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Electrical World TheEngjneering andMining Journal 
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Caihvay Age Gazette American Machinist 

Signal EngiriGGr AraericanEngneer 

Electric Railway Journal Coal Age 

Metallurgical and Chemical Engineering Power 






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Copyright, 1914, by the 
McGraw-Hill Book Company, Inc. 

• • • 


I 9 I V 


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 appa- 
ratus several hundred miles to be mended could often 
be saved if some of the laboratory force could seal on a 
new stop-cock, replace a broken tube, or make some 
temporary repairs. Many men in physical or chemical 
laboratories have occasion to modify some piece of appa- 
ratus 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 originaUty is claimed for the methods here de- 
scribed. 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 per- 
form 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 stop-cocks, 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 wilUng to spend a very large amount of time 
in practice. For similar reasons the manipulation of 
quartz glass has been omitted. 


vi Preface 

The author will be grateful for all suggestions and crit- 
icisms 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 Uttle details in the manipulation which 
often spell success or failure in glass-blowing. 

F. C. F. 
Minneapolis, Minn., 
January J 1914. 



Preface v 


Materials and Apparatus 1 

Varieties and defects of glass — Devitrification — Anneal- 
ing glass — Blowpipe and bellows — ^Light — Arrangement 
of exercises. 


General Operations 7 

Cutting, bending, constricting and flanging the tubing — 
Methods of rotation and blowing. 


Elementary Exercises 16 

Joining two pieces of tubing of the same diameter — The 
"tee" tube — Joining two tubes of different diameters — 
Blowing bulbs. 


Advanced Exercises 35 

Sealing a tube through another tube: The gas- washing 
tube, suction pump, and Kjeldahl trap. 


Modified Methods and Special Operations 43 

Capillary tubing — Glass rod — Mending stopcocks — 
Closed circuits of tubing — Spirals — Groimd joints — 
Sealing in platinum wire — Sealing vacuum tubes — Closed 
tubes for heating under pressure. 

Index 59 


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 tem- 
perature, (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- 


2 Laboratory Manual of Glass-blowing 

called ''soft glass" varies a good deal, and is best deter- 
mined 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 elimi- 
nate 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 tem- 
perature 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 manufac- 
ture. 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 indica- 
tion of hard, inferior glass. Crookedness and non-uni- 
formity 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 

Materials and Apparatus 3 

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 main- 
tained 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 compara- 
tively soft glass which devitrifies almost at once in a 
''hissing" flame can be worked without serious difiiculty 
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 jlame 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 appar- 
ently 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 


4 Laboratory Manual ok Glass-blowing 

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. 
AH 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 welt 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 cer- 
tain 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 precipi- 
tates, 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 opera- 
tions 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 satis- 
factory 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 

Materials and Apparatus 5 

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 ceas- 
ing to support it with both hands. 

Glass-blowing should be done in a good light, but pref- 
erably 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. Steadi- 
ness 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 

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 rota- 
tion of glass, the proper temperature, blowing and shrink- 
ing the glass may be learned with a minimum expenditure 

6 Laboratory Manual of Glass-blowing 

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 exer- 
cise, for example, imtil 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 suflBce 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. 

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 for- 
get 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 d^- 


8 Laboratory Manual of Glass-blowing 

sired direction, it may be led along with a hot point of 
glass. This is put a little beyond the end of the crack, 
and as the latter grows out toward it, moved along the 
path where the crack is desired. This point of glass is 
also very useful in breaking off very short ends of tubes, 
where there is not room to get a firm enough hold and 
sufficient leverage to break the tube in the ordinary 
way, and for breaking tubes attached to large or heavy 
objects, which would be likely to make trouble if treated 
in the ordinary way. 

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 aide. After about ten seconds 
of heating, it is removed from the flame and the hot por- 
tion 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-^Iass 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 com- 
monest operations in the laboratory, it is assumed that 
the reader knows how to perform it. However, it 

General Operations ' 9 

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 tub- 
ing 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 tub- 
ing. This is partly on account of the difficulty of heat- 
ing large tubing uniformly to a high temperature, and 

10 Labohatort Manual of Glass-blowing 

partly in order to prevent making the conical part of 
the tube too thin for subsequent operations. 

Constricting a Tube.— Where a constriction \a 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 out- 
side 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 
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 ilame, and the ends cau- 
tiously and gently drawn apart, 

_ „ ' continuing the rotation of the tube 

Fig, 1.— Constricting a , , -. . i . . ■ . 

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, 

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 diflicult 
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 re- 
duced, 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 JIame, while the rotation is 


General Operations 11 

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 char- 
acteristic 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 heat- 

FiG. 2. — Flanging tool. 

ing, 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. 

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 ^vtfc. '^ 

12 Laboratory Manual of Glass-blowing 

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, 6=1 inch; (2) a = l inch, 6=1 inch. 
When the end of the tube is softened, the tool is inserted 

Fig. 3. — Flanging a tube with flanging tool. 

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 insuflBcient 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 paraflBn. After the flange is com- 
plete, the end must be heated again to the softening tem- 
perature and cooled slowly, to prevent it from cracking 

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 

General Operations 13 

rotated about its axis. For large heavy tubes a larger 
carbon would be used. 

Rotation of the Tube. — This is the fundamental ma- 
nipulation 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 regu- 

14 Laboratory Manual of Glass-blowing 

larly on its axis, but firm enough to carry all the weight 
of the tube, leaving the thumb and first finger nothing 
to do but rotate it. The hand must be so turned, and 
the other fingers so bent, that the thimib and first finger 
stretch out nearly to their full length to grasp the tube 

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 angu- 
lar velocity, even though they may be of different diame- 
ters, 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 con- 
stantly 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. 

General Operations 15 

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 
imiformly 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. 

Elementary Exercises 


Joining Two Pieces of Tubing, End to End — First 


This exercise is most easily learned on tubing with an ex- 
terior diameter of 1/4 inch, or a little less, having moder- 
ately heavy walls. A piece of such tubing is heated before 

Fig. 5. — Softening ends of two pieces of tubing. 

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 


Elementary Exercises 


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 




Fig. 6. — Joining two pieces of tubing .end to end— first method. 

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 6. 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). 

As the tube softens and tends to shrink, the two ends 
are pressed together a little and the walls allowed to 

18 Laboratory Manual of Glass-blowing 

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 to- 
gether 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/, 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 

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 (6) 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 

Elementary Exercises 19 

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, pro- 
vided 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 accom- 
plished, 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; 

20 Laboratory Manual of Glass-blowing 

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 /i, and 
the tube will be likely to break if ever reheated at this 
point after it becomes cold. The operations d, 6, /, 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 / 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 (/ 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. 


Joining Two Tubes End to End — Second Method 

The method described in Exercise No. 1 is very satis- 
factory 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 

Elementary Exercises 21 

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 (6, 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 uni- 
formly 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 

22 Laboratory Manual of Glass-blowing 

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 conse- 
quent pull on the end of the apparatus, and makes rota- 
tion difficult. 


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. 

Elementary Exercises 23 

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 tap- 
ering from the thick walls of the a 

tube to a very thin wall at the 
top. The sides of this bulb, be- 
low 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 soft- 
ened 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 indi- p^^ 7 .^he "tee" tube, 
eated in 6, Fig. 7. This will usu- 
ally be so very thin that a stroke of the file or glass- 
knife will break it oflf 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 

24 Laboratory Manual of Glass-blowing 

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 cir- 
cumference 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 forma- 
tion 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 I (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 

Elementary Exercises 25 

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 supply- 
ing 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. 


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 awk- 
ward 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 fe, 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 

26 Laboratory Manual of Glass-blowing 

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. 


X — 

y _1 




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. 

Elementary Exercises 27 

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 (/) 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 over- 
heating 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 

28 Laboratory Manual of Glass-blowing 

right wall-thickness the cone must be'made too long (gr, 
Fig. 8). This does not look well, and usually will be 
irregular in shape. 


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 

-r> r\ 

Fig. 9. — Tube for condensing sulphur dioxide. 

in the same plane, as shown, and their ends fire-polished 
(Fig. 9). 


Bulb at the End of a Tube 

For this exercise tubing of 1/4 inch diameter and moder- 
ately 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 

Elementary Exercises 29 

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 ^^^ io_Biowing a bulb on 

a. Fig. 10, when properly ma- 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 fe. Fig. 10. 
Otherwise the result will be a series of bulbs, as in e, 

30 Laboratory Manual of Glass-blowing 

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 diame- 
ter, 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 rf. 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, con- 
tinuing 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 /, 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 

Elementary Exercises 31 

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 

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, fur- 
rowed or ridged, or lopsided, 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 

32 Laboratory Manual of Glass-blowing 

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 econom- 
ical 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 col- 
lect 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. 


Blowing a Bulb in a Tube 

The tube is selected and one end closed as in the pre- 
vious exercise, but it should be cut a little longer, say 

Elementary Exercises 33 

about twelve inches. Beginning at a point about four 
inches from the closed end, glass is collected and blown in- 
to 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 'Mine 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 rota- 
tion. 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 blow- 
ing 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 ma- 
nipulation 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 

34 Laboratory Manual of Glass-blowing 

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 at- 
tached 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 par- 
ticularly needed. 

Advanced Exercises 


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 pro- 
vide 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 prac- 
tice 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 



Laboratory Manual of Glass-blowing 

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 pusheid into 
contact with the center of the end of the large tube, as 




Fig. 11. — Gas-washing tube. 

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 

Advanced Exercises 37 

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 pre- 
pared, and laid ready with the other (unbored) cork for 
the large 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 pre- 
pared for it, and the short outer tube is joined to the tube 
that has just been blown out, so that the joint appears 
like 6, 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 

38 Laboratory Manual of Glass-blowing 

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 oflf 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 oflf 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 oflf square and fire- 

Discussion. — After the joint has once been made, great 
care must be taken that it is kept hot during all the sub- 
sequent 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 w*hich 
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-thick- 
ness and the **clean-cuf 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 afifords 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 verj* nearly a right angle. 
For this reason the two tubes should not be of too near 
the same size, or if ttus cannot be avoided, a smaU 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. WTiere 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 readilj- be broken when 


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 oflf 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 

40 Laboratory Manual of Glass-blowing 

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 oflf 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 pro- 
vided with a tail drawn out as indicated in 6, so that when 
cut oflf at about 2 1/2 or 3 inches from the main tube its 
inner diameter may be slightly less than that of the nar- 
rowest point of the tube a. A small thick-walled bulb 
is blown at the point indicated by the dotted lines, and 



i. — -M. 

a b 


/ — ^ 


Fig. 12. — Suction pump. 

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. 

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, 

Advanced Exercises 41 

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 

Discussion. — As in the first method, the secret of suc- 
cess 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 

42 Laboratory Manual of Glass-blowing 

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. 



Fig. 13. — a, Kjeldahl trap; 6, 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 
6, Fig. 13. ^^See page 10 for method.) But it is more 
difficult to make a square joint on such small tubing. 

CHAPTER tV' . / 
Modified Methods and SpIicial-' Operations 


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 care- a 

fully 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 yiq. 14. Capillary 

to a piece of ordinary tubing if de- tubing, 

sired. 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 irregulari- 
ties. It is necessary that the bore of the joint be ap- 
proximately that of the main tube, and care must be 
taken that the latter is not constricted at the point 
where the joint begins. 

Especial care must be taken to warm the tube slowly 
when starting and cool it slowly when through, as the 


44 Laboratory Manual of Glass-blowing 

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 (6, 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 

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 suit- 
able size sealed in to provide material for the bulb. 


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 accumulat- 
ing 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 

Modified Methods and Special Operations 45 

By joining pieces side by side, pressing with carbon 
plates or a plate and a rod, and other suitable manipula- 
tions, 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 


Mending the Plug. — The plug of the stopcock occa- 
sionally 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 


Laboratory Manual of Glass-blowing 

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 

Fig. 15. — Stopcock plug. 

of the plug (6, 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 

Modified Methods and Special Operations 47 

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 an- 
nealed. 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. 

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 grind- 
ing 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 con- 
tinued with a little fresh abrasive. If contact appears 

48 Laboratory Manual of Glass-blowing 

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 suc- 
cessfully 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 stop- 
cock, 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. 

Modified Methods and Special Operations 49 


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 soften- 
ing 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 

J J J 

50 Laboratory Manual of Glass-blowing 

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 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 

Fig. 16. — Making a spiral. 

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 begim. 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 6, 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. 

Modified Methods and Special Operations 51 

Especial pains is to be taken with the first turn of the 
spiral (6 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 accom- 
plished, 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 

Fig. 17.— Ground joint. 

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. 


It is sometimes required to join two pieces of tubing 
end to end, \>y 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 ^ 

52 Laboratory Manual of Glass-blowing 

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 car- 
bon. 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 impreg- 
nating it with paraflSn or beeswax, and is extremely use- 
ful wherever a conical surface has to be formed from the 
inside of a tube. 

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 stopcock^. 


Very often it is necessary to seal platinum wire into 
the wall of a tube. Professional glass-blowers usually 

Modified Methods and Special Operations 53 

use a special sort of glass ("Einschmelzglas") which 
is usually a lead glass, and is made of such composi- 
tion that it has the same or practically the same 
coeflScient 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 



Fig. 18. 

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 an- 
nealed carefully. (2) The end of the wire which is to 
be outside the tube is attached to the end of a thin scrap 

54 Laboratory Manual of Glass-blowing 

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 (6, 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 re- 
heated a little if necessary to make it shrink back into 
line with the walls of the tube. The whole circumfer- 
ence of the tube is heated at that point and annealed as 

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 with- 
out changing the thickness of the latter, and consequently 
without developing undue stresses at that point. Such 

Modified Methods and Special Operations 55 

a joint must of course be carefully reheated and an- 
nealed. With fine platinum wire there is very little 
risk of the tube cracking if care is taken to avoid forma- 
tion 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. 


Tubes which have been evacuated usually are sealed 
ofif 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. 


{Carius method for determination of the halogens and 
sidphur.) 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 accoimt of the thick walls. A 

56 Laboratory Manual of Glass-blowing 

length is gradually warmed in the center, finally heated 
at that point until soft, drawn out, cut apart and an- 
nealed. 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 pre- 
vent 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, t>ut of sufficient 
internal diameter to admit the tube containing the sub- 
stance. 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 in- 
clined 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 flrst, 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 

Modified Methods and SpeciaIj Operations 57 

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 ofif. 
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. 


Annealing glass, 4, 24 

Bellows, 4 
Bending glass, 8 
Blowing glass, 13, 19, 20, 21, 24, 

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 imder 

pressure, 55 
Collecting glass for bulb, 29, 31, 

Constricting a tube, 10 
Crystallization of glass, see 

Cutting glass, 7, 25 

Devitrification, 1, 2 
Drawing out a tube, 9, 18, 19, 

Glass, bending, 8 

blowing, 13, 19, 20, 21, 24, 

collecting for bulb, 29, 31, 

cutting, 7 

defects, 2 

grinding, 47 

hard, 1 

knife, 7 

lead, 1 

qualities desired, 1 

rod and tube, joining, 45 

rod, workmg, 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, 

Hard glass, 1 
Holding tube, 13, 14 

Insertion of tube through an- 
other, see Sealing a 
tube through another 

Flanging a tube, 11, 14 
tool, 11 

Gas-washing tube, 35 
Glass, annealing, 4, 24 

Joints, groimd, 51 
Joining rod and tube, 45 

tubing end to end: first 
method, 16 

second method, 20 




Joining tubes of different diam- 
eters, 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 

Quab'ty of glass, 1 

Rod, glass, working, 44 
Rotation of the tube, 13, 19 
Roimded end of tube, 35, 38 
Rubber tube used for blowing, 

Sealing a tube through an- 
other tube, 35, 39 

Sealing vacuum tubes, 55 
Shrinking glass, 18, 19, 22, 26, 

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, 
removed, 30, 35 
Tubes, closed, for heating imder 

pressure, 55 
"Tee" tube, 22 

on capiUary tubing, 43 
small side tube on a large 
tube, 24 

Vacuum tubes, sealing, 55 

Working temperature of glass, 
1, 13, 19, 27 


To avoid fine, this book should be returned on 
or before the date last stamped below. 

DEC iZ 1930 

iM -5 1932 

OCT 7 5 m 

C63 Prary, F.C. 40528 

G5P8 Laboratory manual of 
^914 gIaB8*lJlowing^ - —