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+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.)
+
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+
+
+
+
+  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
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