A Handbook of
Bernard D. Bolas
Max S. Marshall, M.D<
A HANDBOOK OF
To my Friends
A Handbook of
BERNARD D. BOLAS
WITH NUMEROUS DIAGRAMS IN THE TEXT
BY NAOMI BOLAS
GEORGE ROUTLEDGE & SONS, LTD
NEW YORK : E. P. BUTTON & CO.
I. Introduction and Preliminary Remarks General
Principles to be observed in Glass Working
Choice of Apparatus Tools and Appliances-
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
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
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.
BERNARD D. BOLAS.
Handbook of Laboratory
Introduction and Preliminary Remarks General Principles to be
observed in Glass Working Choice of Apparatus Tools and
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.
2 LABORATORY GLASS-BLOWING
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
LABORATORY GLASS-BLOWING 3
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
roughness in the inside of the air jet, d shows
a satisfactory flame.
For many purposes, it is an advantage to
4 LABORATORY GLASS-BLOWING
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
LABORATORY GLASS-BLOWING 5
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
6 LABORATORY GLASS-BLOWING
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
LABORATORY GLASS-BLOWING 7
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
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
8 LABORATORY GLASS-BLOWING
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-
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.
LABORATORY GLASS-BLOWING 9
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
LABORATORY GLASS-BLOWING 11
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
12 LABORATORY GLASS-BLOWING
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
LABORATORY GLASS-BLOWING 13
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
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
14 LABORATORY GLASS-BLOWING
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
LABORATORY GLASS-BLOWING 15
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
16 LABORATORY GLASS-BLOWING
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-
LABORATORY GLASS-BLOWING i;
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
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
i8 LABORATORY GLASS-BLOWING
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
LABORATORY GLASS-BLOWING 19
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
20 LABORATORY GLASS-BLOWING
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
LABORATORY GLASS-BLOWING 21
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
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.
22 LABORATORY GLASS-BLOWING
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
LABORATORY GLASS-BLOWING 23
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
24 LABORATORY GLASS-BLOWING
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
A Thermo- Regulator for Gas. Fig. 7, a
e, shows an easily constructed thermo-regulator.
LABORATORY GLASS-BLOWING 25
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
26 LABORATORY GLASS-BLOWING
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
LABORATORY GLASS-BLOWING 27
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 /&,
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
28 LABORATORY GLASS-BLOWING
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 ;
LABORATORY GLASS-BLOWING 29
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
30 LABORATORY GLASS-BLOWING
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-
LABORATORY GLASS-BLOWING 31
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,
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
LABORATORY GLASS-BLOWING 33
tubing, which should be cut into two pieces,
each being about eight inches long.
QI V^x a.
First seal the end of one tube as described
on page 13, heat the sealed end and expand to a
34 LABORATORY GLASS-BLOWING
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
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
LABORATORY GLASS-BLOWING 35
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
36 LABORATORY GLASS-BLOWING
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
LABORATORY GLASS-BLOWING 37
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,
38 LABORATORY GLASS-BLOWING
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.
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
LABORATORY GLASS-BLOWING 39
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.
40 LABORATORY GLASS-BLOWING
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
LABORATORY GLASS-BLOWING 41
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
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
42 LABORATORY GLASS-BLOWING
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
LABORATORY GLASS-BLOWING 43
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,
44 LABORATORY GLASS-BLOWING
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
LABORATORY GLASS-BLOWING 45
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
An Alarm Thermometer. A thermometer
which will complete an electric circuit when a
certain temperature is reached may be made by
46 LABORATORY GLASS-BLOWING
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,
LABORATOEY GLASS-BLOWING 47
and the top of the outer tube is closed as shown
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
48 LABORATORY GLASS-BLOWING
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
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
LABORATORY GLASS-BLOWING 49
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
SO LABORATORY GLASS-BLOWING
inches long ; the measurement being taken
from the junction of the exhaustion branch
with the fall-tube to the top of the turned-up
A MacLeod Pump. One form of this is
illustrated by b, Fig. 12. It has the advantage
LABORATORY GLASS-BLOWING 51
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
52 LABORATORY GLASS-BLOWING
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
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
LABORATORY GLASS-BLOWING 53
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
54 LABORATORY GLASS-BLOWING
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.
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
56 LABORATORY GLASS-BLOWING
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
LABORATORY GLASS-BLOWING 57
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
58 LABORATORY GLASS-BLOWING
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
LABORATORY GLASS-BLOWING 59
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
60 LABORATORY GLASS-BLOWING
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
LABORATORY GLASS-BLOWING 61
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
62 LABORATORY GLASS-BLOWING
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
LABORATORY GLASS-BLOWING 63
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,
64 LABORATORY GLASS-BLOWING
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
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
LABORATORY GLASS-BLOWING 65
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
66 LABORATORY GLASS-BLOWING
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
LABORATORY GLASS-BLOWING 67
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
68 LABORATORY GLASS-BLOWING
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
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
LABORATORY GLASS-BLOWING 69
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-
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-
;o LABORATORY GLASS-BLOWING
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
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
LABORATORY GLASS-BLOWING 71
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
72 LABORATORY GLASS-BLOWING
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
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
LABORATORY GLASS-BLOWING 73
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
74 LABORATORY GLASS-BLOWING
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
LABORATORY GLASS-BLOWING 75
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
;6 LABORATORY GLASS-BLOWING
" 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
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
LABORATORY GLASS-BLOWING 77
glass, slightly acid zinc chloride being used as
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
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
There are many formulae for the silvering
solution, but that used in Martin's method may
be given :
78 LABORATORY GLASS-BLOWING
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
LABORATOEY GLASS-BLOWING 79
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
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.
LABORATORY GLASS-BLOWING 81
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
82 LABORATORY GLASS-BLOWING
the best relative positions of flame and blow-
pipe jet. The complete apparatus is shown by
a, Fig. 1 6.
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
LABORATORY GLASS-BLOWING 83
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
84 LABORATORY GLASS-BLOWING
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
LABORATORY GLASS-BLOWING 85
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
86 LABORATORY GLASS-BLOWING
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
LABORATORY GLASS-BLOWING 87
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
88 LABORATORY GLASS-BLOWING
in the presence of air, without undergoing any
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.
LABORATORY GLASS-BLOWING 89
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
90 LABORATORY GLASS-BLOWING
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
LABORATORY GLASS-BLOWING 91
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
92 LABORATORY GLASS-BLOWING
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
LABORATORY GLASS-BLOWING 93
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
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 ;
94 LABORATORY GLASS-BLOWING
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
LABORATORY GLASS-BLOWING 95
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
96 LABORATORY GLASS-BLOWING
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
LABORATORY GLASS-BLOWING 97
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
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
SUMMARY OF CONDITIONS NECESSARY FOR
SUCCESS IN GLASS- BLOWING.
For the convenience of the student, it may
be well to summarise the chief essentials for
98 LABORATORY GLASS-BLOWING
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
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
LABORATORY GLASS-BLOWING 99
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.
ioo LABORATORY GLASS-BLOWING
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-
LABORATORY GLASS-BLOWING 101
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
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
102 LABORATORY GLASS-BLOWING
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 ;
LABORATORY GLASS-BLOWING 103
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
104 LABORATORY GLASS-BLOWING
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.
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.
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
Fuels various, 82, 86, 87, 89.
Funnel, thistle, 23.
General principles and precautions,
Glass, varieties of, 9, 55, 91-97.
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,
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.
Spirals, 23, 95.
Spray arrester, 34.
Spray producers, 36.
Sprengel pumps, 49, 50.
Spinning glass, 51.
Stopcocks, 60, 66.
Stirrers, 28, 29.
Summary as to precautions and
Taps, 60, 66.
Thermometers, Various, 44-49.
Thistle Funnel, 23.
Tools, Various small, 7.
Turn-pins, 7, 8, 99.
Turning out open ends, 14, 99.
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UNIVERSITY OF CALIFORNIA
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