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A HANDBOOK OF LABORATORY GLASS-BLOWING
_To my Friends
Eric Reid
and
Sidney Wilkinson_
A Handbook of Laboratory Glass-Blowing
BY
BERNARD D. BOLAS
WITH NUMEROUS DIAGRAMS IN THE TEXT
BY NAOMI BOLAS
[Illustration]
LONDON
GEORGE ROUTLEDGE & SONS, LTD
NEW YORK: E. P. DUTTON & CO.
1921
CONTENTS
CHAP. PAGE
I. Introduction and Preliminary Remarks--General Principles
to be observed in Glass Working--Choice of Apparatus--Tools
and Appliances--Glass 1
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, Electrode Work, Enclosed Thermometers, Alarm
Thermometers ... Recording Thermometers, "Spinning" Glass 32
IV. Glass, its Composition and
Characteristics--Annealing--Drilling, Grinding, and Shaping
Glass by methods other than Fusion--Stopcocks--Marking
Glass--Calibration and Graduation of
Apparatus--Thermometers--Exhaustion of Apparatus--Joining
Glass and Metal--Silvering Glass 55
V. Extemporised Glass-Blowing Apparatus--The use of Oil or
other Fuels--Making Small Rods and Tubes from Glass
Scraps--The Examination of Manufactured Apparatus with a view
to Discovering the Methods used in Manufacture--Summary of
Conditions necessary for Successful Glass-Blowing 80
Index 105
PREFACE
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
without 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 disjointed 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 Glass-Blowing
CHAPTER I
Introduction and Preliminary Remarks--General Principles to
be observed in Glass Working--Choice of Apparatus--Tools and
Appliances--Glass.
Glass-blowing is neither very easy nor very difficult; there are
operations so easy that the youngest laboratory boy should be able to
repeat them successfully after once having been shown the way, there are
operations so difficult that years are needed to train eye and hand and
judgment to carry them out; but the greater number of scientific needs
lie between these two extremes. Yet a surprisingly large number of
scientific workers fail even to join a glass tube or make a T piece that
will not crack spontaneously, and the fault is rather one of
understanding than of lack of ability to carry out the necessary
manipulation.
In following the scheme of instruction adopted in this handbook, it will
be well for the student to pay particular attention to the reason given
for each detail of the desirable procedure, and, as far as may be, to
memorise it. Once having mastered the underlying reason, he can evolve
schemes of manipulation to suit his own particular needs, although, as a
rule, those given in the following pages will be found to embody the
result of many years' experience.
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 blowpipe 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.
1. It is desirable to have the three centring screws as shown, in order
to adjust the position of the air jet and obtain a well-shaped flame,
but these screws are sometimes omitted. Fig. 1, _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.
[Illustration: Fig 1]
For many purposes, it is an advantage to have what is sometimes known
as a "quick-change" blowpipe; that is one in which jets of varying size
may be brought into position without stopping the work for more than a
fraction of a second. Such a device is made by Messrs. Letcher, and is
shown by _e_, and in section by _f_ Fig. 1. It is only necessary to
rotate the desired jet into position in order to connect it with both
gas and air supplies. A small bye-pass ignites the gas, and adjustment
of gas and air may be made by a partial rotation of the cylinder which
carries the jets.
For specially heavy work, where it is needed to heat a large mass of
glass, a multiple blowpipe jet of the pattern invented by my father,
Thomas Bolas, as the result of a suggestion derived from a study of the
jet used in Griffin's gas furnace, is of considerable value. This jet
consists of a block of metal in which are drilled seven holes, one being
central and the other six arranged in a close circle around the central
hole. To each of these holes is a communication way leading to the gas
supply, and an air jet is arranged centrally in each. Each hole has also
an extension tube fitted into it, the whole effect being that of seven
blowpipes. In order to provide a final adjustment for the flame, a
perforated plate having seven holes which correspond in size and
position to the outer tubes is arranged to slide on parallel guides in
front of these outer tubes.
[Illustration: Fig. 2]
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
infrequently happens that the spring in the wind chamber is too strong
for glass-blowing, and hence the air supply tends to vary in pressure.
This can be improved by fitting a weaker spring, but an easier way and
one that usually gives fairly satisfactory results, is to place an
ordinary screw-clip on the rubber tube leading from the bellows to the
blowpipe, and to tighten this until an even blast is obtained.
Another form of bellows, made by Messrs. Fletcher and Co., and common in
most laboratories, is shown by _b_; the wind chamber consists of a disc
of india-rubber clamped under a circular frame or tied on to a circular
rim. This form is shown by Fig. 2, _b_.
The third form, and one which my own experience has caused me to prefer
to any other, is cylindrical, and stands inside the pedestal of the
blowpipe-table. A blowpipe-table of this description is made by Enfer of
Paris.
There is no need, however, to purchase an expensive table for laboratory
use. All the work described in this book can quite well be done with a
simple foot bellows and a quick-change blowpipe. Nearly all of it can be
done with a single jet blowpipe, such as that described first, or even
with the still simpler apparatus mentioned on page 84, but I do not
advise the beginner to practise with quite so simple a form at first,
and for that reason have postponed a description of it until the last
chapter.
Glass-blowers' tools and appliances are many and various, quite a number
of them are better rejected than used, but there are a few essentials.
These are,--file, glass-knife, small turn-pin, large turn-pin, carbon
cones, carbon plate, rubber tube of small diameter, various sizes of
corks, and an asbestos heat reflector. For ordinary work, an annealing
oven is not necessary, but one is described on page 60 in connection
with the special cases where annealing is desirable.
Fig. 3 illustrates the tools and appliances. _a_ is an end view of the
desirable form of file, and shows the best method of grinding the edges
in order to obtain a highly satisfactory tool. _b_ is a glass knife,
shown both in perspective and end view, it is made of glass-hard steel
and should be sharpened on a rough stone, such as a scythe-stone, in
order to give a slightly irregular edge. _c_ is a small turn-pin which
may be made by flattening and filing the end of a six-inch nail. _d_ is
the large turn-pin and consists of a polished iron spike, about five
inches long and a quarter of an inch diameter at its largest part. This
should be mounted in a wooden handle. _e_ and _f_ are carbon cones. A
thin rubber tube is also useful; it may be attached 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.
[Illustration: Fig. 3]
Glass, as usually supplied by chemical apparatus 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 convenient 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 composition
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.