LABORATORY MANUAL
OF
GLASS-BLOWING
McGraw-Hill Book Company
_Publishers of Books for_
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LABORATORY MANUAL
OF
GLASS-BLOWING
BY
FRANCIS C. FRARY, PH. D.
ASSISTANT PROFESSOR OF CHEMISTRY
UNIVERSITY OF MINNESOTA
McGRAW-HILL BOOK COMPANY, INC.
239 WEST 39TH STREET, NEW YORK
6 BOUVERIE STREET, LONDON, E. C.
1914
COPYRIGHT, 1914, BY THE
McGRAW-HILL BOOK COMPANY, INC.
PREFACE
The purpose of this little book is to provide a clear and detailed
discussion of the elements of glass-blowing. Many laboratories in this
country, especially in the west, are located a long way from any
professional glass-blower, and the time and money spent in shipping
broken apparatus several hundred miles to be mended could often be saved
if some of the laboratory force could seal on a new stopcock, replace a
broken tube, or make some temporary repairs. Many men in physical or
chemical laboratories have occasion to modify some piece of apparatus
designed perhaps for other uses, or to design new apparatus. To such
also, the ability to perform some of the operations herein described may
be very valuable.
No originality is claimed for the methods here described. They are those
which the author has found most suitable and convenient in his own work,
and most easily learned by students. The aim has been to describe each
operation in such detail that a beginner can follow the process without
help and, with practice, attain satisfactory results. It is, however,
much easier to perform any of the operations described, after seeing
some one else perform it correctly; since the temperature, the exact
time to begin blowing the glass, and many other little details are very
difficult to obtain from a description.
It has not been thought worth while to describe the process of making
stopcocks, thermometers, vacuum tubes, etc., as such things can be
purchased more cheaply and of much better quality than any amateur can
make unless he is willing to spend a very large amount of time in
practice. For similar reasons the manipulation of quartz glass has been
omitted.
The author will be grateful for all suggestions and criticisms tending
to improve the methods presented. If some of them appear to be given in
excessive detail, the reader will remember that many things which are
obvious to the experienced worker are not so to the beginner, and that
it is the little details in the manipulation which often spell success
or failure in glass-blowing.
F. C. F.
MINNEAPOLIS, MINN.,
_January, 1914._
CONTENTS
PAGE
Preface v
CHAPTER I
MATERIALS AND APPARATUS 1
Varieties and defects of glass--Devitrification--Annealing
glass--Blowpipe and bellows--Light--Arrangement of exercises.
CHAPTER II
GENERAL OPERATIONS 7
Cutting, bending, constricting and flanging the tubing--Methods
of rotation and blowing.
CHAPTER III
ELEMENTARY EXERCISES 16
Joining two pieces of tubing of the same diameter--The "tee"
tube--Joining two tubes of different diameters--Blowing bulbs.
CHAPTER IV
ADVANCED EXERCISES 35
Sealing a tube through another tube: The gas-washing tube, suction
pump, and Kjeldahl trap.
CHAPTER V
MODIFIED METHODS AND SPECIAL OPERATIONS 43
Capillary tubing--Glass rod--Mending stopcocks--Closed circuits of
tubing--Spirals--Ground joints--Sealing in platinum wire--Sealing
vacuum tubes--Closed tubes for heating under pressure.
INDEX 59
LABORATORY
MANUAL OF GLASS-BLOWING
CHAPTER I
MATERIALS AND APPARATUS
One of the most important factors in the success of any piece of
glass-blowing is the glass employed. As is well known, there are two
general varieties of glass: Lead glass and soda glass. Formerly much
apparatus was made of lead glass, but at present it is very seldom met
with, except in the little drops of special glass used to seal platinum
wires into the larger sizes of tubes. Lead glass is softer and more
readily fusible than soda glass, but has the disagreeable property of
growing black in a few seconds unless worked in a strong oxidizing
flame. This may be prevented by using a "hissing" flame, with a large
excess of air, and working in the extreme end of the flame; or the black
lead formed may thus be reoxidized, and the glass restored to its
original clearness.
Almost all the soft glass on the market is a soda glass, although
sometimes part of the soda is replaced by potash. Most of the hard glass
appears to be a potash glass. The following qualities are desirable in a
glass for ordinary working: (1) moderately low working temperature, (2)
freedom from air bubbles, striations and irregularities, (3) proper
composition, so that the glass will not devitrify or crystallize while
being handled at its working temperature, (4) ability to withstand rapid
heating without cracking.
The working temperature of different samples of so-called "soft glass"
varies a good deal, and is best determined by trial. The glass should
become almost soft enough for blowing in a flame that still shows a
little yellow near the tip, so that at the highest temperature of the
flame it may flow fairly freely and thus easily eliminate irregularities
in thickness. If the glass is too hard, the shrinking of the glass,
collection of material for a bulb, and in fact most of the working
processes will be slower, and the glass will not stay at its working
temperature long enough after its removal from the flame to permit it to
be properly blown.
Air bubbles in the original batch of glass are drawn out into long
hair-like tubes during the process of manufacture. When such tubing is
worked, the walls of these microscopic tubes collapse in spots, and the
air thus enclosed will often collect as a small bubble in the wall, thus
weakening it. Irregularities are of various kinds. Some of the larger
sizes of thin-walled tubing often have one half of their walls much
thicker than the other, and such tubing should only be used for the
simplest work. Some tubing has occasional knots or lumps of unfused
material. The rest of the tube is usually all right, but often the
defective part must be cut out. The presence of striations running along
the tube is generally an indication of hard, inferior glass. Crookedness
and non-uniformity of diameter are troublesome only when long pieces
must be used.
Devitrification is one of the worst faults glass can possibly have. It
is especially common in old glass, and in glass which has contained
acids. It seems to be of two sorts. One variety manifests itself on the
surface of the glass before it reaches its working temperature, but if
the glass be heated to the highest temperature of the flame it will
disappear except in the portion at the edge of the heated part. The
glass seems to work all right, but an ugly crystallized ring is left at
the edge of the portion heated. This kind appears most frequently in old
glass which was originally of good quality, but has in time been
superficially altered, probably by the loss of alkalies. The other
variety of devitrification does not appear when the glass is first
heated; but after it has been maintained at or above its working
temperature for a longer or shorter time, it will be noticed that the
outer surface has lost its smoothness, and appears to be covered with
minute wrinkles. It will also be found that the glass has become harder,
so that it becomes impossible to work it easily. Further heating only
makes the matter worse, as does the use of a higher temperature from the
start. In fact it will often be found that a piece of comparatively soft
glass which devitrifies almost at once in a "hissing" flame can be
worked without serious difficulty if care be taken to use a flame still
decidedly tinged with yellow. Even good glass will begin to devitrify in
this way if heated too long at the highest temperature of the flame, so
care should always be taken (1) _to reduce the time of heating of any
spot of glass to a minimum_; _i.e._, get the desired result at the first
attempt, if possible, or at least with the minimum of reheating and
"doctoring," and (2) _avoid keeping the glass at the highest temperature
of the flame any longer than necessary_. This may be accomplished by
doing all heating, shrinking, etc., of the glass in a flame more or less
tinged with yellow, and only raising the temperature to the highest
point when ready to blow the glass. This kind of devitrification is
apparently due to volatilization of the alkalies from the glass in the
flame, and it is said that it can be partly remedied or prevented by
holding a swab of cotton saturated with a strong solution of common salt
in the flame from time to time as the glass is heated.
The toughness of glass, _i.e._, its ability to withstand variations of
temperature, depends on its composition and the care taken in its
annealing. In general, large pieces of glass should be heated very
slowly in the smoky flame, and the larger the diameter of the tube the
greater the length which must be kept warm to prevent cracking. All
large pieces should be carefully heated over their whole circumference
to the point where the soot deposit burns off, before being finally
cooled. After being thus heated they are cooled in a large smoky flame
until well coated with soot, then the flame is gradually reduced in size
and the object finally cooled in the hot air above it until it will not
set fire to cotton. If thought necessary, it may then be well wrapped in
cotton and allowed to cool in the air. If not properly annealed the
place heated may crack spontaneously when cold, and it is quite certain
to crack if it is reheated later.
Next in importance to the glass are the blow-pipe and the bellows. Any
good blast lamp, such as is ordinarily used in a chemical laboratory for
the ignition of precipitates, will be satisfactory; provided it gives a
smooth regular flame of sufficient size for the work in hand, and when
turned down will give a sharp-pointed flame with well-defined parts.
Where gas is not available, an ordinary gasoline blow-torch does very
well for all operations requiring a large flame, and a mouth blow-pipe
arranged to blow through a kerosene flame does well for a small flame.
Several dealers make blow-torches for oil or alcohol which are arranged
to give a small well-defined flame, and they would doubtless be very
satisfactory for glass-work. Any good bellows will be satisfactory if it
does not leak and will give a steady supply of air under sufficient
pressure for the maximum size of flame given by the lamp used. A bellows
with a leaky valve will give a pulsating flame which is very annoying
and makes good work very difficult. When compressed air is available it
can be used, but if possible it should be arranged so that the supply
can be controlled by the foot, as both hands are usually needed to hold
the work. For the same reason the supply of air is usually regulated by
varying the rate of operation of the bellows, rather than by adjusting
the valve of the blast-lamp. On the other hand, it will be found best to
always adjust the flow of the gas by means of the cock on the lamp,
rather than that at the supply pipe. The operator must have complete
control over the flame, and be able to change its size and character at
short notice without giving the work a chance to cool, and often without
ceasing to support it with both hands.
Glass-blowing should be done in a good light, but preferably not in
direct sunlight. The operator should be seated in a chair or on a stool
of such a height that when working he may comfortably rest one or both
elbows on the table. The comfort of the operator has a decided influence
on the character of his work; especially in the case of a beginner, who
often defeats his purpose by assuming uncomfortable and strained
positions. Steadiness and exact control of both hands are essential in
most operations; any uncomfortable or strained position tires the
muscles and weakens the control of the operator over them.
In the arrangement of the exercises here presented, several factors have
been considered. It is important that the first exercises be simple,
although not necessarily the simplest, and they should teach the
fundamental operations which will be used and amplified later. They
should in themselves be things which are of importance and commonly used
in glass-work, and they should be so arranged that the fundamental
points, such as the rotation of glass, the proper temperature, blowing
and shrinking the glass may be learned with a minimum expenditure of
time, glass and gas. It is therefore recommended that the beginner take
them up in the order given, at least as far as No. 7, and that each be
mastered before attempting the next. The beginner should not leave the
first exercise, for example, until he can join together two pieces of
tubing so that they form one piece of substantially uniform inner and
outer diameter, and without thick or thin spots. From two to four
practice periods of two hours each should suffice for this. This chapter
and the following one should also be frequently read over, as many of
the points discussed will not be understood at first and many of the
manipulations described will not be necessary in the simpler exercises.