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diff --git a/.gitattributes b/.gitattributes new file mode 100644 index 0000000..6833f05 --- /dev/null +++ b/.gitattributes @@ -0,0 +1,3 @@ +* text=auto +*.txt text +*.md text diff --git a/30066-0.txt b/30066-0.txt new file mode 100644 index 0000000..30294c9 --- /dev/null +++ b/30066-0.txt @@ -0,0 +1,1899 @@ +*** START OF THE PROJECT GUTENBERG EBOOK 30066 *** + + LABORATORY MANUAL + + OF + + GLASS-BLOWING + + + + + McGraw-Hill Book Company + + _Publishers of Books for_ + + + Electrical World + Engineering Record + Railway Age Gazette + Signal Engineer + Electric Railway Journal + Metallurgical and Chemical Engineering + The Engineering and Mining Journal + Engineering News + American Machinist + American Engineer + Coal Age + Power + + + + + LABORATORY MANUAL + OF + GLASS-BLOWING + + BY + FRANCIS C. FRARY, PH. D. + + ASSISTANT PROFESSOR OF CHEMISTRY + UNIVERSITY OF MINNESOTA + + McGRAW-HILL BOOK COMPANY, INC. + 239 WEST 39TH STREET, NEW YORK + 6 BOUVERIE STREET, LONDON, E. C. + + 1914 + + + + + COPYRIGHT, 1914, BY THE + McGRAW-HILL BOOK COMPANY, INC. + + + + +PREFACE + + +The purpose of this little book is to provide a clear and detailed +discussion of the elements of glass-blowing. Many laboratories in this +country, especially in the west, are located a long way from any +professional glass-blower, and the time and money spent in shipping +broken apparatus several hundred miles to be mended could often be saved +if some of the laboratory force could seal on a new stopcock, replace a +broken tube, or make some temporary repairs. Many men in physical or +chemical laboratories have occasion to modify some piece of apparatus +designed perhaps for other uses, or to design new apparatus. To such +also, the ability to perform some of the operations herein described may +be very valuable. + +No originality is claimed for the methods here described. They are those +which the author has found most suitable and convenient in his own work, +and most easily learned by students. The aim has been to describe each +operation in such detail that a beginner can follow the process without +help and, with practice, attain satisfactory results. It is, however, +much easier to perform any of the operations described, after seeing +some one else perform it correctly; since the temperature, the exact +time to begin blowing the glass, and many other little details are very +difficult to obtain from a description. + +It has not been thought worth while to describe the process of making +stopcocks, thermometers, vacuum tubes, etc., as such things can be +purchased more cheaply and of much better quality than any amateur can +make unless he is willing to spend a very large amount of time in +practice. For similar reasons the manipulation of quartz glass has been +omitted. + +The author will be grateful for all suggestions and criticisms tending +to improve the methods presented. If some of them appear to be given in +excessive detail, the reader will remember that many things which are +obvious to the experienced worker are not so to the beginner, and that +it is the little details in the manipulation which often spell success +or failure in glass-blowing. + + F. C. F. + +MINNEAPOLIS, MINN., +_January, 1914._ + + + + + CONTENTS + + + + PAGE + + Preface v + + + CHAPTER I + + MATERIALS AND APPARATUS 1 + + Varieties and defects of glass--Devitrification--Annealing + glass--Blowpipe and bellows--Light--Arrangement of exercises. + + + CHAPTER II + + GENERAL OPERATIONS 7 + + Cutting, bending, constricting and flanging the tubing--Methods + of rotation and blowing. + + + CHAPTER III + + ELEMENTARY EXERCISES 16 + + Joining two pieces of tubing of the same diameter--The "tee" + tube--Joining two tubes of different diameters--Blowing bulbs. + + + CHAPTER IV + + ADVANCED EXERCISES 35 + + Sealing a tube through another tube: The gas-washing tube, suction + pump, and Kjeldahl trap. + + + CHAPTER V + + MODIFIED METHODS AND SPECIAL OPERATIONS 43 + + Capillary tubing--Glass rod--Mending stopcocks--Closed circuits of + tubing--Spirals--Ground joints--Sealing in platinum wire--Sealing + vacuum tubes--Closed tubes for heating under pressure. + + + INDEX 59 + + + + +LABORATORY +MANUAL OF GLASS-BLOWING + + + + +CHAPTER I + +MATERIALS AND APPARATUS + + +One of the most important factors in the success of any piece of +glass-blowing is the glass employed. As is well known, there are two +general varieties of glass: Lead glass and soda glass. Formerly much +apparatus was made of lead glass, but at present it is very seldom met +with, except in the little drops of special glass used to seal platinum +wires into the larger sizes of tubes. Lead glass is softer and more +readily fusible than soda glass, but has the disagreeable property of +growing black in a few seconds unless worked in a strong oxidizing +flame. This may be prevented by using a "hissing" flame, with a large +excess of air, and working in the extreme end of the flame; or the black +lead formed may thus be reoxidized, and the glass restored to its +original clearness. + +Almost all the soft glass on the market is a soda glass, although +sometimes part of the soda is replaced by potash. Most of the hard glass +appears to be a potash glass. The following qualities are desirable in a +glass for ordinary working: (1) moderately low working temperature, (2) +freedom from air bubbles, striations and irregularities, (3) proper +composition, so that the glass will not devitrify or crystallize while +being handled at its working temperature, (4) ability to withstand rapid +heating without cracking. + +The working temperature of different samples of so-called "soft glass" +varies a good deal, and is best determined by trial. The glass should +become almost soft enough for blowing in a flame that still shows a +little yellow near the tip, so that at the highest temperature of the +flame it may flow fairly freely and thus easily eliminate irregularities +in thickness. If the glass is too hard, the shrinking of the glass, +collection of material for a bulb, and in fact most of the working +processes will be slower, and the glass will not stay at its working +temperature long enough after its removal from the flame to permit it to +be properly blown. + +Air bubbles in the original batch of glass are drawn out into long +hair-like tubes during the process of manufacture. When such tubing is +worked, the walls of these microscopic tubes collapse in spots, and the +air thus enclosed will often collect as a small bubble in the wall, thus +weakening it. Irregularities are of various kinds. Some of the larger +sizes of thin-walled tubing often have one half of their walls much +thicker than the other, and such tubing should only be used for the +simplest work. Some tubing has occasional knots or lumps of unfused +material. The rest of the tube is usually all right, but often the +defective part must be cut out. The presence of striations running along +the tube is generally an indication of hard, inferior glass. Crookedness +and non-uniformity of diameter are troublesome only when long pieces +must be used. + +Devitrification is one of the worst faults glass can possibly have. It +is especially common in old glass, and in glass which has contained +acids. It seems to be of two sorts. One variety manifests itself on the +surface of the glass before it reaches its working temperature, but if +the glass be heated to the highest temperature of the flame it will +disappear except in the portion at the edge of the heated part. The +glass seems to work all right, but an ugly crystallized ring is left at +the edge of the portion heated. This kind appears most frequently in old +glass which was originally of good quality, but has in time been +superficially altered, probably by the loss of alkalies. The other +variety of devitrification does not appear when the glass is first +heated; but after it has been maintained at or above its working +temperature for a longer or shorter time, it will be noticed that the +outer surface has lost its smoothness, and appears to be covered with +minute wrinkles. It will also be found that the glass has become harder, +so that it becomes impossible to work it easily. Further heating only +makes the matter worse, as does the use of a higher temperature from the +start. In fact it will often be found that a piece of comparatively soft +glass which devitrifies almost at once in a "hissing" flame can be +worked without serious difficulty if care be taken to use a flame still +decidedly tinged with yellow. Even good glass will begin to devitrify in +this way if heated too long at the highest temperature of the flame, so +care should always be taken (1) _to reduce the time of heating of any +spot of glass to a minimum_; _i.e._, get the desired result at the first +attempt, if possible, or at least with the minimum of reheating and +"doctoring," and (2) _avoid keeping the glass at the highest temperature +of the flame any longer than necessary_. This may be accomplished by +doing all heating, shrinking, etc., of the glass in a flame more or less +tinged with yellow, and only raising the temperature to the highest +point when ready to blow the glass. This kind of devitrification is +apparently due to volatilization of the alkalies from the glass in the +flame, and it is said that it can be partly remedied or prevented by +holding a swab of cotton saturated with a strong solution of common salt +in the flame from time to time as the glass is heated. + +The toughness of glass, _i.e._, its ability to withstand variations of +temperature, depends on its composition and the care taken in its +annealing. In general, large pieces of glass should be heated very +slowly in the smoky flame, and the larger the diameter of the tube the +greater the length which must be kept warm to prevent cracking. All +large pieces should be carefully heated over their whole circumference +to the point where the soot deposit burns off, before being finally +cooled. After being thus heated they are cooled in a large smoky flame +until well coated with soot, then the flame is gradually reduced in size +and the object finally cooled in the hot air above it until it will not +set fire to cotton. If thought necessary, it may then be well wrapped in +cotton and allowed to cool in the air. If not properly annealed the +place heated may crack spontaneously when cold, and it is quite certain +to crack if it is reheated later. + +Next in importance to the glass are the blow-pipe and the bellows. Any +good blast lamp, such as is ordinarily used in a chemical laboratory for +the ignition of precipitates, will be satisfactory; provided it gives a +smooth regular flame of sufficient size for the work in hand, and when +turned down will give a sharp-pointed flame with well-defined parts. +Where gas is not available, an ordinary gasoline blow-torch does very +well for all operations requiring a large flame, and a mouth blow-pipe +arranged to blow through a kerosene flame does well for a small flame. +Several dealers make blow-torches for oil or alcohol which are arranged +to give a small well-defined flame, and they would doubtless be very +satisfactory for glass-work. Any good bellows will be satisfactory if it +does not leak and will give a steady supply of air under sufficient +pressure for the maximum size of flame given by the lamp used. A bellows +with a leaky valve will give a pulsating flame which is very annoying +and makes good work very difficult. When compressed air is available it +can be used, but if possible it should be arranged so that the supply +can be controlled by the foot, as both hands are usually needed to hold +the work. For the same reason the supply of air is usually regulated by +varying the rate of operation of the bellows, rather than by adjusting +the valve of the blast-lamp. On the other hand, it will be found best to +always adjust the flow of the gas by means of the cock on the lamp, +rather than that at the supply pipe. The operator must have complete +control over the flame, and be able to change its size and character at +short notice without giving the work a chance to cool, and often without +ceasing to support it with both hands. + +Glass-blowing should be done in a good light, but preferably not in +direct sunlight. The operator should be seated in a chair or on a stool +of such a height that when working he may comfortably rest one or both +elbows on the table. The comfort of the operator has a decided influence +on the character of his work; especially in the case of a beginner, who +often defeats his purpose by assuming uncomfortable and strained +positions. Steadiness and exact control of both hands are essential in +most operations; any uncomfortable or strained position tires the +muscles and weakens the control of the operator over them. + +In the arrangement of the exercises here presented, several factors have +been considered. It is important that the first exercises be simple, +although not necessarily the simplest, and they should teach the +fundamental operations which will be used and amplified later. They +should in themselves be things which are of importance and commonly used +in glass-work, and they should be so arranged that the fundamental +points, such as the rotation of glass, the proper temperature, blowing +and shrinking the glass may be learned with a minimum expenditure of +time, glass and gas. It is therefore recommended that the beginner take +them up in the order given, at least as far as No. 7, and that each be +mastered before attempting the next. The beginner should not leave the +first exercise, for example, until he can join together two pieces of +tubing so that they form one piece of substantially uniform inner and +outer diameter, and without thick or thin spots. From two to four +practice periods of two hours each should suffice for this. This chapter +and the following one should also be frequently read over, as many of +the points discussed will not be understood at first and many of the +manipulations described will not be necessary in the simpler exercises. + + + + +CHAPTER II + +GENERAL OPERATIONS + + +=Cutting the Glass.=--For this purpose a "glass-knife" is preferred to a +file, if the glass is cold: if it is hot a file must always be used, and +its edge slightly moistened to prevent drawing the temper. The +glass-knife is simply a flat piece of hard steel, with the edges ground +sharp on an emery wheel. The bevel of the edge should be from 30 to 60 +degrees. An old flat file can easily be ground into a suitable knife. +The glass-knife makes a narrower scratch than the file but appears more +likely to start the minute crack which is to cause the tube to break at +that point, and the break is more likely to give a good square end. The +scratch should be made by passing part of the knife or file once across +the glass, never by "sawing" the tool back and forth. This latter +procedure dulls the tool very quickly. + +In breaking a piece of glass tubing, many persons forget that it is +necessary to _pull_ the ends apart, as well as to bend the tube very +_slightly_ in such a direction as to open up the minute crack started in +the scratch. Care in breaking the tube is essential, as it is impossible +to do as good work with uneven ends as with square ones. + +When tubing of large diameter or thin wall is to be cut, it is often +better not to attempt to break it in the usual way, but to heat a very +small globule of glass (1/16 to 1/8 inch diameter) to red heat, and +touch it to the scratch. This will usually start the crack around the +tube; if it has not proceeded far enough, or has not gone in the +desired direction, it may be led along with a hot point of glass. This +is put a little beyond the end of the crack, and as the latter grows out +toward it, moved along the path where the crack is desired. This point +of glass is also very useful in breaking off very short ends of tubes, +where there is not room to get a firm enough hold and sufficient +leverage to break the tube in the ordinary way, and for breaking tubes +attached to large or heavy objects, which would be likely to make +trouble if treated in the ordinary way. + +Another way of cutting large tubing, especially if it has rather thick +walls, is to make a scratch in the usual way, and then turn on the +smallest and sharpest possible flame of the blast lamp. The tube is next +taken in both hands and held horizontally above the flame so that the +scratch is exactly over it. The tubing is now rotated rapidly about its +axis, and lowered so that the flame is just tangent to its lower side. +After about ten seconds of heating, it is removed from the flame and the +hot portion quickly breathed upon, when it will generally crack apart +very nicely. Care must be taken to hold the tube at right angles to the +flame during the heating, and to rotate it so that only a narrow strip +of the circumference is heated, and the scratch should be in the center +of this heated strip. By this means tubing as large as two inches in +diameter is readily broken. + +Griffin's glass cutter, which contains a hardened steel wheel, like that +on any ordinary window-glass cutter, and a device by which this can be +made to make a true cut clear around the tube, is a very handy article, +especially for large tubing, and may be obtained from any dealers in +chemical apparatus. + +=Bending Glass.=--Inasmuch as this is one of the commonest operations in +the laboratory, it is assumed that the reader knows how to perform it. +However, it should be noted that in order to obtain the best results a +broad (fish-tail burner) flame should generally be used, and the tube +rotated on its axis during the heating, and allowed to bend mostly by +its own weight. If large tubing is to be bent, one end must be stoppered +and great care used. Whenever the tube shows signs of collapsing or +becoming deformed, it must be gently blown out into shape, heating the +desired spot locally if necessary. A blast-lamp is likely to be more +useful here than the fish-tail burner. + +=Drawing Out a Tube.=--Most students learn this the first day of their +laboratory work in chemistry, but few take pains to do it well. The tube +should be heated in the flame of a Bunsen burner, or blast lamp +(preferably the latter) until it is very soft. During this time it must +be continuously rotated about its axis, and so held that the edges of +the heated zone are sharply defined; _i.e._, it should not be allowed to +move back and forth along its own axis. When so hot that it cannot +longer be held in shape, the tube is removed from the flame, and the +ends slowly and regularly drawn apart, _continuing the rotation of the +tube about its axis_. By regulating the rate of drawing and the length +of tube heated, the desired length and diameter of capillary may be +obtained. The tube should always be rotated and kept in a straight line +until the glass has set, so that the capillary may have the same axis as +the main tube. This capillary or "tail" is often a very necessary handle +in glass-blowing, and if it is not straight and true, will continually +make trouble. + +In drawing out very large tubing, say from one to two inches in +diameter, it is often necessary to draw the tube _in the flame_, +proceeding very slowly and at a lower temperature than would be used +with small tubing. This is partly on account of the difficulty of +heating large tubing uniformly to a high temperature, and partly in +order to prevent making the conical part of the tube too thin for +subsequent operations. + +=Constricting a Tube.=--Where a constriction is to be made in a tube, +the above method must be modified, as the strength of the tube must be +maintained, and the constricted portion is usually short. Small tubes +are often constricted without materially changing their outside +diameter, by a process of thickening the walls. The tube is heated +before the blast lamp, rotating it about its axis as later described, +and as it softens is gradually pushed together so as to thicken the +walls at the heated point, as in _a_, Fig. 1. When this operation has +proceeded far enough, the tube is removed from the flame, and the ends +cautiously and gently drawn apart, continuing the rotation of the tube +about its axis and taking care not to draw too rapidly at first. The +resulting tube should have a uniform exterior diameter, as shown in _b_, +Fig. 1. + +[Illustration: FIG. 1.--Constricting a tube.] + +This method of constriction is not suited to tubes much over 1/4 inch in +diameter, since the mass of glass in the constricted part becomes so +thick as to be difficult to handle when hot, and likely to crack on +cooling. Larger tubes are therefore constricted by heating in a narrow +flame, with constant rotation, and when soft, alternately gently pulling +the ends apart and pushing them together, each motion being so regulated +that the diameter of a short section of the tube is gradually reduced, +while the thickness of the wall of the reduced portion remains the same +as that of the rest of the tube, or increases only slightly. This +pulling and pushing of the glass takes place _in the flame_, while the +rotation is being continued regularly. The result may appear as +indicated in _c_, Fig. 1. The strength of the work depends upon the +thickness of the walls of the constricted portion, which should never be +less than that in the main tube, and usually a little greater. This +operation is most successful with tubing having a relatively thin wall. + +=Flanging a Tube.=--This operation produces the characteristic flange +seen on test-tubes, necks of flasks, etc., the object being twofold: to +finish the end neatly and to strengthen it so that a cork may be +inserted without breaking it. This flanging may be done in several ways. +In any case the first operation is to cut the tube to a square end, and +then heat this end so that the extreme sixteenth or eighth of an inch of +it is soft and begins to shrink. The tube is of course rotated during +this heating, which should take place in a flame of slightly greater +diameter than the tube, if possible. The flange is now produced by +expanding this softened part with some suitable tool. A cone of charcoal +has been recommended for this purpose, and works fairly well, if made so +its height is about equal to the diameter of its base. The tube is +rotated and the cone, held in the other hand, is pressed into the open +end until the flange is formed. A pyramid with eight or ten sides would +probably be better than the cone. + +[Illustration: FIG. 2.--Flanging tool.] + +A better flanging tool is made from a triangular piece of copper or +brass, about 1/16 inch thick, and mounted in a suitable handle. Such a +tool is shown in Fig. 2, being cut from a sheet of copper and provided +with a handle made by wrapping asbestos paper moistened with sodium +silicate solution about the shank of the tool. It is well to have +several sizes and shapes of these tools, for different sizes of tubing. +The two sizes most used will be those having about the following +dimensions: (1) _a_ = 2 inches, _b_ = 1 inch; (2) _a_ = 1 inch, _b_ = 1 +inch. When the end of the tube is softened, the tool is inserted at an +angle, as indicated in Fig. 3, and pressed against the soft part, while +the tube is quickly rotated about its axis. If the flange is +insufficient the operation may be repeated. The tool should always be +warmed in the flame before use, and occasionally greased by touching it +to a piece of wax or paraffin. After the flange is complete, the end +must be heated again to the softening temperature and cooled slowly, to +prevent it from cracking. + +[Illustration: FIG. 3.--Flanging a tube with flanging tool.] + +[Illustration: FIG. 4.--Flanging a tube with carbon rod or wire.] + +Some glass-blowers use a small carbon rod, about 3/16 inch in diameter, +as a flanging tool for tubes larger than about 3/8 inch diameter, and a +small iron wire or similar piece of metal for smaller tubes. In this +case the tube is heated as above described, and the rod or wire inserted +in the end at an angle and pressed against the softened part, as +indicated in Fig. 4, while the tube is rotated about its axis. For +large heavy tubes a larger carbon would be used. + +=Rotation of the Tube.=--This is the fundamental manipulation in +glass-blowing, and upon it more than all else depends the uniformity and +finish of the work, and often the possibility of accomplishing the work +at all. Directions for it will be given on the assumption that the +reader is right-handed; if otherwise, the position of the hands is of +course reversed. The object of rotation is to insure even heating of the +whole circumference of the tube at the point of attack, to equalize the +effect of gravity on the hot glass and prevent it from falling out of +shape when soft, and to keep the parts of the tube on each side of the +heated portion in the same straight line. + +In rotating the tube, both hands must be used, so that the two ends may +revolve at the same rate and the glass in the hot part not be twisted. +The rotation is performed by the thumb and first finger of each hand, +the other fingers serving to support the tube. As it is almost always +necessary to follow rotating and heating a tube by blowing it, the hands +should be so placed that it will be easy to bring the right-hand end up +to the mouth without shifting the hold on the glass. For this reason the +left hand grasps the glass with the palm down, and the right hand with +the palm turned toward the left. If there is any choice, the longer and +heavier part of the tube is usually given to the left hand, and it is +planned to blow into the shorter end. This is because it is easier to +support the tube with the hand which has the palm down. This support is +accomplished by bending the hand at the wrist so that it points slightly +downward, and then curling the second, third and little fingers in under +the tube, which is held between them and the palm. This support should +be loose enough so that the thumb and first finger can easily cause the +tube to rotate regularly on its axis, but firm enough to carry all the +weight of the tube, leaving the thumb and first finger nothing to do but +rotate it. The hand must be so turned, and the other fingers so bent, +that the thumb and first finger stretch out nearly to their full length +to grasp the tube comfortably. + +The right hand is held with the palm toward the left, the fingers except +the first slightly bent, and the tube held between the first finger and +the thumb while it rests on the second finger and that portion of the +hand between the base of the first finger and the thumb. Rotation of the +tube is accomplished by rolling it between the thumbs and first fingers: +the rotation being continued in the same direction regularly, and not +reversed. It is better to roll slowly and evenly, with a series of light +touches, each of which moves the tube a little, than to attempt to turn +the tube a half a revolution or so with each motion of the hands. The +hands must be held steady, and the tube must be under good control at +all times, so that both ends may be rotated at the same angular +velocity, even though they may be of different diameters, and the tube +be neither drawn apart nor pushed together unless such a motion is +expressly desired, as it sometimes is. The hot part of the glass must be +constantly watched to see that it is uniformly rotated and not twisted, +nor pulled out or pushed together more than is desired. Care must also +be taken to keep the parts of the tube in the same straight line, or as +near it as possible, during the heating and all other manipulations. + +When flanging a tube, it is held and rotated with the left hand as above +described, while the right hand holds the flanging tool. + +When part of the end of a tube must be heated, as in Exercise 6, and +rotation must be very carefully performed and continued during the +blowing, both hands are used. The right hand is held as above +described, and the left hand close to it and either as above described +or else with the palm toward the right, grasping the tube in the same +way as the right hand does. This puts both hands in a position where the +tube may be blown and rotated uniformly while its axis is kept +horizontal. + +Smoothness and exactness are the two things for which the beginner must +constantly strive in glass-blowing, and they are only attained by a +careful attention to the details of manipulation, with a steady hand and +watchful eye. Every move must count, and the exercise must be finished +with a minimum of reheating and retouching, for the best results. + + + + +CHAPTER III + +ELEMENTARY EXERCISES + + +EXERCISE NO. 1 + +JOINING TWO PIECES OF TUBING, END TO END--FIRST METHOD + +This exercise is most easily learned on tubing with an exterior diameter +of 1/4 inch, or a little less, having moderately heavy walls. A piece of +such tubing is heated before the blow-pipe at a point ten or twelve +inches from the end, and there drawn out to a capillary as previously +described (page 9). The capillary is sealed off about two inches from +the main tube, and the latter is cut near the middle. Care should be +taken to get square ends where the cut is made (page 7). The flame is +now so regulated that it is a little broader than the diameter of the +tube, the sealed half of the tube taken in the left hand and the other +half in the right. The open end of the sealed part and one of the ends +of the other part are now held in opposite sides of the flame, inclined +at a slight angle to one another as indicated in Fig. 5, and rotated and +heated until the surfaces of both ends are just softened. The two ends +are then carefully and quickly brought together (_a_, Fig. 6), removed +from the flame and pulled apart a little, to reduce the lump formed at +the joint as much as possible, as indicated in _b_. The joint is then +tested by blowing into the open end of the tube to see if it is tight. +If so, the flame is reduced to half or less than half of its former +size, and the joint heated in it, holding the tube and continually +rotating it as directed in the last chapter (page 13). + +[Illustration: FIG. 5.--Softening ends of two pieces of tubing.] + +[Illustration: FIG. 6.--Joining two pieces of tubing end to end--first +method.] + +As the tube softens and tends to shrink, the two ends are pressed +together a little and the walls allowed to thicken slightly, as in _c_. +It is then quickly removed from the flame and gently blown as indicated +in _d_, continuing the rotation of the tube during the blowing, and at +the same time pressing the ends of the tube together a little so as to +make a _short_ thick-walled bulb. The joint is then returned to the +flame and reheated, rotating as before, shrinking to about the shape of +_e_. When this stage is reached, the glass should be very hot and fluid, +and the mass of hot glass thick enough to remain at its working +temperature for about five seconds after removal from the flame. The +glass is now reblown as indicated in _f_, to form a bulb having walls of +practically the same thickness as the original tube. As soon as the bulb +is blown, the tube is removed from the mouth, held horizontally in front +of the worker, and gently drawn out to form one continuous tube, as +indicated in _g_. During both the blowing and drawing of this bulb the +rotation must be continued, and both blowing and drawing must be +carefully regulated so that the resulting tube may have the same +internal and external diameter at the joint as elsewhere. + +=Discussion.=--In making the original joint, (_a_, Fig. 6), care should +be taken that the lump formed is as small as possible so that it may be +entirely removed during the subsequent operations. For this reason, only +the very tip ends of the two pieces of tubing are held in the flame, and +the softening should not extend more than 1/16 inch down the tube. As +soon as the ends are sufficiently soft to stick together, they are made +to do so. The first drawing of the tube (_b_) should take place +immediately, and reduce the lump as much as possible without making the +adjacent walls of the tube thin. The whole purpose of the rest of the +manipulation is to absorb or "iron out" the lump at the joint. For this +reason, care is taken that this lump is always in the center of the +flame while the joint is being heated, and a small flame is used so +that little of the main tube may be softened. During the first shrinking +of the joint (_c_) the walls next the lump, being thinner than it is, +reach the softening temperature first and are thickened by the slight +pushing together of the ends, so that they taper from the lump to the +unchanged wall. Upon blowing this joint, these thickened walls blow out +with the lump, but as they are thinnest next the unchanged tube, they +stiffen there first. Then as the thicker parts are still hot, these blow +out more, and with the lump make a more or less uniform wall. By this +first operation most of the lump will have been removed, provided it was +not too large at first, and the tube was hot enough when it was blown. +Beginners almost invariably have the glass too cool here, and find +difficulty in blowing out a satisfactory bulb. Under such circumstances +the lump will be scarcely affected by the operation. + +During the shrinking of this bulb, the thinner parts of course are the +first to reach the softening point, and thus contract more than the +thick parts, so that practically all of the lump can be absorbed, and a +uniformly thickened part of the tube left as in _e_. When this is just +accomplished, the second bulb must be blown during one or two seconds, +and the tube then drawn out as described, so as to change the bulb to a +tube. The drawing must proceed with care: portions nearest the unchanged +tubes are the first to reach the proper diameter, and must be given time +to just set at that point before the center of the bulb is finally drawn +into shape. The drawing is perhaps best done intermittently in a series +of quick pulls, each drawing the tube perhaps 1/16 inch, and each taking +place as the thumbs and first fingers grasp the tube for a new turn in +the rotation. If the tube is not rotated during the blowing, the bulbs +will be lop-sided and it will be impossible to get a joint of uniform +wall-thickness; if rotation is omitted during the drawing, the tube +will almost invariably be quite crooked. + +If the lump still shows distinctly after the operations described, the +cross-section of the tube will be as in _h_, and the tube will be likely +to break if ever reheated at this point after it becomes cold. The +operations _d_, _e_, _f_, and _g_ may be repeated upon it, and it may be +possible to get it to come out all right. + +Care must be taken not to blow the bulbs _d_ and _f_ too thin as they +then become very difficult to handle, and the joint is usually spoiled. +The wall-thickness of these bulbs must never be much less than that of +the original tube. If the joint as completed has thinner walls than the +rest of the tube, it will be more easily broken. It should be remembered +that the length of the finished tube must be exactly the same as that of +the original piece, if the walls of the joint are to be of their +original thickness. Therefore the pushing together during the two +operations _c_ and _d_ must shorten the tube just as much as the final +drawing (_f_ to _g_) lengthens it. + +The interval between the removal of the work from the flame and the +beginning of the blowing must be made as short as possible, or else the +portions next the main parts of the tube will set before they can be +blown out, and cause irregular shrunken areas. + + +EXERCISE NO. 2 + +JOINING TWO TUBES END TO END--SECOND METHOD + +The method described in Exercise No. 1 is very satisfactory for joining +short lengths of straight tubing, but becomes inconvenient or impossible +when the pieces are long or bent, on account of the difficulty in +uniformly rotating such work. In such cases, this second method is +used. It does not usually give as smooth and pretty a joint as the first +method, and takes a little longer. + +The joint is begun exactly as in the first method, and the manipulation +is the same until after the preliminary tight joint (_b_, Fig. 6) is +made. The flame is reduced as usual, but instead of rotating the tube in +the flame, only one part of the circumference is heated, and this is +allowed to shrink thoroughly before blowing. It is then blown gently so +that it becomes a slight swelling on the tube, and the operation +repeated on an adjoining part of the joint. Three or four repetitions of +the operation will usually cover the whole circumference of the joint, +in a small tube, the result being a swelling roughly similar to the +first thick bulb in the first method (_d_, Fig. 6). If all the lumps of +the original joint have not been removed by this operation, it may now +be repeated upon such parts as may require it. The thickness of the wall +in the bulb should be about the same as that in the original tube. The +whole of the expanded joint is now heated as uniformly as may be until +soft enough so that it begins to shrink a little, and the swelling is +gently drawn down to the same diameter as the main tube, as in the first +case. Any irregularities in the finished joint may be corrected by local +reheating, shrinking or blowing as required. + +=Discussion.=--In using this method, especially with larger sizes of +tubing, it is very important to keep the whole circumference of the +joint hot enough during the operation so that it does not crack apart at +the part which has not yet been worked. For that reason the first +heating, shrinking and blowing should be performed as quickly as +possible, leaving the resulting irregularities to be corrected later, +rather than attempting to reblow the same part of the joint several +times in succession until it is satisfactory. Care must be taken in this +as in the first method that the blowing follows immediately upon the +completion of the shrinking and removal of the object from the flame: +delay in blowing will cause shrunken places where the joint meets the +original tubes, on account of the cooling and setting of the glass +before it was blown. Most beginners err in being afraid to shrink the +part of the joint enough before blowing it. On small tubing, the +shrinkage may often extend so far that the inner surface of the shrunken +part reaches the center of the tube. Insufficient shrinking results in +failure to remove the lump formed at the original joint. It is often of +advantage, after blowing out part of the joint, to allow that part a few +seconds to set before going on with the rest, keeping the whole joint +warm meanwhile in or near the smoky flame. This helps to prevent the +twisting of the joint, or other distortion incident to the handling of a +piece of work of awkward shape. + +In making a joint on a very long or heavy piece by this method, it is +often advantageous to attach a piece of rubber tubing to the open end, +hold the other end of this tubing in the mouth during the process, and +blow through it, rather than attempt to bring the end of the glass up to +the mouth. This enables one to keep closer watch on the joint, and avoid +drawing it out or distorting it in handling. On the other hand, the +rubber tube is an inconvenience on account of its weight and the +consequent pull on the end of the apparatus, and makes rotation +difficult. + + +EXERCISE NO. 3 + +THE "TEE" TUBE + +The operations involved are two: the blowing of a short side tube on a +piece of tubing, and sealing another piece of tubing on this, by what is +essentially the second method as just described. + +[Illustration: FIG. 7.--The "tee" tube.] + +The two pieces of tubing to be used each have one end cut square and the +other sealed in the usual manner. The longer of the two is now heated at +the point at which the joint is to be made, until it begins to color the +flame. A small flame is used, and the tube rotated until the flame +begins to be colored, when the rotation is stopped, and only one spot +heated until a spot the diameter of the tube to be sealed on has become +red hot and begun to shrink. This is now gently blown out into a small +bulb, as in _a_, Fig. 7, and it will be noted that this bulb will have +walls tapering from the thick walls of the tube to a very thin wall at +the top. The sides of this bulb, below the dotted line, are to form the +small side tube to which the main side tube is to be sealed. The top of +the bulb is now softened by directing a small flame directly upon it, +and as soon as it shrinks to the level indicated by the dotted line, it +is removed from the flame and quickly blown out to form a thin bulb, as +indicated in _b_, Fig. 7. This will usually be so very thin that a +stroke of the file or glass-knife will break it off at the dotted line, +leaving the side tube, to which the short piece of tubing is now sealed +according to the second method (Exercise No 2). In doing this, care is +taken to direct the flame partly on the main tube in the two crotches, +so that both tubes blow out a little and give space for the gases to +turn in, as indicated in _c_, Fig. 7, and at the same time increase the +mechanical strength of the job. On the other hand, care is taken not to +deform the main tube, and not to produce such a bulge or bulb at the +joint as will prevent the finished tube from lying flat on a table. + +=Discussion.=--Most beginners tend to err in the first steps of this +operation, by blowing too hard and too long when blowing out the little +bulb. The result is a large, very thin bulb, which breaks off in such a +way as to leave a hole in the main tube, occupying nearly half the +circumference of the tube at that point, instead of the neat side tube +which they should have. It is not difficult to seal a tube on this side +tube, but it is very difficult to seal a tube into a hole in another +tube. Care should be taken here, as in the two previous exercises, that +the lump obtained at the joint when the two tubes are put together is +made as small as possible, and reduced if possible by gently drawing on +the side tube as soon as the tubes have actually joined. It is much +easier to prevent the formation of a lump at the joint than it is to +remove the lump after it is formed. The remarks previously made about +blowing quickly after removing the work from the flame apply here with +especial force. A "tee" tube, from its very nature, is exposed to a good +many strains, so care must be taken that the walls of the joint are of +uniform thickness with the rest of the tube. + +The beginner will find it easiest to make this tube out of two pieces of +the same tube, about 1/4 inch in diameter. Larger or smaller tubing is +usually more difficult. If tubing much more than 1/4 inch is used, the +whole joint, including part of the main tube, must be heated nearly to +the softening point at the close of the operation, and well annealed, as +described in Chapter 1 (page 3) or it will be almost certain to crack. +In the larger sizes of tube it will be necessary to heat the whole +circumference of the main tube frequently during the operation, to +prevent it from cracking. + +In sealing a small tube on the side of a large one, it is usually +advisable, after warming the spot where the joint is to be made, to +attach a small drop of glass to the tube at that point, and direct the +flame upon that, thus supplying at the same time both a definite point +to be heated and an extra supply of glass for the little side tube which +is desired. In this way it is also easier to blow out a side tube with a +sufficiently small diameter. If the diameter of this tube should be much +greater than that of the small tube, the latter may be enlarged with a +carbon or a flanging tool. + + +EXERCISE NO. 4 + +TO JOIN TWO TUBES OF DIFFERENT DIAMETERS + +In this case the first method (Exercise No. 1) is to be used whenever +possible, as it gives a much smoother joint than the second method. The +directions given will describe the adaptation of this method to the +problem: if the second method must be used on account of awkward shape, +etc., of the work, the modifications required will be obvious to any one +who has learned to make the joint by the first method. + +After sealing or corking one end of the larger tube, the other end is +drawn out to form a tail as described on page 9, taking care to have the +tube uniformly heated, and to draw the tail rapidly enough so that the +cone is short, as indicated in _a_, Fig. 8. The tube is now rotated, a +small flame directed against the cone at right angles to an element of +it, and it is allowed to shrink a little, as indicated in _b_, Fig. 8, +so that its walls will thicken. When the tail is cut off, at the dotted +line, the diameter of the opening and the thickness of the walls at that +point should correspond with the dimensions of the tube to be sealed on. +As the glass is hot, the scratch for cutting it must be made with a file +(moisten the edge!), and it often will not break square across. Before +proceeding to seal on the small tube, any large projections on the cut +end are best removed, by warming the cut surface a little, directing the +small flame upon each projection in turn and touching it with a warm +scrap of glass. It will adhere to this and may then be removed by +rotating this scrap a little so as to wind up the projection on it, and +then drawing it off, while the flame is still playing on the spot. This +must be done rapidly and care taken not to soften the main part of the +cone. + +[Illustration: FIG. 8.--Joining two tubes of different diameters.] + +The large tube is now taken in the left hand, the small one in the +right, the ends heated and joined in the usual manner, taking care not +to get any larger lump at the joint than necessary. A small flame is now +directed on the cone at right angles to its elements as before, and the +tube rotated so as to heat the whole circumference. The flame should be +just large enough to heat the whole of the cone. As the latter shrinks, +the lump at the joint is brought into the edge of the flame, and it and +a very little of the small tube allowed to shrink with the cone. + +When well shrunk and heated to blowing temperature the joint is removed +from the flame and blown gently with careful rotation, pushing the tubes +together a little when the blowing is about finished, so that the cone +becomes a short thick half-bulb, as shown in _d_, Fig. 8. This +corresponds to the first thick bulb in the first method (_d_, Fig. 6), +and is treated similarly. It is again heated and shrunk, taking care not +to involve either the large tube or the small one in the shrinking, +blown quickly to about the same shape as before, (_d_, Fig. 8), and then +gently drawn out into a smooth cone (_e_), exactly as in the first +exercise. Care should be taken not to draw too rapidly or too far, as +then the resulting cone (_f_) is weaker than it should be, and does not +look well. + +=Discussion.=--The beginner will find that this operation is best +learned on two tubes which are not too nearly of the same diameter. A +tube about 5/8 inch in diameter and one a little less than 1/4 inch will +be suitable. Both should have moderately heavy walls (1/16 inch or a +trifle over for the large tube, and a trifle less for the small one) but +the large tube should not be too heavy or else it will be hard to +prevent melting down too much of the small tube, and getting this drawn +out too thin during the process. One of the troublesome features of this +exercise is the difficulty of rotating two tubes of different diameters +with the same angular velocity, so as not to twist the joint. Another +difficulty is found in getting the cone uniformly heated to blowing +temperature without overheating and overshrinking the small tube. The +reason for this is obviously the much greater circumference of the cone, +especially at its large end, so that relatively much less of it is being +heated at any time. The beginner is also inclined to start with too long +a cone, or else heat so much of the large tube that part of its glass is +included in the cone, with the result that in order to get the right +wall-thickness the cone must be made too long (_g_, Fig. 8). This does +not look well, and usually will be irregular in shape. + + +EXERCISE NO. 5 + +TUBE FOR CONDENSING SULPHUR DIOXIDE + +This is useful as a test of mastery of the preceding exercise. A piece +of 3/16 or 7/32 inch tubing is joined to each end of a piece of tubing +5/8 by about 5 inches, and two constrictions made in the large tube, by +the method described on page 10. The small tubes are then bent in the +same plane, as shown, and their ends fire-polished (Fig. 9). + +[Illustration: FIG. 9.--Tube for condensing sulphur dioxide.] + + +EXERCISE NO. 6 + +BULB AT THE END OF A TUBE + +For this exercise tubing of 1/4 inch diameter and moderately strong +walls is selected. A tail is drawn out on one end of the tube, and a +piece of tubing about nine or ten inches long is cut off. The tail +should be carefully drawn in the axis of the tube, and in the same +straight line with it, as it is to be used as a handle in assembling the +glass for the bulb. This tail must be long enough so that it can be +conveniently held in the left hand, as described on page 13, and rotated +about the same axis as the main tube. Holding the main tube in the right +hand and the tail in the left, the tube is rotated in a large flame so +that a piece of it, beginning where the tail stops and extending about +an inch to the right, may be uniformly heated to the highest temperature +at which it can be kept in shape. As soon as this temperature is +reached, the tube is removed from the flame, continuing the rotation and +taking care not to draw out the heated part, and gently blown. The +rotation is carefully continued during the blowing, holding the tube in +approximately a horizontal position. As soon as the tube has expanded a +little the tail is pushed gently toward the main tube, continuing the +gentle blowing. If this is properly done, the heated piece of tube will +become a short bulb of about double its original diameter, and about the +same wall thickness as the original tube. It will have somewhat the +appearance of _a_, Fig. 10, when properly manipulated. + +[Illustration: FIG. 10.--Blowing a bulb on the end of a tube.] + +The tube is now reheated as before, taking care this time that the +heating extends over all that part of the bulb to the right of the +dotted line in the figure, as well as part of the main tube adjoining. +If this heating has been properly placed, when the operation of blowing +and pushing together is repeated the result will be to lengthen the bulb +into a uniform cylinder, as shown in _b_, Fig. 10. Otherwise the result +will be a series of bulbs, as in _c_, Fig. 10, separated by thickened +ridges which will be almost impossible of removal later and will +disfigure the final bulb. This operation of heating, blowing and pushing +together is repeated several times, until the cylinder becomes as long +as can be conveniently handled (about 1-1/4 inches to 1-1/2 inches). If +more glass is needed than is then contained in the cylinder, the latter +may now be heated as a whole, and blown and pushed gently into a shorter +cylinder of a slightly greater diameter, and more glass then added as +before. + +When enough glass has been collected for the bulb, it is all well heated +and blown gently a couple of times, pushing the mass together as +required, until a thick bulb like _d_, Fig. 10, is obtained. The tail +must now be removed at the point indicated by the dotted line. To do +this, a very fine flame is directed on the point where the tail joins +the bulb, and the tube well rotated as the glass softens at that point. +When sufficiently soft, the work is raised a little, so that the flame +instead of striking the glass squarely at the point indicated passes +below and tangential to it. The tail is now drawn off slowly, continuing +the rotation, raising the work just out of the flame whenever the thread +of glass drawn off becomes too thin, and lowering it again to the point +where the flame just touches it when the glass stiffens a little. By +this means the tail may be drawn off without leaving an appreciable lump +behind, as indicated in _e_ and _f_, Fig. 10. When as much of the extra +glass has been removed as is practicable, the flame is brought to play +squarely upon the little lump left, the last of the tail removed, and +the lump heated and gently blown to a small excrescence on the main +bulb. The whole end of the latter is now heated until it begins to +shrink a little, and gently blown to make it uniform in thickness. The +whole bulb is then heated in a flame of the proper size, so that it all +may shrink to about two-thirds of its diameter. The flame must be very +carefully chosen and directed, so as to shrink all the bulb, right up to +the main tube, but not soften the latter. As soon as this stage is +reached, the bulb is removed from the flame, continuing the even +rotation, and blown to the desired size, preferably by a series of +gentle puffs following one another at very short intervals. During the +blowing, the main tube is held in a horizontal position, and any +tendency of the bulb to fall out of line is corrected by the rotation. +If the shape of the bulb or its size are not satisfactory, it may be +shrunk again and reblown. Such shrinking should begin in a large yellow +flame, with just enough air to give it direction. The amount of air may +be gradually increased as the bulb shrinks and the walls become thick +enough to bear it without collapsing. If the bulb starts to collapse at +any time, it must be immediately blown enough to regain its convex +surface, before the shrinking proceeds further. + +=Discussion.=--In collecting the glass for the bulb, enough must be +gathered to give the walls the desired strength. Since the area of a +sphere is proportional to the cube of its diameter, it is evident that +doubling the size of a bulb diminishes the thickness of its walls to a +very large extent. The limit of diameter for a strong bulb on ordinary +1/4-inch tubing, collecting the glass as above, is about 1-1/2 inches, +and the beginner will do well not to blow his bulbs more than an inch in +diameter. + +The collection of the glass is one of the most important parts of the +process. If the mass of glass be twisted, furrowed or ridged, or +lop-sided, it is very difficult to get a good, even, spherical bulb, no +matter how many times it is shrunk and blown. The greatest care should +therefore be taken to get a uniform cylinder, on the same axis as the +main tube; and to this end the rotation of the tube must be carried on +very evenly. For method of holding the tube, see page 14. + +If a very large bulb is required, it will often be economical to seal on +the end of the tube a short piece of a large tube, provided with the +proper tail, and use the glass in the large tube for the bulb instead of +attempting to collect it from the small tube. In this case part of the +small tube will usually be included in the bulb, so that the joint comes +in the latter, and not where it joins the tube. As the amount of glass +carried on the end of the tube increases in weight and size the +difficulties of heating it uniformly, keeping it in the proper position +and handling it increase rapidly. + +In collecting glass, it is usually best not to leave the part of the +cylinder next the tube with too thick walls. This is always the coolest +part during the preparation for blowing the bulb, consequently it does +not get blown out, and causes an ugly thickened appearance on that end +of the bulb. + +If the bulb grows too long or pear-shaped, it may be easily shortened by +heating to the blowing temperature, and then blowing gently with the +main tube in a vertical position, and the bulb at the top of it. Gravity +will then shorten the bulb nicely. + +The finished bulb should be a nearly perfect sphere, with the axis of +the tube passing through its center, and the portion of the tube +adjoining the bulb must not be distorted, twisted, or blown out. In +order to prevent the distortion of the tube, care must be taken that it +is never heated quite to its softening point during the process. + + +EXERCISE NO. 7 + +BLOWING A BULB IN A TUBE + +The tube is selected and one end closed as in the previous exercise, but +it should be cut a little longer, say about twelve inches. Beginning at +a point about four inches from the closed end, glass is collected and +blown into a thick-walled bulb, exactly as in the previous exercise. +Greater care must be taken, however, that the cylinder collected and +this thick bulb are of uniform thickness and set squarely in the axis of +the tube. Instead of removing the tail, the bulb must be blown in this +case with both pieces of tubing attached, and care must be taken that +they "line up" properly, _i.e._, are in the same straight line, and that +this line passes as near as may be through the center of the bulb. The +tube is held in approximately horizontal position during the blowing of +the bulb, as in the previous case, and especial care taken with the +rotation. Both pieces of tube must of course be rotated at the same +rate, and their softened ends must be kept at exactly the proper +distance from each other, so that the bulb may be spherical and not +elongated. If the blowing of the bulb be quickly and accurately done, it +may usually be completed before the glass is quite set, and the +alignment of the two tubes may then be rectified while looking straight +through the bore of the tube. + +=Discussion.=--The two points of greatest importance are the collection +of the glass, and the uniform rotation of the tube. A larger tube may be +sealed in the middle of a small one when a large amount of glass is +necessary. The piece of tubing used for the exercise must be long enough +so that the fingers may be kept on a cool part of the glass without +getting uncomfortably near the ends of the tube. It should not be any +longer than necessary, however, as the extra weight and length make the +manipulation of the hot glass more difficult. + +When a string of bulbs are required on the same tube, a piece of glass +18 inches long may be used at the start, and the first bulb made near +the closed end, as described. Each succeeding bulb will then be in plain +view during the blowing, and when the open end becomes too short for +comfort, it may be dried out, cut off, and another piece joined to it, +starting as in the first method (Exercise No. 1), but instead of drawing +out the thick bulb to a tube, it is made part of the glass collected for +the next bulb. If the string of bulbs becomes awkward to handle on +account of its length and weight, it may be made in several parts and +these later sealed together by the second method, preferably blowing +through a rubber tube attached to the open end, as described on page 22. + +Very neat small bulbs may be made on tubing of a diameter of 3/16 inch +or a little less, but the beginner is advised to start with tubing of +about 1/4 inch diameter. The use of tubing with too thick walls usually +produces bulbs which are thick-walled at the point where they leave the +tube, but inclined to be too thin at the point of maximum diameter +(perpendicular to the axis of the tube) where most of the strain comes +and strength is particularly needed. + + + + +CHAPTER IV + +ADVANCED EXERCISES + + +EXERCISE NO. 8 + +SEALING A TUBE THROUGH ANOTHER TUBE + +_First Method--Making a Gas-washing Tube_ + +This first method can be used whenever one can work through an open end +opposite to the end of the tube where the joint is to be made. To +illustrate it, take a piece of rather thin-walled tubing, about 3/4 inch +in diameter, and some pieces of rather strong tubing a little less than +1/4 inch in diameter. Draw off the large tube in a short cone, then draw +off the tail as in the making of the bulb on the end of the tube, blow +out the little lump slightly, shrink the whole cone a little and blow +gently to form a rounded end like that on a test-tube, with walls about +the thickness of those of the rest of the tube. Cut this tube to a +suitable length, say about six inches, and provide two corks which will +fit the open end of it. Now cut a piece of the small tubing of the +proper length to form the piece which is to be inside the large tube. +For practice purposes, this piece should be about an inch shorter than +the large tube. Flange one end of this tube a little, and anneal the +flange well in the smoky flame. Bore one of the corks so that a piece of +the small tubing will fit it, and cut a couple of notches in the side of +this cork so that air can pass between it and the glass. Pass a short +piece of the small tubing through this cork, and attach the flanged +piece of small tube to this by means of a short piece of rubber tubing, +so that when the whole is inserted in the large tube it is arranged as +in _a_, Fig. 11. The piece of glass tubing projecting out through the +cork is now cut off so as to leave an end about 1/2 inch long when the +cork is firmly seated and the inner tube pushed into contact with the +center of the end of the large tube, as shown in the drawing. Care +should be taken that the little rubber tube which joins the two pieces +is arranged as in the figure; _i.e._, most of it on the piece of tubing +which passes through the cork, and very little on the other piece, so +that when the cork is removed after the small tube has been sealed +through the large one, the rubber tube may easily come with it. Select a +short piece of the small tubing of suitable length for the piece which +is to be on the outside of the large tube as a continuation of the +piece inside, and another piece for the delivery tube. A small bulb may +be blown in the latter at a point about 2-1/2 inches from the closed +end, and the open end cut off about 1-1/2 inches from the bulb. A cork +or cork-boring of suitable size to stopper the small tube is prepared, +and laid ready with the other (unbored) cork for the large tube. + +[Illustration: FIG. 11.--Gas-washing tube.] + +When everything is in readiness, the rounded end of the large tube is +slowly heated until it softens and joins firmly to the small tube +inside. After it has shrunk down well, it is blown out to its original +size, placing the whole end of the large tube, cork and all, in the +mouth. Now with a fine-pointed flame the glass covering the end of the +small tube is heated to the softening temperature, and then is blown out +to an excrescence by blowing on the end of the small tube which passes +through the cork. The end of this excrescence is heated and blown off in +the usual way, so as to leave the small tube sealed on the inside of the +large one and opening through it into this short tube which has been +blown out. The end of the small tube which passes through the cork is +now closed with the cork prepared for it, and the short outer tube is +joined to the tube that has just been blown out, so that the joint +appears like _b_, Fig. 11. Use the first method (Exercise No. 1) for +this joint. Reheat the whole of the end of the tube nearly to the +softening temperature, anneal it a little, and allow to cool a few +seconds until well set. Now remove the cork, short glass tube and rubber +tube from the open end of the large tube and insert the solid cork in +their place. Warm the joint and the whole of that end of the tube again +carefully up to about the softening point, then seal on the side tube +for the delivery of the gas in the usual way, taking care that the whole +of the end and the joint are kept warm meanwhile. When thoroughly +sealed, the delivery tube is bent up parallel to the tube through which +the gas enters, and then out at right angles to it, as shown in _c_. The +whole of the end of the tube is now cautiously reheated and then cooled +slowly to anneal it. + +The cork may now be removed from the open end of the large tube, this +end heated in a large flame, caught together with a scrap of glass +tubing and drawn off into a cone so that the base of the cone is about +opposite the end of the inner tube. The lump of glass is drawn off the +point of this cone and it is reblown to form a rounded end, as +previously described. + +After this cools, the tube through which the gas enters may be heated at +the proper point and bent at right angles to form the finished apparatus +as shown in _d_. The ends of the small tube are cut off square and +fire-polished. + +=Discussion.=--After the joint has once been made, great care must be +taken that it is kept hot during all the subsequent manipulations, and +if it becomes somewhat cool at any time it must be reheated very slowly. +It is obvious that the rate of heating and cooling of the inner tube +will be slower than that of the outer tube, and this will readily +produce stresses which tend to crack the tube at the joint. The amount +of heating and cooling which such a joint will stand depends upon its +form. The beginner should examine such a joint on regular factory-made +apparatus, and note the uniformity of wall-thickness and the "clean-cut" +appearance of the joint, as a model for his imitation. A ragged joint, +where the line of joining of the inner and outer tubes wavers instead of +going squarely around the tube, is almost sure to crack during the +cooling and heating unless extra precautions are taken with it. The +presence of a small lump of glass at any point on the joint affords an +excellent starting place for a crack, as do also the points on a ragged +joint where the inner tube comes farther down on the outer tube than at +other points. + +In order to insure a joint which is square and not ragged, it is +essential that the angle between the inner and outer tubes at the joint +be very nearly a right angle. For this reason the two tubes should not +be of too near the same size, or if this cannot be avoided, a small bulb +should be blown on the end where the joint is to be made. If this bulb +be made with the same wall-thickness as the rest of the tube, and +somewhat pear-shaped, it may be drawn out to the same size as the rest +of the tube, if necessary, after the joint has been made. + +This method is used wherever possible in preference to the second method +(Exercise No. 9), as it is easier to get a good joint with it. It may +also be used where it is desired to seal the tube through the side of a +tube, or for a tube sealed through the wall of a bulb, as in a Geissler +potash bulb or similar apparatus. Where there is not space to join the +inner tube to the blowing tube by a rubber tube, this joint may be made +with a small piece of gummed paper, which can readily be broken when +desired. + + +EXERCISE NO. 9 + +SEALING A TUBE THROUGH ANOTHER TUBE + +_Second Method--Making a Suction Pump_ + +Select a piece of tubing 3/8 to 1/2 inch in diameter, with walls about +1/16 inch or a little less in thickness, heat a place about 4 inches +from one end and draw it out so that when cut off at the proper point it +will look like _a_, Fig. 12; the open end of the drawn out part being +small enough to slip inside another piece of the original tube. A small +thick-walled bulb is now blown as indicated by the dotted lines, and +annealed. A piece of the original tubing is now prepared, 7 or 8 inches +long, with one end cut square off and the other closed. A piece of +1/4-in tubing about 2 inches long, and drawn out at one end to a tail +several inches long is also prepared, to form the inlet tube for the +air. Another piece of the 3/8-inch tube is prepared, about 4 inches +long, and provided with a tail drawn out as indicated in _b_, so that +when cut off at about 2-1/2 or 3 inches from the main tube its inner +diameter may be slightly less than that of the narrowest point of the +tube _a_. A small thick-walled bulb is blown at the point indicated by +the dotted lines, and annealed. Care must be taken in drawing the +capillary and blowing the bulb in both _a_ and _b_ that the capillary +tubes are in the axis of the main tube, and in the same straight line +with it. + +[Illustration: FIG. 12.--Suction pump.] + +The open end of the 8-inch piece of tube and the bulb of the piece _a_ +are now warmed together, the end of the tube only moderately and the +bulb to about its softening temperature. The tube _a_ is now inserted in +the open end of the large tube, and the bulb softened with a suitable +flame and pressed into good contact with the tube. It is then reheated, +including the joint, blown a little and pulled out to form a straight +tube in line with the main tube. By warming the joint a little, and +proper rotation, the capillary may be brought into the same straight +line with the rest of the tube. + +Keeping this joint hot, a place about an inch from it on the tube _a_ is +warmed, and the piece of 1/4-inch tubing previously prepared is sealed +on at that point. The joint is then well annealed and allowed to cool. + +The tube _a_ is now cut at such a place that when _b_ is inserted in the +open end the point will come near the end of the constriction of _a_, as +shown in _c_. Care is taken to get a clean square cut. The side tube is +now cut off about an inch from the main tube and corked. Tube _b_ is +sealed into the open end of _a_, in the same way as _a_ was sealed into +the large tube, and the joint carefully annealed. + +=Discussion.=--As in the first method, the secret of success lies in +getting a square joint, and having the inner tube leave the outer one at +nearly right angles. All the remarks about annealing, lumps, etc., made +under the previous method apply here. + +This method may be applied in sealing a small tube into the end of a +large one, the latter being either drawn to a cone and cut off at the +desired diameter, or else given a rounded end like a test-tube and a +hole the proper size blown in the center of it. A suitable thick-walled +bulb is to be blown on the small tube, as in the case described above. +This method is also used in making the Kjeldahl trap (_a_, Fig. 13), the +small tube to be inserted being first drawn, the thick bulb blown at its +point of union with the main tube, and then the small tube bent and cut. +The large bulb is best made with rather heavy wall, being either blown +in the middle of a tube, and one piece of the tube drawn or cut off, or +else made on the end of a tube. In the latter case a drop of glass must +be put on the point where the joint is to be, so as to get a hole of the +proper size with enough glass around it to prevent it from growing +larger when it is heated. The author prefers to blow the bulb in the +middle of the tube, draw off one end of the bulb, and blow out the +desired hole where the tube was drawn off. The whole bulb must generally +be reheated and blown a little at the end of the process, and well +annealed. + +[Illustration: FIG. 13.--_a_, Kjeldahl trap; _b_, suction pump on +smaller tubing.] + +The suction pump can also be made on 1/4-inch tubing, and one joint +saved if desired, by constricting the tube to form the raceway for the +water and air, as shown in _b_, Fig. 13. (See page 10 for method.) But +it is more difficult to make a square joint on such small tubing. + + + + +CHAPTER V + +MODIFIED METHODS AND SPECIAL OPERATIONS + + +CAPILLARY TUBING + +This is commonly used in many forms of apparatus for gas analysis, and +one is often called upon to join two pieces or to make a tee on it. The +methods are nearly the same as with other tubing, except that more care +and patience are required. The work must be done much more slowly on +account of the thickness of the walls, and open ends of the tube must +always be enlarged before joining them to anything. This is best done by +carefully sealing the end and then blowing, with several suitable +reheatings, to form a pear-shaped bulb as in _a_, Fig. 14. The end of +this is then heated and blown off, and the piece is ready to be joined +to another similar end, or to a piece of ordinary tubing if desired. The +joints are best not blown too much, as thick walls shrink very slowly. +Much may be done by gently pushing the tube together or pulling it apart +in the flame, to remove lumps and irregularities. It is necessary that +the bore of the joint be approximately that of the main tube, and care +must be taken that the latter is not constricted at the point where the +joint begins. + +[Illustration: FIG. 14.--Capillary tubing.] + +Especial care must be taken to warm the tube slowly when starting and +cool it slowly when through, as the thick walls frequently crack if not +carefully handled. For this reason the whole neighborhood of the joint +must be heated somewhat so that there may not be stresses set up between +the heated and unheated portions. + +In making the tee (_b_, Fig. 14) the inability to blow the joint makes +itself decidedly felt, but if the side tube is properly enlarged as +previously described, a good joint can be made by alternately pulling +and pushing on the end of the side tube, and shrinking well. + +Very fine capillary tubing should be blown with a rubber bulb instead of +the mouth, so as not to get moisture into the tube. The rubber bulb may +also be used to advantage on some of the coarser capillary tubing. + +When a bulb is to be joined to a piece of capillary tubing, the joint is +preferably made before blowing the bulb, and will then be taken up a +little way on the bulb during the process. Care must of course be taken +not to constrict the capillary; the pear-shaped bulb blown on the end +(_a_, Fig. 14) may well extend back a little further than usual into the +tube so as to prevent this. If a bulb is required in the middle of a +capillary tube, the latter is usually best cut and a piece of ordinary +tubing of suitable size sealed in to provide material for the bulb. + + +GLASS ROD + +Joints, tees, etc., in glass rod are made on the same principle as in +tubing, except that of course they cannot be blown, and regularity must +be obtained by accumulating a small mass of uniformly heated glass, and +then drawing it to a suitable rod, on the same principle as Exercise No. +1. + +Great care must be taken in heating and cooling this, as in the case of +the capillary tubing, and for the same reasons. + +By joining pieces side by side, pressing with carbon plates or a plate +and a rod, and other suitable manipulations, stirrers, spatulas, and +other objects may easily be made from rod, and its manipulation is +relatively easy on account of the fact that one does not have to worry +about the bore of the tube. But the same general rule about not having +thick and thin spots in contact, and making all changes in diameter on a +taper if possible instead of abruptly, applies here. Thick pieces will +cool and contract at different rates from thin ones, and cracks are +likely to develop where they join. Work which has been formed with any +tool must always be heated to the softening point afterward before +allowing it to cool in order to remove the stresses caused by the +contact of the tool with the hot glass. + +When it is necessary to join a piece of rod to the side of a piece of +tubing, the end of the rod is made very hot while the wall of the tube +at the spot desired is heated to just below the softening temperature. +The rod can then be pressed into firm union with the tube and drawn a +little to remove the excess of glass without deforming the tube. + + +MENDING STOPCOCKS + +=Mending the Plug.=--The plug of the stopcock occasionally falls out and +is broken. If the break is in the main part of the plug, nothing can be +done except to search for a spare plug of suitable size and grind it to +fit, as described below. If only the little cross-piece at the end is +broken off, it can easily be replaced. In most ordinary stopcocks the +plug is solid, but the little handle is hollow. What has been said above +regarding care in heating and cooling glass rod applies with especial +force here. It is usually best to wind the whole of the plug with +several thicknesses of asbestos cord, leaving bare only the end where +the handle is to be joined. This diminishes the danger of cracking the +plug by too rapid heating, and also makes it more comfortable to hold. A +piece of rather thick-walled tubing of suitable diameter is chosen, +drawn out so as to have a suitable taper (taking care to heat enough of +the tube so that the capillary tail has good wall-thickness and +strength), and then a corresponding taper is drawn to form the other +side of the handle. The result is shown in Fig. 15, _a_. The capillary +tail is now heated and bent back to form a handle which will be in the +same straight line as the axis of the plug (_b_, Fig. 15) and the main +part of the tube drawn off at the dotted line, making a neat seal at +that point. The broken end of the plug is now slowly warmed in the smoky +flame, the heat gradually increased by a gentle stream of air from the +bellows, and the point at which this handle is to be attached finally +brought to the temperature at which the glass flows freely. In the mean +time, the little handle has been warmed almost to the softening point. +It is now quickly pushed into place (_c_, Fig. 15), taking care that its +axis is parallel to the hole in the plug, and then drawn away from the +plug just enough to make a graceful neck instead of the bulging one +indicated by the arrow in the figure. With a fine pointed flame the +little tail is now drawn off at the point indicated by the dotted line +(_c_, Fig. 15) and the whole carefully annealed. If necessary, the +handle can be blown a little before the tail is removed. Local heating +and blowing at the point where the handle joins the plug is often +necessary in order to make a smooth job. + +[Illustration: FIG. 15.--Stopcock plug.] + +=Regrinding.=--This is sometimes necessary to make stopcocks tight, when +the grinding has not been properly done in the factory. For this, a very +little fine flour of emery or carborundum is the best and quickest. If +this is not at hand, some clean sand may be ground in an agate mortar, +and if possible sieved. Only material which passes the 100-mesh sieve +should be used. It will be ground still finer in the process. For the +final polishing, a little infusorial earth or even kaolin will do. + +The surface to be ground is moistened with water and dusted over with a +little of the abrasive. The plug is now inserted in the stopcock, and +turned with a gentle pressure. This turning should be in the same +direction for several revolutions, then in the opposite direction for +several more revolutions, etc. As the abrasive becomes finer during the +grinding, a little more may be added if necessary. In general, only a +little grinding will be required, and one small pinch of carborundum or +emery will be ample. The beginner usually grinds too much, and with too +coarse material. As the grinding surface becomes dry, water is added +drop by drop, and the grinding continued until the abrasive seems to be +reduced to an impalpable powder, most of which has been squeezed out of +the stopcock. The two surfaces in the stopcock are usually grinding upon +each other at this stage, and inspection will show whether the contact +between them is uniformly good. If not, the grinding must be continued +with a little fresh abrasive. If contact appears to be good, the +surfaces are ground together for a little with practically no abrasive, +so as to polish them, and the joint is then washed out and tested. + +In grinding in a new plug to replace a broken one, the plug selected +should have practically the same taper as the seat into which it is to +be ground, and should be a very little too large. Care must be taken to +so distribute the abrasive material as to grind mostly on the places +where the plug fits tightly. + +=Sealing on a New Tube.=--It frequently happens that one of the tubes of +the stopcock is broken off close to the cock itself, and a new one must +be joined to the stub of the old one. With care, this may often be +successfully done even where the break is within 1/4 inch of the +stopcock. The first step is to clean and dry the stopcock, remove the +plug, cork the open ends of the stopcock sleeve and the other tube, and +wind a couple of layers of asbestos cord carefully over the sleeve and +the most of the corks which close it. A suitable tube, having as near as +possible the same diameter and wall strength as the one broken off, is +selected and a piece the desired length cut off. The broken end of the +tube on the stopcock is now squared off as well as possible, by cutting +or by heating and drawing off the projections, and the new tube sealed +on, usually with the first method (Exercise No. 1). If the break is very +close to the stopcock, very little reheating and blowing can be done, on +account of the danger of getting the stopcock sleeve out of shape, and +the work must be heated very slowly to prevent cracking. The main +reliance is then placed on making a good joint when the tubes are +brought together, and then drawing out this joint a little, at once, to +get an even wall. + + +CLOSED CIRCUITS OF TUBING. + +In some pieces of apparatus closed circuits of circular or rectangular +shape are required. A similar problem is involved in apparatus like the +ordinary Soxhlet extractor, where a small tube is joined to the side of +a large one, bent to form a siphon, and attached again to a continuation +of the original large tube. The difficulty in all such cases is to +provide for the contraction taking place as the last joint cools. If +part of the circuit has the shape of the letter S, or is a spiral, the +natural springiness of the glass will take care of this. If not, the +side of the circuit opposite to the joint and parallel to it must be +heated also, the two being finally heated together to the softening +point after the joint is completed, and then allowed to cool together. + +To make the last joint, the rest of the tube is made in approximately +the desired form, the two pieces which are to be joined to make the last +joint being just enough out of the desired position to allow them to +pass one another. The final joint is preferably made in the middle of a +straight piece of tube, not at a tee. The two pieces which are to be +joined are bent so as to just pass each other, marked at the right point +with the glass-knife, and cut there, preferably with a small bead of hot +glass. One or both of these tubes are now warmed to the softening point +in such a place that the tubes can be made to meet properly, and the two +cut ends pressed together. They are now warmed in the flame, and joined +together, either by simultaneously warming the opposite side of the +circuit or some other suitable part, so as to allow the two ends to be +pushed together again after they are softened, or by gently touching the +places that do not unite with a hot bead of glass, and using the glass +to fill up the crack where the ends do not quite meet. Care must be +taken not to leave knots or lumps of glass in the finished joint, and +the latter should be well reblown, and if necessary left as a small bulb +or enlargement, rather than have it have too thick walls. + + +SPIRALS + + + +Spirals of glass tubing are probably best made free-hand before the +blow-pipe, unless one has a great many of them to make, and extreme +accuracy is desired. To begin with, a piece of tubing of the desired +size (say 3/16 inch in diameter) and a convenient length (about two +feet) is selected, one end closed, and a right-angle bend made about six +inches from the closed end. Holding the closed end in the left hand and +the long open one in the right, the spiral is begun. The short closed +end is to be parallel to the axis of the spiral, and preferably in that +axis. Using a moderate-sized flame, of somewhat yellow color, and taking +care to heat the whole circumference of the tube, the long open end is +wound little by little into a spiral having the short end _a_ (Fig. 16) +as an axis. The bend at _b_, where the tube changes from the radius to +the circumference of the circle, must be rather short, but the tube must +not be flattened or constricted here. Especial pains is to be taken +with the first turn of the spiral (_b_ to _c_, Fig. 16), as the shape of +this determines the diameter of the whole spiral, and serves as a guide +for the rest of the turns. The winding of the tube is best accomplished, +after a portion has been softened, by slowly turning the short end _a_ a +little about its own axis, while the long open end remains where it was. +This winds the tube into a spiral, just as if there were a solid +cylinder in the center of it, and this cylinder was being turned about +its axis, and was winding up the soft glass upon its circumference. As +the cylinder is not actually there, the curve of the turns must be +carefully estimated by the eye, so that the spiral may be uniform and +moderately smooth. When the original piece of tube has been used up, +another piece is sealed on to the open end, and the operation continued +as far as may be required. + +[Illustration: FIG. 16.--Making a spiral.] + + +GROUND JOINTS + +It is sometimes required to join two pieces of tubing end to end, by +means of a ground joint. Whenever possible, a regular sealed joint +should be used instead of this ground joint, as it is quicker to make, +and more certain to be tight. Where a ground joint is necessary, +however, it is best made in the conical form shown in _c_, Fig. 17. If +the wall of the tube to be used is not very thick, it is thickened by +collecting glass as for a bulb on the ends of two tubes (Exercise No. +6), and drawing to form cones of suitable shape (_a_ and _b_, Fig. 17) +and of such relative sizes that a will slip about half way into _b_. In +order to make _a_ straight and give it the proper angle, it may be +rolled when hot, upon a hot plate of carbon. Blowing during this rolling +is often helpful to remove depressions. After _b_ has been drawn to +nearly the proper size and shape, it may be smoothed by the use of a +small carbon rod, held inside it at a slight angle, or better by the use +of a truncated hexagonal pyramid of carbon, whose edges have the proper +slant to make the inside of the cone right. The proper taper for both +these cones is the same as that used in stopcocks of similar size. The +hexagonal carbon can easily be made by carefully filing down an electric +light carbon, and finally impregnating it with paraffin or beeswax, and +is extremely useful wherever a conical surface has to be formed from the +inside of a tube. + +[Illustration: FIG. 17.--Ground joint.] + +The tail is allowed to remain on piece _a_, as a sort of guide in +grinding, and should therefore be in the axis of the tube and have +rather thick walls. Grind with emery or carborundum, as described under +a previous head. (Regrinding plug for stopcock.) If many such joints are +to be made, it will pay to have a little sleeve of brass made with the +proper taper, and rough down the plug _a_ in it to about the proper +size, while _b_ is roughed down by means of a brass or iron plug having +the same taper. This prevents excessive grinding of one-half of the +joint in order to remove a defect in the other half, and is the method +commercially used in making stopcocks. + + +SEALING IN PLATINUM WIRE + +Very often it is necessary to seal platinum wire into the wall of a +tube. Professional glass-blowers usually use a special sort of glass +("Einschmelzglas") which is usually a lead glass, and is made of such +composition that it has the same or practically the same coefficient of +expansion as platinum. A little globule of this glass is sealed into the +tube in such a way that it joins the platinum to the glass of the tube. +To do this, the small globule of special glass is fused on the platinum +wire at the proper point and the tube into which the wire is to be +sealed is heated and a small tail drawn out at the point where the wire +is to be inserted. The lump of the special glass should be from 3/32 to +1/8 inch in diameter, and the tail drawn on the tube should have a +slightly less diameter at the point (about 1/8 inch or less from the +tube) where it is cut off. There are now two ways of sealing in the +wire. (1) The wire with the globule of glass is placed inside the tube +and the latter revolved until the end of the wire sticks out of the cut +tail (_a_, Fig. 18). The latter is now gently heated, and the two glass +surfaces fused together, taking care to use only the end of the hissing +flame, if the special glass contains lead. (See Chapter I, page 1.) The +whole circumference of the tube is then heated and annealed carefully. +(2) The end of the wire which is to be outside the tube is attached to +the end of a thin scrap of glass, by heating the glass and thrusting +the wire into it a very little way. Using this piece of glass as a +handle, the wire is inserted in the cut tail (_b_, Fig. 18) and the +globule brought near to the end of the tail. (If the main tube is cold, +it must of course first be warmed.) With the end of the hissing flame, +as in the first method, the globule of glass is melted and the end of +the tail softened. The wire is now pushed into place, the handle removed +by heating the end and withdrawing it, and the tail reheated a little if +necessary to make it shrink back into line with the walls of the tube. +The whole circumference of the tube is heated at that point and annealed +as usual. + +[Illustration: FIG. 18.] + +The use of this special glass is not absolutely necessary if the +platinum wire is small (1/4 millimeter or less in diameter), and in fact +it is often better in such cases not to use it, unless the apparatus is +to be subjected to a very high vacuum. On small tubes, especially, it is +undesirable to use the special glass, as a lump of it will usually cause +the tube to crack on cooling. When such glass is not at hand or is not +to be used, the procedure is altered somewhat. The tail which is drawn +out is very fine, having only a sufficient diameter so that when it is +cut off the wire can be inserted in it. Such a fine tail is readily made +by heating a small spot on the tube, touching it with a warm platinum +wire, removing from the flame and drawing out the tail with the wire. +After cutting off the tail the wire is inserted in it, being held on a +scrap of glass as in the previous case, and the wire and tail heated +until the latter shrinks back into line with the walls of the tube. If +too great shrinkage occurs, the place may be blown out gently after +reheating. Thus the wire is sealed through the wall of the tube without +changing the thickness of the latter, and consequently without +developing undue stresses at that point. Such a joint must of course be +carefully reheated and annealed. With fine platinum wire there is very +little risk of the tube cracking if care is taken to avoid formation of +any lump and to reheat the whole circumference of the tube at that +point. + +Any glass adhering to the end of the platinum wire, where the scrap of +glass was sealed on for a handle, may be removed when the glass has +cooled by crushing it carefully with a pair of pliers. + + +SEALING VACUUM TUBES + +Tubes which have been evacuated usually are sealed off while they are +still connected to the vacuum pump. The connection should be through a +small, rather thick-walled tube. When this is to be sealed, it is slowly +heated toward the softening point. As the glass just begins to soften, +the air-pressure will force it in, and care must be taken that the +softening is uniform over the whole circumference of the tube. As the +shrinking goes on, the tube is gently drawn out to make a thick-walled +cone at that place, and the end is drawn off as soon as the tube is +sealed. The principal point to be guarded is the thickness of the walls +of the cone, and uniform heating. A thin place or a hot place will give +way under the air-pressure and be sucked into the tube. + + +CLOSED TUBES FOR HEATING UNDER PRESSURE + +(_Carius method for determination of the halogens and sulphur._) In this +case the tubing used must have thick walls (usually about 3/32 inch) to +withstand the pressure. Its external diameter is usually about 3/4 inch. +One length will usually make two tubes of standard length for the cannon +furnace. Especial care must be taken in heating and cooling it on +account of the thick walls. A length is gradually warmed in the center, +finally heated at that point until soft, drawn out, cut apart and +annealed. Taking one of the pieces, the cone is carefully heated and +shrunk, as in Exercise 4, until its walls are as thick as those of the +main tube. A flame with a little tinge of yellow should be used for this +operation to prevent devitrification (page 2), as the thick glass +shrinks slowly. The tail is now drawn off and the whole end heated and +gently blown several times to make a rounded end, like a test-tube, with +walls as thick as those of the main tube. This must be carefully +annealed. It is more important that the walls be thick than that the end +be nicely rounded: it may indeed be left somewhat conical in shape. + +At a point about two inches from the open end of the tube, it is slowly +warmed and finally heated to the softening point. Grasping the open end +with a pair of crucible tongs, it is cautiously pulled out, a little at +a time, usually during rotation in the flame, to make a constriction of +moderate wall-thickness, but of sufficient internal diameter to admit +the tube containing the substance. After annealing this, cooling and +cleaning the tube, the acid and salt are introduced (the former by means +of a long-stemmed funnel) and the tube is inclined and rotated about its +axis so that the acid wets its surface about half way up from the +bottom. The substance is now weighed out in a piece of thin-walled glass +tubing, closed at one end, and about two inches long. Inclining the +large tube at a suitable angle, the small one is introduced, closed end +first, and allowed to slide down the walls of the large tube until it +reaches the place where the acid has wet the tube. Here it will stop, +and if the tube is kept inclined during the rest of the operation it +will roll around inside the tube at this point and thus not get down +where any acid is likely to get into it and produce any pressure by +decomposing it before the open end of the tube is sealed. Now the tube +is held in an inclined position, taking care that the acid does not +reach up to the substance, the constricted portion cautiously warmed and +shrunk. It is finally shrunk and drawn out into a somewhat elongated +cone, with walls as thick as the rest of the tube, and when this is +accomplished the end of the cone is sealed and the waste piece drawn +off. Anneal with great care, and cool in such a position that the acid +cannot reach the hot glass. The shrinking of this cone takes a good deal +of patience, and is one of the most important parts of the process. If +the walls are left too thin, the tube may burst when heated, and the +whole labor is lost. If care is taken, the same tube can be used for a +number of determinations, until it becomes quite short. + + + + + INDEX + + + Annealing glass, 4, 24 + + + Bellows, 4 + + Bending glass, 8 + + Blowing glass, 13, 19, 20, 21, 24, 29, 31 + with a rubber tube, 22 + + Blowpipe, 4 + + Bulb at end of tube, 28 + in middle of tube, 32 + very large, 32 + + Bulbs, string of, 33 + + + Capillary tube, drawing on larger tube, 9, 54 + tubing, working, 43 + + Carius method, tubes for, 55 + + Closed circuits of tubing, 48 + tubes, for heating under pressure, 55 + + Collecting glass for bulb, 29, 31, 32 + + Constricting a tube, 10 + + Crystallization of glass, see Devitrification. + + Cutting glass, 7, 25 + + + Devitrification, 1, 2 + + Drawing out a tube, 9, 18, 19, 27 + + + Flanging a tube, 11, 14 + tool, 11 + + + Gas-washing tube, 35 + + Glass, annealing, 4, 24 + + Glass, bending, 8 + blowing, 13, 19, 20, 21, 24, 29, 31 + collecting for bulb, 29, 31, 32 + cutting, 7 + defects, 2 + grinding, 47 + hard, 1 + knife, 7 + lead, 1 + qualities desired, 1 + rod and tube, joining, 45 + rod, working, 44 + shrinking, 18, 19, 22, 26 + soft, 1 + working temperature, 1, 13, 19, 27 + + Grinding stopcock or joint, 47 + + Ground joints, 51 + + + Handle on stopcock, mending, 45 + + Hard glass, 1 + + Holding tube, 13, 14 + + + Insertion of tube through another, see Sealing a tube through + another tube. + + + Joints, ground, 51 + + Joining rod and tube, 45 + tubing end to end: first method, 16 + second method, 20 + + Joining tubes of different diameters, 25 + a new tube to a stopcock, 48 + + + Kjeldahl trap, 41 + + + Lead glass, 1 + + Lump of glass, removed, 18, 19, 20, 21, 24, 26, 30, 38 + + + Platinum wires, sealed into glass, 1, 52 + + Position for glass-working, 5 + + Pressure, tubes for heating under, 55 + + + Quality of glass, 1 + + + Rod, glass, working, 44 + + Rotation of the tube, 13, 19 + + Rounded end of tube, 35, 38 + + Rubber tube used for blowing, 22 + + + Sealing a tube through another tube, 35, 39 + + Sealing vacuum tubes, 55 + + Shrinking glass, 18, 19, 22, 26, 31 + + Side tube, blowing, 22, 25 + + Soda glass, 1 + + Soft glass, 1 + + Spirals, making, 50 + + Stopcocks, mending, 45 + + Suction pump, 39, 42 + + Sulphur dioxide tube, 28 + + + "Tail" of glass, drawing out, 9, 54 + removed, 30, 35 + + Tubes, closed, for heating under pressure, 55 + + "Tee" tube, 22 + on capillary tubing, 43 + small side tube on a large tube, 24 + + + Vacuum tubes, sealing, 55 + + + Working temperature of glass, 1, 13, 19, 27 + ++----------------------------------------------------------------------+ +| | +| | +| Transcriber's note:- | +| | +| Words in italics are indicated by the use of _underscores_ and words | +| | +| in =bold= by the use of equals signs as shown. | +| | +| | +| | ++----------------------------------------------------------------------+ + + + + + + +End of the Project Gutenberg EBook of Laboratory Manual of Glass-Blowing, by +Francis C. Frary + +*** END OF THE PROJECT GUTENBERG EBOOK 30066 *** diff --git a/30066-h.zip b/30066-h.zip Binary files differnew file mode 100644 index 0000000..cba10aa --- /dev/null +++ b/30066-h.zip diff --git a/30066-h/30066-h.htm b/30066-h/30066-h.htm new file mode 100644 index 0000000..9e6efe3 --- /dev/null +++ b/30066-h/30066-h.htm @@ -0,0 +1,2356 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" + "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> + +<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> + <head> + <meta http-equiv="Content-Type" content="text/html;charset=UTF-8" /> + <meta http-equiv="Content-Style-Type" content="text/css" /> + <title> + The Project Gutenberg eBook of Laboratory Manual Of Glass-blowing, by Francis C. Frary. + </title> + <style type="text/css"> + +body { + margin-left: 10%; + margin-right: 10%; +} + + h1,h2,h3,h4,h5,h6 { + text-align: center; /* all headings centered */ + clear: both; +} + +p { + margin-top: .75em; + text-align: justify; + margin-bottom: .75em; +} + +p.citation {text-align: right;} + +hr { + width: 33%; + margin-top: 2em; + margin-bottom: 2em; + margin-left: auto; + margin-right: auto; + clear: both; +} + +table { + margin-left: auto; + margin-right: auto; +} + +.pagenum { /* uncomment the next line for invisible page numbers */ + /* visibility: hidden; */ + position: absolute; + left: 92%; + font-size: smaller; + text-align: right; +} /* page numbers */ + +.center {text-align: center;} + +.smcap {font-variant: small-caps;} + +.caption {font-weight: bold;} + +/* Images */ +.figcenter { + margin: auto; + text-align: center; +} + + </style> + </head> +<body> +<div>*** START OF THE PROJECT GUTENBERG EBOOK 30066 ***</div> + +<h1>LABORATORY MANUAL</h1> + +<h3>OF</h3> + +<h1>GLASS-BLOWING<br /></h1> + +<div class="figcenter" style="width: 400px;"> +<img src="images/002.png" width="400" height="255" alt="Publisher book list" title="" /> +</div> + +<p><br /><br /></p> + +<h2>LABORATORY MANUAL</h2> +<h4>OF</h4> +<h2>GLASS-BLOWING<br /><br /><br /></h2> + +<h4>BY</h4> +<h3>FRANCIS C. FRARY, <span class="smcap">Ph. D.</span></h3> + +<h5>ASSISTANT PROFESSOR OF CHEMISTRY<br /> +UNIVERSITY OF MINNESOTA<br /><br /><br /><br /></h5> + +<h3><span class="smcap">McGRAW-HILL BOOK COMPANY, Inc.</span></h3> +<h4>239 WEST 39TH STREET, NEW YORK<br /> +6 BOUVERIE STREET, LONDON, E. C.<br /> +1914<br /><br /><br /><br /><br /></h4> + +<h5><span class="smcap">Copyright, 1914, by the<br /> +McGraw-Hill Book Company, Inc.</span><br /></h5> + +<hr style="width: 65%;" /> + +<p><span class="pagenum"><a name="Page_v" id="Page_v">[Pg v]</a></span></p> + +<h2>PREFACE</h2> + +<p>The purpose of this little book is to provide a clear and +detailed discussion of the elements of glass-blowing. +Many laboratories in this country, especially in the west, +are located a long way from any professional glass-blower, +and the time and money spent in shipping broken apparatus +several hundred miles to be mended could often +be saved if some of the laboratory force could seal on a +new stopcock, replace a broken tube, or make some +temporary repairs. Many men in physical or chemical +laboratories have occasion to modify some piece of apparatus +designed perhaps for other uses, or to design new +apparatus. To such also, the ability to perform some of +the operations herein described may be very valuable.</p> + +<p>No originality is claimed for the methods here described. +They are those which the author has found +most suitable and convenient in his own work, and most +easily learned by students. The aim has been to describe +each operation in such detail that a beginner can follow +the process without help and, with practice, attain +satisfactory results. It is, however, much easier to perform +any of the operations described, after seeing some +one else perform it correctly; since the temperature, the +exact time to begin blowing the glass, and many other little +details are very difficult to obtain from a description.</p> + +<p>It has not been thought worth while to describe the +process of making stopcocks, thermometers, vacuum +tubes, etc., as such things can be purchased more cheaply +and of much better quality than any amateur can make +unless he is willing to spend a very large amount of time +in practice. For similar reasons the manipulation of +quartz glass has been omitted.</p> + +<p>The author will be grateful for all suggestions and criticisms +tending to improve the methods presented. If +some of them appear to be given in excessive detail, the +reader will remember that many things which are obvious +to the experienced worker are not so to the beginner, and +that it is the little details in the manipulation which +often spell success or failure in glass-blowing.</p> + + +<p class="citation">F. C. F.<br /></p> +<p><span class="smcap">Minneapolis, Minn.,</span><br /> +<i>January, 1914.</i><br /><br /><br /></p> + +<p><span class="pagenum"><a name="Page_vi" id="Page_vi">[Pg vi]</a></span></p> + +<h3>CONTENTS</h3> + + + + +<div class="center"> + +<table border="0" cellpadding="4" cellspacing="0" summary="Contents"> + +<tr><td align="left"></td> +<td align="right"><span class="smcap">Page</span></td></tr> + +<tr><td align="left">Preface</td> +<td align="right"><a href="#Page_v">v</a></td></tr> + +<tr><td align="left"></td></tr> +<tr><td align="left"></td></tr> + +<tr><td align="left">CHAPTER I</td></tr> +<tr><td align="left"><span class="smcap">Materials and Apparatus</span></td> +<td align="right"><a href="#Page_1">1</a></td></tr> +<tr><td align="left">Varieties and defects of glass—Devitrification—Annealing</td></tr> +<tr><td align="left">glass—Blowpipe and bellows—Light—Arrangement</td></tr> +<tr><td align="left">of exercises.</td></tr> + +<tr><td align="left"></td></tr> +<tr><td align="left"></td></tr> + +<tr><td align="left">CHAPTER II</td></tr> +<tr><td align="left"><span class="smcap">General Operations</span></td><td align="right"><a href="#Page_7">7</a></td></tr> +<tr><td align="left">Cutting, bending, constricting and flanging the tubing—Methods</td></tr> +<tr><td align="left">of rotation and blowing.</td></tr> + +<tr><td align="left"></td></tr> +<tr><td align="left"></td></tr> + +<tr><td align="left">CHAPTER III</td></tr> +<tr><td align="left"><span class="smcap">Elementary Exercises</span></td><td align="right"><a href="#Page_16">16</a></td></tr> +<tr><td align="left">Joining two pieces of tubing of the same diameter—The</td></tr> +<tr><td align="left">"tee" tube—Joining two tubes of different diameters—Blowing</td></tr> +<tr><td align="left">bulbs.</td></tr> + +<tr><td align="left"></td></tr> +<tr><td align="left"></td></tr> + +<tr><td align="left">CHAPTER IV</td></tr> +<tr><td align="left"><span class="smcap">Advanced Exercises</span></td><td align="right"><a href="#Page_35">35</a></td></tr> +<tr><td align="left">Sealing a tube through another tube: The gas-washing</td></tr> +<tr><td align="left">tube, suction pump, and Kjeldahl trap.</td></tr> + +<tr><td align="left"></td></tr> +<tr><td align="left"></td></tr> + +<tr><td align="left">CHAPTER V</td></tr> +<tr><td align="left"><span class="smcap">Modified Methods and Special Operations</span></td><td align="right"><a href="#Page_43">43</a></td></tr> +<tr><td align="left">Capillary tubing—Glass rod—Mending stopcocks—Closed</td></tr> +<tr><td align="left">circuits of tubing—Spirals—Ground joints—Sealing</td></tr> +<tr><td align="left">in platinum wire—Sealing vacuum tubes—Closed</td></tr> +<tr><td align="left">tubes for heating under pressure.</td></tr> + +<tr><td align="left"></td></tr> +<tr><td align="left"></td></tr> + +<tr><td align="left"><span class="smcap">Index</span></td><td align="right"><a href="#Page_59">59</a></td></tr> + +</table></div> + + +<hr style="width: 65%;" /> + +<p><span class="pagenum"><a name="Page_1" id="Page_1">[Pg 1]</a></span></p> + +<h2>LABORATORY<br />MANUAL OF GLASS-BLOWING</h2> + + +<hr style="width: 65%;" /> +<h2>CHAPTER I</h2> + +<h3><span class="smcap">Materials and Apparatus</span></h3> + +<p>One of the most important factors in the success of any +piece of glass-blowing is the glass employed. As is well +known, there are two general varieties of glass: Lead +glass and soda glass. Formerly much apparatus was +made of lead glass, but at present it is very seldom met +with, except in the little drops of special glass used to seal +platinum wires into the larger sizes of tubes. Lead glass +is softer and more readily fusible than soda glass, but has +the disagreeable property of growing black in a few +seconds unless worked in a strong oxidizing flame. This +may be prevented by using a "hissing" flame, with a large +excess of air, and working in the extreme end of the flame; +or the black lead formed may thus be reoxidized, and the +glass restored to its original clearness.</p> + +<p>Almost all the soft glass on the market is a soda glass, +although sometimes part of the soda is replaced by +potash. Most of the hard glass appears to be a potash +glass. The following qualities are desirable in a glass for +ordinary working: (1) moderately low working temperature, +(2) freedom from air bubbles, striations and +irregularities, (3) proper composition, so that the glass +will not devitrify or crystallize while being handled at its +working temperature, (4) ability to withstand rapid +heating without cracking.</p> + +<p>The working temperature of different samples of so<span class="pagenum"><a name="Page_2" id="Page_2">[Pg 2]</a></span>-called +"soft glass" varies a good deal, and is best determined +by trial. The glass should become almost soft +enough for blowing in a flame that still shows a little +yellow near the tip, so that at the highest temperature of +the flame it may flow fairly freely and thus easily eliminate +irregularities in thickness. If the glass is too hard, +the shrinking of the glass, collection of material for a +bulb, and in fact most of the working processes will be +slower, and the glass will not stay at its working temperature +long enough after its removal from the flame +to permit it to be properly blown.</p> + +<p>Air bubbles in the original batch of glass are drawn out +into long hair-like tubes during the process of manufacture. +When such tubing is worked, the walls of these +microscopic tubes collapse in spots, and the air thus +enclosed will often collect as a small bubble in the wall, +thus weakening it. Irregularities are of various kinds. +Some of the larger sizes of thin-walled tubing often have +one half of their walls much thicker than the other, and +such tubing should only be used for the simplest work. +Some tubing has occasional knots or lumps of unfused +material. The rest of the tube is usually all right, but +often the defective part must be cut out. The presence +of striations running along the tube is generally an indication +of hard, inferior glass. Crookedness and non-uniformity +of diameter are troublesome only when long +pieces must be used.</p> + +<p>Devitrification is one of the worst faults glass can +possibly have. It is especially common in old glass, and +in glass which has contained acids. It seems to be of two +sorts. One variety manifests itself on the surface of the +glass before it reaches its working temperature, but if +the glass be heated to the highest temperature of the +flame it will disappear except in the portion at the edge +of the heated part. The glass seems to work all right, but<span class="pagenum"><a name="Page_3" id="Page_3">[Pg 3]</a></span> +an ugly crystallized ring is left at the edge of the portion +heated. This kind appears most frequently in old glass +which was originally of good quality, but has in time been +superficially altered, probably by the loss of alkalies. +The other variety of devitrification does not appear +when the glass is first heated; but after it has been maintained +at or above its working temperature for a longer +or shorter time, it will be noticed that the outer surface +has lost its smoothness, and appears to be covered with +minute wrinkles. It will also be found that the glass has +become harder, so that it becomes impossible to work it +easily. Further heating only makes the matter worse, +as does the use of a higher temperature from the start. +In fact it will often be found that a piece of comparatively +soft glass which devitrifies almost at once in a +"hissing" flame can be worked without serious difficulty +if care be taken to use a flame still decidedly tinged with +yellow. Even good glass will begin to devitrify in this +way if heated too long at the highest temperature of the +flame, so care should always be taken (1) <i>to reduce the +time of heating of any spot of glass to a minimum</i>; <i>i.e.</i>, get +the desired result at the first attempt, if possible, or at +least with the minimum of reheating and "doctoring," +and (2) <i>avoid keeping the glass at the highest temperature +of the flame any longer than necessary</i>. This may be +accomplished by doing all heating, shrinking, etc., of the +glass in a flame more or less tinged with yellow, and only +raising the temperature to the highest point when ready +to blow the glass. This kind of devitrification is apparently +due to volatilization of the alkalies from the glass in +the flame, and it is said that it can be partly remedied or +prevented by holding a swab of cotton saturated with a +strong solution of common salt in the flame from time to +time as the glass is heated.</p> + +<p>The toughness of glass, <i>i.e.</i>, its ability to withstand<span class="pagenum"><a name="Page_4" id="Page_4">[Pg 4]</a></span> +variations of temperature, depends on its composition +and the care taken in its annealing. In general, large +pieces of glass should be heated very slowly in the smoky +flame, and the larger the diameter of the tube the greater +the length which must be kept warm to prevent cracking. +All large pieces should be carefully heated over their +whole circumference to the point where the soot deposit +burns off, before being finally cooled. After being thus +heated they are cooled in a large smoky flame until well +coated with soot, then the flame is gradually reduced in +size and the object finally cooled in the hot air above it +until it will not set fire to cotton. If thought necessary, +it may then be well wrapped in cotton and allowed to +cool in the air. If not properly annealed the place heated +may crack spontaneously when cold, and it is quite certain +to crack if it is reheated later.</p> + +<p>Next in importance to the glass are the blow-pipe and +the bellows. Any good blast lamp, such as is ordinarily +used in a chemical laboratory for the ignition of precipitates, +will be satisfactory; provided it gives a smooth +regular flame of sufficient size for the work in hand, +and when turned down will give a sharp-pointed flame +with well-defined parts. Where gas is not available, an +ordinary gasoline blow-torch does very well for all operations +requiring a large flame, and a mouth blow-pipe +arranged to blow through a kerosene flame does well for +a small flame. Several dealers make blow-torches for +oil or alcohol which are arranged to give a small well-defined +flame, and they would doubtless be very satisfactory +for glass-work. Any good bellows will be +satisfactory if it does not leak and will give a steady +supply of air under sufficient pressure for the maximum +size of flame given by the lamp used. A bellows with a +leaky valve will give a pulsating flame which is very +annoying and makes good work very difficult. When<span class="pagenum"><a name="Page_5" id="Page_5">[Pg 5]</a></span> +compressed air is available it can be used, but if possible +it should be arranged so that the supply can be controlled +by the foot, as both hands are usually needed to hold the +work. For the same reason the supply of air is usually +regulated by varying the rate of operation of the bellows, +rather than by adjusting the valve of the blast-lamp. +On the other hand, it will be found best to always adjust +the flow of the gas by means of the cock on the lamp, +rather than that at the supply pipe. The operator must +have complete control over the flame, and be able to +change its size and character at short notice without +giving the work a chance to cool, and often without ceasing +to support it with both hands.</p> + +<p>Glass-blowing should be done in a good light, but preferably +not in direct sunlight. The operator should be +seated in a chair or on a stool of such a height that when +working he may comfortably rest one or both elbows on +the table. The comfort of the operator has a decided +influence on the character of his work; especially in the +case of a beginner, who often defeats his purpose by +assuming uncomfortable and strained positions. Steadiness +and exact control of both hands are essential in most +operations; any uncomfortable or strained position tires +the muscles and weakens the control of the operator over +them.</p> + +<p>In the arrangement of the exercises here presented, +several factors have been considered. It is important +that the first exercises be simple, although not necessarily +the simplest, and they should teach the fundamental +operations which will be used and amplified later. They +should in themselves be things which are of importance +and commonly used in glass-work, and they should be so +arranged that the fundamental points, such as the rotation +of glass, the proper temperature, blowing and shrinking +the glass may be learned with a minimum expenditure<span class="pagenum"><a name="Page_6" id="Page_6">[Pg 6]</a></span> +of time, glass and gas. It is therefore recommended that +the beginner take them up in the order given, at least as +far as No. 7, and that each be mastered before attempting +the next. The beginner should not leave the first exercise, +for example, until he can join together two pieces +of tubing so that they form one piece of substantially +uniform inner and outer diameter, and without thick or +thin spots. From two to four practice periods of two +hours each should suffice for this. This chapter and the +following one should also be frequently read over, as many +of the points discussed will not be understood at first and +many of the manipulations described will not be necessary +in the simpler exercises.</p> + + + +<hr style="width: 65%;"/> + +<p><span class="pagenum"><a name="Page_7" id="Page_7">[Pg 7]</a></span></p> + +<h2>CHAPTER II</h2> + +<h3><span class="smcap">General Operations</span></h3> + + +<p><b>Cutting the Glass.</b>—For this purpose a "glass-knife" +is preferred to a file, if the glass is cold: if it is hot a file +must always be used, and its edge slightly moistened to +prevent drawing the temper. The glass-knife is simply +a flat piece of hard steel, with the edges ground sharp on +an emery wheel. The bevel of the edge should be from +30 to 60 degrees. An old flat file can easily be ground +into a suitable knife. The glass-knife makes a narrower +scratch than the file but appears more likely to start the +minute crack which is to cause the tube to break at that +point, and the break is more likely to give a good square +end. The scratch should be made by passing part of +the knife or file once across the glass, never by "sawing" +the tool back and forth. This latter procedure dulls the +tool very quickly.</p> + +<p>In breaking a piece of glass tubing, many persons forget +that it is necessary to <i>pull</i> the ends apart, as well +as to bend the tube very <i>slightly</i> in such a direction as to +open up the minute crack started in the scratch. Care +in breaking the tube is essential, as it is impossible to do +as good work with uneven ends as with square ones.</p> + +<p>When tubing of large diameter or thin wall is to be cut, +it is often better not to attempt to break it in the usual +way, but to heat a very small globule of glass (<span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">16</span> to <span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">8</span> +inch diameter) to red heat, and touch it to the scratch. +This will usually start the crack around the tube; if it +has not proceeded far enough, or has not gone in the de<span class="pagenum"><a name="Page_8" id="Page_8">[Pg 8]</a></span>sired +direction, it may be led along with a hot point of +glass. This is put a little beyond the end of the crack, +and as the latter grows out toward it, moved along the +path where the crack is desired. This point of glass is +also very useful in breaking off very short ends of tubes, +where there is not room to get a firm enough hold and +sufficient leverage to break the tube in the ordinary +way, and for breaking tubes attached to large or heavy +objects, which would be likely to make trouble if treated +in the ordinary way.</p> + +<p>Another way of cutting large tubing, especially if it +has rather thick walls, is to make a scratch in the usual +way, and then turn on the smallest and sharpest possible +flame of the blast lamp. The tube is next taken in both +hands and held horizontally above the flame so that the +scratch is exactly over it. The tubing is now rotated +rapidly about its axis, and lowered so that the flame is +just tangent to its lower side. After about ten seconds +of heating, it is removed from the flame and the hot portion +quickly breathed upon, when it will generally crack +apart very nicely. Care must be taken to hold the tube +at right angles to the flame during the heating, and to +rotate it so that only a narrow strip of the circumference +is heated, and the scratch should be in the center of this +heated strip. By this means tubing as large as two inches +in diameter is readily broken.</p> + +<p>Griffin's glass cutter, which contains a hardened steel +wheel, like that on any ordinary window-glass cutter, and +a device by which this can be made to make a true cut +clear around the tube, is a very handy article, especially +for large tubing, and may be obtained from any dealers +in chemical apparatus.</p> + +<p><b>Bending Glass.</b>—Inasmuch as this is one of the commonest +operations in the laboratory, it is assumed that +the reader knows how to perform it. However, it<span class="pagenum"><a name="Page_9" id="Page_9">[Pg 9]</a></span> +should be noted that in order to obtain the best results +a broad (fish-tail burner) flame should generally be used, +and the tube rotated on its axis during the heating, and +allowed to bend mostly by its own weight. If large tubing +is to be bent, one end must be stoppered and great +care used. Whenever the tube shows signs of collapsing +or becoming deformed, it must be gently blown out into +shape, heating the desired spot locally if necessary. A +blast-lamp is likely to be more useful here than the fish-tail +burner.</p> + +<p><b>Drawing Out a Tube.</b>—Most students learn this the +first day of their laboratory work in chemistry, but few +take pains to do it well. The tube should be heated in +the flame of a Bunsen burner, or blast lamp (preferably +the latter) until it is very soft. During this time it must +be continuously rotated about its axis, and so held that +the edges of the heated zone are sharply defined; <i>i.e.</i>, +it should not be allowed to move back and forth along +its own axis. When so hot that it cannot longer be held +in shape, the tube is removed from the flame, and the +ends slowly and regularly drawn apart, <i>continuing the +rotation of the tube about its axis</i>. By regulating the rate +of drawing and the length of tube heated, the desired +length and diameter of capillary may be obtained. The +tube should always be rotated and kept in a straight line +until the glass has set, so that the capillary may have the +same axis as the main tube. This capillary or "tail" +is often a very necessary handle in glass-blowing, and if +it is not straight and true, will continually make trouble.</p> + +<p>In drawing out very large tubing, say from one to +two inches in diameter, it is often necessary to draw the +tube <i>in the flame</i>, proceeding very slowly and at a +lower temperature than would be used with small tubing. +This is partly on account of the difficulty of heating +large tubing uniformly to a high temperature, and<span class="pagenum"><a name="Page_10" id="Page_10">[Pg 10]</a></span> +partly in order to prevent making the conical part of +the tube too thin for subsequent operations.</p> + +<p><b>Constricting a Tube.</b>—Where a constriction is to be +made in a tube, the above method must be modified, as +the strength of the tube must be maintained, and the +constricted portion is usually short. Small tubes are +often constricted without materially changing their outside +diameter, by a process of thickening the walls. The +tube is heated before the blast lamp, rotating it about +its axis as later described, and as +it softens is gradually pushed +together so as to thicken the walls +at the heated point, as in <i>a</i>, Fig. 1. +When this operation has proceeded +far enough, the tube is removed +from the flame, and the ends cautiously +and gently drawn apart, +continuing the rotation of the tube +about its axis and taking care not +to draw too rapidly at first. The +resulting tube should have a uniform exterior diameter, +as shown in <i>b</i>, Fig. 1.</p> + +<div class="figcenter" style="width: 355px;"> +<img src="images/i018.png" width="355" height="400" alt="" title="" /> +<span class="caption">Fig. 1.—Constricting a +tube.</span><br /><br /> +</div> + +<p>This method of constriction is not suited to tubes +much over <span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">4</span> inch in diameter, since the mass of glass +in the constricted part becomes so thick as to be difficult +to handle when hot, and likely to crack on cooling. +Larger tubes are therefore constricted by heating in a +narrow flame, with constant rotation, and when soft, +alternately gently pulling the ends apart and pushing +them together, each motion being so regulated that the +diameter of a short section of the tube is gradually reduced, +while the thickness of the wall of the reduced +portion remains the same as that of the rest of the tube, +or increases only slightly. This pulling and pushing of +the glass takes place <i>in the flame</i>, while the rotation is<span class="pagenum"><a name="Page_11" id="Page_11">[Pg 11]</a></span> +being continued regularly. The result may appear as +indicated in <i>c</i>, Fig. 1. The strength of the work depends +upon the thickness of the walls of the constricted portion, +which should never be less than that in the main tube, +and usually a little greater. This operation is most +successful with tubing having a relatively thin wall.</p> + +<p><b>Flanging a Tube.</b>—This operation produces the characteristic +flange seen on test-tubes, necks of flasks, etc., +the object being twofold: to finish the end neatly and to +strengthen it so that a cork may be inserted without +breaking it. This flanging may be done in several ways. +In any case the first operation is to cut the tube to a +square end, and then heat this end so that the extreme +sixteenth or eighth of an inch of it is soft and begins to +shrink. The tube is of course rotated during this heating, +which should take place in a flame of slightly greater +diameter than the tube, if possible. The flange is now +produced by expanding this softened part with some +suitable tool. A cone of charcoal has been recommended +for this purpose, and works fairly well, if made so its +height is about equal to the diameter of its base. The +tube is rotated and the cone, held in the other hand, is +pressed into the open end until the flange is formed. A +pyramid with eight or ten sides would probably be better +than the cone.<br /><br /></p> + +<div class="figcenter" style="width: 400px;"> +<img src="images/i019.png" width="400" height="90" alt="" title="" /> +<span class="caption">Fig. 2.—Flanging tool.</span> +<br /><br /></div> + +<p>A better flanging tool is made from a triangular piece +of copper or brass, about <span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">16</span> inch thick, and mounted +in a suitable handle. Such a tool is shown in Fig. 2, +being cut from a sheet of copper and provided with a<span class="pagenum"><a name="Page_12" id="Page_12">[Pg 12]</a></span> +handle made by wrapping asbestos paper moistened with +sodium silicate solution about the shank of the tool. +It is well to have several sizes and shapes of these tools, +for different sizes of tubing. The two sizes most used +will be those having about the following dimensions: +(1) <i>a</i> = 2 inches, <i>b</i> = 1 inch; (2) <i>a</i> = 1 inch, <i>b</i> = 1 inch. +When the end of the tube is softened, the tool is inserted +at an angle, as indicated in Fig. 3, and pressed against +the soft part, while the tube is quickly rotated about its +axis. If the flange is insufficient the operation may be +repeated. The tool should always be warmed in the +flame before use, and occasionally greased by touching +it to a piece of wax or paraffin. After the flange is complete, +the end must be heated again to the softening temperature +and cooled slowly, to prevent it from cracking.<br /><br /></p> + +<div class="figcenter" style="width: 400px;"> +<img src="images/i020a.png" width="400" height="119" alt="" title="" /> +<span class="caption">Fig. 3.—Flanging a tube with flanging tool.</span> +<br /><br /><br /><br /></div> + +<div class="figcenter" style="width: 400px;"> +<img src="images/i020b.png" width="400" height="101" alt="" title="" /> +<span class="caption">Fig. 4.—Flanging a tube with carbon rod or wire.</span> +<br /><br /></div> + +<p>Some glass-blowers use a small carbon rod, about +<span style="font-size: 0.8em"><sup>3</sup></span>⁄<span style="font-size: 0.6em;">16</span> inch in diameter, as a flanging tool for tubes larger +than about <span style="font-size: 0.8em"><sup>3</sup></span>⁄<span style="font-size: 0.6em;">8</span> inch diameter, and a small iron wire or +similar piece of metal for smaller tubes. In this case the +tube is heated as above described, and the rod or wire +inserted in the end at an angle and pressed against the +softened part, as indicated in Fig. 4, while the tube is<span class="pagenum"><a name="Page_13" id="Page_13">[Pg 13]</a></span> +rotated about its axis. For large heavy tubes a larger +carbon would be used.</p> + +<p><b>Rotation of the Tube.</b>—This is the fundamental manipulation +in glass-blowing, and upon it more than all +else depends the uniformity and finish of the work, and +often the possibility of accomplishing the work at all. +Directions for it will be given on the assumption that +the reader is right-handed; if otherwise, the position of +the hands is of course reversed. The object of rotation +is to insure even heating of the whole circumference of +the tube at the point of attack, to equalize the effect of +gravity on the hot glass and prevent it from falling out of +shape when soft, and to keep the parts of the tube on +each side of the heated portion in the same straight line.</p> + +<p>In rotating the tube, both hands must be used, so that +the two ends may revolve at the same rate and the glass +in the hot part not be twisted. The rotation is performed +by the thumb and first finger of each hand, the other +fingers serving to support the tube. As it is almost +always necessary to follow rotating and heating a tube by +blowing it, the hands should be so placed that it will be +easy to bring the right-hand end up to the mouth without +shifting the hold on the glass. For this reason the left +hand grasps the glass with the palm down, and the right +hand with the palm turned toward the left. If there is +any choice, the longer and heavier part of the tube is +usually given to the left hand, and it is planned to blow +into the shorter end. This is because it is easier to +support the tube with the hand which has the palm +down. This support is accomplished by bending the +hand at the wrist so that it points slightly downward, and +then curling the second, third and little fingers in under +the tube, which is held between them and the palm. +This support should be loose enough so that the thumb +and first finger can easily cause the tube to rotate regu<span class="pagenum"><a name="Page_14" id="Page_14">[Pg 14]</a></span>larly +on its axis, but firm enough to carry all the weight +of the tube, leaving the thumb and first finger nothing +to do but rotate it. The hand must be so turned, and +the other fingers so bent, that the thumb and first finger +stretch out nearly to their full length to grasp the tube +comfortably.</p> + +<p>The right hand is held with the palm toward the left, +the fingers except the first slightly bent, and the tube +held between the first finger and the thumb while it +rests on the second finger and that portion of the hand +between the base of the first finger and the thumb. +Rotation of the tube is accomplished by rolling it between +the thumbs and first fingers: the rotation being continued +in the same direction regularly, and not reversed. It +is better to roll slowly and evenly, with a series of light +touches, each of which moves the tube a little, than to +attempt to turn the tube a half a revolution or so with +each motion of the hands. The hands must be held +steady, and the tube must be under good control at all +times, so that both ends may be rotated at the same angular +velocity, even though they may be of different diameters, +and the tube be neither drawn apart nor pushed +together unless such a motion is expressly desired, as it +sometimes is. The hot part of the glass must be constantly +watched to see that it is uniformly rotated and +not twisted, nor pulled out or pushed together more than +is desired. Care must also be taken to keep the parts of +the tube in the same straight line, or as near it as possible, +during the heating and all other manipulations.</p> + +<p>When flanging a tube, it is held and rotated with the +left hand as above described, while the right hand holds +the flanging tool.</p> + +<p>When part of the end of a tube must be heated, as in +Exercise 6, and rotation must be very carefully performed +and continued during the blowing, both hands are used.<span class="pagenum"><a name="Page_15" id="Page_15">[Pg 15]</a></span> +The right hand is held as above described, and the left +hand close to it and either as above described or else +with the palm toward the right, grasping the tube in the +same way as the right hand does. This puts both hands +in a position where the tube may be blown and rotated +uniformly while its axis is kept horizontal.</p> + +<p>Smoothness and exactness are the two things for which +the beginner must constantly strive in glass-blowing, and +they are only attained by a careful attention to the +details of manipulation, with a steady hand and watchful +eye. Every move must count, and the exercise must be +finished with a minimum of reheating and retouching, for +the best results.</p> + + + +<hr style="width: 65%;"/> + +<p><span class="pagenum"><a name="Page_16" id="Page_16">[Pg 16]</a></span></p> + +<h2>CHAPTER III</h2> + +<h3><span class="smcap">ELEMENTARY EXERCISES</span></h3> + + +<h3>EXERCISE NO. 1</h3> + +<h4><span class="smcap">Joining Two Pieces of Tubing, End to End—First +Method</span><br /><br /></h4> + +<p>This exercise is most easily learned on tubing with an exterior +diameter of <span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">4</span> inch, or a little less, having moderately +heavy walls. A piece of such tubing is heated before +the blow-pipe at a point ten or twelve inches from +the end, and there drawn out to a capillary as previously +described (page 9). The capillary is sealed off about +two inches from the main tube, and the latter is cut near +the middle. Care should be taken to get square ends<span class="pagenum"><a name="Page_17" id="Page_17">[Pg 17]</a></span> +where the cut is made (page 7). The flame is now so +regulated that it is a little broader than the diameter of +the tube, the sealed half of the tube taken in the left +hand and the other half in the right. The open end of +the sealed part and one of the ends of the other part +are now held in opposite sides of the flame, inclined at a +slight angle to one another as indicated in Fig. 5, and +rotated and heated until the surfaces of both ends are +just softened. The two ends are then carefully and +quickly brought together (<i>a</i>, Fig. 6), removed from the +flame and pulled apart a little, to reduce the lump formed +at the joint as much as possible, as indicated in <i>b</i>. The +joint is then tested by blowing into the open end of the +tube to see if it is tight. If so, the flame is reduced to +half or less than half of its former size, and the joint +heated in it, holding the tube and continually rotating it +as directed in the last chapter (page 13).<br /><br /></p> + +<div class="figcenter" style="width: 400px;"> +<img src="images/i024.png" width="400" height="341" alt="" title="" /> +<span class="caption">Fig. 5.—Softening ends of two pieces of tubing.</span> +<br /><br /><br /><br /></div> + +<div class="figcenter" style="width: 400px;"> +<img src="images/i025.png" width="400" height="359" alt="" title="" /> +<span class="caption">Fig. 6.—Joining two pieces of tubing end to end—first method.</span> +<br /><br /></div> + +<p>As the tube softens and tends to shrink, the two ends +are pressed together a little and the walls allowed to<span class="pagenum"><a name="Page_18" id="Page_18">[Pg 18]</a></span> +thicken slightly, as in <i>c</i>. It is then quickly removed +from the flame and gently blown as indicated in <i>d</i>, +continuing the rotation of the tube during the blowing, +and at the same time pressing the ends of the tube together +a little so as to make a <i>short</i> thick-walled bulb. +The joint is then returned to the flame and reheated, +rotating as before, shrinking to about the shape of <i>e</i>. +When this stage is reached, the glass should be very hot +and fluid, and the mass of hot glass thick enough to +remain at its working temperature for about five seconds +after removal from the flame. The glass is now reblown +as indicated in <i>f</i>, to form a bulb having walls of practically +the same thickness as the original tube. As soon as the +bulb is blown, the tube is removed from the mouth, held +horizontally in front of the worker, and gently drawn out +to form one continuous tube, as indicated in <i>g</i>. During +both the blowing and drawing of this bulb the rotation +must be continued, and both blowing and drawing must +be carefully regulated so that the resulting tube may have +the same internal and external diameter at the joint as +elsewhere.</p> + +<p><b>Discussion.</b>—In making the original joint, (<i>a</i>, Fig. 6), +care should be taken that the lump formed is as small as +possible so that it may be entirely removed during the +subsequent operations. For this reason, only the very +tip ends of the two pieces of tubing are held in the flame, +and the softening should not extend more than <span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">16</span> +inch down the tube. As soon as the ends are sufficiently +soft to stick together, they are made to do so. The first +drawing of the tube (<i>b</i>) should take place immediately, +and reduce the lump as much as possible without making +the adjacent walls of the tube thin. The whole purpose +of the rest of the manipulation is to absorb or "iron out" +the lump at the joint. For this reason, care is taken that +this lump is always in the center of the flame while the<span class="pagenum"><a name="Page_19" id="Page_19">[Pg 19]</a></span> +joint is being heated, and a small flame is used so that +little of the main tube may be softened. During the first +shrinking of the joint (<i>c</i>) the walls next the lump, being +thinner than it is, reach the softening temperature first +and are thickened by the slight pushing together of the +ends, so that they taper from the lump to the unchanged +wall. Upon blowing this joint, these thickened walls +blow out with the lump, but as they are thinnest next the +unchanged tube, they stiffen there first. Then as the +thicker parts are still hot, these blow out more, and with +the lump make a more or less uniform wall. By this first +operation most of the lump will have been removed, provided +it was not too large at first, and the tube was hot +enough when it was blown. Beginners almost invariably +have the glass too cool here, and find difficulty in blowing +out a satisfactory bulb. Under such circumstances the +lump will be scarcely affected by the operation.</p> + +<p>During the shrinking of this bulb, the thinner parts of +course are the first to reach the softening point, and thus +contract more than the thick parts, so that practically all +of the lump can be absorbed, and a uniformly thickened +part of the tube left as in <i>e</i>. When this is just accomplished, +the second bulb must be blown during one or +two seconds, and the tube then drawn out as described, +so as to change the bulb to a tube. The drawing must +proceed with care: portions nearest the unchanged tubes +are the first to reach the proper diameter, and must be +given time to just set at that point before the center of +the bulb is finally drawn into shape. The drawing is +perhaps best done intermittently in a series of quick +pulls, each drawing the tube perhaps <span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">16</span> inch, and each +taking place as the thumbs and first fingers grasp the tube +for a new turn in the rotation. If the tube is not rotated +during the blowing, the bulbs will be lop-sided and it will +be impossible to get a joint of uniform wall-thickness;<span class="pagenum"><a name="Page_20" id="Page_20">[Pg 20]</a></span> +if rotation is omitted during the drawing, the tube will +almost invariably be quite crooked.</p> + +<p>If the lump still shows distinctly after the operations +described, the cross-section of the tube will be as in <i>h</i>, and +the tube will be likely to break if ever reheated at this +point after it becomes cold. The operations <i>d</i>, <i>e</i>, <i>f</i>, and +<i>g</i> may be repeated upon it, and it may be possible to get +it to come out all right.</p> + +<p>Care must be taken not to blow the bulbs <i>d</i> and <i>f</i> too +thin as they then become very difficult to handle, and the +joint is usually spoiled. The wall-thickness of these +bulbs must never be much less than that of the original +tube. If the joint as completed has thinner walls than +the rest of the tube, it will be more easily broken. It +should be remembered that the length of the finished +tube must be exactly the same as that of the original +piece, if the walls of the joint are to be of their original +thickness. Therefore the pushing together during the +two operations <i>c</i> and <i>d</i> must shorten the tube just as +much as the final drawing (<i>f</i> to <i>g</i>) lengthens it.</p> + +<p>The interval between the removal of the work from +the flame and the beginning of the blowing must be made +as short as possible, or else the portions next the main +parts of the tube will set before they can be blown out, +and cause irregular shrunken areas.</p> + + +<h3>EXERCISE NO. 2</h3> + +<h4><span class="smcap">Joining Two Tubes End to End—Second Method</span></h4> + +<p>The method described in Exercise No. 1 is very satisfactory +for joining short lengths of straight tubing, but +becomes inconvenient or impossible when the pieces are +long or bent, on account of the difficulty in uniformly +rotating such work. In such cases, this second method is<span class="pagenum"><a name="Page_21" id="Page_21">[Pg 21]</a></span> +used. It does not usually give as smooth and pretty a +joint as the first method, and takes a little longer.</p> + +<p>The joint is begun exactly as in the first method, and +the manipulation is the same until after the preliminary +tight joint (<i>b</i>, Fig. 6) is made. The flame is reduced as +usual, but instead of rotating the tube in the flame, only +one part of the circumference is heated, and this is +allowed to shrink thoroughly before blowing. It is then +blown gently so that it becomes a slight swelling on the +tube, and the operation repeated on an adjoining part of +the joint. Three or four repetitions of the operation will +usually cover the whole circumference of the joint, in a +small tube, the result being a swelling roughly similar +to the first thick bulb in the first method (<i>d</i>, Fig. 6). If +all the lumps of the original joint have not been removed +by this operation, it may now be repeated upon such parts +as may require it. The thickness of the wall in the bulb +should be about the same as that in the original tube. +The whole of the expanded joint is now heated as uniformly +as may be until soft enough so that it begins to +shrink a little, and the swelling is gently drawn down to +the same diameter as the main tube, as in the first case. +Any irregularities in the finished joint may be corrected +by local reheating, shrinking or blowing as required.</p> + +<p><b>Discussion.</b>—In using this method, especially with +larger sizes of tubing, it is very important to keep the +whole circumference of the joint hot enough during the +operation so that it does not crack apart at the part +which has not yet been worked. For that reason the +first heating, shrinking and blowing should be performed +as quickly as possible, leaving the resulting irregularities +to be corrected later, rather than attempting to reblow +the same part of the joint several times in succession +until it is satisfactory. Care must be taken in this as in +the first method that the blowing follows immediately<span class="pagenum"><a name="Page_22" id="Page_22">[Pg 22]</a></span> +upon the completion of the shrinking and removal of +the object from the flame: delay in blowing will cause +shrunken places where the joint meets the original tubes, +on account of the cooling and setting of the glass before +it was blown. Most beginners err in being afraid to +shrink the part of the joint enough before blowing it. +On small tubing, the shrinkage may often extend so far +that the inner surface of the shrunken part reaches the +center of the tube. Insufficient shrinking results in +failure to remove the lump formed at the original joint. +It is often of advantage, after blowing out part of the +joint, to allow that part a few seconds to set before going +on with the rest, keeping the whole joint warm meanwhile +in or near the smoky flame. This helps to prevent the +twisting of the joint, or other distortion incident to the +handling of a piece of work of awkward shape.</p> + +<p>In making a joint on a very long or heavy piece by +this method, it is often advantageous to attach a piece +of rubber tubing to the open end, hold the other end of +this tubing in the mouth during the process, and blow +through it, rather than attempt to bring the end of the +glass up to the mouth. This enables one to keep closer +watch on the joint, and avoid drawing it out or distorting +it in handling. On the other hand, the rubber tube is an +inconvenience on account of its weight and the consequent +pull on the end of the apparatus, and makes rotation +difficult.</p> + + +<h3>EXERCISE NO. 3</h3> + +<h4><span class="smcap">The "Tee" Tube</span></h4> + +<p>The operations involved are two: the blowing of a +short side tube on a piece of tubing, and sealing another +piece of tubing on this, by what is essentially the second +method as just described.<span class="pagenum"><a name="Page_23" id="Page_23">[Pg 23]</a></span><br /><br /></p> + +<div class="figcenter" style="width: 230px;"> +<img src="images/i031.png" width="230" height="400" alt="" title="" /> +<span class="caption">Fig. 7.—The "tee" tube.</span> +<br /><br /></div> + +<p>The two pieces of tubing to be used each have one end +cut square and the other sealed in the usual manner. +The longer of the two is now heated at the point at which +the joint is to be made, until it begins to color the flame. +A small flame is used, and the tube rotated until the +flame begins to be colored, when the rotation is stopped, +and only one spot heated until a spot the diameter of the +tube to be sealed on has become red hot and begun to +shrink. This is now gently blown out into a small bulb, +as in <i>a</i>, Fig. 7, and it will be noted +that this bulb will have walls tapering +from the thick walls of the +tube to a very thin wall at the +top. The sides of this bulb, below +the dotted line, are to form +the small side tube to which the +main side tube is to be sealed. +The top of the bulb is now softened +by directing a small flame +directly upon it, and as soon as +it shrinks to the level indicated +by the dotted line, it is removed +from the flame and quickly blown +out to form a thin bulb, as indicated +in <i>b</i>, Fig. 7. This will usually +be so very thin that a stroke of the file or glass-knife +will break it off at the dotted line, leaving the +side tube, to which the short piece of tubing is now +sealed according to the second method (Exercise No 2). +In doing this, care is taken to direct the flame partly on +the main tube in the two crotches, so that both tubes blow +out a little and give space for the gases to turn in, as +indicated in <i>c</i>, Fig. 7, and at the same time increase the +mechanical strength of the job. On the other hand, +care is taken not to deform the main tube, and not to<span class="pagenum"><a name="Page_24" id="Page_24">[Pg 24]</a></span> +produce such a bulge or bulb at the joint as will prevent +the finished tube from lying flat on a table.</p> + +<p><b>Discussion.</b>—Most beginners tend to err in the first +steps of this operation, by blowing too hard and too long +when blowing out the little bulb. The result is a large, +very thin bulb, which breaks off in such a way as to leave +a hole in the main tube, occupying nearly half the circumference +of the tube at that point, instead of the neat +side tube which they should have. It is not difficult to +seal a tube on this side tube, but it is very difficult to seal +a tube into a hole in another tube. Care should be taken +here, as in the two previous exercises, that the lump +obtained at the joint when the two tubes are put together +is made as small as possible, and reduced if possible by +gently drawing on the side tube as soon as the tubes have +actually joined. It is much easier to prevent the formation +of a lump at the joint than it is to remove the lump +after it is formed. The remarks previously made about +blowing quickly after removing the work from the flame +apply here with especial force. A "tee" tube, from its +very nature, is exposed to a good many strains, so care +must be taken that the walls of the joint are of uniform +thickness with the rest of the tube.</p> + +<p>The beginner will find it easiest to make this tube out +of two pieces of the same tube, about <span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">4</span> inch in diameter. +Larger or smaller tubing is usually more difficult. If +tubing much more than <span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">4</span> inch is used, the whole joint, +including part of the main tube, must be heated nearly +to the softening point at the close of the operation, and +well annealed, as described in Chapter 1 (page 3) or it +will be almost certain to crack. In the larger sizes of +tube it will be necessary to heat the whole circumference +of the main tube frequently during the operation, to +prevent it from cracking.</p> + +<p>In sealing a small tube on the side of a large one, it is<span class="pagenum"><a name="Page_25" id="Page_25">[Pg 25]</a></span> +usually advisable, after warming the spot where the joint +is to be made, to attach a small drop of glass to the tube +at that point, and direct the flame upon that, thus supplying +at the same time both a definite point to be heated +and an extra supply of glass for the little side tube which +is desired. In this way it is also easier to blow out a +side tube with a sufficiently small diameter. If the +diameter of this tube should be much greater than that +of the small tube, the latter may be enlarged with a +carbon or a flanging tool.</p> + + +<h3>EXERCISE NO. 4</h3> + +<h4><span class="smcap">To Join Two Tubes of Different Diameters</span></h4> + +<p>In this case the first method (Exercise No. 1) is to be +used whenever possible, as it gives a much smoother joint +than the second method. The directions given will +describe the adaptation of this method to the problem: +if the second method must be used on account of awkward +shape, etc., of the work, the modifications required +will be obvious to any one who has learned to make the +joint by the first method.</p> + +<p>After sealing or corking one end of the larger tube, the +other end is drawn out to form a tail as described on page +9, taking care to have the tube uniformly heated, and +to draw the tail rapidly enough so that the cone is short, +as indicated in <i>a</i>, Fig. 8. The tube is now rotated, a +small flame directed against the cone at right angles +to an element of it, and it is allowed to shrink a little, +as indicated in <i>b</i>, Fig. 8, so that its walls will thicken. +When the tail is cut off, at the dotted line, the diameter +of the opening and the thickness of the walls at that point +should correspond with the dimensions of the tube to be +sealed on. As the glass is hot, the scratch for cutting it +must be made with a file (moisten the edge!), and it<span class="pagenum"><a name="Page_26" id="Page_26">[Pg 26]</a></span> +often will not break square across. Before proceeding +to seal on the small tube, any large projections on the +cut end are best removed, by warming the cut surface a +little, directing the small flame upon each projection in +turn and touching it with a warm scrap of glass. It will +adhere to this and may then be removed by rotating this +scrap a little so as to wind up the projection on it, and +then drawing it off, while the flame is still playing on the +spot. This must be done rapidly and care taken not to +soften the main part of the cone.<br /><br /></p> + +<div class="figcenter" style="width: 400px;"> +<img src="images/i034.png" width="400" height="256" alt="" title="" /> +<span class="caption">Fig. 8.—Joining two tubes of different diameters.</span> +<br /><br /></div> + +<p>The large tube is now taken in the left hand, the small +one in the right, the ends heated and joined in the usual +manner, taking care not to get any larger lump at the +joint than necessary. A small flame is now directed on +the cone at right angles to its elements as before, and the +tube rotated so as to heat the whole circumference. The +flame should be just large enough to heat the whole of +the cone. As the latter shrinks, the lump at the joint +is brought into the edge of the flame, and it and a very +little of the small tube allowed to shrink with the cone.</p> + +<p>When well shrunk and heated to blowing temperature<span class="pagenum"><a name="Page_27" id="Page_27">[Pg 27]</a></span> +the joint is removed from the flame and blown gently +with careful rotation, pushing the tubes together a little +when the blowing is about finished, so that the cone +becomes a short thick half-bulb, as shown in <i>d</i>, Fig. 8. +This corresponds to the first thick bulb in the first method +(<i>d</i>, Fig. 6), and is treated similarly. It is again heated +and shrunk, taking care not to involve either the large +tube or the small one in the shrinking, blown quickly to +about the same shape as before, (<i>d</i>, Fig. 8), and then +gently drawn out into a smooth cone (<i>e</i>), exactly as in the +first exercise. Care should be taken not to draw too +rapidly or too far, as then the resulting cone (<i>f</i>) is weaker +than it should be, and does not look well.</p> + +<p><b>Discussion.</b>—The beginner will find that this operation +is best learned on two tubes which are not too nearly of +the same diameter. A tube about <span style="font-size: 0.8em"><sup>5</sup></span>⁄<span style="font-size: 0.6em;">8</span> inch in diameter +and one a little less than <span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">4</span> inch will be suitable. Both +should have moderately heavy walls (<span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">16</span> inch or a +trifle over for the large tube, and a trifle less for the small +one) but the large tube should not be too heavy or else it +will be hard to prevent melting down too much of the +small tube, and getting this drawn out too thin during the +process. One of the troublesome features of this exercise +is the difficulty of rotating two tubes of different diameters +with the same angular velocity, so as not to twist the +joint. Another difficulty is found in getting the cone +uniformly heated to blowing temperature without overheating +and overshrinking the small tube. The reason +for this is obviously the much greater circumference of +the cone, especially at its large end, so that relatively +much less of it is being heated at any time. The beginner +is also inclined to start with too long a cone, or else heat +so much of the large tube that part of its glass is included +in the cone, with the result that in order to get the<span class="pagenum"><a name="Page_28" id="Page_28">[Pg 28]</a></span> +right wall-thickness the cone must be made too long (<i>g</i>, +Fig. 8). This does not look well, and usually will be +irregular in shape.</p> + + +<h3>EXERCISE NO. 5</h3> + +<h4><span class="smcap">Tube for Condensing Sulphur Dioxide</span></h4> + +<p>This is useful as a test of mastery of the preceding +exercise. A piece of <span style="font-size: 0.8em"><sup>3</sup></span>⁄<span style="font-size: 0.6em;">16</span> or <span style="font-size: 0.8em"><sup>7</sup></span>⁄<span style="font-size: 0.6em;">32</span> inch tubing is joined +to each end of a piece of tubing <span style="font-size: 0.8em"><sup>5</sup></span>⁄<span style="font-size: 0.6em;">8</span> by about 5 inches, and +two constrictions made in the large tube, by the method +described on page 10. The small tubes are then bent +in the same plane, as shown, and their ends fire-polished +(Fig. 9).<br /><br /></p> + +<div class="figcenter" style="width: 400px;"> +<img src="images/i036.png" width="400" height="98" alt="" title="" /> +<span class="caption">Fig. 9.—Tube for condensing sulphur dioxide.</span> +<br /><br /></div> + +<h3>EXERCISE NO. 6</h3> + +<h4><span class="smcap">Bulb at the End of a Tube</span></h4> + +<p>For this exercise tubing of <span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">4</span> inch diameter and moderately +strong walls is selected. A tail is drawn out on one +end of the tube, and a piece of tubing about nine or ten +inches long is cut off. The tail should be carefully drawn +in the axis of the tube, and in the same straight line with +it, as it is to be used as a handle in assembling the glass +for the bulb. This tail must be long enough so that it +can be conveniently held in the left hand, as described on +page 13, and rotated about the same axis as the main +tube. Holding the main tube in the right hand and the +tail in the left, the tube is rotated in a large flame so<span class="pagenum"><a name="Page_29" id="Page_29">[Pg 29]</a></span> +that a piece of it, beginning where the tail stops and +extending about an inch to the right, may be uniformly +heated to the highest temperature at which it can be +kept in shape. As soon as +this temperature is reached, +the tube is removed from the +flame, continuing the rotation +and taking care not to draw +out the heated part, and +gently blown. The rotation +is carefully continued during +the blowing, holding the tube +in approximately a horizontal +position. As soon as the tube +has expanded a little the tail +is pushed gently toward the +main tube, continuing the +gentle blowing. If this is +properly done, the heated +piece of tube will become a +short bulb of about double its +original diameter, and about +the same wall thickness as the +original tube. It will have +somewhat the appearance of +<i>a</i>, Fig. 10, when properly manipulated.<br /><br /></p> + +<div class="figcenter" style="width: 189px;"> +<img src="images/i037.png" width="189" height="400" alt="" title="" /> +<span class="caption">Fig. 10.—Blowing a bulb on +the end of a tube.</span> +<br /><br /></div> + +<p>The tube is now reheated as before, taking care this +time that the heating extends over all that part of the +bulb to the right of the dotted line in the figure, as well +as part of the main tube adjoining. If this heating has +been properly placed, when the operation of blowing and +pushing together is repeated the result will be to lengthen +the bulb into a uniform cylinder, as shown in <i>b</i>, Fig. 10. +Otherwise the result will be a series of bulbs, as in <i>c</i>,<span class="pagenum"><a name="Page_30" id="Page_30">[Pg 30]</a></span> +Fig. 10, separated by thickened ridges which will be +almost impossible of removal later and will disfigure the +final bulb. This operation of heating, blowing and +pushing together is repeated several times, until the +cylinder becomes as long as can be conveniently handled +(about 1-<span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">4</span> inches to 1-<span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">2</span> inches). If more glass is +needed than is then contained in the cylinder, the latter +may now be heated as a whole, and blown and pushed +gently into a shorter cylinder of a slightly greater diameter, +and more glass then added as before.</p> + +<p>When enough glass has been collected for the bulb, it +is all well heated and blown gently a couple of times, +pushing the mass together as required, until a thick bulb +like <i>d</i>, Fig. 10, is obtained. The tail must now be +removed at the point indicated by the dotted line. To +do this, a very fine flame is directed on the point where +the tail joins the bulb, and the tube well rotated as the +glass softens at that point. When sufficiently soft, the +work is raised a little, so that the flame instead of striking +the glass squarely at the point indicated passes below and +tangential to it. The tail is now drawn off slowly, continuing +the rotation, raising the work just out of the +flame whenever the thread of glass drawn off becomes too +thin, and lowering it again to the point where the flame +just touches it when the glass stiffens a little. By this +means the tail may be drawn off without leaving an +appreciable lump behind, as indicated in <i>e</i> and <i>f</i>, Fig. 10. +When as much of the extra glass has been removed as is +practicable, the flame is brought to play squarely upon +the little lump left, the last of the tail removed, and the +lump heated and gently blown to a small excrescence on +the main bulb. The whole end of the latter is now heated +until it begins to shrink a little, and gently blown to +make it uniform in thickness. The whole bulb is then +heated in a flame of the proper size, so that it all may<span class="pagenum"><a name="Page_31" id="Page_31">[Pg 31]</a></span> +shrink to about two-thirds of its diameter. The flame +must be very carefully chosen and directed, so as to +shrink all the bulb, right up to the main tube, but not +soften the latter. As soon as this stage is reached, the +bulb is removed from the flame, continuing the even +rotation, and blown to the desired size, preferably by a +series of gentle puffs following one another at very short +intervals. During the blowing, the main tube is held in +a horizontal position, and any tendency of the bulb to +fall out of line is corrected by the rotation. If the shape +of the bulb or its size are not satisfactory, it may be +shrunk again and reblown. Such shrinking should begin +in a large yellow flame, with just enough air to give it +direction. The amount of air may be gradually increased +as the bulb shrinks and the walls become thick enough to +bear it without collapsing. If the bulb starts to collapse +at any time, it must be immediately blown enough to +regain its convex surface, before the shrinking proceeds +further.</p> + +<p><b>Discussion.</b>—In collecting the glass for the bulb, +enough must be gathered to give the walls the desired +strength. Since the area of a sphere is proportional to +the cube of its diameter, it is evident that doubling the +size of a bulb diminishes the thickness of its walls to a +very large extent. The limit of diameter for a strong +bulb on ordinary <span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">4</span>-inch tubing, collecting the glass as +above, is about 1-<span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">2</span> inches, and the beginner will do well +not to blow his bulbs more than an inch in diameter.</p> + +<p>The collection of the glass is one of the most important +parts of the process. If the mass of glass be twisted, furrowed +or ridged, or lop-sided, it is very difficult to get a +good, even, spherical bulb, no matter how many times it +is shrunk and blown. The greatest care should therefore +be taken to get a uniform cylinder, on the same axis as +the main tube; and to this end the rotation of the tube<span class="pagenum"><a name="Page_32" id="Page_32">[Pg 32]</a></span> +must be carried on very evenly. For method of holding +the tube, see page 14.</p> + +<p>If a very large bulb is required, it will often be economical +to seal on the end of the tube a short piece of a large +tube, provided with the proper tail, and use the glass in +the large tube for the bulb instead of attempting to collect +it from the small tube. In this case part of the small +tube will usually be included in the bulb, so that the joint +comes in the latter, and not where it joins the tube. As +the amount of glass carried on the end of the tube +increases in weight and size the difficulties of heating it +uniformly, keeping it in the proper position and handling +it increase rapidly.</p> + +<p>In collecting glass, it is usually best not to leave the +part of the cylinder next the tube with too thick walls. +This is always the coolest part during the preparation for +blowing the bulb, consequently it does not get blown out, +and causes an ugly thickened appearance on that end of +the bulb.</p> + +<p>If the bulb grows too long or pear-shaped, it may be +easily shortened by heating to the blowing temperature, +and then blowing gently with the main tube in a vertical +position, and the bulb at the top of it. Gravity will then +shorten the bulb nicely.</p> + +<p>The finished bulb should be a nearly perfect sphere, +with the axis of the tube passing through its center, and +the portion of the tube adjoining the bulb must not be +distorted, twisted, or blown out. In order to prevent the +distortion of the tube, care must be taken that it is never +heated quite to its softening point during the process.</p> + + +<h3>EXERCISE NO. 7</h3> + +<h4><span class="smcap">Blowing a Bulb in a Tube</span></h4> + +<p>The tube is selected and one end closed as in the previous +exercise, but it should be cut a little longer, say<span class="pagenum"><a name="Page_33" id="Page_33">[Pg 33]</a></span> +about twelve inches. Beginning at a point about four +inches from the closed end, glass is collected and blown into +a thick-walled bulb, exactly as in the previous exercise. +Greater care must be taken, however, that the cylinder +collected and this thick bulb are of uniform thickness and +set squarely in the axis of the tube. Instead of removing +the tail, the bulb must be blown in this case with both +pieces of tubing attached, and care must be taken that +they "line up" properly, <i>i.e.</i>, are in the same straight +line, and that this line passes as near as may be through +the center of the bulb. The tube is held in approximately +horizontal position during the blowing of the bulb, as in +the previous case, and especial care taken with the rotation. +Both pieces of tube must of course be rotated at +the same rate, and their softened ends must be kept at +exactly the proper distance from each other, so that the +bulb may be spherical and not elongated. If the blowing +of the bulb be quickly and accurately done, it may +usually be completed before the glass is quite set, and the +alignment of the two tubes may then be rectified while +looking straight through the bore of the tube.</p> + +<p><b>Discussion.</b>—The two points of greatest importance +are the collection of the glass, and the uniform rotation +of the tube. A larger tube may be sealed in the middle of +a small one when a large amount of glass is necessary. +The piece of tubing used for the exercise must be long +enough so that the fingers may be kept on a cool part of +the glass without getting uncomfortably near the ends +of the tube. It should not be any longer than necessary, +however, as the extra weight and length make the manipulation +of the hot glass more difficult.</p> + +<p>When a string of bulbs are required on the same tube, a +piece of glass 18 inches long may be used at the start, +and the first bulb made near the closed end, as described. +Each succeeding bulb will then be in plain view during the<span class="pagenum"><a name="Page_34" id="Page_34">[Pg 34]</a></span> +blowing, and when the open end becomes too short for +comfort, it may be dried out, cut off, and another piece +joined to it, starting as in the first method (Exercise +No. 1), but instead of drawing out the thick bulb to a +tube, it is made part of the glass collected for the next +bulb. If the string of bulbs becomes awkward to handle +on account of its length and weight, it may be made in +several parts and these later sealed together by the second +method, preferably blowing through a rubber tube attached +to the open end, as described on page 22.</p> + +<p>Very neat small bulbs may be made on tubing of a +diameter of <span style="font-size: 0.8em"><sup>3</sup></span>⁄<span style="font-size: 0.6em;">16</span> inch or a little less, but the beginner is +advised to start with tubing of about <span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">4</span> inch diameter. +The use of tubing with too thick walls usually produces +bulbs which are thick-walled at the point where they +leave the tube, but inclined to be too thin at the point of +maximum diameter (perpendicular to the axis of the tube) +where most of the strain comes and strength is particularly +needed.</p> + +<hr style="width: 65%;" /> + +<p><span class="pagenum"><a name="Page_35" id="Page_35">[Pg 35]</a></span></p> + +<h2>CHAPTER IV</h2> + +<h3><span class="smcap">Advanced Exercises</span></h3> + + +<h3>EXERCISE NO. 8</h3> + +<h4><span class="smcap">Sealing a Tube Through Another Tube</span></h4> + +<h4><i>First Method—Making a Gas-washing Tube</i><br /><br /></h4> + +<p>This first method can be used whenever one can work +through an open end opposite to the end of the tube +where the joint is to be made. To illustrate it, take a +piece of rather thin-walled tubing, about <span style="font-size: 0.8em"><sup>3</sup></span>⁄<span style="font-size: 0.6em;">4</span> inch in +diameter, and some pieces of rather strong tubing a little +less than <span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">4</span> inch in diameter. Draw off the large tube +in a short cone, then draw off the tail as in the making of +the bulb on the end of the tube, blow out the little lump +slightly, shrink the whole cone a little and blow gently to +form a rounded end like that on a test-tube, with walls +about the thickness of those of the rest of the tube. Cut +this tube to a suitable length, say about six inches, and provide +two corks which will fit the open end of it. Now cut +a piece of the small tubing of the proper length to form +the piece which is to be inside the large tube. For practice +purposes, this piece should be about an inch shorter +than the large tube. Flange one end of this tube a little, +and anneal the flange well in the smoky flame. Bore one +of the corks so that a piece of the small tubing will fit it, +and cut a couple of notches in the side of this cork so that +air can pass between it and the glass. Pass a short piece +of the small tubing through this cork, and attach the<span class="pagenum"><a name="Page_36" id="Page_36">[Pg 36]</a></span> +flanged piece of small tube to this by means of a short +piece of rubber tubing, so that when the whole is inserted +in the large tube it is arranged as in <i>a</i>, Fig. 11. The piece +of glass tubing projecting out through the cork is now cut +off so as to leave an end about <span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">2</span> inch long when the +cork is firmly seated and the inner tube pushed into +contact with the center of the end of the large tube, as +shown in the drawing. Care should be taken that the +little rubber tube which joins the two pieces is arranged +as in the figure; <i>i.e.</i>, most of it on the piece of tubing which +passes through the cork, and very little on the other +piece, so that when the cork is removed after the small +tube has been sealed through the large one, the rubber +tube may easily come with it. Select a short piece of the +small tubing of suitable length for the piece which is to<span class="pagenum"><a name="Page_37" id="Page_37">[Pg 37]</a></span> +be on the outside of the large tube as a continuation of +the piece inside, and another piece for the delivery tube. +A small bulb may be blown in the latter at a point about +2-<span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">2</span> inches from the closed end, and the open end cut +off about 1-<span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">2</span> inches from the bulb. A cork or cork-boring +of suitable size to stopper the small tube is prepared, +and laid ready with the other (unbored) cork for +the large tube.<br /><br /></p> + +<div class="figcenter" style="width: 400px;"> +<img src="images/i044.png" width="400" height="375" alt="" title="" /> +<span class="caption">Fig. 11.—Gas-washing tube.</span> +<br /><br /></div> + +<p>When everything is in readiness, the rounded end of the +large tube is slowly heated until it softens and joins firmly +to the small tube inside. After it has shrunk down well, +it is blown out to its original size, placing the whole end +of the large tube, cork and all, in the mouth. Now with a +fine-pointed flame the glass covering the end of the small +tube is heated to the softening temperature, and then is +blown out to an excrescence by blowing on the end of the +small tube which passes through the cork. The end of +this excrescence is heated and blown off in the usual way, +so as to leave the small tube sealed on the inside of the +large one and opening through it into this short tube which +has been blown out. The end of the small tube which +passes through the cork is now closed with the cork prepared +for it, and the short outer tube is joined to the tube +that has just been blown out, so that the joint appears +like <i>b</i>, Fig. 11. Use the first method (Exercise No. 1) +for this joint. Reheat the whole of the end of the tube +nearly to the softening temperature, anneal it a little, +and allow to cool a few seconds until well set. Now +remove the cork, short glass tube and rubber tube from +the open end of the large tube and insert the solid cork +in their place. Warm the joint and the whole of that +end of the tube again carefully up to about the softening +point, then seal on the side tube for the delivery of the +gas in the usual way, taking care that the whole of the +end and the joint are kept warm meanwhile. When<span class="pagenum"><a name="Page_38" id="Page_38">[Pg 38]</a></span> +thoroughly sealed, the delivery tube is bent up parallel +to the tube through which the gas enters, and then out +at right angles to it, as shown in <i>c</i>. The whole of the +end of the tube is now cautiously reheated and then cooled +slowly to anneal it.</p> + +<p>The cork may now be removed from the open end of +the large tube, this end heated in a large flame, caught +together with a scrap of glass tubing and drawn off into +a cone so that the base of the cone is about opposite the +end of the inner tube. The lump of glass is drawn off the +point of this cone and it is reblown to form a rounded +end, as previously described.</p> + +<p>After this cools, the tube through which the gas enters +may be heated at the proper point and bent at right +angles to form the finished apparatus as shown in <i>d</i>. +The ends of the small tube are cut off square and fire-polished.</p> + +<p><b>Discussion.</b>—After the joint has once been made, great +care must be taken that it is kept hot during all the subsequent +manipulations, and if it becomes somewhat +cool at any time it must be reheated very slowly. It is +obvious that the rate of heating and cooling of the inner +tube will be slower than that of the outer tube, and this +will readily produce stresses which tend to crack the tube +at the joint. The amount of heating and cooling which +such a joint will stand depends upon its form. The +beginner should examine such a joint on regular factory-made +apparatus, and note the uniformity of wall-thickness +and the "clean-cut" appearance of the joint, as a +model for his imitation. A ragged joint, where the line +of joining of the inner and outer tubes wavers instead of +going squarely around the tube, is almost sure to crack +during the cooling and heating unless extra precautions +are taken with it. The presence of a small lump of glass +at any point on the joint affords an excellent starting<span class="pagenum"><a name="Page_39" id="Page_39">[Pg 39]</a></span> +place for a crack, as do also the points on a ragged joint +where the inner tube comes farther down on the outer +tube than at other points.</p> + +<p>In order to insure a joint which is square and not +ragged, it is essential that the angle between the inner +and outer tubes at the joint be very nearly a right angle. +For this reason the two tubes should not be of too near +the same size, or if this cannot be avoided, a small bulb +should be blown on the end where the joint is to be made. +If this bulb be made with the same wall-thickness as the +rest of the tube, and somewhat pear-shaped, it may be +drawn out to the same size as the rest of the tube, if +necessary, after the joint has been made.</p> + +<p>This method is used wherever possible in preference to +the second method (Exercise No. 9), as it is easier to get +a good joint with it. It may also be used where it is +desired to seal the tube through the side of a tube, or for +a tube sealed through the wall of a bulb, as in a Geissler +potash bulb or similar apparatus. Where there is not +space to join the inner tube to the blowing tube by a +rubber tube, this joint may be made with a small piece +of gummed paper, which can readily be broken when +desired.</p> + + +<h3>EXERCISE NO. 9</h3> + +<h4><span class="smcap">Sealing a Tube Through Another Tube</span></h4> + +<h4><i>Second Method—Making a Suction Pump</i></h4> + +<p>Select a piece of tubing <span style="font-size: 0.8em"><sup>3</sup></span>⁄<span style="font-size: 0.6em;">8</span> to <span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">2</span> inch in diameter, +with walls about <span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">16</span> inch or a little less in thickness, +heat a place about 4 inches from one end and draw it +out so that when cut off at the proper point it will look +like <i>a</i>, Fig. 12; the open end of the drawn out part being +small enough to slip inside another piece of the original +tube. A small thick-walled bulb is now blown as<span class="pagenum"><a name="Page_40" id="Page_40">[Pg 40]</a></span> +indicated by the dotted lines, and annealed. A piece of +the original tubing is now prepared, 7 or 8 inches long, +with one end cut square off and the other closed. A +piece of <span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">4</span>-inch tubing about 2 inches long, and drawn out +at one end to a tail several inches long is also prepared, to +form the inlet tube for the air. Another piece of the +<span style="font-size: 0.8em"><sup>3</sup></span>⁄<span style="font-size: 0.6em;">8</span>-inch tube is prepared, about 4 inches long, and provided +with a tail drawn out as indicated in <i>b</i>, so that when +cut off at about 2-<span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">2</span> or 3 inches from the main tube its +inner diameter may be slightly less than that of the narrowest +point of the tube <i>a</i>. A small thick-walled bulb +is blown at the point indicated by the dotted lines, and +annealed. Care must be taken in drawing the capillary +and blowing the bulb in both <i>a</i> and <i>b</i> that the capillary +tubes are in the axis of the main tube, and in the same +straight line with it.<br /><br /></p> + +<div class="figcenter" style="width: 400px;"> +<img src="images/i048.png" width="400" height="160" alt="" title="" /> +<span class="caption">Fig. 12.—Suction pump.</span> +<br /><br /></div> + +<p>The open end of the 8-inch piece of tube and the bulb +of the piece <i>a</i> are now warmed together, the end of the +tube only moderately and the bulb to about its softening +temperature. The tube <i>a</i> is now inserted in the open end +of the large tube, and the bulb softened with a suitable +flame and pressed into good contact with the tube. It +is then reheated, including the joint, blown a little and +pulled out to form a straight tube in line with the main +tube. By warming the joint a little, and proper rotation,<span class="pagenum"><a name="Page_41" id="Page_41">[Pg 41]</a></span> +the capillary may be brought into the same straight line +with the rest of the tube.</p> + +<p>Keeping this joint hot, a place about an inch from it on +the tube <i>a</i> is warmed, and the piece of <span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">4</span>-inch tubing +previously prepared is sealed on at that point. The +joint is then well annealed and allowed to cool.</p> + +<p>The tube <i>a</i> is now cut at such a place that when <i>b</i> is +inserted in the open end the point will come near the +end of the constriction of <i>a</i>, as shown in <i>c</i>. Care is +taken to get a clean square cut. The side tube is now +cut off about an inch from the main tube and corked. +Tube <i>b</i> is sealed into the open end of <i>a</i>, in the same way as +<i>a</i> was sealed into the large tube, and the joint carefully +annealed.</p> + +<p><b>Discussion.</b>—As in the first method, the secret of success +lies in getting a square joint, and having the inner +tube leave the outer one at nearly right angles. All the +remarks about annealing, lumps, etc., made under the +previous method apply here.</p> + +<p>This method may be applied in sealing a small tube +into the end of a large one, the latter being either drawn +to a cone and cut off at the desired diameter, or else +given a rounded end like a test-tube and a hole the proper +size blown in the center of it. A suitable thick-walled +bulb is to be blown on the small tube, as in the case +described above. This method is also used in making +the Kjeldahl trap (<i>a</i>, Fig. 13), the small tube to be +inserted being first drawn, the thick bulb blown at its +point of union with the main tube, and then the small +tube bent and cut. The large bulb is best made with +rather heavy wall, being either blown in the middle of +a tube, and one piece of the tube drawn or cut off, or +else made on the end of a tube. In the latter case a drop +of glass must be put on the point where the joint is to +be, so as to get a hole of the proper size with enough glass<span class="pagenum"><a name="Page_42" id="Page_42">[Pg 42]</a></span> +around it to prevent it from growing larger when it is +heated. The author prefers to blow the bulb in the +middle of the tube, draw off one end of the bulb, and +blow out the desired hole where the tube was drawn off. +The whole bulb must generally be reheated and blown +a little at the end of the process, and well annealed.<br /><br /></p> + +<div class="figcenter" style="width: 400px;"> +<img src="images/i050.png" width="400" height="328" alt="" title="" /> +<span class="caption">Fig. 13.—a, Kjeldahl trap; b, suction pump on smaller tubing.</span> +<br /><br /></div> + +<p>The suction pump can also be made on <span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">4</span>-inch tubing, +and one joint saved if desired, by constricting the tube +to form the raceway for the water and air, as shown in +<i>b</i>, Fig. 13. (See page 10 for method.) But it is more +difficult to make a square joint on such small tubing.</p> + + + +<hr style="width: 65%;"/><p><span class="pagenum"><a name="Page_43" id="Page_43">[Pg 43]</a></span></p> +<h2>CHAPTER V</h2> + +<h3><span class="smcap">Modified Methods and Special Operations</span></h3> + + +<h4>CAPILLARY TUBING</h4> + +<p>This is commonly used in many forms of apparatus +for gas analysis, and one is often called upon to join two +pieces or to make a tee on it. The methods are nearly +the same as with other tubing, except that more care and +patience are required. The work must be done much +more slowly on account of the thickness of the walls, and +open ends of the tube must always +be enlarged before joining them to +anything. This is best done by carefully +sealing the end and then blowing, +with several suitable reheatings, to +form a pear-shaped bulb as in <i>a</i>, Fig. +14. The end of this is then heated +and blown off, and the piece is ready +to be joined to another similar end, or +to a piece of ordinary tubing if desired. +The joints are best not blown +too much, as thick walls shrink very slowly. Much may +be done by gently pushing the tube together or pulling +it apart in the flame, to remove lumps and irregularities. +It is necessary that the bore of the joint be approximately +that of the main tube, and care must be +taken that the latter is not constricted at the point +where the joint begins.<br /><br /></p> + +<div class="figcenter" style="width: 255px;"> +<img src="images/i051.png" width="255" height="300" alt="" title="" /> +<span class="caption">Fig. 14.—Capillary +tubing.</span> +<br /><br /></div> + +<p>Especial care must be taken to warm the tube slowly +when starting and cool it slowly when through, as the<span class="pagenum"><a name="Page_44" id="Page_44">[Pg 44]</a></span> +thick walls frequently crack if not carefully handled. +For this reason the whole neighborhood of the joint must +be heated somewhat so that there may not be stresses set +up between the heated and unheated portions.</p> + +<p>In making the tee (<i>b</i>, Fig. 14) the inability to blow the +joint makes itself decidedly felt, but if the side tube is +properly enlarged as previously described, a good joint +can be made by alternately pulling and pushing on the +end of the side tube, and shrinking well.</p> + +<p>Very fine capillary tubing should be blown with a +rubber bulb instead of the mouth, so as not to get +moisture into the tube. The rubber bulb may also be +used to advantage on some of the coarser capillary +tubing.</p> + +<p>When a bulb is to be joined to a piece of capillary +tubing, the joint is preferably made before blowing the +bulb, and will then be taken up a little way on the bulb +during the process. Care must of course be taken not to +constrict the capillary; the pear-shaped bulb blown on +the end (<i>a</i>, Fig. 14) may well extend back a little further +than usual into the tube so as to prevent this. If a bulb +is required in the middle of a capillary tube, the latter +is usually best cut and a piece of ordinary tubing of suitable +size sealed in to provide material for the bulb.</p> + + +<h4>GLASS ROD</h4> + +<p>Joints, tees, etc., in glass rod are made on the same +principle as in tubing, except that of course they cannot +be blown, and regularity must be obtained by accumulating +a small mass of uniformly heated glass, and then +drawing it to a suitable rod, on the same principle as +Exercise No. 1.</p> + +<p>Great care must be taken in heating and cooling this, +as in the case of the capillary tubing, and for the same +reasons.</p> + +<p>By joining pieces side by side, pressing with carbon<span class="pagenum"><a name="Page_45" id="Page_45">[Pg 45]</a></span> +plates or a plate and a rod, and other suitable manipulations, +stirrers, spatulas, and other objects may easily +be made from rod, and its manipulation is relatively easy +on account of the fact that one does not have to worry +about the bore of the tube. But the same general rule +about not having thick and thin spots in contact, and +making all changes in diameter on a taper if possible +instead of abruptly, applies here. Thick pieces will cool +and contract at different rates from thin ones, and cracks +are likely to develop where they join. Work which +has been formed with any tool must always be heated to +the softening point afterward before allowing it to cool +in order to remove the stresses caused by the contact of +the tool with the hot glass.</p> + +<p>When it is necessary to join a piece of rod to the side +of a piece of tubing, the end of the rod is made very hot +while the wall of the tube at the spot desired is heated to +just below the softening temperature. The rod can then +be pressed into firm union with the tube and drawn a +little to remove the excess of glass without deforming the +tube.</p> + + +<h4>MENDING STOPCOCKS</h4> + +<p><b>Mending the Plug.</b>—The plug of the stopcock occasionally +falls out and is broken. If the break is in the +main part of the plug, nothing can be done except to +search for a spare plug of suitable size and grind it to +fit, as described below. If only the little cross-piece at +the end is broken off, it can easily be replaced. In +most ordinary stopcocks the plug is solid, but the little +handle is hollow. What has been said above regarding +care in heating and cooling glass rod applies with especial +force here. It is usually best to wind the whole of the +plug with several thicknesses of asbestos cord, leaving<span class="pagenum"><a name="Page_46" id="Page_46">[Pg 46]</a></span> +bare only the end where the handle is to be joined. This +diminishes the danger of cracking the plug by too rapid +heating, and also makes it more comfortable to hold. A +piece of rather thick-walled tubing of suitable diameter is +chosen, drawn out so as to have a suitable taper (taking +care to heat enough of the tube so that the capillary tail +has good wall-thickness and strength), and then a +corresponding taper is drawn to form the other side +of the handle. The result is shown in Fig. 15, <i>a</i>. The +capillary tail is now heated and bent back to form a +handle which will be in the same straight line as the axis +of the plug (<i>b</i>, Fig. 15) and the main part of the tube +drawn off at the dotted line, making a neat seal at that +point. The broken end of the plug is now slowly warmed +in the smoky flame, the heat gradually increased by a +gentle stream of air from the bellows, and the point at +which this handle is to be attached finally brought to +the temperature at which the glass flows freely. In the +mean time, the little handle has been warmed almost to +the softening point. It is now quickly pushed into place +(<i>c</i>, Fig. 15), taking care that its axis is parallel to the hole +in the plug, and then drawn away from the plug just +enough to make a graceful neck instead of the bulging one<span class="pagenum"><a name="Page_47" id="Page_47">[Pg 47]</a></span> +indicated by the arrow in the figure. With a fine pointed +flame the little tail is now drawn off at the point indicated +by the dotted line (<i>c</i>, Fig. 15) and the whole carefully annealed. +If necessary, the handle can be blown a little +before the tail is removed. Local heating and blowing at +the point where the handle joins the plug is often necessary +in order to make a smooth job.<br /><br /></p> + +<div class="figcenter" style="width: 400px;"> +<img src="images/i054.png" width="400" height="217" alt="" title="" /> +<span class="caption">Fig. 15.—Stopcock plug.</span> +<br /><br /></div> + +<p><b>Regrinding.</b>—This is sometimes necessary to make +stopcocks tight, when the grinding has not been properly +done in the factory. For this, a very little fine flour of +emery or carborundum is the best and quickest. If this +is not at hand, some clean sand may be ground in an agate +mortar, and if possible sieved. Only material which +passes the 100-mesh sieve should be used. It will be +ground still finer in the process. For the final polishing, +a little infusorial earth or even kaolin will do.</p> + +<p>The surface to be ground is moistened with water and +dusted over with a little of the abrasive. The plug is +now inserted in the stopcock, and turned with a gentle +pressure. This turning should be in the same direction +for several revolutions, then in the opposite direction for +several more revolutions, etc. As the abrasive becomes +finer during the grinding, a little more may be added if +necessary. In general, only a little grinding will be +required, and one small pinch of carborundum or emery +will be ample. The beginner usually grinds too much, +and with too coarse material. As the grinding surface +becomes dry, water is added drop by drop, and the grinding +continued until the abrasive seems to be reduced to +an impalpable powder, most of which has been squeezed +out of the stopcock. The two surfaces in the stopcock +are usually grinding upon each other at this stage, and +inspection will show whether the contact between them +is uniformly good. If not, the grinding must be continued +with a little fresh abrasive. If contact appears<span class="pagenum"><a name="Page_48" id="Page_48">[Pg 48]</a></span> +to be good, the surfaces are ground together for a little +with practically no abrasive, so as to polish them, and +the joint is then washed out and tested.</p> + +<p>In grinding in a new plug to replace a broken one, the +plug selected should have practically the same taper as +the seat into which it is to be ground, and should be a +very little too large. Care must be taken to so distribute +the abrasive material as to grind mostly on the places +where the plug fits tightly.</p> + +<p><b>Sealing on a New Tube.</b>—It frequently happens that +one of the tubes of the stopcock is broken off close to +the cock itself, and a new one must be joined to the +stub of the old one. With care, this may often be successfully +done even where the break is within <span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">4</span> inch +of the stopcock. The first step is to clean and dry the +stopcock, remove the plug, cork the open ends of the +stopcock sleeve and the other tube, and wind a couple +of layers of asbestos cord carefully over the sleeve and +the most of the corks which close it. A suitable tube, +having as near as possible the same diameter and wall +strength as the one broken off, is selected and a piece +the desired length cut off. The broken end of the tube +on the stopcock is now squared off as well as possible, +by cutting or by heating and drawing off the projections, +and the new tube sealed on, usually with the first method +(Exercise No. 1). If the break is very close to the stopcock, +very little reheating and blowing can be done, on +account of the danger of getting the stopcock sleeve out +of shape, and the work must be heated very slowly to +prevent cracking. The main reliance is then placed on +making a good joint when the tubes are brought together, +and then drawing out this joint a little, at once, to get an +even wall.</p> + + +<h4>CLOSED CIRCUITS OF TUBING.</h4> + +<p><span class="pagenum"><a name="Page_49" id="Page_49">[Pg 49]</a></span></p> + +<p>In some pieces of apparatus closed circuits of circular +or rectangular shape are required. A similar problem +is involved in apparatus like the ordinary Soxhlet +extractor, where a small tube is joined to the side +of a large one, bent to form a siphon, and attached +again to a continuation of the original large tube. +The difficulty in all such cases is to provide for the +contraction taking place as the last joint cools. If +part of the circuit has the shape of the letter S, or is a +spiral, the natural springiness of the glass will take care +of this. If not, the side of the circuit opposite to the +joint and parallel to it must be heated also, the two being +finally heated together to the softening point after the +joint is completed, and then allowed to cool together.</p> + +<p>To make the last joint, the rest of the tube is made in +approximately the desired form, the two pieces which are +to be joined to make the last joint being just enough out +of the desired position to allow them to pass one another. +The final joint is preferably made in the middle of a +straight piece of tube, not at a tee. The two pieces +which are to be joined are bent so as to just pass each +other, marked at the right point with the glass-knife, +and cut there, preferably with a small bead of hot glass. +One or both of these tubes are now warmed to the softening +point in such a place that the tubes can be made to +meet properly, and the two cut ends pressed together. +They are now warmed in the flame, and joined together, +either by simultaneously warming the opposite side of +the circuit or some other suitable part, so as to allow the +two ends to be pushed together again after they are +softened, or by gently touching the places that do not +unite with a hot bead of glass, and using the glass to fill +up the crack where the ends do not quite meet. Care<span class="pagenum"><a name="Page_50" id="Page_50">[Pg 50]</a></span> +must be taken not to leave knots or lumps of glass in the +finished joint, and the latter should be well reblown, and +if necessary left as a small bulb or enlargement, rather +than have it have too thick walls.</p> + + +<h4>SPIRALS<br /><br /></h4> + +<p>Spirals of glass tubing are probably best made free-hand +before the blow-pipe, unless one has a great many of +them to make, and extreme accuracy is desired. To +begin with, a piece of tubing of the desired size (say <span style="font-size: 0.8em"><sup>3</sup></span>⁄<span style="font-size: 0.6em;">16</span> +inch in diameter) and a convenient length (about two feet) +is selected, one end closed, and a right-angle bend made +about six inches from the closed end. Holding the closed +end in the left hand and the long open one in the right, +the spiral is begun. The short closed end is to be parallel +to the axis of the spiral, and preferably in that axis. +Using a moderate-sized flame, of somewhat yellow color, +and taking care to heat the whole circumference of the +tube, the long open end is wound little by little into a +spiral having the short end <i>a</i> (Fig. 16) as an axis. The +bend at <i>b</i>, where the tube changes from the radius to the +circumference of the circle, must be rather short, but +the tube must not be flattened or constricted here.<span class="pagenum"><a name="Page_51" id="Page_51">[Pg 51]</a></span> +Especial pains is to be taken with the first turn of the +spiral (<i>b</i> to <i>c</i>, Fig. 16), as the shape of this determines the +diameter of the whole spiral, and serves as a guide for the +rest of the turns. The winding of the tube is best accomplished, +after a portion has been softened, by slowly +turning the short end <i>a</i> a little about its own axis, while +the long open end remains where it was. This winds +the tube into a spiral, just as if there were a solid cylinder +in the center of it, and this cylinder was being turned +about its axis, and was winding up the soft glass upon its +circumference. As the cylinder is not actually there, the +curve of the turns must be carefully estimated by the +eye, so that the spiral may be uniform and moderately +smooth. When the original piece of tube has been used +up, another piece is sealed on to the open end, and the +operation continued as far as may be required.<br /><br /></p> + +<div class="figcenter" style="width: 400px;"> +<img src="images/i058.png" width="400" height="228" alt="" title="" /> +<span class="caption">Fig. 16.—Making a spiral.</span> +<br /><br /></div> + + +<h4>GROUND JOINTS</h4> + +<p>It is sometimes required to join two pieces of tubing +end to end, by means of a ground joint. Whenever +possible, a regular sealed joint should be used instead +of this ground joint, as it is quicker to make, and +more certain to be tight. Where a ground joint is +necessary, however, it is best made in the conical form +shown in <i>c</i>, Fig. 17. If the wall of the tube to be used<span class="pagenum"><a name="Page_52" id="Page_52">[Pg 52]</a></span> +is not very thick, it is thickened by collecting glass as +for a bulb on the ends of two tubes (Exercise No. 6), and +drawing to form cones of suitable shape (<i>a</i> and <i>b</i>, Fig. 17) +and of such relative sizes that a will slip about half way +into <i>b</i>. In order to make <i>a</i> straight and give it the proper +angle, it may be rolled when hot, upon a hot plate of carbon. +Blowing during this rolling is often helpful to +remove depressions. After <i>b</i> has been drawn to nearly +the proper size and shape, it may be smoothed by the use +of a small carbon rod, held inside it at a slight angle, or +better by the use of a truncated hexagonal pyramid of +carbon, whose edges have the proper slant to make the +inside of the cone right. The proper taper for both these +cones is the same as that used in stopcocks of similar size. +The hexagonal carbon can easily be made by carefully +filing down an electric light carbon, and finally impregnating +it with paraffin or beeswax, and is extremely useful +wherever a conical surface has to be formed from the +inside of a tube.<br /><br /></p> + +<div class="figcenter" style="width: 400px;"> +<img src="images/i059.png" width="400" height="223" alt="" title="" /> +<span class="caption">Fig. 17.—Ground joint.</span> +<br /><br /></div> + +<p>The tail is allowed to remain on piece <i>a</i>, as a sort of +guide in grinding, and should therefore be in the axis of +the tube and have rather thick walls. Grind with emery +or carborundum, as described under a previous head. +(Regrinding plug for stopcock.) If many such joints are +to be made, it will pay to have a little sleeve of brass made +with the proper taper, and rough down the plug <i>a</i> in it +to about the proper size, while <i>b</i> is roughed down by +means of a brass or iron plug having the same taper. +This prevents excessive grinding of one-half of the joint +in order to remove a defect in the other half, and is the +method commercially used in making stopcocks.</p> + + +<h4>SEALING IN PLATINUM WIRE</h4> + +<p>Very often it is necessary to seal platinum wire into +the wall of a tube. Professional glass-blowers usually<span class="pagenum"><a name="Page_53" id="Page_53">[Pg 53]</a></span> +use a special sort of glass ("Einschmelzglas") which +is usually a lead glass, and is made of such composition +that it has the same or practically the same +coefficient of expansion as platinum. A little globule +of this glass is sealed into the tube in such a way that +it joins the platinum to the glass of the tube. To do +this, the small globule of special glass is fused on the +platinum wire at the proper point and the tube into +which the wire is to be sealed is heated and a small tail +drawn out at the point where the wire is to be inserted. +The lump of the special glass should be from <span style="font-size: 0.8em"><sup>3</sup></span>⁄<span style="font-size: 0.6em;">32</span> to +<span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">8</span> inch in diameter, and the tail drawn on the tube +should have a slightly less diameter at the point (about +<span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">8</span> inch or less from the tube) where it is cut off. There +are now two ways of sealing in the wire. (1) The wire +with the globule of glass is placed inside the tube and +the latter revolved until the end of the wire sticks out +of the cut tail (<i>a</i>, Fig. 18). The latter is now gently +heated, and the two glass surfaces fused together, taking +care to use only the end of the hissing flame, if the special +glass contains lead. (See Chapter I, page 1.) The +whole circumference of the tube is then heated and annealed +carefully. (2) The end of the wire which is to +be outside the tube is attached to the end of a thin scrap<span class="pagenum"><a name="Page_54" id="Page_54">[Pg 54]</a></span> +of glass, by heating the glass and thrusting the wire into +it a very little way. Using this piece of glass as a handle, +the wire is inserted in the cut tail (<i>b</i>, Fig. 18) and the +globule brought near to the end of the tail. (If the main +tube is cold, it must of course first be warmed.) With +the end of the hissing flame, as in the first method, the +globule of glass is melted and the end of the tail softened. +The wire is now pushed into place, the handle removed +by heating the end and withdrawing it, and the tail reheated +a little if necessary to make it shrink back into +line with the walls of the tube. The whole circumference +of the tube is heated at that point and annealed as +usual.<br /><br /></p> + +<div class="figcenter" style="width: 400px;"> +<img src="images/i061.png" width="400" height="249" alt="" title="" /> +<span class="caption">Fig. 18.</span> +<br /><br /></div> + +<p>The use of this special glass is not absolutely necessary +if the platinum wire is small (<span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">4</span> millimeter or less in +diameter), and in fact it is often better in such cases +not to use it, unless the apparatus is to be subjected to +a very high vacuum. On small tubes, especially, it is +undesirable to use the special glass, as a lump of it will +usually cause the tube to crack on cooling. When such +glass is not at hand or is not to be used, the procedure +is altered somewhat. The tail which is drawn out is +very fine, having only a sufficient diameter so that when +it is cut off the wire can be inserted in it. Such a fine +tail is readily made by heating a small spot on the tube, +touching it with a warm platinum wire, removing from +the flame and drawing out the tail with the wire. After +cutting off the tail the wire is inserted in it, being held +on a scrap of glass as in the previous case, and the wire +and tail heated until the latter shrinks back into line +with the walls of the tube. If too great shrinkage occurs, +the place may be blown out gently after reheating. +Thus the wire is sealed through the wall of the tube without +changing the thickness of the latter, and consequently +without developing undue stresses at that point. Such<span class="pagenum"><a name="Page_55" id="Page_55">[Pg 55]</a></span> +a joint must of course be carefully reheated and annealed. +With fine platinum wire there is very little +risk of the tube cracking if care is taken to avoid formation +of any lump and to reheat the whole circumference +of the tube at that point.</p> + +<p>Any glass adhering to the end of the platinum wire, +where the scrap of glass was sealed on for a handle, may +be removed when the glass has cooled by crushing it +carefully with a pair of pliers.</p> + + +<h4>SEALING VACUUM TUBES</h4> + +<p>Tubes which have been evacuated usually are sealed +off while they are still connected to the vacuum pump. +The connection should be through a small, rather +thick-walled tube. When this is to be sealed, it is slowly +heated toward the softening point. As the glass just +begins to soften, the air-pressure will force it in, and +care must be taken that the softening is uniform over +the whole circumference of the tube. As the shrinking +goes on, the tube is gently drawn out to make a thick-walled +cone at that place, and the end is drawn off as +soon as the tube is sealed. The principal point to be +guarded is the thickness of the walls of the cone, and +uniform heating. A thin place or a hot place will give +way under the air-pressure and be sucked into the tube.</p> + + +<h4>CLOSED TUBES FOR HEATING UNDER PRESSURE</h4> + +<p>(<i>Carius method for determination of the halogens and +sulphur.</i>) In this case the tubing used must have thick +walls (usually about <span style="font-size: 0.8em"><sup>3</sup></span>⁄<span style="font-size: 0.6em;">32</span> inch) to withstand the pressure. +Its external diameter is usually about <span style="font-size: 0.8em"><sup>3</sup></span>⁄<span style="font-size: 0.6em;">4</span> inch. One +length will usually make two tubes of standard length +for the cannon furnace. Especial care must be taken in +heating and cooling it on account of the thick walls. A<span class="pagenum"><a name="Page_56" id="Page_56">[Pg 56]</a></span> +length is gradually warmed in the center, finally heated +at that point until soft, drawn out, cut apart and annealed. +Taking one of the pieces, the cone is carefully +heated and shrunk, as in Exercise 4, until its walls are +as thick as those of the main tube. A flame with a little +tinge of yellow should be used for this operation to prevent +devitrification (page 2), as the thick glass shrinks +slowly. The tail is now drawn off and the whole end +heated and gently blown several times to make a rounded +end, like a test-tube, with walls as thick as those of the +main tube. This must be carefully annealed. It is +more important that the walls be thick than that the end +be nicely rounded: it may indeed be left somewhat +conical in shape.</p> + +<p>At a point about two inches from the open end of the +tube, it is slowly warmed and finally heated to the +softening point. Grasping the open end with a pair of +crucible tongs, it is cautiously pulled out, a little at a +time, usually during rotation in the flame, to make a +constriction of moderate wall-thickness, but of sufficient +internal diameter to admit the tube containing the substance. +After annealing this, cooling and cleaning the +tube, the acid and salt are introduced (the former by +means of a long-stemmed funnel) and the tube is inclined +and rotated about its axis so that the acid wets +its surface about half way up from the bottom. The +substance is now weighed out in a piece of thin-walled +glass tubing, closed at one end, and about two inches long. +Inclining the large tube at a suitable angle, the small one +is introduced, closed end first, and allowed to slide down +the walls of the large tube until it reaches the place where +the acid has wet the tube. Here it will stop, and if the +tube is kept inclined during the rest of the operation it +will roll around inside the tube at this point and thus +not get down where any acid is likely to get into it and<span class="pagenum"><a name="Page_57" id="Page_57">[Pg 57]</a></span> +produce any pressure by decomposing it before the open +end of the tube is sealed. Now the tube is held in an +inclined position, taking care that the acid does not reach +up to the substance, the constricted portion cautiously +warmed and shrunk. It is finally shrunk and drawn out +into a somewhat elongated cone, with walls as thick as +the rest of the tube, and when this is accomplished the +end of the cone is sealed and the waste piece drawn off. +Anneal with great care, and cool in such a position that +the acid cannot reach the hot glass. The shrinking of +this cone takes a good deal of patience, and is one of the +most important parts of the process. If the walls are +left too thin, the tube may burst when heated, and the +whole labor is lost. If care is taken, the same tube can +be used for a number of determinations, until it becomes +quite short.</p> + + + +<hr style="width: 65%;"/> + +<p><span class="pagenum"><a name="Page_58" id="Page_58">[Pg 58]</a></span></p> + +<p> </p> + +<p><span class="pagenum"><a name="Page_59" id="Page_59">[Pg 59]</a></span></p> + +<h2>INDEX</h2> + +<p> +Annealing glass, <a href="#Page_4">4</a>, <a href="#Page_24">24</a>, <br /><br /><br /> + +Bellows, <a href="#Page_4">4</a>, <br /><br /> + +Bending glass, <a href="#Page_8">8</a>, <br /><br /> + +Blowing glass, <a href="#Page_13">13</a>, <a href="#Page_19">19</a>, <a href="#Page_20">20</a>, <a href="#Page_21">21</a>, <a href="#Page_24">24</a>, <a href="#Page_29">29</a>, <a href="#Page_31">31</a>, <br /> +Â Â with a rubber tube, <a href="#Page_22">22</a>, <br /><br /> + +Blowpipe, <a href="#Page_4">4</a>, <br /><br /> + +Bulb at end of tube, <a href="#Page_28">28</a>, <br /> +Â Â in middle of tube, <a href="#Page_32">32</a>, <br /> +Â Â very large, <a href="#Page_32">32</a>, <br /><br /> + +Bulbs, string of, <a href="#Page_33">33</a>, <br /><br /><br /> + +Capillary tube, drawing on larger tube, <a href="#Page_9">9</a>, <a href="#Page_54">54</a>,<br /> +Â Â tubing, working, <a href="#Page_43">43</a>,<br /><br /> + +Carius method, tubes for, <a href="#Page_55">55</a>,<br /><br /> + +Closed circuits of tubing, <a href="#Page_48">48</a>,<br /> +Â Â tubes, for heating under pressure, <a href="#Page_55">55</a>,<br /><br /> + +Collecting glass for bulb, <a href="#Page_29">29</a>, <a href="#Page_31">31</a>, <a href="#Page_32">32</a>,<br /><br /> + +Constricting a tube, <a href="#Page_10">10</a>,<br /><br /> + +Crystallization of glass, see Devitrification.<br /><br /> + +Cutting glass, <a href="#Page_7">7</a>, <a href="#Page_25">25</a>,<br /><br /><br /> + + +Devitrification, <a href="#Page_1">1</a>, <a href="#Page_2">2</a>,<br /><br /> + +Drawing out a tube, <a href="#Page_9">9</a>, <a href="#Page_18">18</a>, <a href="#Page_19">19</a>, <a href="#Page_27">27</a>,<br /><br /><br /> + + +Flanging a tube, <a href="#Page_11">11</a>, <a href="#Page_14">14</a>,<br /> +Â Â tool, <a href="#Page_11">11</a>,<br /><br /><br /> + + +Gas-washing tube, <a href="#Page_35">35</a>,<br /><br /> + +Glass, annealing, <a href="#Page_4">4</a>, <a href="#Page_24">24</a>,<br /><br /> + +Glass, bending, <a href="#Page_8">8</a>,<br /> +Â Â blowing, <a href="#Page_13">13</a>, <a href="#Page_19">19</a>, <a href="#Page_20">20</a>, <a href="#Page_21">21</a>, <a href="#Page_24">24</a>, <a href="#Page_29">29</a>, <a href="#Page_31">31</a>,<br /> +Â Â collecting for bulb, <a href="#Page_29">29</a>, <a href="#Page_31">31</a>, <a href="#Page_32">32</a>,<br /> +Â Â cutting, <a href="#Page_7">7</a>,<br /> +Â Â defects, <a href="#Page_2">2</a>,<br /> +Â Â grinding, <a href="#Page_47">47</a>,<br /> +Â Â hard, <a href="#Page_1">1</a>,<br /> +Â Â knife, <a href="#Page_7">7</a>,<br /> +Â Â lead, <a href="#Page_1">1</a>,<br /> +Â Â qualities desired, <a href="#Page_1">1</a>,<br /> +Â Â rod and tube, joining, <a href="#Page_45">45</a>,<br /> +Â Â rod, working, <a href="#Page_44">44</a>,<br /> +Â Â shrinking, <a href="#Page_18">18</a>, <a href="#Page_19">19</a>, <a href="#Page_22">22</a>, <a href="#Page_26">26</a>,<br /> +Â Â soft, <a href="#Page_1">1</a>,<br /> +Â Â working temperature, <a href="#Page_1">1</a>, <a href="#Page_13">13</a>, <a href="#Page_19">19</a>, <a href="#Page_27">27</a>,<br /><br /> + +Grinding stopcock or joint, <a href="#Page_47">47</a>,<br /><br /> + +Ground joints, <a href="#Page_51">51</a>,<br /><br /><br /> + + +Handle on stopcock, mending, <a href="#Page_45">45</a>,<br /><br /> + +Hard glass, <a href="#Page_1">1</a>,<br /><br /> + +Holding tube, <a href="#Page_13">13</a>, <a href="#Page_14">14</a>,<br /><br /><br /> + + +Insertion of tube through another, see Sealing a tube through another tube.<br /><br /><br /> + + +Joints, ground, <a href="#Page_51">51</a>,<br /><br /> + +Joining rod and tube, <a href="#Page_45">45</a>,<br /> +Â Â tubing end to end: first method, <a href="#Page_16">16</a>,<br /> +Â Â second method, <a href="#Page_20">20</a>,<br /><br /> +<span class="pagenum"><a name="Page_60" id="Page_60">[Pg 60]</a></span> + +Joining tubes of different diameters, <a href="#Page_25">25</a>,<br /> +Â Â a new tube to a stopcock, <a href="#Page_48">48</a>,<br /><br /><br /> + + +Kjeldahl trap, <a href="#Page_41">41</a>,<br /><br /><br /> + + +Lead glass, <a href="#Page_1">1</a>,<br /><br /> + +Lump of glass, removed, <a href="#Page_18">18</a>, <a href="#Page_19">19</a>, <a href="#Page_20">20</a>, <a href="#Page_21">21</a>, <a href="#Page_24">24</a>, <a href="#Page_26">26</a>, <a href="#Page_30">30</a>, <a href="#Page_38">38</a>,<br /><br /><br /> + + +Platinum wires, sealed into glass, <a href="#Page_1">1</a>, <a href="#Page_52">52</a>,<br /><br /> + +Position for glass-working, <a href="#Page_5">5</a>,<br /><br /> + +Pressure, tubes for heating under, <a href="#Page_55">55</a>,<br /><br /><br /> + + +Quality of glass, <a href="#Page_1">1</a>,<br /><br /><br /> + + +Rod, glass, working, <a href="#Page_44">44</a>,<br /><br /> + +Rotation of the tube, <a href="#Page_13">13</a>, <a href="#Page_19">19</a>,<br /><br /> + +Rounded end of tube, <a href="#Page_35">35</a>, <a href="#Page_38">38</a>,<br /><br /> + +Rubber tube used for blowing, <a href="#Page_22">22</a>,<br /><br /><br /> + + +Sealing a tube through another tube, <a href="#Page_35">35</a>, <a href="#Page_39">39</a>,<br /><br /> + +Sealing vacuum tubes, <a href="#Page_55">55</a>,<br /><br /> + +Shrinking glass, <a href="#Page_18">18</a>, <a href="#Page_19">19</a>, <a href="#Page_22">22</a>, <a href="#Page_26">26</a>, <a href="#Page_31">31</a>,<br /><br /> + +Side tube, blowing, <a href="#Page_22">22</a>, <a href="#Page_25">25</a>,<br /><br /> + +Soda glass, <a href="#Page_1">1</a>,<br /><br /> + +Soft glass, <a href="#Page_1">1</a>,<br /><br /> + +Spirals, making, <a href="#Page_50">50</a>,<br /><br /> + +Stopcocks, mending, <a href="#Page_45">45</a>,<br /><br /> + +Suction pump, <a href="#Page_39">39</a>, <a href="#Page_42">42</a>,<br /><br /> + +Sulphur dioxide tube, <a href="#Page_28">28</a>,<br /><br /><br /> + + +"Tail" of glass, drawing out, <a href="#Page_9">9</a>, <a href="#Page_54">54</a>,<br /> +Â Â removed, <a href="#Page_30">30</a>, <a href="#Page_35">35</a>,<br /><br /> + +Tubes, closed, for heating under pressure, <a href="#Page_55">55</a>,<br /><br /> + +"Tee" tube, <a href="#Page_22">22</a>,<br /> +Â Â on capillary tubing, <a href="#Page_43">43</a>,<br /> +Â Â small side tube on a large tube, <a href="#Page_24">24</a>,<br /><br /><br /> + + +Vacuum tubes, sealing, <a href="#Page_55">55</a>,<br /><br /><br /> + + +Working temperature of glass, <a href="#Page_1">1</a>, <a href="#Page_13">13</a>, <a href="#Page_19">19</a>, <a href="#Page_27">27</a>,<br /> +</p> + +<div>*** END OF THE PROJECT GUTENBERG EBOOK 30066 ***</div> +</body> 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file mode 100644 index 0000000..10a21d9 --- /dev/null +++ b/30066-h/images/i059.png diff --git a/30066-h/images/i061.png b/30066-h/images/i061.png Binary files differnew file mode 100644 index 0000000..e425c6c --- /dev/null +++ b/30066-h/images/i061.png diff --git a/30066.txt b/30066.txt new file mode 100644 index 0000000..8af7230 --- /dev/null +++ b/30066.txt @@ -0,0 +1,2295 @@ +Project Gutenberg's Laboratory Manual of Glass-Blowing, by Francis C. Frary + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: Laboratory Manual of Glass-Blowing + +Author: Francis C. Frary + +Release Date: September 22, 2009 [EBook #30066] + +Language: English + +Character set encoding: ASCII + +*** START OF THIS PROJECT GUTENBERG EBOOK LABORATORY MANUAL OF GLASS-BLOWING *** + + + + +Produced by Woodie4 and the Online Distributed Proofreading +Team at https://www.pgdp.net. (This file was produced from +images generously made available by The Internet +Archive/American Libraries.) + + + + + + + + + + LABORATORY MANUAL + + OF + + GLASS-BLOWING + + + + + McGraw-Hill Book Company + + _Publishers of Books for_ + + + Electrical World + Engineering Record + Railway Age Gazette + Signal Engineer + Electric Railway Journal + Metallurgical and Chemical Engineering + The Engineering and Mining Journal + Engineering News + American Machinist + American Engineer + Coal Age + Power + + + + + LABORATORY MANUAL + OF + GLASS-BLOWING + + BY + FRANCIS C. FRARY, PH. D. + + ASSISTANT PROFESSOR OF CHEMISTRY + UNIVERSITY OF MINNESOTA + + McGRAW-HILL BOOK COMPANY, INC. + 239 WEST 39TH STREET, NEW YORK + 6 BOUVERIE STREET, LONDON, E. C. + + 1914 + + + + + COPYRIGHT, 1914, BY THE + McGRAW-HILL BOOK COMPANY, INC. + + + + +PREFACE + + +The purpose of this little book is to provide a clear and detailed +discussion of the elements of glass-blowing. Many laboratories in this +country, especially in the west, are located a long way from any +professional glass-blower, and the time and money spent in shipping +broken apparatus several hundred miles to be mended could often be saved +if some of the laboratory force could seal on a new stopcock, replace a +broken tube, or make some temporary repairs. Many men in physical or +chemical laboratories have occasion to modify some piece of apparatus +designed perhaps for other uses, or to design new apparatus. To such +also, the ability to perform some of the operations herein described may +be very valuable. + +No originality is claimed for the methods here described. They are those +which the author has found most suitable and convenient in his own work, +and most easily learned by students. The aim has been to describe each +operation in such detail that a beginner can follow the process without +help and, with practice, attain satisfactory results. It is, however, +much easier to perform any of the operations described, after seeing +some one else perform it correctly; since the temperature, the exact +time to begin blowing the glass, and many other little details are very +difficult to obtain from a description. + +It has not been thought worth while to describe the process of making +stopcocks, thermometers, vacuum tubes, etc., as such things can be +purchased more cheaply and of much better quality than any amateur can +make unless he is willing to spend a very large amount of time in +practice. For similar reasons the manipulation of quartz glass has been +omitted. + +The author will be grateful for all suggestions and criticisms tending +to improve the methods presented. If some of them appear to be given in +excessive detail, the reader will remember that many things which are +obvious to the experienced worker are not so to the beginner, and that +it is the little details in the manipulation which often spell success +or failure in glass-blowing. + + F. C. F. + +MINNEAPOLIS, MINN., +_January, 1914._ + + + + + CONTENTS + + + + PAGE + + Preface v + + + CHAPTER I + + MATERIALS AND APPARATUS 1 + + Varieties and defects of glass--Devitrification--Annealing + glass--Blowpipe and bellows--Light--Arrangement of exercises. + + + CHAPTER II + + GENERAL OPERATIONS 7 + + Cutting, bending, constricting and flanging the tubing--Methods + of rotation and blowing. + + + CHAPTER III + + ELEMENTARY EXERCISES 16 + + Joining two pieces of tubing of the same diameter--The "tee" + tube--Joining two tubes of different diameters--Blowing bulbs. + + + CHAPTER IV + + ADVANCED EXERCISES 35 + + Sealing a tube through another tube: The gas-washing tube, suction + pump, and Kjeldahl trap. + + + CHAPTER V + + MODIFIED METHODS AND SPECIAL OPERATIONS 43 + + Capillary tubing--Glass rod--Mending stopcocks--Closed circuits of + tubing--Spirals--Ground joints--Sealing in platinum wire--Sealing + vacuum tubes--Closed tubes for heating under pressure. + + + INDEX 59 + + + + +LABORATORY +MANUAL OF GLASS-BLOWING + + + + +CHAPTER I + +MATERIALS AND APPARATUS + + +One of the most important factors in the success of any piece of +glass-blowing is the glass employed. As is well known, there are two +general varieties of glass: Lead glass and soda glass. Formerly much +apparatus was made of lead glass, but at present it is very seldom met +with, except in the little drops of special glass used to seal platinum +wires into the larger sizes of tubes. Lead glass is softer and more +readily fusible than soda glass, but has the disagreeable property of +growing black in a few seconds unless worked in a strong oxidizing +flame. This may be prevented by using a "hissing" flame, with a large +excess of air, and working in the extreme end of the flame; or the black +lead formed may thus be reoxidized, and the glass restored to its +original clearness. + +Almost all the soft glass on the market is a soda glass, although +sometimes part of the soda is replaced by potash. Most of the hard glass +appears to be a potash glass. The following qualities are desirable in a +glass for ordinary working: (1) moderately low working temperature, (2) +freedom from air bubbles, striations and irregularities, (3) proper +composition, so that the glass will not devitrify or crystallize while +being handled at its working temperature, (4) ability to withstand rapid +heating without cracking. + +The working temperature of different samples of so-called "soft glass" +varies a good deal, and is best determined by trial. The glass should +become almost soft enough for blowing in a flame that still shows a +little yellow near the tip, so that at the highest temperature of the +flame it may flow fairly freely and thus easily eliminate irregularities +in thickness. If the glass is too hard, the shrinking of the glass, +collection of material for a bulb, and in fact most of the working +processes will be slower, and the glass will not stay at its working +temperature long enough after its removal from the flame to permit it to +be properly blown. + +Air bubbles in the original batch of glass are drawn out into long +hair-like tubes during the process of manufacture. When such tubing is +worked, the walls of these microscopic tubes collapse in spots, and the +air thus enclosed will often collect as a small bubble in the wall, thus +weakening it. Irregularities are of various kinds. Some of the larger +sizes of thin-walled tubing often have one half of their walls much +thicker than the other, and such tubing should only be used for the +simplest work. Some tubing has occasional knots or lumps of unfused +material. The rest of the tube is usually all right, but often the +defective part must be cut out. The presence of striations running along +the tube is generally an indication of hard, inferior glass. Crookedness +and non-uniformity of diameter are troublesome only when long pieces +must be used. + +Devitrification is one of the worst faults glass can possibly have. It +is especially common in old glass, and in glass which has contained +acids. It seems to be of two sorts. One variety manifests itself on the +surface of the glass before it reaches its working temperature, but if +the glass be heated to the highest temperature of the flame it will +disappear except in the portion at the edge of the heated part. The +glass seems to work all right, but an ugly crystallized ring is left at +the edge of the portion heated. This kind appears most frequently in old +glass which was originally of good quality, but has in time been +superficially altered, probably by the loss of alkalies. The other +variety of devitrification does not appear when the glass is first +heated; but after it has been maintained at or above its working +temperature for a longer or shorter time, it will be noticed that the +outer surface has lost its smoothness, and appears to be covered with +minute wrinkles. It will also be found that the glass has become harder, +so that it becomes impossible to work it easily. Further heating only +makes the matter worse, as does the use of a higher temperature from the +start. In fact it will often be found that a piece of comparatively soft +glass which devitrifies almost at once in a "hissing" flame can be +worked without serious difficulty if care be taken to use a flame still +decidedly tinged with yellow. Even good glass will begin to devitrify in +this way if heated too long at the highest temperature of the flame, so +care should always be taken (1) _to reduce the time of heating of any +spot of glass to a minimum_; _i.e._, get the desired result at the first +attempt, if possible, or at least with the minimum of reheating and +"doctoring," and (2) _avoid keeping the glass at the highest temperature +of the flame any longer than necessary_. This may be accomplished by +doing all heating, shrinking, etc., of the glass in a flame more or less +tinged with yellow, and only raising the temperature to the highest +point when ready to blow the glass. This kind of devitrification is +apparently due to volatilization of the alkalies from the glass in the +flame, and it is said that it can be partly remedied or prevented by +holding a swab of cotton saturated with a strong solution of common salt +in the flame from time to time as the glass is heated. + +The toughness of glass, _i.e._, its ability to withstand variations of +temperature, depends on its composition and the care taken in its +annealing. In general, large pieces of glass should be heated very +slowly in the smoky flame, and the larger the diameter of the tube the +greater the length which must be kept warm to prevent cracking. All +large pieces should be carefully heated over their whole circumference +to the point where the soot deposit burns off, before being finally +cooled. After being thus heated they are cooled in a large smoky flame +until well coated with soot, then the flame is gradually reduced in size +and the object finally cooled in the hot air above it until it will not +set fire to cotton. If thought necessary, it may then be well wrapped in +cotton and allowed to cool in the air. If not properly annealed the +place heated may crack spontaneously when cold, and it is quite certain +to crack if it is reheated later. + +Next in importance to the glass are the blow-pipe and the bellows. Any +good blast lamp, such as is ordinarily used in a chemical laboratory for +the ignition of precipitates, will be satisfactory; provided it gives a +smooth regular flame of sufficient size for the work in hand, and when +turned down will give a sharp-pointed flame with well-defined parts. +Where gas is not available, an ordinary gasoline blow-torch does very +well for all operations requiring a large flame, and a mouth blow-pipe +arranged to blow through a kerosene flame does well for a small flame. +Several dealers make blow-torches for oil or alcohol which are arranged +to give a small well-defined flame, and they would doubtless be very +satisfactory for glass-work. Any good bellows will be satisfactory if it +does not leak and will give a steady supply of air under sufficient +pressure for the maximum size of flame given by the lamp used. A bellows +with a leaky valve will give a pulsating flame which is very annoying +and makes good work very difficult. When compressed air is available it +can be used, but if possible it should be arranged so that the supply +can be controlled by the foot, as both hands are usually needed to hold +the work. For the same reason the supply of air is usually regulated by +varying the rate of operation of the bellows, rather than by adjusting +the valve of the blast-lamp. On the other hand, it will be found best to +always adjust the flow of the gas by means of the cock on the lamp, +rather than that at the supply pipe. The operator must have complete +control over the flame, and be able to change its size and character at +short notice without giving the work a chance to cool, and often without +ceasing to support it with both hands. + +Glass-blowing should be done in a good light, but preferably not in +direct sunlight. The operator should be seated in a chair or on a stool +of such a height that when working he may comfortably rest one or both +elbows on the table. The comfort of the operator has a decided influence +on the character of his work; especially in the case of a beginner, who +often defeats his purpose by assuming uncomfortable and strained +positions. Steadiness and exact control of both hands are essential in +most operations; any uncomfortable or strained position tires the +muscles and weakens the control of the operator over them. + +In the arrangement of the exercises here presented, several factors have +been considered. It is important that the first exercises be simple, +although not necessarily the simplest, and they should teach the +fundamental operations which will be used and amplified later. They +should in themselves be things which are of importance and commonly used +in glass-work, and they should be so arranged that the fundamental +points, such as the rotation of glass, the proper temperature, blowing +and shrinking the glass may be learned with a minimum expenditure of +time, glass and gas. It is therefore recommended that the beginner take +them up in the order given, at least as far as No. 7, and that each be +mastered before attempting the next. The beginner should not leave the +first exercise, for example, until he can join together two pieces of +tubing so that they form one piece of substantially uniform inner and +outer diameter, and without thick or thin spots. From two to four +practice periods of two hours each should suffice for this. This chapter +and the following one should also be frequently read over, as many of +the points discussed will not be understood at first and many of the +manipulations described will not be necessary in the simpler exercises. + + + + +CHAPTER II + +GENERAL OPERATIONS + + +=Cutting the Glass.=--For this purpose a "glass-knife" is preferred to a +file, if the glass is cold: if it is hot a file must always be used, and +its edge slightly moistened to prevent drawing the temper. The +glass-knife is simply a flat piece of hard steel, with the edges ground +sharp on an emery wheel. The bevel of the edge should be from 30 to 60 +degrees. An old flat file can easily be ground into a suitable knife. +The glass-knife makes a narrower scratch than the file but appears more +likely to start the minute crack which is to cause the tube to break at +that point, and the break is more likely to give a good square end. The +scratch should be made by passing part of the knife or file once across +the glass, never by "sawing" the tool back and forth. This latter +procedure dulls the tool very quickly. + +In breaking a piece of glass tubing, many persons forget that it is +necessary to _pull_ the ends apart, as well as to bend the tube very +_slightly_ in such a direction as to open up the minute crack started in +the scratch. Care in breaking the tube is essential, as it is impossible +to do as good work with uneven ends as with square ones. + +When tubing of large diameter or thin wall is to be cut, it is often +better not to attempt to break it in the usual way, but to heat a very +small globule of glass (1/16 to 1/8 inch diameter) to red heat, and +touch it to the scratch. This will usually start the crack around the +tube; if it has not proceeded far enough, or has not gone in the +desired direction, it may be led along with a hot point of glass. This +is put a little beyond the end of the crack, and as the latter grows out +toward it, moved along the path where the crack is desired. This point +of glass is also very useful in breaking off very short ends of tubes, +where there is not room to get a firm enough hold and sufficient +leverage to break the tube in the ordinary way, and for breaking tubes +attached to large or heavy objects, which would be likely to make +trouble if treated in the ordinary way. + +Another way of cutting large tubing, especially if it has rather thick +walls, is to make a scratch in the usual way, and then turn on the +smallest and sharpest possible flame of the blast lamp. The tube is next +taken in both hands and held horizontally above the flame so that the +scratch is exactly over it. The tubing is now rotated rapidly about its +axis, and lowered so that the flame is just tangent to its lower side. +After about ten seconds of heating, it is removed from the flame and the +hot portion quickly breathed upon, when it will generally crack apart +very nicely. Care must be taken to hold the tube at right angles to the +flame during the heating, and to rotate it so that only a narrow strip +of the circumference is heated, and the scratch should be in the center +of this heated strip. By this means tubing as large as two inches in +diameter is readily broken. + +Griffin's glass cutter, which contains a hardened steel wheel, like that +on any ordinary window-glass cutter, and a device by which this can be +made to make a true cut clear around the tube, is a very handy article, +especially for large tubing, and may be obtained from any dealers in +chemical apparatus. + +=Bending Glass.=--Inasmuch as this is one of the commonest operations in +the laboratory, it is assumed that the reader knows how to perform it. +However, it should be noted that in order to obtain the best results a +broad (fish-tail burner) flame should generally be used, and the tube +rotated on its axis during the heating, and allowed to bend mostly by +its own weight. If large tubing is to be bent, one end must be stoppered +and great care used. Whenever the tube shows signs of collapsing or +becoming deformed, it must be gently blown out into shape, heating the +desired spot locally if necessary. A blast-lamp is likely to be more +useful here than the fish-tail burner. + +=Drawing Out a Tube.=--Most students learn this the first day of their +laboratory work in chemistry, but few take pains to do it well. The tube +should be heated in the flame of a Bunsen burner, or blast lamp +(preferably the latter) until it is very soft. During this time it must +be continuously rotated about its axis, and so held that the edges of +the heated zone are sharply defined; _i.e._, it should not be allowed to +move back and forth along its own axis. When so hot that it cannot +longer be held in shape, the tube is removed from the flame, and the +ends slowly and regularly drawn apart, _continuing the rotation of the +tube about its axis_. By regulating the rate of drawing and the length +of tube heated, the desired length and diameter of capillary may be +obtained. The tube should always be rotated and kept in a straight line +until the glass has set, so that the capillary may have the same axis as +the main tube. This capillary or "tail" is often a very necessary handle +in glass-blowing, and if it is not straight and true, will continually +make trouble. + +In drawing out very large tubing, say from one to two inches in +diameter, it is often necessary to draw the tube _in the flame_, +proceeding very slowly and at a lower temperature than would be used +with small tubing. This is partly on account of the difficulty of +heating large tubing uniformly to a high temperature, and partly in +order to prevent making the conical part of the tube too thin for +subsequent operations. + +=Constricting a Tube.=--Where a constriction is to be made in a tube, +the above method must be modified, as the strength of the tube must be +maintained, and the constricted portion is usually short. Small tubes +are often constricted without materially changing their outside +diameter, by a process of thickening the walls. The tube is heated +before the blast lamp, rotating it about its axis as later described, +and as it softens is gradually pushed together so as to thicken the +walls at the heated point, as in _a_, Fig. 1. When this operation has +proceeded far enough, the tube is removed from the flame, and the ends +cautiously and gently drawn apart, continuing the rotation of the tube +about its axis and taking care not to draw too rapidly at first. The +resulting tube should have a uniform exterior diameter, as shown in _b_, +Fig. 1. + +[Illustration: FIG. 1.--Constricting a tube.] + +This method of constriction is not suited to tubes much over 1/4 inch in +diameter, since the mass of glass in the constricted part becomes so +thick as to be difficult to handle when hot, and likely to crack on +cooling. Larger tubes are therefore constricted by heating in a narrow +flame, with constant rotation, and when soft, alternately gently pulling +the ends apart and pushing them together, each motion being so regulated +that the diameter of a short section of the tube is gradually reduced, +while the thickness of the wall of the reduced portion remains the same +as that of the rest of the tube, or increases only slightly. This +pulling and pushing of the glass takes place _in the flame_, while the +rotation is being continued regularly. The result may appear as +indicated in _c_, Fig. 1. The strength of the work depends upon the +thickness of the walls of the constricted portion, which should never be +less than that in the main tube, and usually a little greater. This +operation is most successful with tubing having a relatively thin wall. + +=Flanging a Tube.=--This operation produces the characteristic flange +seen on test-tubes, necks of flasks, etc., the object being twofold: to +finish the end neatly and to strengthen it so that a cork may be +inserted without breaking it. This flanging may be done in several ways. +In any case the first operation is to cut the tube to a square end, and +then heat this end so that the extreme sixteenth or eighth of an inch of +it is soft and begins to shrink. The tube is of course rotated during +this heating, which should take place in a flame of slightly greater +diameter than the tube, if possible. The flange is now produced by +expanding this softened part with some suitable tool. A cone of charcoal +has been recommended for this purpose, and works fairly well, if made so +its height is about equal to the diameter of its base. The tube is +rotated and the cone, held in the other hand, is pressed into the open +end until the flange is formed. A pyramid with eight or ten sides would +probably be better than the cone. + +[Illustration: FIG. 2.--Flanging tool.] + +A better flanging tool is made from a triangular piece of copper or +brass, about 1/16 inch thick, and mounted in a suitable handle. Such a +tool is shown in Fig. 2, being cut from a sheet of copper and provided +with a handle made by wrapping asbestos paper moistened with sodium +silicate solution about the shank of the tool. It is well to have +several sizes and shapes of these tools, for different sizes of tubing. +The two sizes most used will be those having about the following +dimensions: (1) _a_ = 2 inches, _b_ = 1 inch; (2) _a_ = 1 inch, _b_ = 1 +inch. When the end of the tube is softened, the tool is inserted at an +angle, as indicated in Fig. 3, and pressed against the soft part, while +the tube is quickly rotated about its axis. If the flange is +insufficient the operation may be repeated. The tool should always be +warmed in the flame before use, and occasionally greased by touching it +to a piece of wax or paraffin. After the flange is complete, the end +must be heated again to the softening temperature and cooled slowly, to +prevent it from cracking. + +[Illustration: FIG. 3.--Flanging a tube with flanging tool.] + +[Illustration: FIG. 4.--Flanging a tube with carbon rod or wire.] + +Some glass-blowers use a small carbon rod, about 3/16 inch in diameter, +as a flanging tool for tubes larger than about 3/8 inch diameter, and a +small iron wire or similar piece of metal for smaller tubes. In this +case the tube is heated as above described, and the rod or wire inserted +in the end at an angle and pressed against the softened part, as +indicated in Fig. 4, while the tube is rotated about its axis. For +large heavy tubes a larger carbon would be used. + +=Rotation of the Tube.=--This is the fundamental manipulation in +glass-blowing, and upon it more than all else depends the uniformity and +finish of the work, and often the possibility of accomplishing the work +at all. Directions for it will be given on the assumption that the +reader is right-handed; if otherwise, the position of the hands is of +course reversed. The object of rotation is to insure even heating of the +whole circumference of the tube at the point of attack, to equalize the +effect of gravity on the hot glass and prevent it from falling out of +shape when soft, and to keep the parts of the tube on each side of the +heated portion in the same straight line. + +In rotating the tube, both hands must be used, so that the two ends may +revolve at the same rate and the glass in the hot part not be twisted. +The rotation is performed by the thumb and first finger of each hand, +the other fingers serving to support the tube. As it is almost always +necessary to follow rotating and heating a tube by blowing it, the hands +should be so placed that it will be easy to bring the right-hand end up +to the mouth without shifting the hold on the glass. For this reason the +left hand grasps the glass with the palm down, and the right hand with +the palm turned toward the left. If there is any choice, the longer and +heavier part of the tube is usually given to the left hand, and it is +planned to blow into the shorter end. This is because it is easier to +support the tube with the hand which has the palm down. This support is +accomplished by bending the hand at the wrist so that it points slightly +downward, and then curling the second, third and little fingers in under +the tube, which is held between them and the palm. This support should +be loose enough so that the thumb and first finger can easily cause the +tube to rotate regularly on its axis, but firm enough to carry all the +weight of the tube, leaving the thumb and first finger nothing to do but +rotate it. The hand must be so turned, and the other fingers so bent, +that the thumb and first finger stretch out nearly to their full length +to grasp the tube comfortably. + +The right hand is held with the palm toward the left, the fingers except +the first slightly bent, and the tube held between the first finger and +the thumb while it rests on the second finger and that portion of the +hand between the base of the first finger and the thumb. Rotation of the +tube is accomplished by rolling it between the thumbs and first fingers: +the rotation being continued in the same direction regularly, and not +reversed. It is better to roll slowly and evenly, with a series of light +touches, each of which moves the tube a little, than to attempt to turn +the tube a half a revolution or so with each motion of the hands. The +hands must be held steady, and the tube must be under good control at +all times, so that both ends may be rotated at the same angular +velocity, even though they may be of different diameters, and the tube +be neither drawn apart nor pushed together unless such a motion is +expressly desired, as it sometimes is. The hot part of the glass must be +constantly watched to see that it is uniformly rotated and not twisted, +nor pulled out or pushed together more than is desired. Care must also +be taken to keep the parts of the tube in the same straight line, or as +near it as possible, during the heating and all other manipulations. + +When flanging a tube, it is held and rotated with the left hand as above +described, while the right hand holds the flanging tool. + +When part of the end of a tube must be heated, as in Exercise 6, and +rotation must be very carefully performed and continued during the +blowing, both hands are used. The right hand is held as above +described, and the left hand close to it and either as above described +or else with the palm toward the right, grasping the tube in the same +way as the right hand does. This puts both hands in a position where the +tube may be blown and rotated uniformly while its axis is kept +horizontal. + +Smoothness and exactness are the two things for which the beginner must +constantly strive in glass-blowing, and they are only attained by a +careful attention to the details of manipulation, with a steady hand and +watchful eye. Every move must count, and the exercise must be finished +with a minimum of reheating and retouching, for the best results. + + + + +CHAPTER III + +ELEMENTARY EXERCISES + + +EXERCISE NO. 1 + +JOINING TWO PIECES OF TUBING, END TO END--FIRST METHOD + +This exercise is most easily learned on tubing with an exterior diameter +of 1/4 inch, or a little less, having moderately heavy walls. A piece of +such tubing is heated before the blow-pipe at a point ten or twelve +inches from the end, and there drawn out to a capillary as previously +described (page 9). The capillary is sealed off about two inches from +the main tube, and the latter is cut near the middle. Care should be +taken to get square ends where the cut is made (page 7). The flame is +now so regulated that it is a little broader than the diameter of the +tube, the sealed half of the tube taken in the left hand and the other +half in the right. The open end of the sealed part and one of the ends +of the other part are now held in opposite sides of the flame, inclined +at a slight angle to one another as indicated in Fig. 5, and rotated and +heated until the surfaces of both ends are just softened. The two ends +are then carefully and quickly brought together (_a_, Fig. 6), removed +from the flame and pulled apart a little, to reduce the lump formed at +the joint as much as possible, as indicated in _b_. The joint is then +tested by blowing into the open end of the tube to see if it is tight. +If so, the flame is reduced to half or less than half of its former +size, and the joint heated in it, holding the tube and continually +rotating it as directed in the last chapter (page 13). + +[Illustration: FIG. 5.--Softening ends of two pieces of tubing.] + +[Illustration: FIG. 6.--Joining two pieces of tubing end to end--first +method.] + +As the tube softens and tends to shrink, the two ends are pressed +together a little and the walls allowed to thicken slightly, as in _c_. +It is then quickly removed from the flame and gently blown as indicated +in _d_, continuing the rotation of the tube during the blowing, and at +the same time pressing the ends of the tube together a little so as to +make a _short_ thick-walled bulb. The joint is then returned to the +flame and reheated, rotating as before, shrinking to about the shape of +_e_. When this stage is reached, the glass should be very hot and fluid, +and the mass of hot glass thick enough to remain at its working +temperature for about five seconds after removal from the flame. The +glass is now reblown as indicated in _f_, to form a bulb having walls of +practically the same thickness as the original tube. As soon as the bulb +is blown, the tube is removed from the mouth, held horizontally in front +of the worker, and gently drawn out to form one continuous tube, as +indicated in _g_. During both the blowing and drawing of this bulb the +rotation must be continued, and both blowing and drawing must be +carefully regulated so that the resulting tube may have the same +internal and external diameter at the joint as elsewhere. + +=Discussion.=--In making the original joint, (_a_, Fig. 6), care should +be taken that the lump formed is as small as possible so that it may be +entirely removed during the subsequent operations. For this reason, only +the very tip ends of the two pieces of tubing are held in the flame, and +the softening should not extend more than 1/16 inch down the tube. As +soon as the ends are sufficiently soft to stick together, they are made +to do so. The first drawing of the tube (_b_) should take place +immediately, and reduce the lump as much as possible without making the +adjacent walls of the tube thin. The whole purpose of the rest of the +manipulation is to absorb or "iron out" the lump at the joint. For this +reason, care is taken that this lump is always in the center of the +flame while the joint is being heated, and a small flame is used so +that little of the main tube may be softened. During the first shrinking +of the joint (_c_) the walls next the lump, being thinner than it is, +reach the softening temperature first and are thickened by the slight +pushing together of the ends, so that they taper from the lump to the +unchanged wall. Upon blowing this joint, these thickened walls blow out +with the lump, but as they are thinnest next the unchanged tube, they +stiffen there first. Then as the thicker parts are still hot, these blow +out more, and with the lump make a more or less uniform wall. By this +first operation most of the lump will have been removed, provided it was +not too large at first, and the tube was hot enough when it was blown. +Beginners almost invariably have the glass too cool here, and find +difficulty in blowing out a satisfactory bulb. Under such circumstances +the lump will be scarcely affected by the operation. + +During the shrinking of this bulb, the thinner parts of course are the +first to reach the softening point, and thus contract more than the +thick parts, so that practically all of the lump can be absorbed, and a +uniformly thickened part of the tube left as in _e_. When this is just +accomplished, the second bulb must be blown during one or two seconds, +and the tube then drawn out as described, so as to change the bulb to a +tube. The drawing must proceed with care: portions nearest the unchanged +tubes are the first to reach the proper diameter, and must be given time +to just set at that point before the center of the bulb is finally drawn +into shape. The drawing is perhaps best done intermittently in a series +of quick pulls, each drawing the tube perhaps 1/16 inch, and each taking +place as the thumbs and first fingers grasp the tube for a new turn in +the rotation. If the tube is not rotated during the blowing, the bulbs +will be lop-sided and it will be impossible to get a joint of uniform +wall-thickness; if rotation is omitted during the drawing, the tube +will almost invariably be quite crooked. + +If the lump still shows distinctly after the operations described, the +cross-section of the tube will be as in _h_, and the tube will be likely +to break if ever reheated at this point after it becomes cold. The +operations _d_, _e_, _f_, and _g_ may be repeated upon it, and it may be +possible to get it to come out all right. + +Care must be taken not to blow the bulbs _d_ and _f_ too thin as they +then become very difficult to handle, and the joint is usually spoiled. +The wall-thickness of these bulbs must never be much less than that of +the original tube. If the joint as completed has thinner walls than the +rest of the tube, it will be more easily broken. It should be remembered +that the length of the finished tube must be exactly the same as that of +the original piece, if the walls of the joint are to be of their +original thickness. Therefore the pushing together during the two +operations _c_ and _d_ must shorten the tube just as much as the final +drawing (_f_ to _g_) lengthens it. + +The interval between the removal of the work from the flame and the +beginning of the blowing must be made as short as possible, or else the +portions next the main parts of the tube will set before they can be +blown out, and cause irregular shrunken areas. + + +EXERCISE NO. 2 + +JOINING TWO TUBES END TO END--SECOND METHOD + +The method described in Exercise No. 1 is very satisfactory for joining +short lengths of straight tubing, but becomes inconvenient or impossible +when the pieces are long or bent, on account of the difficulty in +uniformly rotating such work. In such cases, this second method is +used. It does not usually give as smooth and pretty a joint as the first +method, and takes a little longer. + +The joint is begun exactly as in the first method, and the manipulation +is the same until after the preliminary tight joint (_b_, Fig. 6) is +made. The flame is reduced as usual, but instead of rotating the tube in +the flame, only one part of the circumference is heated, and this is +allowed to shrink thoroughly before blowing. It is then blown gently so +that it becomes a slight swelling on the tube, and the operation +repeated on an adjoining part of the joint. Three or four repetitions of +the operation will usually cover the whole circumference of the joint, +in a small tube, the result being a swelling roughly similar to the +first thick bulb in the first method (_d_, Fig. 6). If all the lumps of +the original joint have not been removed by this operation, it may now +be repeated upon such parts as may require it. The thickness of the wall +in the bulb should be about the same as that in the original tube. The +whole of the expanded joint is now heated as uniformly as may be until +soft enough so that it begins to shrink a little, and the swelling is +gently drawn down to the same diameter as the main tube, as in the first +case. Any irregularities in the finished joint may be corrected by local +reheating, shrinking or blowing as required. + +=Discussion.=--In using this method, especially with larger sizes of +tubing, it is very important to keep the whole circumference of the +joint hot enough during the operation so that it does not crack apart at +the part which has not yet been worked. For that reason the first +heating, shrinking and blowing should be performed as quickly as +possible, leaving the resulting irregularities to be corrected later, +rather than attempting to reblow the same part of the joint several +times in succession until it is satisfactory. Care must be taken in this +as in the first method that the blowing follows immediately upon the +completion of the shrinking and removal of the object from the flame: +delay in blowing will cause shrunken places where the joint meets the +original tubes, on account of the cooling and setting of the glass +before it was blown. Most beginners err in being afraid to shrink the +part of the joint enough before blowing it. On small tubing, the +shrinkage may often extend so far that the inner surface of the shrunken +part reaches the center of the tube. Insufficient shrinking results in +failure to remove the lump formed at the original joint. It is often of +advantage, after blowing out part of the joint, to allow that part a few +seconds to set before going on with the rest, keeping the whole joint +warm meanwhile in or near the smoky flame. This helps to prevent the +twisting of the joint, or other distortion incident to the handling of a +piece of work of awkward shape. + +In making a joint on a very long or heavy piece by this method, it is +often advantageous to attach a piece of rubber tubing to the open end, +hold the other end of this tubing in the mouth during the process, and +blow through it, rather than attempt to bring the end of the glass up to +the mouth. This enables one to keep closer watch on the joint, and avoid +drawing it out or distorting it in handling. On the other hand, the +rubber tube is an inconvenience on account of its weight and the +consequent pull on the end of the apparatus, and makes rotation +difficult. + + +EXERCISE NO. 3 + +THE "TEE" TUBE + +The operations involved are two: the blowing of a short side tube on a +piece of tubing, and sealing another piece of tubing on this, by what is +essentially the second method as just described. + +[Illustration: FIG. 7.--The "tee" tube.] + +The two pieces of tubing to be used each have one end cut square and the +other sealed in the usual manner. The longer of the two is now heated at +the point at which the joint is to be made, until it begins to color the +flame. A small flame is used, and the tube rotated until the flame +begins to be colored, when the rotation is stopped, and only one spot +heated until a spot the diameter of the tube to be sealed on has become +red hot and begun to shrink. This is now gently blown out into a small +bulb, as in _a_, Fig. 7, and it will be noted that this bulb will have +walls tapering from the thick walls of the tube to a very thin wall at +the top. The sides of this bulb, below the dotted line, are to form the +small side tube to which the main side tube is to be sealed. The top of +the bulb is now softened by directing a small flame directly upon it, +and as soon as it shrinks to the level indicated by the dotted line, it +is removed from the flame and quickly blown out to form a thin bulb, as +indicated in _b_, Fig. 7. This will usually be so very thin that a +stroke of the file or glass-knife will break it off at the dotted line, +leaving the side tube, to which the short piece of tubing is now sealed +according to the second method (Exercise No 2). In doing this, care is +taken to direct the flame partly on the main tube in the two crotches, +so that both tubes blow out a little and give space for the gases to +turn in, as indicated in _c_, Fig. 7, and at the same time increase the +mechanical strength of the job. On the other hand, care is taken not to +deform the main tube, and not to produce such a bulge or bulb at the +joint as will prevent the finished tube from lying flat on a table. + +=Discussion.=--Most beginners tend to err in the first steps of this +operation, by blowing too hard and too long when blowing out the little +bulb. The result is a large, very thin bulb, which breaks off in such a +way as to leave a hole in the main tube, occupying nearly half the +circumference of the tube at that point, instead of the neat side tube +which they should have. It is not difficult to seal a tube on this side +tube, but it is very difficult to seal a tube into a hole in another +tube. Care should be taken here, as in the two previous exercises, that +the lump obtained at the joint when the two tubes are put together is +made as small as possible, and reduced if possible by gently drawing on +the side tube as soon as the tubes have actually joined. It is much +easier to prevent the formation of a lump at the joint than it is to +remove the lump after it is formed. The remarks previously made about +blowing quickly after removing the work from the flame apply here with +especial force. A "tee" tube, from its very nature, is exposed to a good +many strains, so care must be taken that the walls of the joint are of +uniform thickness with the rest of the tube. + +The beginner will find it easiest to make this tube out of two pieces of +the same tube, about 1/4 inch in diameter. Larger or smaller tubing is +usually more difficult. If tubing much more than 1/4 inch is used, the +whole joint, including part of the main tube, must be heated nearly to +the softening point at the close of the operation, and well annealed, as +described in Chapter 1 (page 3) or it will be almost certain to crack. +In the larger sizes of tube it will be necessary to heat the whole +circumference of the main tube frequently during the operation, to +prevent it from cracking. + +In sealing a small tube on the side of a large one, it is usually +advisable, after warming the spot where the joint is to be made, to +attach a small drop of glass to the tube at that point, and direct the +flame upon that, thus supplying at the same time both a definite point +to be heated and an extra supply of glass for the little side tube which +is desired. In this way it is also easier to blow out a side tube with a +sufficiently small diameter. If the diameter of this tube should be much +greater than that of the small tube, the latter may be enlarged with a +carbon or a flanging tool. + + +EXERCISE NO. 4 + +TO JOIN TWO TUBES OF DIFFERENT DIAMETERS + +In this case the first method (Exercise No. 1) is to be used whenever +possible, as it gives a much smoother joint than the second method. The +directions given will describe the adaptation of this method to the +problem: if the second method must be used on account of awkward shape, +etc., of the work, the modifications required will be obvious to any one +who has learned to make the joint by the first method. + +After sealing or corking one end of the larger tube, the other end is +drawn out to form a tail as described on page 9, taking care to have the +tube uniformly heated, and to draw the tail rapidly enough so that the +cone is short, as indicated in _a_, Fig. 8. The tube is now rotated, a +small flame directed against the cone at right angles to an element of +it, and it is allowed to shrink a little, as indicated in _b_, Fig. 8, +so that its walls will thicken. When the tail is cut off, at the dotted +line, the diameter of the opening and the thickness of the walls at that +point should correspond with the dimensions of the tube to be sealed on. +As the glass is hot, the scratch for cutting it must be made with a file +(moisten the edge!), and it often will not break square across. Before +proceeding to seal on the small tube, any large projections on the cut +end are best removed, by warming the cut surface a little, directing the +small flame upon each projection in turn and touching it with a warm +scrap of glass. It will adhere to this and may then be removed by +rotating this scrap a little so as to wind up the projection on it, and +then drawing it off, while the flame is still playing on the spot. This +must be done rapidly and care taken not to soften the main part of the +cone. + +[Illustration: FIG. 8.--Joining two tubes of different diameters.] + +The large tube is now taken in the left hand, the small one in the +right, the ends heated and joined in the usual manner, taking care not +to get any larger lump at the joint than necessary. A small flame is now +directed on the cone at right angles to its elements as before, and the +tube rotated so as to heat the whole circumference. The flame should be +just large enough to heat the whole of the cone. As the latter shrinks, +the lump at the joint is brought into the edge of the flame, and it and +a very little of the small tube allowed to shrink with the cone. + +When well shrunk and heated to blowing temperature the joint is removed +from the flame and blown gently with careful rotation, pushing the tubes +together a little when the blowing is about finished, so that the cone +becomes a short thick half-bulb, as shown in _d_, Fig. 8. This +corresponds to the first thick bulb in the first method (_d_, Fig. 6), +and is treated similarly. It is again heated and shrunk, taking care not +to involve either the large tube or the small one in the shrinking, +blown quickly to about the same shape as before, (_d_, Fig. 8), and then +gently drawn out into a smooth cone (_e_), exactly as in the first +exercise. Care should be taken not to draw too rapidly or too far, as +then the resulting cone (_f_) is weaker than it should be, and does not +look well. + +=Discussion.=--The beginner will find that this operation is best +learned on two tubes which are not too nearly of the same diameter. A +tube about 5/8 inch in diameter and one a little less than 1/4 inch will +be suitable. Both should have moderately heavy walls (1/16 inch or a +trifle over for the large tube, and a trifle less for the small one) but +the large tube should not be too heavy or else it will be hard to +prevent melting down too much of the small tube, and getting this drawn +out too thin during the process. One of the troublesome features of this +exercise is the difficulty of rotating two tubes of different diameters +with the same angular velocity, so as not to twist the joint. Another +difficulty is found in getting the cone uniformly heated to blowing +temperature without overheating and overshrinking the small tube. The +reason for this is obviously the much greater circumference of the cone, +especially at its large end, so that relatively much less of it is being +heated at any time. The beginner is also inclined to start with too long +a cone, or else heat so much of the large tube that part of its glass is +included in the cone, with the result that in order to get the right +wall-thickness the cone must be made too long (_g_, Fig. 8). This does +not look well, and usually will be irregular in shape. + + +EXERCISE NO. 5 + +TUBE FOR CONDENSING SULPHUR DIOXIDE + +This is useful as a test of mastery of the preceding exercise. A piece +of 3/16 or 7/32 inch tubing is joined to each end of a piece of tubing +5/8 by about 5 inches, and two constrictions made in the large tube, by +the method described on page 10. The small tubes are then bent in the +same plane, as shown, and their ends fire-polished (Fig. 9). + +[Illustration: FIG. 9.--Tube for condensing sulphur dioxide.] + + +EXERCISE NO. 6 + +BULB AT THE END OF A TUBE + +For this exercise tubing of 1/4 inch diameter and moderately strong +walls is selected. A tail is drawn out on one end of the tube, and a +piece of tubing about nine or ten inches long is cut off. The tail +should be carefully drawn in the axis of the tube, and in the same +straight line with it, as it is to be used as a handle in assembling the +glass for the bulb. This tail must be long enough so that it can be +conveniently held in the left hand, as described on page 13, and rotated +about the same axis as the main tube. Holding the main tube in the right +hand and the tail in the left, the tube is rotated in a large flame so +that a piece of it, beginning where the tail stops and extending about +an inch to the right, may be uniformly heated to the highest temperature +at which it can be kept in shape. As soon as this temperature is +reached, the tube is removed from the flame, continuing the rotation and +taking care not to draw out the heated part, and gently blown. The +rotation is carefully continued during the blowing, holding the tube in +approximately a horizontal position. As soon as the tube has expanded a +little the tail is pushed gently toward the main tube, continuing the +gentle blowing. If this is properly done, the heated piece of tube will +become a short bulb of about double its original diameter, and about the +same wall thickness as the original tube. It will have somewhat the +appearance of _a_, Fig. 10, when properly manipulated. + +[Illustration: FIG. 10.--Blowing a bulb on the end of a tube.] + +The tube is now reheated as before, taking care this time that the +heating extends over all that part of the bulb to the right of the +dotted line in the figure, as well as part of the main tube adjoining. +If this heating has been properly placed, when the operation of blowing +and pushing together is repeated the result will be to lengthen the bulb +into a uniform cylinder, as shown in _b_, Fig. 10. Otherwise the result +will be a series of bulbs, as in _c_, Fig. 10, separated by thickened +ridges which will be almost impossible of removal later and will +disfigure the final bulb. This operation of heating, blowing and pushing +together is repeated several times, until the cylinder becomes as long +as can be conveniently handled (about 1-1/4 inches to 1-1/2 inches). If +more glass is needed than is then contained in the cylinder, the latter +may now be heated as a whole, and blown and pushed gently into a shorter +cylinder of a slightly greater diameter, and more glass then added as +before. + +When enough glass has been collected for the bulb, it is all well heated +and blown gently a couple of times, pushing the mass together as +required, until a thick bulb like _d_, Fig. 10, is obtained. The tail +must now be removed at the point indicated by the dotted line. To do +this, a very fine flame is directed on the point where the tail joins +the bulb, and the tube well rotated as the glass softens at that point. +When sufficiently soft, the work is raised a little, so that the flame +instead of striking the glass squarely at the point indicated passes +below and tangential to it. The tail is now drawn off slowly, continuing +the rotation, raising the work just out of the flame whenever the thread +of glass drawn off becomes too thin, and lowering it again to the point +where the flame just touches it when the glass stiffens a little. By +this means the tail may be drawn off without leaving an appreciable lump +behind, as indicated in _e_ and _f_, Fig. 10. When as much of the extra +glass has been removed as is practicable, the flame is brought to play +squarely upon the little lump left, the last of the tail removed, and +the lump heated and gently blown to a small excrescence on the main +bulb. The whole end of the latter is now heated until it begins to +shrink a little, and gently blown to make it uniform in thickness. The +whole bulb is then heated in a flame of the proper size, so that it all +may shrink to about two-thirds of its diameter. The flame must be very +carefully chosen and directed, so as to shrink all the bulb, right up to +the main tube, but not soften the latter. As soon as this stage is +reached, the bulb is removed from the flame, continuing the even +rotation, and blown to the desired size, preferably by a series of +gentle puffs following one another at very short intervals. During the +blowing, the main tube is held in a horizontal position, and any +tendency of the bulb to fall out of line is corrected by the rotation. +If the shape of the bulb or its size are not satisfactory, it may be +shrunk again and reblown. Such shrinking should begin in a large yellow +flame, with just enough air to give it direction. The amount of air may +be gradually increased as the bulb shrinks and the walls become thick +enough to bear it without collapsing. If the bulb starts to collapse at +any time, it must be immediately blown enough to regain its convex +surface, before the shrinking proceeds further. + +=Discussion.=--In collecting the glass for the bulb, enough must be +gathered to give the walls the desired strength. Since the area of a +sphere is proportional to the cube of its diameter, it is evident that +doubling the size of a bulb diminishes the thickness of its walls to a +very large extent. The limit of diameter for a strong bulb on ordinary +1/4-inch tubing, collecting the glass as above, is about 1-1/2 inches, +and the beginner will do well not to blow his bulbs more than an inch in +diameter. + +The collection of the glass is one of the most important parts of the +process. If the mass of glass be twisted, furrowed or ridged, or +lop-sided, it is very difficult to get a good, even, spherical bulb, no +matter how many times it is shrunk and blown. The greatest care should +therefore be taken to get a uniform cylinder, on the same axis as the +main tube; and to this end the rotation of the tube must be carried on +very evenly. For method of holding the tube, see page 14. + +If a very large bulb is required, it will often be economical to seal on +the end of the tube a short piece of a large tube, provided with the +proper tail, and use the glass in the large tube for the bulb instead of +attempting to collect it from the small tube. In this case part of the +small tube will usually be included in the bulb, so that the joint comes +in the latter, and not where it joins the tube. As the amount of glass +carried on the end of the tube increases in weight and size the +difficulties of heating it uniformly, keeping it in the proper position +and handling it increase rapidly. + +In collecting glass, it is usually best not to leave the part of the +cylinder next the tube with too thick walls. This is always the coolest +part during the preparation for blowing the bulb, consequently it does +not get blown out, and causes an ugly thickened appearance on that end +of the bulb. + +If the bulb grows too long or pear-shaped, it may be easily shortened by +heating to the blowing temperature, and then blowing gently with the +main tube in a vertical position, and the bulb at the top of it. Gravity +will then shorten the bulb nicely. + +The finished bulb should be a nearly perfect sphere, with the axis of +the tube passing through its center, and the portion of the tube +adjoining the bulb must not be distorted, twisted, or blown out. In +order to prevent the distortion of the tube, care must be taken that it +is never heated quite to its softening point during the process. + + +EXERCISE NO. 7 + +BLOWING A BULB IN A TUBE + +The tube is selected and one end closed as in the previous exercise, but +it should be cut a little longer, say about twelve inches. Beginning at +a point about four inches from the closed end, glass is collected and +blown into a thick-walled bulb, exactly as in the previous exercise. +Greater care must be taken, however, that the cylinder collected and +this thick bulb are of uniform thickness and set squarely in the axis of +the tube. Instead of removing the tail, the bulb must be blown in this +case with both pieces of tubing attached, and care must be taken that +they "line up" properly, _i.e._, are in the same straight line, and that +this line passes as near as may be through the center of the bulb. The +tube is held in approximately horizontal position during the blowing of +the bulb, as in the previous case, and especial care taken with the +rotation. Both pieces of tube must of course be rotated at the same +rate, and their softened ends must be kept at exactly the proper +distance from each other, so that the bulb may be spherical and not +elongated. If the blowing of the bulb be quickly and accurately done, it +may usually be completed before the glass is quite set, and the +alignment of the two tubes may then be rectified while looking straight +through the bore of the tube. + +=Discussion.=--The two points of greatest importance are the collection +of the glass, and the uniform rotation of the tube. A larger tube may be +sealed in the middle of a small one when a large amount of glass is +necessary. The piece of tubing used for the exercise must be long enough +so that the fingers may be kept on a cool part of the glass without +getting uncomfortably near the ends of the tube. It should not be any +longer than necessary, however, as the extra weight and length make the +manipulation of the hot glass more difficult. + +When a string of bulbs are required on the same tube, a piece of glass +18 inches long may be used at the start, and the first bulb made near +the closed end, as described. Each succeeding bulb will then be in plain +view during the blowing, and when the open end becomes too short for +comfort, it may be dried out, cut off, and another piece joined to it, +starting as in the first method (Exercise No. 1), but instead of drawing +out the thick bulb to a tube, it is made part of the glass collected for +the next bulb. If the string of bulbs becomes awkward to handle on +account of its length and weight, it may be made in several parts and +these later sealed together by the second method, preferably blowing +through a rubber tube attached to the open end, as described on page 22. + +Very neat small bulbs may be made on tubing of a diameter of 3/16 inch +or a little less, but the beginner is advised to start with tubing of +about 1/4 inch diameter. The use of tubing with too thick walls usually +produces bulbs which are thick-walled at the point where they leave the +tube, but inclined to be too thin at the point of maximum diameter +(perpendicular to the axis of the tube) where most of the strain comes +and strength is particularly needed. + + + + +CHAPTER IV + +ADVANCED EXERCISES + + +EXERCISE NO. 8 + +SEALING A TUBE THROUGH ANOTHER TUBE + +_First Method--Making a Gas-washing Tube_ + +This first method can be used whenever one can work through an open end +opposite to the end of the tube where the joint is to be made. To +illustrate it, take a piece of rather thin-walled tubing, about 3/4 inch +in diameter, and some pieces of rather strong tubing a little less than +1/4 inch in diameter. Draw off the large tube in a short cone, then draw +off the tail as in the making of the bulb on the end of the tube, blow +out the little lump slightly, shrink the whole cone a little and blow +gently to form a rounded end like that on a test-tube, with walls about +the thickness of those of the rest of the tube. Cut this tube to a +suitable length, say about six inches, and provide two corks which will +fit the open end of it. Now cut a piece of the small tubing of the +proper length to form the piece which is to be inside the large tube. +For practice purposes, this piece should be about an inch shorter than +the large tube. Flange one end of this tube a little, and anneal the +flange well in the smoky flame. Bore one of the corks so that a piece of +the small tubing will fit it, and cut a couple of notches in the side of +this cork so that air can pass between it and the glass. Pass a short +piece of the small tubing through this cork, and attach the flanged +piece of small tube to this by means of a short piece of rubber tubing, +so that when the whole is inserted in the large tube it is arranged as +in _a_, Fig. 11. The piece of glass tubing projecting out through the +cork is now cut off so as to leave an end about 1/2 inch long when the +cork is firmly seated and the inner tube pushed into contact with the +center of the end of the large tube, as shown in the drawing. Care +should be taken that the little rubber tube which joins the two pieces +is arranged as in the figure; _i.e._, most of it on the piece of tubing +which passes through the cork, and very little on the other piece, so +that when the cork is removed after the small tube has been sealed +through the large one, the rubber tube may easily come with it. Select a +short piece of the small tubing of suitable length for the piece which +is to be on the outside of the large tube as a continuation of the +piece inside, and another piece for the delivery tube. A small bulb may +be blown in the latter at a point about 2-1/2 inches from the closed +end, and the open end cut off about 1-1/2 inches from the bulb. A cork +or cork-boring of suitable size to stopper the small tube is prepared, +and laid ready with the other (unbored) cork for the large tube. + +[Illustration: FIG. 11.--Gas-washing tube.] + +When everything is in readiness, the rounded end of the large tube is +slowly heated until it softens and joins firmly to the small tube +inside. After it has shrunk down well, it is blown out to its original +size, placing the whole end of the large tube, cork and all, in the +mouth. Now with a fine-pointed flame the glass covering the end of the +small tube is heated to the softening temperature, and then is blown out +to an excrescence by blowing on the end of the small tube which passes +through the cork. The end of this excrescence is heated and blown off in +the usual way, so as to leave the small tube sealed on the inside of the +large one and opening through it into this short tube which has been +blown out. The end of the small tube which passes through the cork is +now closed with the cork prepared for it, and the short outer tube is +joined to the tube that has just been blown out, so that the joint +appears like _b_, Fig. 11. Use the first method (Exercise No. 1) for +this joint. Reheat the whole of the end of the tube nearly to the +softening temperature, anneal it a little, and allow to cool a few +seconds until well set. Now remove the cork, short glass tube and rubber +tube from the open end of the large tube and insert the solid cork in +their place. Warm the joint and the whole of that end of the tube again +carefully up to about the softening point, then seal on the side tube +for the delivery of the gas in the usual way, taking care that the whole +of the end and the joint are kept warm meanwhile. When thoroughly +sealed, the delivery tube is bent up parallel to the tube through which +the gas enters, and then out at right angles to it, as shown in _c_. The +whole of the end of the tube is now cautiously reheated and then cooled +slowly to anneal it. + +The cork may now be removed from the open end of the large tube, this +end heated in a large flame, caught together with a scrap of glass +tubing and drawn off into a cone so that the base of the cone is about +opposite the end of the inner tube. The lump of glass is drawn off the +point of this cone and it is reblown to form a rounded end, as +previously described. + +After this cools, the tube through which the gas enters may be heated at +the proper point and bent at right angles to form the finished apparatus +as shown in _d_. The ends of the small tube are cut off square and +fire-polished. + +=Discussion.=--After the joint has once been made, great care must be +taken that it is kept hot during all the subsequent manipulations, and +if it becomes somewhat cool at any time it must be reheated very slowly. +It is obvious that the rate of heating and cooling of the inner tube +will be slower than that of the outer tube, and this will readily +produce stresses which tend to crack the tube at the joint. The amount +of heating and cooling which such a joint will stand depends upon its +form. The beginner should examine such a joint on regular factory-made +apparatus, and note the uniformity of wall-thickness and the "clean-cut" +appearance of the joint, as a model for his imitation. A ragged joint, +where the line of joining of the inner and outer tubes wavers instead of +going squarely around the tube, is almost sure to crack during the +cooling and heating unless extra precautions are taken with it. The +presence of a small lump of glass at any point on the joint affords an +excellent starting place for a crack, as do also the points on a ragged +joint where the inner tube comes farther down on the outer tube than at +other points. + +In order to insure a joint which is square and not ragged, it is +essential that the angle between the inner and outer tubes at the joint +be very nearly a right angle. For this reason the two tubes should not +be of too near the same size, or if this cannot be avoided, a small bulb +should be blown on the end where the joint is to be made. If this bulb +be made with the same wall-thickness as the rest of the tube, and +somewhat pear-shaped, it may be drawn out to the same size as the rest +of the tube, if necessary, after the joint has been made. + +This method is used wherever possible in preference to the second method +(Exercise No. 9), as it is easier to get a good joint with it. It may +also be used where it is desired to seal the tube through the side of a +tube, or for a tube sealed through the wall of a bulb, as in a Geissler +potash bulb or similar apparatus. Where there is not space to join the +inner tube to the blowing tube by a rubber tube, this joint may be made +with a small piece of gummed paper, which can readily be broken when +desired. + + +EXERCISE NO. 9 + +SEALING A TUBE THROUGH ANOTHER TUBE + +_Second Method--Making a Suction Pump_ + +Select a piece of tubing 3/8 to 1/2 inch in diameter, with walls about +1/16 inch or a little less in thickness, heat a place about 4 inches +from one end and draw it out so that when cut off at the proper point it +will look like _a_, Fig. 12; the open end of the drawn out part being +small enough to slip inside another piece of the original tube. A small +thick-walled bulb is now blown as indicated by the dotted lines, and +annealed. A piece of the original tubing is now prepared, 7 or 8 inches +long, with one end cut square off and the other closed. A piece of +1/4-in tubing about 2 inches long, and drawn out at one end to a tail +several inches long is also prepared, to form the inlet tube for the +air. Another piece of the 3/8-inch tube is prepared, about 4 inches +long, and provided with a tail drawn out as indicated in _b_, so that +when cut off at about 2-1/2 or 3 inches from the main tube its inner +diameter may be slightly less than that of the narrowest point of the +tube _a_. A small thick-walled bulb is blown at the point indicated by +the dotted lines, and annealed. Care must be taken in drawing the +capillary and blowing the bulb in both _a_ and _b_ that the capillary +tubes are in the axis of the main tube, and in the same straight line +with it. + +[Illustration: FIG. 12.--Suction pump.] + +The open end of the 8-inch piece of tube and the bulb of the piece _a_ +are now warmed together, the end of the tube only moderately and the +bulb to about its softening temperature. The tube _a_ is now inserted in +the open end of the large tube, and the bulb softened with a suitable +flame and pressed into good contact with the tube. It is then reheated, +including the joint, blown a little and pulled out to form a straight +tube in line with the main tube. By warming the joint a little, and +proper rotation, the capillary may be brought into the same straight +line with the rest of the tube. + +Keeping this joint hot, a place about an inch from it on the tube _a_ is +warmed, and the piece of 1/4-inch tubing previously prepared is sealed +on at that point. The joint is then well annealed and allowed to cool. + +The tube _a_ is now cut at such a place that when _b_ is inserted in the +open end the point will come near the end of the constriction of _a_, as +shown in _c_. Care is taken to get a clean square cut. The side tube is +now cut off about an inch from the main tube and corked. Tube _b_ is +sealed into the open end of _a_, in the same way as _a_ was sealed into +the large tube, and the joint carefully annealed. + +=Discussion.=--As in the first method, the secret of success lies in +getting a square joint, and having the inner tube leave the outer one at +nearly right angles. All the remarks about annealing, lumps, etc., made +under the previous method apply here. + +This method may be applied in sealing a small tube into the end of a +large one, the latter being either drawn to a cone and cut off at the +desired diameter, or else given a rounded end like a test-tube and a +hole the proper size blown in the center of it. A suitable thick-walled +bulb is to be blown on the small tube, as in the case described above. +This method is also used in making the Kjeldahl trap (_a_, Fig. 13), the +small tube to be inserted being first drawn, the thick bulb blown at its +point of union with the main tube, and then the small tube bent and cut. +The large bulb is best made with rather heavy wall, being either blown +in the middle of a tube, and one piece of the tube drawn or cut off, or +else made on the end of a tube. In the latter case a drop of glass must +be put on the point where the joint is to be, so as to get a hole of the +proper size with enough glass around it to prevent it from growing +larger when it is heated. The author prefers to blow the bulb in the +middle of the tube, draw off one end of the bulb, and blow out the +desired hole where the tube was drawn off. The whole bulb must generally +be reheated and blown a little at the end of the process, and well +annealed. + +[Illustration: FIG. 13.--_a_, Kjeldahl trap; _b_, suction pump on +smaller tubing.] + +The suction pump can also be made on 1/4-inch tubing, and one joint +saved if desired, by constricting the tube to form the raceway for the +water and air, as shown in _b_, Fig. 13. (See page 10 for method.) But +it is more difficult to make a square joint on such small tubing. + + + + +CHAPTER V + +MODIFIED METHODS AND SPECIAL OPERATIONS + + +CAPILLARY TUBING + +This is commonly used in many forms of apparatus for gas analysis, and +one is often called upon to join two pieces or to make a tee on it. The +methods are nearly the same as with other tubing, except that more care +and patience are required. The work must be done much more slowly on +account of the thickness of the walls, and open ends of the tube must +always be enlarged before joining them to anything. This is best done by +carefully sealing the end and then blowing, with several suitable +reheatings, to form a pear-shaped bulb as in _a_, Fig. 14. The end of +this is then heated and blown off, and the piece is ready to be joined +to another similar end, or to a piece of ordinary tubing if desired. The +joints are best not blown too much, as thick walls shrink very slowly. +Much may be done by gently pushing the tube together or pulling it apart +in the flame, to remove lumps and irregularities. It is necessary that +the bore of the joint be approximately that of the main tube, and care +must be taken that the latter is not constricted at the point where the +joint begins. + +[Illustration: FIG. 14.--Capillary tubing.] + +Especial care must be taken to warm the tube slowly when starting and +cool it slowly when through, as the thick walls frequently crack if not +carefully handled. For this reason the whole neighborhood of the joint +must be heated somewhat so that there may not be stresses set up between +the heated and unheated portions. + +In making the tee (_b_, Fig. 14) the inability to blow the joint makes +itself decidedly felt, but if the side tube is properly enlarged as +previously described, a good joint can be made by alternately pulling +and pushing on the end of the side tube, and shrinking well. + +Very fine capillary tubing should be blown with a rubber bulb instead of +the mouth, so as not to get moisture into the tube. The rubber bulb may +also be used to advantage on some of the coarser capillary tubing. + +When a bulb is to be joined to a piece of capillary tubing, the joint is +preferably made before blowing the bulb, and will then be taken up a +little way on the bulb during the process. Care must of course be taken +not to constrict the capillary; the pear-shaped bulb blown on the end +(_a_, Fig. 14) may well extend back a little further than usual into the +tube so as to prevent this. If a bulb is required in the middle of a +capillary tube, the latter is usually best cut and a piece of ordinary +tubing of suitable size sealed in to provide material for the bulb. + + +GLASS ROD + +Joints, tees, etc., in glass rod are made on the same principle as in +tubing, except that of course they cannot be blown, and regularity must +be obtained by accumulating a small mass of uniformly heated glass, and +then drawing it to a suitable rod, on the same principle as Exercise No. +1. + +Great care must be taken in heating and cooling this, as in the case of +the capillary tubing, and for the same reasons. + +By joining pieces side by side, pressing with carbon plates or a plate +and a rod, and other suitable manipulations, stirrers, spatulas, and +other objects may easily be made from rod, and its manipulation is +relatively easy on account of the fact that one does not have to worry +about the bore of the tube. But the same general rule about not having +thick and thin spots in contact, and making all changes in diameter on a +taper if possible instead of abruptly, applies here. Thick pieces will +cool and contract at different rates from thin ones, and cracks are +likely to develop where they join. Work which has been formed with any +tool must always be heated to the softening point afterward before +allowing it to cool in order to remove the stresses caused by the +contact of the tool with the hot glass. + +When it is necessary to join a piece of rod to the side of a piece of +tubing, the end of the rod is made very hot while the wall of the tube +at the spot desired is heated to just below the softening temperature. +The rod can then be pressed into firm union with the tube and drawn a +little to remove the excess of glass without deforming the tube. + + +MENDING STOPCOCKS + +=Mending the Plug.=--The plug of the stopcock occasionally falls out and +is broken. If the break is in the main part of the plug, nothing can be +done except to search for a spare plug of suitable size and grind it to +fit, as described below. If only the little cross-piece at the end is +broken off, it can easily be replaced. In most ordinary stopcocks the +plug is solid, but the little handle is hollow. What has been said above +regarding care in heating and cooling glass rod applies with especial +force here. It is usually best to wind the whole of the plug with +several thicknesses of asbestos cord, leaving bare only the end where +the handle is to be joined. This diminishes the danger of cracking the +plug by too rapid heating, and also makes it more comfortable to hold. A +piece of rather thick-walled tubing of suitable diameter is chosen, +drawn out so as to have a suitable taper (taking care to heat enough of +the tube so that the capillary tail has good wall-thickness and +strength), and then a corresponding taper is drawn to form the other +side of the handle. The result is shown in Fig. 15, _a_. The capillary +tail is now heated and bent back to form a handle which will be in the +same straight line as the axis of the plug (_b_, Fig. 15) and the main +part of the tube drawn off at the dotted line, making a neat seal at +that point. The broken end of the plug is now slowly warmed in the smoky +flame, the heat gradually increased by a gentle stream of air from the +bellows, and the point at which this handle is to be attached finally +brought to the temperature at which the glass flows freely. In the mean +time, the little handle has been warmed almost to the softening point. +It is now quickly pushed into place (_c_, Fig. 15), taking care that its +axis is parallel to the hole in the plug, and then drawn away from the +plug just enough to make a graceful neck instead of the bulging one +indicated by the arrow in the figure. With a fine pointed flame the +little tail is now drawn off at the point indicated by the dotted line +(_c_, Fig. 15) and the whole carefully annealed. If necessary, the +handle can be blown a little before the tail is removed. Local heating +and blowing at the point where the handle joins the plug is often +necessary in order to make a smooth job. + +[Illustration: FIG. 15.--Stopcock plug.] + +=Regrinding.=--This is sometimes necessary to make stopcocks tight, when +the grinding has not been properly done in the factory. For this, a very +little fine flour of emery or carborundum is the best and quickest. If +this is not at hand, some clean sand may be ground in an agate mortar, +and if possible sieved. Only material which passes the 100-mesh sieve +should be used. It will be ground still finer in the process. For the +final polishing, a little infusorial earth or even kaolin will do. + +The surface to be ground is moistened with water and dusted over with a +little of the abrasive. The plug is now inserted in the stopcock, and +turned with a gentle pressure. This turning should be in the same +direction for several revolutions, then in the opposite direction for +several more revolutions, etc. As the abrasive becomes finer during the +grinding, a little more may be added if necessary. In general, only a +little grinding will be required, and one small pinch of carborundum or +emery will be ample. The beginner usually grinds too much, and with too +coarse material. As the grinding surface becomes dry, water is added +drop by drop, and the grinding continued until the abrasive seems to be +reduced to an impalpable powder, most of which has been squeezed out of +the stopcock. The two surfaces in the stopcock are usually grinding upon +each other at this stage, and inspection will show whether the contact +between them is uniformly good. If not, the grinding must be continued +with a little fresh abrasive. If contact appears to be good, the +surfaces are ground together for a little with practically no abrasive, +so as to polish them, and the joint is then washed out and tested. + +In grinding in a new plug to replace a broken one, the plug selected +should have practically the same taper as the seat into which it is to +be ground, and should be a very little too large. Care must be taken to +so distribute the abrasive material as to grind mostly on the places +where the plug fits tightly. + +=Sealing on a New Tube.=--It frequently happens that one of the tubes of +the stopcock is broken off close to the cock itself, and a new one must +be joined to the stub of the old one. With care, this may often be +successfully done even where the break is within 1/4 inch of the +stopcock. The first step is to clean and dry the stopcock, remove the +plug, cork the open ends of the stopcock sleeve and the other tube, and +wind a couple of layers of asbestos cord carefully over the sleeve and +the most of the corks which close it. A suitable tube, having as near as +possible the same diameter and wall strength as the one broken off, is +selected and a piece the desired length cut off. The broken end of the +tube on the stopcock is now squared off as well as possible, by cutting +or by heating and drawing off the projections, and the new tube sealed +on, usually with the first method (Exercise No. 1). If the break is very +close to the stopcock, very little reheating and blowing can be done, on +account of the danger of getting the stopcock sleeve out of shape, and +the work must be heated very slowly to prevent cracking. The main +reliance is then placed on making a good joint when the tubes are +brought together, and then drawing out this joint a little, at once, to +get an even wall. + + +CLOSED CIRCUITS OF TUBING. + +In some pieces of apparatus closed circuits of circular or rectangular +shape are required. A similar problem is involved in apparatus like the +ordinary Soxhlet extractor, where a small tube is joined to the side of +a large one, bent to form a siphon, and attached again to a continuation +of the original large tube. The difficulty in all such cases is to +provide for the contraction taking place as the last joint cools. If +part of the circuit has the shape of the letter S, or is a spiral, the +natural springiness of the glass will take care of this. If not, the +side of the circuit opposite to the joint and parallel to it must be +heated also, the two being finally heated together to the softening +point after the joint is completed, and then allowed to cool together. + +To make the last joint, the rest of the tube is made in approximately +the desired form, the two pieces which are to be joined to make the last +joint being just enough out of the desired position to allow them to +pass one another. The final joint is preferably made in the middle of a +straight piece of tube, not at a tee. The two pieces which are to be +joined are bent so as to just pass each other, marked at the right point +with the glass-knife, and cut there, preferably with a small bead of hot +glass. One or both of these tubes are now warmed to the softening point +in such a place that the tubes can be made to meet properly, and the two +cut ends pressed together. They are now warmed in the flame, and joined +together, either by simultaneously warming the opposite side of the +circuit or some other suitable part, so as to allow the two ends to be +pushed together again after they are softened, or by gently touching the +places that do not unite with a hot bead of glass, and using the glass +to fill up the crack where the ends do not quite meet. Care must be +taken not to leave knots or lumps of glass in the finished joint, and +the latter should be well reblown, and if necessary left as a small bulb +or enlargement, rather than have it have too thick walls. + + +SPIRALS + + + +Spirals of glass tubing are probably best made free-hand before the +blow-pipe, unless one has a great many of them to make, and extreme +accuracy is desired. To begin with, a piece of tubing of the desired +size (say 3/16 inch in diameter) and a convenient length (about two +feet) is selected, one end closed, and a right-angle bend made about six +inches from the closed end. Holding the closed end in the left hand and +the long open one in the right, the spiral is begun. The short closed +end is to be parallel to the axis of the spiral, and preferably in that +axis. Using a moderate-sized flame, of somewhat yellow color, and taking +care to heat the whole circumference of the tube, the long open end is +wound little by little into a spiral having the short end _a_ (Fig. 16) +as an axis. The bend at _b_, where the tube changes from the radius to +the circumference of the circle, must be rather short, but the tube must +not be flattened or constricted here. Especial pains is to be taken +with the first turn of the spiral (_b_ to _c_, Fig. 16), as the shape of +this determines the diameter of the whole spiral, and serves as a guide +for the rest of the turns. The winding of the tube is best accomplished, +after a portion has been softened, by slowly turning the short end _a_ a +little about its own axis, while the long open end remains where it was. +This winds the tube into a spiral, just as if there were a solid +cylinder in the center of it, and this cylinder was being turned about +its axis, and was winding up the soft glass upon its circumference. As +the cylinder is not actually there, the curve of the turns must be +carefully estimated by the eye, so that the spiral may be uniform and +moderately smooth. When the original piece of tube has been used up, +another piece is sealed on to the open end, and the operation continued +as far as may be required. + +[Illustration: FIG. 16.--Making a spiral.] + + +GROUND JOINTS + +It is sometimes required to join two pieces of tubing end to end, by +means of a ground joint. Whenever possible, a regular sealed joint +should be used instead of this ground joint, as it is quicker to make, +and more certain to be tight. Where a ground joint is necessary, +however, it is best made in the conical form shown in _c_, Fig. 17. If +the wall of the tube to be used is not very thick, it is thickened by +collecting glass as for a bulb on the ends of two tubes (Exercise No. +6), and drawing to form cones of suitable shape (_a_ and _b_, Fig. 17) +and of such relative sizes that a will slip about half way into _b_. In +order to make _a_ straight and give it the proper angle, it may be +rolled when hot, upon a hot plate of carbon. Blowing during this rolling +is often helpful to remove depressions. After _b_ has been drawn to +nearly the proper size and shape, it may be smoothed by the use of a +small carbon rod, held inside it at a slight angle, or better by the use +of a truncated hexagonal pyramid of carbon, whose edges have the proper +slant to make the inside of the cone right. The proper taper for both +these cones is the same as that used in stopcocks of similar size. The +hexagonal carbon can easily be made by carefully filing down an electric +light carbon, and finally impregnating it with paraffin or beeswax, and +is extremely useful wherever a conical surface has to be formed from the +inside of a tube. + +[Illustration: FIG. 17.--Ground joint.] + +The tail is allowed to remain on piece _a_, as a sort of guide in +grinding, and should therefore be in the axis of the tube and have +rather thick walls. Grind with emery or carborundum, as described under +a previous head. (Regrinding plug for stopcock.) If many such joints are +to be made, it will pay to have a little sleeve of brass made with the +proper taper, and rough down the plug _a_ in it to about the proper +size, while _b_ is roughed down by means of a brass or iron plug having +the same taper. This prevents excessive grinding of one-half of the +joint in order to remove a defect in the other half, and is the method +commercially used in making stopcocks. + + +SEALING IN PLATINUM WIRE + +Very often it is necessary to seal platinum wire into the wall of a +tube. Professional glass-blowers usually use a special sort of glass +("Einschmelzglas") which is usually a lead glass, and is made of such +composition that it has the same or practically the same coefficient of +expansion as platinum. A little globule of this glass is sealed into the +tube in such a way that it joins the platinum to the glass of the tube. +To do this, the small globule of special glass is fused on the platinum +wire at the proper point and the tube into which the wire is to be +sealed is heated and a small tail drawn out at the point where the wire +is to be inserted. The lump of the special glass should be from 3/32 to +1/8 inch in diameter, and the tail drawn on the tube should have a +slightly less diameter at the point (about 1/8 inch or less from the +tube) where it is cut off. There are now two ways of sealing in the +wire. (1) The wire with the globule of glass is placed inside the tube +and the latter revolved until the end of the wire sticks out of the cut +tail (_a_, Fig. 18). The latter is now gently heated, and the two glass +surfaces fused together, taking care to use only the end of the hissing +flame, if the special glass contains lead. (See Chapter I, page 1.) The +whole circumference of the tube is then heated and annealed carefully. +(2) The end of the wire which is to be outside the tube is attached to +the end of a thin scrap of glass, by heating the glass and thrusting +the wire into it a very little way. Using this piece of glass as a +handle, the wire is inserted in the cut tail (_b_, Fig. 18) and the +globule brought near to the end of the tail. (If the main tube is cold, +it must of course first be warmed.) With the end of the hissing flame, +as in the first method, the globule of glass is melted and the end of +the tail softened. The wire is now pushed into place, the handle removed +by heating the end and withdrawing it, and the tail reheated a little if +necessary to make it shrink back into line with the walls of the tube. +The whole circumference of the tube is heated at that point and annealed +as usual. + +[Illustration: FIG. 18.] + +The use of this special glass is not absolutely necessary if the +platinum wire is small (1/4 millimeter or less in diameter), and in fact +it is often better in such cases not to use it, unless the apparatus is +to be subjected to a very high vacuum. On small tubes, especially, it is +undesirable to use the special glass, as a lump of it will usually cause +the tube to crack on cooling. When such glass is not at hand or is not +to be used, the procedure is altered somewhat. The tail which is drawn +out is very fine, having only a sufficient diameter so that when it is +cut off the wire can be inserted in it. Such a fine tail is readily made +by heating a small spot on the tube, touching it with a warm platinum +wire, removing from the flame and drawing out the tail with the wire. +After cutting off the tail the wire is inserted in it, being held on a +scrap of glass as in the previous case, and the wire and tail heated +until the latter shrinks back into line with the walls of the tube. If +too great shrinkage occurs, the place may be blown out gently after +reheating. Thus the wire is sealed through the wall of the tube without +changing the thickness of the latter, and consequently without +developing undue stresses at that point. Such a joint must of course be +carefully reheated and annealed. With fine platinum wire there is very +little risk of the tube cracking if care is taken to avoid formation of +any lump and to reheat the whole circumference of the tube at that +point. + +Any glass adhering to the end of the platinum wire, where the scrap of +glass was sealed on for a handle, may be removed when the glass has +cooled by crushing it carefully with a pair of pliers. + + +SEALING VACUUM TUBES + +Tubes which have been evacuated usually are sealed off while they are +still connected to the vacuum pump. The connection should be through a +small, rather thick-walled tube. When this is to be sealed, it is slowly +heated toward the softening point. As the glass just begins to soften, +the air-pressure will force it in, and care must be taken that the +softening is uniform over the whole circumference of the tube. As the +shrinking goes on, the tube is gently drawn out to make a thick-walled +cone at that place, and the end is drawn off as soon as the tube is +sealed. The principal point to be guarded is the thickness of the walls +of the cone, and uniform heating. A thin place or a hot place will give +way under the air-pressure and be sucked into the tube. + + +CLOSED TUBES FOR HEATING UNDER PRESSURE + +(_Carius method for determination of the halogens and sulphur._) In this +case the tubing used must have thick walls (usually about 3/32 inch) to +withstand the pressure. Its external diameter is usually about 3/4 inch. +One length will usually make two tubes of standard length for the cannon +furnace. Especial care must be taken in heating and cooling it on +account of the thick walls. A length is gradually warmed in the center, +finally heated at that point until soft, drawn out, cut apart and +annealed. Taking one of the pieces, the cone is carefully heated and +shrunk, as in Exercise 4, until its walls are as thick as those of the +main tube. A flame with a little tinge of yellow should be used for this +operation to prevent devitrification (page 2), as the thick glass +shrinks slowly. The tail is now drawn off and the whole end heated and +gently blown several times to make a rounded end, like a test-tube, with +walls as thick as those of the main tube. This must be carefully +annealed. It is more important that the walls be thick than that the end +be nicely rounded: it may indeed be left somewhat conical in shape. + +At a point about two inches from the open end of the tube, it is slowly +warmed and finally heated to the softening point. Grasping the open end +with a pair of crucible tongs, it is cautiously pulled out, a little at +a time, usually during rotation in the flame, to make a constriction of +moderate wall-thickness, but of sufficient internal diameter to admit +the tube containing the substance. After annealing this, cooling and +cleaning the tube, the acid and salt are introduced (the former by means +of a long-stemmed funnel) and the tube is inclined and rotated about its +axis so that the acid wets its surface about half way up from the +bottom. The substance is now weighed out in a piece of thin-walled glass +tubing, closed at one end, and about two inches long. Inclining the +large tube at a suitable angle, the small one is introduced, closed end +first, and allowed to slide down the walls of the large tube until it +reaches the place where the acid has wet the tube. Here it will stop, +and if the tube is kept inclined during the rest of the operation it +will roll around inside the tube at this point and thus not get down +where any acid is likely to get into it and produce any pressure by +decomposing it before the open end of the tube is sealed. Now the tube +is held in an inclined position, taking care that the acid does not +reach up to the substance, the constricted portion cautiously warmed and +shrunk. It is finally shrunk and drawn out into a somewhat elongated +cone, with walls as thick as the rest of the tube, and when this is +accomplished the end of the cone is sealed and the waste piece drawn +off. Anneal with great care, and cool in such a position that the acid +cannot reach the hot glass. The shrinking of this cone takes a good deal +of patience, and is one of the most important parts of the process. If +the walls are left too thin, the tube may burst when heated, and the +whole labor is lost. If care is taken, the same tube can be used for a +number of determinations, until it becomes quite short. + + + + + INDEX + + + Annealing glass, 4, 24 + + + Bellows, 4 + + Bending glass, 8 + + Blowing glass, 13, 19, 20, 21, 24, 29, 31 + with a rubber tube, 22 + + Blowpipe, 4 + + Bulb at end of tube, 28 + in middle of tube, 32 + very large, 32 + + Bulbs, string of, 33 + + + Capillary tube, drawing on larger tube, 9, 54 + tubing, working, 43 + + Carius method, tubes for, 55 + + Closed circuits of tubing, 48 + tubes, for heating under pressure, 55 + + Collecting glass for bulb, 29, 31, 32 + + Constricting a tube, 10 + + Crystallization of glass, see Devitrification. + + Cutting glass, 7, 25 + + + Devitrification, 1, 2 + + Drawing out a tube, 9, 18, 19, 27 + + + Flanging a tube, 11, 14 + tool, 11 + + + Gas-washing tube, 35 + + Glass, annealing, 4, 24 + + Glass, bending, 8 + blowing, 13, 19, 20, 21, 24, 29, 31 + collecting for bulb, 29, 31, 32 + cutting, 7 + defects, 2 + grinding, 47 + hard, 1 + knife, 7 + lead, 1 + qualities desired, 1 + rod and tube, joining, 45 + rod, working, 44 + shrinking, 18, 19, 22, 26 + soft, 1 + working temperature, 1, 13, 19, 27 + + Grinding stopcock or joint, 47 + + Ground joints, 51 + + + Handle on stopcock, mending, 45 + + Hard glass, 1 + + Holding tube, 13, 14 + + + Insertion of tube through another, see Sealing a tube through + another tube. + + + Joints, ground, 51 + + Joining rod and tube, 45 + tubing end to end: first method, 16 + second method, 20 + + Joining tubes of different diameters, 25 + a new tube to a stopcock, 48 + + + Kjeldahl trap, 41 + + + Lead glass, 1 + + Lump of glass, removed, 18, 19, 20, 21, 24, 26, 30, 38 + + + Platinum wires, sealed into glass, 1, 52 + + Position for glass-working, 5 + + Pressure, tubes for heating under, 55 + + + Quality of glass, 1 + + + Rod, glass, working, 44 + + Rotation of the tube, 13, 19 + + Rounded end of tube, 35, 38 + + Rubber tube used for blowing, 22 + + + Sealing a tube through another tube, 35, 39 + + Sealing vacuum tubes, 55 + + Shrinking glass, 18, 19, 22, 26, 31 + + Side tube, blowing, 22, 25 + + Soda glass, 1 + + Soft glass, 1 + + Spirals, making, 50 + + Stopcocks, mending, 45 + + Suction pump, 39, 42 + + Sulphur dioxide tube, 28 + + + "Tail" of glass, drawing out, 9, 54 + removed, 30, 35 + + Tubes, closed, for heating under pressure, 55 + + "Tee" tube, 22 + on capillary tubing, 43 + small side tube on a large tube, 24 + + + Vacuum tubes, sealing, 55 + + + Working temperature of glass, 1, 13, 19, 27 + ++----------------------------------------------------------------------+ +| | +| | +| Transcriber's note:- | +| | +| Words in italics are indicated by the use of _underscores_ and words | +| | +| in =bold= by the use of equals signs as shown. | +| | +| | +| | ++----------------------------------------------------------------------+ + + + + + + +End of the Project Gutenberg EBook of Laboratory Manual of Glass-Blowing, by +Francis C. 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Frary + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: Laboratory Manual of Glass-Blowing + +Author: Francis C. Frary + +Release Date: September 22, 2009 [EBook #30066] + +Language: English + +Character set encoding: ISO-8859-1 + +*** START OF THIS PROJECT GUTENBERG EBOOK LABORATORY MANUAL OF GLASS-BLOWING *** + + + + +Produced by Woodie4 and the Online Distributed Proofreading +Team at https://www.pgdp.net. (This file was produced from +images generously made available by The Internet +Archive/American Libraries.) + + + + + + +</pre> + + + +<h1>LABORATORY MANUAL</h1> + +<h3>OF</h3> + +<h1>GLASS-BLOWING<br /></h1> + +<div class="figcenter" style="width: 400px;"> +<img src="images/002.png" width="400" height="255" alt="Publisher book list" title="" /> +</div> + +<p><br /><br /></p> + +<h2>LABORATORY MANUAL</h2> +<h4>OF</h4> +<h2>GLASS-BLOWING<br /><br /><br /></h2> + +<h4>BY</h4> +<h3>FRANCIS C. FRARY, <span class="smcap">Ph. D.</span></h3> + +<h5>ASSISTANT PROFESSOR OF CHEMISTRY<br /> +UNIVERSITY OF MINNESOTA<br /><br /><br /><br /></h5> + +<h3><span class="smcap">McGRAW-HILL BOOK COMPANY, Inc.</span></h3> +<h4>239 WEST 39TH STREET, NEW YORK<br /> +6 BOUVERIE STREET, LONDON, E. C.<br /> +1914<br /><br /><br /><br /><br /></h4> + +<h5><span class="smcap">Copyright, 1914, by the<br /> +McGraw-Hill Book Company, Inc.</span><br /></h5> + +<hr style="width: 65%;" /> + +<p><span class="pagenum"><a name="Page_v" id="Page_v">[Pg v]</a></span></p> + +<h2>PREFACE</h2> + +<p>The purpose of this little book is to provide a clear and +detailed discussion of the elements of glass-blowing. +Many laboratories in this country, especially in the west, +are located a long way from any professional glass-blower, +and the time and money spent in shipping broken apparatus +several hundred miles to be mended could often +be saved if some of the laboratory force could seal on a +new stopcock, replace a broken tube, or make some +temporary repairs. Many men in physical or chemical +laboratories have occasion to modify some piece of apparatus +designed perhaps for other uses, or to design new +apparatus. To such also, the ability to perform some of +the operations herein described may be very valuable.</p> + +<p>No originality is claimed for the methods here described. +They are those which the author has found +most suitable and convenient in his own work, and most +easily learned by students. The aim has been to describe +each operation in such detail that a beginner can follow +the process without help and, with practice, attain +satisfactory results. It is, however, much easier to perform +any of the operations described, after seeing some +one else perform it correctly; since the temperature, the +exact time to begin blowing the glass, and many other little +details are very difficult to obtain from a description.</p> + +<p>It has not been thought worth while to describe the +process of making stopcocks, thermometers, vacuum +tubes, etc., as such things can be purchased more cheaply +and of much better quality than any amateur can make +unless he is willing to spend a very large amount of time +in practice. For similar reasons the manipulation of +quartz glass has been omitted.</p> + +<p>The author will be grateful for all suggestions and criticisms +tending to improve the methods presented. If +some of them appear to be given in excessive detail, the +reader will remember that many things which are obvious +to the experienced worker are not so to the beginner, and +that it is the little details in the manipulation which +often spell success or failure in glass-blowing.</p> + + +<p class="citation">F. C. F.<br /></p> +<p><span class="smcap">Minneapolis, Minn.,</span><br /> +<i>January, 1914.</i><br /><br /><br /></p> + +<p><span class="pagenum"><a name="Page_vi" id="Page_vi">[Pg vi]</a></span></p> + +<h3>CONTENTS</h3> + + + + +<div class="center"> + +<table border="0" cellpadding="4" cellspacing="0" summary="Contents"> + +<tr><td align="left"></td> +<td align="right"><span class="smcap">Page</span></td></tr> + +<tr><td align="left">Preface</td> +<td align="right"><a href="#Page_v">v</a></td></tr> + +<tr><td align="left"></td></tr> +<tr><td align="left"></td></tr> + +<tr><td align="left">CHAPTER I</td></tr> +<tr><td align="left"><span class="smcap">Materials and Apparatus</span></td> +<td align="right"><a href="#Page_1">1</a></td></tr> +<tr><td align="left">Varieties and defects of glass—Devitrification—Annealing</td></tr> +<tr><td align="left">glass—Blowpipe and bellows—Light—Arrangement</td></tr> +<tr><td align="left">of exercises.</td></tr> + +<tr><td align="left"></td></tr> +<tr><td align="left"></td></tr> + +<tr><td align="left">CHAPTER II</td></tr> +<tr><td align="left"><span class="smcap">General Operations</span></td><td align="right"><a href="#Page_7">7</a></td></tr> +<tr><td align="left">Cutting, bending, constricting and flanging the tubing—Methods</td></tr> +<tr><td align="left">of rotation and blowing.</td></tr> + +<tr><td align="left"></td></tr> +<tr><td align="left"></td></tr> + +<tr><td align="left">CHAPTER III</td></tr> +<tr><td align="left"><span class="smcap">Elementary Exercises</span></td><td align="right"><a href="#Page_16">16</a></td></tr> +<tr><td align="left">Joining two pieces of tubing of the same diameter—The</td></tr> +<tr><td align="left">"tee" tube—Joining two tubes of different diameters—Blowing</td></tr> +<tr><td align="left">bulbs.</td></tr> + +<tr><td align="left"></td></tr> +<tr><td align="left"></td></tr> + +<tr><td align="left">CHAPTER IV</td></tr> +<tr><td align="left"><span class="smcap">Advanced Exercises</span></td><td align="right"><a href="#Page_35">35</a></td></tr> +<tr><td align="left">Sealing a tube through another tube: The gas-washing</td></tr> +<tr><td align="left">tube, suction pump, and Kjeldahl trap.</td></tr> + +<tr><td align="left"></td></tr> +<tr><td align="left"></td></tr> + +<tr><td align="left">CHAPTER V</td></tr> +<tr><td align="left"><span class="smcap">Modified Methods and Special Operations</span></td><td align="right"><a href="#Page_43">43</a></td></tr> +<tr><td align="left">Capillary tubing—Glass rod—Mending stopcocks—Closed</td></tr> +<tr><td align="left">circuits of tubing—Spirals—Ground joints—Sealing</td></tr> +<tr><td align="left">in platinum wire—Sealing vacuum tubes—Closed</td></tr> +<tr><td align="left">tubes for heating under pressure.</td></tr> + +<tr><td align="left"></td></tr> +<tr><td align="left"></td></tr> + +<tr><td align="left"><span class="smcap">Index</span></td><td align="right"><a href="#Page_59">59</a></td></tr> + +</table></div> + + +<hr style="width: 65%;" /> + +<p><span class="pagenum"><a name="Page_1" id="Page_1">[Pg 1]</a></span></p> + +<h2>LABORATORY<br />MANUAL OF GLASS-BLOWING</h2> + + +<hr style="width: 65%;" /> +<h2>CHAPTER I</h2> + +<h3><span class="smcap">Materials and Apparatus</span></h3> + +<p>One of the most important factors in the success of any +piece of glass-blowing is the glass employed. As is well +known, there are two general varieties of glass: Lead +glass and soda glass. Formerly much apparatus was +made of lead glass, but at present it is very seldom met +with, except in the little drops of special glass used to seal +platinum wires into the larger sizes of tubes. Lead glass +is softer and more readily fusible than soda glass, but has +the disagreeable property of growing black in a few +seconds unless worked in a strong oxidizing flame. This +may be prevented by using a "hissing" flame, with a large +excess of air, and working in the extreme end of the flame; +or the black lead formed may thus be reoxidized, and the +glass restored to its original clearness.</p> + +<p>Almost all the soft glass on the market is a soda glass, +although sometimes part of the soda is replaced by +potash. Most of the hard glass appears to be a potash +glass. The following qualities are desirable in a glass for +ordinary working: (1) moderately low working temperature, +(2) freedom from air bubbles, striations and +irregularities, (3) proper composition, so that the glass +will not devitrify or crystallize while being handled at its +working temperature, (4) ability to withstand rapid +heating without cracking.</p> + +<p>The working temperature of different samples of so<span class="pagenum"><a name="Page_2" id="Page_2">[Pg 2]</a></span>-called +"soft glass" varies a good deal, and is best determined +by trial. The glass should become almost soft +enough for blowing in a flame that still shows a little +yellow near the tip, so that at the highest temperature of +the flame it may flow fairly freely and thus easily eliminate +irregularities in thickness. If the glass is too hard, +the shrinking of the glass, collection of material for a +bulb, and in fact most of the working processes will be +slower, and the glass will not stay at its working temperature +long enough after its removal from the flame +to permit it to be properly blown.</p> + +<p>Air bubbles in the original batch of glass are drawn out +into long hair-like tubes during the process of manufacture. +When such tubing is worked, the walls of these +microscopic tubes collapse in spots, and the air thus +enclosed will often collect as a small bubble in the wall, +thus weakening it. Irregularities are of various kinds. +Some of the larger sizes of thin-walled tubing often have +one half of their walls much thicker than the other, and +such tubing should only be used for the simplest work. +Some tubing has occasional knots or lumps of unfused +material. The rest of the tube is usually all right, but +often the defective part must be cut out. The presence +of striations running along the tube is generally an indication +of hard, inferior glass. Crookedness and non-uniformity +of diameter are troublesome only when long +pieces must be used.</p> + +<p>Devitrification is one of the worst faults glass can +possibly have. It is especially common in old glass, and +in glass which has contained acids. It seems to be of two +sorts. One variety manifests itself on the surface of the +glass before it reaches its working temperature, but if +the glass be heated to the highest temperature of the +flame it will disappear except in the portion at the edge +of the heated part. The glass seems to work all right, but<span class="pagenum"><a name="Page_3" id="Page_3">[Pg 3]</a></span> +an ugly crystallized ring is left at the edge of the portion +heated. This kind appears most frequently in old glass +which was originally of good quality, but has in time been +superficially altered, probably by the loss of alkalies. +The other variety of devitrification does not appear +when the glass is first heated; but after it has been maintained +at or above its working temperature for a longer +or shorter time, it will be noticed that the outer surface +has lost its smoothness, and appears to be covered with +minute wrinkles. It will also be found that the glass has +become harder, so that it becomes impossible to work it +easily. Further heating only makes the matter worse, +as does the use of a higher temperature from the start. +In fact it will often be found that a piece of comparatively +soft glass which devitrifies almost at once in a +"hissing" flame can be worked without serious difficulty +if care be taken to use a flame still decidedly tinged with +yellow. Even good glass will begin to devitrify in this +way if heated too long at the highest temperature of the +flame, so care should always be taken (1) <i>to reduce the +time of heating of any spot of glass to a minimum</i>; <i>i.e.</i>, get +the desired result at the first attempt, if possible, or at +least with the minimum of reheating and "doctoring," +and (2) <i>avoid keeping the glass at the highest temperature +of the flame any longer than necessary</i>. This may be +accomplished by doing all heating, shrinking, etc., of the +glass in a flame more or less tinged with yellow, and only +raising the temperature to the highest point when ready +to blow the glass. This kind of devitrification is apparently +due to volatilization of the alkalies from the glass in +the flame, and it is said that it can be partly remedied or +prevented by holding a swab of cotton saturated with a +strong solution of common salt in the flame from time to +time as the glass is heated.</p> + +<p>The toughness of glass, <i>i.e.</i>, its ability to withstand<span class="pagenum"><a name="Page_4" id="Page_4">[Pg 4]</a></span> +variations of temperature, depends on its composition +and the care taken in its annealing. In general, large +pieces of glass should be heated very slowly in the smoky +flame, and the larger the diameter of the tube the greater +the length which must be kept warm to prevent cracking. +All large pieces should be carefully heated over their +whole circumference to the point where the soot deposit +burns off, before being finally cooled. After being thus +heated they are cooled in a large smoky flame until well +coated with soot, then the flame is gradually reduced in +size and the object finally cooled in the hot air above it +until it will not set fire to cotton. If thought necessary, +it may then be well wrapped in cotton and allowed to +cool in the air. If not properly annealed the place heated +may crack spontaneously when cold, and it is quite certain +to crack if it is reheated later.</p> + +<p>Next in importance to the glass are the blow-pipe and +the bellows. Any good blast lamp, such as is ordinarily +used in a chemical laboratory for the ignition of precipitates, +will be satisfactory; provided it gives a smooth +regular flame of sufficient size for the work in hand, +and when turned down will give a sharp-pointed flame +with well-defined parts. Where gas is not available, an +ordinary gasoline blow-torch does very well for all operations +requiring a large flame, and a mouth blow-pipe +arranged to blow through a kerosene flame does well for +a small flame. Several dealers make blow-torches for +oil or alcohol which are arranged to give a small well-defined +flame, and they would doubtless be very satisfactory +for glass-work. Any good bellows will be +satisfactory if it does not leak and will give a steady +supply of air under sufficient pressure for the maximum +size of flame given by the lamp used. A bellows with a +leaky valve will give a pulsating flame which is very +annoying and makes good work very difficult. When<span class="pagenum"><a name="Page_5" id="Page_5">[Pg 5]</a></span> +compressed air is available it can be used, but if possible +it should be arranged so that the supply can be controlled +by the foot, as both hands are usually needed to hold the +work. For the same reason the supply of air is usually +regulated by varying the rate of operation of the bellows, +rather than by adjusting the valve of the blast-lamp. +On the other hand, it will be found best to always adjust +the flow of the gas by means of the cock on the lamp, +rather than that at the supply pipe. The operator must +have complete control over the flame, and be able to +change its size and character at short notice without +giving the work a chance to cool, and often without ceasing +to support it with both hands.</p> + +<p>Glass-blowing should be done in a good light, but preferably +not in direct sunlight. The operator should be +seated in a chair or on a stool of such a height that when +working he may comfortably rest one or both elbows on +the table. The comfort of the operator has a decided +influence on the character of his work; especially in the +case of a beginner, who often defeats his purpose by +assuming uncomfortable and strained positions. Steadiness +and exact control of both hands are essential in most +operations; any uncomfortable or strained position tires +the muscles and weakens the control of the operator over +them.</p> + +<p>In the arrangement of the exercises here presented, +several factors have been considered. It is important +that the first exercises be simple, although not necessarily +the simplest, and they should teach the fundamental +operations which will be used and amplified later. They +should in themselves be things which are of importance +and commonly used in glass-work, and they should be so +arranged that the fundamental points, such as the rotation +of glass, the proper temperature, blowing and shrinking +the glass may be learned with a minimum expenditure<span class="pagenum"><a name="Page_6" id="Page_6">[Pg 6]</a></span> +of time, glass and gas. It is therefore recommended that +the beginner take them up in the order given, at least as +far as No. 7, and that each be mastered before attempting +the next. The beginner should not leave the first exercise, +for example, until he can join together two pieces +of tubing so that they form one piece of substantially +uniform inner and outer diameter, and without thick or +thin spots. From two to four practice periods of two +hours each should suffice for this. This chapter and the +following one should also be frequently read over, as many +of the points discussed will not be understood at first and +many of the manipulations described will not be necessary +in the simpler exercises.</p> + + + +<hr style="width: 65%;"/> + +<p><span class="pagenum"><a name="Page_7" id="Page_7">[Pg 7]</a></span></p> + +<h2>CHAPTER II</h2> + +<h3><span class="smcap">General Operations</span></h3> + + +<p><b>Cutting the Glass.</b>—For this purpose a "glass-knife" +is preferred to a file, if the glass is cold: if it is hot a file +must always be used, and its edge slightly moistened to +prevent drawing the temper. The glass-knife is simply +a flat piece of hard steel, with the edges ground sharp on +an emery wheel. The bevel of the edge should be from +30 to 60 degrees. An old flat file can easily be ground +into a suitable knife. The glass-knife makes a narrower +scratch than the file but appears more likely to start the +minute crack which is to cause the tube to break at that +point, and the break is more likely to give a good square +end. The scratch should be made by passing part of +the knife or file once across the glass, never by "sawing" +the tool back and forth. This latter procedure dulls the +tool very quickly.</p> + +<p>In breaking a piece of glass tubing, many persons forget +that it is necessary to <i>pull</i> the ends apart, as well +as to bend the tube very <i>slightly</i> in such a direction as to +open up the minute crack started in the scratch. Care +in breaking the tube is essential, as it is impossible to do +as good work with uneven ends as with square ones.</p> + +<p>When tubing of large diameter or thin wall is to be cut, +it is often better not to attempt to break it in the usual +way, but to heat a very small globule of glass (<span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">16</span> to <span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">8</span> +inch diameter) to red heat, and touch it to the scratch. +This will usually start the crack around the tube; if it +has not proceeded far enough, or has not gone in the de<span class="pagenum"><a name="Page_8" id="Page_8">[Pg 8]</a></span>sired +direction, it may be led along with a hot point of +glass. This is put a little beyond the end of the crack, +and as the latter grows out toward it, moved along the +path where the crack is desired. This point of glass is +also very useful in breaking off very short ends of tubes, +where there is not room to get a firm enough hold and +sufficient leverage to break the tube in the ordinary +way, and for breaking tubes attached to large or heavy +objects, which would be likely to make trouble if treated +in the ordinary way.</p> + +<p>Another way of cutting large tubing, especially if it +has rather thick walls, is to make a scratch in the usual +way, and then turn on the smallest and sharpest possible +flame of the blast lamp. The tube is next taken in both +hands and held horizontally above the flame so that the +scratch is exactly over it. The tubing is now rotated +rapidly about its axis, and lowered so that the flame is +just tangent to its lower side. After about ten seconds +of heating, it is removed from the flame and the hot portion +quickly breathed upon, when it will generally crack +apart very nicely. Care must be taken to hold the tube +at right angles to the flame during the heating, and to +rotate it so that only a narrow strip of the circumference +is heated, and the scratch should be in the center of this +heated strip. By this means tubing as large as two inches +in diameter is readily broken.</p> + +<p>Griffin's glass cutter, which contains a hardened steel +wheel, like that on any ordinary window-glass cutter, and +a device by which this can be made to make a true cut +clear around the tube, is a very handy article, especially +for large tubing, and may be obtained from any dealers +in chemical apparatus.</p> + +<p><b>Bending Glass.</b>—Inasmuch as this is one of the commonest +operations in the laboratory, it is assumed that +the reader knows how to perform it. However, it<span class="pagenum"><a name="Page_9" id="Page_9">[Pg 9]</a></span> +should be noted that in order to obtain the best results +a broad (fish-tail burner) flame should generally be used, +and the tube rotated on its axis during the heating, and +allowed to bend mostly by its own weight. If large tubing +is to be bent, one end must be stoppered and great +care used. Whenever the tube shows signs of collapsing +or becoming deformed, it must be gently blown out into +shape, heating the desired spot locally if necessary. A +blast-lamp is likely to be more useful here than the fish-tail +burner.</p> + +<p><b>Drawing Out a Tube.</b>—Most students learn this the +first day of their laboratory work in chemistry, but few +take pains to do it well. The tube should be heated in +the flame of a Bunsen burner, or blast lamp (preferably +the latter) until it is very soft. During this time it must +be continuously rotated about its axis, and so held that +the edges of the heated zone are sharply defined; <i>i.e.</i>, +it should not be allowed to move back and forth along +its own axis. When so hot that it cannot longer be held +in shape, the tube is removed from the flame, and the +ends slowly and regularly drawn apart, <i>continuing the +rotation of the tube about its axis</i>. By regulating the rate +of drawing and the length of tube heated, the desired +length and diameter of capillary may be obtained. The +tube should always be rotated and kept in a straight line +until the glass has set, so that the capillary may have the +same axis as the main tube. This capillary or "tail" +is often a very necessary handle in glass-blowing, and if +it is not straight and true, will continually make trouble.</p> + +<p>In drawing out very large tubing, say from one to +two inches in diameter, it is often necessary to draw the +tube <i>in the flame</i>, proceeding very slowly and at a +lower temperature than would be used with small tubing. +This is partly on account of the difficulty of heating +large tubing uniformly to a high temperature, and<span class="pagenum"><a name="Page_10" id="Page_10">[Pg 10]</a></span> +partly in order to prevent making the conical part of +the tube too thin for subsequent operations.</p> + +<p><b>Constricting a Tube.</b>—Where a constriction is to be +made in a tube, the above method must be modified, as +the strength of the tube must be maintained, and the +constricted portion is usually short. Small tubes are +often constricted without materially changing their outside +diameter, by a process of thickening the walls. The +tube is heated before the blast lamp, rotating it about +its axis as later described, and as +it softens is gradually pushed +together so as to thicken the walls +at the heated point, as in <i>a</i>, Fig. 1. +When this operation has proceeded +far enough, the tube is removed +from the flame, and the ends cautiously +and gently drawn apart, +continuing the rotation of the tube +about its axis and taking care not +to draw too rapidly at first. The +resulting tube should have a uniform exterior diameter, +as shown in <i>b</i>, Fig. 1.</p> + +<div class="figcenter" style="width: 355px;"> +<img src="images/i018.png" width="355" height="400" alt="" title="" /> +<span class="caption">Fig. 1.—Constricting a +tube.</span><br /><br /> +</div> + +<p>This method of constriction is not suited to tubes +much over <span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">4</span> inch in diameter, since the mass of glass +in the constricted part becomes so thick as to be difficult +to handle when hot, and likely to crack on cooling. +Larger tubes are therefore constricted by heating in a +narrow flame, with constant rotation, and when soft, +alternately gently pulling the ends apart and pushing +them together, each motion being so regulated that the +diameter of a short section of the tube is gradually reduced, +while the thickness of the wall of the reduced +portion remains the same as that of the rest of the tube, +or increases only slightly. This pulling and pushing of +the glass takes place <i>in the flame</i>, while the rotation is<span class="pagenum"><a name="Page_11" id="Page_11">[Pg 11]</a></span> +being continued regularly. The result may appear as +indicated in <i>c</i>, Fig. 1. The strength of the work depends +upon the thickness of the walls of the constricted portion, +which should never be less than that in the main tube, +and usually a little greater. This operation is most +successful with tubing having a relatively thin wall.</p> + +<p><b>Flanging a Tube.</b>—This operation produces the characteristic +flange seen on test-tubes, necks of flasks, etc., +the object being twofold: to finish the end neatly and to +strengthen it so that a cork may be inserted without +breaking it. This flanging may be done in several ways. +In any case the first operation is to cut the tube to a +square end, and then heat this end so that the extreme +sixteenth or eighth of an inch of it is soft and begins to +shrink. The tube is of course rotated during this heating, +which should take place in a flame of slightly greater +diameter than the tube, if possible. The flange is now +produced by expanding this softened part with some +suitable tool. A cone of charcoal has been recommended +for this purpose, and works fairly well, if made so its +height is about equal to the diameter of its base. The +tube is rotated and the cone, held in the other hand, is +pressed into the open end until the flange is formed. A +pyramid with eight or ten sides would probably be better +than the cone.<br /><br /></p> + +<div class="figcenter" style="width: 400px;"> +<img src="images/i019.png" width="400" height="90" alt="" title="" /> +<span class="caption">Fig. 2.—Flanging tool.</span> +<br /><br /></div> + +<p>A better flanging tool is made from a triangular piece +of copper or brass, about <span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">16</span> inch thick, and mounted +in a suitable handle. Such a tool is shown in Fig. 2, +being cut from a sheet of copper and provided with a<span class="pagenum"><a name="Page_12" id="Page_12">[Pg 12]</a></span> +handle made by wrapping asbestos paper moistened with +sodium silicate solution about the shank of the tool. +It is well to have several sizes and shapes of these tools, +for different sizes of tubing. The two sizes most used +will be those having about the following dimensions: +(1) <i>a</i> = 2 inches, <i>b</i> = 1 inch; (2) <i>a</i> = 1 inch, <i>b</i> = 1 inch. +When the end of the tube is softened, the tool is inserted +at an angle, as indicated in Fig. 3, and pressed against +the soft part, while the tube is quickly rotated about its +axis. If the flange is insufficient the operation may be +repeated. The tool should always be warmed in the +flame before use, and occasionally greased by touching +it to a piece of wax or paraffin. After the flange is complete, +the end must be heated again to the softening temperature +and cooled slowly, to prevent it from cracking.<br /><br /></p> + +<div class="figcenter" style="width: 400px;"> +<img src="images/i020a.png" width="400" height="119" alt="" title="" /> +<span class="caption">Fig. 3.—Flanging a tube with flanging tool.</span> +<br /><br /><br /><br /></div> + +<div class="figcenter" style="width: 400px;"> +<img src="images/i020b.png" width="400" height="101" alt="" title="" /> +<span class="caption">Fig. 4.—Flanging a tube with carbon rod or wire.</span> +<br /><br /></div> + +<p>Some glass-blowers use a small carbon rod, about +<span style="font-size: 0.8em"><sup>3</sup></span>⁄<span style="font-size: 0.6em;">16</span> inch in diameter, as a flanging tool for tubes larger +than about <span style="font-size: 0.8em"><sup>3</sup></span>⁄<span style="font-size: 0.6em;">8</span> inch diameter, and a small iron wire or +similar piece of metal for smaller tubes. In this case the +tube is heated as above described, and the rod or wire +inserted in the end at an angle and pressed against the +softened part, as indicated in Fig. 4, while the tube is<span class="pagenum"><a name="Page_13" id="Page_13">[Pg 13]</a></span> +rotated about its axis. For large heavy tubes a larger +carbon would be used.</p> + +<p><b>Rotation of the Tube.</b>—This is the fundamental manipulation +in glass-blowing, and upon it more than all +else depends the uniformity and finish of the work, and +often the possibility of accomplishing the work at all. +Directions for it will be given on the assumption that +the reader is right-handed; if otherwise, the position of +the hands is of course reversed. The object of rotation +is to insure even heating of the whole circumference of +the tube at the point of attack, to equalize the effect of +gravity on the hot glass and prevent it from falling out of +shape when soft, and to keep the parts of the tube on +each side of the heated portion in the same straight line.</p> + +<p>In rotating the tube, both hands must be used, so that +the two ends may revolve at the same rate and the glass +in the hot part not be twisted. The rotation is performed +by the thumb and first finger of each hand, the other +fingers serving to support the tube. As it is almost +always necessary to follow rotating and heating a tube by +blowing it, the hands should be so placed that it will be +easy to bring the right-hand end up to the mouth without +shifting the hold on the glass. For this reason the left +hand grasps the glass with the palm down, and the right +hand with the palm turned toward the left. If there is +any choice, the longer and heavier part of the tube is +usually given to the left hand, and it is planned to blow +into the shorter end. This is because it is easier to +support the tube with the hand which has the palm +down. This support is accomplished by bending the +hand at the wrist so that it points slightly downward, and +then curling the second, third and little fingers in under +the tube, which is held between them and the palm. +This support should be loose enough so that the thumb +and first finger can easily cause the tube to rotate regu<span class="pagenum"><a name="Page_14" id="Page_14">[Pg 14]</a></span>larly +on its axis, but firm enough to carry all the weight +of the tube, leaving the thumb and first finger nothing +to do but rotate it. The hand must be so turned, and +the other fingers so bent, that the thumb and first finger +stretch out nearly to their full length to grasp the tube +comfortably.</p> + +<p>The right hand is held with the palm toward the left, +the fingers except the first slightly bent, and the tube +held between the first finger and the thumb while it +rests on the second finger and that portion of the hand +between the base of the first finger and the thumb. +Rotation of the tube is accomplished by rolling it between +the thumbs and first fingers: the rotation being continued +in the same direction regularly, and not reversed. It +is better to roll slowly and evenly, with a series of light +touches, each of which moves the tube a little, than to +attempt to turn the tube a half a revolution or so with +each motion of the hands. The hands must be held +steady, and the tube must be under good control at all +times, so that both ends may be rotated at the same angular +velocity, even though they may be of different diameters, +and the tube be neither drawn apart nor pushed +together unless such a motion is expressly desired, as it +sometimes is. The hot part of the glass must be constantly +watched to see that it is uniformly rotated and +not twisted, nor pulled out or pushed together more than +is desired. Care must also be taken to keep the parts of +the tube in the same straight line, or as near it as possible, +during the heating and all other manipulations.</p> + +<p>When flanging a tube, it is held and rotated with the +left hand as above described, while the right hand holds +the flanging tool.</p> + +<p>When part of the end of a tube must be heated, as in +Exercise 6, and rotation must be very carefully performed +and continued during the blowing, both hands are used.<span class="pagenum"><a name="Page_15" id="Page_15">[Pg 15]</a></span> +The right hand is held as above described, and the left +hand close to it and either as above described or else +with the palm toward the right, grasping the tube in the +same way as the right hand does. This puts both hands +in a position where the tube may be blown and rotated +uniformly while its axis is kept horizontal.</p> + +<p>Smoothness and exactness are the two things for which +the beginner must constantly strive in glass-blowing, and +they are only attained by a careful attention to the +details of manipulation, with a steady hand and watchful +eye. Every move must count, and the exercise must be +finished with a minimum of reheating and retouching, for +the best results.</p> + + + +<hr style="width: 65%;"/> + +<p><span class="pagenum"><a name="Page_16" id="Page_16">[Pg 16]</a></span></p> + +<h2>CHAPTER III</h2> + +<h3><span class="smcap">ELEMENTARY EXERCISES</span></h3> + + +<h3>EXERCISE NO. 1</h3> + +<h4><span class="smcap">Joining Two Pieces of Tubing, End to End—First +Method</span><br /><br /></h4> + +<p>This exercise is most easily learned on tubing with an exterior +diameter of <span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">4</span> inch, or a little less, having moderately +heavy walls. A piece of such tubing is heated before +the blow-pipe at a point ten or twelve inches from +the end, and there drawn out to a capillary as previously +described (page 9). The capillary is sealed off about +two inches from the main tube, and the latter is cut near +the middle. Care should be taken to get square ends<span class="pagenum"><a name="Page_17" id="Page_17">[Pg 17]</a></span> +where the cut is made (page 7). The flame is now so +regulated that it is a little broader than the diameter of +the tube, the sealed half of the tube taken in the left +hand and the other half in the right. The open end of +the sealed part and one of the ends of the other part +are now held in opposite sides of the flame, inclined at a +slight angle to one another as indicated in Fig. 5, and +rotated and heated until the surfaces of both ends are +just softened. The two ends are then carefully and +quickly brought together (<i>a</i>, Fig. 6), removed from the +flame and pulled apart a little, to reduce the lump formed +at the joint as much as possible, as indicated in <i>b</i>. The +joint is then tested by blowing into the open end of the +tube to see if it is tight. If so, the flame is reduced to +half or less than half of its former size, and the joint +heated in it, holding the tube and continually rotating it +as directed in the last chapter (page 13).<br /><br /></p> + +<div class="figcenter" style="width: 400px;"> +<img src="images/i024.png" width="400" height="341" alt="" title="" /> +<span class="caption">Fig. 5.—Softening ends of two pieces of tubing.</span> +<br /><br /><br /><br /></div> + +<div class="figcenter" style="width: 400px;"> +<img src="images/i025.png" width="400" height="359" alt="" title="" /> +<span class="caption">Fig. 6.—Joining two pieces of tubing end to end—first method.</span> +<br /><br /></div> + +<p>As the tube softens and tends to shrink, the two ends +are pressed together a little and the walls allowed to<span class="pagenum"><a name="Page_18" id="Page_18">[Pg 18]</a></span> +thicken slightly, as in <i>c</i>. It is then quickly removed +from the flame and gently blown as indicated in <i>d</i>, +continuing the rotation of the tube during the blowing, +and at the same time pressing the ends of the tube together +a little so as to make a <i>short</i> thick-walled bulb. +The joint is then returned to the flame and reheated, +rotating as before, shrinking to about the shape of <i>e</i>. +When this stage is reached, the glass should be very hot +and fluid, and the mass of hot glass thick enough to +remain at its working temperature for about five seconds +after removal from the flame. The glass is now reblown +as indicated in <i>f</i>, to form a bulb having walls of practically +the same thickness as the original tube. As soon as the +bulb is blown, the tube is removed from the mouth, held +horizontally in front of the worker, and gently drawn out +to form one continuous tube, as indicated in <i>g</i>. During +both the blowing and drawing of this bulb the rotation +must be continued, and both blowing and drawing must +be carefully regulated so that the resulting tube may have +the same internal and external diameter at the joint as +elsewhere.</p> + +<p><b>Discussion.</b>—In making the original joint, (<i>a</i>, Fig. 6), +care should be taken that the lump formed is as small as +possible so that it may be entirely removed during the +subsequent operations. For this reason, only the very +tip ends of the two pieces of tubing are held in the flame, +and the softening should not extend more than <span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">16</span> +inch down the tube. As soon as the ends are sufficiently +soft to stick together, they are made to do so. The first +drawing of the tube (<i>b</i>) should take place immediately, +and reduce the lump as much as possible without making +the adjacent walls of the tube thin. The whole purpose +of the rest of the manipulation is to absorb or "iron out" +the lump at the joint. For this reason, care is taken that +this lump is always in the center of the flame while the<span class="pagenum"><a name="Page_19" id="Page_19">[Pg 19]</a></span> +joint is being heated, and a small flame is used so that +little of the main tube may be softened. During the first +shrinking of the joint (<i>c</i>) the walls next the lump, being +thinner than it is, reach the softening temperature first +and are thickened by the slight pushing together of the +ends, so that they taper from the lump to the unchanged +wall. Upon blowing this joint, these thickened walls +blow out with the lump, but as they are thinnest next the +unchanged tube, they stiffen there first. Then as the +thicker parts are still hot, these blow out more, and with +the lump make a more or less uniform wall. By this first +operation most of the lump will have been removed, provided +it was not too large at first, and the tube was hot +enough when it was blown. Beginners almost invariably +have the glass too cool here, and find difficulty in blowing +out a satisfactory bulb. Under such circumstances the +lump will be scarcely affected by the operation.</p> + +<p>During the shrinking of this bulb, the thinner parts of +course are the first to reach the softening point, and thus +contract more than the thick parts, so that practically all +of the lump can be absorbed, and a uniformly thickened +part of the tube left as in <i>e</i>. When this is just accomplished, +the second bulb must be blown during one or +two seconds, and the tube then drawn out as described, +so as to change the bulb to a tube. The drawing must +proceed with care: portions nearest the unchanged tubes +are the first to reach the proper diameter, and must be +given time to just set at that point before the center of +the bulb is finally drawn into shape. The drawing is +perhaps best done intermittently in a series of quick +pulls, each drawing the tube perhaps <span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">16</span> inch, and each +taking place as the thumbs and first fingers grasp the tube +for a new turn in the rotation. If the tube is not rotated +during the blowing, the bulbs will be lop-sided and it will +be impossible to get a joint of uniform wall-thickness;<span class="pagenum"><a name="Page_20" id="Page_20">[Pg 20]</a></span> +if rotation is omitted during the drawing, the tube will +almost invariably be quite crooked.</p> + +<p>If the lump still shows distinctly after the operations +described, the cross-section of the tube will be as in <i>h</i>, and +the tube will be likely to break if ever reheated at this +point after it becomes cold. The operations <i>d</i>, <i>e</i>, <i>f</i>, and +<i>g</i> may be repeated upon it, and it may be possible to get +it to come out all right.</p> + +<p>Care must be taken not to blow the bulbs <i>d</i> and <i>f</i> too +thin as they then become very difficult to handle, and the +joint is usually spoiled. The wall-thickness of these +bulbs must never be much less than that of the original +tube. If the joint as completed has thinner walls than +the rest of the tube, it will be more easily broken. It +should be remembered that the length of the finished +tube must be exactly the same as that of the original +piece, if the walls of the joint are to be of their original +thickness. Therefore the pushing together during the +two operations <i>c</i> and <i>d</i> must shorten the tube just as +much as the final drawing (<i>f</i> to <i>g</i>) lengthens it.</p> + +<p>The interval between the removal of the work from +the flame and the beginning of the blowing must be made +as short as possible, or else the portions next the main +parts of the tube will set before they can be blown out, +and cause irregular shrunken areas.</p> + + +<h3>EXERCISE NO. 2</h3> + +<h4><span class="smcap">Joining Two Tubes End to End—Second Method</span></h4> + +<p>The method described in Exercise No. 1 is very satisfactory +for joining short lengths of straight tubing, but +becomes inconvenient or impossible when the pieces are +long or bent, on account of the difficulty in uniformly +rotating such work. In such cases, this second method is<span class="pagenum"><a name="Page_21" id="Page_21">[Pg 21]</a></span> +used. It does not usually give as smooth and pretty a +joint as the first method, and takes a little longer.</p> + +<p>The joint is begun exactly as in the first method, and +the manipulation is the same until after the preliminary +tight joint (<i>b</i>, Fig. 6) is made. The flame is reduced as +usual, but instead of rotating the tube in the flame, only +one part of the circumference is heated, and this is +allowed to shrink thoroughly before blowing. It is then +blown gently so that it becomes a slight swelling on the +tube, and the operation repeated on an adjoining part of +the joint. Three or four repetitions of the operation will +usually cover the whole circumference of the joint, in a +small tube, the result being a swelling roughly similar +to the first thick bulb in the first method (<i>d</i>, Fig. 6). If +all the lumps of the original joint have not been removed +by this operation, it may now be repeated upon such parts +as may require it. The thickness of the wall in the bulb +should be about the same as that in the original tube. +The whole of the expanded joint is now heated as uniformly +as may be until soft enough so that it begins to +shrink a little, and the swelling is gently drawn down to +the same diameter as the main tube, as in the first case. +Any irregularities in the finished joint may be corrected +by local reheating, shrinking or blowing as required.</p> + +<p><b>Discussion.</b>—In using this method, especially with +larger sizes of tubing, it is very important to keep the +whole circumference of the joint hot enough during the +operation so that it does not crack apart at the part +which has not yet been worked. For that reason the +first heating, shrinking and blowing should be performed +as quickly as possible, leaving the resulting irregularities +to be corrected later, rather than attempting to reblow +the same part of the joint several times in succession +until it is satisfactory. Care must be taken in this as in +the first method that the blowing follows immediately<span class="pagenum"><a name="Page_22" id="Page_22">[Pg 22]</a></span> +upon the completion of the shrinking and removal of +the object from the flame: delay in blowing will cause +shrunken places where the joint meets the original tubes, +on account of the cooling and setting of the glass before +it was blown. Most beginners err in being afraid to +shrink the part of the joint enough before blowing it. +On small tubing, the shrinkage may often extend so far +that the inner surface of the shrunken part reaches the +center of the tube. Insufficient shrinking results in +failure to remove the lump formed at the original joint. +It is often of advantage, after blowing out part of the +joint, to allow that part a few seconds to set before going +on with the rest, keeping the whole joint warm meanwhile +in or near the smoky flame. This helps to prevent the +twisting of the joint, or other distortion incident to the +handling of a piece of work of awkward shape.</p> + +<p>In making a joint on a very long or heavy piece by +this method, it is often advantageous to attach a piece +of rubber tubing to the open end, hold the other end of +this tubing in the mouth during the process, and blow +through it, rather than attempt to bring the end of the +glass up to the mouth. This enables one to keep closer +watch on the joint, and avoid drawing it out or distorting +it in handling. On the other hand, the rubber tube is an +inconvenience on account of its weight and the consequent +pull on the end of the apparatus, and makes rotation +difficult.</p> + + +<h3>EXERCISE NO. 3</h3> + +<h4><span class="smcap">The "Tee" Tube</span></h4> + +<p>The operations involved are two: the blowing of a +short side tube on a piece of tubing, and sealing another +piece of tubing on this, by what is essentially the second +method as just described.<span class="pagenum"><a name="Page_23" id="Page_23">[Pg 23]</a></span><br /><br /></p> + +<div class="figcenter" style="width: 230px;"> +<img src="images/i031.png" width="230" height="400" alt="" title="" /> +<span class="caption">Fig. 7.—The "tee" tube.</span> +<br /><br /></div> + +<p>The two pieces of tubing to be used each have one end +cut square and the other sealed in the usual manner. +The longer of the two is now heated at the point at which +the joint is to be made, until it begins to color the flame. +A small flame is used, and the tube rotated until the +flame begins to be colored, when the rotation is stopped, +and only one spot heated until a spot the diameter of the +tube to be sealed on has become red hot and begun to +shrink. This is now gently blown out into a small bulb, +as in <i>a</i>, Fig. 7, and it will be noted +that this bulb will have walls tapering +from the thick walls of the +tube to a very thin wall at the +top. The sides of this bulb, below +the dotted line, are to form +the small side tube to which the +main side tube is to be sealed. +The top of the bulb is now softened +by directing a small flame +directly upon it, and as soon as +it shrinks to the level indicated +by the dotted line, it is removed +from the flame and quickly blown +out to form a thin bulb, as indicated +in <i>b</i>, Fig. 7. This will usually +be so very thin that a stroke of the file or glass-knife +will break it off at the dotted line, leaving the +side tube, to which the short piece of tubing is now +sealed according to the second method (Exercise No 2). +In doing this, care is taken to direct the flame partly on +the main tube in the two crotches, so that both tubes blow +out a little and give space for the gases to turn in, as +indicated in <i>c</i>, Fig. 7, and at the same time increase the +mechanical strength of the job. On the other hand, +care is taken not to deform the main tube, and not to<span class="pagenum"><a name="Page_24" id="Page_24">[Pg 24]</a></span> +produce such a bulge or bulb at the joint as will prevent +the finished tube from lying flat on a table.</p> + +<p><b>Discussion.</b>—Most beginners tend to err in the first +steps of this operation, by blowing too hard and too long +when blowing out the little bulb. The result is a large, +very thin bulb, which breaks off in such a way as to leave +a hole in the main tube, occupying nearly half the circumference +of the tube at that point, instead of the neat +side tube which they should have. It is not difficult to +seal a tube on this side tube, but it is very difficult to seal +a tube into a hole in another tube. Care should be taken +here, as in the two previous exercises, that the lump +obtained at the joint when the two tubes are put together +is made as small as possible, and reduced if possible by +gently drawing on the side tube as soon as the tubes have +actually joined. It is much easier to prevent the formation +of a lump at the joint than it is to remove the lump +after it is formed. The remarks previously made about +blowing quickly after removing the work from the flame +apply here with especial force. A "tee" tube, from its +very nature, is exposed to a good many strains, so care +must be taken that the walls of the joint are of uniform +thickness with the rest of the tube.</p> + +<p>The beginner will find it easiest to make this tube out +of two pieces of the same tube, about <span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">4</span> inch in diameter. +Larger or smaller tubing is usually more difficult. If +tubing much more than <span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">4</span> inch is used, the whole joint, +including part of the main tube, must be heated nearly +to the softening point at the close of the operation, and +well annealed, as described in Chapter 1 (page 3) or it +will be almost certain to crack. In the larger sizes of +tube it will be necessary to heat the whole circumference +of the main tube frequently during the operation, to +prevent it from cracking.</p> + +<p>In sealing a small tube on the side of a large one, it is<span class="pagenum"><a name="Page_25" id="Page_25">[Pg 25]</a></span> +usually advisable, after warming the spot where the joint +is to be made, to attach a small drop of glass to the tube +at that point, and direct the flame upon that, thus supplying +at the same time both a definite point to be heated +and an extra supply of glass for the little side tube which +is desired. In this way it is also easier to blow out a +side tube with a sufficiently small diameter. If the +diameter of this tube should be much greater than that +of the small tube, the latter may be enlarged with a +carbon or a flanging tool.</p> + + +<h3>EXERCISE NO. 4</h3> + +<h4><span class="smcap">To Join Two Tubes of Different Diameters</span></h4> + +<p>In this case the first method (Exercise No. 1) is to be +used whenever possible, as it gives a much smoother joint +than the second method. The directions given will +describe the adaptation of this method to the problem: +if the second method must be used on account of awkward +shape, etc., of the work, the modifications required +will be obvious to any one who has learned to make the +joint by the first method.</p> + +<p>After sealing or corking one end of the larger tube, the +other end is drawn out to form a tail as described on page +9, taking care to have the tube uniformly heated, and +to draw the tail rapidly enough so that the cone is short, +as indicated in <i>a</i>, Fig. 8. The tube is now rotated, a +small flame directed against the cone at right angles +to an element of it, and it is allowed to shrink a little, +as indicated in <i>b</i>, Fig. 8, so that its walls will thicken. +When the tail is cut off, at the dotted line, the diameter +of the opening and the thickness of the walls at that point +should correspond with the dimensions of the tube to be +sealed on. As the glass is hot, the scratch for cutting it +must be made with a file (moisten the edge!), and it<span class="pagenum"><a name="Page_26" id="Page_26">[Pg 26]</a></span> +often will not break square across. Before proceeding +to seal on the small tube, any large projections on the +cut end are best removed, by warming the cut surface a +little, directing the small flame upon each projection in +turn and touching it with a warm scrap of glass. It will +adhere to this and may then be removed by rotating this +scrap a little so as to wind up the projection on it, and +then drawing it off, while the flame is still playing on the +spot. This must be done rapidly and care taken not to +soften the main part of the cone.<br /><br /></p> + +<div class="figcenter" style="width: 400px;"> +<img src="images/i034.png" width="400" height="256" alt="" title="" /> +<span class="caption">Fig. 8.—Joining two tubes of different diameters.</span> +<br /><br /></div> + +<p>The large tube is now taken in the left hand, the small +one in the right, the ends heated and joined in the usual +manner, taking care not to get any larger lump at the +joint than necessary. A small flame is now directed on +the cone at right angles to its elements as before, and the +tube rotated so as to heat the whole circumference. The +flame should be just large enough to heat the whole of +the cone. As the latter shrinks, the lump at the joint +is brought into the edge of the flame, and it and a very +little of the small tube allowed to shrink with the cone.</p> + +<p>When well shrunk and heated to blowing temperature<span class="pagenum"><a name="Page_27" id="Page_27">[Pg 27]</a></span> +the joint is removed from the flame and blown gently +with careful rotation, pushing the tubes together a little +when the blowing is about finished, so that the cone +becomes a short thick half-bulb, as shown in <i>d</i>, Fig. 8. +This corresponds to the first thick bulb in the first method +(<i>d</i>, Fig. 6), and is treated similarly. It is again heated +and shrunk, taking care not to involve either the large +tube or the small one in the shrinking, blown quickly to +about the same shape as before, (<i>d</i>, Fig. 8), and then +gently drawn out into a smooth cone (<i>e</i>), exactly as in the +first exercise. Care should be taken not to draw too +rapidly or too far, as then the resulting cone (<i>f</i>) is weaker +than it should be, and does not look well.</p> + +<p><b>Discussion.</b>—The beginner will find that this operation +is best learned on two tubes which are not too nearly of +the same diameter. A tube about <span style="font-size: 0.8em"><sup>5</sup></span>⁄<span style="font-size: 0.6em;">8</span> inch in diameter +and one a little less than <span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">4</span> inch will be suitable. Both +should have moderately heavy walls (<span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">16</span> inch or a +trifle over for the large tube, and a trifle less for the small +one) but the large tube should not be too heavy or else it +will be hard to prevent melting down too much of the +small tube, and getting this drawn out too thin during the +process. One of the troublesome features of this exercise +is the difficulty of rotating two tubes of different diameters +with the same angular velocity, so as not to twist the +joint. Another difficulty is found in getting the cone +uniformly heated to blowing temperature without overheating +and overshrinking the small tube. The reason +for this is obviously the much greater circumference of +the cone, especially at its large end, so that relatively +much less of it is being heated at any time. The beginner +is also inclined to start with too long a cone, or else heat +so much of the large tube that part of its glass is included +in the cone, with the result that in order to get the<span class="pagenum"><a name="Page_28" id="Page_28">[Pg 28]</a></span> +right wall-thickness the cone must be made too long (<i>g</i>, +Fig. 8). This does not look well, and usually will be +irregular in shape.</p> + + +<h3>EXERCISE NO. 5</h3> + +<h4><span class="smcap">Tube for Condensing Sulphur Dioxide</span></h4> + +<p>This is useful as a test of mastery of the preceding +exercise. A piece of <span style="font-size: 0.8em"><sup>3</sup></span>⁄<span style="font-size: 0.6em;">16</span> or <span style="font-size: 0.8em"><sup>7</sup></span>⁄<span style="font-size: 0.6em;">32</span> inch tubing is joined +to each end of a piece of tubing <span style="font-size: 0.8em"><sup>5</sup></span>⁄<span style="font-size: 0.6em;">8</span> by about 5 inches, and +two constrictions made in the large tube, by the method +described on page 10. The small tubes are then bent +in the same plane, as shown, and their ends fire-polished +(Fig. 9).<br /><br /></p> + +<div class="figcenter" style="width: 400px;"> +<img src="images/i036.png" width="400" height="98" alt="" title="" /> +<span class="caption">Fig. 9.—Tube for condensing sulphur dioxide.</span> +<br /><br /></div> + +<h3>EXERCISE NO. 6</h3> + +<h4><span class="smcap">Bulb at the End of a Tube</span></h4> + +<p>For this exercise tubing of <span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">4</span> inch diameter and moderately +strong walls is selected. A tail is drawn out on one +end of the tube, and a piece of tubing about nine or ten +inches long is cut off. The tail should be carefully drawn +in the axis of the tube, and in the same straight line with +it, as it is to be used as a handle in assembling the glass +for the bulb. This tail must be long enough so that it +can be conveniently held in the left hand, as described on +page 13, and rotated about the same axis as the main +tube. Holding the main tube in the right hand and the +tail in the left, the tube is rotated in a large flame so<span class="pagenum"><a name="Page_29" id="Page_29">[Pg 29]</a></span> +that a piece of it, beginning where the tail stops and +extending about an inch to the right, may be uniformly +heated to the highest temperature at which it can be +kept in shape. As soon as +this temperature is reached, +the tube is removed from the +flame, continuing the rotation +and taking care not to draw +out the heated part, and +gently blown. The rotation +is carefully continued during +the blowing, holding the tube +in approximately a horizontal +position. As soon as the tube +has expanded a little the tail +is pushed gently toward the +main tube, continuing the +gentle blowing. If this is +properly done, the heated +piece of tube will become a +short bulb of about double its +original diameter, and about +the same wall thickness as the +original tube. It will have +somewhat the appearance of +<i>a</i>, Fig. 10, when properly manipulated.<br /><br /></p> + +<div class="figcenter" style="width: 189px;"> +<img src="images/i037.png" width="189" height="400" alt="" title="" /> +<span class="caption">Fig. 10.—Blowing a bulb on +the end of a tube.</span> +<br /><br /></div> + +<p>The tube is now reheated as before, taking care this +time that the heating extends over all that part of the +bulb to the right of the dotted line in the figure, as well +as part of the main tube adjoining. If this heating has +been properly placed, when the operation of blowing and +pushing together is repeated the result will be to lengthen +the bulb into a uniform cylinder, as shown in <i>b</i>, Fig. 10. +Otherwise the result will be a series of bulbs, as in <i>c</i>,<span class="pagenum"><a name="Page_30" id="Page_30">[Pg 30]</a></span> +Fig. 10, separated by thickened ridges which will be +almost impossible of removal later and will disfigure the +final bulb. This operation of heating, blowing and +pushing together is repeated several times, until the +cylinder becomes as long as can be conveniently handled +(about 1-<span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">4</span> inches to 1-<span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">2</span> inches). If more glass is +needed than is then contained in the cylinder, the latter +may now be heated as a whole, and blown and pushed +gently into a shorter cylinder of a slightly greater diameter, +and more glass then added as before.</p> + +<p>When enough glass has been collected for the bulb, it +is all well heated and blown gently a couple of times, +pushing the mass together as required, until a thick bulb +like <i>d</i>, Fig. 10, is obtained. The tail must now be +removed at the point indicated by the dotted line. To +do this, a very fine flame is directed on the point where +the tail joins the bulb, and the tube well rotated as the +glass softens at that point. When sufficiently soft, the +work is raised a little, so that the flame instead of striking +the glass squarely at the point indicated passes below and +tangential to it. The tail is now drawn off slowly, continuing +the rotation, raising the work just out of the +flame whenever the thread of glass drawn off becomes too +thin, and lowering it again to the point where the flame +just touches it when the glass stiffens a little. By this +means the tail may be drawn off without leaving an +appreciable lump behind, as indicated in <i>e</i> and <i>f</i>, Fig. 10. +When as much of the extra glass has been removed as is +practicable, the flame is brought to play squarely upon +the little lump left, the last of the tail removed, and the +lump heated and gently blown to a small excrescence on +the main bulb. The whole end of the latter is now heated +until it begins to shrink a little, and gently blown to +make it uniform in thickness. The whole bulb is then +heated in a flame of the proper size, so that it all may<span class="pagenum"><a name="Page_31" id="Page_31">[Pg 31]</a></span> +shrink to about two-thirds of its diameter. The flame +must be very carefully chosen and directed, so as to +shrink all the bulb, right up to the main tube, but not +soften the latter. As soon as this stage is reached, the +bulb is removed from the flame, continuing the even +rotation, and blown to the desired size, preferably by a +series of gentle puffs following one another at very short +intervals. During the blowing, the main tube is held in +a horizontal position, and any tendency of the bulb to +fall out of line is corrected by the rotation. If the shape +of the bulb or its size are not satisfactory, it may be +shrunk again and reblown. Such shrinking should begin +in a large yellow flame, with just enough air to give it +direction. The amount of air may be gradually increased +as the bulb shrinks and the walls become thick enough to +bear it without collapsing. If the bulb starts to collapse +at any time, it must be immediately blown enough to +regain its convex surface, before the shrinking proceeds +further.</p> + +<p><b>Discussion.</b>—In collecting the glass for the bulb, +enough must be gathered to give the walls the desired +strength. Since the area of a sphere is proportional to +the cube of its diameter, it is evident that doubling the +size of a bulb diminishes the thickness of its walls to a +very large extent. The limit of diameter for a strong +bulb on ordinary <span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">4</span>-inch tubing, collecting the glass as +above, is about 1-<span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">2</span> inches, and the beginner will do well +not to blow his bulbs more than an inch in diameter.</p> + +<p>The collection of the glass is one of the most important +parts of the process. If the mass of glass be twisted, furrowed +or ridged, or lop-sided, it is very difficult to get a +good, even, spherical bulb, no matter how many times it +is shrunk and blown. The greatest care should therefore +be taken to get a uniform cylinder, on the same axis as +the main tube; and to this end the rotation of the tube<span class="pagenum"><a name="Page_32" id="Page_32">[Pg 32]</a></span> +must be carried on very evenly. For method of holding +the tube, see page 14.</p> + +<p>If a very large bulb is required, it will often be economical +to seal on the end of the tube a short piece of a large +tube, provided with the proper tail, and use the glass in +the large tube for the bulb instead of attempting to collect +it from the small tube. In this case part of the small +tube will usually be included in the bulb, so that the joint +comes in the latter, and not where it joins the tube. As +the amount of glass carried on the end of the tube +increases in weight and size the difficulties of heating it +uniformly, keeping it in the proper position and handling +it increase rapidly.</p> + +<p>In collecting glass, it is usually best not to leave the +part of the cylinder next the tube with too thick walls. +This is always the coolest part during the preparation for +blowing the bulb, consequently it does not get blown out, +and causes an ugly thickened appearance on that end of +the bulb.</p> + +<p>If the bulb grows too long or pear-shaped, it may be +easily shortened by heating to the blowing temperature, +and then blowing gently with the main tube in a vertical +position, and the bulb at the top of it. Gravity will then +shorten the bulb nicely.</p> + +<p>The finished bulb should be a nearly perfect sphere, +with the axis of the tube passing through its center, and +the portion of the tube adjoining the bulb must not be +distorted, twisted, or blown out. In order to prevent the +distortion of the tube, care must be taken that it is never +heated quite to its softening point during the process.</p> + + +<h3>EXERCISE NO. 7</h3> + +<h4><span class="smcap">Blowing a Bulb in a Tube</span></h4> + +<p>The tube is selected and one end closed as in the previous +exercise, but it should be cut a little longer, say<span class="pagenum"><a name="Page_33" id="Page_33">[Pg 33]</a></span> +about twelve inches. Beginning at a point about four +inches from the closed end, glass is collected and blown into +a thick-walled bulb, exactly as in the previous exercise. +Greater care must be taken, however, that the cylinder +collected and this thick bulb are of uniform thickness and +set squarely in the axis of the tube. Instead of removing +the tail, the bulb must be blown in this case with both +pieces of tubing attached, and care must be taken that +they "line up" properly, <i>i.e.</i>, are in the same straight +line, and that this line passes as near as may be through +the center of the bulb. The tube is held in approximately +horizontal position during the blowing of the bulb, as in +the previous case, and especial care taken with the rotation. +Both pieces of tube must of course be rotated at +the same rate, and their softened ends must be kept at +exactly the proper distance from each other, so that the +bulb may be spherical and not elongated. If the blowing +of the bulb be quickly and accurately done, it may +usually be completed before the glass is quite set, and the +alignment of the two tubes may then be rectified while +looking straight through the bore of the tube.</p> + +<p><b>Discussion.</b>—The two points of greatest importance +are the collection of the glass, and the uniform rotation +of the tube. A larger tube may be sealed in the middle of +a small one when a large amount of glass is necessary. +The piece of tubing used for the exercise must be long +enough so that the fingers may be kept on a cool part of +the glass without getting uncomfortably near the ends +of the tube. It should not be any longer than necessary, +however, as the extra weight and length make the manipulation +of the hot glass more difficult.</p> + +<p>When a string of bulbs are required on the same tube, a +piece of glass 18 inches long may be used at the start, +and the first bulb made near the closed end, as described. +Each succeeding bulb will then be in plain view during the<span class="pagenum"><a name="Page_34" id="Page_34">[Pg 34]</a></span> +blowing, and when the open end becomes too short for +comfort, it may be dried out, cut off, and another piece +joined to it, starting as in the first method (Exercise +No. 1), but instead of drawing out the thick bulb to a +tube, it is made part of the glass collected for the next +bulb. If the string of bulbs becomes awkward to handle +on account of its length and weight, it may be made in +several parts and these later sealed together by the second +method, preferably blowing through a rubber tube attached +to the open end, as described on page 22.</p> + +<p>Very neat small bulbs may be made on tubing of a +diameter of <span style="font-size: 0.8em"><sup>3</sup></span>⁄<span style="font-size: 0.6em;">16</span> inch or a little less, but the beginner is +advised to start with tubing of about <span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">4</span> inch diameter. +The use of tubing with too thick walls usually produces +bulbs which are thick-walled at the point where they +leave the tube, but inclined to be too thin at the point of +maximum diameter (perpendicular to the axis of the tube) +where most of the strain comes and strength is particularly +needed.</p> + +<hr style="width: 65%;" /> + +<p><span class="pagenum"><a name="Page_35" id="Page_35">[Pg 35]</a></span></p> + +<h2>CHAPTER IV</h2> + +<h3><span class="smcap">Advanced Exercises</span></h3> + + +<h3>EXERCISE NO. 8</h3> + +<h4><span class="smcap">Sealing a Tube Through Another Tube</span></h4> + +<h4><i>First Method—Making a Gas-washing Tube</i><br /><br /></h4> + +<p>This first method can be used whenever one can work +through an open end opposite to the end of the tube +where the joint is to be made. To illustrate it, take a +piece of rather thin-walled tubing, about <span style="font-size: 0.8em"><sup>3</sup></span>⁄<span style="font-size: 0.6em;">4</span> inch in +diameter, and some pieces of rather strong tubing a little +less than <span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">4</span> inch in diameter. Draw off the large tube +in a short cone, then draw off the tail as in the making of +the bulb on the end of the tube, blow out the little lump +slightly, shrink the whole cone a little and blow gently to +form a rounded end like that on a test-tube, with walls +about the thickness of those of the rest of the tube. Cut +this tube to a suitable length, say about six inches, and provide +two corks which will fit the open end of it. Now cut +a piece of the small tubing of the proper length to form +the piece which is to be inside the large tube. For practice +purposes, this piece should be about an inch shorter +than the large tube. Flange one end of this tube a little, +and anneal the flange well in the smoky flame. Bore one +of the corks so that a piece of the small tubing will fit it, +and cut a couple of notches in the side of this cork so that +air can pass between it and the glass. Pass a short piece +of the small tubing through this cork, and attach the<span class="pagenum"><a name="Page_36" id="Page_36">[Pg 36]</a></span> +flanged piece of small tube to this by means of a short +piece of rubber tubing, so that when the whole is inserted +in the large tube it is arranged as in <i>a</i>, Fig. 11. The piece +of glass tubing projecting out through the cork is now cut +off so as to leave an end about <span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">2</span> inch long when the +cork is firmly seated and the inner tube pushed into +contact with the center of the end of the large tube, as +shown in the drawing. Care should be taken that the +little rubber tube which joins the two pieces is arranged +as in the figure; <i>i.e.</i>, most of it on the piece of tubing which +passes through the cork, and very little on the other +piece, so that when the cork is removed after the small +tube has been sealed through the large one, the rubber +tube may easily come with it. Select a short piece of the +small tubing of suitable length for the piece which is to<span class="pagenum"><a name="Page_37" id="Page_37">[Pg 37]</a></span> +be on the outside of the large tube as a continuation of +the piece inside, and another piece for the delivery tube. +A small bulb may be blown in the latter at a point about +2-<span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">2</span> inches from the closed end, and the open end cut +off about 1-<span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">2</span> inches from the bulb. A cork or cork-boring +of suitable size to stopper the small tube is prepared, +and laid ready with the other (unbored) cork for +the large tube.<br /><br /></p> + +<div class="figcenter" style="width: 400px;"> +<img src="images/i044.png" width="400" height="375" alt="" title="" /> +<span class="caption">Fig. 11.—Gas-washing tube.</span> +<br /><br /></div> + +<p>When everything is in readiness, the rounded end of the +large tube is slowly heated until it softens and joins firmly +to the small tube inside. After it has shrunk down well, +it is blown out to its original size, placing the whole end +of the large tube, cork and all, in the mouth. Now with a +fine-pointed flame the glass covering the end of the small +tube is heated to the softening temperature, and then is +blown out to an excrescence by blowing on the end of the +small tube which passes through the cork. The end of +this excrescence is heated and blown off in the usual way, +so as to leave the small tube sealed on the inside of the +large one and opening through it into this short tube which +has been blown out. The end of the small tube which +passes through the cork is now closed with the cork prepared +for it, and the short outer tube is joined to the tube +that has just been blown out, so that the joint appears +like <i>b</i>, Fig. 11. Use the first method (Exercise No. 1) +for this joint. Reheat the whole of the end of the tube +nearly to the softening temperature, anneal it a little, +and allow to cool a few seconds until well set. Now +remove the cork, short glass tube and rubber tube from +the open end of the large tube and insert the solid cork +in their place. Warm the joint and the whole of that +end of the tube again carefully up to about the softening +point, then seal on the side tube for the delivery of the +gas in the usual way, taking care that the whole of the +end and the joint are kept warm meanwhile. When<span class="pagenum"><a name="Page_38" id="Page_38">[Pg 38]</a></span> +thoroughly sealed, the delivery tube is bent up parallel +to the tube through which the gas enters, and then out +at right angles to it, as shown in <i>c</i>. The whole of the +end of the tube is now cautiously reheated and then cooled +slowly to anneal it.</p> + +<p>The cork may now be removed from the open end of +the large tube, this end heated in a large flame, caught +together with a scrap of glass tubing and drawn off into +a cone so that the base of the cone is about opposite the +end of the inner tube. The lump of glass is drawn off the +point of this cone and it is reblown to form a rounded +end, as previously described.</p> + +<p>After this cools, the tube through which the gas enters +may be heated at the proper point and bent at right +angles to form the finished apparatus as shown in <i>d</i>. +The ends of the small tube are cut off square and fire-polished.</p> + +<p><b>Discussion.</b>—After the joint has once been made, great +care must be taken that it is kept hot during all the subsequent +manipulations, and if it becomes somewhat +cool at any time it must be reheated very slowly. It is +obvious that the rate of heating and cooling of the inner +tube will be slower than that of the outer tube, and this +will readily produce stresses which tend to crack the tube +at the joint. The amount of heating and cooling which +such a joint will stand depends upon its form. The +beginner should examine such a joint on regular factory-made +apparatus, and note the uniformity of wall-thickness +and the "clean-cut" appearance of the joint, as a +model for his imitation. A ragged joint, where the line +of joining of the inner and outer tubes wavers instead of +going squarely around the tube, is almost sure to crack +during the cooling and heating unless extra precautions +are taken with it. The presence of a small lump of glass +at any point on the joint affords an excellent starting<span class="pagenum"><a name="Page_39" id="Page_39">[Pg 39]</a></span> +place for a crack, as do also the points on a ragged joint +where the inner tube comes farther down on the outer +tube than at other points.</p> + +<p>In order to insure a joint which is square and not +ragged, it is essential that the angle between the inner +and outer tubes at the joint be very nearly a right angle. +For this reason the two tubes should not be of too near +the same size, or if this cannot be avoided, a small bulb +should be blown on the end where the joint is to be made. +If this bulb be made with the same wall-thickness as the +rest of the tube, and somewhat pear-shaped, it may be +drawn out to the same size as the rest of the tube, if +necessary, after the joint has been made.</p> + +<p>This method is used wherever possible in preference to +the second method (Exercise No. 9), as it is easier to get +a good joint with it. It may also be used where it is +desired to seal the tube through the side of a tube, or for +a tube sealed through the wall of a bulb, as in a Geissler +potash bulb or similar apparatus. Where there is not +space to join the inner tube to the blowing tube by a +rubber tube, this joint may be made with a small piece +of gummed paper, which can readily be broken when +desired.</p> + + +<h3>EXERCISE NO. 9</h3> + +<h4><span class="smcap">Sealing a Tube Through Another Tube</span></h4> + +<h4><i>Second Method—Making a Suction Pump</i></h4> + +<p>Select a piece of tubing <span style="font-size: 0.8em"><sup>3</sup></span>⁄<span style="font-size: 0.6em;">8</span> to <span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">2</span> inch in diameter, +with walls about <span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">16</span> inch or a little less in thickness, +heat a place about 4 inches from one end and draw it +out so that when cut off at the proper point it will look +like <i>a</i>, Fig. 12; the open end of the drawn out part being +small enough to slip inside another piece of the original +tube. A small thick-walled bulb is now blown as<span class="pagenum"><a name="Page_40" id="Page_40">[Pg 40]</a></span> +indicated by the dotted lines, and annealed. A piece of +the original tubing is now prepared, 7 or 8 inches long, +with one end cut square off and the other closed. A +piece of <span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">4</span>-inch tubing about 2 inches long, and drawn out +at one end to a tail several inches long is also prepared, to +form the inlet tube for the air. Another piece of the +<span style="font-size: 0.8em"><sup>3</sup></span>⁄<span style="font-size: 0.6em;">8</span>-inch tube is prepared, about 4 inches long, and provided +with a tail drawn out as indicated in <i>b</i>, so that when +cut off at about 2-<span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">2</span> or 3 inches from the main tube its +inner diameter may be slightly less than that of the narrowest +point of the tube <i>a</i>. A small thick-walled bulb +is blown at the point indicated by the dotted lines, and +annealed. Care must be taken in drawing the capillary +and blowing the bulb in both <i>a</i> and <i>b</i> that the capillary +tubes are in the axis of the main tube, and in the same +straight line with it.<br /><br /></p> + +<div class="figcenter" style="width: 400px;"> +<img src="images/i048.png" width="400" height="160" alt="" title="" /> +<span class="caption">Fig. 12.—Suction pump.</span> +<br /><br /></div> + +<p>The open end of the 8-inch piece of tube and the bulb +of the piece <i>a</i> are now warmed together, the end of the +tube only moderately and the bulb to about its softening +temperature. The tube <i>a</i> is now inserted in the open end +of the large tube, and the bulb softened with a suitable +flame and pressed into good contact with the tube. It +is then reheated, including the joint, blown a little and +pulled out to form a straight tube in line with the main +tube. By warming the joint a little, and proper rotation,<span class="pagenum"><a name="Page_41" id="Page_41">[Pg 41]</a></span> +the capillary may be brought into the same straight line +with the rest of the tube.</p> + +<p>Keeping this joint hot, a place about an inch from it on +the tube <i>a</i> is warmed, and the piece of <span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">4</span>-inch tubing +previously prepared is sealed on at that point. The +joint is then well annealed and allowed to cool.</p> + +<p>The tube <i>a</i> is now cut at such a place that when <i>b</i> is +inserted in the open end the point will come near the +end of the constriction of <i>a</i>, as shown in <i>c</i>. Care is +taken to get a clean square cut. The side tube is now +cut off about an inch from the main tube and corked. +Tube <i>b</i> is sealed into the open end of <i>a</i>, in the same way as +<i>a</i> was sealed into the large tube, and the joint carefully +annealed.</p> + +<p><b>Discussion.</b>—As in the first method, the secret of success +lies in getting a square joint, and having the inner +tube leave the outer one at nearly right angles. All the +remarks about annealing, lumps, etc., made under the +previous method apply here.</p> + +<p>This method may be applied in sealing a small tube +into the end of a large one, the latter being either drawn +to a cone and cut off at the desired diameter, or else +given a rounded end like a test-tube and a hole the proper +size blown in the center of it. A suitable thick-walled +bulb is to be blown on the small tube, as in the case +described above. This method is also used in making +the Kjeldahl trap (<i>a</i>, Fig. 13), the small tube to be +inserted being first drawn, the thick bulb blown at its +point of union with the main tube, and then the small +tube bent and cut. The large bulb is best made with +rather heavy wall, being either blown in the middle of +a tube, and one piece of the tube drawn or cut off, or +else made on the end of a tube. In the latter case a drop +of glass must be put on the point where the joint is to +be, so as to get a hole of the proper size with enough glass<span class="pagenum"><a name="Page_42" id="Page_42">[Pg 42]</a></span> +around it to prevent it from growing larger when it is +heated. The author prefers to blow the bulb in the +middle of the tube, draw off one end of the bulb, and +blow out the desired hole where the tube was drawn off. +The whole bulb must generally be reheated and blown +a little at the end of the process, and well annealed.<br /><br /></p> + +<div class="figcenter" style="width: 400px;"> +<img src="images/i050.png" width="400" height="328" alt="" title="" /> +<span class="caption">Fig. 13.—a, Kjeldahl trap; b, suction pump on smaller tubing.</span> +<br /><br /></div> + +<p>The suction pump can also be made on <span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">4</span>-inch tubing, +and one joint saved if desired, by constricting the tube +to form the raceway for the water and air, as shown in +<i>b</i>, Fig. 13. (See page 10 for method.) But it is more +difficult to make a square joint on such small tubing.</p> + + + +<hr style="width: 65%;"/><p><span class="pagenum"><a name="Page_43" id="Page_43">[Pg 43]</a></span></p> +<h2>CHAPTER V</h2> + +<h3><span class="smcap">Modified Methods and Special Operations</span></h3> + + +<h4>CAPILLARY TUBING</h4> + +<p>This is commonly used in many forms of apparatus +for gas analysis, and one is often called upon to join two +pieces or to make a tee on it. The methods are nearly +the same as with other tubing, except that more care and +patience are required. The work must be done much +more slowly on account of the thickness of the walls, and +open ends of the tube must always +be enlarged before joining them to +anything. This is best done by carefully +sealing the end and then blowing, +with several suitable reheatings, to +form a pear-shaped bulb as in <i>a</i>, Fig. +14. The end of this is then heated +and blown off, and the piece is ready +to be joined to another similar end, or +to a piece of ordinary tubing if desired. +The joints are best not blown +too much, as thick walls shrink very slowly. Much may +be done by gently pushing the tube together or pulling +it apart in the flame, to remove lumps and irregularities. +It is necessary that the bore of the joint be approximately +that of the main tube, and care must be +taken that the latter is not constricted at the point +where the joint begins.<br /><br /></p> + +<div class="figcenter" style="width: 255px;"> +<img src="images/i051.png" width="255" height="300" alt="" title="" /> +<span class="caption">Fig. 14.—Capillary +tubing.</span> +<br /><br /></div> + +<p>Especial care must be taken to warm the tube slowly +when starting and cool it slowly when through, as the<span class="pagenum"><a name="Page_44" id="Page_44">[Pg 44]</a></span> +thick walls frequently crack if not carefully handled. +For this reason the whole neighborhood of the joint must +be heated somewhat so that there may not be stresses set +up between the heated and unheated portions.</p> + +<p>In making the tee (<i>b</i>, Fig. 14) the inability to blow the +joint makes itself decidedly felt, but if the side tube is +properly enlarged as previously described, a good joint +can be made by alternately pulling and pushing on the +end of the side tube, and shrinking well.</p> + +<p>Very fine capillary tubing should be blown with a +rubber bulb instead of the mouth, so as not to get +moisture into the tube. The rubber bulb may also be +used to advantage on some of the coarser capillary +tubing.</p> + +<p>When a bulb is to be joined to a piece of capillary +tubing, the joint is preferably made before blowing the +bulb, and will then be taken up a little way on the bulb +during the process. Care must of course be taken not to +constrict the capillary; the pear-shaped bulb blown on +the end (<i>a</i>, Fig. 14) may well extend back a little further +than usual into the tube so as to prevent this. If a bulb +is required in the middle of a capillary tube, the latter +is usually best cut and a piece of ordinary tubing of suitable +size sealed in to provide material for the bulb.</p> + + +<h4>GLASS ROD</h4> + +<p>Joints, tees, etc., in glass rod are made on the same +principle as in tubing, except that of course they cannot +be blown, and regularity must be obtained by accumulating +a small mass of uniformly heated glass, and then +drawing it to a suitable rod, on the same principle as +Exercise No. 1.</p> + +<p>Great care must be taken in heating and cooling this, +as in the case of the capillary tubing, and for the same +reasons.</p> + +<p>By joining pieces side by side, pressing with carbon<span class="pagenum"><a name="Page_45" id="Page_45">[Pg 45]</a></span> +plates or a plate and a rod, and other suitable manipulations, +stirrers, spatulas, and other objects may easily +be made from rod, and its manipulation is relatively easy +on account of the fact that one does not have to worry +about the bore of the tube. But the same general rule +about not having thick and thin spots in contact, and +making all changes in diameter on a taper if possible +instead of abruptly, applies here. Thick pieces will cool +and contract at different rates from thin ones, and cracks +are likely to develop where they join. Work which +has been formed with any tool must always be heated to +the softening point afterward before allowing it to cool +in order to remove the stresses caused by the contact of +the tool with the hot glass.</p> + +<p>When it is necessary to join a piece of rod to the side +of a piece of tubing, the end of the rod is made very hot +while the wall of the tube at the spot desired is heated to +just below the softening temperature. The rod can then +be pressed into firm union with the tube and drawn a +little to remove the excess of glass without deforming the +tube.</p> + + +<h4>MENDING STOPCOCKS</h4> + +<p><b>Mending the Plug.</b>—The plug of the stopcock occasionally +falls out and is broken. If the break is in the +main part of the plug, nothing can be done except to +search for a spare plug of suitable size and grind it to +fit, as described below. If only the little cross-piece at +the end is broken off, it can easily be replaced. In +most ordinary stopcocks the plug is solid, but the little +handle is hollow. What has been said above regarding +care in heating and cooling glass rod applies with especial +force here. It is usually best to wind the whole of the +plug with several thicknesses of asbestos cord, leaving<span class="pagenum"><a name="Page_46" id="Page_46">[Pg 46]</a></span> +bare only the end where the handle is to be joined. This +diminishes the danger of cracking the plug by too rapid +heating, and also makes it more comfortable to hold. A +piece of rather thick-walled tubing of suitable diameter is +chosen, drawn out so as to have a suitable taper (taking +care to heat enough of the tube so that the capillary tail +has good wall-thickness and strength), and then a +corresponding taper is drawn to form the other side +of the handle. The result is shown in Fig. 15, <i>a</i>. The +capillary tail is now heated and bent back to form a +handle which will be in the same straight line as the axis +of the plug (<i>b</i>, Fig. 15) and the main part of the tube +drawn off at the dotted line, making a neat seal at that +point. The broken end of the plug is now slowly warmed +in the smoky flame, the heat gradually increased by a +gentle stream of air from the bellows, and the point at +which this handle is to be attached finally brought to +the temperature at which the glass flows freely. In the +mean time, the little handle has been warmed almost to +the softening point. It is now quickly pushed into place +(<i>c</i>, Fig. 15), taking care that its axis is parallel to the hole +in the plug, and then drawn away from the plug just +enough to make a graceful neck instead of the bulging one<span class="pagenum"><a name="Page_47" id="Page_47">[Pg 47]</a></span> +indicated by the arrow in the figure. With a fine pointed +flame the little tail is now drawn off at the point indicated +by the dotted line (<i>c</i>, Fig. 15) and the whole carefully annealed. +If necessary, the handle can be blown a little +before the tail is removed. Local heating and blowing at +the point where the handle joins the plug is often necessary +in order to make a smooth job.<br /><br /></p> + +<div class="figcenter" style="width: 400px;"> +<img src="images/i054.png" width="400" height="217" alt="" title="" /> +<span class="caption">Fig. 15.—Stopcock plug.</span> +<br /><br /></div> + +<p><b>Regrinding.</b>—This is sometimes necessary to make +stopcocks tight, when the grinding has not been properly +done in the factory. For this, a very little fine flour of +emery or carborundum is the best and quickest. If this +is not at hand, some clean sand may be ground in an agate +mortar, and if possible sieved. Only material which +passes the 100-mesh sieve should be used. It will be +ground still finer in the process. For the final polishing, +a little infusorial earth or even kaolin will do.</p> + +<p>The surface to be ground is moistened with water and +dusted over with a little of the abrasive. The plug is +now inserted in the stopcock, and turned with a gentle +pressure. This turning should be in the same direction +for several revolutions, then in the opposite direction for +several more revolutions, etc. As the abrasive becomes +finer during the grinding, a little more may be added if +necessary. In general, only a little grinding will be +required, and one small pinch of carborundum or emery +will be ample. The beginner usually grinds too much, +and with too coarse material. As the grinding surface +becomes dry, water is added drop by drop, and the grinding +continued until the abrasive seems to be reduced to +an impalpable powder, most of which has been squeezed +out of the stopcock. The two surfaces in the stopcock +are usually grinding upon each other at this stage, and +inspection will show whether the contact between them +is uniformly good. If not, the grinding must be continued +with a little fresh abrasive. If contact appears<span class="pagenum"><a name="Page_48" id="Page_48">[Pg 48]</a></span> +to be good, the surfaces are ground together for a little +with practically no abrasive, so as to polish them, and +the joint is then washed out and tested.</p> + +<p>In grinding in a new plug to replace a broken one, the +plug selected should have practically the same taper as +the seat into which it is to be ground, and should be a +very little too large. Care must be taken to so distribute +the abrasive material as to grind mostly on the places +where the plug fits tightly.</p> + +<p><b>Sealing on a New Tube.</b>—It frequently happens that +one of the tubes of the stopcock is broken off close to +the cock itself, and a new one must be joined to the +stub of the old one. With care, this may often be successfully +done even where the break is within <span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">4</span> inch +of the stopcock. The first step is to clean and dry the +stopcock, remove the plug, cork the open ends of the +stopcock sleeve and the other tube, and wind a couple +of layers of asbestos cord carefully over the sleeve and +the most of the corks which close it. A suitable tube, +having as near as possible the same diameter and wall +strength as the one broken off, is selected and a piece +the desired length cut off. The broken end of the tube +on the stopcock is now squared off as well as possible, +by cutting or by heating and drawing off the projections, +and the new tube sealed on, usually with the first method +(Exercise No. 1). If the break is very close to the stopcock, +very little reheating and blowing can be done, on +account of the danger of getting the stopcock sleeve out +of shape, and the work must be heated very slowly to +prevent cracking. The main reliance is then placed on +making a good joint when the tubes are brought together, +and then drawing out this joint a little, at once, to get an +even wall.</p> + + +<h4>CLOSED CIRCUITS OF TUBING.</h4> + +<p><span class="pagenum"><a name="Page_49" id="Page_49">[Pg 49]</a></span></p> + +<p>In some pieces of apparatus closed circuits of circular +or rectangular shape are required. A similar problem +is involved in apparatus like the ordinary Soxhlet +extractor, where a small tube is joined to the side +of a large one, bent to form a siphon, and attached +again to a continuation of the original large tube. +The difficulty in all such cases is to provide for the +contraction taking place as the last joint cools. If +part of the circuit has the shape of the letter S, or is a +spiral, the natural springiness of the glass will take care +of this. If not, the side of the circuit opposite to the +joint and parallel to it must be heated also, the two being +finally heated together to the softening point after the +joint is completed, and then allowed to cool together.</p> + +<p>To make the last joint, the rest of the tube is made in +approximately the desired form, the two pieces which are +to be joined to make the last joint being just enough out +of the desired position to allow them to pass one another. +The final joint is preferably made in the middle of a +straight piece of tube, not at a tee. The two pieces +which are to be joined are bent so as to just pass each +other, marked at the right point with the glass-knife, +and cut there, preferably with a small bead of hot glass. +One or both of these tubes are now warmed to the softening +point in such a place that the tubes can be made to +meet properly, and the two cut ends pressed together. +They are now warmed in the flame, and joined together, +either by simultaneously warming the opposite side of +the circuit or some other suitable part, so as to allow the +two ends to be pushed together again after they are +softened, or by gently touching the places that do not +unite with a hot bead of glass, and using the glass to fill +up the crack where the ends do not quite meet. Care<span class="pagenum"><a name="Page_50" id="Page_50">[Pg 50]</a></span> +must be taken not to leave knots or lumps of glass in the +finished joint, and the latter should be well reblown, and +if necessary left as a small bulb or enlargement, rather +than have it have too thick walls.</p> + + +<h4>SPIRALS<br /><br /></h4> + +<p>Spirals of glass tubing are probably best made free-hand +before the blow-pipe, unless one has a great many of +them to make, and extreme accuracy is desired. To +begin with, a piece of tubing of the desired size (say <span style="font-size: 0.8em"><sup>3</sup></span>⁄<span style="font-size: 0.6em;">16</span> +inch in diameter) and a convenient length (about two feet) +is selected, one end closed, and a right-angle bend made +about six inches from the closed end. Holding the closed +end in the left hand and the long open one in the right, +the spiral is begun. The short closed end is to be parallel +to the axis of the spiral, and preferably in that axis. +Using a moderate-sized flame, of somewhat yellow color, +and taking care to heat the whole circumference of the +tube, the long open end is wound little by little into a +spiral having the short end <i>a</i> (Fig. 16) as an axis. The +bend at <i>b</i>, where the tube changes from the radius to the +circumference of the circle, must be rather short, but +the tube must not be flattened or constricted here.<span class="pagenum"><a name="Page_51" id="Page_51">[Pg 51]</a></span> +Especial pains is to be taken with the first turn of the +spiral (<i>b</i> to <i>c</i>, Fig. 16), as the shape of this determines the +diameter of the whole spiral, and serves as a guide for the +rest of the turns. The winding of the tube is best accomplished, +after a portion has been softened, by slowly +turning the short end <i>a</i> a little about its own axis, while +the long open end remains where it was. This winds +the tube into a spiral, just as if there were a solid cylinder +in the center of it, and this cylinder was being turned +about its axis, and was winding up the soft glass upon its +circumference. As the cylinder is not actually there, the +curve of the turns must be carefully estimated by the +eye, so that the spiral may be uniform and moderately +smooth. When the original piece of tube has been used +up, another piece is sealed on to the open end, and the +operation continued as far as may be required.<br /><br /></p> + +<div class="figcenter" style="width: 400px;"> +<img src="images/i058.png" width="400" height="228" alt="" title="" /> +<span class="caption">Fig. 16.—Making a spiral.</span> +<br /><br /></div> + + +<h4>GROUND JOINTS</h4> + +<p>It is sometimes required to join two pieces of tubing +end to end, by means of a ground joint. Whenever +possible, a regular sealed joint should be used instead +of this ground joint, as it is quicker to make, and +more certain to be tight. Where a ground joint is +necessary, however, it is best made in the conical form +shown in <i>c</i>, Fig. 17. If the wall of the tube to be used<span class="pagenum"><a name="Page_52" id="Page_52">[Pg 52]</a></span> +is not very thick, it is thickened by collecting glass as +for a bulb on the ends of two tubes (Exercise No. 6), and +drawing to form cones of suitable shape (<i>a</i> and <i>b</i>, Fig. 17) +and of such relative sizes that a will slip about half way +into <i>b</i>. In order to make <i>a</i> straight and give it the proper +angle, it may be rolled when hot, upon a hot plate of carbon. +Blowing during this rolling is often helpful to +remove depressions. After <i>b</i> has been drawn to nearly +the proper size and shape, it may be smoothed by the use +of a small carbon rod, held inside it at a slight angle, or +better by the use of a truncated hexagonal pyramid of +carbon, whose edges have the proper slant to make the +inside of the cone right. The proper taper for both these +cones is the same as that used in stopcocks of similar size. +The hexagonal carbon can easily be made by carefully +filing down an electric light carbon, and finally impregnating +it with paraffin or beeswax, and is extremely useful +wherever a conical surface has to be formed from the +inside of a tube.<br /><br /></p> + +<div class="figcenter" style="width: 400px;"> +<img src="images/i059.png" width="400" height="223" alt="" title="" /> +<span class="caption">Fig. 17.—Ground joint.</span> +<br /><br /></div> + +<p>The tail is allowed to remain on piece <i>a</i>, as a sort of +guide in grinding, and should therefore be in the axis of +the tube and have rather thick walls. Grind with emery +or carborundum, as described under a previous head. +(Regrinding plug for stopcock.) If many such joints are +to be made, it will pay to have a little sleeve of brass made +with the proper taper, and rough down the plug <i>a</i> in it +to about the proper size, while <i>b</i> is roughed down by +means of a brass or iron plug having the same taper. +This prevents excessive grinding of one-half of the joint +in order to remove a defect in the other half, and is the +method commercially used in making stopcocks.</p> + + +<h4>SEALING IN PLATINUM WIRE</h4> + +<p>Very often it is necessary to seal platinum wire into +the wall of a tube. Professional glass-blowers usually<span class="pagenum"><a name="Page_53" id="Page_53">[Pg 53]</a></span> +use a special sort of glass ("Einschmelzglas") which +is usually a lead glass, and is made of such composition +that it has the same or practically the same +coefficient of expansion as platinum. A little globule +of this glass is sealed into the tube in such a way that +it joins the platinum to the glass of the tube. To do +this, the small globule of special glass is fused on the +platinum wire at the proper point and the tube into +which the wire is to be sealed is heated and a small tail +drawn out at the point where the wire is to be inserted. +The lump of the special glass should be from <span style="font-size: 0.8em"><sup>3</sup></span>⁄<span style="font-size: 0.6em;">32</span> to +<span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">8</span> inch in diameter, and the tail drawn on the tube +should have a slightly less diameter at the point (about +<span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">8</span> inch or less from the tube) where it is cut off. There +are now two ways of sealing in the wire. (1) The wire +with the globule of glass is placed inside the tube and +the latter revolved until the end of the wire sticks out +of the cut tail (<i>a</i>, Fig. 18). The latter is now gently +heated, and the two glass surfaces fused together, taking +care to use only the end of the hissing flame, if the special +glass contains lead. (See Chapter I, page 1.) The +whole circumference of the tube is then heated and annealed +carefully. (2) The end of the wire which is to +be outside the tube is attached to the end of a thin scrap<span class="pagenum"><a name="Page_54" id="Page_54">[Pg 54]</a></span> +of glass, by heating the glass and thrusting the wire into +it a very little way. Using this piece of glass as a handle, +the wire is inserted in the cut tail (<i>b</i>, Fig. 18) and the +globule brought near to the end of the tail. (If the main +tube is cold, it must of course first be warmed.) With +the end of the hissing flame, as in the first method, the +globule of glass is melted and the end of the tail softened. +The wire is now pushed into place, the handle removed +by heating the end and withdrawing it, and the tail reheated +a little if necessary to make it shrink back into +line with the walls of the tube. The whole circumference +of the tube is heated at that point and annealed as +usual.<br /><br /></p> + +<div class="figcenter" style="width: 400px;"> +<img src="images/i061.png" width="400" height="249" alt="" title="" /> +<span class="caption">Fig. 18.</span> +<br /><br /></div> + +<p>The use of this special glass is not absolutely necessary +if the platinum wire is small (<span style="font-size: 0.8em"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">4</span> millimeter or less in +diameter), and in fact it is often better in such cases +not to use it, unless the apparatus is to be subjected to +a very high vacuum. On small tubes, especially, it is +undesirable to use the special glass, as a lump of it will +usually cause the tube to crack on cooling. When such +glass is not at hand or is not to be used, the procedure +is altered somewhat. The tail which is drawn out is +very fine, having only a sufficient diameter so that when +it is cut off the wire can be inserted in it. Such a fine +tail is readily made by heating a small spot on the tube, +touching it with a warm platinum wire, removing from +the flame and drawing out the tail with the wire. After +cutting off the tail the wire is inserted in it, being held +on a scrap of glass as in the previous case, and the wire +and tail heated until the latter shrinks back into line +with the walls of the tube. If too great shrinkage occurs, +the place may be blown out gently after reheating. +Thus the wire is sealed through the wall of the tube without +changing the thickness of the latter, and consequently +without developing undue stresses at that point. Such<span class="pagenum"><a name="Page_55" id="Page_55">[Pg 55]</a></span> +a joint must of course be carefully reheated and annealed. +With fine platinum wire there is very little +risk of the tube cracking if care is taken to avoid formation +of any lump and to reheat the whole circumference +of the tube at that point.</p> + +<p>Any glass adhering to the end of the platinum wire, +where the scrap of glass was sealed on for a handle, may +be removed when the glass has cooled by crushing it +carefully with a pair of pliers.</p> + + +<h4>SEALING VACUUM TUBES</h4> + +<p>Tubes which have been evacuated usually are sealed +off while they are still connected to the vacuum pump. +The connection should be through a small, rather +thick-walled tube. When this is to be sealed, it is slowly +heated toward the softening point. As the glass just +begins to soften, the air-pressure will force it in, and +care must be taken that the softening is uniform over +the whole circumference of the tube. As the shrinking +goes on, the tube is gently drawn out to make a thick-walled +cone at that place, and the end is drawn off as +soon as the tube is sealed. The principal point to be +guarded is the thickness of the walls of the cone, and +uniform heating. A thin place or a hot place will give +way under the air-pressure and be sucked into the tube.</p> + + +<h4>CLOSED TUBES FOR HEATING UNDER PRESSURE</h4> + +<p>(<i>Carius method for determination of the halogens and +sulphur.</i>) In this case the tubing used must have thick +walls (usually about <span style="font-size: 0.8em"><sup>3</sup></span>⁄<span style="font-size: 0.6em;">32</span> inch) to withstand the pressure. +Its external diameter is usually about <span style="font-size: 0.8em"><sup>3</sup></span>⁄<span style="font-size: 0.6em;">4</span> inch. One +length will usually make two tubes of standard length +for the cannon furnace. Especial care must be taken in +heating and cooling it on account of the thick walls. A<span class="pagenum"><a name="Page_56" id="Page_56">[Pg 56]</a></span> +length is gradually warmed in the center, finally heated +at that point until soft, drawn out, cut apart and annealed. +Taking one of the pieces, the cone is carefully +heated and shrunk, as in Exercise 4, until its walls are +as thick as those of the main tube. A flame with a little +tinge of yellow should be used for this operation to prevent +devitrification (page 2), as the thick glass shrinks +slowly. The tail is now drawn off and the whole end +heated and gently blown several times to make a rounded +end, like a test-tube, with walls as thick as those of the +main tube. This must be carefully annealed. It is +more important that the walls be thick than that the end +be nicely rounded: it may indeed be left somewhat +conical in shape.</p> + +<p>At a point about two inches from the open end of the +tube, it is slowly warmed and finally heated to the +softening point. Grasping the open end with a pair of +crucible tongs, it is cautiously pulled out, a little at a +time, usually during rotation in the flame, to make a +constriction of moderate wall-thickness, but of sufficient +internal diameter to admit the tube containing the substance. +After annealing this, cooling and cleaning the +tube, the acid and salt are introduced (the former by +means of a long-stemmed funnel) and the tube is inclined +and rotated about its axis so that the acid wets +its surface about half way up from the bottom. The +substance is now weighed out in a piece of thin-walled +glass tubing, closed at one end, and about two inches long. +Inclining the large tube at a suitable angle, the small one +is introduced, closed end first, and allowed to slide down +the walls of the large tube until it reaches the place where +the acid has wet the tube. Here it will stop, and if the +tube is kept inclined during the rest of the operation it +will roll around inside the tube at this point and thus +not get down where any acid is likely to get into it and<span class="pagenum"><a name="Page_57" id="Page_57">[Pg 57]</a></span> +produce any pressure by decomposing it before the open +end of the tube is sealed. Now the tube is held in an +inclined position, taking care that the acid does not reach +up to the substance, the constricted portion cautiously +warmed and shrunk. It is finally shrunk and drawn out +into a somewhat elongated cone, with walls as thick as +the rest of the tube, and when this is accomplished the +end of the cone is sealed and the waste piece drawn off. +Anneal with great care, and cool in such a position that +the acid cannot reach the hot glass. The shrinking of +this cone takes a good deal of patience, and is one of the +most important parts of the process. If the walls are +left too thin, the tube may burst when heated, and the +whole labor is lost. If care is taken, the same tube can +be used for a number of determinations, until it becomes +quite short.</p> + + + +<hr style="width: 65%;"/> + +<p><span class="pagenum"><a name="Page_58" id="Page_58">[Pg 58]</a></span></p> + +<p> </p> + +<p><span class="pagenum"><a name="Page_59" id="Page_59">[Pg 59]</a></span></p> + +<h2>INDEX</h2> + +<p> +Annealing glass, <a href="#Page_4">4</a>, <a href="#Page_24">24</a>, <br /><br /><br /> + +Bellows, <a href="#Page_4">4</a>, <br /><br /> + +Bending glass, <a href="#Page_8">8</a>, <br /><br /> + +Blowing glass, <a href="#Page_13">13</a>, <a href="#Page_19">19</a>, <a href="#Page_20">20</a>, <a href="#Page_21">21</a>, <a href="#Page_24">24</a>, <a href="#Page_29">29</a>, <a href="#Page_31">31</a>, <br /> + with a rubber tube, <a href="#Page_22">22</a>, <br /><br /> + +Blowpipe, <a href="#Page_4">4</a>, <br /><br /> + +Bulb at end of tube, <a href="#Page_28">28</a>, <br /> + in middle of tube, <a href="#Page_32">32</a>, <br /> + very large, <a href="#Page_32">32</a>, <br /><br /> + +Bulbs, string of, <a href="#Page_33">33</a>, <br /><br /><br /> + +Capillary tube, drawing on larger tube, <a href="#Page_9">9</a>, <a href="#Page_54">54</a>,<br /> + tubing, working, <a href="#Page_43">43</a>,<br /><br /> + +Carius method, tubes for, <a href="#Page_55">55</a>,<br /><br /> + +Closed circuits of tubing, <a href="#Page_48">48</a>,<br /> + tubes, for heating under pressure, <a href="#Page_55">55</a>,<br /><br /> + +Collecting glass for bulb, <a href="#Page_29">29</a>, <a href="#Page_31">31</a>, <a href="#Page_32">32</a>,<br /><br /> + +Constricting a tube, <a href="#Page_10">10</a>,<br /><br /> + +Crystallization of glass, see Devitrification.<br /><br /> + +Cutting glass, <a href="#Page_7">7</a>, <a href="#Page_25">25</a>,<br /><br /><br /> + + +Devitrification, <a href="#Page_1">1</a>, <a href="#Page_2">2</a>,<br /><br /> + +Drawing out a tube, <a href="#Page_9">9</a>, <a href="#Page_18">18</a>, <a href="#Page_19">19</a>, <a href="#Page_27">27</a>,<br /><br /><br /> + + +Flanging a tube, <a href="#Page_11">11</a>, <a href="#Page_14">14</a>,<br /> + tool, <a href="#Page_11">11</a>,<br /><br /><br /> + + +Gas-washing tube, <a href="#Page_35">35</a>,<br /><br /> + +Glass, annealing, <a href="#Page_4">4</a>, <a href="#Page_24">24</a>,<br /><br /> + +Glass, bending, <a href="#Page_8">8</a>,<br /> + blowing, <a href="#Page_13">13</a>, <a href="#Page_19">19</a>, <a href="#Page_20">20</a>, <a href="#Page_21">21</a>, <a href="#Page_24">24</a>, <a href="#Page_29">29</a>, <a href="#Page_31">31</a>,<br /> + collecting for bulb, <a href="#Page_29">29</a>, <a href="#Page_31">31</a>, <a href="#Page_32">32</a>,<br /> + cutting, <a href="#Page_7">7</a>,<br /> + defects, <a href="#Page_2">2</a>,<br /> + grinding, <a href="#Page_47">47</a>,<br /> + hard, <a href="#Page_1">1</a>,<br /> + knife, <a href="#Page_7">7</a>,<br /> + lead, <a href="#Page_1">1</a>,<br /> + qualities desired, <a href="#Page_1">1</a>,<br /> + rod and tube, joining, <a href="#Page_45">45</a>,<br /> + rod, working, <a href="#Page_44">44</a>,<br /> + shrinking, <a href="#Page_18">18</a>, <a href="#Page_19">19</a>, <a href="#Page_22">22</a>, <a href="#Page_26">26</a>,<br /> + soft, <a href="#Page_1">1</a>,<br /> + working temperature, <a href="#Page_1">1</a>, <a href="#Page_13">13</a>, <a href="#Page_19">19</a>, <a href="#Page_27">27</a>,<br /><br /> + +Grinding stopcock or joint, <a href="#Page_47">47</a>,<br /><br /> + +Ground joints, <a href="#Page_51">51</a>,<br /><br /><br /> + + +Handle on stopcock, mending, <a href="#Page_45">45</a>,<br /><br /> + +Hard glass, <a href="#Page_1">1</a>,<br /><br /> + +Holding tube, <a href="#Page_13">13</a>, <a href="#Page_14">14</a>,<br /><br /><br /> + + +Insertion of tube through another, see Sealing a tube through another tube.<br /><br /><br /> + + +Joints, ground, <a href="#Page_51">51</a>,<br /><br /> + +Joining rod and tube, <a href="#Page_45">45</a>,<br /> + tubing end to end: first method, <a href="#Page_16">16</a>,<br /> + second method, <a href="#Page_20">20</a>,<br /><br /> +<span class="pagenum"><a name="Page_60" id="Page_60">[Pg 60]</a></span> + +Joining tubes of different diameters, <a href="#Page_25">25</a>,<br /> + a new tube to a stopcock, <a href="#Page_48">48</a>,<br /><br /><br /> + + +Kjeldahl trap, <a href="#Page_41">41</a>,<br /><br /><br /> + + +Lead glass, <a href="#Page_1">1</a>,<br /><br /> + +Lump of glass, removed, <a href="#Page_18">18</a>, <a href="#Page_19">19</a>, <a href="#Page_20">20</a>, <a href="#Page_21">21</a>, <a href="#Page_24">24</a>, <a href="#Page_26">26</a>, <a href="#Page_30">30</a>, <a href="#Page_38">38</a>,<br /><br /><br /> + + +Platinum wires, sealed into glass, <a href="#Page_1">1</a>, <a href="#Page_52">52</a>,<br /><br /> + +Position for glass-working, <a href="#Page_5">5</a>,<br /><br /> + +Pressure, tubes for heating under, <a href="#Page_55">55</a>,<br /><br /><br /> + + +Quality of glass, <a href="#Page_1">1</a>,<br /><br /><br /> + + +Rod, glass, working, <a href="#Page_44">44</a>,<br /><br /> + +Rotation of the tube, <a href="#Page_13">13</a>, <a href="#Page_19">19</a>,<br /><br /> + +Rounded end of tube, <a href="#Page_35">35</a>, <a href="#Page_38">38</a>,<br /><br /> + +Rubber tube used for blowing, <a href="#Page_22">22</a>,<br /><br /><br /> + + +Sealing a tube through another tube, <a href="#Page_35">35</a>, <a href="#Page_39">39</a>,<br /><br /> + +Sealing vacuum tubes, <a href="#Page_55">55</a>,<br /><br /> + +Shrinking glass, <a href="#Page_18">18</a>, <a href="#Page_19">19</a>, <a href="#Page_22">22</a>, <a href="#Page_26">26</a>, <a href="#Page_31">31</a>,<br /><br /> + +Side tube, blowing, <a href="#Page_22">22</a>, <a href="#Page_25">25</a>,<br /><br /> + +Soda glass, <a href="#Page_1">1</a>,<br /><br /> + +Soft glass, <a href="#Page_1">1</a>,<br /><br /> + +Spirals, making, <a href="#Page_50">50</a>,<br /><br /> + +Stopcocks, mending, <a href="#Page_45">45</a>,<br /><br /> + +Suction pump, <a href="#Page_39">39</a>, <a href="#Page_42">42</a>,<br /><br /> + +Sulphur dioxide tube, <a href="#Page_28">28</a>,<br /><br /><br /> + + +"Tail" of glass, drawing out, <a href="#Page_9">9</a>, <a href="#Page_54">54</a>,<br /> + removed, <a href="#Page_30">30</a>, <a href="#Page_35">35</a>,<br /><br /> + +Tubes, closed, for heating under pressure, <a href="#Page_55">55</a>,<br /><br /> + +"Tee" tube, <a href="#Page_22">22</a>,<br /> + on capillary tubing, <a href="#Page_43">43</a>,<br /> + small side tube on a large tube, <a href="#Page_24">24</a>,<br /><br /><br /> + + +Vacuum tubes, sealing, <a href="#Page_55">55</a>,<br /><br /><br /> + + +Working temperature of glass, <a href="#Page_1">1</a>, <a href="#Page_13">13</a>, <a href="#Page_19">19</a>, <a href="#Page_27">27</a>,<br /> +</p> + + + + + + + + +<pre> + + + + + +End of the Project Gutenberg EBook of Laboratory Manual of Glass-Blowing, by +Francis C. 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Frary + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: Laboratory Manual of Glass-Blowing + +Author: Francis C. Frary + +Release Date: September 22, 2009 [EBook #30066] + +Language: English + +Character set encoding: ASCII + +*** START OF THIS PROJECT GUTENBERG EBOOK LABORATORY MANUAL OF GLASS-BLOWING *** + + + + +Produced by Woodie4 and the Online Distributed Proofreading +Team at https://www.pgdp.net. (This file was produced from +images generously made available by The Internet +Archive/American Libraries.) + + + + + + + + + + LABORATORY MANUAL + + OF + + GLASS-BLOWING + + + + + McGraw-Hill Book Company + + _Publishers of Books for_ + + + Electrical World + Engineering Record + Railway Age Gazette + Signal Engineer + Electric Railway Journal + Metallurgical and Chemical Engineering + The Engineering and Mining Journal + Engineering News + American Machinist + American Engineer + Coal Age + Power + + + + + LABORATORY MANUAL + OF + GLASS-BLOWING + + BY + FRANCIS C. FRARY, PH. D. + + ASSISTANT PROFESSOR OF CHEMISTRY + UNIVERSITY OF MINNESOTA + + McGRAW-HILL BOOK COMPANY, INC. + 239 WEST 39TH STREET, NEW YORK + 6 BOUVERIE STREET, LONDON, E. C. + + 1914 + + + + + COPYRIGHT, 1914, BY THE + McGRAW-HILL BOOK COMPANY, INC. + + + + +PREFACE + + +The purpose of this little book is to provide a clear and detailed +discussion of the elements of glass-blowing. Many laboratories in this +country, especially in the west, are located a long way from any +professional glass-blower, and the time and money spent in shipping +broken apparatus several hundred miles to be mended could often be saved +if some of the laboratory force could seal on a new stopcock, replace a +broken tube, or make some temporary repairs. Many men in physical or +chemical laboratories have occasion to modify some piece of apparatus +designed perhaps for other uses, or to design new apparatus. To such +also, the ability to perform some of the operations herein described may +be very valuable. + +No originality is claimed for the methods here described. They are those +which the author has found most suitable and convenient in his own work, +and most easily learned by students. The aim has been to describe each +operation in such detail that a beginner can follow the process without +help and, with practice, attain satisfactory results. It is, however, +much easier to perform any of the operations described, after seeing +some one else perform it correctly; since the temperature, the exact +time to begin blowing the glass, and many other little details are very +difficult to obtain from a description. + +It has not been thought worth while to describe the process of making +stopcocks, thermometers, vacuum tubes, etc., as such things can be +purchased more cheaply and of much better quality than any amateur can +make unless he is willing to spend a very large amount of time in +practice. For similar reasons the manipulation of quartz glass has been +omitted. + +The author will be grateful for all suggestions and criticisms tending +to improve the methods presented. If some of them appear to be given in +excessive detail, the reader will remember that many things which are +obvious to the experienced worker are not so to the beginner, and that +it is the little details in the manipulation which often spell success +or failure in glass-blowing. + + F. C. F. + +MINNEAPOLIS, MINN., +_January, 1914._ + + + + + CONTENTS + + + + PAGE + + Preface v + + + CHAPTER I + + MATERIALS AND APPARATUS 1 + + Varieties and defects of glass--Devitrification--Annealing + glass--Blowpipe and bellows--Light--Arrangement of exercises. + + + CHAPTER II + + GENERAL OPERATIONS 7 + + Cutting, bending, constricting and flanging the tubing--Methods + of rotation and blowing. + + + CHAPTER III + + ELEMENTARY EXERCISES 16 + + Joining two pieces of tubing of the same diameter--The "tee" + tube--Joining two tubes of different diameters--Blowing bulbs. + + + CHAPTER IV + + ADVANCED EXERCISES 35 + + Sealing a tube through another tube: The gas-washing tube, suction + pump, and Kjeldahl trap. + + + CHAPTER V + + MODIFIED METHODS AND SPECIAL OPERATIONS 43 + + Capillary tubing--Glass rod--Mending stopcocks--Closed circuits of + tubing--Spirals--Ground joints--Sealing in platinum wire--Sealing + vacuum tubes--Closed tubes for heating under pressure. + + + INDEX 59 + + + + +LABORATORY +MANUAL OF GLASS-BLOWING + + + + +CHAPTER I + +MATERIALS AND APPARATUS + + +One of the most important factors in the success of any piece of +glass-blowing is the glass employed. As is well known, there are two +general varieties of glass: Lead glass and soda glass. Formerly much +apparatus was made of lead glass, but at present it is very seldom met +with, except in the little drops of special glass used to seal platinum +wires into the larger sizes of tubes. Lead glass is softer and more +readily fusible than soda glass, but has the disagreeable property of +growing black in a few seconds unless worked in a strong oxidizing +flame. This may be prevented by using a "hissing" flame, with a large +excess of air, and working in the extreme end of the flame; or the black +lead formed may thus be reoxidized, and the glass restored to its +original clearness. + +Almost all the soft glass on the market is a soda glass, although +sometimes part of the soda is replaced by potash. Most of the hard glass +appears to be a potash glass. The following qualities are desirable in a +glass for ordinary working: (1) moderately low working temperature, (2) +freedom from air bubbles, striations and irregularities, (3) proper +composition, so that the glass will not devitrify or crystallize while +being handled at its working temperature, (4) ability to withstand rapid +heating without cracking. + +The working temperature of different samples of so-called "soft glass" +varies a good deal, and is best determined by trial. The glass should +become almost soft enough for blowing in a flame that still shows a +little yellow near the tip, so that at the highest temperature of the +flame it may flow fairly freely and thus easily eliminate irregularities +in thickness. If the glass is too hard, the shrinking of the glass, +collection of material for a bulb, and in fact most of the working +processes will be slower, and the glass will not stay at its working +temperature long enough after its removal from the flame to permit it to +be properly blown. + +Air bubbles in the original batch of glass are drawn out into long +hair-like tubes during the process of manufacture. When such tubing is +worked, the walls of these microscopic tubes collapse in spots, and the +air thus enclosed will often collect as a small bubble in the wall, thus +weakening it. Irregularities are of various kinds. Some of the larger +sizes of thin-walled tubing often have one half of their walls much +thicker than the other, and such tubing should only be used for the +simplest work. Some tubing has occasional knots or lumps of unfused +material. The rest of the tube is usually all right, but often the +defective part must be cut out. The presence of striations running along +the tube is generally an indication of hard, inferior glass. Crookedness +and non-uniformity of diameter are troublesome only when long pieces +must be used. + +Devitrification is one of the worst faults glass can possibly have. It +is especially common in old glass, and in glass which has contained +acids. It seems to be of two sorts. One variety manifests itself on the +surface of the glass before it reaches its working temperature, but if +the glass be heated to the highest temperature of the flame it will +disappear except in the portion at the edge of the heated part. The +glass seems to work all right, but an ugly crystallized ring is left at +the edge of the portion heated. This kind appears most frequently in old +glass which was originally of good quality, but has in time been +superficially altered, probably by the loss of alkalies. The other +variety of devitrification does not appear when the glass is first +heated; but after it has been maintained at or above its working +temperature for a longer or shorter time, it will be noticed that the +outer surface has lost its smoothness, and appears to be covered with +minute wrinkles. It will also be found that the glass has become harder, +so that it becomes impossible to work it easily. Further heating only +makes the matter worse, as does the use of a higher temperature from the +start. In fact it will often be found that a piece of comparatively soft +glass which devitrifies almost at once in a "hissing" flame can be +worked without serious difficulty if care be taken to use a flame still +decidedly tinged with yellow. Even good glass will begin to devitrify in +this way if heated too long at the highest temperature of the flame, so +care should always be taken (1) _to reduce the time of heating of any +spot of glass to a minimum_; _i.e._, get the desired result at the first +attempt, if possible, or at least with the minimum of reheating and +"doctoring," and (2) _avoid keeping the glass at the highest temperature +of the flame any longer than necessary_. This may be accomplished by +doing all heating, shrinking, etc., of the glass in a flame more or less +tinged with yellow, and only raising the temperature to the highest +point when ready to blow the glass. This kind of devitrification is +apparently due to volatilization of the alkalies from the glass in the +flame, and it is said that it can be partly remedied or prevented by +holding a swab of cotton saturated with a strong solution of common salt +in the flame from time to time as the glass is heated. + +The toughness of glass, _i.e._, its ability to withstand variations of +temperature, depends on its composition and the care taken in its +annealing. In general, large pieces of glass should be heated very +slowly in the smoky flame, and the larger the diameter of the tube the +greater the length which must be kept warm to prevent cracking. All +large pieces should be carefully heated over their whole circumference +to the point where the soot deposit burns off, before being finally +cooled. After being thus heated they are cooled in a large smoky flame +until well coated with soot, then the flame is gradually reduced in size +and the object finally cooled in the hot air above it until it will not +set fire to cotton. If thought necessary, it may then be well wrapped in +cotton and allowed to cool in the air. If not properly annealed the +place heated may crack spontaneously when cold, and it is quite certain +to crack if it is reheated later. + +Next in importance to the glass are the blow-pipe and the bellows. Any +good blast lamp, such as is ordinarily used in a chemical laboratory for +the ignition of precipitates, will be satisfactory; provided it gives a +smooth regular flame of sufficient size for the work in hand, and when +turned down will give a sharp-pointed flame with well-defined parts. +Where gas is not available, an ordinary gasoline blow-torch does very +well for all operations requiring a large flame, and a mouth blow-pipe +arranged to blow through a kerosene flame does well for a small flame. +Several dealers make blow-torches for oil or alcohol which are arranged +to give a small well-defined flame, and they would doubtless be very +satisfactory for glass-work. Any good bellows will be satisfactory if it +does not leak and will give a steady supply of air under sufficient +pressure for the maximum size of flame given by the lamp used. A bellows +with a leaky valve will give a pulsating flame which is very annoying +and makes good work very difficult. When compressed air is available it +can be used, but if possible it should be arranged so that the supply +can be controlled by the foot, as both hands are usually needed to hold +the work. For the same reason the supply of air is usually regulated by +varying the rate of operation of the bellows, rather than by adjusting +the valve of the blast-lamp. On the other hand, it will be found best to +always adjust the flow of the gas by means of the cock on the lamp, +rather than that at the supply pipe. The operator must have complete +control over the flame, and be able to change its size and character at +short notice without giving the work a chance to cool, and often without +ceasing to support it with both hands. + +Glass-blowing should be done in a good light, but preferably not in +direct sunlight. The operator should be seated in a chair or on a stool +of such a height that when working he may comfortably rest one or both +elbows on the table. The comfort of the operator has a decided influence +on the character of his work; especially in the case of a beginner, who +often defeats his purpose by assuming uncomfortable and strained +positions. Steadiness and exact control of both hands are essential in +most operations; any uncomfortable or strained position tires the +muscles and weakens the control of the operator over them. + +In the arrangement of the exercises here presented, several factors have +been considered. It is important that the first exercises be simple, +although not necessarily the simplest, and they should teach the +fundamental operations which will be used and amplified later. They +should in themselves be things which are of importance and commonly used +in glass-work, and they should be so arranged that the fundamental +points, such as the rotation of glass, the proper temperature, blowing +and shrinking the glass may be learned with a minimum expenditure of +time, glass and gas. It is therefore recommended that the beginner take +them up in the order given, at least as far as No. 7, and that each be +mastered before attempting the next. The beginner should not leave the +first exercise, for example, until he can join together two pieces of +tubing so that they form one piece of substantially uniform inner and +outer diameter, and without thick or thin spots. From two to four +practice periods of two hours each should suffice for this. This chapter +and the following one should also be frequently read over, as many of +the points discussed will not be understood at first and many of the +manipulations described will not be necessary in the simpler exercises. + + + + +CHAPTER II + +GENERAL OPERATIONS + + +=Cutting the Glass.=--For this purpose a "glass-knife" is preferred to a +file, if the glass is cold: if it is hot a file must always be used, and +its edge slightly moistened to prevent drawing the temper. The +glass-knife is simply a flat piece of hard steel, with the edges ground +sharp on an emery wheel. The bevel of the edge should be from 30 to 60 +degrees. An old flat file can easily be ground into a suitable knife. +The glass-knife makes a narrower scratch than the file but appears more +likely to start the minute crack which is to cause the tube to break at +that point, and the break is more likely to give a good square end. The +scratch should be made by passing part of the knife or file once across +the glass, never by "sawing" the tool back and forth. This latter +procedure dulls the tool very quickly. + +In breaking a piece of glass tubing, many persons forget that it is +necessary to _pull_ the ends apart, as well as to bend the tube very +_slightly_ in such a direction as to open up the minute crack started in +the scratch. Care in breaking the tube is essential, as it is impossible +to do as good work with uneven ends as with square ones. + +When tubing of large diameter or thin wall is to be cut, it is often +better not to attempt to break it in the usual way, but to heat a very +small globule of glass (1/16 to 1/8 inch diameter) to red heat, and +touch it to the scratch. This will usually start the crack around the +tube; if it has not proceeded far enough, or has not gone in the +desired direction, it may be led along with a hot point of glass. This +is put a little beyond the end of the crack, and as the latter grows out +toward it, moved along the path where the crack is desired. This point +of glass is also very useful in breaking off very short ends of tubes, +where there is not room to get a firm enough hold and sufficient +leverage to break the tube in the ordinary way, and for breaking tubes +attached to large or heavy objects, which would be likely to make +trouble if treated in the ordinary way. + +Another way of cutting large tubing, especially if it has rather thick +walls, is to make a scratch in the usual way, and then turn on the +smallest and sharpest possible flame of the blast lamp. The tube is next +taken in both hands and held horizontally above the flame so that the +scratch is exactly over it. The tubing is now rotated rapidly about its +axis, and lowered so that the flame is just tangent to its lower side. +After about ten seconds of heating, it is removed from the flame and the +hot portion quickly breathed upon, when it will generally crack apart +very nicely. Care must be taken to hold the tube at right angles to the +flame during the heating, and to rotate it so that only a narrow strip +of the circumference is heated, and the scratch should be in the center +of this heated strip. By this means tubing as large as two inches in +diameter is readily broken. + +Griffin's glass cutter, which contains a hardened steel wheel, like that +on any ordinary window-glass cutter, and a device by which this can be +made to make a true cut clear around the tube, is a very handy article, +especially for large tubing, and may be obtained from any dealers in +chemical apparatus. + +=Bending Glass.=--Inasmuch as this is one of the commonest operations in +the laboratory, it is assumed that the reader knows how to perform it. +However, it should be noted that in order to obtain the best results a +broad (fish-tail burner) flame should generally be used, and the tube +rotated on its axis during the heating, and allowed to bend mostly by +its own weight. If large tubing is to be bent, one end must be stoppered +and great care used. Whenever the tube shows signs of collapsing or +becoming deformed, it must be gently blown out into shape, heating the +desired spot locally if necessary. A blast-lamp is likely to be more +useful here than the fish-tail burner. + +=Drawing Out a Tube.=--Most students learn this the first day of their +laboratory work in chemistry, but few take pains to do it well. The tube +should be heated in the flame of a Bunsen burner, or blast lamp +(preferably the latter) until it is very soft. During this time it must +be continuously rotated about its axis, and so held that the edges of +the heated zone are sharply defined; _i.e._, it should not be allowed to +move back and forth along its own axis. When so hot that it cannot +longer be held in shape, the tube is removed from the flame, and the +ends slowly and regularly drawn apart, _continuing the rotation of the +tube about its axis_. By regulating the rate of drawing and the length +of tube heated, the desired length and diameter of capillary may be +obtained. The tube should always be rotated and kept in a straight line +until the glass has set, so that the capillary may have the same axis as +the main tube. This capillary or "tail" is often a very necessary handle +in glass-blowing, and if it is not straight and true, will continually +make trouble. + +In drawing out very large tubing, say from one to two inches in +diameter, it is often necessary to draw the tube _in the flame_, +proceeding very slowly and at a lower temperature than would be used +with small tubing. This is partly on account of the difficulty of +heating large tubing uniformly to a high temperature, and partly in +order to prevent making the conical part of the tube too thin for +subsequent operations. + +=Constricting a Tube.=--Where a constriction is to be made in a tube, +the above method must be modified, as the strength of the tube must be +maintained, and the constricted portion is usually short. Small tubes +are often constricted without materially changing their outside +diameter, by a process of thickening the walls. The tube is heated +before the blast lamp, rotating it about its axis as later described, +and as it softens is gradually pushed together so as to thicken the +walls at the heated point, as in _a_, Fig. 1. When this operation has +proceeded far enough, the tube is removed from the flame, and the ends +cautiously and gently drawn apart, continuing the rotation of the tube +about its axis and taking care not to draw too rapidly at first. The +resulting tube should have a uniform exterior diameter, as shown in _b_, +Fig. 1. + +[Illustration: FIG. 1.--Constricting a tube.] + +This method of constriction is not suited to tubes much over 1/4 inch in +diameter, since the mass of glass in the constricted part becomes so +thick as to be difficult to handle when hot, and likely to crack on +cooling. Larger tubes are therefore constricted by heating in a narrow +flame, with constant rotation, and when soft, alternately gently pulling +the ends apart and pushing them together, each motion being so regulated +that the diameter of a short section of the tube is gradually reduced, +while the thickness of the wall of the reduced portion remains the same +as that of the rest of the tube, or increases only slightly. This +pulling and pushing of the glass takes place _in the flame_, while the +rotation is being continued regularly. The result may appear as +indicated in _c_, Fig. 1. The strength of the work depends upon the +thickness of the walls of the constricted portion, which should never be +less than that in the main tube, and usually a little greater. This +operation is most successful with tubing having a relatively thin wall. + +=Flanging a Tube.=--This operation produces the characteristic flange +seen on test-tubes, necks of flasks, etc., the object being twofold: to +finish the end neatly and to strengthen it so that a cork may be +inserted without breaking it. This flanging may be done in several ways. +In any case the first operation is to cut the tube to a square end, and +then heat this end so that the extreme sixteenth or eighth of an inch of +it is soft and begins to shrink. The tube is of course rotated during +this heating, which should take place in a flame of slightly greater +diameter than the tube, if possible. The flange is now produced by +expanding this softened part with some suitable tool. A cone of charcoal +has been recommended for this purpose, and works fairly well, if made so +its height is about equal to the diameter of its base. The tube is +rotated and the cone, held in the other hand, is pressed into the open +end until the flange is formed. A pyramid with eight or ten sides would +probably be better than the cone. + +[Illustration: FIG. 2.--Flanging tool.] + +A better flanging tool is made from a triangular piece of copper or +brass, about 1/16 inch thick, and mounted in a suitable handle. Such a +tool is shown in Fig. 2, being cut from a sheet of copper and provided +with a handle made by wrapping asbestos paper moistened with sodium +silicate solution about the shank of the tool. It is well to have +several sizes and shapes of these tools, for different sizes of tubing. +The two sizes most used will be those having about the following +dimensions: (1) _a_ = 2 inches, _b_ = 1 inch; (2) _a_ = 1 inch, _b_ = 1 +inch. When the end of the tube is softened, the tool is inserted at an +angle, as indicated in Fig. 3, and pressed against the soft part, while +the tube is quickly rotated about its axis. If the flange is +insufficient the operation may be repeated. The tool should always be +warmed in the flame before use, and occasionally greased by touching it +to a piece of wax or paraffin. After the flange is complete, the end +must be heated again to the softening temperature and cooled slowly, to +prevent it from cracking. + +[Illustration: FIG. 3.--Flanging a tube with flanging tool.] + +[Illustration: FIG. 4.--Flanging a tube with carbon rod or wire.] + +Some glass-blowers use a small carbon rod, about 3/16 inch in diameter, +as a flanging tool for tubes larger than about 3/8 inch diameter, and a +small iron wire or similar piece of metal for smaller tubes. In this +case the tube is heated as above described, and the rod or wire inserted +in the end at an angle and pressed against the softened part, as +indicated in Fig. 4, while the tube is rotated about its axis. For +large heavy tubes a larger carbon would be used. + +=Rotation of the Tube.=--This is the fundamental manipulation in +glass-blowing, and upon it more than all else depends the uniformity and +finish of the work, and often the possibility of accomplishing the work +at all. Directions for it will be given on the assumption that the +reader is right-handed; if otherwise, the position of the hands is of +course reversed. The object of rotation is to insure even heating of the +whole circumference of the tube at the point of attack, to equalize the +effect of gravity on the hot glass and prevent it from falling out of +shape when soft, and to keep the parts of the tube on each side of the +heated portion in the same straight line. + +In rotating the tube, both hands must be used, so that the two ends may +revolve at the same rate and the glass in the hot part not be twisted. +The rotation is performed by the thumb and first finger of each hand, +the other fingers serving to support the tube. As it is almost always +necessary to follow rotating and heating a tube by blowing it, the hands +should be so placed that it will be easy to bring the right-hand end up +to the mouth without shifting the hold on the glass. For this reason the +left hand grasps the glass with the palm down, and the right hand with +the palm turned toward the left. If there is any choice, the longer and +heavier part of the tube is usually given to the left hand, and it is +planned to blow into the shorter end. This is because it is easier to +support the tube with the hand which has the palm down. This support is +accomplished by bending the hand at the wrist so that it points slightly +downward, and then curling the second, third and little fingers in under +the tube, which is held between them and the palm. This support should +be loose enough so that the thumb and first finger can easily cause the +tube to rotate regularly on its axis, but firm enough to carry all the +weight of the tube, leaving the thumb and first finger nothing to do but +rotate it. The hand must be so turned, and the other fingers so bent, +that the thumb and first finger stretch out nearly to their full length +to grasp the tube comfortably. + +The right hand is held with the palm toward the left, the fingers except +the first slightly bent, and the tube held between the first finger and +the thumb while it rests on the second finger and that portion of the +hand between the base of the first finger and the thumb. Rotation of the +tube is accomplished by rolling it between the thumbs and first fingers: +the rotation being continued in the same direction regularly, and not +reversed. It is better to roll slowly and evenly, with a series of light +touches, each of which moves the tube a little, than to attempt to turn +the tube a half a revolution or so with each motion of the hands. The +hands must be held steady, and the tube must be under good control at +all times, so that both ends may be rotated at the same angular +velocity, even though they may be of different diameters, and the tube +be neither drawn apart nor pushed together unless such a motion is +expressly desired, as it sometimes is. The hot part of the glass must be +constantly watched to see that it is uniformly rotated and not twisted, +nor pulled out or pushed together more than is desired. Care must also +be taken to keep the parts of the tube in the same straight line, or as +near it as possible, during the heating and all other manipulations. + +When flanging a tube, it is held and rotated with the left hand as above +described, while the right hand holds the flanging tool. + +When part of the end of a tube must be heated, as in Exercise 6, and +rotation must be very carefully performed and continued during the +blowing, both hands are used. The right hand is held as above +described, and the left hand close to it and either as above described +or else with the palm toward the right, grasping the tube in the same +way as the right hand does. This puts both hands in a position where the +tube may be blown and rotated uniformly while its axis is kept +horizontal. + +Smoothness and exactness are the two things for which the beginner must +constantly strive in glass-blowing, and they are only attained by a +careful attention to the details of manipulation, with a steady hand and +watchful eye. Every move must count, and the exercise must be finished +with a minimum of reheating and retouching, for the best results. + + + + +CHAPTER III + +ELEMENTARY EXERCISES + + +EXERCISE NO. 1 + +JOINING TWO PIECES OF TUBING, END TO END--FIRST METHOD + +This exercise is most easily learned on tubing with an exterior diameter +of 1/4 inch, or a little less, having moderately heavy walls. A piece of +such tubing is heated before the blow-pipe at a point ten or twelve +inches from the end, and there drawn out to a capillary as previously +described (page 9). The capillary is sealed off about two inches from +the main tube, and the latter is cut near the middle. Care should be +taken to get square ends where the cut is made (page 7). The flame is +now so regulated that it is a little broader than the diameter of the +tube, the sealed half of the tube taken in the left hand and the other +half in the right. The open end of the sealed part and one of the ends +of the other part are now held in opposite sides of the flame, inclined +at a slight angle to one another as indicated in Fig. 5, and rotated and +heated until the surfaces of both ends are just softened. The two ends +are then carefully and quickly brought together (_a_, Fig. 6), removed +from the flame and pulled apart a little, to reduce the lump formed at +the joint as much as possible, as indicated in _b_. The joint is then +tested by blowing into the open end of the tube to see if it is tight. +If so, the flame is reduced to half or less than half of its former +size, and the joint heated in it, holding the tube and continually +rotating it as directed in the last chapter (page 13). + +[Illustration: FIG. 5.--Softening ends of two pieces of tubing.] + +[Illustration: FIG. 6.--Joining two pieces of tubing end to end--first +method.] + +As the tube softens and tends to shrink, the two ends are pressed +together a little and the walls allowed to thicken slightly, as in _c_. +It is then quickly removed from the flame and gently blown as indicated +in _d_, continuing the rotation of the tube during the blowing, and at +the same time pressing the ends of the tube together a little so as to +make a _short_ thick-walled bulb. The joint is then returned to the +flame and reheated, rotating as before, shrinking to about the shape of +_e_. When this stage is reached, the glass should be very hot and fluid, +and the mass of hot glass thick enough to remain at its working +temperature for about five seconds after removal from the flame. The +glass is now reblown as indicated in _f_, to form a bulb having walls of +practically the same thickness as the original tube. As soon as the bulb +is blown, the tube is removed from the mouth, held horizontally in front +of the worker, and gently drawn out to form one continuous tube, as +indicated in _g_. During both the blowing and drawing of this bulb the +rotation must be continued, and both blowing and drawing must be +carefully regulated so that the resulting tube may have the same +internal and external diameter at the joint as elsewhere. + +=Discussion.=--In making the original joint, (_a_, Fig. 6), care should +be taken that the lump formed is as small as possible so that it may be +entirely removed during the subsequent operations. For this reason, only +the very tip ends of the two pieces of tubing are held in the flame, and +the softening should not extend more than 1/16 inch down the tube. As +soon as the ends are sufficiently soft to stick together, they are made +to do so. The first drawing of the tube (_b_) should take place +immediately, and reduce the lump as much as possible without making the +adjacent walls of the tube thin. The whole purpose of the rest of the +manipulation is to absorb or "iron out" the lump at the joint. For this +reason, care is taken that this lump is always in the center of the +flame while the joint is being heated, and a small flame is used so +that little of the main tube may be softened. During the first shrinking +of the joint (_c_) the walls next the lump, being thinner than it is, +reach the softening temperature first and are thickened by the slight +pushing together of the ends, so that they taper from the lump to the +unchanged wall. Upon blowing this joint, these thickened walls blow out +with the lump, but as they are thinnest next the unchanged tube, they +stiffen there first. Then as the thicker parts are still hot, these blow +out more, and with the lump make a more or less uniform wall. By this +first operation most of the lump will have been removed, provided it was +not too large at first, and the tube was hot enough when it was blown. +Beginners almost invariably have the glass too cool here, and find +difficulty in blowing out a satisfactory bulb. Under such circumstances +the lump will be scarcely affected by the operation. + +During the shrinking of this bulb, the thinner parts of course are the +first to reach the softening point, and thus contract more than the +thick parts, so that practically all of the lump can be absorbed, and a +uniformly thickened part of the tube left as in _e_. When this is just +accomplished, the second bulb must be blown during one or two seconds, +and the tube then drawn out as described, so as to change the bulb to a +tube. The drawing must proceed with care: portions nearest the unchanged +tubes are the first to reach the proper diameter, and must be given time +to just set at that point before the center of the bulb is finally drawn +into shape. The drawing is perhaps best done intermittently in a series +of quick pulls, each drawing the tube perhaps 1/16 inch, and each taking +place as the thumbs and first fingers grasp the tube for a new turn in +the rotation. If the tube is not rotated during the blowing, the bulbs +will be lop-sided and it will be impossible to get a joint of uniform +wall-thickness; if rotation is omitted during the drawing, the tube +will almost invariably be quite crooked. + +If the lump still shows distinctly after the operations described, the +cross-section of the tube will be as in _h_, and the tube will be likely +to break if ever reheated at this point after it becomes cold. The +operations _d_, _e_, _f_, and _g_ may be repeated upon it, and it may be +possible to get it to come out all right. + +Care must be taken not to blow the bulbs _d_ and _f_ too thin as they +then become very difficult to handle, and the joint is usually spoiled. +The wall-thickness of these bulbs must never be much less than that of +the original tube. If the joint as completed has thinner walls than the +rest of the tube, it will be more easily broken. It should be remembered +that the length of the finished tube must be exactly the same as that of +the original piece, if the walls of the joint are to be of their +original thickness. Therefore the pushing together during the two +operations _c_ and _d_ must shorten the tube just as much as the final +drawing (_f_ to _g_) lengthens it. + +The interval between the removal of the work from the flame and the +beginning of the blowing must be made as short as possible, or else the +portions next the main parts of the tube will set before they can be +blown out, and cause irregular shrunken areas. + + +EXERCISE NO. 2 + +JOINING TWO TUBES END TO END--SECOND METHOD + +The method described in Exercise No. 1 is very satisfactory for joining +short lengths of straight tubing, but becomes inconvenient or impossible +when the pieces are long or bent, on account of the difficulty in +uniformly rotating such work. In such cases, this second method is +used. It does not usually give as smooth and pretty a joint as the first +method, and takes a little longer. + +The joint is begun exactly as in the first method, and the manipulation +is the same until after the preliminary tight joint (_b_, Fig. 6) is +made. The flame is reduced as usual, but instead of rotating the tube in +the flame, only one part of the circumference is heated, and this is +allowed to shrink thoroughly before blowing. It is then blown gently so +that it becomes a slight swelling on the tube, and the operation +repeated on an adjoining part of the joint. Three or four repetitions of +the operation will usually cover the whole circumference of the joint, +in a small tube, the result being a swelling roughly similar to the +first thick bulb in the first method (_d_, Fig. 6). If all the lumps of +the original joint have not been removed by this operation, it may now +be repeated upon such parts as may require it. The thickness of the wall +in the bulb should be about the same as that in the original tube. The +whole of the expanded joint is now heated as uniformly as may be until +soft enough so that it begins to shrink a little, and the swelling is +gently drawn down to the same diameter as the main tube, as in the first +case. Any irregularities in the finished joint may be corrected by local +reheating, shrinking or blowing as required. + +=Discussion.=--In using this method, especially with larger sizes of +tubing, it is very important to keep the whole circumference of the +joint hot enough during the operation so that it does not crack apart at +the part which has not yet been worked. For that reason the first +heating, shrinking and blowing should be performed as quickly as +possible, leaving the resulting irregularities to be corrected later, +rather than attempting to reblow the same part of the joint several +times in succession until it is satisfactory. Care must be taken in this +as in the first method that the blowing follows immediately upon the +completion of the shrinking and removal of the object from the flame: +delay in blowing will cause shrunken places where the joint meets the +original tubes, on account of the cooling and setting of the glass +before it was blown. Most beginners err in being afraid to shrink the +part of the joint enough before blowing it. On small tubing, the +shrinkage may often extend so far that the inner surface of the shrunken +part reaches the center of the tube. Insufficient shrinking results in +failure to remove the lump formed at the original joint. It is often of +advantage, after blowing out part of the joint, to allow that part a few +seconds to set before going on with the rest, keeping the whole joint +warm meanwhile in or near the smoky flame. This helps to prevent the +twisting of the joint, or other distortion incident to the handling of a +piece of work of awkward shape. + +In making a joint on a very long or heavy piece by this method, it is +often advantageous to attach a piece of rubber tubing to the open end, +hold the other end of this tubing in the mouth during the process, and +blow through it, rather than attempt to bring the end of the glass up to +the mouth. This enables one to keep closer watch on the joint, and avoid +drawing it out or distorting it in handling. On the other hand, the +rubber tube is an inconvenience on account of its weight and the +consequent pull on the end of the apparatus, and makes rotation +difficult. + + +EXERCISE NO. 3 + +THE "TEE" TUBE + +The operations involved are two: the blowing of a short side tube on a +piece of tubing, and sealing another piece of tubing on this, by what is +essentially the second method as just described. + +[Illustration: FIG. 7.--The "tee" tube.] + +The two pieces of tubing to be used each have one end cut square and the +other sealed in the usual manner. The longer of the two is now heated at +the point at which the joint is to be made, until it begins to color the +flame. A small flame is used, and the tube rotated until the flame +begins to be colored, when the rotation is stopped, and only one spot +heated until a spot the diameter of the tube to be sealed on has become +red hot and begun to shrink. This is now gently blown out into a small +bulb, as in _a_, Fig. 7, and it will be noted that this bulb will have +walls tapering from the thick walls of the tube to a very thin wall at +the top. The sides of this bulb, below the dotted line, are to form the +small side tube to which the main side tube is to be sealed. The top of +the bulb is now softened by directing a small flame directly upon it, +and as soon as it shrinks to the level indicated by the dotted line, it +is removed from the flame and quickly blown out to form a thin bulb, as +indicated in _b_, Fig. 7. This will usually be so very thin that a +stroke of the file or glass-knife will break it off at the dotted line, +leaving the side tube, to which the short piece of tubing is now sealed +according to the second method (Exercise No 2). In doing this, care is +taken to direct the flame partly on the main tube in the two crotches, +so that both tubes blow out a little and give space for the gases to +turn in, as indicated in _c_, Fig. 7, and at the same time increase the +mechanical strength of the job. On the other hand, care is taken not to +deform the main tube, and not to produce such a bulge or bulb at the +joint as will prevent the finished tube from lying flat on a table. + +=Discussion.=--Most beginners tend to err in the first steps of this +operation, by blowing too hard and too long when blowing out the little +bulb. The result is a large, very thin bulb, which breaks off in such a +way as to leave a hole in the main tube, occupying nearly half the +circumference of the tube at that point, instead of the neat side tube +which they should have. It is not difficult to seal a tube on this side +tube, but it is very difficult to seal a tube into a hole in another +tube. Care should be taken here, as in the two previous exercises, that +the lump obtained at the joint when the two tubes are put together is +made as small as possible, and reduced if possible by gently drawing on +the side tube as soon as the tubes have actually joined. It is much +easier to prevent the formation of a lump at the joint than it is to +remove the lump after it is formed. The remarks previously made about +blowing quickly after removing the work from the flame apply here with +especial force. A "tee" tube, from its very nature, is exposed to a good +many strains, so care must be taken that the walls of the joint are of +uniform thickness with the rest of the tube. + +The beginner will find it easiest to make this tube out of two pieces of +the same tube, about 1/4 inch in diameter. Larger or smaller tubing is +usually more difficult. If tubing much more than 1/4 inch is used, the +whole joint, including part of the main tube, must be heated nearly to +the softening point at the close of the operation, and well annealed, as +described in Chapter 1 (page 3) or it will be almost certain to crack. +In the larger sizes of tube it will be necessary to heat the whole +circumference of the main tube frequently during the operation, to +prevent it from cracking. + +In sealing a small tube on the side of a large one, it is usually +advisable, after warming the spot where the joint is to be made, to +attach a small drop of glass to the tube at that point, and direct the +flame upon that, thus supplying at the same time both a definite point +to be heated and an extra supply of glass for the little side tube which +is desired. In this way it is also easier to blow out a side tube with a +sufficiently small diameter. If the diameter of this tube should be much +greater than that of the small tube, the latter may be enlarged with a +carbon or a flanging tool. + + +EXERCISE NO. 4 + +TO JOIN TWO TUBES OF DIFFERENT DIAMETERS + +In this case the first method (Exercise No. 1) is to be used whenever +possible, as it gives a much smoother joint than the second method. The +directions given will describe the adaptation of this method to the +problem: if the second method must be used on account of awkward shape, +etc., of the work, the modifications required will be obvious to any one +who has learned to make the joint by the first method. + +After sealing or corking one end of the larger tube, the other end is +drawn out to form a tail as described on page 9, taking care to have the +tube uniformly heated, and to draw the tail rapidly enough so that the +cone is short, as indicated in _a_, Fig. 8. The tube is now rotated, a +small flame directed against the cone at right angles to an element of +it, and it is allowed to shrink a little, as indicated in _b_, Fig. 8, +so that its walls will thicken. When the tail is cut off, at the dotted +line, the diameter of the opening and the thickness of the walls at that +point should correspond with the dimensions of the tube to be sealed on. +As the glass is hot, the scratch for cutting it must be made with a file +(moisten the edge!), and it often will not break square across. Before +proceeding to seal on the small tube, any large projections on the cut +end are best removed, by warming the cut surface a little, directing the +small flame upon each projection in turn and touching it with a warm +scrap of glass. It will adhere to this and may then be removed by +rotating this scrap a little so as to wind up the projection on it, and +then drawing it off, while the flame is still playing on the spot. This +must be done rapidly and care taken not to soften the main part of the +cone. + +[Illustration: FIG. 8.--Joining two tubes of different diameters.] + +The large tube is now taken in the left hand, the small one in the +right, the ends heated and joined in the usual manner, taking care not +to get any larger lump at the joint than necessary. A small flame is now +directed on the cone at right angles to its elements as before, and the +tube rotated so as to heat the whole circumference. The flame should be +just large enough to heat the whole of the cone. As the latter shrinks, +the lump at the joint is brought into the edge of the flame, and it and +a very little of the small tube allowed to shrink with the cone. + +When well shrunk and heated to blowing temperature the joint is removed +from the flame and blown gently with careful rotation, pushing the tubes +together a little when the blowing is about finished, so that the cone +becomes a short thick half-bulb, as shown in _d_, Fig. 8. This +corresponds to the first thick bulb in the first method (_d_, Fig. 6), +and is treated similarly. It is again heated and shrunk, taking care not +to involve either the large tube or the small one in the shrinking, +blown quickly to about the same shape as before, (_d_, Fig. 8), and then +gently drawn out into a smooth cone (_e_), exactly as in the first +exercise. Care should be taken not to draw too rapidly or too far, as +then the resulting cone (_f_) is weaker than it should be, and does not +look well. + +=Discussion.=--The beginner will find that this operation is best +learned on two tubes which are not too nearly of the same diameter. A +tube about 5/8 inch in diameter and one a little less than 1/4 inch will +be suitable. Both should have moderately heavy walls (1/16 inch or a +trifle over for the large tube, and a trifle less for the small one) but +the large tube should not be too heavy or else it will be hard to +prevent melting down too much of the small tube, and getting this drawn +out too thin during the process. One of the troublesome features of this +exercise is the difficulty of rotating two tubes of different diameters +with the same angular velocity, so as not to twist the joint. Another +difficulty is found in getting the cone uniformly heated to blowing +temperature without overheating and overshrinking the small tube. The +reason for this is obviously the much greater circumference of the cone, +especially at its large end, so that relatively much less of it is being +heated at any time. The beginner is also inclined to start with too long +a cone, or else heat so much of the large tube that part of its glass is +included in the cone, with the result that in order to get the right +wall-thickness the cone must be made too long (_g_, Fig. 8). This does +not look well, and usually will be irregular in shape. + + +EXERCISE NO. 5 + +TUBE FOR CONDENSING SULPHUR DIOXIDE + +This is useful as a test of mastery of the preceding exercise. A piece +of 3/16 or 7/32 inch tubing is joined to each end of a piece of tubing +5/8 by about 5 inches, and two constrictions made in the large tube, by +the method described on page 10. The small tubes are then bent in the +same plane, as shown, and their ends fire-polished (Fig. 9). + +[Illustration: FIG. 9.--Tube for condensing sulphur dioxide.] + + +EXERCISE NO. 6 + +BULB AT THE END OF A TUBE + +For this exercise tubing of 1/4 inch diameter and moderately strong +walls is selected. A tail is drawn out on one end of the tube, and a +piece of tubing about nine or ten inches long is cut off. The tail +should be carefully drawn in the axis of the tube, and in the same +straight line with it, as it is to be used as a handle in assembling the +glass for the bulb. This tail must be long enough so that it can be +conveniently held in the left hand, as described on page 13, and rotated +about the same axis as the main tube. Holding the main tube in the right +hand and the tail in the left, the tube is rotated in a large flame so +that a piece of it, beginning where the tail stops and extending about +an inch to the right, may be uniformly heated to the highest temperature +at which it can be kept in shape. As soon as this temperature is +reached, the tube is removed from the flame, continuing the rotation and +taking care not to draw out the heated part, and gently blown. The +rotation is carefully continued during the blowing, holding the tube in +approximately a horizontal position. As soon as the tube has expanded a +little the tail is pushed gently toward the main tube, continuing the +gentle blowing. If this is properly done, the heated piece of tube will +become a short bulb of about double its original diameter, and about the +same wall thickness as the original tube. It will have somewhat the +appearance of _a_, Fig. 10, when properly manipulated. + +[Illustration: FIG. 10.--Blowing a bulb on the end of a tube.] + +The tube is now reheated as before, taking care this time that the +heating extends over all that part of the bulb to the right of the +dotted line in the figure, as well as part of the main tube adjoining. +If this heating has been properly placed, when the operation of blowing +and pushing together is repeated the result will be to lengthen the bulb +into a uniform cylinder, as shown in _b_, Fig. 10. Otherwise the result +will be a series of bulbs, as in _c_, Fig. 10, separated by thickened +ridges which will be almost impossible of removal later and will +disfigure the final bulb. This operation of heating, blowing and pushing +together is repeated several times, until the cylinder becomes as long +as can be conveniently handled (about 1-1/4 inches to 1-1/2 inches). If +more glass is needed than is then contained in the cylinder, the latter +may now be heated as a whole, and blown and pushed gently into a shorter +cylinder of a slightly greater diameter, and more glass then added as +before. + +When enough glass has been collected for the bulb, it is all well heated +and blown gently a couple of times, pushing the mass together as +required, until a thick bulb like _d_, Fig. 10, is obtained. The tail +must now be removed at the point indicated by the dotted line. To do +this, a very fine flame is directed on the point where the tail joins +the bulb, and the tube well rotated as the glass softens at that point. +When sufficiently soft, the work is raised a little, so that the flame +instead of striking the glass squarely at the point indicated passes +below and tangential to it. The tail is now drawn off slowly, continuing +the rotation, raising the work just out of the flame whenever the thread +of glass drawn off becomes too thin, and lowering it again to the point +where the flame just touches it when the glass stiffens a little. By +this means the tail may be drawn off without leaving an appreciable lump +behind, as indicated in _e_ and _f_, Fig. 10. When as much of the extra +glass has been removed as is practicable, the flame is brought to play +squarely upon the little lump left, the last of the tail removed, and +the lump heated and gently blown to a small excrescence on the main +bulb. The whole end of the latter is now heated until it begins to +shrink a little, and gently blown to make it uniform in thickness. The +whole bulb is then heated in a flame of the proper size, so that it all +may shrink to about two-thirds of its diameter. The flame must be very +carefully chosen and directed, so as to shrink all the bulb, right up to +the main tube, but not soften the latter. As soon as this stage is +reached, the bulb is removed from the flame, continuing the even +rotation, and blown to the desired size, preferably by a series of +gentle puffs following one another at very short intervals. During the +blowing, the main tube is held in a horizontal position, and any +tendency of the bulb to fall out of line is corrected by the rotation. +If the shape of the bulb or its size are not satisfactory, it may be +shrunk again and reblown. Such shrinking should begin in a large yellow +flame, with just enough air to give it direction. The amount of air may +be gradually increased as the bulb shrinks and the walls become thick +enough to bear it without collapsing. If the bulb starts to collapse at +any time, it must be immediately blown enough to regain its convex +surface, before the shrinking proceeds further. + +=Discussion.=--In collecting the glass for the bulb, enough must be +gathered to give the walls the desired strength. Since the area of a +sphere is proportional to the cube of its diameter, it is evident that +doubling the size of a bulb diminishes the thickness of its walls to a +very large extent. The limit of diameter for a strong bulb on ordinary +1/4-inch tubing, collecting the glass as above, is about 1-1/2 inches, +and the beginner will do well not to blow his bulbs more than an inch in +diameter. + +The collection of the glass is one of the most important parts of the +process. If the mass of glass be twisted, furrowed or ridged, or +lop-sided, it is very difficult to get a good, even, spherical bulb, no +matter how many times it is shrunk and blown. The greatest care should +therefore be taken to get a uniform cylinder, on the same axis as the +main tube; and to this end the rotation of the tube must be carried on +very evenly. For method of holding the tube, see page 14. + +If a very large bulb is required, it will often be economical to seal on +the end of the tube a short piece of a large tube, provided with the +proper tail, and use the glass in the large tube for the bulb instead of +attempting to collect it from the small tube. In this case part of the +small tube will usually be included in the bulb, so that the joint comes +in the latter, and not where it joins the tube. As the amount of glass +carried on the end of the tube increases in weight and size the +difficulties of heating it uniformly, keeping it in the proper position +and handling it increase rapidly. + +In collecting glass, it is usually best not to leave the part of the +cylinder next the tube with too thick walls. This is always the coolest +part during the preparation for blowing the bulb, consequently it does +not get blown out, and causes an ugly thickened appearance on that end +of the bulb. + +If the bulb grows too long or pear-shaped, it may be easily shortened by +heating to the blowing temperature, and then blowing gently with the +main tube in a vertical position, and the bulb at the top of it. Gravity +will then shorten the bulb nicely. + +The finished bulb should be a nearly perfect sphere, with the axis of +the tube passing through its center, and the portion of the tube +adjoining the bulb must not be distorted, twisted, or blown out. In +order to prevent the distortion of the tube, care must be taken that it +is never heated quite to its softening point during the process. + + +EXERCISE NO. 7 + +BLOWING A BULB IN A TUBE + +The tube is selected and one end closed as in the previous exercise, but +it should be cut a little longer, say about twelve inches. Beginning at +a point about four inches from the closed end, glass is collected and +blown into a thick-walled bulb, exactly as in the previous exercise. +Greater care must be taken, however, that the cylinder collected and +this thick bulb are of uniform thickness and set squarely in the axis of +the tube. Instead of removing the tail, the bulb must be blown in this +case with both pieces of tubing attached, and care must be taken that +they "line up" properly, _i.e._, are in the same straight line, and that +this line passes as near as may be through the center of the bulb. The +tube is held in approximately horizontal position during the blowing of +the bulb, as in the previous case, and especial care taken with the +rotation. Both pieces of tube must of course be rotated at the same +rate, and their softened ends must be kept at exactly the proper +distance from each other, so that the bulb may be spherical and not +elongated. If the blowing of the bulb be quickly and accurately done, it +may usually be completed before the glass is quite set, and the +alignment of the two tubes may then be rectified while looking straight +through the bore of the tube. + +=Discussion.=--The two points of greatest importance are the collection +of the glass, and the uniform rotation of the tube. A larger tube may be +sealed in the middle of a small one when a large amount of glass is +necessary. The piece of tubing used for the exercise must be long enough +so that the fingers may be kept on a cool part of the glass without +getting uncomfortably near the ends of the tube. It should not be any +longer than necessary, however, as the extra weight and length make the +manipulation of the hot glass more difficult. + +When a string of bulbs are required on the same tube, a piece of glass +18 inches long may be used at the start, and the first bulb made near +the closed end, as described. Each succeeding bulb will then be in plain +view during the blowing, and when the open end becomes too short for +comfort, it may be dried out, cut off, and another piece joined to it, +starting as in the first method (Exercise No. 1), but instead of drawing +out the thick bulb to a tube, it is made part of the glass collected for +the next bulb. If the string of bulbs becomes awkward to handle on +account of its length and weight, it may be made in several parts and +these later sealed together by the second method, preferably blowing +through a rubber tube attached to the open end, as described on page 22. + +Very neat small bulbs may be made on tubing of a diameter of 3/16 inch +or a little less, but the beginner is advised to start with tubing of +about 1/4 inch diameter. The use of tubing with too thick walls usually +produces bulbs which are thick-walled at the point where they leave the +tube, but inclined to be too thin at the point of maximum diameter +(perpendicular to the axis of the tube) where most of the strain comes +and strength is particularly needed. + + + + +CHAPTER IV + +ADVANCED EXERCISES + + +EXERCISE NO. 8 + +SEALING A TUBE THROUGH ANOTHER TUBE + +_First Method--Making a Gas-washing Tube_ + +This first method can be used whenever one can work through an open end +opposite to the end of the tube where the joint is to be made. To +illustrate it, take a piece of rather thin-walled tubing, about 3/4 inch +in diameter, and some pieces of rather strong tubing a little less than +1/4 inch in diameter. Draw off the large tube in a short cone, then draw +off the tail as in the making of the bulb on the end of the tube, blow +out the little lump slightly, shrink the whole cone a little and blow +gently to form a rounded end like that on a test-tube, with walls about +the thickness of those of the rest of the tube. Cut this tube to a +suitable length, say about six inches, and provide two corks which will +fit the open end of it. Now cut a piece of the small tubing of the +proper length to form the piece which is to be inside the large tube. +For practice purposes, this piece should be about an inch shorter than +the large tube. Flange one end of this tube a little, and anneal the +flange well in the smoky flame. Bore one of the corks so that a piece of +the small tubing will fit it, and cut a couple of notches in the side of +this cork so that air can pass between it and the glass. Pass a short +piece of the small tubing through this cork, and attach the flanged +piece of small tube to this by means of a short piece of rubber tubing, +so that when the whole is inserted in the large tube it is arranged as +in _a_, Fig. 11. The piece of glass tubing projecting out through the +cork is now cut off so as to leave an end about 1/2 inch long when the +cork is firmly seated and the inner tube pushed into contact with the +center of the end of the large tube, as shown in the drawing. Care +should be taken that the little rubber tube which joins the two pieces +is arranged as in the figure; _i.e._, most of it on the piece of tubing +which passes through the cork, and very little on the other piece, so +that when the cork is removed after the small tube has been sealed +through the large one, the rubber tube may easily come with it. Select a +short piece of the small tubing of suitable length for the piece which +is to be on the outside of the large tube as a continuation of the +piece inside, and another piece for the delivery tube. A small bulb may +be blown in the latter at a point about 2-1/2 inches from the closed +end, and the open end cut off about 1-1/2 inches from the bulb. A cork +or cork-boring of suitable size to stopper the small tube is prepared, +and laid ready with the other (unbored) cork for the large tube. + +[Illustration: FIG. 11.--Gas-washing tube.] + +When everything is in readiness, the rounded end of the large tube is +slowly heated until it softens and joins firmly to the small tube +inside. After it has shrunk down well, it is blown out to its original +size, placing the whole end of the large tube, cork and all, in the +mouth. Now with a fine-pointed flame the glass covering the end of the +small tube is heated to the softening temperature, and then is blown out +to an excrescence by blowing on the end of the small tube which passes +through the cork. The end of this excrescence is heated and blown off in +the usual way, so as to leave the small tube sealed on the inside of the +large one and opening through it into this short tube which has been +blown out. The end of the small tube which passes through the cork is +now closed with the cork prepared for it, and the short outer tube is +joined to the tube that has just been blown out, so that the joint +appears like _b_, Fig. 11. Use the first method (Exercise No. 1) for +this joint. Reheat the whole of the end of the tube nearly to the +softening temperature, anneal it a little, and allow to cool a few +seconds until well set. Now remove the cork, short glass tube and rubber +tube from the open end of the large tube and insert the solid cork in +their place. Warm the joint and the whole of that end of the tube again +carefully up to about the softening point, then seal on the side tube +for the delivery of the gas in the usual way, taking care that the whole +of the end and the joint are kept warm meanwhile. When thoroughly +sealed, the delivery tube is bent up parallel to the tube through which +the gas enters, and then out at right angles to it, as shown in _c_. The +whole of the end of the tube is now cautiously reheated and then cooled +slowly to anneal it. + +The cork may now be removed from the open end of the large tube, this +end heated in a large flame, caught together with a scrap of glass +tubing and drawn off into a cone so that the base of the cone is about +opposite the end of the inner tube. The lump of glass is drawn off the +point of this cone and it is reblown to form a rounded end, as +previously described. + +After this cools, the tube through which the gas enters may be heated at +the proper point and bent at right angles to form the finished apparatus +as shown in _d_. The ends of the small tube are cut off square and +fire-polished. + +=Discussion.=--After the joint has once been made, great care must be +taken that it is kept hot during all the subsequent manipulations, and +if it becomes somewhat cool at any time it must be reheated very slowly. +It is obvious that the rate of heating and cooling of the inner tube +will be slower than that of the outer tube, and this will readily +produce stresses which tend to crack the tube at the joint. The amount +of heating and cooling which such a joint will stand depends upon its +form. The beginner should examine such a joint on regular factory-made +apparatus, and note the uniformity of wall-thickness and the "clean-cut" +appearance of the joint, as a model for his imitation. A ragged joint, +where the line of joining of the inner and outer tubes wavers instead of +going squarely around the tube, is almost sure to crack during the +cooling and heating unless extra precautions are taken with it. The +presence of a small lump of glass at any point on the joint affords an +excellent starting place for a crack, as do also the points on a ragged +joint where the inner tube comes farther down on the outer tube than at +other points. + +In order to insure a joint which is square and not ragged, it is +essential that the angle between the inner and outer tubes at the joint +be very nearly a right angle. For this reason the two tubes should not +be of too near the same size, or if this cannot be avoided, a small bulb +should be blown on the end where the joint is to be made. If this bulb +be made with the same wall-thickness as the rest of the tube, and +somewhat pear-shaped, it may be drawn out to the same size as the rest +of the tube, if necessary, after the joint has been made. + +This method is used wherever possible in preference to the second method +(Exercise No. 9), as it is easier to get a good joint with it. It may +also be used where it is desired to seal the tube through the side of a +tube, or for a tube sealed through the wall of a bulb, as in a Geissler +potash bulb or similar apparatus. Where there is not space to join the +inner tube to the blowing tube by a rubber tube, this joint may be made +with a small piece of gummed paper, which can readily be broken when +desired. + + +EXERCISE NO. 9 + +SEALING A TUBE THROUGH ANOTHER TUBE + +_Second Method--Making a Suction Pump_ + +Select a piece of tubing 3/8 to 1/2 inch in diameter, with walls about +1/16 inch or a little less in thickness, heat a place about 4 inches +from one end and draw it out so that when cut off at the proper point it +will look like _a_, Fig. 12; the open end of the drawn out part being +small enough to slip inside another piece of the original tube. A small +thick-walled bulb is now blown as indicated by the dotted lines, and +annealed. A piece of the original tubing is now prepared, 7 or 8 inches +long, with one end cut square off and the other closed. A piece of +1/4-in tubing about 2 inches long, and drawn out at one end to a tail +several inches long is also prepared, to form the inlet tube for the +air. Another piece of the 3/8-inch tube is prepared, about 4 inches +long, and provided with a tail drawn out as indicated in _b_, so that +when cut off at about 2-1/2 or 3 inches from the main tube its inner +diameter may be slightly less than that of the narrowest point of the +tube _a_. A small thick-walled bulb is blown at the point indicated by +the dotted lines, and annealed. Care must be taken in drawing the +capillary and blowing the bulb in both _a_ and _b_ that the capillary +tubes are in the axis of the main tube, and in the same straight line +with it. + +[Illustration: FIG. 12.--Suction pump.] + +The open end of the 8-inch piece of tube and the bulb of the piece _a_ +are now warmed together, the end of the tube only moderately and the +bulb to about its softening temperature. The tube _a_ is now inserted in +the open end of the large tube, and the bulb softened with a suitable +flame and pressed into good contact with the tube. It is then reheated, +including the joint, blown a little and pulled out to form a straight +tube in line with the main tube. By warming the joint a little, and +proper rotation, the capillary may be brought into the same straight +line with the rest of the tube. + +Keeping this joint hot, a place about an inch from it on the tube _a_ is +warmed, and the piece of 1/4-inch tubing previously prepared is sealed +on at that point. The joint is then well annealed and allowed to cool. + +The tube _a_ is now cut at such a place that when _b_ is inserted in the +open end the point will come near the end of the constriction of _a_, as +shown in _c_. Care is taken to get a clean square cut. The side tube is +now cut off about an inch from the main tube and corked. Tube _b_ is +sealed into the open end of _a_, in the same way as _a_ was sealed into +the large tube, and the joint carefully annealed. + +=Discussion.=--As in the first method, the secret of success lies in +getting a square joint, and having the inner tube leave the outer one at +nearly right angles. All the remarks about annealing, lumps, etc., made +under the previous method apply here. + +This method may be applied in sealing a small tube into the end of a +large one, the latter being either drawn to a cone and cut off at the +desired diameter, or else given a rounded end like a test-tube and a +hole the proper size blown in the center of it. A suitable thick-walled +bulb is to be blown on the small tube, as in the case described above. +This method is also used in making the Kjeldahl trap (_a_, Fig. 13), the +small tube to be inserted being first drawn, the thick bulb blown at its +point of union with the main tube, and then the small tube bent and cut. +The large bulb is best made with rather heavy wall, being either blown +in the middle of a tube, and one piece of the tube drawn or cut off, or +else made on the end of a tube. In the latter case a drop of glass must +be put on the point where the joint is to be, so as to get a hole of the +proper size with enough glass around it to prevent it from growing +larger when it is heated. The author prefers to blow the bulb in the +middle of the tube, draw off one end of the bulb, and blow out the +desired hole where the tube was drawn off. The whole bulb must generally +be reheated and blown a little at the end of the process, and well +annealed. + +[Illustration: FIG. 13.--_a_, Kjeldahl trap; _b_, suction pump on +smaller tubing.] + +The suction pump can also be made on 1/4-inch tubing, and one joint +saved if desired, by constricting the tube to form the raceway for the +water and air, as shown in _b_, Fig. 13. (See page 10 for method.) But +it is more difficult to make a square joint on such small tubing. + + + + +CHAPTER V + +MODIFIED METHODS AND SPECIAL OPERATIONS + + +CAPILLARY TUBING + +This is commonly used in many forms of apparatus for gas analysis, and +one is often called upon to join two pieces or to make a tee on it. The +methods are nearly the same as with other tubing, except that more care +and patience are required. The work must be done much more slowly on +account of the thickness of the walls, and open ends of the tube must +always be enlarged before joining them to anything. This is best done by +carefully sealing the end and then blowing, with several suitable +reheatings, to form a pear-shaped bulb as in _a_, Fig. 14. The end of +this is then heated and blown off, and the piece is ready to be joined +to another similar end, or to a piece of ordinary tubing if desired. The +joints are best not blown too much, as thick walls shrink very slowly. +Much may be done by gently pushing the tube together or pulling it apart +in the flame, to remove lumps and irregularities. It is necessary that +the bore of the joint be approximately that of the main tube, and care +must be taken that the latter is not constricted at the point where the +joint begins. + +[Illustration: FIG. 14.--Capillary tubing.] + +Especial care must be taken to warm the tube slowly when starting and +cool it slowly when through, as the thick walls frequently crack if not +carefully handled. For this reason the whole neighborhood of the joint +must be heated somewhat so that there may not be stresses set up between +the heated and unheated portions. + +In making the tee (_b_, Fig. 14) the inability to blow the joint makes +itself decidedly felt, but if the side tube is properly enlarged as +previously described, a good joint can be made by alternately pulling +and pushing on the end of the side tube, and shrinking well. + +Very fine capillary tubing should be blown with a rubber bulb instead of +the mouth, so as not to get moisture into the tube. The rubber bulb may +also be used to advantage on some of the coarser capillary tubing. + +When a bulb is to be joined to a piece of capillary tubing, the joint is +preferably made before blowing the bulb, and will then be taken up a +little way on the bulb during the process. Care must of course be taken +not to constrict the capillary; the pear-shaped bulb blown on the end +(_a_, Fig. 14) may well extend back a little further than usual into the +tube so as to prevent this. If a bulb is required in the middle of a +capillary tube, the latter is usually best cut and a piece of ordinary +tubing of suitable size sealed in to provide material for the bulb. + + +GLASS ROD + +Joints, tees, etc., in glass rod are made on the same principle as in +tubing, except that of course they cannot be blown, and regularity must +be obtained by accumulating a small mass of uniformly heated glass, and +then drawing it to a suitable rod, on the same principle as Exercise No. +1. + +Great care must be taken in heating and cooling this, as in the case of +the capillary tubing, and for the same reasons. + +By joining pieces side by side, pressing with carbon plates or a plate +and a rod, and other suitable manipulations, stirrers, spatulas, and +other objects may easily be made from rod, and its manipulation is +relatively easy on account of the fact that one does not have to worry +about the bore of the tube. But the same general rule about not having +thick and thin spots in contact, and making all changes in diameter on a +taper if possible instead of abruptly, applies here. Thick pieces will +cool and contract at different rates from thin ones, and cracks are +likely to develop where they join. Work which has been formed with any +tool must always be heated to the softening point afterward before +allowing it to cool in order to remove the stresses caused by the +contact of the tool with the hot glass. + +When it is necessary to join a piece of rod to the side of a piece of +tubing, the end of the rod is made very hot while the wall of the tube +at the spot desired is heated to just below the softening temperature. +The rod can then be pressed into firm union with the tube and drawn a +little to remove the excess of glass without deforming the tube. + + +MENDING STOPCOCKS + +=Mending the Plug.=--The plug of the stopcock occasionally falls out and +is broken. If the break is in the main part of the plug, nothing can be +done except to search for a spare plug of suitable size and grind it to +fit, as described below. If only the little cross-piece at the end is +broken off, it can easily be replaced. In most ordinary stopcocks the +plug is solid, but the little handle is hollow. What has been said above +regarding care in heating and cooling glass rod applies with especial +force here. It is usually best to wind the whole of the plug with +several thicknesses of asbestos cord, leaving bare only the end where +the handle is to be joined. This diminishes the danger of cracking the +plug by too rapid heating, and also makes it more comfortable to hold. A +piece of rather thick-walled tubing of suitable diameter is chosen, +drawn out so as to have a suitable taper (taking care to heat enough of +the tube so that the capillary tail has good wall-thickness and +strength), and then a corresponding taper is drawn to form the other +side of the handle. The result is shown in Fig. 15, _a_. The capillary +tail is now heated and bent back to form a handle which will be in the +same straight line as the axis of the plug (_b_, Fig. 15) and the main +part of the tube drawn off at the dotted line, making a neat seal at +that point. The broken end of the plug is now slowly warmed in the smoky +flame, the heat gradually increased by a gentle stream of air from the +bellows, and the point at which this handle is to be attached finally +brought to the temperature at which the glass flows freely. In the mean +time, the little handle has been warmed almost to the softening point. +It is now quickly pushed into place (_c_, Fig. 15), taking care that its +axis is parallel to the hole in the plug, and then drawn away from the +plug just enough to make a graceful neck instead of the bulging one +indicated by the arrow in the figure. With a fine pointed flame the +little tail is now drawn off at the point indicated by the dotted line +(_c_, Fig. 15) and the whole carefully annealed. If necessary, the +handle can be blown a little before the tail is removed. Local heating +and blowing at the point where the handle joins the plug is often +necessary in order to make a smooth job. + +[Illustration: FIG. 15.--Stopcock plug.] + +=Regrinding.=--This is sometimes necessary to make stopcocks tight, when +the grinding has not been properly done in the factory. For this, a very +little fine flour of emery or carborundum is the best and quickest. If +this is not at hand, some clean sand may be ground in an agate mortar, +and if possible sieved. Only material which passes the 100-mesh sieve +should be used. It will be ground still finer in the process. For the +final polishing, a little infusorial earth or even kaolin will do. + +The surface to be ground is moistened with water and dusted over with a +little of the abrasive. The plug is now inserted in the stopcock, and +turned with a gentle pressure. This turning should be in the same +direction for several revolutions, then in the opposite direction for +several more revolutions, etc. As the abrasive becomes finer during the +grinding, a little more may be added if necessary. In general, only a +little grinding will be required, and one small pinch of carborundum or +emery will be ample. The beginner usually grinds too much, and with too +coarse material. As the grinding surface becomes dry, water is added +drop by drop, and the grinding continued until the abrasive seems to be +reduced to an impalpable powder, most of which has been squeezed out of +the stopcock. The two surfaces in the stopcock are usually grinding upon +each other at this stage, and inspection will show whether the contact +between them is uniformly good. If not, the grinding must be continued +with a little fresh abrasive. If contact appears to be good, the +surfaces are ground together for a little with practically no abrasive, +so as to polish them, and the joint is then washed out and tested. + +In grinding in a new plug to replace a broken one, the plug selected +should have practically the same taper as the seat into which it is to +be ground, and should be a very little too large. Care must be taken to +so distribute the abrasive material as to grind mostly on the places +where the plug fits tightly. + +=Sealing on a New Tube.=--It frequently happens that one of the tubes of +the stopcock is broken off close to the cock itself, and a new one must +be joined to the stub of the old one. With care, this may often be +successfully done even where the break is within 1/4 inch of the +stopcock. The first step is to clean and dry the stopcock, remove the +plug, cork the open ends of the stopcock sleeve and the other tube, and +wind a couple of layers of asbestos cord carefully over the sleeve and +the most of the corks which close it. A suitable tube, having as near as +possible the same diameter and wall strength as the one broken off, is +selected and a piece the desired length cut off. The broken end of the +tube on the stopcock is now squared off as well as possible, by cutting +or by heating and drawing off the projections, and the new tube sealed +on, usually with the first method (Exercise No. 1). If the break is very +close to the stopcock, very little reheating and blowing can be done, on +account of the danger of getting the stopcock sleeve out of shape, and +the work must be heated very slowly to prevent cracking. The main +reliance is then placed on making a good joint when the tubes are +brought together, and then drawing out this joint a little, at once, to +get an even wall. + + +CLOSED CIRCUITS OF TUBING. + +In some pieces of apparatus closed circuits of circular or rectangular +shape are required. A similar problem is involved in apparatus like the +ordinary Soxhlet extractor, where a small tube is joined to the side of +a large one, bent to form a siphon, and attached again to a continuation +of the original large tube. The difficulty in all such cases is to +provide for the contraction taking place as the last joint cools. If +part of the circuit has the shape of the letter S, or is a spiral, the +natural springiness of the glass will take care of this. If not, the +side of the circuit opposite to the joint and parallel to it must be +heated also, the two being finally heated together to the softening +point after the joint is completed, and then allowed to cool together. + +To make the last joint, the rest of the tube is made in approximately +the desired form, the two pieces which are to be joined to make the last +joint being just enough out of the desired position to allow them to +pass one another. The final joint is preferably made in the middle of a +straight piece of tube, not at a tee. The two pieces which are to be +joined are bent so as to just pass each other, marked at the right point +with the glass-knife, and cut there, preferably with a small bead of hot +glass. One or both of these tubes are now warmed to the softening point +in such a place that the tubes can be made to meet properly, and the two +cut ends pressed together. They are now warmed in the flame, and joined +together, either by simultaneously warming the opposite side of the +circuit or some other suitable part, so as to allow the two ends to be +pushed together again after they are softened, or by gently touching the +places that do not unite with a hot bead of glass, and using the glass +to fill up the crack where the ends do not quite meet. Care must be +taken not to leave knots or lumps of glass in the finished joint, and +the latter should be well reblown, and if necessary left as a small bulb +or enlargement, rather than have it have too thick walls. + + +SPIRALS + + + +Spirals of glass tubing are probably best made free-hand before the +blow-pipe, unless one has a great many of them to make, and extreme +accuracy is desired. To begin with, a piece of tubing of the desired +size (say 3/16 inch in diameter) and a convenient length (about two +feet) is selected, one end closed, and a right-angle bend made about six +inches from the closed end. Holding the closed end in the left hand and +the long open one in the right, the spiral is begun. The short closed +end is to be parallel to the axis of the spiral, and preferably in that +axis. Using a moderate-sized flame, of somewhat yellow color, and taking +care to heat the whole circumference of the tube, the long open end is +wound little by little into a spiral having the short end _a_ (Fig. 16) +as an axis. The bend at _b_, where the tube changes from the radius to +the circumference of the circle, must be rather short, but the tube must +not be flattened or constricted here. Especial pains is to be taken +with the first turn of the spiral (_b_ to _c_, Fig. 16), as the shape of +this determines the diameter of the whole spiral, and serves as a guide +for the rest of the turns. The winding of the tube is best accomplished, +after a portion has been softened, by slowly turning the short end _a_ a +little about its own axis, while the long open end remains where it was. +This winds the tube into a spiral, just as if there were a solid +cylinder in the center of it, and this cylinder was being turned about +its axis, and was winding up the soft glass upon its circumference. As +the cylinder is not actually there, the curve of the turns must be +carefully estimated by the eye, so that the spiral may be uniform and +moderately smooth. When the original piece of tube has been used up, +another piece is sealed on to the open end, and the operation continued +as far as may be required. + +[Illustration: FIG. 16.--Making a spiral.] + + +GROUND JOINTS + +It is sometimes required to join two pieces of tubing end to end, by +means of a ground joint. Whenever possible, a regular sealed joint +should be used instead of this ground joint, as it is quicker to make, +and more certain to be tight. Where a ground joint is necessary, +however, it is best made in the conical form shown in _c_, Fig. 17. If +the wall of the tube to be used is not very thick, it is thickened by +collecting glass as for a bulb on the ends of two tubes (Exercise No. +6), and drawing to form cones of suitable shape (_a_ and _b_, Fig. 17) +and of such relative sizes that a will slip about half way into _b_. In +order to make _a_ straight and give it the proper angle, it may be +rolled when hot, upon a hot plate of carbon. Blowing during this rolling +is often helpful to remove depressions. After _b_ has been drawn to +nearly the proper size and shape, it may be smoothed by the use of a +small carbon rod, held inside it at a slight angle, or better by the use +of a truncated hexagonal pyramid of carbon, whose edges have the proper +slant to make the inside of the cone right. The proper taper for both +these cones is the same as that used in stopcocks of similar size. The +hexagonal carbon can easily be made by carefully filing down an electric +light carbon, and finally impregnating it with paraffin or beeswax, and +is extremely useful wherever a conical surface has to be formed from the +inside of a tube. + +[Illustration: FIG. 17.--Ground joint.] + +The tail is allowed to remain on piece _a_, as a sort of guide in +grinding, and should therefore be in the axis of the tube and have +rather thick walls. Grind with emery or carborundum, as described under +a previous head. (Regrinding plug for stopcock.) If many such joints are +to be made, it will pay to have a little sleeve of brass made with the +proper taper, and rough down the plug _a_ in it to about the proper +size, while _b_ is roughed down by means of a brass or iron plug having +the same taper. This prevents excessive grinding of one-half of the +joint in order to remove a defect in the other half, and is the method +commercially used in making stopcocks. + + +SEALING IN PLATINUM WIRE + +Very often it is necessary to seal platinum wire into the wall of a +tube. Professional glass-blowers usually use a special sort of glass +("Einschmelzglas") which is usually a lead glass, and is made of such +composition that it has the same or practically the same coefficient of +expansion as platinum. A little globule of this glass is sealed into the +tube in such a way that it joins the platinum to the glass of the tube. +To do this, the small globule of special glass is fused on the platinum +wire at the proper point and the tube into which the wire is to be +sealed is heated and a small tail drawn out at the point where the wire +is to be inserted. The lump of the special glass should be from 3/32 to +1/8 inch in diameter, and the tail drawn on the tube should have a +slightly less diameter at the point (about 1/8 inch or less from the +tube) where it is cut off. There are now two ways of sealing in the +wire. (1) The wire with the globule of glass is placed inside the tube +and the latter revolved until the end of the wire sticks out of the cut +tail (_a_, Fig. 18). The latter is now gently heated, and the two glass +surfaces fused together, taking care to use only the end of the hissing +flame, if the special glass contains lead. (See Chapter I, page 1.) The +whole circumference of the tube is then heated and annealed carefully. +(2) The end of the wire which is to be outside the tube is attached to +the end of a thin scrap of glass, by heating the glass and thrusting +the wire into it a very little way. Using this piece of glass as a +handle, the wire is inserted in the cut tail (_b_, Fig. 18) and the +globule brought near to the end of the tail. (If the main tube is cold, +it must of course first be warmed.) With the end of the hissing flame, +as in the first method, the globule of glass is melted and the end of +the tail softened. The wire is now pushed into place, the handle removed +by heating the end and withdrawing it, and the tail reheated a little if +necessary to make it shrink back into line with the walls of the tube. +The whole circumference of the tube is heated at that point and annealed +as usual. + +[Illustration: FIG. 18.] + +The use of this special glass is not absolutely necessary if the +platinum wire is small (1/4 millimeter or less in diameter), and in fact +it is often better in such cases not to use it, unless the apparatus is +to be subjected to a very high vacuum. On small tubes, especially, it is +undesirable to use the special glass, as a lump of it will usually cause +the tube to crack on cooling. When such glass is not at hand or is not +to be used, the procedure is altered somewhat. The tail which is drawn +out is very fine, having only a sufficient diameter so that when it is +cut off the wire can be inserted in it. Such a fine tail is readily made +by heating a small spot on the tube, touching it with a warm platinum +wire, removing from the flame and drawing out the tail with the wire. +After cutting off the tail the wire is inserted in it, being held on a +scrap of glass as in the previous case, and the wire and tail heated +until the latter shrinks back into line with the walls of the tube. If +too great shrinkage occurs, the place may be blown out gently after +reheating. Thus the wire is sealed through the wall of the tube without +changing the thickness of the latter, and consequently without +developing undue stresses at that point. Such a joint must of course be +carefully reheated and annealed. With fine platinum wire there is very +little risk of the tube cracking if care is taken to avoid formation of +any lump and to reheat the whole circumference of the tube at that +point. + +Any glass adhering to the end of the platinum wire, where the scrap of +glass was sealed on for a handle, may be removed when the glass has +cooled by crushing it carefully with a pair of pliers. + + +SEALING VACUUM TUBES + +Tubes which have been evacuated usually are sealed off while they are +still connected to the vacuum pump. The connection should be through a +small, rather thick-walled tube. When this is to be sealed, it is slowly +heated toward the softening point. As the glass just begins to soften, +the air-pressure will force it in, and care must be taken that the +softening is uniform over the whole circumference of the tube. As the +shrinking goes on, the tube is gently drawn out to make a thick-walled +cone at that place, and the end is drawn off as soon as the tube is +sealed. The principal point to be guarded is the thickness of the walls +of the cone, and uniform heating. A thin place or a hot place will give +way under the air-pressure and be sucked into the tube. + + +CLOSED TUBES FOR HEATING UNDER PRESSURE + +(_Carius method for determination of the halogens and sulphur._) In this +case the tubing used must have thick walls (usually about 3/32 inch) to +withstand the pressure. Its external diameter is usually about 3/4 inch. +One length will usually make two tubes of standard length for the cannon +furnace. Especial care must be taken in heating and cooling it on +account of the thick walls. A length is gradually warmed in the center, +finally heated at that point until soft, drawn out, cut apart and +annealed. Taking one of the pieces, the cone is carefully heated and +shrunk, as in Exercise 4, until its walls are as thick as those of the +main tube. A flame with a little tinge of yellow should be used for this +operation to prevent devitrification (page 2), as the thick glass +shrinks slowly. The tail is now drawn off and the whole end heated and +gently blown several times to make a rounded end, like a test-tube, with +walls as thick as those of the main tube. This must be carefully +annealed. It is more important that the walls be thick than that the end +be nicely rounded: it may indeed be left somewhat conical in shape. + +At a point about two inches from the open end of the tube, it is slowly +warmed and finally heated to the softening point. Grasping the open end +with a pair of crucible tongs, it is cautiously pulled out, a little at +a time, usually during rotation in the flame, to make a constriction of +moderate wall-thickness, but of sufficient internal diameter to admit +the tube containing the substance. After annealing this, cooling and +cleaning the tube, the acid and salt are introduced (the former by means +of a long-stemmed funnel) and the tube is inclined and rotated about its +axis so that the acid wets its surface about half way up from the +bottom. The substance is now weighed out in a piece of thin-walled glass +tubing, closed at one end, and about two inches long. Inclining the +large tube at a suitable angle, the small one is introduced, closed end +first, and allowed to slide down the walls of the large tube until it +reaches the place where the acid has wet the tube. Here it will stop, +and if the tube is kept inclined during the rest of the operation it +will roll around inside the tube at this point and thus not get down +where any acid is likely to get into it and produce any pressure by +decomposing it before the open end of the tube is sealed. Now the tube +is held in an inclined position, taking care that the acid does not +reach up to the substance, the constricted portion cautiously warmed and +shrunk. It is finally shrunk and drawn out into a somewhat elongated +cone, with walls as thick as the rest of the tube, and when this is +accomplished the end of the cone is sealed and the waste piece drawn +off. Anneal with great care, and cool in such a position that the acid +cannot reach the hot glass. The shrinking of this cone takes a good deal +of patience, and is one of the most important parts of the process. If +the walls are left too thin, the tube may burst when heated, and the +whole labor is lost. If care is taken, the same tube can be used for a +number of determinations, until it becomes quite short. + + + + + INDEX + + + Annealing glass, 4, 24 + + + Bellows, 4 + + Bending glass, 8 + + Blowing glass, 13, 19, 20, 21, 24, 29, 31 + with a rubber tube, 22 + + Blowpipe, 4 + + Bulb at end of tube, 28 + in middle of tube, 32 + very large, 32 + + Bulbs, string of, 33 + + + Capillary tube, drawing on larger tube, 9, 54 + tubing, working, 43 + + Carius method, tubes for, 55 + + Closed circuits of tubing, 48 + tubes, for heating under pressure, 55 + + Collecting glass for bulb, 29, 31, 32 + + Constricting a tube, 10 + + Crystallization of glass, see Devitrification. + + Cutting glass, 7, 25 + + + Devitrification, 1, 2 + + Drawing out a tube, 9, 18, 19, 27 + + + Flanging a tube, 11, 14 + tool, 11 + + + Gas-washing tube, 35 + + Glass, annealing, 4, 24 + + Glass, bending, 8 + blowing, 13, 19, 20, 21, 24, 29, 31 + collecting for bulb, 29, 31, 32 + cutting, 7 + defects, 2 + grinding, 47 + hard, 1 + knife, 7 + lead, 1 + qualities desired, 1 + rod and tube, joining, 45 + rod, working, 44 + shrinking, 18, 19, 22, 26 + soft, 1 + working temperature, 1, 13, 19, 27 + + Grinding stopcock or joint, 47 + + Ground joints, 51 + + + Handle on stopcock, mending, 45 + + Hard glass, 1 + + Holding tube, 13, 14 + + + Insertion of tube through another, see Sealing a tube through + another tube. + + + Joints, ground, 51 + + Joining rod and tube, 45 + tubing end to end: first method, 16 + second method, 20 + + Joining tubes of different diameters, 25 + a new tube to a stopcock, 48 + + + Kjeldahl trap, 41 + + + Lead glass, 1 + + Lump of glass, removed, 18, 19, 20, 21, 24, 26, 30, 38 + + + Platinum wires, sealed into glass, 1, 52 + + Position for glass-working, 5 + + Pressure, tubes for heating under, 55 + + + Quality of glass, 1 + + + Rod, glass, working, 44 + + Rotation of the tube, 13, 19 + + Rounded end of tube, 35, 38 + + Rubber tube used for blowing, 22 + + + Sealing a tube through another tube, 35, 39 + + Sealing vacuum tubes, 55 + + Shrinking glass, 18, 19, 22, 26, 31 + + Side tube, blowing, 22, 25 + + Soda glass, 1 + + Soft glass, 1 + + Spirals, making, 50 + + Stopcocks, mending, 45 + + Suction pump, 39, 42 + + Sulphur dioxide tube, 28 + + + "Tail" of glass, drawing out, 9, 54 + removed, 30, 35 + + Tubes, closed, for heating under pressure, 55 + + "Tee" tube, 22 + on capillary tubing, 43 + small side tube on a large tube, 24 + + + Vacuum tubes, sealing, 55 + + + Working temperature of glass, 1, 13, 19, 27 + ++----------------------------------------------------------------------+ +| | +| | +| Transcriber's note:- | +| | +| Words in italics are indicated by the use of _underscores_ and words | +| | +| in =bold= by the use of equals signs as shown. | +| | +| | +| | ++----------------------------------------------------------------------+ + + + + + + +End of the Project Gutenberg EBook of Laboratory Manual of Glass-Blowing, by +Francis C. 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