ,journal of the ,chemical ,society for ,september1 #aibj4 ,in one of these methods the glass is coated with platinum by covering it with a suspension of platinum chloride in oil of lavender and heating until the oil is burnt off4 ,the metal tube is then tinned on its inner side and soldered to the prepared glass1 slightly acid zinc chloride being used as a flux4 ,in the second method1 a joint is made by means of the ,kraus flux1 which consists of equal weights of zinc oxide1 borax1 and powdered soda-glass fused together4 ,this is coated on the inner surface of the metal tube1 and the hot glass tube1 which has had the end slightly flanged to give support1 is inserted4 ,fusion of the flux is completed by heating the outside of metal tube4 ,silvering ,glass4--,in all cases where it is intended to deposit a silver mirror on a glass surface1 thorough cleaning is essential4 ,prolonged soaking in a hot solution of potassium bichromate which has been acidified with sulphuric acid will often prove useful4 ,the glass should then be washed thoroughly1 rinsed in distilled water1 and the solution should then be used4 ,there are many formul for the silvering solution1 but that used in ,martin's method may be given3-- ,a--,nitrate of ,silver #dj grammes ,distilled ,water #ajjj c4 cm4 ,b--,nitrate of ,ammonium #fj grammes ,distilled ,water #ajjj c4 cm4 ,c--,pure ,caustic ,potash #ajj grammes ,distilled ,water #ajjj c4 cm4 ,d--,pure ,sugar ,candy #ajj grammes ,distilled ,water #ajjj c4 cm4 ,dissolve and add3-- ,tartaric ,acid #bc grammes ,boil for ten minutes1 and when cool add3-- ,alcohol #bjj c4 cm4 ,distilled ,water to #bjjj c4 cm4 ,for use take equal parts of ,a and ,b4 ,mix together also equal parts of ,c and ,d in another vessel4 ,then mix both liquids together in the silvering vessel and suspend the glass to be silvered face downwards in the solution4 ,or if a vessel has to be silvered on the inside1 the solution is poured in4 ,in this case1 the deposition of silver may be hastened by immersing the vessel to be silvered in warm water4 ,in working with a silver solution containing ammonia or ammonium salts there is sometimes the possibility of forming an explosive silver compound4 ,it is well1 therefore1 to avoid keeping such solutions longer than is necessary1 and to bear in mind that any deposit formed by solutions containing both silver and ammonia may have explosive properties1 especially when dry4 ,,chapter ,v ,extemporised ,glass-,blowing ,apparatus--,the ,use of ,oil or other ,fuels--,making ,small ,rods and ,tubes from ,glass ,scrap--,the ,examination of ,manufactured ,apparatus with the ,view to ,discovering the ,methods ,used in ,manufacture--,summary of ,conditions ,necessary for ,successful ,glass-,blowing4 ,if1 in the early stages of his study of glass-blowing1 the student should attempt to work with the very simplest appliances1 it is probable that his progress will be hindered2 the use of the apparatus will require an undue amount of care and his attention will be distracted from the actual manipulation of the glass4 ,the case is widely different after he has acquired a certain facility in glass-blowing4 ,a ,simple ,form of ,blowpipe4--,although there are even more simple forms than that described here1 we are not concerned with them4 ,the form described is the simplest with which any considerable amount of glass-blowing can be carried out with certainty4 ,this form consists of a tube through which air may be blown with the mouth1 a condensation chamber in which any moisture from the breath can condense1 a blowpipe jet1 a supporting piece and a source of flame4 ,the tube1 condensation chamber1 and jet are combined in the ordinary ,black's blowpipe1 such as is used for blowpipe tests in qualitative analysis2 it consists of a conical tin tube having a mouthpiece at the small end and a side tube which carries a brass jet4 ,a support for such a blowpipe may be cut out of a piece of brass or tin-plate1 and should be fastened to a small1 flat1 wooden board4 ,a source of flame may consist of an ordinary brass elbow1 such as is used on gas fittings1 and into which a piece of thin brass tube 7the body of a fish-tail burner from which the perforated non-metallic plug has been removed will serve quite well7 has been fitted4 ,it is an advantage to flatten the brass tube somewhat and to file the flattened end to a slope which corresponds with the angle at which the blowpipe jet enters the burner4 ,the whole source of the flame should be mounted on a separate base1 in order that it may be moved while adjusting the apparatus to the best relative positions of flame and blowpipe jet4 ,the complete apparatus is shown by a1 ,fig4 #af4 ,illustration3 ,fig4 #af ,in order to take full advantage of this blowpipe1 it is desirable that the student should learn to maintain a steady steam of air with his mouth and1 at the same time1 be able to breathe4 ,this requires a little practice4 ,as a first exercise in breathing1 before trying to breathe while using the mouth blowpipe1 the student should close his mouth and inflate his cheeks with air2 now1 still keeping his cheeks tightly inflated1 he should attempt to breathe through the nose4 ,at first1 this may be found rather difficult1 but it becomes remarkably easy after a little practice4 ,when he has mastered this1 the student may practise the same operation1 but with the blowpipe4 ,it is important to bear in mind that the cheeks1 not the lungs1 form the reservoir for air used in maintaining the blowpipe flame4 ,after a while1 the student will find that he can maintain a steady air pressure and yet breathe with complete comfort4 ,in adjusting the flame1 care should be taken not to blow so hard as to produce a ragged and noisy cone of fire4 ,a small jet1 such as that commonly used on a mouth blowpipe1 will with care give a pointed and quiet flame1 having an appearance similar to that shown in the illustration4 ,with a blowpipe like this1 it is quite easy to seal glass tubes up to an inch in diameter1 to join tubes up to half an inch in diameter1 to bend tubes1 to blow small bulbs1 and to make the simpler forms of internal seal2 but the provision for condensation of moisture is not ideal1 and prolonged use of such a blowpipe also tends to produce undue fatigue4 ,a ,mouth ,blowpipe ,with an ,expanding ,reservoir4--,this form of blowpipe can be made to give most excellent results2 it is highly portable1 and does not produce nearly so much fatigue when used continuously as the blowpipe described in the last section4 ,various slight modifications have been made in its construction during the last eighty years1 but that described below will be found quite satisfactory4 ,the apparatus consists of a tube through which air is blown from the mouth1 a valve through which the air passes into an expanding reservoir1 and a blowpipe jet in communication with the reservoir4 ,in making the valve1 several essentials have to be remembered2 it must allow a free passage of air into the reservoir1 it must open easily1 and must close quickly4 ,a satisfactory form of valve is that shown by b1 ,fig4 #af4 ,the moving part consists of a light glass bulb of about three-eights of an inch diameter and having a glass stem of rather under one-eighth diameter and about an inch and a half long4 ,this stem rests in a guide at the end of a brass tube1 the bulb contacting against the other end which is approximately shaped4 ,the bulb and its seating are ground air-tight4 ,a very light spring holds the bulb in position4 ,this valve is fitted into a metal or glass ,t piece1 one limb of which leads to the air reservoir and the other limb leads to the blowpipe jet2 the limb containing the valve leads to the tube through which the air is blown in4 ,a convenient reservoir may be made from a fairly large football bladder4 ,a network of string should be fitted over the outside of the bladder and the strings should terminate in a hook on which a weight can be hung1 in order to provide a means of adjusting the pressure at which the air is delivered to the jet4 ,this bladder should be washed out and allowed to drain after use4 ,the air tube which passes from the valve to the mouth may conveniently be made of brass1 but1 in order to avoid the continued contact of metal with the lips of the operator1 it should be fitted with a non-metallic mouthpiece4 ,it is an advantage from the point of view of portability to have the air tube easily detachable from the ,t piece containing the valve4 ,the blowpipe jets1 of which there may be several with advantage1 may be made of glass tubing1 bent to the most convenient angle and having an enlargement or bulb at some point in the tube4 ,this bulb serves as a final condensing place for any traces of moisture that may escape from the larger reservoir4 ,the whole device1 blowing tube1 reservoir1 and ,t piece may be fastened to a clamp1 so that it can be secured on the edge of any table where blowpipe work is to be carried out4 ,if the blowpipe is to be used with gas1 the form of burner described under4 ,a ,simple ,form of ,blowpipe will be found quite satisfactory4 ,the ,use of ,oil1 or ,other ,non-,gaseous ,fuels4--,although gas1 when available1 is usually preferred on account of its convenience1 there are several other fuels which give a hotter flame4 ,they have1 also1 the additional advantage of not requiring any connecting pipes2 but each has its own disadvantage4 ,one liquid fuel deserves special mention as being rather less desirable than the others2 this is alcohol4 ,although very convenient in use1 it has the disadvantage of being rather too highly inflammable and capable of burning without a wick1 thus involving a certain fire risk2 the flame is scarcely visible in a bright light1 and the heat given by either the ordinary flame or the blowpipe flame produced from alcohol is considerably less than that from a similar flame in which coal gas is used4 ,for small work1 however1 the facility with which a spirit lamp may be lighted may more than counterbalance these disadvantages at times4 ,paraffin ,wax4--,where there is no coal gas available and the blowpipe is only required at intervals1 and especially where high portability is required1 there are few fuels so convenient as paraffin wax4 ,this may be obtained in pieces of a satisfactory size by cutting paraffin candles1 from which the wick has been withdrawn1 into lengths of about half an inch4 ,these cut pieces have the advantage over any oily fuel1 such as colza oil1 that they can be wrapped in paper or carried in a cardboard box2 further they will keep indefinitely1 even in the presence of air1 without undergoing any perceptible change4 ,forms of ,lamp for ,paraffin ,wax4--,probably1 the best form is that devised by ,thomas ,bolas1 and described by him in the ,journal of the ,society of ,arts1 ,december #bnd1 #ahih4 ,this lamp consists of a small open tray of iron1 through which pass three or more flat tubes1 and between these tubes are placed small flat pieces of wick1 the fit being such that the pieces of wick may be adjusted easily by means of a pair of pointed tweezers4 ,the flame thus obtained1 instead of having one large hollow1 is broken or divided so that the combustion is concentrated into a smaller area1 and the air blast1 which is directed across the flame1 carries the flame with it in a more complete manner than is the case with the ordinary flame2 a more thorough combustion being realised by this arrangement4 ,another advantage is the ease with which the wick may be changed and a larger or smaller wick inserted to suit the flame to any size of air jet4 ,this form of lamp may be used for oily fuel1 although it is specially suitable for paraffin wax4 ,two small pieces of bent tin-plate may be used as side covers1 and these serve to adjust the flame within certain limits4 ,a tin-plate cover which fits easily over the whole lamp serves as an extinguisher4 ,the complete lamp is shown by d1 ,fig4 #af1 and this figure shows also a quick-change air-jet device1 the whole arrangement forming a blowpipe for use where a non-gaseous fuel is to be employed4 ,although the lamp just described is desirable when complete control over the size of the flame is necessary1 and if the ideal conditions and maximum heat are to be obtained1 yet a simpler form of lamp will be found to give very good results4 ,such a lamp may consist of a flat tin tray1 having a diameter of about three and a half inches and a depth of about one inch4 ,in this tray is a tin support for the wick1 and the wick itself may consist of a bundle of soft cotton1 for example1 a loosely rolled piece of cotton cloth1 but in either case the top of the wick should be cut to approximately the same angle as that at which the blowpipe jet meets the flame4 ,in using paraffin wax as a fuel1 it is necessary to see that sufficient wax reaches the wick to prevent charring during the first few minutes before the bulk of the wax is melted4 ,animal and ,vegetable ,oils4--,almost any oil may be used as a fuel1 but many tend to become hard and gummy if allowed to stand in the air for any considerable time4 ,when this happens1 the wick becomes clogged and it is impossible to obtain a good flame4 ,a number of the oils tend1 also1 to produce rather strongly smelling smoke4 ,a ,flame-,guard for ,use ,with ,non-,gaseous ,fuels4--,in order to avoid the eye-strain produced by the luminous base of the flame from a wick burning paraffin wax or oil1 it is often advantageous to make a small tunnel of tin-plate1 which can be rested on the sides of the lamp and rises over the top of the wick4 ,such a flame guard is shown by e1 ,fig4 #af4 ,small ,rods and ,tubes from ,glass ,scrap3--,it is scarcely practicable to make small quantities of good glass with the blowpipe flame as the only source of heat1 but it is less difficult to make small rods or tubes from glass scrap1 and the ability to do this is sometimes of considerable value when a small tube has to be joined on to some special piece of apparatus made of glass of unknown composition4 ,it may be possible to obtain some fragments of similar glass1 either from a broken part of the apparatus or from a similar piece1 and from these fragments small tubes or rods can be made4 ,the fragments of glass may be melted together on the end of a clay pipe-stem1 care being taken to avoid trapping air bubbles as fresh fragments are added to the molten mass4 ,when a sufficient quantity of glass has been accumulated1 the viscous mass may be drawn out into a rod by bringing another pipe-stem into contact with the hot mass1 rotating both pipe-stems steadily1 and separating them until a rod of the desired size has been obtained4 ,if1 on the other hand1 it is desired to produce a tube from the mass of heated glass1 the mass should be blown hollow before the pipe-stems supporting it are separated4 ,methods of ,manufacture4--,when the student has familiarised himself with the more common operations and processes used in glass-blowing1 he will be in a position to increase his skill and knowledge of special methods by a critical examination of various examples of commercial work4 ,there are few exercises more valuable than such an examination1 combined with an attempt to reconstruct the stages and the methods by which the article chosen for examination was made4 ,obviously1 it is impossible to give full details of all constructions in a small text-book2 but it is easy to give an example of the constructional methods employed in the making of almost any piece of light blown-glass apparatus1 and these methods should prove of special value when apparatus of a new pattern has to be evolved for the purposes of research4 ,that is to say1 one designs the apparatus required1 applies known methods of construction as far as possible1 and1 by the examination of commercial apparatus having similar features1 evolves the new methods required4 ,for an exercise in such a process of reconstruction we may well take an ordinary commercial vacuum tube1 such as that shown by a1 ,fig4 #ag4 ,illustration3 ,fig4 #ag ,in the tube from which this drawing was made1 it was found that the spiral in the middle bulb was of a slightly yellowish colour and gave a green fluorescence when the electric discharge was passed through the tube2 that is to say1 the spiral is made of uranium-glass1 which is usually a soda-glass containing trace of uranium1 and hence differing slightly in composition from the ordinary glasses4 ,the two enclosed tubes which are bent into a series of ,s bends gave a pink fluorescence1 which indicates lead-glass2 and the remainder of the tube fluoresced with an apple-green colour2 this suggests ordinary soda-glass4 ,we have1 therefore1 a piece of apparatus in which three dissimilar glasses are joined1 while1 at the same time1 that apparatus contains a number of internal seals1 and it is not probable that the dissimilar glasses will have their coefficients of expansion so nearly alike as to permit of a stable internal seal being made if one part of the seal consists of a glass differing from that of the other part4 ,these considerations lead us to a closer examination of the joins where the dissimilar glasses are introduced1 and we find that in no case is the internal seal made between dissimilar glasses1 but that a soda-glass extension is joined on to both the uranium-glass tube and the lead-glass tubes at a point about half an inch before the internal seal commences4 ,careful examination of these joins shows that the change from one glass to another is not abrupt but gradual4 ,such a transitional joint may be made by taking a length of soda-glass tubing1 sealing the end and fusing a minute bead of the other glass on to the sealed end1 the end is then expanded and another bead of the other glass added1 this bead is expanded and the operation is repeated1 thus building up a tube1 and1 finally1 the tube of the other glass is joined on to the end of this4 ,we are now concerned with the question of the insertion of the uranium-glass spiral into the bulb 7see p4 #ch74 ,obviously the spiral is too large to pass through the necks of the bulb1 and it is difficult to imagine that the spiral was obtained by the insertion of a length of straight tubing which was bent after entering the bulb2 therefore1 the only remaining method is that the spiral was made first and the soda-glass extensions fastened on1 and that the bulb was blown1 cut in halves and the spiral inserted1 and the two halves were then rejoined4 ,that this was actually the case is confirmed by traces of a join which are just visible round the middle of the bulb4 ,the insertion of the spiral and the making of the first internal seal are shown by b1 and c4 ,there is one detail in making the second join of the spiral to the bulb which calls for attention1 and the small branch1 similar to an exhaustion branch1 at the side of the bulb provides a clue to this4 ,if an attempt were made to complete the second internal seal through a closed bulb it would be impossible to obtain a good result1 as the air-pressure in the bulb would not be under control when once union was effected1 and further heating of the air in the bulb would cause expansion and perforate the wall near the second internal seal2 we therefore make a small branch which can be left open and through which such air-pressure as may be found necessary can be maintained4 ,the third join1 by which the lead-glass tube is joined to the soda-glass is made in stages similar to those in which the soda-glass and uranium-glass were joined2 but the internal seal is most conveniently made by sliding a length of tubing over the lead-glass and fusing this tubing to the large diameter soda-glass tube to which the lead-glass is already joined4 ,the first stage of this operation is illustrated by d4 ,when this seal is completed1 the end of the soda-glass tube is drawn off and sealed as shown in e1 and at this stage a side tube or branch is joined on4 ,the sealed end of the outer and large diameter soda-glass tube is heated until it contracts and fuses to the enlargement that has previously been joined to the lead-glass tube1 and the end is burst out as shown in f4 ,another length of soda-glass is then joined on to the burst-out end1 and this length of soda-glass tubing is drawn out to a thin-walled contraction2 the non-contracted part is expanded to form the bulb1 and a small exhaustion branch made on the side1 the drawn-out portion being cut off1 and an electrode1 previously prepared by coating a part of its length with a suitable enamel1 is introduced4 ,the tube is tilted to keep the electrode away from the drawn-out end1 which is melted off and sealed4 ,a small perforation is made with a hot platinum or iron wire in the sealed end1 the electrode is shaken into position1 and the sealing is completed as explained on page #db4 ,the remainder of the tube1 that is to say the lead-glass tube and the bulb on the other side of the middle bulb1 is completed in a similar manner4 ,,summary ,,of ,,conditions ,,necessary ,,for ,,success ,,in ,,glass-,,blowing4 ,for the convenience of the student1 it may be well to summarise the chief essentials for success in glass-blowing1 and at the same time to add such brief notes on the various methods as may seem desirable4 ,adjustment of ,blowpipe4--,the air jet should be clean internally1 and so centered as to give a flame having a well-defined blue portion1 the tip of the flame should not be only slightly luminous but purple in colour4 ,in the case of a blowpipe burning oil or wax fuel the flame may be a trifle more ragged without disadvantage4 ,bellows and ,blowing4--,the bellows should be adjusted to deliver air at constant pressure1 either by insertion of a tap or1 better1 by attention to the wind reservoir if necessary4 ,the movement of the foot in blowing should be steady1 not jerky4 ,heating ,glass4--,the tube or rod should be heated cautiously until it has reached its softening point in its thickest part4 ,steady rotation of the glass during the heating is almost essential4 ,blowing a ,bulb or ,expanding a ,join4--,prolonged heating is necessary in order that the thick parts may be heated completely through4 ,blowing should take place by stages1 in order that the thin parts1 which tend to expand first1 have time to cool4 ,the thick parts can then be expanded by further blowing and thus a bulb or expansion of even thickness can be obtained4 ,cutting ,glass4--,the most useful method for general use is by means of the file or glass-blowers' knife4 ,either file or knife must be kept sharp by grinding4 ,neither file nor knife should be used on hot glass4 ,the diamond and wheel cutter are useful for cutting sheet-glass1 and when the diamond is employed a singing noise is an indication of a satisfactory cut4 ,leading a ,crack4--,a crack may be led in any desired direction by means of a bead of hot glass or a small gas flame4 ,the glass which it is desired to crack should be heated at a point slightly in advance of the crack1 which will extend in the direction of the source of the heat4 ,turning ,out the ,end of a ,tube4--,this is done by heating the end of the tube and rotating it against an iron rod4 ,the rod must be kept polished and free from rust1 and it must not be allowed to become too hot while in use1 otherwise the glass will stick to it4 ,joining ,unlike ,glasses4--,joints between unlike glasses are often unstable4 ,when such joints are made it is desirable to blow them as thin as possible1 and to avoid the junction of unlike glasses in any complex joint1 such as an internal seal4 ,a transitional portion of tubing may be built up by the successive addition and interfusion of beads of one of the glasses to the end of a sealed tube consisting of the other glass4 ,joining a ,tube to a ,very ,thin ,bulb4--,the bulb may be thickened at the point of union by fusing on a bead of glass and expanding this slightly4 ,a small central portion of the expanded part may then be perforated by bursting and the tube joined on4 ,insertion of ,one ,bulb ,within ,another4--,a bulb may be divided into two halves by leading a crack round it and the inner bulb is then introduced4 ,the two halves of the outer bulb may be fitted together 7care being taken to avoid any damage to the edges71 and the bulb may be completed by rotating the contacting edges before the blowpipe until they are soft1 and then expanding slightly by means of air-pressure4 ,annealing4--,for most purposes1 in the case of thin1 blowpipe-made or lamp-blown glass apparatus1 it is sufficient to cool slowly by rotating the finished article over a smoky flame and setting it aside in a place free from draughts1 and where the hot glass will not come in contact with anything4 ,simple bulbs and joints do not even need this smoking2 but thick articles1 and especially those that are to be subjected to the stress of grinding1 need more prolonged annealing in a special oven4 ,use of ,lead-,glass4--,when lead-glass is to be used1 the blowpipe flame should be in good adjustment and the glass should not be allowed to approach so near to the blue cone as to be blackened4 ,slight blackening may often be removed by heating the glass in the extreme end of the flame4 ,lead-glass articles tend to be rather more stable than similar articles of soda-glass4 ,combustion-,glass4--,this may be worked more easily if a small percentage of oxygen is introduced into the air with which the blowpipe flame is produced4 ,if the air is replaced entirely by oxygen there is a risk of damaging the blowpipe jet1 unless a special blowpipe is employed4 ,internal ,seal4--,there are two ways of making these1 one1 in which the inner portion of the tube is fused on to the inside of the bulb or tube through which it is to pass1 an opening is made by bursting and the outer tube is joined on4 ,this is a quick and in some ways more satisfactory method than the other1 in which there is no separate inner piece4 ,rubber ,blowing ,tube4--,in complicated work it is often convenient to use a thin rubber blowing-tube which is connected with the work either by a cork and piece of glass tubing or by fitting over a drawn-out end4 ,the use of such a blowing-tube avoids the inconvenience of raising the work to the mouth when internal air-pressure is required4 ,one end of the rubber tube is retained in the mouth during work4 ,general ,notes4--,a large amount of glass-blowing is spoiled through carelessness in arranging the work beforehand4 ,the student should have every detail of his manipulation clearly in mind before he commences the work2 he should not trust to evolving the method during the actual manipulation4 ,undue haste is another fruitful source of failure4 ,practically every operation in glass-blowing can be carried out in a perfectly leisurely manner1 and it is better to err rather on the side of deliberation than on the side of haste4 ,if1 as will doubtless happen at times1 a piece of work gives trouble and it is necessary to pause and consider the whole question1 or if for any other reason it is necessary to stop during the construction of a partially finished join or other operation1 great care should be taken not to allow the work to cool4 ,a large1 brush-like flame may be produced by increasing the amount of gas admitted to the blowpipe1 and the work should be held just in front of the current of hot air produced by such a flame4 ,it will then be possible to continue work on this without causing it to crack when further heat is applied4 ,as time goes on1 the student will find an increasing confidence in his ability to manipulate the soft glass1 and with increasing confidence will come rapidly increasing power of manipulation4 ,perhaps the greatest obstacle to success in glass-blowing is undue haste in manipulation4 ,,index ,absorption bulbs1 #ba1 #bc4 ,airtube1 flexible1 #h1 #ajb4 ,alarm thermometer1 #de4 ,annealing1 #g1 #fj4 ,bellows1 adjusting pressure of1 #e1 #f4 ,bellows1 foot1 #e1 #f4 ,bending tubes1 #bc4 ,blackening1 #eh1 #aja4 ,branching1 #ah1 #ai4 ,brushes of spun glass1 #ec4 ,blowpipe flame1 quality of1 #c4 ,blowpipe for mouth blast1 #hj1 #hb1 #hd4 ,blowpipe1 for paraffin wax1 #hb1 #hh4 ,blowpipe1 ,herepath's1 #b4 ,blowpipe jet1 centring1 #c1 #ih4 ,blowpipe jet1 dirt in1 #c4 ,blowpipe jet1 multiple1 #d1 #dj4 ,blowpipe1 ,letcher's1 change1 #d4 ,blowpipe1 simple form of1 #hj4 ,bulb1 medially on tube1 #bb4 ,bulbs1 #ai1 #bj1 #bb1 #ch1 #ih4 ,bulbs1 absorption1 7,liebig's71 #ba1 #bc4 ,bulbs1 dividing1 #ci1 #ie4 ,bulbs from rod1 #be4 ,bulbs1 internal1 #ch4 ,bulbs1 thick1 #ba4 ,cages1 from glass rod1 #bd1 #be1 #bg4 ,calibration1 #gb4 ,carius tubes1 #af4 ,condenser1 ,liebig's1 #cg4 ,condensers1 various1 #cg1 #ch4 ,cone1 carbon1 #h4 ,crack1 leading1 #cj1 #ii4 ,cracking1 subversive1 #ajc4 ,cutting glass with diamond1 #cj4 ,cutting tubes1 #aa1 #ii4 ,diamond 7glazier's71 use of1 #cj4 ,dissimilar glass1 joining of1 #bb1 #id4 ,drilling1 #fa4 ,electrodes1 sealing in1 #db1 #ig4 ,etching glass1 #gj4 ,extemporised appliances1 #hj4 ,examination of apparatus1 #ic4 ,failure1 ,haste chief ,source of1 #ajc4 ,failures1 ,notes as to1 #ig4 ,file1 with oblique ground edge1 #g4 ,filing glass1 #fc4 ,filter pumps1 #ce ,foot1 #be ,fuels various1 #hb1 #hf1 #hg1 #hi4 ,funnel1 thistle1 #bc4 ,general principles and precautions1 #a1 #ig ,glass1 varieties of1 #i1 #ee1 #ia-ig4 ,graduation1 #gb-gf ,haste1 ,source of ,failure1 #ajc ,heat reflector1 asbestos1 #g4 ,heating1 intensive1 #g1 #eg4 ,heating precautions1 #ab1 #ih ,joining dissimilar glass1 #bb4 ,joining glass to metal1 #gf4 ,joining tubes1 #af1 #id1 #ajj4 ,knife1 ,glass blower's1 #g1 #ii4 ,lenses1 grinding1 #fc4 ,marking glass1 #fi4 ,methods1 analytic study of1 #ia1 #ic4 ,oxygen for intensive heating1 #eg1 #aja4 ,precautions and ,general ,principles1 #a1 #ig4 ,pumps1 ,filter1 #ce4 ,pumps1 ,sprengel1 #di1 #ej4 ,re-entering branch1 #dj4 ,reflector of heat1 asbestos1 #g4 ,rod1 uses and articles from1 #ag1 #be1 #bg1 #bh4 ,rod1 blowing to hollow1 #ag1 #be1 #bf1 #ia4 ,scrap glass1 working1 #ij4 ,sealing tubes1 #ab1 #ac1 #ad4 ,sealed tubes for pressure1 #ae1 #af4 ,sealing in of ,electrodes1 #db1 #ig4 ,seals1 internal 7airtraps71 #cb1 #ajb4 ,silvering glass1 #gg4 ,soldering glass1 #gf4 ,soxhlet-tube1 #dj4 ,spirals1 #bc1 #ie4 ,spray arrester1 #cd4 ,spray producers1 #cf4 ,sprengel pumps1 #di1 #ej4 ,spinning glass1 #ea4 ,stopcocks1 #fj1 #ff4 ,stoppering1 #fc4 ,stirrers1 #bh1 #bi4 ,summary as to precautions and failures1 #ig4 ,taps1 #fj1 #ff4 ,thermometers1 ,various1 #dd-di4 ,thermo-regulator1 #bd4 ,thistle ,funnel1 #bc4 ,tools1 ,various small1 #g4 ,turn-pins1 #g1 #h1 #ii4 ,turning out open ends1 #ad1 #ii4 ,,printed ,,in ,,great ,,britain ,,by ,w4 ,,jolly ,,sons1 ,,ltd41 ,,printers1 ,,aberdeen4