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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

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| Transcriber's note:-                                                 |
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| Words in italics are indicated by the use of _underscores_ and words |
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| in =bold= by the use of equals signs as shown.                        |
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End of the Project Gutenberg EBook of Laboratory Manual of Glass-Blowing, by 
Francis C. Frary

*** 