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A Handbook of 


Laboratory Glass-Blowing 

Bernard D. Bolas 


Gift of 
Max S. Marshall, M.D< 

**** " 


To my Friends 
Eric Reid 

Sidney Wilkinson 

A Handbook of 
Laboratory Glass-Blowing 








I. Introduction and Preliminary Remarks General 
Principles to be observed in Glass Working 
Choice of Apparatus Tools and Appliances- 
Glass i 

II. Easy Examples of Laboratory Glass -Blowing 
Cutting and Sealing Tubes, Tubes for High 
Temperature Experiments Thermometer-Bulbs 
Bulbs of Special Glass, Pipettes, Absorption- 
Bulbs or Washing Bulbs Joining Tubes, 
Branches, Exhaustion-Branches, Branches of 
Dissimilar Glass, Blowing Bulbs, A Thistle 
Funnel, Cracking and Breaking Glass, Leading 
and Direction of Cracks Use of Glass Rod or 
Strips of Window-Glass, Joining Rod, Feet and 
Supports Gripping Devices for use in Corrosive 
Solutions The Building up of Special Forms 
from Solid Glass 10 

III. Internal Seals, Air-Traps, Spray Arresters, Filter- 

Pumps Sprays, Condensers ; plain, double 
surface, and spherical Soxhlet Tubes and Fat 
Extraction Apparatus Vacuum Tubes, Elec- 
trode Work, Enclosed Thermometers, Alarm 
Thermometers . . . Recording Thermometers, 
"Spinning" Glass .' 32 

IV. Glass, its Composition and Characteristics Anneal- 

ing Drilling, Grinding, and Shaping Glass by 
methods other than Fusion Stop -cocks 



Marking Glass Calibration and Graduation of 
Apparatus Thermometers Exhaustion of Ap- 
paratus Joining Glass and Metal Silvering 
Glass 55 

V. Extemporised Glass-Blowing Apparatus The use 
of Oil or other Fuels Making Small Rods and 
Tubes from Glass Scraps The Examination of 
Manufactured Apparatus with a view to Dis- 
covering the Methods used in Manufacture 
Summary of Conditions necessary for Successful 
Glass-Blowing 80 

Index 105 


To cover the whole field of glass-blowing in a 
small handbook would be impossible. To 
attempt even a complete outline of the methods 
used in making commercial apparatus would 
involve more than could be undertaken with- 
out omitting the essential details of manipulation 
that a novice needs. I have, therefore, confined 
myself as far as possible to such work as will 
find practical application in the laboratory and 
will, I hope, prove of value to those whose 
interests lie therein. 

The method of treatment and somewhat dis- 
jointed style of writing have been chosen 
solely with the view to economy of space 
without the undue sacrifice of clearness. 


Handbook of Laboratory 
Glass- Blowing 


Introduction and Preliminary Remarks General Principles to be 
observed in Glass Working Choice of Apparatus Tools and 
Appliances Glass. 

GLASS-BLOWING is neither very easy nor very 
difficult ; there are operations so easy that the 
youngest laboratory boy should be able to 
repeat them successfully after once having 
been shown the way, there are operations so 
difficult that years are needed to train eye and 
hand and judgment to carry them out ; but 
the greater number of scientific needs lie be- 
tween these two extremes. Yet a surprisingly 
large number of scientific workers fail even to 
join a glass tube or make a T piece that will 
not crack spontaneously, and the fault is rather 
one of understanding than of lack of ability to 
carry out the necessary manipulation. 


In following the scheme of instruction 
adopted in this handbook, it will be well for 
the student to pay particular attention to the 
reason given for each detail of the desirable 
procedure, and, as far as may be, to memorise 
it. Once having mastered the underlying 
reason, he can evolve schemes of manipulation 
to suit his own particular needs, although, as a 
rule, those given in the following pages will be 
found to embody the result of many years' 

There is a wide choice of apparatus, from a 
simple mouth-blowpipe and a candle flame to a 
power-driven blower and a multiple-jet heating 
device. All are useful, and all have their 
special applications, but, for the present, we 
will consider the ordinary types of bellows and 
blowpipes, such as one usually finds in a 
chemical or physical laboratory. 

The usual, or Herepath, type of gas blow- 
pipe consists of an outer tube through which 
coal gas can be passed and an inner tube 
through which a stream of air may be blown. 
Such a blowpipe is shown in section by Fig. i. 
It is desirable to have the three centring 
screws as shown, in order to adjust the position 


of the air jet and obtain a well-shaped flame, 
but these screws are sometimes omitted. Fig. 
i, a and b show the effects of defective centring 
of the air jet, c shows the effect of dirt or 

Fig i 

roughness in the inside of the air jet, d shows 
a satisfactory flame. 

For many purposes, it is an advantage to 


have what is sometimes known as a "quick- 
change " blowpipe ; that is one in which jets of 
varying size may be brought into position 
without stopping the work for more than a 
fraction of a second. Such a device is made 
by Messrs. Letcher, and is shown by e, and in 
section by f Fig. i. It is only necessary to 
rotate the desired jet into position in order to 
connect it with both gas and air supplies. A 
small bye-pass ignites the gas, and adjustment 
of gas and air may be made by a partial 
rotation of the cylinder which carries the jets. 

For specially heavy work, where it is 
needed to heat a large mass of glass, a multiple 
blowpipe jet of the pattern invented by my 
father, Thomas Bolas, as the result of a 
suggestion derived from a study of the jet 
used in Griffin's gas furnace, is of considerable 
value. This jet consists of a block of metal in 
which are drilled seven holes, one being central 
and the other six arranged in a close circle 
around the central hole. To each of these 
holes is a communication way leading to the 
gas supply, and an air jet is arranged centrally 
in each. Each hole has also an extension tube 
fitted into it, the whole effect being that of 


seven blowpipes. In order to provide a final 
adjustment for the flame, a perforated plate 
having seven holes which correspond in size 
and position to the outer tubes is arranged to 
slide on parallel guides in front of these outer 

The next piece of apparatus for consideration 
is the bellows, of which there are three or 
more types on the market, although all consist 
of two essential parts, the blower or bellows 
proper and the wind chamber or reservoir. 
Two patterns are shown in Fig. 2 ; a, is the 

form which is commonly used by jewellers and 
metal workers to supply the air blast necessary 
for heating small furnaces. Such a bellows 
may be obtained at almost any jewellers' 
supply dealer in Clerkenwell, but it not in- 
frequently happens that the spring in the wind 


chamber is too strong for glass-blowing, and 
hence the air supply tends to vary in pressure. 
This can be improved by fitting a weaker 
spring, but an easier way and one that usually 
gives fairly satisfactory results, is to place an 
ordinary screw-clip on the rubber tube leading 
from the bellows to the blowpipe, and to 
tighten this until an even blast is obtained. 

Another form of bellows, made by Messrs. 
Fletcher and Co., and common in most 
laboratories, is shown by b ; the wind chamber 
consists of a disc of india-rubber clamped under 
a circular frame or tied on to a circular rim. 
This form is shown by Fig. 2, b. 

The third form, and one which my own 
experience has caused me to prefer to any 
other, is cylindrical, and stands inside the 
pedestal of the blowpipe-table. A blowpipe- 
table of this description is made by Enfer of 

There is no need, however, to purchase an 
expensive table for laboratory use. All the 
work described in this book can quite well be 
done with a simple foot bellows and a quick- 
change blowpipe. Nearly all of it can be done 
with a single jet blowpipe, such as that described 


first, or even with the still simpler apparatus 
mentioned on page 84, but I do not advise the 
beginner to practise with quite so simple a form 
at first, and for that reason have postponed a 
description of it until the last chapter. 

Glass-blowers' tools and appliances are many 
and various, quite a number of them are better 
rejected than used, but there are a few essentials. 
These are, file, glass-knife, small turn-pin, 
large turn-pin, carbon cones, carbon plate, 
rubber tube of small diameter, various sizes 
of corks, and an asbestos heat reflector. For 
ordinary work, an annealing oven is not neces- 
sary, but one is described on page 60 in con- 
nection with the special cases where annealing 
is desirable. 

Fig. 3 illustrates the tools and appliances. 
a is an end view of the desirable form of file, 
and shows the best method of grinding the 
edges in order to obtain a highly satisfactory 
tool, b is a glass knife, shown both in per- 
spective and end view, it is made of glass-hard 
steel and should be sharpened on a rough 
stone, such as a scythe-stone, in order to give 
a slightly irregular edge, c is a small turn-pin 
which may be made by flattening and filing the 


end of a six-inch nail, d is the large turn-pin 
and consists of a polished iron spike, about five 
inches long and a quarter of an inch diameter 
at its largest part. This should be mounted 
in a wooden handle, e and /"are carbon cones. 
A thin rubber tube is also useful ; it may be at- 

Fig. 3 

tached to the work and serve as a blowing tube, 
thus obviating the necessity of moving the work 
to the mouth when internal air pressure is to be 
applied. In order to avoid undue repetition, 
the uses of these tools and appliances will be 
described as they occur. 


Glass, as usually supplied by chemical appar- 
atus dealers is of the composition known as 
"soda-glass." They also supply " hard " or 
"combustion" glass, but this is only used for 
special purposes, as it is too infusible for con- 
venient working in the ordinary blowpipe flame. 

Soda-glass consists primarily of silicate of 
sodium with smaller quantities of silicate of 
aluminum and potassium. Its exact composi- 
tion varies. It is not blackened, as lead glass 
is, by exposure to the reducing gases which 
are present in the blue cone of a blowpipe 
flame, and hence is easier for a beginner to 
work without producing discolouration. 

Further notes on glasses will be found on 
page 55, but for ordinary purposes soda-glass 
will probably be used. 


Easy Examples of Laboratory Glass-BlowingCutting and Sealing 
Tubes for Various Purposes ; Test-Tubes, Pressure-Tubes, Tubes for 
High Temperature Experiments Thermometer-Bulbs, Bulbs of 
Special Glass, Pipettes, Absorption-Bulbs or Washing-Bulbs Joining 
Tubes ; Branches, Exhaustien-Branches, Branches of Dissimilar Glass 
Blowing Bulbs ; A Thistle Funnel ; Cracking and Breaking Glass ; 
Leading and Direction of Cracks Use of Glass Rod or Strips of 
Window-Glass ; Joining Rod, Feet and Supports Gripping Devices 
for use in Corrosive Solutions The Building Up of Special Forms 
from Solid Glass. 

PERHAPS the most common need of the glass- 
blower whose work is connected with that of 
the laboratory is for a sealed tube ; and the 
sealing of a tube is an excellent preliminary 
exercise in glass-blowing. 

We will assume that the student has adjusted 
the blowpipe to give a flame similar to that 
shown in d y Fig. i, and that he has learned 
to maintain a steady blast of air with the 
bellows ; further, we will assume that the tube 
he wishes to seal is of moderate size, say not 
more than half an inch in diameter and with 


walls of from one-tenth to one-fifth of an inch 

A convenient length of tube for the first trial 
is about one foot ; this should be cut off from 
the longer piece, in which it is usually supplied, 
as follows : lay the tube on a flat surface and 
make a deep cut with the edge of a file. Do 

not "saw" the file to and fro over the glass. 
If the file edge has been ground as shown in a, 
Fig. 3, such a procedure will be quite unneces- 
sary and only involve undue wear ; one move- 
ment with sufficient pressure to make the file 
"bite" will give a deep cut. Now rotate the 
tube through about one-eighth of a turn and 


make another cut in continuation of the first. 
Take the tube in the hands, as shown in a, Fig. 
4, and apply pressure with the thumbs, at the 
same time straining at the ends. The tube 
should break easily. If it does not, do not 
strain too hard, as it may shatter and cause 
serious injuries to the hands, but repeat the 
operation with the file and so deepen the 
original cuts. In holding a tube for breaking, 
it is important to place the hands as shown in 
sketch, as this method is least likely to cause 
shattering and also minimises the risk of injury 
even if the tube should shatter. To cut a large 
tube, or one having very thick walls, it is better 
to avoid straining altogether and to break by 
applying a small bead of intensely heated glass 
to the file cut. If the walls are very thin, a 
glass-blower's knife should be used instead of a 
file. The tube and glass-blower's knife should 
be held in the hand, and the tube rotated 
against the edge of the knife ; this will not 
produce a deep cut, but is less likely to break 
the tube. A bead of hot glass should be used 
to complete the work. 

The next operation is to heat the glass tube 
in the middle ; this must be done gradually 


and evenly ; that is to say the tube must be 
rotated during heating and held some con- 
siderable distance in front of the flame at first ; 
otherwise the outer surface of the glass will 
expand before the interior is affected and the 
tube will break. From two to five minutes, 
heating at a distance of about eight inches in 
front of the flame will be found sufficient in 
most cases, and another minute should be 
taken in bringing the tube into the flame. 
Gradual heating is important, but even heating 
is still more important and this can only be 
obtained by uniform and steady rotation. Until 
the student can rotate a tube steadily without 
thinking about it, real progress in glass-blowing 
is impossible. 

When the tube is in the flame it must be 
held just in front of the blue cone and rotated 
until the glass is soft enough to permit the ends 
to be drawn apart. Continue to separate the 
ends and, at the same time, move the tube 
very slightly along its own axis, so that the 
flame tends to play a little more on the thicker 
part than on the drawn-out portion. If this is 
done carefully, the drawn-out portion can be 
separated off, leaving only a slight "bleb" on 


the portion it is desired to seal. This is 
illustrated by b, Fig. 4. 

To convert the seal at b, Fig. 4., into the 
ordinary form of test-tube seal, it is only 
necessary to heat the " bleb " a little more 
strongly, blow gently into the tube until the 
thick portion is slightly expanded, re-heat the 
whole of the rounded end until it is beginning 
to collapse, and give a final shaping by careful 
blowing after it has commenced to cool. In 
each case the glass must be removed from the 
flame before blowing. The finished seal is 
shown by c, Fig. 4. If desired, the open end 
may now be finished by heating and rotating 
the soft glass against the large turn-pin, as 
illustrated in d, but the turn-pin must not be 
allowed to become too hot, as if this happens 
it will stick to the glass. After turning 
out the end, the lip of glass must be 
heated to redness and allowed to cool without 
coming in contact with anything ; otherwise it 
will be in a condition of strain and liable to 
crack spontaneously. The finished test-tube 
is shown by e. 

When it is necessary to seal a substance 
inside a glass tube, the bottom of the tube is 


first closed, as explained above, and allowed 
to cool ; the substance, if a solid, is now in- 
troduced, but should not come to within less 
than two inches of the point where the second 
seal is to be made. If the substance is a 
liquid it can more conveniently be introduced 
at a later stage. 

Now bring the tube into the blowpipe flame 
gradually, and rotate it, while heating, at the 
place where it is to be closed. Allow the glass 
to soften and commence to run together until 
the diameter of the tube is reduced to about 
half its original size. Remove from the flame 
and draw the ends apart, this should give a 
long, thick extension as shown by f y Fig. 4. 
If any liquid is to be introduced, it may now 
be done by inserting a thin rubber or other 
tube through the opening and running the 
liquid in. A glass tube should be used with 
caution for introducing the liquid, as any hard 
substance will tend to scratch the inside of the 
glass and cause cracking. The final closure is 
made by melting the drawn-out extension in 
the blowpipe flame ; the finished seal being 
shown by g, Fig. 4. 

If the sealed tube has to stand internal 


pressure, it is desirable to allow the glass to 
thicken somewhat more before drawing out, 
and the bottom seal should also be made 
thicker. For such a tube, and especially when 
it has to stand heating, as in a Carius deter- 
mination of chlorine, each seal should be cooled 
very slowly by rotating it in a gas flame until 
the surface is covered with a thick layer of 
soot, and it should then be placed aside in a 
position where the hot glass will not come in 
contact with anything, and where it will be 
screened from all draughts. 

Joining Tube. We will now consider the 
various forms of join in glass tubing which are 
met with in the laboratory. First, as being 
easiest, we will deal with the end-to-end 
joining of two tubes of similar glass, a, b, and 
r, Fig. 5, illustrate this. One end of one of 
the tubes should be closed, a lip should be 
turned out on each of the ends to be joined, 
and both lips heated simultaneously until the 
glass is thoroughly soft. Now bring the lips 
together gently, until they are in contact at all 
points and there are no places at which air 
can escape ; remove from the flame, and blow 
slowly and very cautiously until the joint is ex- 


panded as shown in b, Fig. 5. Reheat in the 
flame until the glass has run down to rather 
less than the original diameter of the tube, and 
give a final shaping by re-blowing. The chief 

Fig. 5 

factors of success in making such a join are, 
thorough heating of the glass before bringing 
the two tubes together, and avoidance of hard 
or sudden blowing when expanding the joint. 
The finished work is shown by c, Fig. 5. 

To join a small glass tube to the end of a 


large one, the large tube should first be sealed, 
a small spot on the extreme end of the seal 
heated, and air pressure used to expand the 
heated spot as shown in d. This expanded 
spot is then re-heated and blown out until it 
bursts as shown in e, the thin fragments of 
glass are removed and the end of the small 
tube turned out as shown in f. After this the 
procedure is similar to that used in jointing 
two tubes of equal size. 

When these two forms of joint have been 
mastered, a " piece will present but little 
difficulty. It is made in three stages as shown 
in Fig. 5, and the procedure is similar to that 
used in joining a large and small tube. Care 
should be taken to avoid softening the top of 
the "T" too much, or the glass will bend and 
distort the finished work ; although a slight 
bend can be rectified by re-heating and bending 
back. Local re-heating is often useful in 
giving the joint its final shape. 

An exhaustion branch is often made by a 
totally different method. This method is 
shown by g t h t and z, Fig. 5 ; g is the tube on 
which the branch is to be made. The end of 
a rod of similar glass should be heated until a 


mass of thoroughly liquid glass has collected, 
as shown, and at the same time a spot should 
be heated on that part of the tube where it is 
desired to make the branch. The mass of hot 
glass on the rod is now brought in contact with 
the heated spot on the tube and expanded by 
blowing as shown by h. The air pressure in 
the tube is still maintained while the rod is 
drawn away as shown by i. This will give a 
hollow branch which may be cut off at any 
desired point, and is then ready for connection 
to the vacuum pump. 

If the rod used is of a dissimilar glass, the 
branch should be blown much thinner. Such 
a branch will often serve as a useful basis for 
joining two tubes of different composition, as 
the ordinary type of branch is more liable to 
crack when made with two glasses having 
different coefficients of expansion. 

Blowing Bulbs. A bulb may be blown on a 
closed tube such as that shown by c, Fig. 5, by 
rotating it in the blowpipe flame until the end 
is softened, removing it from the flame and 
blowing cautiously. It is desirable to continue 
the rotation during blowing. In the case of a 
very small tube, it is sufficient to melt the end 


without previous sealing, rotate it in the flame 
until enough glass has collected, remove from 
the flame and blow while keeping the tube in 

Thermometer Bulbs. If the thermometer 
is to be filled with mercury, it is desirable to 
use a rubber bulb for blowing, as moisture is 
liable to condense inside the tube when the 
mouth is used, and this moisture will cause the 
mercury thread to break. In any case, a slight 
pressure should be maintained inside the 
thermometer tube while it is in the flame ; 
otherwise the fine capillary tube will close and 
it will be very difficult to expand the heated 
glass into a bulb. 

Large Bulbs. When a large bulb is needed 
on a small or medium sized tube, it is often 
necessary to provide more glass than would be 
obtained if the bulb were blown in the ordinary 
way. One method is to expand the tube in 
successive stages along its axis, as shown by a, 
Fig. 6. These expanded portions are then 
reheated, so that they run together into one 
hollow mass from which the bulb is blown ; b 
and c^ illustrate this. Another method, and 
one which is useful for very large bulbs, is to 


fuse on a length of large, thick- walled, tubing. 
The heat reflector, g, Fig. 3, should be used, if 
necesssary, when making large bulbs. It 

Fig. 6 

consists of a sheet of asbestos mounted in a 
foot, and is used by being placed close to the 
mass of glass on the side away from the blow- 
pipe flame while the glass is being heated. 


Bulbs of Dissimilar Glass. These may be 
made by the second method given under 
" Large Bulbs," but the joint should be blown 
as thin as possible. Further instructions in the 
use of unlike glasses are given on page 94. 

A Bulb in the Middle of a Tube. Unless 
the bulb is to be quite small, it will be 
necessary to join in a piece of thick glass 
tubing, or to draw the thin tube out from a 
larger piece, thus leaving a thick ir.ass in the 
middle as shown by d, Fig. 6. This mass of 
glass should now be rotated in the blowpipe 
flame until it is quite soft and on the point of 
running together. Considerable practice will 
be necessary before the two ends of the tube 
can be rotated at the same speed and without 
" wobbling," but this power must be acquired. 
When the glass is thoroughly hot, remove from 
the flame, hold in a horizontal position, and 
expand by blowing. It is essential to continue 
the rotation while this is done. Should one 
part of the bulb tend to expand more than the 
other, turn the expanded part to the bottom, 
pause for about a second, both in rotating and 
blowing, in order that the lower portion may 


be cooled by ascending air-currents ; then 
continue blowing and turning as before. 

Absorption Bulbs or Washing Bulbs. 
These are made by an elaboration of the 
processes given in the last paragraph, g, h, and 
z, Fig. 6, illustrate this. 

A Thistle Funnel. This is made by 
blowing a fairly thick-walled bulb on a glass 
tube, bursting a hole by heating and blowing, 
and enlarging the burst-out part by heating 
and rotating against a turn-pin. 

Bending Glass Tube. Small tubing may be 
bent in a flat flame gas burner and offers no 
special difficulty. Large or thin-walled tubing 
should be heated in the blowpipe flame and a 
slight bend made ; another zone of the tube, 
just touching the first bend, should now be 
heated and another slight bend made. In this 
way it is possible to avoid flattening and a 
bend having any required angle can gradually 
be produced. A final shaping of the bend may 
be made by heating in a large blowpipe flame 
and expanding slightly by air pressure. 

Glass Spirals. If a tube is heated by 
means of a long, flat-flame burner, the softened 
tube may be wound on to an iron mandrel 


which has previously been covered with 
asbestos. The mandrel should be made 
slightly conical in order to facilitate withdrawal. 
It is desirable to heat the surface of the 
asbestos almost to redness by means of a 
second burner, and thus avoid undue chilling 


of the glass and the consequent production of 
internal strain. 

A Thermo- Regulator for Gas. Fig. 7, a 
e, shows an easily constructed thermo-regulator. 


The mercury reservoir, a, and the upper part, 
6, are made by joining two larger pieces of 
tubing on to the capillary. The gas inlet 
passes through a rubber stopper, in order to 
allow of adjustment for depth of insertion, and 
the bye-pass branches, d and , are connected 
by a piece of rubber tubing which can be 
compressed by means of a screw clip, thus 
providing a means of regulating the bye-pass. 

Use of Glass Rod. Apart from its most 
common laboratory use for stirring ; glass rod 
may be used in building up such articles as 
insulating feet for electrical apparatus or acid- 
resisting cages for chemical purposes. Such a 
cage is shown by/, g and h, Fig. 7. Further, 
by an elaboration of the method of making an 
exhaustion branch, given on page 18, blown 
articles may also be constructed from rod. 
Note the added parts of 0, Fig. 9. 

A Simple Foot. The form of foot shown by 
Fig. 7, k, is easy to make and has many uses. 
First join a glass rod to a length of glass 
tubing as shown (the joint should be expanded 
slightly by blowing), cut off the tube and heat 
the piece remaining on the rod until it can be 
turned out as shown by i. This should be 


done with the large turn-pin, and care should 
be taken not to heat the supporting rod too 
strongly, otherwise the piece of tube will 
become bent and distorted ; it is better to 
commence by heating the edge of the piece of 
tube and turn out a lip, then extend the heating 
by degrees and turn out more and more until 
the foot looks like that shown by z. 

We now need to make three projections of 
glass rod. These are produced as follows : 
Heat the end of the glass rod until a thoroughly 
melted mass of glass has accumulated (the rod 
must be rotated while this is being done, other- 
wise the glass will drop off) ; when sufficient 
melted glass has been obtained, the edge of the 
turned-out foot should be heated to dull redness 
over about one-third of its circumference, and 
the melted glass on the rod should be drawn 
along the heated portion until both are so 
completely in contact as to form one mass of 
semi-fluid glass. The rod should now be 
drawn away slowly, and, finally, separated by 
melting off, thus producing a flat projection. 
A repetition of the process will give the other 
two projections, and the finished foot may be 
adjusted to stand upright by heating the 


projections slightly and standing it on the 
carbon plate mentioned on page 7. After the 
foot is adjusted it should be annealed slightly 
by heating to just below the softening point of 
the glass and then rotating in a smoky gas 
flame until it is covered with a deposit of 
carbon, after which it should be allowed to 
cool in a place free from draughts and where 
the hot glass will not come in contact with 
anything. The finished foot is shown by /&, 
Fig. 7. 

Building up from Glass Rod. A glass 
skeleton-work can be constructed from rod 
without much difficulty, and is sometimes use- 
ful as a container for a substance which has to 
be treated with acid, or for similar purposes. 
The method is almost sufficiently explained by 
the illustration in Fig. 7 ; f shows the initial 
stage, g the method of construction of the 
net-work, and h the finished container. It 
is convenient to introduce the substance at 
the stage indicated by g. The important 
points to observe in making this contrivance 
are that the glass rod must be kept hot by- 
working while it is actually in the flame, and 
that the skeleton must be made as thin as 


possible with the avoidance of heavy masses 
of glass at any place. If these details are 
neglected it will be almost certain to crack. 

Stirrers. These are usually made from 
glass rod, and no special instructions are neces- 
sary for their construction, except that the 
glass should be in a thoroughly fused condition 
before making any joins and the finished join 
should be annealed slightly by covering with a 
deposit of soot, as explained on page 16. The 
flat ends shown in a, Fig. 8, are made by 
squeezing the soft glass rod between two pieces 
of carbon, and should be reheated to dull red- 
ness after shaping. Fig. 8 also shows various 
forms of stirrer. 

In order to carry out stirring operations in 
the presence of a gas or mixture of gases other 
than air, some form of gland or seal may be 
necessary where the stirrer passes through the 
bearing in which it runs. A flask to which is 
fitted a stirrer and gas seal is shown in section 
by b, Fig. 8. The liquid used in this seal may 
be mercury, petroleum, or any other that the 
experimental conditions indicate. 

If the bearing for a stirrer is made of glass 
tube, it is desirable to lubricate rather freely ; 


otherwise heat will be produced by the friction 
of the stirrer and the tube will probably crack. 
Such lubrication may be supplied by turning 
out the top of the bearing tube and filling the 

turned-out portion with petroleum jelly mixed 
with a small quantity of finely ground or, better, 
colloidal graphite, and the bearing should also 


be lubricated with the same composition. Care 
should be taken not to employ so soft a lubri- 
cant or so large an excess as to cause* it to run 
down the stirrer into the liquid which is being 

Leading a Crack. It sometimes happens that 
a large bulb or specially thin-walled tube has 
to be divided. In such a case it is scarcely 
practicable to use the method recommended for 
small tubes on page 12, but it is quite easy to 
lead a crack in any desired direction. A con- 
venient starting point is a file cut ; this is 
touched with hot glass until a crack is initiated. 
A small flame or a bead of hot glass is now 
used to heat the article at a point about a 
quarter of an inch from the end of the crack 
and in whatever direction it has to be led. The 
crack will now extend towards the source of 
heat, which should be moved farther away 
as the crack advances. In this manner a crack 
may be caused to take any desired path and 
can be led round a large bulb. 

Cutting Glass with the Diamond. Slips of 
window-glass can be used in place of glass rod 
for some purposes, and as cutting them involves 
the use of the glaziers' diamond or a wheel- 


cutter, they may well be mentioned under this 

In cutting a sheet of glass with the diamond, 
one needs a flat surface on which to rest the 
glass, and a rule against which to guide the 
diamond. The diamond should be held in an 
almost vertical position, and drawn over the 
surface of the glass with slight pressure. While 
this is being done the angle of the diamond 
should be changed by bringing the top of the 
handle forward until the sound changes from 
one of scratching to a clear singing note. 
When this happens the diamond is cutting. 
A few trials will teach the student the correct 
angle for the diamond with which he works, 
and the glass, if properly cut, will break easily. 
If the cut fails it is better to turn the glass over 
and make a corresponding cut on the other side 
rather tHan make any attempt to improve the 
original cut. The diamond is seldom used for 
cutting small glass tubes. 

The use of the wheel-cutter calls for no 
special mention as it will cut at any angle, 
although the pressure required is somewhat 
greater than that needed by most diamonds. 


Internal Seals, Air-Traps, Spray Arresters, Filter-PumpsSprays, 
Condensers ; Plain, Double Surface, and Spherical Soxhlet Tubes and 
Fat Extraction Apparatus Vacuum Tubes, Electrode Work, Enclosed 
Thermometers, Alarm Thermometers, Recording Thermometers, 
"Spinning" Glass. 

Internal Seals. It is convenient to class 
those cases in which a glass tube passes through 
the wall of another tube or bulb under the 
heading of " Internal Seals," These are met 
with in barometers, spray arresters, and filter 
pumps, in condensers and some forms of 
vacuum tube. The two principal methods of 
making such seals will be considered first and 
their special application afterwards. 

An Air Trap on a Barometer Tube. This 
involves the use of the first method, and is per- 
haps the simplest example that can be given. 
Fig. 9, a, ai and #2, show the stages by which 
this form of internal seal is made. For the first 
trials, it is well to work with fairly thick-walled 


tubing, which should be cut into two pieces, 
each being about eight inches long. 

<J **. 

QI V^x a. 

Fig. 9 

First seal the end of one tube as described 
on page 13, heat the sealed end and expand to a 


thick walled bulb. Fuse the end of the other 
tube, attach a piece of glass rod to serve as a 
handle, and draw out ; cut off the drawn-out 
portion : leaving an end like a. 

Now heat a small spot at the end of the 
bulb, blow, burst out, and remove the thin 
fragments of glass. Heat a zone on the 
other tube at the point where the drawn- 
out portion commences and expand as shown 
by ai. 

The next stage is to join the tubes. Heat 
the ragged edges of the burst-out portion until 
they are thoroughly rounded. At the same 
time heat the drawn-out tube to just below 
softening point. Then, while the rounded 
edges of the burst-out portion are still soft, 
insert the other tube ; rotate the join in the 
blowpipe flame until it is quite soft, and ex- 
pand by blowing. If necessary, reheat and 
expand again. The finished seal, which 
should be slightly annealed by smoking in a 
sooty flame, is shown by az. 

A Spray Arrester. This is made by the 
second method, in which the piece of tube 
which projects inside the bulb is fused in 
position first and the outer tube is then joined 


on. The various stages of making are 
illustrated by b, bi and 62, Fig. 9. 

A bulb is blown between two tubes by the 
method given on page 22, the larger tube is then 
cut off and the small piece of tube introduced 
into the bulb after having been shaped as 
shown in by b, Fig. 9. The opening in the 
bulb is sealed as shown by bi. The sealed 
part is now heated and the bulb inclined 
downwards until the inner tube comes in 
contact with the seal and is fused in position. 
This operation requires some practice in order 
to prevent the inner tube either falling through 
the soft glass or becoming unsymmetrical. The 
end of the bulb, where the inner tube comes in 
contact with it, is now perforated by heating 
and blowing, thus giving the form shown by 
2, and the outer tube is joined on. The 
finished spray arrester is shown by ^3. 
Practice alone will give the power to produce 
a symmetrical and stable piece of work. 

Two Forms of Filter Pump. That illus- 
trated by d, Fig. 9, is made by the method 
explained under " An Air Trap on a Baro- 
meter Tube." That illustrated by c is made 
by the method explained under "A Spray 


Arrester." No new manipulation is involved, 
and the construction should be clear from a 
study of the drawings. 

Multiple and Branched Internal Seals. A 
fuller consideration of these will be found on 
page 39, but one general principle may well be 
borne in mind ; that, as far as is possible, a 
tube having both ends fastened inside another 
tube or bulb should be curved or have a spiral 
or bulb at some point in its length, otherwise 
any expansion or contraction will put great 
strain on the joints. 

Sprays. A spray which is easy to make, 
easy to adjust, and easy to clean after use is 
shown by e, Fig. 9. The opening on the top 
of the bulb is made by melting on a bead of 
glass, expanding, bursting, and fusing the 
ragged edges. The two branches which form 
the spray producing junction are made by the 
method used for an exhaustion branch and 
described on page 18. 

A spray which can be introduced through 
the neck of a bottle is shown by h, Fig. 9. 
The various stages in making this are illustrated 
by f, and g. If the inner tube is made by 
drawing out from a larger piece of glass so 


that two supporting pieces are left on each side 
of the place where it is intended to make the 
final bend, that bend can be made in a fiat- 
flame gas burner without causing the inner 
tube to come in contact with the walls of the 
outer tube. Care must be taken when joining 
on the side piece that the inner tube is not 
heated enough to fuse it. The small hole in 
the side of the outer tube is produced by 
heating and bursting. 

A Liebigs Condenser. This consists of a 
straight glass tube passing through an outer 
cooling jacket. In practice it is better to 
make the jacket as a separate piece, and to 
effect a water-tight junction by means of two 
short rubber tubes. It may, however, be made 
with two internal seals of the class described 
under " A Spray Arrester." There is much less 
risk of these seals cracking if the inner tube is 
made in the form of a spiral or has a number of 
bulbs blown on it in order to give a certain 
amount of elasticity. 

A Double- Surf ace Condenser. Fig. 10 
shows a condenser of this nature which is 
supplied by Messrs. Baird and Tatlock. It 
may be built up in stages as shown by a, b, 


and c, but the work involved requires consider- 
able skill, and the majority of laboratory workers 
will find it cheaper to buy than to make. 

Fig. 10 

A Spherical Condenser. Such a condenser 
as that shown byf. Fig 10, involves a method 
which may find application in a number of 
cases. The outer bulb is blown from a thick 
piece of tubing which has been inserted in a 


smaller piece (see d, Fig. 6) ; then the inner bulb 
by similar method. It is now necessary to intro- 
duce the smaller bulb into the larger, and for 
this purpose the larger bulb must be cut into 
halves. A small but deep cut is made with the 
file or glass-blowers' knife in the middle of the 
larger bulb, and at right angles to the axis of 
the tube on which it is blown. A minute bead 
of intensely heated glass is now brought in 
contact with the cut in order to start a crack. 
This crack may now be led round the bulb as 
described on page 30. If the work is carried 
out with care, it is possible to obtain the bulb 
in two halves as shown by d, and these two 
halves will correspond so exactly that when the 
cut edges are placed in contact they will be 
almost air-tight. The two tubes from the 
smaller bulb should be cut to such a length that 
they will just rest inside the larger, and the 
ends should be expanded. Place the inner 
bulb in position and fit the two halves of the 
outer bulb together, taking great care not to 
chip the edges. If the length of the tubes on 
the inner bulb has been adjusted properly, the 
inner bulb will be supported in position by 
their contact with the tubes on the outer bulb. 


Now rotate the cracked portion of the outer 
bulb in front of a blowpipe flame and press the 
halves together very gently as the glass softens. 
Expand slightly by blowing if necessary. If a 
small pin-hole develops at the joint it is some- 
times possible to close this with a bead of hot 
glass ; but if the bulb has been cut properly 
there should be no pin-holes formed. The 
condenser is finished by joining on the side 
tubes and sealing the inner tube through by the 
methods already given. In order to blow 
bulbs large enough to make a useful condenser, 
it will be convenient to employ the multiple-jet 
blowpipe described on page 4. 

A Soxhlet- Tube or Extraction Apparatus. 
This involves the construction of a re-entrant 
join where the syphon flows into the lower 
tube. It is of considerable value as an exercise 
and the complete apparatus is easy to make. 

A large tube is sealed at the bottom and the 
top is lipped, as in making a test-tube. A 
smaller tube is then joined on by a method 
similar to that given on page 18, but without 
making a perforation in the bottom of the large 
tube. Heating and expanding by air pressure, 
first through the large tube, then through the 


smaller tube and then again through the large 
tube, will give a satisfactory finish to this part 
of the work. 

The syphon tube is now joined on to the 
large tube as shown by a, Fig. IT, care being 

Fig. u 

taken to seal the other end of the syphon tube 
before joining. The details of the final and 
re-entrant joint of the syphon tube are shown 
at the lower part of a. This join is made by 
expanding the sealed end of the syphon tube 
into a small, thick-walled bulb, and the bottom 


of this bulb is burst out by local heating and 
blowing ; the fragments of glass are removed 
and the edges made smooth by melting. A 
similar operation is carried out on the side of 
the tube to which the syphon tube is to be 
joined. This stage is shown by a. Now heat 
the syphon tube at the upper bend until it is 
flexible, and press the bulb at its end into the 
opening on the side of the other tube. Hold 
the glass thus until the syphon is no longer 
flexible. The final join is made by heating the 
two contacting surfaces, if necessary pressing 
the edges in contact with the end of a turn-pin, 
fusing together and expanding. The finished 
apparatus is shown by c. 

Electrodes. A thin platinum wire may be 
sealed into a capillary tube without any special 
precautions being necessary. The capillary 
tube may be drawn out from the side of a 
larger tube by heating a spot on the glass, 
touching with a glass rod and drawing the rod 
away ; or the exhaustion branch described on 
page 1 8 may be used for the introduction of an 
electrode. It is convenient sometimes to carry 
out the exhaustion through the same tube that 
will afterwards serve for the electrode. The 


electrode wire is laid inside the branch before 
connecting to the exhaustion pump. When 
exhaustion is completed the tube is heated 
until the soft glass flows round the platinum 
and makes the seal air-tight. The branch is 
now cut off close to the seal on the pump side, 
a loop is made in the projecting end of the 
platinum wire, and the seal is finished by 
melting the cut-offend. 

Platinum is usually employed for such work, 
but if care is taken to avoid oxidation it is not 
impossible to make fairly satisfactory seals with 
clean iron or nickel wire. Hard rods of fine 
graphite, such as are used in some pencils, may 
also be sealed into glass, but it seems probable 
that air would diffuse through the graphite in 
the course of time. 

Another method for the introduction of an 
electrode is illustrated by d, e,f3.ndg, Fig. n. 
In this case the bulb or thin-walled tube into 
which the electrode is to be sealed is perforated 
by a quick stab with an intensely heated wire- 
preferably of platinum which is then withdrawn 
before the glass has had time to harden, and 
thus a minute circular hole is made. The 
electrode is coated with a layer of similar glass, 


or of the specially made enamel which is sold 
for this purpose, inserted into the bulb or tube 
by any convenient opening, and adjusted by 
careful shaking until the platinum wire projects 
through the small hole. The bulb or tube is 
then fused to the coating of the electrode and 
the whole spot expanded slightly by blowing. 
The appearance of the finished seal is shown 
by^-. It is well to anneal slightly by smoking. 

Thermometers. Apart from the notes on 
page 20 with respect to the blowing of a 
suitable bulb on capillary tubing there is little 
to say in connection with the glass working 
needed in making a plain thermometer. The 
size desirable for the bulb will be determined 
by the bore of the capillary tube, the coefficient 
of expansion of the liquid used for filling, and 
the range of temperature for which the thermo- 
meter is intended. 

Filling may be carried out as follows : Fit 
a small funnel to the open end of the capillary 
by means of a rubber tube, and pour into the 
funnel rather more than enough of the liquid to 
be used than is required to fill the bulb. 
Mercury or alcohol will be used in practice, 
most probably. Warm the bulb until a few air 


bubbles have escaped through the liquid and 
then allow to cool. This will suck a certain 
amount of liquid into the bulb. Now heat the 
bulb again, and at the same time heat the capil- 
lary tube over a second burner. The liquid 
will boil and sweep out the residual air, but it 
is necessary to heat the capillary tube as well 
in order to prevent condensation. Allow the 
bulb and tube to cool, then repeat the heating 
once more. By this time the bulb and tube 
should be free from air, and cooling should give 
a completely filled thermometer. Remove the 
funnel and heat the thermometer to a few 
degrees above the maximum temperature for 
which it is to be used ; the mercury or other 
filling liquid will overflow from the top, and, as 
the temperature falls, will recede, thus allowing 
the end of the capillary to be drawn out. Re- 
heat again until the liquid rises to the top of 
the tube, then seal by means of the blowpipe 
flame. The thermometer is now finished 
except for graduation ; this is dealt with on 

page 75- 

An Alarm Thermometer. A thermometer 
which will complete an electric circuit when a 
certain temperature is reached may be made by 


sealing an electrode in the bulb and introducing 
a wire into the top, which in this case is not 
sealed. Naturally, this thermometer will be 
filled with mercury. There is considerable 
difficulty in filling such a bulb without causing 
it to crack. 

Several elaborations of this form are made, in 
which electrodes are sealed through the walls 
of the capillary tube, thus making it possible to 
detect electrically the variation of temperature 
when it exceeds any given limits. 

An Enclosed or Floating Thermometer. 
The construction of this type of thermometer is 
shown by h and z, Fig n. It is made in the 
following stages : A bulb is blown on the 
drawn-out end of a thin-walled tube as shown 
by h. A small bulb is blown on the end of a 
capillary tube, burst, and turned out to form a 
lip which will rest in the drawn-out part of the 
thin-walled tube but is just too large to enter 
the bulb. The capillary tube is introduced and 
sealed in position, care being taken to expand 
the joint a little. The thermometer is filled 
and the top of the capillary tube closed by the 
use of a small blowpipe flame. A paper scale 
having the necessary graduations is inserted, 


and the top of the outer tube is closed as shown 
by i. 

A Maximum and Minimum Thermometer. 
If a small dumb-bell-shaped rod of glass or 
metal is introduced into the capillary tube of a 
horizontally placed, mercury-filled thermometer 
in such a position that the rising mercury 
column will come in contact with it, the rod 
will be pushed forward. When the mercury 
falls again the rod will be left behind and thus 
indicate the maximum temperature attained. 
If a similar dumb-bell-shaped rod is introduced 
into an alcohol-filled thermometer and pushed 
down until it is within the alcohol column, it 
will be drawn down by surface tension as the 
column falls ; but the rising column will flow 
passed it without causing any displacement ; thus 
the minimum temperature will be recorded. 

Six's combined maximum and minimum ther- 
mometer is shown by b, Fig. n. In this case 
both maximum and minimum records are ob- 
tained from a mercury column, although the 
thermometer bulb is filled with alcohol. It is 
an advantage to make the dumb-bell-shaped 
rods of iron, as the thermometer can then be 
reset by the use of a small magnet, another 


advantage consequent on the use of metal 
being that the rods can be easily adjusted, by 
slight bending, so as to remain stationary in 
the tubes when the thermometer is hanging 
vertically, and yet to move with sufficient 
freedom to yield to the pressure of the 
recording column. 

The thermometer may be filled by the 
following method : When the straight tube 
has been made the first dumb-bell is introduced 
and shaken down well towards the lower bulb, 
the tube is now bent to its final shape and the 
whole thermometer filled with alcohol as de- 
scribed on page 44. Now heat the thermometer 
to a little above the maximum temperature that 
it is intended to record, and pour clean mercury 
into the open bulb while holding the ther- 
mometer vertically. Allow to cool, and the 
mercury will be sucked down. The second 
dumb-bell is now introduced, sufficient alcohol 
being allowed to remain in the open bulb to 
about half fill it, and the alcohol in this bulb is 
boiled to expel air. The tube through which 
the bulb was filled in now sealed. 

Clinical Thermometers. The clinical ther- 
mometer is a maximum thermometer of a 


different type. In this case there is a con- 
striction of the bore at a point just above the 
bulb. When the mercury in the bulb com- 
mences to contract, the mercury column breaks 
at the constriction and remains stationary in 
the tube, thus showing the maximum temper- 
ature to which it has risen. 

Vacuum Tubes. There are so many forms 
of these that it is scarcely practicable or 
desirable to give detailed instructions for 
making them ; but an application of the various 
methods of glass-working which have already 
been explained should enable the student to 
construct most of the simpler varieties. An 
interesting vacuum tube is made which has no 
electrodes, but contains a quantity of mercury. 
When the tube is rocked so as to cause friction 
between the mercury and the glass sufficient 
charge is produced to cause the tube to glow. 

A Sprengel Tump. This, in its simplest 
form, is illustrated by a, Fig. 12. Such a form, 
although highly satisfactory in action, needs 
constant watching while in action, as should 
the mercury funnel become empty air will 
enter the exhausted vessel. Obviously, the 
fall-tube must be made not less than thirty 


inches long ; the measurement being taken 
from the junction of the exhaustion branch 
with the fall-tube to the top of the turned-up 




I m 



Fig. 12 

A MacLeod Pump. One form of this is 
illustrated by b, Fig. 12. It has the advantage 


that the mercury reservoir may be allowed to 
become empty without affecting the vacuum in 
the vessel being exhausted. 

"Spinning" Glass. By the use of suitable 
appliances, it is quite possible to draw out a 
continuous thread of glass, which is so thin as 
to have almost the flexibility and apparent 
softness of woollen fibre ; a mass of such 
threads constitutes the " glass wool " of 

The appliances necessary are : a blowpipe 
capable of giving a well-formed flame of about 
six or eight inches in length, a wheel of from 
eighteen inches to three feet in diameter and 
having a flat rim of about three inches wide, 
and a device for rotating the wheel at a speed 
of about three hundred revolutions per minute. 

A very satisfactory arrangement may be 
made from an old bicycle ; the back wheel 
having the tyre removed and a flat rim of tin 
fastened on in its place. The chain drive 
should be retained, but one of the cranks 
removed and a handle substituted for the 
remaining pedal. The whole device is shown 
by Fig. 13. 

The procedure in "spinning" glass is as 


follows : First melt the end of a glass rod and 
obtain a large mass of thoroughly softened 
glass, now spin the wheel at such a speed that 
its own momemtum will keep it spinning for 
several seconds. Touch the end of the melted 
rod with another piece of glass and, without 

Fig. 13 

withdrawing the original rod from the blow- 
pipe flame, draw out a thread of molten glass 
and twist it round the spinning wheel. If this 
is done properly, the thread of glass will grip 


on the flat rim, and by continuing to turn the 
wheel by hand it is possible to draw out a 
continuous thread from the melted rod, which 
must be advanced in the blowpipe flame as it 
is drawn on the wheel. If the rod is not 
advanced sufficiently the thread will melt off, 
if it is advanced too much, so as to heat the 
thick part and allow the glass to become too 
cool at the point of drawing out, then the 
thread will become too thick, but it is easy 
after a little practice to obtain the right con- 
ditions. Practice is necessary also in order to 
find the right speed for the wheel. 

When sufficient glass has been "spun," the 
whole "hank " of thin thread may be removed 
by drawing the thumb-nail across the wheel 
at any point on its flat rim, thus breaking the 
threads, and allowing the "hank" to open. 

Brushes for Use tvttk Strong Acids. Glass 
wool, if of fine enough texture to be highly 
flexible, can be used to make acid-resisting 
brushes. A convenient method for mounting 
the spun glass is to melt the ends of the threads 
together into a bead, and then to fuse the bead 
on to a rod ; thus giving a brush. If a pointed 
brush is necessary, the point may be ground on 


an ordinary grindstone or carborundum wheel 
by pressing the loose end of the spun glass 
against the grinding wheel with a thin piece of 

When using brushes of this description, it is 
well to bear in mind the fact that -there is 
always a liability of a few threads of glass 
breaking off during use. 


Glass, Its Composition and Characteristics. Annealing. Drilling, 
Grinding, and Shaping Glass by methods other than Fusion. Stop- 
cocks. Marking Glass. Calibration and Graduation of Apparatus. 
Thermometers. Exhaustion of Apparatus. Joining Glass and Metal. 
Silvering Glass. 

THERE are three kinds of glass rod and tubing 
which are easily obtainable ; these are soda- 
glass, which is that usually supplied by chemical 
apparatus dealers when no particular glass is 
specified ; combustion -glass, which is supplied 
for work requiring a glass that does not so 
easily soften or fuse as soda-glass ; and lead- 
glass, which is less common. There are also 
resistance-glass, made for use where very slight 
solubility in water or other solutions is desirable, 
and a number of other special glasses ; but of 
these soda-glass, combustion-glass, lead-glass, 
and resistance-glass are the most important 
to the glass-blower whose work is connected 
with laboratory needs. 

Soda-Glass. Consists chiefly of sodium 


silicate, but contains smaller quantities of 
aluminum silicate, and often of calcium silicate ; 
there may also be traces of several other 

The ordinary soda-glass tubing melts easily 
in the blowpipe flame, it has not a long 
intermediate or viscous stage during fusion, but 
becomes highly fluid rather suddenly ; it does 
not blacken in the reducing flame. Bad soda- 
glass or that which has been kept for many 
years, tends to devitrify when worked. That 
is to say the glass becomes more or less 
crystalline and infusible while it is in the flame ; 
and in this case it is often impossible to do 
good work with that particular sample of glass ; 
although the devitrification may sometimes be 
remedied by heating the devitrified glass to a 
higher temperature. The presence of aluminum 
compounds appears to have some influence on 
the tendency of the glass to resist devitrification. 
Soda-glass, as a rule, is more liable to crack by 
sudden heating than lead-glass, and articles 
made from soda-glass often tend to crack 
spontaneouly if badly made or, in the case of 
heavier and thicker articles, if insufficiently 


Combustion-Glass. Is usually a glass con- 
taining more calcium silicate and potassium 
silicate than the ordinary "soft" soda-glass. 
It is much less fusible than ordinary soda-glass, 
and passes through a longer intermediate or 
viscous stage when heated. Such a glass is 
not very suitable for use with the blowpipe 
owing to the difficulty experienced in obtaining 
a sufficiently high temperature. If, however, 
a certain amount of oxygen is mixed with the 
air used in producing the blowpipe flame this 
difficulty is minimised. 

Resistance-Glass. May contain zinc, mag- 
nesium, and other substances. As a rule it is 
harder than ordinary soda-glass, and less 
suitable for working in the blowpipe flame. It 
should have very little tendency to dissolve in 
water, and hence is used when traces of alkali 
or silicates would prove injurious in the 
solutions for which the glass vessels are to be 

Lead-Glass. This, or " flint" glass as it is 
often called from the fact that silica in the form 
of crushed and calcined flint was often used in 
making the English lead-glasses, contains a 
considerable proportion of lead silicate. Such 


a glass has, usually, a particularly bright 
appearance, a high refractive index, and is 
specially suitable for the production of the 
heavy " cut-glass " ware. 

Lead-glass tubing is easy to work in the 
blowpipe flame, melts easily, but does not be- 
come fluid quite so suddenly as most soda- 
glasses ; articles made from it are remarkably 
stable and free from tendency to spontaneous 
cracking, although, as is essential for all the 
heavy or "glass-house" work, the massive 
articles need annealing in the oven. 

The two chief disadvantages of lead-glass 
for laboratory work are that it is blackened by 
the reducing gases if held too near to the blue 
cone of the blowpipe flame, and that it is rather 
easily attacked by chemical reagents ; thus 
ammonium sulphide will cause blackening. 

The effect of the reducing flame on lead is 
not altogether a disadvantage, however ; be- 
cause a little care in adjusting the blowpipe and 
a little care in holding the glass in the right 
position will enable the student to work lead- 
glass without producing the faintest trace of 
blackening. This, in addition to being a 
valuable exercise in manipulation, will teach 


him to keep his blowpipe in good order, and 
prove a useful aid in his early efforts to judge 
as to the condition of the flame. It prevents 
discouragement if the student does his pre- 
liminary work with the soda-glass, but he 
should certainly make experiments with lead- 
glass as soon as he has acquired reasonable 
dexterity with soda-glass. 

Annealing. Annealing is a process by 
which any condition of strain which has been 
set up in a glass article, either by rapid cooling 
of one part while another part still remains hot, 
or by the application of mechanical stress after 
cooling is relieved. Annealing is carried out 
by subjecting the article to a temperature just 
below the softening point of the glass, main- 
taining that temperature until the whole article 
has become heated through the thicker part, 
and then reducing the temperature very gradu- 
ally ; thus avoiding any marked cooling of the 
thinner and outer parts first. 

For thin glass apparatus of the lamp-blown 
or blowpipe-made variety in which there are no 
marked difference of thickness, such as joins on 
tubes, ordinary seals, bulbs, etc., there is little 
need for annealing ; and even those having 


rather marked changes of thickness, such as 
filter pumps, can be annealed sufficiently by 
taking care that the last step in making is 
heating to just below visible redness in the 
blowpipe flame and then rotating in a sooty 
gas flame until covered with a deposit of 
carbon. The article should then be allowed to 
cool in a place free from draughts and where 
the hot glass will not come in contact with 

A few of the blowpipe- made articles, such, 
for example, as glass stopcocks, need more 
careful annealing, and for this purpose a small 
sheet-iron oven which can be heated to dull 
redness over a collection of gas burners will 
serve. Better still, a small clay muffle can be 
used. In either case, the article to be annealed 
should be laid on a clean, smooth, fireclay 
surface, the temperature should be maintained 
at a very dull red for two or three hours and 
then reduced steadily until the oven is cold. 
This cooling should take anything from three to 
twelve hours, according to the nature of the 
article to be annealed. A thick article, or one 
having great irregularities in thickness will 
need much longer annealing than one thinner 


or more regular. As a rule, soda-glass will 
need more annealing than lead-glass. 

Drilling Glass. Small holes may be drilled 
in glass by means of a rod of hard steel which 
has been broken off, thus giving a more or less 
irregular and crystalline end. 

There are several conditions necessary to 
enable the drilling of small holes to be carried 
out successfully : the first of these is that the 
" drill " should be driven at a high speed. This 
may be done by means of a geared hand-drill 
such as the American pattern drill, although a 
somewhat higher speed than this will give is 
even more satisfactory. The second condition 
is that the pressure on the drill is neither too 
light nor too heavy ; this is conveniently re- 
gulated by hand. The third condition is that 
the drill be prevented from " stray ing" over 
the surface of the glass ; for this purpose a 
small metal guide is useful. The fourth con- 
dition is that a suitable lubricant be used ; a 
strong solution of camphor in oil of turpentine 
is perhaps the most suitable. For commercial 
work, a diamond drill is often used, but this is 
scarcely necessary for the occasional work of a 


Larger Holes in Glass. The method of 
drilling with a hard steel rod is not highly 
satisfactory for anything but small holes. 
When a larger hole, say one of an eighth of an 
inch or more, is needed it is better to use a 
copper or brass tube. This tube may be held 
in an American hand-drill, but a mixture of 
carborundum or emery and water is supplied 
to the rotating end. Tube or drill must be 
lifted at frequent intervals in order to allow a 
fresh supply of the grinding material to reach 
the end. In this case, also, a guide is quite 
essential in the early stages of drilling ; other- 
wise the end of the tube will stray. The speed 
of cutting may be increased slightly by making 
a number of radial slots in the end of the tube ; 
these serve to hold a supply of the grinding 

Grinding Lenses. This is scarcely within the 
scope of a book on glass-blowing for laboratory 
purposes, but it may be said that the lens may 
be ground by means of a permutating mould of 
hard lead or type-metal. The rough shaping 
is done with coarse carborundum or emery, and 
successive stages are carried on with finer and 
finer material. The last polishing is by the 


use of jewellers' rouge on the mould, now lined 
with a fine textile. 

Filing Glass. If a new file, thoroughly 
lubricated with a solution of camphor in oil of 
turpentine, is used, there is but little difficulty 
in filing the softer glasses. A slow movement 
of the file, without excessive pressure but with- 
out allowing the file to slip, is desirable. After 
a time the cutting edges of the file teeth will 
wear down and it will be necessary to replace 
the file by another, 

Grinding Stoppers. This is, perhaps, the 
most common form of grinding that the labora- 
tory worker will need to perform, and for that 
reason, rather full details of the proceedure are 

A very crude form of ground-in stopper may 
be made by drawing out the neck and the mass 
of glass which is intended to form the stopper 
to approximately corresponding angles, wetting 
the surfaces with a mixture of the abrasive 
material and water, and grinding the stopper in 
by hand. Frequent lifting of the stopper is 
necessary during grinding, in order to allow 
fresh supplies of abrasive material to reach the 
contacts. When an approximate fit is obtained, 


the coarse abrasive should be washed off, care 
being taken that the washing is complete, and 
a finer abrasive substituted. After a while, 
this is replaced in its turn by a still finer 
grinding material. 

Such a method of grinding may give a satis- 
factory stoppering if the angles of the plug and 
socket correspond very closely before grinding 
is commenced ; but if there is a wide difference 
in the original angles, then no amount of grind- 
ing by this method will produce a good result. 
The reason for this is that the plug will become 
so worn in the preliminary grinding as to 
assume the form of a highly truncated cone ; 
the socket will assume a reverse form, and the 
end result will be a loose-fitting plug and socket. 

Satisfactory grinding may be carried out by 
the use of copper or type-metal cones for the 
preliminary shaping. Such cones should be 
mounted on a mandrel which will fit into the 
chuck of the American hand-drill and turned 
on the lathe to the desirable angle for stop, 
pering. A number of these cones will be 
necessary. A number of similar moulds, that 
is to say blocks of type-metal or hard lead in 
which is a hole corresponding in size and angle 


to the plug desired, should be made also. 
These must be rotated, either in the lathe or 
by other means, and are used for the preliminary 
shaping of the plug. If but few plugs are to be 
ground it is unnecessary to provide a means of 
rotating the moulds, as the plug may be held in 
the hand and ground into the mould in a 
manner similar to that used in the first method 
of stoppering. 

Fig. 14 


When the socket and plug have been ground, 
by the successive use of cones and moulds, to 
the desired angle, so that they correspond 
almost exactly, the plug is given its final fitting 
into the socket by grinding-in with a fine 
abrasive, in the manner first described. 

Stopcocks. Although it would be more 
strictly in keeping with the form of this book 
to divide the making of stopcocks into two 
parts ; shaping by heat and grinding, we will 
consider the whole operation here, and take for 
our example a simple stopcock such as that 
illustrated by Fig. 14. 

The " blank," /, that is the socket before 
grinding, is made by drawing out a piece of 
fairly thick-walled tubing into the form shown 
by a. Two zones on this tube are then heated 
by means of a small, pointed flame, and the tube 
is compressed along its axis, thus producing 
two raised rings as shown by b. Two zones, 
slightly towards the outer sides of these two 
raised rings are heated and the tube is drawn 
while air pressure is maintained within. This 
produces two thin-walled bulbs or extensions 
similar to those shown by c. One of these 
extensions is now broken off by means of a 


sharp blow with the edge of a file or other piece 
of metal, and the edges of the broken glass are 
rounded in the flame. The other extension is 
left to serve as a handle. We have now a 
piece of glass like that shown by d. Now heat 
a spot on the side of this, medially between the 
raised rings, until the glass is on the point of 
becoming deformed, and bring the intensely 
heated end of a smaller tube in contact with 
the heated spot. Without disturbing the relative 
positions of the two tubes, press the smaller 
tube down on a thin steel wire, so that the wire 
passes along the tube and enters the soft glass ; 
thus forming a projection inside the sockets as 
shown by e. The wire must be withdrawn, 
again immediately. When the wire has been 
withdrawn, heat the place where it entered to 
dull redness, in order to relieve any strain ; 
break off the thin extension, which up to the 
present has served as a handle, round off the 
broken edges in the flame, and join on and 
indent a similar piece of small tubing to the 
opposite side of the socket ; the socket at this 
stage being shown by f. The " blank" for 
the socket is now completed, but it must be 
heated to dull redness in order to relieve strain 


and be placed in an annealing oven, where it 
should be annealed for some hours. 

The "blank" for the plug offers no special 
difficulty ; it is made by heating a glass rod 
and compressing it axially until a mass having 
the form shown by g t Fig. 14, is produced ; the 
end of this is heated intensely and brought in 
contact with the rather less heated side of a 
glass tube which has been drawn to the shape 
desired for the handle ; when contact is made 
a slight air pressure is maintained in the glass 
tube, thus producing a hollow join. The ends 
of the tube are sealed and the bottom of the 
plug is drawn off, thus giving the finished 
" blank" as shown by h. This blank is now 
held in a pair of asbestos-covered tongs, heated 
to dull redness all over, and transferred to the 
annealing oven. 

When cold, the socket is ground out by the 
second method given under " Grinding Stop- 
pers"; that is to say, by means of type-metal or 
copper cone, and the plug is ground to fit in a 
corresponding mould. When the fit is almost 
perfect, the transverse hole is drilled in the plug, 
and the final finishing is made with fine abrasive 
powder. Great care must be taken in the 


final grinding that there is no accumulation of 
abrasive material in the transverse hole of the 
plug ; if this is allowed to occur there will be a 
ring ground out of the socket where the holes 
move, and the tightness of the finished stopcock 
will be lost. 

Marking Glass. As a preliminary to a 
consideration of the methods of graduating and 
calibrating glass apparatus, it is convenient to 
consider the various methods which are avail- 
able for marking glass. Among these are, the 
writing diamond, the carborundum or abrasive 
pencil, the cutting-wheel, and etching by means 
of hydrofluoric acid. Each produces a different 
class of marking and each is worthy of indepen- 
dent consideration. 

The Writing Diamond. This is the name 
given to a small irregular fragment of "bort" 
which is usually mounted in a thin brass rod. 
Such a diamond, if properly selected, has none 
of the characteristics of a cutting diamond ; 
although one occasionally finds so-called " writ- 
ing diamonds " which will produce a definite cut. 
These should be rejected. 

The writing diamond is used in much the 
same way as a pencil, but is held more perpen- 


dicularly to the object, and a certain amount of 
pressure is necessary. The mark produced is 
a thin scratch which, although fairly definite, 
lacks breadth, and this is a disadvantage where 
the marking has to be read at a distance. 
This disadvantage may to some extent be 
overcome by making a number of parrallel 

The Abrasive Pencil. A rod of car- 
borundum composition may be ground or filed 
to a point, and this forms a very useful pencil 
for general work. The marking produced is 
rather less definite than that produced by a 
writing diamond, but has the advantage of 
being broader. 

The Cutting Wheel. ''Cutting" in this case 
is scarcely the ideal expression, it should rather 
be " grinding," but " cutting " is more commonly 
used. Exceedingly good graduations may be 
made by the edge of a small, thin, abrasive 
wheel which is mounted on the end of a small 
mandrel and driven by a flexible shaft from an 
electric motor or any other convenient source 
of power. The depth of the mark can be 
controlled, and very light pressure will suffice. 

Etching. This is often the quickest and 


easiest way of marking glass apparatus. The 
object to be marked should first be warmed 
and coated very thoroughly with a thin film of 
paraffin wax. When cold, the marking is made 
through the paraffin wax by means of a needle 
point, and the object is then exposed to the 
action of hydrofluoric acid. If a shallow but 
clearly visible marking is desired, it is well to 
use the vapour of the acid ; this may be done 
by bending up a sheet-lead trough on which 
the object can rest with the marked surface 
downwards. A little of the commercial hydro- 
fluoric acid, or a mixture of a fluoride and 
sulphuric acid, is distributed over the bottom 
of the trough, and the whole arrangement is 
allowed to stand for about an hour. The 
object is washed thoroughly and the paraffin 
wax removed, either by melting and wiping off 
or by the use of a solvent, and the marking is 

If a deep marking is desired, in order that 
it may afterwards be filled with some pigment, 
a better result is obtained by the use of liquid 
commercial hydrofluoric acid, which is a so- 
lution of hydrogen fluoride in water. The 
acid is mopped on to the object after the 


markings have been made on the paraffin wax 
film, and allowed to remain in contact for a few 
minutes. It is advantageous to repeat the 
mopping-on process at intervals during the 

In all cases where hydrofluoric acid is used, 
or stored, it is of great importance to keep it 
well away from any optical instruments, as the 
most minute trace of vapour in the air will 
produce a highly destructive corrosion of any 
glass surfaces. 

Methods of Calibration. In the case of 
apparatus for volumetric work, this is usually 
carried out by weighing, although some of the 
smaller subdivisions are often made by measure- 
ment. When the subdivisions are made in this 
way it is of importance to see that the walls of 
the tube or vessel to be calibrated are parallel. 
Great errors arise in some of the commercial 
apparatus from neglect of this precaution. A 
convenient method of testing for parallelism, in 
the case of a wide tube, is to close one end 
and to weigh in successive quantities of mercury. 
An observation of the length occupied by each 
successive quantity will indicate any change in 
the bore. In the case of capillary tubes, it is 


convenient to introduce an unweighed quantity 
of mercury, measure its length accurately, and 
then to move it along the tube in stages, either 
by tilting the tube or by the application of 
air pressure. A measurement of the length 
at each stage will indicate whether the bore is 
approximately parallel or not. Neither of these 
methods is to be relied on without a careful 
examination of the tube, as it may happen that 
there are local irregularities in the bore which 
compensate for each other, and do not, there- 
fore, affect the volume of a given length. 
Obviously, the smaller the quantity of mercury 
with which the test is carried out and the 
greater the number of observations made, the 
less risk will there be of such an error. A 
liquid, such as water or alcohol, which wets the 
glass is not suitable for such a test, unless 
special precautions are taken. 

When, however, a pipette or burette has to 
be calibrated to deliver a certain volume of 
water, the final calibration must be made with 
this liquid. Thus, the burette would first be 
calibrated by weighing in definite quantities of 
mercury of say 13*54 grammes (i cc at l5 c .), 
each of the 1 cc divisions should be marked by 


some temporary marking. The burette is now 
filled with a solution of potassium bichromate 
and sulphuric acid and allowed to soak for some 
time ; the bichromate is washed out and distilled 
water is put in. Successive quantities of water 
are run out of the jet, a fixed time being 
allowed for draining, and the weights of the 
quantities delivered are noted. This procedure 
will give the necessary data for altering the 
marking so that it may correspond to i cc 
delivered. Each i cc division is now divided 
into tenths by the method described below. 
A final verification of the markings should be 
made when the subdivision is completed. 

Subdivision of Graduations. Mark out the 
spaces to be subdivided on a sheet of paper. 
Take a reliable ruler on which any convenient 
length is divided into the desired number and 
place it across the lines at such an angle that 
the limits noted on the rule exactly bridge the 
gap. Now draw parallel lines through the 

Copying a Scale. When a scale has been 
prepared on paper and it is necessary to copy 
that scale on the waxed-glass surface for 
etching, a convenient method is to employ a 


long wooden bar having a sharp needle passing- 
through it at either end. The scale and object 
to be marked are fastened in line with one 
another, and the caliper bar is used from step 
to step. The mark is made by moving the 
bar through a minute portion of a circle, which 
provided that the bar is two or three feet in 
length, will not introduce any perceptible error 
in a scale of say a quarter of an inch in width. 
The arrangement is shown by Fig. 15. 

r~T F^- *s YI 

Graduating a Thermometer. Assuming that 
the thermometer has been made of carefully 
selected tubing in which the bore is parallel 
and free from any small irregularities, we have 
only to fix the freezing point and boiling point. 
The intervening space may then be divided 
into 100 (if the thermometer is to be Centi- 
grade) or 1 80 (if Farenheit). This division 
may be carried out by the method given under 


" Subdivisions of Graduations." A thermo- 
meter should not be calibrated until some 
weeks after making, as the glass bulb tends to 

Joining Glass and Metal. It sometimes 
happens that one needs to make a more 
permanent and less flexible joint between a 
glass and metal tube than can be obtained by 
means of a rubber tube. To this end, any one 
of three slightly different methods may be em- 
ployed. In the method of Chatelier one first 
coats the glass with platinum or silver, which 
may be done by moistening the glass with 
platinum chloride or silver nitrate and then 
heating to redness ; a layer of copper is then 
deposited electrolytically on the treated surface 
of the glass, and soldering is carried out in the 
usual manner. 

McKelvy and Taylor call attention to two 
other methods in the Journal of the Chemical 
Society for September, 1920. In one of these 
methods the glass is coated with platinum by 
covering it with a suspension of platinum 
chloride in oil of lavender and heating until the 
oil is burnt off. The metal tube is then tinned 
on its inner side and soldered to the prepared 


glass, slightly acid zinc chloride being used as 
a flux. 

In the second method, a joint is made by 
means of the Kraus flux, which consists of 
equal weights of zinc oxide, borax, and powdered 
soda-glass fused together. This is coated on 
the inner surface of the metal tube, and the hot 
glass tube, which has had the end slightly 
flanged to give support, is inserted. Fusion of 
the flux is completed by heating the outside of 
metal tube. 

Silvering Glass. In all cases where it is 
intended to deposit a silver mirror on a glass 
surface, thorough cleaning is essential. Pro- 
longed soaking in a hot solution of potassium 
bichromate which has been acidified with 
sulphuric acid will often prove useful. The 
glass should then be washed thoroughly, rinsed 
in distilled water, and the solution should then 
be used. 

There are many formulae for the silvering 
solution, but that used in Martin's method may 
be given : 


A Nitrate of Silver 40 grammes 

Distilled Water 1000 c. cm. 

B Nitrate of Ammonium 60 grammes 

Distilled Water 1000 c. cm. 

C Pure Caustic Potash 100 grammes 

Distilled Water 1000 c. cm. 

D Pure Sugar Candy 100 grammes 

Distilled Water 1000 c. cm. 
Dissolve and add : 

Tartaric Acid 23 grammes 
Boil for ten minutes, and when cool add : 

Alcohol 200 c. cm. 

Distilled Water to 2000 c. cm. 

For use take equal parts of A and B. Mix 
together also equal parts of C and D in another 
vessel. Then mix both liquids together in the 
silvering vessel and suspend the glass to be 
silvered face downwards in the solution. Or if 
a vessel has to be silvered on the inside, the 
solution is poured in. In this case, the deposi- 
tion of silver may be hastened by immersing 
the vessel to be silvered in warm water. 

In working with a silver solution containing 
ammonia or ammonium salts there is some- 
times the possibility of forming an explosive 
silver compound. It is well, therefore, to 
avoid keeping such solutions longer than is 
necessary, and to bear in mind that any deposit 


formed by solutions containing both silver and 
ammonia may have explosive properties, 
especially when dry. 


Extemporised Glass-Blowing Apparatus The Use of Oil or other 
Fuels Making Small Rods and Tubes from Glass Scrap The Ex- 
amination of Manufactured Apparatus with the View to Discovering the 
Methods Used in Manufacture Summary of Conditions Necessary for 
Successful Glass-Blowing. 

IF, in the early stages of his study of glass- 
blowing, the student should attempt to work 
with the very simplest appliances, it is probable 
that his progress will be hindered ; the use of 
the apparatus will require an undue amount of 
care and his attention will be distracted from 
the actual manipulation of the glass. The case 
is widely different after he has acquired a 
certain facility in glass-blowing. 

A Simple Form of Blowpipe. Although 
there are even more simple forms than that 
described here, we are not concerned with 
them. The form described is the simplest with 
which any considerable amount of glass-blowing 
can be carried out with certainty. 


This form consists of a tube through which 
air may be blown with the mouth, a condensa- 
tion chamber in which any moisture from the 
breath can condense, a blowpipe jet, a sup- 
porting piece and a source of flame. 

The tube, condensation chamber, and jet are 
combined in the ordinary Black's blowpipe, 
such as is used for blowpipe tests in qualitative 
analysis ; it consists of a conical tin tube having 
a mouthpiece at the small end and a side tube 
which carries a brass jet. A support for such 
a blowpipe may be cut out of a piece of brass 
or tin-plate, and should be fastened to a small, 
flat, wooden board. A source of flame may 
consist of an ordinary brass elbow, such as is 
used on gas fittings, and into which a piece of 
thin brass tube (the body of a fish-tail burner 
from which the perforated non-metallic plug 
has been removed will serve quite well) has 
been fitted. It is an advantage to flatten the 
brass tube somewhat and to file the flattened 
end to a slope which corresponds with the 
angle at which the blowpipe jet enters the 
burner. The whole source of the flame should 
be mounted on a separate base, in order that it 

may be moved while adjusting the apparatus to 


the best relative positions of flame and blow- 
pipe jet. The complete apparatus is shown by 
a, Fig. 1 6. 

Fig. 16 

In order to take full advantage of this blow- 
pipe, it is desirable that the student should 
learn to maintain a steady steam of air with his 


mouth and, at the same time, be able to breathe. 
This requires a little practice. 

As a first exercise in breathing, before trying 
to breathe while using the mouth blowpipe, the 
student should close his mouth and inflate his 
cheeks with air ; now, still keeping his cheeks 
tightly inflated, he should attempt to breathe 
through the nose. At first, this may be found 
rather difficult, but it becomes remarkably easy 
after a little practice. When he has mastered 
this, the student may practise the same opera- 
tion, but with the blowpipe. It is important to 
bear in mind that the cheeks, not the lungs, 
form the reservoir for air used in maintaining 
the blowpipe flame. After a while, the student 
will find that he can maintain a steady air 
pressure and yet breathe with complete comfort. 

In adjusting the flame, care should be taken 
not to blow so hard as to produce a ragged and 
noisy cone of fire. A small jet, such as that 
commonly used on a mouth blowpipe, will with 
care give a pointed and quiet flame, having 
an appearance similar to that shown in the 

With a blowpipe like this, it is quite easy to 
seal glass tubes up to an inch in diameter, to 


join tubes up to half an inch in diameter, 
to bend tubes, to blow small bulbs, and to make 
the simpler forms of internal seal ; but the pro- 
vision for condensation of moisture is not ideal, 
and prolonged use of such a blowpipe also 
tends to produce undue fatigue. 

A Mouth Blowpipe With an Expanding 
Reservoir. This form of blowpipe can be 
made to give most excellent results ; it is highly 
portable, and does not produce nearly so much 
fatigue when used continuously as the blowpipe 
described in the last section. Various slight 
modifications have been made in its construction 
during the last eighty years, but that described 
below will be found quite satisfactory. 

The apparatus consists of a tube through 
which air is blown from the mouth, a valve 
through which the air passes into an expanding 
reservoir, and a blowpipe jet in communication 
with the reservoir. 

In making the valve, several essentials have 
to be remembered ; it must allow a free passage 
of air into the reservoir, it must open easily, 
and must close quickly. A satisfactory form 
of valve is that shown by b, Fig 16. The 
moving part consists of a light glass bulb of 


about three-eights of an inch diameter and 
having a glass stem of rather under one-eighth 
diameter and about an inch and a half long. 
This stem rests in a guide at the end of a brass 
tube, the bulb contacting against the other end 
which is approximately shaped. The bulb and 
its seating are ground air-tight. A very light 
spring holds the bulb in position. 

This valve is fitted into a metal or glass T 
piece, one limb of which leads to the air 
reservoir and the other limb leads to the blow- 
pipe jet ; the limb containing the valve leads 
to the tube through which the air is blown in. 

A convenient reservoir may be made from a 
fairly large football bladder. A network of 
string should be fitted over the outside of the 
bladder and the strings should terminate in a 
hook on which a weight can be hung, in order 
to provide a means of adjusting the pressure 
at which the air is delivered to the jet. This 
bladder should be washed out and allowed to 
drain after use. 

The air tube which passes from the valve to 
the mouth may conveniently be made of brass, 
but, in order to avoid the continued contact of 
metal with the lips of the operator, it should be 


fitted with a non-metallic mouthpiece. It is an 
advantage from the point of view of portability 
to have the air tube easily detachable from the 
T piece containing the valve. 

The blowpipe jets, of which there may be 
several with advantage, may be made of glass 
tubing, bent to the most convenient angle and 
having an enlargement or bulb at some point 
in the tube. This bulb serves as a final 
condensing place for any traces of moisture 
that may escape from the larger reservoir. 

The whole device, blowing tube, reservoir, 
and T piece may be fastened to a clamp, so 
that it can be secured on the edge of any table 
where blowpipe work is to be carried out. If 
the blowpipe is to be used with gas, the form 
of burner described under. " A Simple Form of 
Blowpipe " will be found quite satisfactory. 

The Use of Oil, or Other Non-Gaseous Fuels. 
Although gas, when available, is usually 
preferred on account of its convenience, there 
are several other fuels which give a hotter 
flame. They have, also, the additional ad- 
vantage of not requiring any connecting pipes ; 
but each has its own disadvantage. 

One liquid fuel deserves special mention as 


being rather less desirable than the others ; this 
is alcohol. Although very convenient in use, 
it has the disadvantage of being rather too 
highly inflammable and capable of burning 
without a wick, thus involving a certain fire 
risk ; the flame is scarcely visible in a bright 
light, and the heat given by either the ordinary 
flame or the blowpipe flame produced from 
alcohol is considerably less than that from a 
similar flame in which coal gas is used, For 
small work, however, the facility with which a 
spirit lamp may be lighted may more 
than counterbalance these disadvantages at 

Paraffin Wax. Where there is no coal gas 
available and the blowpipe is only required at 
intervals, and especially where high portability 
is required, there are few fuels so convenient 
as paraffin wax. This may be obtained in 
pieces of a satisfactory size by cutting paraffin 
candles, from which the wick has been with- 
drawn, into lengths of about half an inch. 
These cut pieces have the advantage over any 
oily fuel, such as colza oil, that they can be 
wrapped in paper or carried in a cardboard 
box ; further they will keep indefinitely, even 


in the presence of air, without undergoing any 
perceptible change. 

Forms of Lamp for Paraffin Wax. 
Probably, the best form is that devised by 
Thomas Bolas, and described by him in the 
Journal of the Society of Arts, December 2nd, 
1898. This lamp consists of a small open tray 
of iron, through which pass three or more flat 
tubes, and between these tubes are placed small 
flat pieces of wick, the fit being such that the 
pieces of wick may be adjusted easily by means 
of a pair of pointed tweezers. 

The flame thus obtained, instead of having 
one large hollow, is broken or divided so that 
the combustion is concentrated into a smaller 
area, and the air blast, which is directed across 
the flame, carries the flame with it in a more 
complete manner than is the case with the 
ordinary flame ; a more thorough combustion 
being realised by this arrangement. 

Another advantage is the ease with which 
the wick may be changed and a larger or 
smaller wick inserted to suit the flame to any 
size of air jet. 

This form of lamp may be used for oily fuel, 
although it is specially suitable for paraffin wax. 


Two small pieces of bent tin-plate may be 
used as side covers, and these serve to adjust 
the flame within certain limits. A tin-plate 
cover which fits easily over the whole lamp 
serves as an extinguisher. The complete lamp 
is shown by d y Fig. 16, and this figure shows 
also a quick-change air-jet device, the whole 
arrangement forming a blowpipe for use where 
a non-gaseous fuel is to be employed. 

Although the lamp just described is desirable 
when complete control over the size of the 
flame is necessary, and if the ideal conditions 
and maximum heat are to be obtained, yet a 
simpler form of lamp will be found to give very 
good results. Such a lamp may consist of a 
flat tin tray, having a diameter of about three 
and a half inches and a depth of about one 
inch. In this tray is a tin support for the 
wick, and the wick itself may consist of a 
bundle of soft cotton, for example, a loosely 
rolled piece of cotton cloth, but in either case 
the top of the wick should be cut to approxi- 
mately the same angle as that at which the 
blowpipe jet meets the flame. 

In using paraffin wax as a fuel, it is 
necessary to see that sufficient wax reaches the 


wick to prevent charring during the first few 
minutes before the bulk of the wax is melted. 

Animal and Vegetable Oils. Almost any 
oil may be used as a fuel, but many tend to 
become hard and gummy if allowed to stand 
in the air for any considerable time. When 
this happens, the wick- becomes clogged and 
it is impossible to obtain a good flame. A 
number of the oils tend, also, to produce rather 
strongly smelling smoke. 

A Flame-Guard for Use With Non-Gaseozis 
Fuels. In order to avoid the eye-strain pro- 
duced by the luminous base of the flame from 
a wick burning paraffin wax or oil, it is often 
advantageous to make a small tunnel of tin- 
plate, which can be rested on the sides of the 
lamp and rises over the top of the wick. Such 
a flame guard is shown by e, Fig 16. 

Small Rods and Tubes from Glass Scrap : 
It is scarcely practicable to make small 
quantities of good glass with the blowpipe 
flame as the only source of heat, but it is less 
difficult to make small rods or tubes from glass 
scrap, and the ability to do this is sometimes 
of considerable value when a small tube has to 
be joined on to some special piece of apparatus 


made of glass of unknown composition. It may 
be possible to obtain some fragments of similar 
glass, either from a broken part of the apparatus 
or from a similar piece, and from these frag- 
ments small tubes or rods can be made. 

The fragments of glass may be melted 
together on the end of a clay pipe-stem, care 
being taken to avoid trapping air bubbles as 
fresh fragments are added to the molten mass. 
When a sufficient quantity of glass has been 
accumulated, the viscous mass may be drawn 
out into a rod by bringing another pipe-stem 
into contact with the hot mass, rotating both 
pipe-stems steadily, and separating them until 
a rod of the desired size has been obtained. 

If, on the other hand, it is desired to produce 
a tube from the mass of heated glass, the mass 
should be blown hollow before the pipe-stems 
supporting it are separated. 

Methods of Manufacture. When the stu- 
dent has familiarised himself with the more 
common operations and processes used in glass- 
blowing, he will be in a position to increase his 
skill and knowledge of special methods by a 
critical examination of various examples of 
commercial work. There are few exercises 


more valuable than such an examination, com- 
bined with an attempt to reconstruct the stages 
and the methods by which the article chosen 
for examination was made. 

Obviously, it is impossible to give full details 
of all constructions in a small text-book ; but 
it is easy to give an example of the con- 
structional methods employed in the making 
of almost any piece of light blown-glass 
apparatus, and these methods should prove of 
special value when apparatus of a new pattern 
has to be evolved for the purposes of research. 
That is to say, one designs the apparatus 
required, applies known methods of con- 
struction as far as possible, and, by the ex- 
amination of commercial apparatus having 
similar features, evolves the new methods 
required. For an exercise in such a process 
of reconstruction we may well take an ordinary 
commercial vacuum tube, such as that shown by 
a, Fig. 17. 

In the tube from which this drawing was 
made, it was found that the spiral in the 
middle bulb was of a slightly yellowish colour 
and gave a green fluorescence when the electric 
discharge was passed through the tube ; that 


is to say, the spiral is made of uranium-glass, 
which is usually a soda-glass containing trace 
of uranium, and hence differing slightly in 
composition from the ordinary glasses. The 

Fig. 17 

two enclosed tubes which are bent into a series 
of S bends gave a pink fluorescence, which 
indicates lead-glass ; and the remainder of 
the tube fluoresced with an apple-green colour ; 


this suggests ordinary soda-glass. We have, 
therefore, a piece of apparatus in which three 
dissimilar glasses are joined, while, at the 
same time, that apparatus contains a number 
of internal seals, and it is not probable that the 
dissimilar glasses will have their coefficients of 
expansion so nearly alike as to permit of a 
stable internal seal being made if one part of 
the seal consists of a glass differing from that 
of the other part. 

These considerations lead us to a closer 
examination of the joins where the dissimilar 
glasses are introduced, and we find that in no 
case is the internal seal made between dis- 
similar glasses, but that a soda-glass extension 
is joined on to both the uranium-glass tube and 
the lead-glass tubes at a point about half an 
inch before the internal seal commences. 
Careful examination of these joins shows that 
the change from one glass to another is not 
abrupt but gradual. Such a transitional joint 
may be made by taking a length of soda-glass 
tubing, sealing the end and fusing a minute 
bead of the other glass on to the sealed end, 
the end is then expanded and another bead of 
the other glass added, this bead is expanded 


and the operation is repeated, thus building up 
a tube, and, finally, the tube of the other glass 
is joined on to the end of this. 

We are now concerned with the question of 
the insertion of the uranium-glass spiral into 
the bulb (see p. 38). Obviously the spiral is too 
large to pass through the necks of the bulb, 
and it is difficult to imagine that the spiral was 
obtained by the insertion of a length of straight 
tubing which was bent after entering the bulb ; 
therefore, the only remaining method is that 
the spiral was made first and the soda-glass 
extensions fastened on, and that the bulb was 
blown, cut in halves and the spiral inserted, 
and the two halves were then rejoined. That 
this was actually the case is confirmed by traces 
of a join which are just visible round the middle 
of the bulb. The insertion of the spiral and 
the making of the first internal seal are shown 
by b y and c. 

There is one detail in making the second 
join of the spiral to the bulb which calls for 
attention, and the small branch, similar to an 
exhaustion branch, at the side of the bulb 
provides a clue to this. If an attempt were 
made to complete the second internal seal 

? : 


through a closed bulb it would be impossible to 
obtain a good result, as the air-pressure in the 
bulb would not be under control when once 
union was effected, and further heating of the 
air in the bulb would cause expansion and 
perforate the wall near the second internal seal ; 
we therefore make a small branch which can 
be left open and through which such air- 
pressure as may be found necessary can be 

The third join, by which the lead-glass tube 
is joined to the soda-glass is made in stages 
similar to those in which the soda-glass and 
uranium-glass were joined ; but the internal seal 
is most conveniently made by sliding a length 
of tubing over the lead-glass and fusing this 
tubing to the large diameter soda-glass tube to 
which the lead-glass is already joined. The 
first stage of this operation is illustrated by d. 
When this seal is completed, the end of the 
soda-glass tube is drawn off and sealed as 
shown in e, and at this stage a side tube or 
branch is joined on. The sealed end of the 
outer and large diameter soda-glass tube is 
heated until it contracts and fuses to the en- 
largement that has previously been joined to 


the lead-glass tube, and the end is burst out as 
shown in f. Another length of soda-glass 
is then joined on to the burst-out end, and 
this length of soda-glass tubing is drawn out to 
a thin- walled contraction ; the non-contracted 
part is expanded to form the bulb, and a small 
exhaustion branch made on the side, the drawn- 
out portion being cut off, and an electrode, 
previously prepared by coating a part of its 
length with a suitable enamel, is introduced. 
The tube is tilted to keep the electrode 
away from the drawn-out end, which is melted 
off and sealed. A small perforation is made 
with a hot platinum or iron wire in the sealed 
end, the electrode is shaken into position, and 
the sealing is completed as explained on 
page 42. 

The remainder of the tube, that is to say the 
lead-glass tube and the bulb on the other side 
of the middle bulb, is completed in a similar 


For the convenience of the student, it may 
be well to summarise the chief essentials for 


success in glass-blowing, and at the same time 
to add such brief notes on the various methods 
as may seem desirable. 

Adjustment of Blowpipe. The air jet should 
be clean internally, and so centered as to give 
a flame having a well-defined blue portion, the 
tip of the flame should not be only slightly 
luminous but purple in colour. In the case of 
a blowpipe burning oil or wax fuel the flame 
may be a trifle more ragged without dis- 

Bellows and Blowing. The bellows should 
be adjusted to deliver air at constant pressure, 
either by insertion of a tap or, better, by 
attention to the wind reservoir if necessary. 
The movement of the foot in blowing should 
be steady, not jerky. 

Heating Glass. The tube or rod should be 
heated cautiously until it has reached its 
softening point in its thickest part. Steady 
rotation of the glass during the heating is 
almost essential. 

Blowing a Bulb or Expanding a Join. Pro- 
longed heating is necessary in order that the 
thick parts may be heated completely through. 
Blowing should take place by stages, in order 


that the thin parts, which tend to expand first, 
have time to cool. The thick parts can then 
be expanded by further blowing and thus a 
bulb or expansion of even thickness can be 

Cutting Glass. The most useful method for 
general use is by means of the file or glass- 
blowers' knife. Either file or knife must be 
kept sharp by grinding. Neither file nor 
knife should be used on hot glass. The 
diamond and wheel cutter are useful for cutting 
sheet-glass, and when the diamond is employed a 
singing noise is an indication of a satisfactory cut. 

Leading a Crack. A crack may be led in 
any desired direction by means of a bead of 
hot glass or a small gas flame. The glass 
which it is desired to crack should be heated at 
a point slightly in advance of the crack, which 
will extend in the direction of the source of the 

Turning Out the End of a Tube. This is 
done by heating the end of the tube and rotating 
it against an iron rod. The rod must be kept 
polished and free from rust, and it must not be 
allowed to become too hot while in use, other- 
wise the glass will stick to it. 


Joining Unlike Glasses. Joints between 
unlike glasses are often unstable. When such 
joints are made it is desirable to blow them as 
thin as possible, and to avoid the junction of 
unlike glasses in any complex joint, such as an 
internal seal. A transitional portion of tubing 
may be built up by the successive addition and 
interfusion of beads of one of the glasses to 
the end of a sealed tube consisting of the other 

Joining a Tube to a Very Thin Bulb. The 
bulb may be thickened at the point of union by 
fusing on a bead of glass and expanding this 
slightly. A small central portion of the 
expanded part may then be perforated by 
bursting and the tube joined on. 

Insertion of One Bulb Within Another. A 
bulb may be divided into two halves by leading 
a crack round it and the inner bulb is then 
introduced. The two halves of the outer bulb 
may be fitted together (care being taken to 
avoid any damage to the edges), and the bulb 
may be completed by rotating the contacting 
edges before the blowpipe until they are soft, 
and then expanding slightly by means of air- 


Annealing. For most purposes, in the case 
of thin, blowpipe-made or lamp-blown glass 
apparatus, it is sufficient to cool slowly by rota- 
ting the finished article over a smoky flame and 
setting it aside in a place free from draughts, 
and where the hot glass will not come in 
contact with anything. 

Simple bulbs and joints do not even need 
this smoking ; but thick articles, and especially 
those that are to be subjected to the stress of 
grinding, need more prolonged annealing in a 
special oven. 

Use of Lead-Glass. When lead-glass is to 
be used, the blowpipe flame should be in good 
adjustment and the glass should not be allowed 
to approach so near to the blue cone as to be 
blackened. Slight blackening may often be 
removed by heating the glass in the extreme 
end of the flame. 

Lead-glass articles tend to be rather more 
stable than similar articles of soda-glass. 

Combustion-Glass. This may be worked 
more easily if a small percentage of oxygen is 
introduced into the air with which the blow- 
pipe flame is produced. If the air is replaced 
entirely by oxygen there is a risk of damaging 


the blowpipe jet, unless a special blowpipe is 

Internal Seal. There are two ways of 
making these, one, in which the inner portion of 
the tube is fused on to the inside of the bulb or 
tube through which it is to pass, an opening is 
made by bursting and the outer tube is joined 
on. This is a quick and in some ways more 
satisfactory method than the other, in which 
there is no separate inner piece. 

Rubber Blowing Tube. In complicated 
work it is often convenient to use a thin rubber 
blowing-tube which is connected with the work 
either by a cork and piece of glass tubing or 
by fitting over a drawn-out end. The use of 
such a blowing-tube avoids the inconvenience 
of raising the work to the mouth when internal 
air-pressure is required. One end of the 
rubber tube is retained in the mouth during 

General Notes. A large amount of glass- 
blowing is spoiled through carelessness in 
arranging the work beforehand. The student 
should have every detail of his manipulation 
clearly in mind before he commences the work ; 


he should not trust to evolving the method 
during the actual manipulation. 

Undue haste is another fruitful source of 
failure. Practically every operation in glass- 
blowing can be carried out in a perfectly 
leisurely manner, and it is better to err rather 
on the side of deliberation than on the side of 

If, as will doubtless happen at times, a piece 
of work gives trouble and it is necessary to 
pause and consider the whole question, or if for 
any other reason it is necessary to stop during 
the construction of a partially finished join or 
other operation, great care should be taken not 
to allow the work to cool. A large, brush-like 
flame may be produced by increasing the 
amount of gas admitted to the blowpipe, and 
the work should be held just in front of the 
current of hot air produced by such a 

It will then be possible to continue work on 
this without causing it to crack when further 
heat is applied. 

As time goes on, the student will find an 
increasing confidence in his ability to manip- 
ulate the soft glass, and with increasing 


confidence will come rapidly increasing power 
of manipulation. Perhaps the greatest obstacle 
to success in glass-blowing is undue haste in 


Absorption bulbs, 21, 23. 
Airtube, flexible, 8, 102. 
Alarm thermometer, 45. 
Annealing, 7, 60. 

Bellows, adjusting pressure of, 5, 6. 
Bellows, foot, 5, 6. 
Bending tubes, 23. 
Blackening, 58, 101. 
Branching, 18, 19. 
Brushes of spun glass, 53. 
Blowpipe flame, quality of, 3. 
Blowpipe for mouth blast, 80, 82, 


Blowpipe, for paraffin wax, 82, 88. 
Blowpipe, Herepath's, 2. 
Blowpipe jet, centring, 3, 98. 
Blowpipe jet, dirt in, 3. 
Blowpipe jet, multiple, 4, 40. 
Blowpipe, Letcher's, change, 4, 
Blowpipe, simple form of, 80. 
Bulb, medially on tube, 22. 
Bulbs, 19, 20, 22, 38, 98. 
Bulbs, absorption, (Liebig's), 21, 


Bulbs, dividing, 39, 95. 
Bulbs from rod, 25. 
Bulbs, internal, 38. 
Bulbs, thick, 21. 

Cages, from glass rod, 24, 25, 27. 
Calibration, 72. 
Carius tubes, 16. 
Condenser, Liebig's, 37. 
Condensers, various, 37, 38. 

Cone, carbon, 8. 
Crack, leading, 30, 99. 
Cracking, subversive, 103. 
Cutting glass with diamond, 30. 
Cutting tubes, 11, 99. 

Diamond (glazier's), use of, 30. 
Dissimilar glass, joining of, 22, 94. 
Drilling, 61. 

Electrodes, sealing in, 42, 97. 
Etching glass, 70. 
Extemporised appliances, 80. 
Examination of apparatus, 93. 

Failure, Haste chief Source of, 103, 

Failures, Notes as to, 97. 

File, with oblique ground edge, 7. 

Filing glass, 63. 

Filter pumps, 35 

Foot, 25 

Fuels various, 82, 86, 87, 89. 

Funnel, thistle, 23. 

General principles and precautions, 


Glass, varieties of, 9, 55, 91-97. 
Graduation, 72-76 

Haste, Source of Failure, 103 
Heat reflector, asbestos, 7. 
Heating, intensive, 7, 57. 
Heating precautions, 12, 98 

Joining dissimilar glass, 22, 




Joining glass to metal, 76 
Joining tubes, 16, 94, 100. 

Knife, Glass blower's, 7, 99. 
Lenses, grinding, 63. 

Marking glass, 69 

Methods, analytic study of, 91, 93. 

Oxygen for intensive heating, 57, 

Precautions and General Principles, 


Pumps, Filter, 35. 
Pumps, Sprengel, 49, 50. 

Re-entering branch, 40. 
Reflector of heat, asbestos, 7. 
Rod, uses and articles from, 17, 25, 

27, 28. 
Rod, blowing to hollow, 17, 25, 26, 


Scrap glass, working, 90. 

Sealing tubes, 12, 13, 14. 
Sealed tubes for pressure, 15, 16. 
Sealing in of Electrodes, 42, 97. 
Seals, internal (airtraps), 32, 


Silvering glass, 77. 
Soldering glass, 76. 
Soxhlet-tube, 40. 
Spirals, 23, 95. 
Spray arrester, 34. 
Spray producers, 36. 
Sprengel pumps, 49, 50. 
Spinning glass, 51. 
Stopcocks, 60, 66. 
Stoppering, 63. 
Stirrers, 28, 29. 
Summary as to precautions and 

failures, 97. 

Taps, 60, 66. 

Thermometers, Various, 44-49. 

Thermo-regulator, 24. 

Thistle Funnel, 23. 

Tools, Various small, 7. 

Turn-pins, 7, 8, 99. 

Turning out open ends, 14, 99. 



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