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Full text of "The methods of glass blowing, and of working silica in the oxy-gas flame;"

TP 



IRLF 




190Z 



LIBRARY 

OF THE 

UNIVERSITY OF CALIFORNIA. 



UL.l1L.linL 



THE METHODS OF GLASS BLOWING 



AND OF 



WORKING SILICA 



BY THE SAME AUTHOR 
New and Revised Edition, with Illustrations, Crown 8v 0, 2s. 

A Practical Introduction to Chemistry. Intended to 

give a practical acquaintance with the Elementary Facts 
and Principles of Chemistry. 



LONGMANS, GREEN, AND CO. 
LONDON, NEW YORK, AND BOMBAY 



The Methods of Glass Blowing 



AND OF 



Working Silica in the Oxy-Gas Flame 



FOR THE USE OF CHEMICAL AND PHYSICAL 
STUDENTS 



BY 



W. A. S HEN STONE, F.R.S. 

LECTURER ON CHEMISTRY IN CLIFTON COLLEGE 



FIFTH EDITION 




LONGMANS, GREEN, AND CO. 

39 PATERNOSTER ROW, LONDON 

NEW YORK AND BOMBAY 

1902 



02- 



PREFACE 

THIS book consists of a reprint of the third edition of 
my Methods of Glass-blowing, together with a new 
chapter in which I have described the comparatively 
new art of working vitreous silica. 

The individual operations of glass-blowing are much 
less difficult than is usually supposed, and considerable 
success in the performance of most of them may be 
attained by any one who is endowed with average 
powers of manipulation and who is moderately per- 
sistent. Constructing finished apparatus is often more 
difficult, as it may involve the performance of s*everal 
operations under disadvantageous conditions, and may 
demand a little ingenuity on the part of the operator. 
But I think the suggestions in Chapter IV. will 
make this comparatively easy also to those who have 
mastered the operations described in Chapter III. 

The working of vitreous silica, though more tedious 

106594 



vi PREFACE. 



and expensive than glass-blowing, is not really more 
difficult, and as it seems certain that this new material 
will soon play a useful part in chemical and physical 
research, I believe the addition now made to the earlier 
book will add considerably to its value. 

As glass is much less expensive to work with than 
silica, the beginner will find it best to spend a few 
days working with the common gas blow-pipe and 
glass before he attempts to manipulate the new and 
more refractory material. Therefore, in writing the 
new chapter, I have assumed that the reader is 
already more or less familiar with the rest of the 
book, and have given only such instructions and 
advice as will be required by one who is already able 
to carry out simple work at the blow-pipe. 



W. A. SHENSTONE. 



CLIFTON COLLEGE, 
Dec. 1901. 



CONTENTS 

CHAPTER I. 
GLASS-BLOWER'S APPARATUS. 

PAGE 

Introductory The Working-place The Blow-pipe The 

Bellows Automatic Blower Blow-pipe Flames, . . 1-11 

CHAPTER II. 

VARIETIES OF GLASS AND THEIR MANAGEMENT. 

Characters of good Glass Cleaning and Preparing a Tube 
Presenting Glass to the Flame Methods of working with 
Lead and Soft Soda Glass respectively Annealing The 
Use of Combustion Tube, . . 12-25 

CHAPTER III. 

CUTTING AND BENDING GLASS FORMING GLASS APPARATUS 
BEFORE THE BLOW-PIPE MAKING AND GRINDING STOPPERS 
TO APPARATUS, ETC. 

Cutting Glass Tubes Bending Glass Tubes Rounding and 
Bordering the Ends of Tubes Sealing Choking, or Con- 
tracting the Bore of a Glass Tube Widening Tubes 
Piercing Tubes Welding, or Uniting Pieces of Glass to 
each other Blowing a Bulb of Glass Making and Grind- 
ing Stoppers, 26-54 



viii CONTENTS. 



CHAPTER IV. 

MAKING THISTLB FUNNELS, U -TUBES, ETC. COMBINING THE PARTS 
OF COMPLICATED APPARATUS MERCURY AND OTHER AIR- 
TIGHT JOINTS VACUUM-TAPS SAFETY-TAPS AIR-TRAPS. 

PAGE 

Electrodes U-Tubes Spiral Tubes Thistle Funnels Closing 
Tubes containing Chemicals Modes of Combining the Parts 
of Heavy Apparatus Mercury Joints Modes of Lubricat- 
ing Taps Air-Traps, 55-69 

CHAPTER V. 

GRADUATING AND CALIBRATING GLASS APPARATUS. 

To Gr.iduate Tubes, etc. To divide a Line into Equal Parts 
To Calibrate a Burette To Calibrate Tubes for Measuring 
Gases, 70-81 

CHAPTER VL 

Diagrams of Glass Tubes, showing the chief sizes in which they 

are made, 82-83 

CHAPTER VII. 
Vitreous Silica, 84-95' 

INDEX, ... . .97 



OF THE 

(^ UNIVERSITY ) 

OF 



OHAPTEE L 

GLASS-BLOWER'S APPARATUS. 

Introductory. I shall endeavour to give such an 
account of the operations required in constructing glass 
apparatus as will be useful to chemical and other students ; 
and as this book probably will come into the hands of 
beginners who are not in a position to secure any further 
assistance, I shall include descriptions even of the simple opera- 
tions which are usually learned during the first few hours of 
practical work in a chemical or physical laboratory. I shall 
not give any particular account of the manufacture of such 
apparatus as thermometers, taps, etc., because, being in large 
demand, they can be bought so cheaply that time is not 
profitably spent in making them. But it will be found 
that what is included will enable any one, who will de- 
vote sufficient time to acquiring the necessary manipulative 
dexterity, to prepare such apparatus as test-tubes, distil- 
lation flasks, apparatus for washing gases, ozone generating 
tubes, etc., when they are required, as they often are, without 
delay or for special purposes. The amateur probably will 
not succeed in turning out apparatus so finished in appear- 
ance as that of the professional glass-blower until after 
long practice, but after a little daily practice for the space 
of a few weeks, any one who is fairly skilful in ordinary 

A 



GLASS-BLO WING. 



manipulation, and who perseveres in the face of failure 
at first, will find himself able to make almost all the 
apparatus he needs for lecture or other experiments, with 
a considerable saving in laboratory expenses, and, which 
very often is more important, without the delay that occurs 
when one depends upon the professional glass-worker. In 
the case of those who, like myself, work in the provinces, 
this latter advantage is a very weighty one. 

After the description of the instruments used in glass-blow- 
ing, which immediately follows, the following arrangement of 
the subject has been adopted. In the first place, an account 
of the two chief kinds of glass is given, and of the peculiarities 
in the behaviour of each of them before the blow-pipe, which 
is followed by a tolerably minute description of the method 
of performing each of the fundamental operations employed 
in fashioning glass apparatus. These are not very numerous, 
and they should be thoroughly mastered in succession, prefer- 
ably upon tubes of both soda and lead glass. Then follows, 
in Chapter IV., an account of the application of these operations 
to setting up complete apparatus, full explanations of the con- 
struction of two or three typical pieces of apparatus being 
given as examples, and also descriptions of the modes of 
making various pieces of apparatus which in each case present 
one or more special difficulties in their construction ; together 
with an account, which, I think, will be found valuable, of 
some apparatus that has been introduced, chiefly during 
recent years, for experimenting upon gases under reduced 
pressure, e.g. vacuum taps and joints. Finally, in Chapter 
V., there is a short account of the methods of graduating 
and calibrating glass apparatus for use -in quantitative 
experiments. 

The Working- place. The blow-pipe must be placed in 
a position perfectly free from draughts. It should not face 



THE WORKING-PLACE. 



a window, nor be in too strong a light, if that can be avoided, 
for a strong light will render the non-luminous flames, which 
are used in glass-blowing, almost invisible, and seriously 
inconvenience the operator, who cannot apply the various 
parts of the flames to his glass with the degree of certainty that 
is necessary ; neither can he perceive the condition of the glass 
so correctly in a strong light, for though in many operations 
the glass-worker is guided by feeling rather than by seeing, yet 
sight plays a very important part in his proceedings. 

My own blow-pipe is placed near a window glazed with 
opaque glass, which looks southwards, but is faced by buildings 
at a short distance. In dull weather the light obtained is 
good ; but on most days I find it advantageous to shade the 
lower half of the window with a green baize screen. Some 
glass-blowers prefer gaslight to daylight. 

The form of the table used is unimportant, provided that it is 
of a convenient height, and allows free play to the foot which 
works the blower underneath it. The blower should be 
fixed in a convenient position, or it will get out of control at 
critical moments. The table, or that part of it which surrounds 
the blow-pipe, should be covered with sheet-iron to protect 
it from the action of the fragments of hot glass that will fall 
upon it. The tubes that supply air and gas to the blow- 
pipe should come from beneath the table, and may pass 
through holes cut for the purpose. 

Many glass-blowers prefer to work at a rather high table, 
and sit on a rather high stool, so that they are well above 
their work. No doubt this gives extra command over the 
work in hand, which is often valuable. On the other hand, it 
is somewhat fatiguing. For a long spell of labour at work 
which is not of a novel character nor specially difficult, I am 
disposed to recommend sitting on a chair or low stool, at a 
table of such height as will enable the elbows to rest easily 
upon it whilst the glass is held in the flame. The precise 



GLASS-BLOWING. 



heights that are desirable for the table and stool, and the 
exact position of the blow-pipe, will depend upon the height 
and length of arm of the individual workman, and it must 
therefore be left to each person to select that which suits him 
best. A moveable rest made of wood, for supporting the 
remote end of a long piece of glass tube a few inches above 
the table, whilst the other end is being heated in the flame, 
will be found convenient 



The Blow-pipe. Formerly a lamp, in which sweet oil or 
tallow was burnt, was employed for glass working, and such 
lamps are still occasionally used. Thus, lamps burning oil or 
tallow were used on board the Challenger for hermetically 
sealing up flasks of water collected at various depths to pre- 
serve them for subsequent examination. I shall not, however, 
give an account of such a lamp, for the gas apparatus is so 
much more convenient for most purposes that it has now 
practically superseded the oil lamps. Fig. 1 shows a gas 
blow-pipe of exceedingly simple construction, which can be 
easily made, and with which good work can be done. 




Fio. 1. 



The tube A is of brass, and has a side tube B brazed to it, 
ten to twelve centimetres from the end E, according to the 
dimensions of the tube. A tube of glass, EC, is fitted into 



THE BLOW-PIPE. 



A by a cork at D. B is connected to a supply of gas by a 
flexible tube, C is similarly connected to the blower. By 
means of CE a stream of air can be forced into gas burning 
at the mouth of the blow-pipe 6r, and various flames, with 
the characters described in a later section, can be produced 
with this instrument. For producing the pointed flame 
(Fig. 3, p. 9) the opening E of the air-tube should be con- 
tracted to the size of a large knitting needle. For producing 
a flame of large size, rich in air (Fig. 4, p. 9), the internal 
diameter of E may be nearly half as great as that of A 
without disadvantage. 

This blow-pipe may be fixed in position by the spike Fj 
which will fit into holes in a block of wood or a large cork. 
Several of these holes in various positions should be made in 
tbe block, so that the position of the blow-pipe may be varied 
easily. Two taps must be provided in convenient positions 
near the edge of the table to enable the workman to regulate 
the supplies of air and gas. These taps should be fixed to 
the table and be connected with the gas and air supplies re- 
spectively on one side, and with the blow-pipe on the other, by 
flexible tubes. If blow-pipes of this kind be used, at least 
two of them should be provided ; one of small dimensions for 
working on small tubes and joints, the other of larger size 
for operations on larger tubes. It will be convenient to 
have both of them ready for use at all times, as it is 
sometimes necessary to employ large and small flames on the 
same piece of work in rapid succession. By having several 
air-tubes of different sizes fitted to each blow-pipe, a greater 
variety of work may be done. 

For the larger blow-pipe, the internal diameter of A may 
be fifteen to seventeen millimetres. 

For the smaller instrument, eleven millimetres for the 
diameter of A would be a useful size. 

When a slightly greater outlay can be afforded it will 



GLASS-BLOWING. 



be most convenient to purchase the blow-pipe. They can be 
obtained of compact form, supported on stands with universal 
joints giving great freedom of movement, and with taps for 
regulating the supplies of gas and "air, at comparatively small 
cost. 

As figures of various blow-pipes can be seen in the price- 
lists of most dealers in apparatus, they are not given here. 
Their introduction would be of but little service, for the 
construction of that which is adopted can be readily ascer- 
tained by taking it to pieces. The simplest blow-pipe usually 
used for glass-working is that of Herapath. This has two 
taps to regulate the air and gas supplies respectively, and will 
give a considerable variety of flames, which will be discussed 
subsequently. 

An excellent blow-pipe, made on the same principle as 
that shown in Fig. 1, but more substantially and with 
interchangeable jets, can be obtained from Messrs. Muller of 
Holborn for a moderate outlay. 

Another very good blow-pipe is the Automaton blow- 
pipe of Mr. Fletcher of Warrington. In this, one tap 
regulates the supply both of air and gas, which is a great 
gain when difficult work is in hand. Automaton blow-pipes 
are made of two sizes. I have found that the larger size, 
with a powerful bellows, heats large pieces of lead glass 
very satisfactorily. On the other hand, the fine-pointed 
oxidising flame of the Herapath blow-pipe is, perhaps, the 
most suitable for working joints of lead glass. Therefore 
a good equipment would be a small Herapath blow-pipe 
and a large-sized Automaton. If only one blow-pipe is pur- 
chased it should be either a medium-sized Herapath, or 
the smaller Automaton, as those are most useful for general 
work. 

Mr. Fletcher also makes an ingenious combination of two 
blow-pipes in which the gas and air supplies are regulated by 



THE BELLOWS: 



a single Ifever-handle. This is very convenient, and gives 
flames that answer well with tubes made of soft soda glass, 
and it is .very useful for general work. For use with lead 
glass the supply of air is rather too small, and does not enable 
one to get such good results. This can be easily amended, 
however. By slightly increasing the size of the air-tube of the 
smaller blow-pipe, and having increased the supply of air to 
the larger blow-pipe also, by reducing the external diameter of 
the end of the innermost tube, I now get medium-sized brush 
flames and pointed flames with this blow-pipe, that are equal 
to any I have used for heating lead glass. 

For small laboratories the inexpensive No. 5 Bunsen burner 
of Mr. Fletcher, which is convertible into a blow-pipe, will be 
very useful. 

Jets of several sizes to fit the air-tubes of blow-pipes may 
be obtained with them, and will serve for regulating the 
supply of air to the flame. 

The Bellows. The usual blowing apparatus is some 
form of foot-blower. These may be obtained fitted to 
small tables with sheet-iron tops. But a much less expensive 
apparatus is the large foot-blower made by Mr. Fletcher of 
Warrington, which can be used at an ordinary table or 
laboratory bench. Good foot-blowers can also be obtained 
from makers of furnace bellows. 

No part of the glass-blower's equipment exceeds the bellows 
in importance. The best blower procurable should therefore 
be adopted. A bellows which, when used with a large blow- 
pipe, will not enable you to heat large pieces of lead glass tube 
to redness without blackening the glass when the directions 
for heating lead glass on pages 17-21 are followed, should on 
no account be received. I am told that at some places, where 
the water-supply is at very high pressure, it is utilised for 
working blow-pipes by means of the apparatus described 



GLASS-BLO WING. 



below, and that some glass-workers find it advantageous to 
use such automatic blowers. But after a little practice, the 
effort of working the blower with the foot whilst manipulating 
the glass is not a source of serious inconvenience. Indeed, as 
it gives a certain degree of control over the flame without the 
use of the hands, the foot-blower is preferable. It is worth 
while to describe an automatic blower, however. 



Automatic Blower (Fig. 2). A strong glass tube 
A is welded into a somewhat larger 
tube B so that its end is about 2 mm. 
from the contraction at G. B has a side 
tube C joined to it. The narrow end of B 
is fixed by an india-rubber cork to a strong 
bottle D of two or three litres capacity. 
The india-rubber cork also carries an exit 
tube E, and D is pierced near its bottom by 
a small hole at F. 

. In using the apparatus A is connected 
with the water-supply, and water passing 
through G, carries air with it into D. The 
water escapes from D by the opening at F, 
and the air is allowed to pass out by the 

tube E, its passage being regulated by a tap. Fresh supplies 

of air enter B by C. 




Blow-pipe Flames The Pointed Flame. If the gas tap 
of a Herapath blow-pipe be adjusted so that comparatively 
little gas can pass, and if the foot-blower be then worked 
cautiously, a long tongue of flame ending in a fine point 
will be produced (Fig. 3). This flame will subsequently be 
described as the pointed flame. It should be quite free from 
luminosity, and as the amount of air necessary for securing a 



BLOW-PIPE FLAMES. 



pointed flame is large, in proportion to the gas, there is excess 

of oxygen towards the 

end G. By adjusting 

the proportions of 

air and gas, pointed 

flames of various 

dimensions can 

obtained with 




be 
the 

same blow-pipe. The 
part of a pointed 
flame to be used in 
glass-working is the 
tip, or in some cases 
the space slightly 
beyond the tip. 

The Brush Flame. If a large supply of gas be turned on and 
a considerable blast of air sent into the flame, a non-luminous 



Fid. 3. 




flame of great size will be obtained (Fig. 4). In form it 
somewhat 'resembles a large camel's hair pencil, and may con- 



io GLASS-BLOWING. 

veniently be described as a brush flame. The chief advantage 
of a large-sized blow-pipe is, that with it a large brush flame 
may be produced, which is often invaluable. By gradually 
diminishing the supply of gas and air smaller brush flames 
may be produced. 

The" jet used to supply air to the Herapath blow-pipe is 
usually too fine, and consequently does not permit the 
passage of sufficient air to produce a brush flame that con- 
tains excess of oxygen, even with the aid of a very powerful 
blower. My own Herapath blow-pipe only gives a satisfactory 
oxidising brush flame when the jet is removed altogether from 
the end of the air-tube. For producing pointed flames the finer 
jet of the air tube must be used, but when a highly oxidising 
flame of large size is required it must be removed. The 
internal diameter of the central air-tube should be nearly half 
as great as that of the outer or gas-supply tube. Fletcher's 
Automaton with the large air jet gives a very liberal supply 
of air, and produces an excellent oxidising brush flame. In 
the case of the larger-sized Automaton a consequence of this 
is, however, that when fitted with the large jet it will not give 
so good a pointed flame as the Herapath, which, in its turn, 
gives an inferior oxidising brush. By fitting finer jets to the 
air tube of Fletcher's apparatus pointed flames can be secured 
when necessary. 

The Smoky Flame. By turning on a very free supply of gas, 
;md only enough air to give an outward direction to the 
burning gas, a smoky flame, chiefly useful for annealing and for 
some simple operations on lead glass, is produced. 

The Gimmingham blow-pipe and Fletcher's combination 
blow-pipe, in addition to the above flames, are also adapted 
to produce a non-luminous flame, resembling that of the 
Bunsen gas-burner, which is very convenient for the pre- 
liminary heating of the glass, and ;ilso for gradually cooling 
finished apparatus. It is not necessary to describe the method 



BLOW-PIPE FLAMES. n 

of using these last-mentioned blow-pipes. With the more 
complicated of them directions for its use are supplied. 

Mr. Madan has suggested the use of oxygen in place of air 
for producing the oxidising flame required for working lead 
glass, and to produce a flame of high temperature for softening 
tubes of hard, or combustion, glass. For the latter purpose 
the employment of oxygen may be adopted with great advan- 
tage. For working lead glass, however, it is quite unneces- 
sary if the directions already given are followed. 

The student's subsequent success will so largely depend upon 
his acquaintance with the resources of his blow-pipe, and on 
the facility with which he can take advantage of them, that 
no pains should be spared in the effort to become expert in 
its management as soon as possible. A few experiments 
should now be made, therefore, upon the adjustment of the 
flame, until the student is able to produce and modify any 
form of flame with promptness and certainty. 

The remaining apparatus used in glass-working consists of 
triangular and other files, charcoal pastils for cutting glass, 
pieces of sound charcoal of various diameters with conical 
ends ; it is convenient to have one end 
somewhat less pointed than the other /~ 

(Fig. 5). Corks of various sizes; the \_ 

smallest, which are most frequently FlG 5 

needed, should be carefully cut with 
sharpened cork borers from larger corks. Besides these 
there should be provided some freshly distilled turpentine in 
which camphor has been dissolved, 1 fine and coarse emery 
powder, and some sheets of cotton-wadding, an india-rubber 
blowing-bottle, glass tubes, a little white enamel, and a pair of 
iron tongs. 



1 Half an ounce of camphor to about six ounces of turpentine will 
do very well. 



12 GLASS-BLOWING. 



CHAPTER IL 

VARIETIES OF GLASS AND THEIR MANAGEMENT. 

ALL the varieties of glass that are ordinarily met with con- 
tain silica (Si0 2 ) associated with metallic oxides. In a true 
glass there are at least two metallic oxides. The unmixed 
silicates are not suitable for the purposes of glass. They are 
not so capable of developing the viscous condition when heated 
as mixtures some of them are easily attacked by water, and 
many of those which are insoluble are comparatively infusible. 
There is generally excess of silica in glass, that is, more than 
is necessary to form normal silicates of the metals present. 
The best proportions of the various constituents have been 
ascertained by glass-makers, after long experience; but the 
relation of these proportions to each other, from a chemical 
point of view, is not easy to make out. 

The varieties of glass from which tubes for chemical glass- 
blowing are made may be placed under three heads, and are 
known as 1 

Soft soda glass. Also known as French glass. 

Lead glass. Also known as English glass. 

Hard glass. 
In purchasing glass tubes, it is well to lay in a considerable 



1 For details of the composition of the various glasses, some work on 
glass-making may be consulted. 



VARIETIES OF GLASS, ETC. 13 

stock of tubes made of each of the two first varieties, 
and, if possible, to obtain them from the manufacturer, for it 
frequently happens that pieces of glass from the same batch 
may be much more readily welded together than pieces of 
slightly different composition. Yet it is not well to lay 
in too large a stock, as sometimes it is found that glass 
deteriorates by prolonged keeping. 

As it is frequently necessary to make additions, alterations, 
or repairs to purchased apparatus, it is best to provide 
supplies both of soft soda glass and lead glass, for though 
purchased glass apparatus is frequently made of lead glass, 
yet sometimes it is formed from the soda glass, and as it is a 
matter of some difficulty to effect a permanent union between 
soda glass and lead glass, it is desirable to be provided with 
tubes of both kinds. 

Many amateurs find that soda glass is in some respects 
easier to work with than lead glass. But, on the other hand, 
it is somewhat more apt to crack during cooling, which causes 
much loss of time and disappointment. Also, perhaps in 
consequence of its lower conductivity for heat, it very often 
breaks under sudden changes of temperature during work. 
If, however, a supply of good soda glass is obtained, and the 
directions given in this book in regard to annealing it are 
thoroughly carried out, these objections to the use of soda glass 
will, to a great extent, be removed. I find, however, that when 
every precaution has been taken, apparatus made of soda glass 
will bear variations of temperature less well than that made of 
lead glass. Therefore, although the comparatively inexpensive 
soda glass may be employed for most purposes without dis- 
trust, yet I should advise those who propose to confine 
themselves to one kind of glass, to take the small extra trouble 
required in learning to work lead glass. 

In order to secure glass of good quality, a few pieces should 
be obtained as a sample, and examined by the directions 



14 GLASS-BLOWING. 

given below. When the larger supply arrives, a number of 
pieces, taken at random, should be examined before the blow- 
pipe, to compare their behaviour with that of the sample 
pieces, and each piece should be separately examined in all 
other respects as described subsequently. 

Hard glass is used for apparatus that is required to with- 
stand great heat. It is difficult to soften, especially in large 
pieces. It should only be employed, therefore, when the low 
melting-points of soda or lead glass would render them un- 
suitable for the purpose to which the finished apparatus is to 
be put. What is sold as Jena combustion tube should be 
preferred when this is the case. 

Characters of good Glass. Glass tubes for glass-blow- 
ing should be as free as possible from knots, air- bubbles, and 
stripes. They should be in straight pieces of uniform thick- 
ness, and cylindrical bore. It is not possible to obtain glass 
tubes of absolutely the same diameter from one end to the 
other in large quantities, but the variations should not be 
considerable. 

When a sharp transverse scratch is made with a good file 
on a piece of tube, and the scratch is touched with a rather 
fine point of red-hot glass (this should be lead glass for a 
lead glass tube, and soda glass for a tube of soda glass), the 
crack which is started should pass round the glass, so that it 
may be broken into two pieces with regular ends. If the 
crack proceeds veiy irregularly, and especially if it tends to 
extend along the tube, the glass has been badly annealed, and 
should not be employed for glass-blowing purposes. It is 
important that the point of hot glass used shall be very 
small, however. Even good glass will frequently give an 
irregular fracture if touched with a large mass of molten 



Finally, glass tube which is thin and of small diameter 



CLEANING AND PREPARING A TUBE. 15 

should not crack when suddenly brought into a flame. But 
larger and thicker tubes will not often withstand this treat- 
ment. They should not crack, however, when they are brought 
into a flame gradually, after having been held in the warm air 
in front of it. for a minute or so. 

Good glass does not readily devitrify when held in the blow- 
pipe flame. As devitrified glass very often may be restored to 
its vitreous condition by fusion, devitrification most frequently 
shows itself round the edges of the heated parts, and may be 
recognised by the production of a certain degree of roughness 
there. It is believed to be due to the separation of certain 
silicates in the crystallised form. Hard glass, which contains 
much calcium, is more apt to devitrify than the more fusible 
varieties. 1 

Glass tubes are made of various sizes. When purchasing a 
supply, it is necessary to be somewhat precise in indicating to 
the vendor the sizes required. I have therefore placed at 
the end of the book, in an appendix, a table of numbered 
diagrams. In ordering tubes it will usually only be neces- 
sary to give the numbers of the sizes wished for, and to 
specify the quantity of each size required. In ordering glass 
tubes by weight, it must be remembered that a great many 
lengths of the smaller sizes, but very few lengths of the 
larger sizes, go to the pound. Larger-sized tubes than those 
on the diagram are also made. In ordering them the 
external diameter and thickness of glass preferred should be 
stated. 

Cleaning and Preparing a Tube. It is frequently 
much easier to clean the tube from which a piece of apparatus 

1 The presence of silicates of calcium and aluminum are considered 
to promote a tendency to devitrification in glass ; and glasses of com- 
plex composition are more apt to devitrify than the simpler varie- 
ties. See Glass-making, by Powell, Chance, and Harris, Chap. IV. 



16 GLASS-BLOWING. 

is to be made than to clean the finished apparatus. A simple 
method of cleaning a tube is to draw a piece of wet rag which 
has been tied to a string through the tube once or twice, or,- 
with small tubes, to push a bit of wet paper or cotton wool 
through them. If the dirt cannot be removed in this way, 
the interior of the tube should be moistened with a little sul- 
phuric acid in which some bichromate of potassium has been 
dissolved. In any case, it must finally be repeatedly rinsed 
with distilled water, and dried by cautiously warming it, and 
sucking or blowing air through it. In order to avoid heating 
delicate apparatus which has become damp and needs drying, 
the water may be washed out with a few drops of spirit, 
which is readily removed at a low temperature. 

Before using a glass tube for an operation in which it will 
be necessary to blow into it, one end of it must be contracted, 
unless it is already of such a size that it can be held between 
the lips with perfect ease ; in any case, its edges must 
be rounded. For descriptions of these operations, see 
page 35. The other end must be closed. This may be done 
by means of a cork. 

Presenting Glass to the Flame. Glass tubes must 
never be brought suddenly into the flame in which they 
are to be heated. All glass is very likely to crack if so 
treated. It should in all cases be held for a little while in 
front of the flame, rotated constantly in the hot air and 
moved about, in order that it may be warmed over a con- 
siderable area. When it has become pretty hot by this 
treatment, it may be gradually brought nearer to the flame, 
and, finally, into contact with it, still with constant rotation 
and movement, so as to warm a considerable part of the 
tube. When the glass has been brought fairly into contact 
with the flame, it will be safe to apply the heat at the required 
part only. Care must be taken in these preliminary opera- 



METHODS OF WORKING WITH LEAD GLASS. 17 

tions to avoid heating the more fusible glasses sufficiently to 
soften them. 

Methods of working with Lead and soft Soda 
Glass respectively. When lead glass is heated in the 
brush flame of the ordinary Herapath blow-pipe, or within the 
point of the pointed flame, it becomes blackened on its sur- 
face, in consequence of a portion of the lead becoming 
reduced to the metallic state by the reducing gases in the 
flame. The same thing will happen in bending a lead glass 
tube if it is made too hot in a luminous flame. A practical 
acquaintance with this phenomenon may be acquired by the 
following experiment : 

Take a piece of lead glass tube, bring it gradually from the 
point of a pointed flame to a position well within the flame, and 
observe what happens. When the glass reaches the point A 
(Fig. 3), or thereabouts, a dark red spot will develop on the 
glass, the area of the spot will increase as the glass is 
brought further in the direction A to B. If the glass be then 
removed from the flame and examined, it will be found that 
a dark metallic stain covers the area of the dark red spot 
previously observed. Repeat the experiment, but at the 
first appearance of the dark spot slowly move the glass in the 
direction A to G. The spot will disappear, and, if the opera- 
tion be properly performed, in its place there will be a charac- 
teristically greenish-yellow luminous spot of highly heated 
glass. In this proceeding the reduced lead of the dark spot 
has been re-oxidised on passing into the hot gases, rich in 
oxygen, which abound at the point of the flame. If one end 
of the tube has been previously closed by a piece of cork, and if 
air be forced into the tube with the mouth from the open end 
before the luminous spot has become cool, the glass will expand. 
If the experiment be repeated several times, with pointed 
flames of various sizes, the operator will quickly learn how to 

B 



i8 GLASS-BLOWING. 

apply the pointed flame to lead glass so that it may be heated 
without becoming stained with reduced lead. 

If the spot of reduced metal produced in the first experi- 
ment be next brought into the oxidising flame, it also may 
gradually be removed. On occasion, therefore, apparatus 
which has become stained with lead during its production, 
may be rendered presentable by suitable treatment in the 
oxidising flame. The process of re-oxidising a consider- 
able surface in this way after it has cooled down is apt 
to be very tedious, however, and, especially in the case of 
thin tubes or bulbs, often is not practicable. In working 
with lead glass, therefore, any reduction that occurs should 
be removed by transferring the glass to the oxidising flame 
at once. 

Small tubes, and small areas on larger tubes of English 
glass, may be softened without reduction by means of the 
pointed oxidising flame ; but it is not easy to heat any con- 
siderable area of glass sufficiently with a pointed flame. And 
though it is possible, with care, to employ the hot space 
immediately in front of the visible end of an ordinary brush 
flame, which is rich in air, yet, in practice, it will not be 
found convenient to heat large masses of lead glass nor tubes 
of large size, to a sufficiently high temperature to get the 
glass into good condition for blowing, by presenting them 
to the common brush flame. 

It may seem that as glass which has become stained with 
reduced lead can be subsequently re-oxidised by heating it 
with the tip of the pointed flame, the difficulty might be 
overcome by heating it for working in the brush flame, and 
subsequently oxidising the reduced lead. It is, however, 
difficult, as previously stated, to re-oxidise a large surface of 
glass which has been seriously reduced by the action of the 
reducing gases of the flame, after it has cooled. Moreover, 
there is this very serious objection, that if, as may be neces- 



METHODS OF WORKING WITH LEAD GLASS. 19 

sary, the action of the reducing flame be prolonged, the 
extensive reduction that takes place diminishes the tendency 
of the glass to acquire the proper degree of viscosity for 
working it, the glass becomes difficult to expand by blowing, 
seriously roughened on its surface, and often assumes a very 
brittle or rotten condition. 

When it is only required to bend or draw out tubes of 
lead glass, they may be softened sufficiently by a smoky 
flame, which, probably owing to its having a comparatively 
low temperature, does not so readily reduce the lead as flames 
of higher temperature. But for making joints, collecting 
masses of glass for making bulbs, and in all cases where it 
is required that the glass sliall be thoroughly softened, the 
smoky flame does not give good results. 

In the glass-works, where large quantities of ornamental 
and other glass goods are made of lead or flint glass, the pots 
in which the glass is melted are so constructed that the gases 
of the furnace do not come into contact with the glass ; l and as 
the intensely-heated sides of the melting-pot maintain a very 
high temperature within it by radiation, the workman has avery 
convenient source of heat to his hand, he has, in fact, only to 
introduce the object, or that part of it which is to be softened, 
into the mouth of the melting-pot, and it is quickly heated 
sufficiently for his purpose, not only without contact of 
reducing gases, but in air. He can therefore easily work 
upon very large masses of glass. In a special case, such a 
source of heat might be devised by the amateur. Usually, 
however, the difficulty may be overcome without special 
apparatus. It is, in fact, only necessary to carry out the 
instructions given below to obtain a considerable brush flame 
rich in air, in which the lead glass can be worked, not only 
without discoloration, but with the greatest facility. 

1 See Principles of Glass-making, p. 31. 



20 GLASS-BLOWING. 

To Produce an Oxidising Brush Flame. The blower used 
must be powerful, the air tube of the blow-pipe must be 
about half as great in diameter as the outer tube which 
supplies the gas. The operator must work his bellows so 
as to supply a strong and steady blast of air, and the 
supply of gas must be regulated so that the brush flame 
produced is free from every sign of incomplete combustion, 1 
which may be known by its outer zone being only faintly 
visible in daylight, and quite free from luminous streaks 
(see Fig. 4, p. 9). When a suitable flame has been produced, 
try it by rotating a piece of lead glass at or near the end of the 
inner blue part of the flame (A Fig. 4) ; the appearance of 
the glass will quickly indicate reduction. When this occurs 
move the glass forward to the end of the outer zone j#, but 
keep it sufficiently within the flame to maintain it at a high 
temperature. If all is right the metallic reduction will quickly 
disappear, the glass will become perfectly transparent once 
more, and will present the appearance previously observed in 
the experiments with the pointed flame, or, if very hot, 
assume a brownish-red appearance. If this does not occur, 
the supply of air must be increased or the supply of gas 
diminished until the proper effects are secured. 

In working upon lead glass with the highly oxidising brush 
flame, it is a good plan to heat it in the reducing part of the 
flame A for thoroughly softening the glass, and to remove it to 
the oxidising flame B to burn away the reduced metal. In 
prolonged operations, in order that reduction may never 
go too far, hold the glass alternately in the hot reducing 
flame and in the oxidising flame. The inferiority of the outer 
oxidising flame to those portions nearer the inner blue zone for 

1 Nevertheless the supply of air must not be so excessive as to reduce 
the temperature of the flame sufficiently to prevent the thorough soften- 
ing of the glass, which will occur if the bellows is worked with too 
much zeal. 



METHODS OF WORKING WITH LEAD GLASS. 21 

softening the glass, may perhaps be accounted for by the pre- 
sence of a larger proportion of unconsumed air in the former, 
which being heated at the expense of the hot gases produced 
by combustion, thereby lowers the temperature of the flame. 
At or near A (Fig. 4) where the combustion is nearly complete, 
but no excess of air exists, the temperature will naturally 
be highest. 

If a very large tube be rotated in the oxidising flame at 
B (Fig. 4) it may happen that the flame is not large enough to 
surround the tube, and that as it is rotated those parts of it 
which are most remote from the flame will cool down too con- 
siderably to allow all parts of the tube to be simultaneously 
brought into the desired condition. This difficulty may be 
overcome by placing two blow-pipes exactly opposite to 
each other, at such a distance that there is an interval of 
about an inch between the extremities of their flames, and 
rotating the tube between the two flames. It may be 
necessary to provide two blowers for the blow-pipes if they 
are large. 

Again, if a very narrow zone of a tube of moderate size 
is to be heated, two pointed flames may be similarly arranged 
with advantage. Occasionally more than two flames are made 
to converge upon one tube in this manner. 

Another method of preventing one side of a tube from 
cooling down whilst the other is presented to the flame, is to 
place a brick at a short distance from the extremity of the 
flame. The brick checks the loss of heat considerably. A 
block of beech wood may be used for the same purpose, the 
wood ignites and thereby itself becomes a source of heat, and 
is even more effective than a brick. 

Fuller details of the management of lead glass under various 
circumstances will be found in the subsequent descriptions 
of operations before the blow-pipe. 

Before proceeding to work with soda glass, the student 



22 GLASS-BLOWING. 



should not only verify by experiments what has been already 
said, but he should familiarise himself with the action of the 
blow-pipe flame on lead glass by trying the glass in every 
part of the flame, varying the proportions of gas and air in 
every way, repeating, and repeating, his experiments until 
he can obtain any desired effect with certainty and prompti- 
tude. He should practice some of the simpler operations 
given in Chapter III. in order to impress what he has learned 
well on his mind. 

Management of Soda Glass. In working with soda 
glass the following points must be constantly kept in mind. 
That as it is much more apt than lead glass to crack when 
suddenly heated, great caution must be exercised in bringing it 
into the flame; and that in making large joints or in making two 
joints near each other, all parts of the tube adjacent to that 
which, for the moment, is being heated, must be kept hot, as it 
is very apt to crack when adjacent parts are unequally heated. 
This may be effected by stopping work at short intervals and 
warming the cooler parts of the tube, or by the use of the 
brick or block of wood to check radiation, or even by placing 
a supplementary blow-pipe or Bunsen burner in such a posi- 
tion that its flame plays upon the more distant parts of the 
work, not coming sufficiently into contact to soften the glass, 
however, but near enough to keep it well heated. Lastly, to 
prevent the finished work from falling to pieces after or during 
cooling, the directions given under the head of annealing 
must be carefully carried out. 

In very much of his work the glass-blower is guided more 
by the fed of the glass than by what he sees. The power of 
feeling glass can only be acquired by practice, and after a 
certain amount of preliminary failure. As a rule I have 
observed that beginners are apt to raise their glass to a higher 
temperature than is necessary, and that they employ larger 



ANNEALING. 23 



flames than are wanted. If glass be made too soft it may 
fall so completely out of shape as to become unworkable 
except in very skilful hands. The following rules, therefore, 
should be strictly adhered to. Always employ in the first 
instance the smallest flame that is likely to do the work 
required. In operations involving blowing out viscous glass, 
attempt to blow the glass at low temperatures before higher 
ones are tried. After a little experience the adoption of the 
right-sized flame for a given purpose, and the perception 
of the best condition of glass for blowing it, become almost 
automatic. 

I may add that glass which is to be bent needs to be much 
less heated than glass which is to be blown. 

Annealing. If apparatus, the glass of which is very thin 
and of uniform substance, be heated, on removal from the source 
of heat it will cool equally throughout, and therefore may often 
be heated and cooled without any special precautions. If the 
glass be thick, and especially if it be of unequal thickness 
in various parts, the thinner portions will cool more quickly 
than those which are more massive ; this will result in the 
production of tension between the thicker and thinner parts 
in consequence of inequality in the rates of contraction, and 
fractures w411 occur either spontaneously or upon any sudden 
shock. ThusJ if a hot tube be touched with cold or wet 
iron, or slightly scratched with a cold file, the inequality of 
the rate of cooling is great, and it breaks at once. It is 
therefore necessary to secure that hot glass shall cool as 
regularly as possible. And this is particularly important in 
the case of articles made of soda glass. Some glass-blowers 
content themselves with permitting the glass to cool gradually 
in a smoky flame till it is covered with carbon, and then leave 
it to cool upon the table. But under this treatment many 
joints made of soda glass which are not quite uniform in sub- 



24 GLASS-BLOWING. 

stance, but otherwise serviceable, will break down. In glass- 
works the annealing is done in ovens so arranged that the 
glass enters at the hottest end of the oven where it is 
uniformly heated to a temperature not much below that at 
which it becomes viscous, and slowly passed through the 
cooler parts of the chamber so that it emerges cold at the 
other end. This method of annealing is not practicable in a 
small laboratory. But fortunately very good results can be 
obtained by the following simple device, viz. : 

By wrapping the hot apparatus that is to be annealed 
closely in cotton wool, and leaving it there till quite cold. 
The glass should be wrapped up immediately after it is 
blown into its final shape, as soon as it is no longer soft 
enough to give way under slight pressure. And it should 
be heated as uniformly as possible, not only at the joint, but 
also about the parts adjacent to the joint, at the moment 
of surrounding it with the cotton. Lead glass appears to cool 
more regularly than soda glass, and these precautions may be 
more safely neglected with apparatus made of lead glass ; but 
not always. At the date of writing I have had several well- 
blown joints of thick-walled capillary tube to No. 16 (see 
diagram, p. 82), break during cooling, in consequence of cir- 
cumstances making it dangerous to heat the neighbourhood of 
the joint so much as was necessary. 

The black carbonaceous coat formed on hot glass when 
it is placed in cotton wool may be removed by wiping 
with methylated spirit, or, if it be very closely adherent, by 
gently rubbing with fine emery, moistened with the spirit. 

Cotton wool is rather dangerously inflammable ; it should 
therefore be kept out of reach of the blow-pipe flame, and 
care should be taken that the^glass is not placed in contact with 
it at a sufficiently high temperature to cause its ignition. 

Another method of annealing is to cover the hot glass with 
hot sand, and allow it to cool therein. 



ANNEALING. 25 



As in the case of lead glass, so with soda glass. A 
thorough acquaintance with the effect of the various parts of 
the flame upon it should be gained before further work is 
entered upon, for which purpose an hour or more spent in 
observing its behaviour in the flame will be fully repaid by 
increased success subsequently. 

The Use of Combustion Tube. It is often necessary 
to construct apparatus of what is known .as hard glass or 
combustion tube. It is almost as easy to work combustion 
tube as to deal with lead and soda glass if the oxy -hydrogen 
flame be employed. 

It is not necessary to set up a special apparatus for this 
purpose ; many of the ordinary blow-pipes can be used with 
oxygen instead of with air. It is only necessary to connect the 
air tube of the blow-pipe with a bottle of compressed oxygen 
instead of with the bellows. The connecting tube should not 
be too wide nor too long, in order to avoid the accumulation 
in it, by accident, of large quantities of explosive mixtures. 

Two precautions are necessary in manipulating hard glass 
in the oxy-hydrogen flame. The glass must not be over- 
heated. At first one is very apt to go wrong in this 
direction. The supply of oxygen must not be too great \ a 
small hissing flame is not what is wanted. If either of these 
precautions are neglected most glass will devitrify badly. 
With a little care and experience, devitrification can be 
absolutely avoided. Ordinary combustion tube can be used, 
but I find that the glass tube (Verbrennungsrohr) made by 
Schott & Co. of Jena, which can be obtained through any firm 
of dealers in apparatus, is far better than the ordinary tube. 

By following these instructions, any one who has learned 
how to work with lead or soda glass will find it easy to 
manipulate hard glass. 



26 GLASS-BLOWING. 



CHAPTER III. 

CUTTING AND BENDING GLASS FORMING GLASS 
APPARATUS BEFORE THE BLOW-PIPE MAKING 
AND GRINDING STOPPERS TO APPARATUS, ETC. 

IN the later pages of this Chapter it will be assumed that the 
operations first described have been mastered. The beginner 
should therefore practise each operation until he finds him- 
self able to perform it with some degree of certainty. Generally 
speaking, however, after the failure of two or three attempts 
to perform any operation, it is best to give up for a few 
hours, and proceed to the work next described, returning to 
that upon which you have failed subsequently. If, unfortu- 
nately, it should happen that the work next in order involves 
the performance of the operation in which the failure has 
occurred, it is best to pass on to some later work which does 
not demand this particular accomplishment, or to rest a whilo, 
and re-attack the difficulty when refreshed. 

% 

Cutting Glass Tubes. The simplest method of cutting 
a glass tube is to make a sharp scratch with a file across the 
glass at the point where it is desired to cut it, and on pulling 
apart the two ends, it will break clean off. It is important 
that the file be sharp. In pulling apart the ends the 
scratch should be held upwards, and the pull should have 
a downward direction, which will tend to open out the 
scratch. In the case of a large tube, a scratch will not 
ensure its breaking clean across. The tube must be filed 
to some depth, half-way, or even all round it. A good 



CUTTING GLASS TUBES 27 



way of breaking a tube is to place the file in the table 
after scratching the glass, to hold the glass tube above 
its edge with one hand on each side of the scratch, and 
to strike the under side of the tube a sharp blow upon 
the edge of the file, directly beneath the scratch. In this 
way very even fractures of large and moderately thin tubes 
may be made. It answers particularly well for removing short 
ends of tube, not long enough to hold ; the tube is held 
firmly upon the file, and a sharp blow given to the short end 
with a piece of large tube or a key. 

A file whose faces have been ground till they are nearly 
smooth, so as to leave very finely-serrated edges, will be 
found useful for cutting glass tubes. Such a file should 
be used almost as a knife is used for cutting a pencil in 
halves. 

The simple methods just described are too violent to be 
applied to delicate apparatus, too tedious when employed upon 
the largest tubes, and very difficult to apply when the tube to 
be cut is very thin, or too short to permit the operator to get 
a good grip of it on either side of the file mark, In such 
cases, one or other of the following methods will be useful : 

1. Make a scratch with a file, and touch it with the end of 
a very small piece of glass drawn out and heated at the tip 
to its melting-point. It is important that the heated point of 
glass be very small, or the fracture is likely to be uneven, or to 
spread in several directions. Also, it is best to use hot soda 
glass for starting cracks in tubes of soda glass, and lead glass for 
doing so in lead glass tubes. If the crack does not pass quite 
round the tube, you may pull it asunder, as previously 
described, or you may bring the heated piece of glass with 
which the crack was started to one end of the crack, and 
slowly move it (nearly touching the glass) in the required 
direction ; the crack will extend, following the movements of 
the hot glass. Instead of hot glass, pastils of charcoal are 
sometimes employed for this purpose. They continue to burn 



28 GLASS-BLOWING. 

when once lighted, and there is no need to re-heat them from 
time to time. They should be brought as close to the glass as 
is possible without touching it, and, when no longer needed, 
should be extinguished by placing the lighted end under 
sand, or some other incombustible powder, for they must not 
be wetted. 

2. A method much practised by the makers of sheet glass, 
and suitable for large objects, is to wrap a thread of hot 
glass round the tube, at once removing it, and touching any 
point of the glass which the thread covered with water or a 
cold iron, when a crack will be started and will pass round 
the glass where it was heated by the thread. 

3. Tubes which are large and slightly conical may have a 
ring of red-hot iron passed over them till it comes into con- 
tact with the glass, then, the iron being removed, and a point 
on the heated glass being at once touched with cold iron as 
before, it will break as desired. Or a string, moistened with 
turpentine, may be loosely twisted round the tube, and the 
turpentine ignited, afterwards the application of sudden cold 
to any point on the zone of hot glass will usually start a crack, 
which, if necessary, may be continued in the usual manner. 
The last three methods are chiefly useful in dealing with the 
largest and thickest tubes, and with bottles. 

A fairly stout copper wire, bent into the form of a bow so 
that it can be applied when hot to a considerable surface of a 
glass tube, will be found superior to the point of hot glass or 
metal usually employed, for leading cracks in glass tubes. 
With such a wire a tube can be cut so that the cross section 
of the end is at any desired angle to the axis of the tube, with 
considerable precision. I am indebted for this suggestion to 
Mr. Vernon Boys and Dr. Ebert 

Bending Glass Tubes. The blow-pipe flame is not a 
suitable source of heat for bending tubes, except in certain 
cases which will be mentioned in a subsequent paragraph. 



BENDING GLASS TUBES. 29 

For small tubes, and those of moderate size, a fish-tail burner, 
such as is used for purposes of illumination, will answer best. 
Use a flame from one to two inches in breadth from A to A 
(Fig. 6), according to the size of the tube which is to be bent. 
If the length of tube that is heated be less than this, the bend 
will probably buckle on its concave side. 




The tube to be heated should be held in the position 
shown in Fig. 6, supported by the hands on each side. It 
should be 1 constantly rotated in the flame, that it may be 
equally heated on all sides. In the figure the hands are 
represented above the tube, with their backs upwards. A 
tube can be held equally well from below, the backs of the 
hands being then directed downwards, and this, I think, is 
the more frequent habit. It is difficult to say which position 
of the hands is to be preferred. I lately observed how a 
tube was held by three skilful amateurs and by a professional 
glass-blower. All the former held the tube with the hands 
below it. The latter, however, held it from above, as in 
Fig. 6. He, however, was working with a rather heavy piece 
of tube, and I am inclined myself to recommend that position 
in such cases. During a long spell of work, the wrist may be 
rested from time to time by changing the position of the 
hands. 

When the tube has softened, remove it from the flame, and 



GLASS-BLOWING. 



gently bend it to the desired angle. The side of the tube 
last exposed to the flame will be slightly hotter, and therefore 
softer, than that which is opposite to it. This hotter side 
should form the concave side of the bent tube. 

The exact condition in which the glass is most suitable for 
bending can only be learned by making a few trials. If it is too 
soft in consequence of being overheated, the sides will collapse. 
If, in the endeavour to heat the side A of Fig. 7 a little 




Fio. 7. 

more than B, B is insufficiently heated, the tube will be likely 
to break on the convex side B. If the bent tube be likely to 
become flattened, and this cannot always be prevented in 
bending very thin tubes, the fault may be avoided by blow- 
ing gently into one end of the tube whilst bending it, for 
which purpose the other end should be closed beforehand. 
A tube already flattened may, to some extent, be blown into 



ROUNDING AND BORDERING ENDS OF TUBES. 31 

shape after closing one end and reheating the bent portion, 
but it is not easy to give it a really good shape. 

When making a bend like that in Fig. 7, to secure that 
the arms of the tube and D, and the curve at B, shall be in 
one plane, the tube should be held in a position perpendicular 
to the body, and brought into the position shown in the 
figure during bending, by which means it will be found easy 
to secure a good result. Lead glass tubes must be removed 
from the flame before they become hot enough to undergo 
reduction. If they should become blackened, however, the 
stain may be removed by re-heating in the oxidising flame 
(seep. 18). 

When a very sharp bend is to be made, it is sometimes 
best to heat a narrow zone of the glass rather highly in the 
blow-pipe flame, and to blow the bend into shape at the 
moment of bending it, as previously described, one end 
having been closed for that purpose beforehand. Lead 
glass should be heated for this purpose in the oxidising 
flame (pp. 17 to 22). 

The processes of bending large tubes, making U -tubes 
and spiral tubes, are more difficult operations, and will be 
explained in Chap. IV. 

Rounding and Bordering the Ends of Tubes. 

After cutting a piece of glass tube in two pieces, the sharp 
edges left at its ends should be rounded by holding them in 
a flame for a few moments till the glass begins to melt. The 
oxidising point of a pointed flame may be used for both kinds 
of glass. The flame will be coloured yellow by soda glass at 
the moment of melting. This indication of the condition of 
soda glass should be noted, for it serves as a criterion of the 
condition of the glass. The ends of soda glass tubes may 
also be rounded in the flame of a common Bunsen's burner. 
When the end of a tube is to be closed with a cork or 



32 GLASS-BLOWING. 



stopper, its mouth should be expanded a little, or bordered. 
To do this, heat the end of the tube by rotating it in 
the flame till it softens, then remove it from the flame, at 
once introduce the charcoal cone (Fig. 5, p. 11), and rotate 
it with gentle pressure against the softened glass till the 
desired effect is produced. In doing this it is very important 
that the end of the tube shall be uniformly heated, in order 
that the enlargement shall be of regular form. If the tube 
cannot be sufficiently expanded at one operation, it should be 
re-heated and the process repeated. 

Borders, such as are seen on test tubes, are made by press- 
ing the softened edge of the tube against a small iron rod. 
The end of the rod should project over the softened edge of 
the tube at a slight angle, and be pressed against it, passing 
the rod round the tube, or rotating the tube under the rod. 

Sealing, that is closing the ends of tubes, or other 
openings, in glass apparatus. 

Jn performing this and all the other operations of glass- 
blowing, the following points must be constantly kept in 
mind : 

(a.) That it is rarely safe to blow glass whilst it is still in the 
flame, except in certain special cases that will be mentioned 
subsequently. Therefore always remove apparatus from the 
flame before blowing. 

(6.) That when heating glass tubes, unless it is specially 
desired to heat one portion only, the tube must be constantly 
rotated in the flame to ensure that it shall be uniformly 
heated, and to prevent the tube or mass of glass from assum- 
ing an irregular form. 

(c.) Always blow gently at first, and slowly increase the 
force applied till you feel or see the glass giving way. . It is 
a good plan to force the air forward in successive short blasts 
rather than in one continued stream. 



SEALING. 33 

(d.) When it is necessary to force air into tubes of fine bore, 
such as thermometer tubes, the mouth must not be used, for 
moisture is thereby introduced into the tube, which it is 
very difficult to remove again in many cases. All tubes of 
very small bore should be blown with the aid of an india- 
rubber blowing-bottle, such as are used for spray producers, 
Galton's whistles, etc. The tube to be blown must be 
securely fixed to the neck of the bottle, which is then held 
in one hand, and air is forced from it into the tube as it is 
required. These bottles are frequently of service to the 
glass-blower e.g., when tubes of very fine bore have to be 
united, it is necessary to maintain an internal pressure 
slightly exceeding that of the air throughout the operation, 
in order to prevent the viscous glass from running together 
and closing the tube. An india-rubber blowing-ball is very 
convenient for this purpose. 

To seal the end of a glass tube (Fig. 8), adjust the flame 
so that it will heat a zone of glass about as broad -as the 
diameter of the tube to be sealed (see A, Fig. 8). Hold 
the tube on each side of the point where it is to be sealed in 
the manner described in the description of bending glass 
tubes (p. 28). Bring the tube gradually into the flame, 
and heat it with constant rotation, till the glass softens (for 
lead glass the oxidising flame must be used, as has been 
already explained). 1 When the glass begins to thicken, 
gently pull asunder the two ends, taking care not to pull out 
the softened glass too much, but to allow the sides to fall 
together, as shown at A. When this has occurred, heat 
the glass at the narrow part till it melts, and pull asunder 

1 Remember that when the lead glass is heated to the proper tempera- 
ture it will present an appearance which may be described as a greenish 
phosphorescence. At higher temperatures it assumes an orange-red 
appearance. If it loses its transparency and assumes a dull appearance, 
it must be moved further into the oxidising parts of the flame. 

C 



34 GLASS-BLOWING. 

the two ends. The closed end should present the appearance 
shown at D. If the glass be drawn out too quickly its 

thickness will be unduly re- 
duced, and it will present the 
appearance shown at B. In 
that case apply a pointed 
flame at b, and repeat the 
previous operation so as to 
contract the tube as at c, 
taking care not to allow the 
glass to become much in- 
creased nor decreased in thick- 




If a considerable mass of 
glass be left at d, it may be 
removed by heating it to red- 
ness, touching it with the 
pointed end of a cold glass 
tube, to which it will adhere, 
and by which it may be pulled 
away. 

When the end of the tube 
presents the appearance shown 
in the diagram Z>, and the 
mass of glass at d is small, the 

small lump that remains must be removed by heating it till 
it softens, and gently blowing with the mouth, so as to round 
the end and distribute the glass more regularly, as shown in E. 
The whole end, from the dotted line e, must then be heated 
with constant rotation in the flame. If this final heating of 
fche end e be done skilfully, the glass will probably collapse 
and flatten, as at F. The end must then be gently blown 
into the form shown at G. 

If a flat end to the tube be desired, the tube may be left 



SEALING. 35 



in the condition shown by F, or a thin rounded end may be 
flattened by pressure on a plate of iron. 

If a concave end be wished for, it is only necessary to gently 
suck air from the tube before the flattened end has become 
solid. 

In each case, immediately after the tube is completed, it 
must be closely wrapped in cotton wool and left to cool. 
With good lead glass this last process, though advantageous, 
is not absolutely necessary ; and as glass cools slowly when 
enveloped in cotton wool, this precaution may frequently 
be neglected in the case of apparatus made from lead glass. 

In order to draw out tubes 

for sealing, close to one end, P 

and thus to avoid waste of A 
material, it is a good plan to 
heat simultaneously the end Fio g 

of the glass tube A which is 

to be sealed, and one end of a piece of waste tube E of about 
the same diameter, and when they are fused to bring them 
together as at DD (Fig. 9). E will then serve as a handle in 
the subsequent operations on A. Such a rough joint as that 
at D must not be allowed to cool too much during the work in 
hand, or E and A may separate at an inconvenient moment. 
Or the glass at the end of the tube may be pressed together 
to close the tube, and the mass of glass may be seized with a 
pair of tongs and drawn away. 

Choking, or Contracting the Bore of a Glass 
Tube. If it be not desired to maintain the uniformity of 
external dimensions of the tube whilst decreasing the diameter 
of the bore, the tube may be heated and drawn out as described 
in the description of sealing tubes on pp. 32-35. This may 
be done as shown at A or B in Fig. 8, according to the use 
to which the contracted tube is to be put. 



GLASS-BLOWING. 



Greater strength and elegance will be secured by pre- 
serving the external diameter of the tube unchanged 
throughout, as shown in Fig. 10. For this purpose heat the 
tube with the pointed flame, if it be small, or in the brush 
flame if it be of large size, constantly rotating it till the 
glass softens and the sides show an inclination to fall together, 

when this occurs, push the 
B A B two ends gently towards A. 

/ v If the tube should become 

too much thickened at A, 
the fault may be corrected by 

removing it from the flame and gently pulling the two ends 
apart till it is of the proper size. If the bore at the con- 
tracted part of the tube should become too much reduced, it 
may be enlarged by closing one end of the tube with a small 
cork, and blowing gently into the open end after sufficiently 
heating the contracted part. The tube should be rotated 
during blowing or the enlargement produced may be 
irregular. 

When the external diameter of the tube is to be increased 
as well as its bore diminished, press together the ends of a 
tube heated at the part to be contracted, as already de- 
scribed, and regulate the size of the bore by blowing into 
the tube if at any time it threatens to become too much 
contracted. 



Widening Tubes. Tubes may be moderately expanded 
at their extremities by means of the charcoal cone (see Border- 
ing, p. 31). They may be slightly expanded at any other part 
by closing one end and gently blowing into the open end of 
the tube, after softening the glass at the part to be widened 
before the blow-pipe. But the best method of obtaining a 
wide tube with narrow extremities (Fig. 11) is to join pieces 



PIERCING TUBES. 37 

of narrow tube A A to the ends of a piece of wider tube B of 
the desired dimensions. The method of performing this 
operation is described under welding, on pp. 39-47. 





PlQ. 11. 

Piercing Tubes. The glass-blower very frequently 
requires to make a large or small opening in some part of a 
tube or other piece of apparatus. This is known as piercing. 
Suppose it is desired to make a small hole at the point a in 
A (Fig. 12). When the tube has been brought to the flame 
with the usual precautions, allow the end of the pointed flame 
to touch it at a till an area corresponding to the desired size 
of the opening is thoroughly softened. Then expand the 



Fio. 12 

softened glass by blowing to the form shown at B. Re-heat 
a, blow a small globe as at C, and carefully break the thin 
glass, then smooth the rough edges by rotating them in 
the flame till they form a mouth like that of D. Instead of 
leaving the bulb to be broken at the third stage C, it is a good 
plan to blow more strongly, so that the bulb becomes very 
thin and bursts, the removal of the thin glass is then accom- 
panied by less risk of producing a crack in the thicker parts 
of the glass. Openings may be made in a similar manner in 
the sides of tubes or in globes, in fact, in almost any position on 



GLASS-BLOWING. 



glass apparatus. If another tube is to be attached at the 
opening, it is a good plan to proceed to this operation before 
the tube has cooled down. 

The openings obtained by the method above described are 
too large when platinum wires are to be sealed into them. 



Fio. 18. 



Suppose that it is necessary to pierce the tube A of Fig. 13 
in order to insert a platinum wire at a ; direct the smallest 
pointed flame that will heat a spot of glass to redness on the 
point a. When the glass is viscous, touch it with the end of 
a platinum wire w, to which the glass will adhere ; withdraw 
the wire and the viscous glass will be drawn out into a 
small tube, as shown at B \ by breaking the end of this 
tube a small opening will be made. Introduce a platinum 
wire into the opening, and again allow the flame to play on 
the glass at that point ; it will melt and close round the wire. 
Before the hot glass has time to cool, blow gently into the 
mouth of the tube to produce a slightly curved surface, 
then heat the neighbouring parts of the tube till the glass 
is about to soften, and let it cool in cotton wool. Unless 
this is done, I find that glass tubes into which platinum 
wires have been sealed are very apt to break during or after 
cooling. 
To ensure that the tube shall be perfectly air-tight, a small 



WELDING. 39 



piece pf white enamel should be attached to the glass at a 
before sealing in the wire. 



Uniting Pieces of Glass to Each Other, known 
as Welding, or Soldering. The larger and more com- 
plicated pieces of glass apparatus are usually made in separate 
sections, and completed by joining together the several 
parts. This is therefore a very important operation, and 
should be thoroughly mastered before proceeding to further 
work. 

In order to produce secure joints, the use of tubes made of 
different kinds of glass must be avoided. Soda glass may be 
joined securely to soda glass, especially if the tubes belong to 
the same batch, and lead glass to lead glass. But, though by 
special care a joint between lead glass and soda glass, if well 
made, will often hold together, yet it is never certain that it 
will do so. 1 

1. To join two Tubes of Equal Diameters. Close one end of 
one of the tubes with a small cork. Heat the open end of 
the closed tube, and either end of the other tube in a small 
flame until they are almost melted, taking care that only the 
ends of the tubes are heated, and not to let the glass be 
thickened ; bring the two ends together with sufficient pres- 
sure to make them adhere, but not sufficient to compress the 
glass to a thickened ring. Before the joint has time to cool too 
much, adjust your blow-pipe for a pointed flame, if you are 
not already working with that kind of flame, and allow the 
point of the flame to play on any spot on the joint till it is 
heated to redness ; rotate the tube a little so as to heat the 
glass adjacent to that which is already red-hot, and repeat this 
till the whole circumference of the rough joint has been 



40 GLASS-BLOWING. 

heated. 1 Repeat the operation last described, but, when each 
spot is red-hot, blow gently into the open end of the tube so 
as to slightly expand the viscous glass. Finally, rotate the 
whole joint in the flame till the glass is softened, and blow 
gently as before into the open end of the tube, still rotating it, 
in order that the joint may be as symmetrical as possible. 
If in the last operation the diameter of the joint becomes 
greater than that of the rest of the tube, it may be cautiously 
re-heated and reduced by pulling it out, or this may be secured 
by gently pulling apart the two ends, whilst the operator 
blows it into its final shape. 

When small tubes, or tubes of fine bore, are to be 

joined, in order to pre- 
vent the fused glass from 
running together and 
closing the tube, it is a 
good plan to border and 
enlarge the ends that are 

to be united, as at A (Fig. 14). Some glass-blowers prefer 
to border all tubes before uniting them. 

When a narrow tube is to be joined to one that is only 
slightly wider, expand the end of the narrow tube till it 
corresponds in size to the larger tube. If the tube be too 
narrow to be enlarged by inserting a charcoal cone, seal one 
end and pierce it as directed (on p. 37). 

For joining small thin-walled tubes Mr. Crookes recom- 
mends the use of a small Buusen flame. 

In welding pieces of lead glass tube, take care that the 
heated glass is perfectly free from reduced lead at the 



1 Some glass-blowers at once work on the glass as next described, 
without this preliminary treatment. I liiid that some glass, usually 
soda glass, will not always bear the necessary movements without 
breaking unless first heated all round. 




WELDING. 41 



moment when the two ends of viscous glass are brought into 
contact. 

To join Tubes of Unequal Sizes End to End (Fig. 15). 
Draw out the larger tube and cut off the drawn-out end 
at the part where its diameter is; equal to that of the smaller 
tube, then seal the smaller tube to the contracted end of 
the larger according to the directions given for joining tubes 
of equal size. When a good joint has been made, the tube 



FIG. 15. 

presents the appearance of A, Fig. 15, the union being at 
about lib. Next heat the whole tube between the dotted 
lines aa, and blow it into the shape of B in which the dotted 
line dd should correspond to the actual line of junction of 
the two tubes. 

In making all joints it is important to leave no thick 
masses of glass about them. If the glass be fairly thin and 
uniformly distributed, it is less likely to break during or after 
annealing under any circumstances, and especially if it has to 
bear alternations of temperature. 

Joining a Tube to the Side of another Tube (Fig. 16). One of 
the tubes must be pierced as at ^4 in Fig. 16 (for the method, 
see p. 37), and its two ends closed with small pieces of cork. 
The edges of the opening, and one end of the other tube, 



GLASS-BLOWING. 



must then be heated till they melt, and united by pressing 
them together. The joint may then be finished as before. 




Fro. 18. 

A properly blown joint will not present the appearance of 
B (Fig. 16), but rather that of C. This is secured by directing 
the pointed flame upon the glass at aa (B) spot by spot, and 
blowing out each spot when it is sufficiently softened. If the 
tubes are large, the whole joint should subsequently be heated 
and blown, but in the case of small tubes this is of less im- 
portance. Finally it is to be wrapped whilst hot in cotton 
wool for the annealing process. 

If a second tube has to be joined near to the first one, 
say at 6, it is well to proceed with it before the joint first 
made cools down, and the joint first made, especially if soda 
glass be used, must be held in the flame from time to time 
during the process of making the second joint to keep it hot ; 
if this be not done the first joint is very likely to break. A 
joint previously made may, however, be re-heated, if well 
made and well annealed. 

A three-way tube, like that in Fig. 17, is made by bending 
A (Fig. 16) to an angle, and joining B to an opening blown 



WELDING. 



43 



\ 



on the convex side of the angle ; or, A of Fig. 1 6 may be 
bent as desired after attaching B in the ordi- 
nary way. VV 

Tubes may also be joined to openings made \\ A 
in the sides of globes or flasks ; great care \ \ 
must be taken, however, especially if the walls 
of the globe be thin, to secure that the tube 
is well attached to the mouth of the opening 
when the melted ends are first brought into 
contact, for, with thin glass, any hole that may FIG. ir. 
be left will probably increase whilst the joint is being' blown 
into shape, owing to cohesion causing the glass to gather in a 
thickened ring round an enlargement of the original opening. 1 

In order to unite a tube of soda glass to a tube of lead 
glass, the end of the soda glass tube must be carefully covered 
with a layer of soft arsenic glass. 2 This must be done so 
perfectly that when the ends to be united are brought 
together the lead and soda glass are separated by the enamel 
at every point. 

To Seal a Tube inside a Larger Tube or Bulb. Suppose that 
an air-trap (3 of Fig. 18) is to be constructed from a small 
bulb (A) blown on a glass tube (1). 




Either cut off the tube close to the bulb at B, or better 
remove the end by melting the glass and pulling it away 

1 If such an opening be observed, it may usually be closed by touch- 
ing its edges with a fused point of glass at the end of a drawn out tube. 

2 This can be obtained from Messrs. Powells, Whitefriars Glassworks. 



44 GLASS-BLOWING. 



from B, and then pierce A at B, No. 2, by heating the glass 
there and blowing out a small bulb as described under Piercing 

Prepare a tube (4) drawn out at E with a bulb blown 
at D. Insert E into the opening B, press D well against 
the mouth B and slowly rotate before the blow-pipe till D 
adheres to B. Then heat and blow the joint spot by spot 
as in other cases, taking care that the glass is blown out on 
each side of the joint ; lastly, heat the whole joint between aa, 
and blow it into its final shape. 

These joints are very apt to break after a few minutes or 
hours if the glass of D be much thicker than that of the bulb 
A. They should be wrapped in cotton wool for annealing 
as soon as possible, as the rate at which the tube E cools is 
likely to be less rapid than that of the parts of the apparatus 
which are more freely exposed to the air ; therefore all such 
internal joints require very careful annealing, and they should 
always be made as thin as is consistent with the use to which 
they are to be put. 

Tubes may also be sealed into the ends or sides of larger 
tubes by piercing them at the point at which the inserted 
tube is to be introduced, and proceeding as in the case of the 
air-trap just described. 

Ozone generators of the form shown on next page (Fig. 19), 
afford an interesting example of the insertion of smaller tubes 
into larger. 

On account of the small space that may be left between 
the inner and outer tubes of an ozone generator, and of 
the length of the inner tube, its construction needs great 
care. I find the following mode of procedure gives good 
results. Select the pieces of tube for this instrument as free 
from curvature as possible. For the inner tube, a tube 
12 mm., or rather more, in external diameter, and of rather 
thin glass, is drawn out, as for closing, until only a very 
narrow tube remains at (7, the end of C is closed the area 



WELDING. 45 



round G is carefully blown into shape, so that by melting off 
C the tube A will be left with a well-rounded end. A small 
bulb of glass is next blown on A at B. This bulb must be of 
slightly greater diameter than the contracted end E of the 
larger tube (II.), so that B will just fail to pass through E. 
The length from to G must not be made greater than 
from E to G on the outside tube. The end at C is then to 
be cut off so as to leave a pin-hole in the end of A. 



\{ 



fi 



Fio. ,19. 

The outer tube (II.), whose diameter may be 5 or 6 mm. 
greater than that of A, is prepared by sealing a side tube on 
it at F, after previously contracting the end E. For this 
purpose the end E should be closed and rounded, and then 
reheated and blown out till the bulb bursts. To ensure that 
the diameter of the opening is less than that of the tube, care 
must be taken not to re-heat too large an area of the end 
before blowing it out. It is very important that the cross 



46 GLA SS-BL O WING. 

section at E shall be in a plane at light angles to the axis of 
the tube. 

Wrap a strip of writing paper, one inch in breadth, closely 
round the end of A at C till the tube and paper will only just 
pass easily into the mouth D of the outer tube, push the inner 
tube A, with the paper upon it, into D, and when the paper is 
entirely within Z>, withdraw A, and cautiously push the paper a 
little further into the outer tube. Insert A into DE through 
E, so that the bulb B is embraced by E. Close D with a 
cork. Ascertain that the paper does not fit sufficiently 
tightly between the two tubes to prevent the free passage of 
air, by blowing into the mouth K of A. Air should escape 
freely from E when this is done. Gradually bring the line of 
contact of B and E and the surrounding parts of the tube 
before a pointed flame, after previously warming them by hold- 
ing near a larger flame, and rotate them before the flame so 
that the glass may soften and adhere. Then heat the joint 
spot by spot as usual. In blowing this joint, take care that 
the glass on each side of the actual joint is slightly ex- 
panded. It should present the form shown by the dotted lines 
in III. (these are purposely exaggerated, however). Finally, 
heat the whole joint between the lines Jl till it softens, and 
simultaneously blow and draw it into its final shape as seen 
at III. 

The side tube F should not be too near the end E. If, 
however, it is necessary to have them close together, the joint 
F must be very carefully annealed when it is made ; it must 
also be very cautiously warmed up before the construction of 
the joint at H is begun, and must be kept warm by letting 
the flame play over it from time to time during the process 
of making the latter joint. 

A good joint may be recognised by its freedom from lumps 
of glass, its regularity of curve, and by a sensibly circular 
line at //, where the two tubes are united. 



BLOWING A BULB. 47 

When the joint after annealing has become quite cold, the 
pin-hole at C on^the inner tube may be closed, after removing 
the paper support, by warming the outer tube, and then 
directing a fine pointed flame through D on to C. And the 
end D of the outer tube may be closed in the ordinary 
manner, or a narrow tube may be sealed to it. As the end of 
glass at D will be too short to be held by the fingers when 
hot, another piece of tube of similar diameter must be 
attached to it to serve as a handle (see p. 35, Fig. 9). 

Blowing a Bulb or Globe of Glass. For this purpose 
it is very important that the glass tube employed shall be of 
uniform substance. The size and thickness of the tube to be 
employed depends partly on the dimensions of the bulb 
desired, and partly on the size of neck that is required for 
the bulb. It is easier to blow large bulbs on large-sized 
tubes than on those of smaller size. When it is necessary to 
make a large globe on a small tube, it can be done, however, 
if great care be taken to avoid overheating that part of the 
small tube which is nearest to the mass of viscous glass from 
which the bulb is to be formed. For the purpose of blowing 
a very large bulb on a small tube, it is best to unite a wide 
tube to that which is to serve as the neck, as it will save 
some time in collecting the necessary mass of glass from 
which to form the globe. 

To blow a Bulb at the End of a Tube. Select a good piece of 
tube, say 1-5 cm. in diameter, and about 30 cm. long; draw 
out one end to a light tail (a, Fig. 20) about 3 inches in 
length. Then heat up a short length of the tube at b, with 
a small brush flame, by rotating the glass in the flame, and 
gently press it together when soft to thicken it ; blow into it 
if necessary to preserve the regularity of its figure. Repeat 
this process on the portion of tube nearest to that which 



GLASS-BLOWING. 



has been first thickened, and so on, till as much glass has 
been heated and thickened as you judge will serve to make a 
bulb of the size desired. You should have* a mass of glass 
somewhat resembling that shown at B (Fig. 20), but pro- 
bably consisting of the results of more successive operations 
than are suggested in that diagram. Apply the flame as 
before to the narrower parts cc of B t gently compress and 





PIO.M. 

blow until all the small bulbs first made are brought together 
into a mass still somewhat resembling the enlarged end of 7>, 
but more nearly cylindrical, with the glass as regularly <li- 
tributed as possible, and of such length from d to the 
tracted part that the whcle of it may easily be heated simul- 
taneously with the large brush flame of your blow-pipe. Take 
great care in the foregoing operations not to allow the si<l* s 
of the mass of glass to fall in and run together, and, on th-- 
other hand, do not reduce the thickness of the glass needlessly 
by blowing it more than is necessary to give the glass as 
regular a form as possible. When you are satisfied with tin- 
mass of glass you have collected, melt off' the tail a, and 



BLOWING A BULB. 49 

remove the pointed end of glass that remains, as directed on 
page 33. Turn on as large a brush flame as is necessary to 
envelop the whole mass of glass that you have collected, and 
heat it with constant rotation, so that it may gradually run 
together to the form seen at C (Fig. 20), taking care that it 
does not get overheated near d, or the tube which is to form 
the neck will soften and give way. 

The position in which the mass of heated glass is to be 
held will depend upon circumstances; if the mass of glass 
be not too great, it is best to keep it in a nearly horizontal 
position. If the mass of glass be very large, it may be neces- 
sary to incline the end B downwards ; but as that is apt 
to result in an excess of glass accumulating towards d, avoid 
doing so if possible by rotating the glass steadily and rapidly. 
If at any time the glass shows indications of collapsing, it 
must be removed from the flame and gently blown into shape, 
during which operation it may be rotated in the perpen- 
dicular position ; indeed, to promote a regular distribution of 
the glass by allowing it plenty of time to collect, it is well 
from time to time to remove the heated mass of glass from 
the flame, and slightly expand it by blowing. Finally, when 
a regular mass of glass, such as is shown at C (Fig. 20) has 
been obtained, remove it from the flame, and blow it to its 
final dimensions. A succession of gentle puffs quickly succeed- 
ing each other should be employed, in order that the progress 
of the bulb may be more easily watched and arrested at the 
right moment. During the process of blowing, the hot glass 
must be steadily rotated. 

To collect the glass for blowing a bulb of lead glass, em- 
ploy the flame described on pp. 17-22 for heating lead glass. 

If the tube be held horizontally whilst the globe is blown, 
its form will most nearly approach that of a true globe. If it 
be held in the perpendicular position, with the mass of glass 
depending from it, the form of the bulb will usually bo 

D 



GLASS-BLOWING. 



somewhat elongated. If it be held perpendicularly, with the 
mass of glass upwards, the resulting bulb will be flattened. 

When a bulb is not of a sufficiently regular form, it may 
sometimes be re-made by re-collecting the glass, and re-blowing 
it The greatest care is needed at the earlier stages of re- 
heating to prevent the glass from collapsing into a formless 
and unworkable mass. This is to be prevented in all such 
cases by gently blowing it into shape from time to time 
whilst gathering the glass. 

To blow a Bulb between two Points (Fig 21). Select a piece of 
suitable tube, seal or cork one end, gather together a mass of 
glass at the desired part, as directed for blowing a bulb at the 
end of a tube; when a mass of glass has been collected of 

sufficient thickness, blow it 
into shape from the open 
end of the tube by a rapid 
succession of short blasts of 
air, till the expanding glass 
attains the desired dimen- 
sions. The tube must be 
held horizontally, and must be rotated steadily during the 
process. By slightly pressing together the glass whil<> 
blowing, the bulb will be flattened ; by slightly drawing apart 
the two ends of the tube, it will be elongated. 

A pear-shaped bulb may be obtained by gently re-heating 
an elongated bulb, say from a to a, and drawing it out It 
is easiest to perform this operation on a bulb which is rather 
thick in the glass. 

If the tubes bb are to be small, and a globe of considerable 
size is wanted, contract a tube as shown in Fig. 22, t.ik 
ing care that the narrow portions of the tube are about the 
same axis as the wider portions, for if this be not the case, the 
mouths of the bulb will not be symmetrically placed ; seal at 
C, cut off" the wider tube at B, and make the bulb, as \ 




FIO. n. 



MAKING AND GRINDING STOPPERS. 51 

viously described, from the glass between A A. If, as pro- 
bably will be the case, the contracted portions of the tube 
be not very regular, they may be cut off, one at a time, near 
the bulb, and replaced by pieces of tube of the size desired. 



FIG. 22. 

When a bulb has to be blown upon a very fine tube, for ex- 
ample upon thermometer tubing, the mouth should not be em- 
ployed, for the moisture introduced by the breath is extremely 
difficult to remove afterwards. A small india-rubber bottle 
or reservoir, such as those which are used in spray-producers, 
Galton's whistles, etc., securely attached to the open end of 
the tube, should be used. With the help of these bottles bulbs? 
can be blown at the closed ends of fine tubes with ease, though 
some care is necessary to produce them of good shape, as it 
is difficult to rotate the hot glass properly when working in 
this way. 

Making and Grinding Stoppers. Apparatus which 
is to contain chemicals that are likely to be affected by the 
free admission of air, needs to have stoppers fitted to it. 
Making a good stopper is a much less tedious process than is 
commonly supposed. ^ 

Suppose that the tube I. of Fig. 23 is to be stoppered at A, 
it must be slightly enlarged by softening the end and opening 
it with a pointed cone of charcoal ; or a conical mouth for 
the stopper may be made by slightly contracting the tube 
near one end, as at 5, cutting off the cylindrical end of the 
tube at the dotted line (7, and then very slightly expanding 
the end at C with a charcoal cone after its edges have been 



GLASS-BLOWING. 



softened by heat. In either case the conical mouth should 
be as long and regular as possible. 

For the stopper take a piece of rather thick tube, of 
such size that it will pass easily, but not too easily, into A 
or 11. Expand this tube at D, as shown in II, by softening 
the glass and gently compressing it The configuration of 
the enlarged tube as shown at D may be obtained by heating 
and compressing two or more zones of the tube that are 
adjacent, one zone being less expanded than the other, so as 
to give the sides of the imperfect stopper as nearly as possible 



in 

9mm. 

the form shown at />, which, however, is much less regular 
than may easily be obtained. Seal off the head of the i 
at H, and heat the glass till it runs together into a nearly 
solid mass; compress this with a pair of iron tongs to th.- 
flattened Qad E.^ In making D, aim at giving it a form 
which will as nearly as possible correspond to that of th.- 
tube into which it is to be ground, and make it slightly 
too large,, so that only the lower part at D can be intro- 
duced into the mouth of A or B. Before it is ground, the 
stopper must be heated nearly to its softening-point an. I 
annealed. 

Moisten D with a solution of camphor in recently distilled 



MAKING AND GRINDING STOPPERS. 53 

turpentine, and dust the wet surface with finely-ground 
emery, then gently grind it into its place till it fits properly. 
In this operation the tail G, which should fit loosely into 
the tube A, will be of assistance by preventing D from 
unduly pressing in any direction on A in consequence 
of irregular movements. The stopper should be com- 
pletely rotated in grinding it. It must not be worked back- 
wards and forwards, or a well-fitting stopper will not be 
produced. Renew the emery and camphorated turpentine 
frequently during the earlier part of the grinding; when 
the stopper almost fits, avoid using fresh emery, but 
continue to remove the stopper frequently at all stages of 
the operation. That added at the earlier stages will be re- 
duced to a state of very fine division, and will therefore leave 
the stopper and mouth of A with smoother surfaces than 
fresh emery. 1 

NOTE. The addition of camphor to the turpentine used 
for grinding glass is very important. Notwithstanding its 
brittle nature, glass will work under a file moistened with 
this solution almost as well as the metals. Small quantities 
should be made at a time, and the solution should be kept 
in a well-closed vessel, for after long exposure to the air 
it is not equally valuable. 

If the stopper is to fit a tube contracted like J5, it must be 
constructed from a piece of tube that will pass through the 
contraction at B. The tail GF will not do such good 
service as it does in the case of a tube which has been opened 
out to receive its stopper, but it will help to guide the 
stopper, and should be retained. 

When the stopper has been ground into its place, melt off 
the tail at F. The flame must be applied very cautiously, as 

1 Mr. Gimmingham recommends giving stoppers a final polish with 
rotten-stone (Proceedings of the Royal Society, p. 396, 1876). 



54 GLASS-BLOWING. 



glass which has been ground is particularly apt to crack on 
heating. To avoid all risk of this, the tail may simply be cut 
off, and its edges filed smooth with a file moistened freely 
with camphorated turpentine. 

The stoppers of bottles are not made exactly in tlic 
manner described above, though, on occasion, a new stopper 
may be made for a bottle by following those directions. Ill- 
fitting stoppers, which are very common, can be very easily 
re-ground with emery and camphorated turpentine. 



ELECTRODES. 55 



CHAPTER IV. 

MAKING THISTLE FUNNELS, \J-TUBES, ETC. COMBIN- 
ING THE PARTS OF COMPLICATED APPARATUS 
MERCUR Y, AND OTHER AIR- TIGHT JOINTS VA CUUM 
TAPS SAFETY TAPS AIR-TRAPS. 

IN Chapter III. the simpler operations used in making the 
separate parts of which apparatus is composed have been 
described. In this Chapter finished apparatus will be 
described, and the combination of the separate parts into 
the more or less complicated arrangements used in experi- 
ments will be so far explained as to enable the student to 
set up such apparatus as he is likely to require. I have 
thought it would be useful that I should add a short account 
of various contrivances that have come much into use of 
late years for experimenting under reduced pressure, such as 
safety taps, air-traps, vacuum joints, etc. 

Electrodes. On page 38 (Fig. 13) is shown a simple 
form of electrode sealed into a glass 
tube, which for many purposes answers 



very well. But frequently, in order wMEEEEjE 
that there may be less risk of leakage 
between the glass and the metal, the 



latter is covered for a considerable 

part of its length with solid glass, which at one extremity is 
united to the apparatus. In Fig 24 W is the metal core of 
the electrode, and G the glass covering around it. The wire 



56 GLASS-BLOWING. 

is fused into the glass, and the glass is then united to the 
apparatus ; a little white enamel should be applied at one 
end and combined with the glass by fusion. 



U -Tubes. A U tube is but a particular case of a bent 
glass tube. It is scarcely possible when bending very large 
tubes in the manner described on p. 29 to produce regular 
curves of sufficient strength. 

To make a U-tube, or to bend a large tube, close one 
end of the tube selected with a cork, soften and compress 
the glass in the flame at the part where it is to be bent 
till a sufficient mass of glass for the bend is collected, thru 
remove the mass of glass from the flame, let it cool a little, 
and simultaneously draw out the thickened glass, bend i 
the proper form, and blow the bend into shape from the < 
end of the tube. Small irregularities may be partly corrected 
afterwards. 

To make a good U-tube of large size, and of uniform dia- 
meter from end to end, requires much practice, but to make a 
tolerably presentable piece of apparatus in which the two 
limbs are bent round till they are parallel, without any o>n 
siderable constriction at the bend, can be accomplished with 
out much difficulty. 1 



Spiral Tubes. These may be made by twisting a tulo 
gradually softened by heat round a metal cylinder. Spin! 
tubes made of small thin tubes possess considerable elasticity, 



1 Large tubes may also be bent by rotating a sufficient length of the 
tube in a large flame till it softens, and bending in the same manner 
as in the case of smaller tubes, and after filling them with sand, closing 
one end completely, and the other so that the sand cannot escape, 
though heated air can do so. 



THISTLE FUNNELS. 57 

and have been used by Mr. Crookes for making air-tight 
connections between separate pieces of apparatus when a 
rigid connection would have been unnecessary and incon- 
venient. By the use of such spiral tubes it is possible to com- 
bine comparatively free movement with all the advantages 
attached to hermetically-sealed joints. 

To make a flexible spiral tube, mount a copper cylinder 
on a screw, so that the cylinder will travel in the direc- 
tion of its axis when it is rotated. Fix a fine glass tube 
to the cylinder, and direct a flame towards the cylinder so 
as to heat and soften the glass, which will then bend to the 
form of the cylinder. Gradually rotate the cylinder before 
the source of heat, so that fresh portions of tube are succes- 
sively brought into position, softened, and bent. Useful spirals 
may also be made by hand without a cylinder. As each 
length of tube is bent, a fresh length may be united to it 
until the spiral is completed. The fine tubes employed are 
prepared by heating and drawing out larger tubes. 




FIG. 25. 



Thistle Funnels (Fig. 25). Seal a moderately thick piece 
of small glass tube at A> then heat a wide zone of it a little 
below A by rotating it horizontally in the blow-pipe flame till 
the glass softens, and expand the glass to a bulb, as shown 



58 GLASS-BLOWING. 

at B of 1 ; during the operation of blowing this bulb, the end 
A must be directed to the ground. 

Soften the end A and a small portion of B as before, and, 
holding the tube horizontally from the mouth, blow out 
the end C as at 2. Heat the end of C gradually, till the 
glass softens and collapses to the dotted line dd, and at once 
blow a steady stream of air into the open end of the t 
rotating it steadily, till it is about to burst ; finally clean off 
the thin glass from round the edges of the funnel, whi.-h 
should have the form shown at 3, and round them. An 
inspection of a purchased thistle funnel will generally show 
that the head B has been formed from a larger tube sealed 
to^at/. 

Closing Tubes containing Chemicals for experiment* 
at high temperatures. Tubes of the hard glass used for organic 

analyses answer best for this 
purpose; the operation of draw- 
ing out the end of such a tube 
" is practically identical with 
*" * what has been described un<l<T 

the head of choking, p. 35. A 

well-sealed tube presents the appearance of that shown by 
Fig. 26. 

In order to secure a thick end to the point of the tube a, 
about an inch or so of the tube near the contracted part 
should be warmed a little, if it is not already warm, at th< 
moment of finally sealing it; the contraction of the air in 
the tube, in consequence of the cooling of the warm 
will then ensure the glass at a running together to a solid cn.l 
when it is melted in the flame. 

If it will be necessary to collect a gas produced <lu: 
chemical action from such a tube, make the contracted en<l 
several inches long, anl UMH! it into the form of a lrlr 






// 

LS, 59 

'-- .A I ir-xx^ 




CLOSING TUBES CONTAINING CHE MIC A 



tube. It will then be possible to break the tip of this under 
a cylinder in a trough of liquid. 

In order to explain the construction of apparatus 
consisting of several parts, it will be suffi- 
cient to take as examples, two very well-known 
instruments, and to describe their construction 
in detail. From what is learned in studying 
these, the student will gather the information 
that is wanted. 

1. To make Hof man's Apparatus for the electro- 
lysis of water (Fig. 27). 

Take two tubes about 35 cm. in length, T 
and 14 mm. in diameter for A A, join taps TT 
to the end B of each of them, draw out the 
other end, as shown at D, after sheets of 
platinum foil with wires attached to them 1 
have been introduced into the tubes, and 
moved by shaking to BB. Then allow the 
platinum wires to pass through the opening 
D left for the purpose, and seal the glass at 
D round the platinum as at E. Pierce the 
tubes at //, and join them by a short piece of 
tube K, about 14 mm, in diameter, to which 
the tube T, carrying the reservoir E, has 
been previously united. R may be made by 
-blowing a bulb from a larger piece of tube 
attached to the end of T. The mouth M of the reservoir 




Fio. 27. 



1 Red-hot platinum welds very well. The wire may be joined to 
the sheet of foil by placing the latter on a small piece of fire-brick, 
holding the wire in contact with it at the place where they are to be 
united, directing a blow-pipe flame upon them till they are at an intense 
heat, and smartly striking the wire with a hammer. The blow should 
be several times repeated after re-heating the metal. 



60 GLASS-RLOWING. 

being formed from the other end of the wide tube after- 
wards. One of the tape can be used for blowing throu-h 
at the later stages. Each joint, especially those at J7, must 
be annealed after it is blown. Some operators might prefer 
to join A A by the tube K in the first instance, then to intro- 
duce the electrodes at E and D. In some respects this plan 
would be rather easier than the other, but, on the whole, it 
is better to make the joints at JJ last in order, as they are 
more apt to be broken than the others during the subsequent 
manipulations. 

2. I have before me the vacuum tube shown by Fig. 28, in 
which the dotted lines relate to details of manipulation only. 




9m. m, 

It is usually possible to detect the parts of which a piece of 
apparatus has been built up, for even the best-made j< 
exhibit evidence of their existence. Thus, although I <li<l n<>t 
make the tube that is before me, and cannot therefore pr< 
to say precisely in what order its parts were made and put 
together, the evidence which it exhibits of joints at the dotted 
lines A, B t C, D, E t F, enables me to give a general idea of 
the processes employed in its construction, and to explain lu.\v 
a similar tube might be constructed. I should advise proceed- 
ing as follows : 

Join a piece of tube somewhat larger than M 
end A t draw out the other end of the larger tube, and )>l<>\v 
a bulb L as directed on p. 47. Then seal the electrol< A 
into the bulb L (p. 55). 

Blow a similar but larger bulb N from a large piece of 



COMBINING PARTS OF HEAVY APPARATUS. 61 

tube sealed between two tubes of similar size to M, as 
described at p. 50. Cut off one of the tubes at B, and join 
the bulb N to M at B. Form the bulb Q in the same manner 
as in the case of L, seal into it the electrode ft, and add the 
tube marked by the dotted lines at F. 

Seal a narrow tube P to the end of a larger tube, 
and blow out the tube at the joint till the glass is thin 
and regular. Take a tube 0, of similar size to M, slightly 
longer than P, contract its mouth slightly to meet the wide 
end of P at D, and after loosely supporting P inside with a 
cork, or otherwise, close the end JVof by sealing or corking it, 
and join P to at D. Cut off just above D at E, and join it 
to the bulb Q, closing either or F for the purpose. Cut off 
the end of at C parallel to the end of P, and connect to JV, 
using F for blowing the joint at C. F may be used subse- 
quently for introducing any gas into the tube, and, when a 
vacuum has been established, may be sealed before the blow- 
pipe. 

Modes of combining the Parts of Heavy Appar- 
atus. It is often necessary to connect pieces of apparatus 
which are too heavy to be freely handled before the blow- 
pipe, and which, therefore, cannot be welded together as 
described on p. 39, by some more effective method than 
the ordinary one of connecting by india-rubber tubing. For 
example, apparatus which is to be exhausted by a Sprengel 
air-pump must be attached to the pump by a joint as per- 
fectly air-tight as can be obtained. This, indeed, often may be 
done by welding the apparatus to be exhausted to the air- 
pump before the blow-pipe. But such a method is open to the 
obvious objection that it is very troublesome to connect and 
disconnect the parts as often as may be necessary, and that 
there is some risk of accidental breakages. Nevertheless it 
may be done on occasion, especially if there be no objection to 



GLASS BLOWING. 



the use of the flexible spiral tubes already alluded to. When 
the use of a spiral connecting-tube is not admissible the diffi- 
culty is considerably increased. For example, the author 
has lately required to attach an ozone generator, of the form 
shown by Fig. 19, which previously had been cemented into a 
heavy copper jacket, to a pressure-gauge rigidly fixed to a sup- 
port, and of considerable size. The employment of a flexible 
spiral connection was prohibited by the fact that it was neces- 
sary that the volume of the connecting-tube should be but a 
small fraction of that of the ozone generator, a condition 
which compelled the use of a tube of almost capillary bore, 
and of inconsiderable length. At the same time the frailness 
of such a connection made it necessary to fix the generator and 
pressure-gauge rigidly to their supports, in order to avoid the 
possibility of breakage by slight accidental movements of 
either of them, and it was obviously necessary to fix tin- 
pieces of apparatus in their final positions before joining 
them, lest the fine tube which connected them should be 
fractured during adjustment The possibility of a strain 
being caused by the contraction that would occur during 
the cooling down of the joint last made had to be pro- 
vided for also. The desired object was 
effected as follows. In Fig. 29 A \ 
sents a section of the ozone generator at 
the point where the tube to connect it 
to the gauge was fixed. B represents the 
top of the gauge, with the side tube C, 
which was to be connected with that 
from A, vis. D. The ends of C and 
rio.19. D were expanded as shown at D (l>y 

melting them and blowing them out i, 
so that one of them, made rather smaller than the other, 
could be overlapped by the larger one. A and B K -in- 
rigidly fixed in their final positions, with C and D in 



o c 



COMBINING PARTS OF HEA VY APPARATUS. 63 

contact, as shown in the figure, all openings in the 
apparatus were closed, except one, to which was attached 
an india-rubber blowing-bottle by means of a tube of 
india-rubber long enough to be held in the hand of the 
operator, and to allow him to observe the operation of joining 
the tubes at D. When everything was in readiness, a very 
small-pointed flame from a moveable blow-pipe held in the 
hand was directed upon the glass at D till it melted and the 
two tubes united. To prevent the fine tube when melted 
from running into a solid mass of glass, and so becoming 
closed, a slight excess of pressure was maintained inside 
the apparatus during the operation by forcing air into it 
with the india-rubber blower from the moment at which C 
and D united. A point of charcoal was kept in readiness to 
support the softened glass at D in case it showed any tendency 
to fall out of shape. 

The V-tube at G served to prevent the subsequent fracture 
of the joint in consequence of any strain caused by the con- 
traction of the glass in cooling. * 

It is not difficult to connect several pieces of apparatus 
buccessively in this manner, nor is this method only useful 
in such cases as that just described. Pieces of apparatus of 
great length and weight may be joined in a similar manner, 
irrespective of the size of the tubes to be united. 

The ends to be joined, prepared as before, so that one 
slightly overlaps the other, must be held firmly in contact by 
clamps, and heated in successive portions by a blow-pipe held 
in the hand of the operator, each patch of glass being 
re-heated and gently blown, after a rough joint has been made. 
Finally, a larger flame may be used to heat up the whole 
joint for its final blowing. It is important to place the 
apparatus so that the operator has free access to it on all 
sides. A revolving table might be employed. An assistant 

1 For a method of joining soda glass to lead glass, see p. 81. 



GLASS-BLO WING. 



to work the bellows is necessary. Or, better still, air may 
be admitted to the blow-pipe from a large gas-bag placed in 
some convenient position. 

But in most cases one or other of the following air-tight j< >i n t s 
can be employed, and will be found to be very convenient : 
Mercury Joints. The simplest form of mercury joint is 
shown at Fig. 30. A and B are the two tubes which are to 
be connected. A larger tube or cup F is attached to A by 
the india-rubber tube E, and placed on A so that 
the end of B may be brought into contact with A 
at C, and connected to it by a well-fitting piece 
of india-rubber tube C. The cup E is then 
brought into the position shown in Fig. 30, and 
"" c mercury is introduced till the india-rubber tube at 
-to C is covered. As mercury and glass do not come 
into true contact, however, such a joint, though 
said to give good results in practice, is not 
theoretically air-tight, for air might gradually tin. I 
pjo ^ its way between the liquid and the glass. By 
covering the mercury with a little sulphuric acid 
or glycerine the risk of this occurring may be removed. 
The same result may be attained by the use of glycerine in 
place of the mercury in the cup F\ but glycerine is less 
pleasant to work with than mercury. 1 

When sulphuric acid is to be employed in such a joint, 
or when for any other reason the use of an india-rubber tube 
is undesirable, the joint may consist of a hollow stopper // 
(Fig. 31), made of glass tube, and ground to fit the neck of a 
thistle funnel A. A and B are joined respectively to tin- 
pieces of apparatus to be connected, and connect inn i- 
made by placing B in position in the neck of A ; th<> 
joint is made air-tight by introducing mercury with sti 

1 If the india-rubber tube C be secured by wires, iron \virc-, not copper 
wire, should be employed. 



VACUUM TAPS. 65 



sulphuric acid above it into the cup A. The joint iflay be 
rendered air-tight by introducing sulphuric acid only into the 
cup. But this plan must not be adopted if the 
interior of the apparatus is to be exhausted, as 
sulphuric acid is easily forced between the ground 
glass surfaces by external pressure. Mercury, 
however, will not pass between well-ground glass \ 
surfaces, and is therefore to be employed for 
connecting apparatus which is to be exhausted, 
and, if necessary, protected by a layer of strong 
sulphuric acid to completely exclude air. 

Tubes placed horizontally may be joined by a 
glycerine or mercury joint such as is shown in 
Fig. 32. The two tubes A and B are joined as 
before by an india-rubber connection (7, or one 
may be ground to fit the other, and the joint is 
then enclosed within a larger jacketing-tube D, Flo 31 
with a mouth at F, which is filled with glycerine 
or mercury. D is easily made by drawing out both ends of 
a piece of tube, leaving them large enough to pass over the 
connection at C, however, and piercing one side at F. 



c 

Fio. .32. 



Vacuum Taps. It is not necessary to enter into a de- 
scription of the construction of ordinary glass taps, which can 
be purchased at very reasonable prices. It may be remarked 
here, however, as a great many of them are very imperfectly 
ground by the makers, that they may easily be made air-tight 
by hand-grinding with camphorated turpentine and fine emery, 
finishing with rotten-stone. A well-ground tap, which is well 

E 



66 



GLASS-BLOWING. 



In) indited, should be practically air-tight under greatly re- 
duced pressure for a short period ; hut when it is necessary 
to have a tap which absolutely forbids the entrance o; 
into apparatus, one of the following may be employed : 





T 



F 

FK 54. 



Flo 55. 



(1.) Mr. Cdtfs Vacuum Tap (Fig. 34): This Up is 
at A and sealed at B, and the cup A is filled with mer< 
when the Up is in use, so that if, for example, the end C 
be attached to a flask, and D to an apparatus for exhau> 
the flask, it will be possible to close the flask by turning off 
the Up E, and if no air be allowed access through /), the 
vacuum produced in the flask at C cannot be affected by air 
leaking through the tap at A or B. 

A passage F must be drilled from the bottom of the plug 
E to meet 0, in order that when the plug is in position no 
residue of air shall be confined within B, whence it mi-.-lit 
gradually lead into any apparatus connected to it 

It is obvious, however, that this tap does not protect a flask 



VACUUM TAPS. 67 



sealed to C from the entrance of air through D, which, in 
fact, is the direction in which air is most likely to effect an 
entrance. When using one of these taps as part of an appa- 
ratus for supplying pure oxygen, I have guarded against this 
by attaching a trap (Fig. 33) to the end j9, being joined to 
the delivery tube from the gas-holder. The structure and 
mode of action of the trap are as follows : 

A narrow tube G is joined to D of Fig. 34, and termin- 
ates in the wide tube /, which is connected above to J?, and 
below to the air-trap /. / is connected at 7iT, by a piece 
of flexible tube, to a reservoir of mercury, from which mer- 
cury enters the air-trap, and passing thence to /, can be em< 
ployed for filling the V-trap HLG. The air trap / is in the 
first instance filled with mercury, and then serves to intercept 
any stray bubbles of air that the mercury may carry with it. 
The particular form of the trap shown at HLG was adopted 
because with it the arm LG is more readily emptied of mercury 
than with any other form of trap made of small tube that I 
have tried. It has been used in my apparatus in the follow- 
ing manner : H was connected with a vessel to be filled with 
pure oxygen, the tap E closed, and the rise of mercury above 
L prevented by a clamp on the flexible tube ; the vessel to be 
filled and the trap were then exhausted by a Sprengel pump, 
and oxygen allowed to flow into the exhausted space by open- 
ing E, the operation of exhausting the tubes and admitting 
oxygen being repeated as often as necessary. 

To prevent access of air to E on disconnecting the vessel 
at H, the mercury was allowed to flow into the trap till it 
reached to MM. E was then closed, and-JJ exposed with- 
out danger of air reaching E, the length of the arms of the 
trap being sufficient to provide against the effects of any 
changes of temperature and pressure that could occur. 

A delivery tube may be connected to H and filled with 
mercury, by closing E and raising the mercury reservoir. All 



68 



GLASS-BLOWING. 



air being in that way expelled from the delivery tube, and 
the supply of mercury cut off by clamping the tube from the 
reservoir, oxygen can be delivered from the tube 
by opening E, when it will send forward the 
mercury, and pass into a tube placed to receive 
it without any risk of air being derived from the 
delivery tube. 

(2.) Gimmingham's Vacuum Tap, 1 shown in 
Fig. 35, consists of three parts. A tube A is 
ground to fit the neck of B. B is closed at 
its lower end, and has a hole d drilled through 
it; when 11 is fitted to C, d can be made to 
coincide with the slit e. When A, B, C are fitted 
together, if d meet e, there is communication 
between any vessels attached to A and any 
other vessel attached to C, entrance of external 
air being prevented by mercury being placed in 
the cups of C and B. The tap may be opened 
and closed at pleasure by rotating B. 

If ^ has to be removed, C may be converted 
into a mercury joint pro tern, by letting a little 
mercury from the upper cup fall into the tube and cover rf, 
the tap being closed. This mercury must be removed by a 
fine pipette in order to use the tap again. It should be 
noted, however, that though external air cannot enter by 
way of the ground glass joints, there is no absolute protection 
against the passage of air between A and C, or vessels joined 
to A and C, even when the tap is closed. The passage of 
air from A to C depends upon the grinding and lubrication 
of the joint at C. 

Lubricating Taps For general purposes resin cerate 
answers very well In special cases burnt india-rubber, or a 

1 From Proceeding* of Royal Society, vol. zzr. p. 396. 




rio. M. 



AIR-TRAPS. 



69 



mixture of burnt india-rubber and vaseline will answer well, 
or vaseline may be used alone. Sulphuric acid and glycerine 
are too fluid. When a lubricant is wanted that will with- 
stand the action of ether, the tap may be lubricated by sprink- 
ling phosphorus pentoxide upon it, and exposing it to air till 
the oxide becomes gummy. The joint must then be protected 
from the further action of the air if possible. For example, 
if a safety tap be used the cup may be filled with mercury. 

Air-Traps. In Fig. 33, p. 66, an air-trap (/) is shown. 
An air-trap is a device for preventing the mercury supplied to 
Sprengel pumps, etc., from carrying air 
into spaces that are exhausted, or are for 
any reason to be kept free from air. 
Figs. 36 and 37 give examples of air- 
traps. In the simpler of the two (Fig. 
36) mercury flowing upwards from C that 
may carry bubbles of air with it passes 
through the bulb A, which is filled with 
mercury before use. 1 Any air which 
accompanies the mercury will collect at a, 
the mercury will flow on through b. So 
long as the level of the mercury in A 
is above b, the trap remains effective. 

In the trap shown by Fig. 37, the tube 
d, which corresponds to b in Fig. 36, is 
protected at its end by the cup E. E pre- 
vents the direct passage of minute bub- 
bles of air through d. This trap, like the other, must be filled 
with mercury before it is used, and it will then remain effec- 
tive for some time. 




FIG. 36. 



FIG. 37. 



1 This may be done by clamping the tube which supplies mercury 
below C, exhausting A, and then opening the clamped tube and allow- 
ing the mercury to rise. 



TO GLASS-fiLOW/NG. 



CHAPTER V. 

GRADUATING AND CALIBRATING GLASS APPARATUS. 

ALTHOUGH the subjects to which this concluding chapter 
is devoted do not, properly speaking, consist of operations in 
! Ulflwin^, they are so allied to the subject, and of > 
gnat importance, that I think a brief account of them may 
advantageously be included. 

Graduating Tubes, etc. It was formerly the custom 
to graduate the apparatus intended for use in qnantitr 
work into parts of equal capacity; for example, into cul>ic 
centimetres and fractions of cubic centimetres. For 
operations of volumetric analysis by liquids this is still done. 
Hut for most purposes it is better to employ a scale of equal 
Inisions by length, usually of millimetres, and to <1< 
in i no the relative values of the divisions afterwards, as 
described under calibration. It rarely happens that the 
tube of which a burette or eudiometer is made has equal 
divisions of its length of exactly equal capacities throughou 
entire length, and indeed, even for ordinary volumetric work, 
no burette should be employed before its accuracy has been 
verified. An excellent method for graduating glass tubes by 
hand 1 has been described in Watts's Dictionary of Chemistry, am 1 
elsewhere. Another excellent plan, which I have permission 

1 Originally suggested by Bansen. 



GRADUATING TUBES, ETC. 



to describe, has been employed by Professor W. Ramsay. 
It will be sufficient if I explain its application to the operation 
of graduating a tube or strip of glass in millimetre divisions. 
The apparatus required consists of a standard metre 
measure, 1 divided into millimetres along each of its edges, 
with centimetre divisions between them, a ruler adapted to 
the standard metre, as subsequently explained, and a style 
with a fine point for marking waxed surfaces. 

u <{0imfK!iammflaMKEvtMm 




10 



12 



mums 



t. 



-D 




FIG. 38. 

Fig. 38 represents the standard measure, and the ruler. 

1 Such measures can be obtained of steel for about fifteen shillings 
each. They are made by Mr. Chesterman of Sheffield. They can be 
obtained also from other makers of philosophical instruments, at prices 
depending upon their delicacy. Those of the greatest accuracy are 
somewhat costly. 



7* GLASS-BLOWING. 

At A A are the millimetre divisions on the edges of the 
measure, the longer transverse lines at BB are placed at 
intervals of five millimetres and of centimetres. The ruler is 
in the form of a right-angled triangle ; it is shown, by the 
dotted lines, in position on the standard metre measure at / ; 
and again, with its under surface upwards, in the smaller 
figure at 2. It consists of a perfectly flat sheet of metal, 
about ten centimetres in length from C to C, sufficiently thick 
to be rigid, and has a ledge, DD in each figure, which is 
pressed against the side of the measure when using it, to 
ensure that the successive positions of the edge (LL) shall be 
parallel to each other. At 00 are two small holes, int 
which fit small screws with fine points. These must be in a 
line parallel to the edge (LL), so that when the ruler is in 
position on the scale, the points of the two screws, which 
project slightly, shall fall into corresponding cuts on t In- 
divided scales (A A). 

To graduate a strip of glass, or a glass tube (////), the sur- 
face to be marked must first be coated with wax, which shouM 
be mixed with a little turpentine, and be applied to the sur- 
face of the glass, previously made irorro and dry, by means of 
a fine brush, so as to completely cover it with a thin, closely- 
adherent, and evenly-distributed coat of wax, which must be 
allowed to cool 

Fix HU firmly on a table, and fix the standard measure by 
the side of ////. If the thickness of //// be about equal to, 
but not greater than that of the standard measure, this 
may be done by large drawing-pins. If, h iwever, a large 
tube or thick sheet of glass is to be graduated, fix it in posit i >n 
by two stripe of wood screwed to the table on each side of it. 
One of these wooden strips, on which the measure may be 
placed, may be about as broad as the standard mea- 
and of such thickness that when the measure lies upon it 
beside the tube to be graduated, the ruler, when moved along 



GRADUATING TUBES, ETC. 73 

the measure, will move freely above the tube, but will not 
be elevated more than is necessary to secure free movement. 
The second strip of wood may be narrower, and of the same 
thickness .as the broader piece on which the standard 
measure rests. In any case, let the standard measure 
and the object to be graduated be very firmly secured in 
their places. Bring the ruler into position at any desired part 
of the tube by placing the points of the screws (GG) in 
corresponding divisions of the scales (AA). With the style, 
which may be a needle mounted in a handle, make a scratch 
in the wax along the edge of the ruler at F, move the ruler so 
that the screws rest in the next divisions, and repeat the opera- 
tion till the required number of lines has been ruled. Longer 
marks may be made at intervals of five and ten millimetres. 
Great care must be taken to hold the needle perpendicularly, 
arid to press it steadily against the edge (LL) of the ruler in 
scratching the divisions. 1 The length of the lines marking 
the millimetre divisions should not be too long ; about 1 mm. 
is a good length. If they are longer than this, the apparent 
distance between them is diminished, and it is less easy to 
read fractions of millimetres. Before removing the scale to 
etch the glass, carefully examine it to see that no mistakes 
have been made. If it is found that any lines have been 
omitted, or that long lines have been scratched in the place 
of short ones, remelt the wax by means of a heated wire, and 
make new marks. Finally, mark the numbers on the scale 
with a needle-point, or better, with a fine steel pen. 

The marks on the wax should cut through it. When they 

1 To avoid variations of the position in which the needle is held when 
marking the divisions, the edge (LL) should not be bevelled ; and an 
upright support may be placed upon the ruler, with a ring through 
which the handle of the needle passes, thereby securing that the angle 
formed by the needle and surface of the ruler is constant, and that 
equal divisions are marked. 



74 GLASS BLO WIKG. 

are satisfactory, they may be etched by one of tho following 
processes: 

(1.) By moistening some cotton wool, tied to a stick, 
with solution of hydrofluoric acid, and gently rubbing this 
over the scratched surface for a minute or so ; then washing 
away the acid with water, and cleaning off the wax. This is 
the simplest method, but the marks made are generally trans- 
parent, and therefore not very easy to read. The sinipl 
of this method is a great recommendation, however. 

(2.) Expose the tube to the fumes of hydrofluoric acid gene- 
rated from a mixture of powdered fluor-spar and strong 
sulphuric acid, in a leaden trough. The marks produced in 
this way are usually opaque, and are therefore very visible, 
and easily read. 

After the above detailed account it will only be necessary 
to give an outline of the other process of graduating tubes. 



r 





fss.ui 

The standard scale to be copied, A, which may in thi- 
case be another graduated tube, or even a paper scale, and 
the object to be ruled, B t are securely fixed, end to end, 
a little distance apart, in a groove made in a board or in the 
top of a table. A stiff bar of wood, C, has a point fixed 
at />, and a knife edge at E, D is placed in any <ii\ 
of A, C is held firmly at and />, and a cut is made by the 
knife through the wax on B, the point D is then moved 
into the next division, and the operation is repeated. T<> 
regulate the length and position of the cuts, B is usually 
held in position by two sheets of brass projecting over tin- 
edges of the groove in which it lies ; the metal sheets I 
notches cut into them at the intervals at which longer marks 
arc to be made. 



TO DIVIDE A GIVEN LINE. 75 

When the scale is completed, the equality of the divisions 
in various parts of it may be, to some extent, verified as 
follows : Adjust a compass so that its points fall into two 
divisions 5, 10, or 20 mm. apart. Then apply the points of 
the compass to various parts of the scale. In every part 
the length of a given number of divisions should be exactly 
the same. The individual divisions should also be carefully 
inspected by the eye ; they should be sensibly equal. If badly 
ruled, long and short divisions will be found on the scale. 
Very often a long and a short division will be adjacent, and 
will be the more easily observed in consequence. 

To Divide a Given Line into Equal Parts. 
Occasionally it is necessary to divide a line of given length 
into x equal parts. For instance, to divide the stem of a 
thermometer from the freezing-point to the boiling-point into 
one hundred degrees. 

The following outline will explain how a line may be 
so divided. Suppose the line AB (Fig. 40) is to be divided 




PIG. 40. 

into nine equal parts. Adjust a hinged rule so that the 
points A and B coincide with the inside edges of the limbs, 
one of them, A, being at the ninth division (e.g. the ninth 
inch) of CE. Then if lines parallel to ED be drawn from 
each division of the scale to meet AB, AB will be divided 
into nine equal parts. 

A very convenient and simple arrangement on this prin- 



GLASS-BLOWING. 



ciple for dividing a line into any number of equal parts v 
considerable accuracy, is described by Miss S. Marks in 
the Proceedings of the Physical Society, July 1885. * One 
limb of a hinged rule D is made to slide upon a plain rule 
fixed to it ; the plain rule carries needles on its under sur- 
face which hold the paper in position. The position of the 
divided rule and line to be divided being adjusted, the hinged 
rule is gently pushed forwards, as indicated by the arrow in 
Fig. 40, till division eight coincides with the line AB. A mark 
is made at the point of coincidence, and division seven on the 
scale is similarly brought to the line AB, and so on. The 
inner edge of EC should have the divisions marked upon it, 
that their coincidence with AB may be more accurately noted. 
The joint E must be a very stiff one. 

A line drawn of given length on a piece of paper may be 
divided into any given number of equal parts, and will then 
serve as the scale A of Fig. 39, p. 74, the thermometer 
or other object to be graduated taking the place of B. 

Scales carefully divided according to any of the methods 
described will be fairly accurate if InuiwtHhy instruments have 
been employed at standards. 

It will be found possible when observing the volume of a gas 
over mercury, or the height of a column of mercury in a tube, 
to measure differences of one-sixth to one-eighth of a milli- 
metre with a considerable degree of accuracy. To obtain 
more delicate measurements a vernier* must be employed. 



To Calibrate Apparatus. The glass tubes of 
graduated apparatus is made are, as already stated, very 

> Since this WM printed I have obeerved that the above method is 
not identical with that described by Miae Marks, tat for ordinary 
purpose* I do not think it will be found to be inferior. 

' For the nature and use of the vernier, ft trcatiae on Physics or 
Physical Measurements may be consulted. 



TO CALIBRATE APPARATUS. 



77 



rarely truly cylindrical throughout their entire lengths. It 
follows that the capacities of equal lengths of a tube will 
usually be unequal, and therefore it is necessary to ascer- 
tain by experiment the true values of equal linear divisions 
of a tube at various parts of it. 

A burette may be calibrated by filling it with distilled water, 
drawing off portions, say of 5 c.c. in succession, into a weigh- 
ing bottle of known weight, and weighing them. 

Great care must be taken in reading the level of the liquid 
at each observation. The best plan is to hold a piece of 
white paper behind the burette, and to read from the lower 
edge of the black line that will be seen. Each operation 
should be repeated two or three times, and the mean of the 
results, which should differ but slightly, may be taken as the 
value of the portion of the tube under examination. 

If the weights of water delivered from equal divisions of the 
tube are found to be equal, the burette is an accurate one, 
but if, as is more likely, different values are obtained, a table 
of results should be drawn up in the laboratory book showing 
the volume of liquid delivered from each portion of the tube 
examined. And subsequently when the burette is used, the 
volumes read from the scale on the burette must be corrected. 
Suppose, for example, that a burette delivered the following 
weights of water from each division of 5 c.c. respectively : 



C.C. 


Grams. 


to 5 ga 


ve 4-90 


5 10 


. 4-91 


10 15 


4-92 


15 20 


, 4-93 


20 25 


4-94 


25 30 


' ' 4-95 


30 35 


4-96 


35 40 


.-' 4-97 


40 45 


: 4-98 


45 50 


4-99 



GLASS-BLOWING. 



and that in two experiments 20 c.c. and 45 c.c. respec- 
tively of a liquid re-agent were employed. The tin. 
volumes calculated from the table would be as 19*66 to 
44-46. 

If the temperature remained constant throughout the above 
series of experiments, and if the temperature selected were 4* 
G. v the weights of water found, taken in grams, give tin- 
volumes in cubic centimetres, for one gram of water at 4* C. 
has a volume of one cubic centimetre. If the temperature 
at which the experiments were made was other than 4* C., 
and if great accuracy be desired, a table of densities u 
be consulted, with the help of which the volume of any 
weight of water at a known temperature can be readily 
calculated 

Pipettes which are to be used as measuring instruments 
should also have the relation one to another of the volumes 
of liquid which they deliver determined, and also the pro- 
portions these bear to the values found for the divis 
of the burettes in conjunction with which they will be 
employed. 

To Calibrate Tubes for Measuring Gases. Prepare 
a small glass tube sealed at one end and ground at the othn 
to a plate of glass. The tube should hold about as mm h 
mercury as will fill 10 mm. divisions of the graduated tul><>. 
Fill this tube with mercury, removing all bubbles of air- 
that adhere to the sides by closing the open end of the tube 
with the thumb, and washing them away with a large air- 
bubble left for the purpose. If any persistently remain, 
remove them by means of a fine piece of bone or wood. Then 
completely fill the tube with mercury, removing any bubbles 
that may be introduced in the operation, and remove the 
excess of mercury by placing the ground-glass plate on 



TO CALIBRATE TUBES. 79 

the mouth of the tube, and pressing it so as to force out all 
excess of mercury between the two surfaces. Clean the out- 
side of the tube, and place it on a small stand (this may be a 
small wide-mouthed glass bottle), with which it has been pre- 
viously weighed when empty, and re-weigh*. Repeat this 
operation several times. From the mean of the results, which 
should differ one from another but very slightly, the capacity 
of the tube can be calculated. 

The purest mercury obtainable should be used. Since the 
density of pure mercury at C. is 13-596, the weight of 
mercury required to fill the tube at C., taken in grams, 
when divided by 13-596, will give the capacity of the tube at 
C. in cubic centimetres. If the experiment be not made at 
C., and if a very exact determination of the capacity of the 
tube be required, the density of mercury must be corrected 
for expansion or contraction. 

Having now a vessel of known capacity, it can be employed 
for ascertaining the capacities of the divisions of a graduated 
tube in the following manner : The graduated tube is fixed 
perpendicularly, mouth upwards, in a secure position. The 
small tube of known capacity is filled with mercury as 
previously described, and its contents are transferred to the 
divided tube. The number of divisions which the known 
volume of mercury occupies is noted after all air-bubbles have 
been removed. This process is repeated until the divided 
tube is filled. A table of results is prepared, showing the 
number of divisions occupied by each known volume of 
mercury introduced. 

In subsequently using the tube the volumes of the gases 
measured in it must be ascertained from the table of values 
thus prepared. 

In observing the level of the mercury, unless a cathetometer 
is available, a slip of mirror should be held behind the 
mercury close to the tube, in such a position that the pupil 



8o 



GLASS-BLOWING. 



which is visible on the looking-glass is divided into two parts 
by the surface of the mercury. 

A correction must be introduced for the error caused 
by the meniscus of the mercury. As the closed end of 
the tube was downwards when each measured volume of 



2 

Fro. 41. 



mercury was introduced, and as the surface of mercmy 
is convex, the volume of mercury in the tube when it is 
filled to any division / (Fig. 41) is represented by A of 1. But 
in subsequently measuring a gas over mercury in the same 
tube, when the mercury stands at the same division /, tic- 
volume of the gas will be as represented by B of 2, which is 
evidently somewhat greater than A. This will be seen still 
more clearly in 3, where a represents the boundary of the 
mercury, and b the boundary of the air, when the tube is 
filled to the mark / with mercury or a gas over mercury 
respectively. 

It is plain that when the level of the mercury in measuring 
gas is read at /, the volume of the gas is greater than the 
volume of the mercury recorded, by twice the difference be- 
tween the volume A of mercury measured, and that which 
would fill the tube to the level /, if its surface were plane. 

The usual mode of finding the true volume of a gas collected 
over mercury is as follows : 

Place the graduated tube mouth upwards, introduce some 
mercury, and, after removing all bubbles, note the division at 



TO CALIBRA TE TUBES. 81 

which it stands. Then add a few drops of solution of mercuric 
chloride ; the surface of the mercury will become level, read 
and record its new position. Then, in any measurement, 
having observed that the mercury stands at n divisions of the 
tube, add twice the difference between the two positions of 
the mercury to n, and ascertain the volume which corre- 
sponds to this reading from the table of capacities. 

To Calibrate the Tube of a Thermometer. Detach 

a thread of mercury from half an inch to one inch in length 
from the body of the mercury. Move it from point to point 
throughout the length of the tube, and note its length in 
each position. If in one part it occupies a length of tube 
corresponding to eight degrees, and at another only seven 
degrees, then at the former point the value of each division is 
only seven-eighths of those at the latter position. 

From the results obtained, a table of corrections for the 
thermometer should be prepared. 

It is sometimes necessary to join soda glass to lead glass. 
In this case the edge of the lead glass tube may be bordered 
with white enamel before making the joint. Enough enamel 
must be used to prevent the lead and soda glasses from ming- 
ling at any point. The enamel is easily reduced, and must be 
heated in the oxidising flame. Dr. Ebert recommends Ferre 
d'umne for this purpose. It is supplied by Herr Gotze of 
Leipzig (Liebigstrasse). 



CHAPTER VL 
CLASS TUBING. 

THE diagrams given below show the sizes and thickness of 
the glass tubes most frequently required In ordering, the 
numbers of these diagrams may be quoted, or the exact 
dimensions desired may be stated. 

Glass tubes are usually sold by weight, and therefore the 
weight of tube of each size that is wished for should be 
indicated, and also whether it is to be of lead or soda glass. 




0Q00 



GLASS TUBING. 







30 




31 




\3 34 35 3S 



84 GLASS-BLOWItfG. 



CHAPTER VII. 
VITRROUS SILICA. 

Introductory. Vitreous Silica was made in fine threads 
by M. Gaudin in 1839, 1 and small tubes of it were made in 
1869 by M. A. Gautier, but its remarkable qualities were 
not really recognised till 1889, when Professor C. V. Boys 
rediscovered the process of making small pieces of apparatus 
of this substance, and used the torsion of "quartz fibres" 
for measuring small forces. More recently the author of 
this book has devised a process for preventing thi ^linu-i- 
ing" of quartz which gave so much trouble to the earlier 
workers, and jointly with Mr. H. G. Lacell, has pro!u< .-,! ; , 
variety of apparatus of much larger dimensions than ha<i 
been attempted previously. At the time of writing we can 
produce by the processes described in the following pages 
tubes 1 to 1*5 cm. in diameter and about 750 cm. in length, 
globes or flasks capable of containing about 50 cc., masses of 
vitreous silica weighing 100 grams or more, and a variety 
of other apparatus. 

Properties of Vitreous Silica. For the conve: 
of those who are not familiar with the literature of this 

1 A brief summary of the history of this subject will be found in 
Naturt, VoL 62, ami in the Proceedings of the Royal Institution, 
1901. 



PROPERTIES OF VITREOUS SILICA. 85 

subject, I may commence this chapter with a brief account 
of the properties and applications of vitreous silica, as far as 
they are at present ascertained. Vitreous silica is less hard 
than chalcedony, but harder than felspar. Tubes and rods 
of it can be cut with a file or with a piece of sharpened 
and hardened steel, and can afterwards be broken like 
similar articles of glass. Its conducting power is low, and 
Mr. Boys has shown that fine fibres of silica insulate remark- 
ably well, even in an atmosphere saturated with moisture. 
The insulating qualities of tubes or rods of large cross 
sections have not yet been fully tested ; one would expect 
them to give good results provided that they are kept 
scrupulously clean. A silica rod which had been much 
handled would probably insulate no better than one of 
glass in a similar condition. The density of vitreous silica 
is very near to that of ordinary amorphous silica. In the 
case of a small rod not absolutely free from minute bubbles 
it was found to be 2-21. 

Vitreous silica is optically inactive, when homogeneous, 
and is highly transparent to ultraviolet radiations. 

The melting point of vitreous silica cannot be definitely 
stated. It is plastic over a considerable range of temperature. 
Professor Callendar has succeeded in measuring the rate of 
contraction of fine rods in cooling from 1200 to 1500 C., 
so that its plasticity must be very slight below the latter 
temperature. If a platinum wire embedded in a thick silica 
tube be heated from without by an oxy-hydrogen flame the 
metal may be melted at temperatures at which the silica tube 
will retain its form for a moderate length of time, but silica 
softens to a marked extent at temperatures a little above 
the melting point of platinum. 

It has been observed by Boys, Callendar, and others that 
fine rods of silica, ^and also the so-called "quartz fibres," are 
apt to become brittle after they have been heated to redness. 



86 GLASS-BLOWING. 

4 



Bat I have not observed this defect in the case of more 
massive objects, such as thick rods or tubes ; and as I have 
repeatedly observed that mere traces of basic matter, such as 
may be conveyed by contact with the hand, seriously injure 
the surface of silica, and have found that silica quickly 
becomes rotten when it is heated to about 1000 in contact 
with an infusible base such as lime, I am disposed to ascribe 
the above-mentioned phenomenon to chemical rather than to 
purely physical causes. 1 It is certain, however, that silica 
apparatus must never be too strongly heated in contact 
with basic substances. Silica is easily attacked by alkalis 
and by lime, less readily by copper oxide, and still less by 
iron oxide. 

The rate of expansion of vitreous silica has been stud in} 
by II. le Chatelier, and more recently by Callendar. 
former found its mean coefficient of expansion to be 
0-0000007 between 0* and 1000,' and that it contra 
when heated above 700*. 

Professor Callendar used rods of silica prepared by the 
author from "Brazil crystal"; these were drawn in the 
oxy-gas flame and had never been heated in contact with 
solid foreign matter, so that they consisted, presumably, of 
very pure silica. His results differ in some respects from 
those obtained by Le Chatelier, for he finds the mean co- 
efficient of expansion to be only 0*00000059, i.e. about one 
seventeenth as great as that of platinum. Callendar found 
the rods of silica expanded very regularly up to 1000 hut 
less regularly above that temperature. Above 1200 t 
contracted when heated. 

1 In a recent communication Professor Callendar tells me that the 
devitrification commences at the outside and is hastened by Articles 
of foreign matter. 

s The silica blocks used were prepared by fusion in an el< trie 
furnace ; it is therefore probable that they were not quite pure. 



PROPERTIES OF VITREOUS SILICA. 87 

The behaviour of vitreous silica under sudden changes 
of temperature is most remarkable. Large masses of it 
may be plunged suddenly when cold into the oxy-gas flame, 
and tubes or rods at a white heat may be thrust into cold 
water, or even into liquid air, with impunity. As a conse- 
quence of this, it is in one respect much more easily worked 
in the flame than any form of glass. Difficult joints can 
be thrust suddenly into the flame, or removed from it, at 
any stage, and they may be heated unequally in different 
parts with impunity. It is safe to say that joints, etc., in 
silica never crack whilst one is making them nor during the 
subsequent cooling. They may be set aside in an unfinished 
state and taken up again without any precautions. There- 
fore it is possible for an amateur to construct apparatus in 
silica which he would be quite unable to produce from 
glass. 

The behaviour of vitreous silica with solvents has not yet 
been fully investigated, but Mr. H. G. Lacell has this subject 
in hand. If it behaves like the other forms of anhydrous 
silica it will withstand the action of all acids except hydro- 
fluoric acid. It is, of course, very readily acted upon by 
solutions of alkalis and alkaline salts. 

As regards the use of silica in experiments with gases, 
it must be remarked that vitreous silica, like platinum, 
is slightly permeable to hydrogen when strongly heated. 
One consequence of this is that traces of moisture are 
almost always to be found inside recently-made silica tubes 
and bulbs, however carefully we may have dried the air forced 
into them during the process of construction. Owing to the 
very low coefficient of expansion of silica, it is not possible 
to- seal platinum wires into silica tubes. Nor can platinum 
be cemented into the silica by means of arsenic enamel, nor 
by any of the softer glasses used for such purposes. I have 
come near to success by using kaolin, but the results with 



88 GLASS-BLOWING. 

this material do not afford a real solution of the problem, 
though they may perhaps point to a hopeful line of attack. 
Possibly platinum wires might be soldered into the tubes 
(see Laboratory Arts, R. Threlfall), but this also is uncertain. 

The process of preparing silica 'tubes, etc., from Lumps of 
Brazil Crystal may be described conveniently under the 
following headings. I describe the various processes fully 
in these pages, at those who are interested in the ma 
will probably wish to try every part of the process in the 
first instance. But I may say that in practice I think 
almost every one will find it advantageous to start with 
purchased silica tubes, just as a glass-worker starts with a 
supply of purchased glass tubes. The manufacturer can 
obtain his oxygen at a lower price than the retail purchaser, 
and a workman who gives much time to such work ran turn 
out silica tube so much more quickly than an amateur, that 1 
think it will be found that both time and money can be 
saved by purchasing the tube. At the same time tin- 
beginner will find it worth while to learn and practise each 
stage of the process at first, as every part of the work 
described may be useful in the production of tini>hi 
apparatus from silica tobea 

This being so, I am glad to be able to add that a lea- 1 in- 
firm of dealers in apparatus 1 has commenced making silica 
goods on a commercial scale, so that the new material is 
now available for all those who need it or wish to examine 
its properties. 

Preparing non - splintering Silica from Brazil 
Pebble. The best variety of native Silica is Br.i/il I VliMf, 
which may be obtained in chips or larger masses. T 

1 Mewrs. Baird ami Tatluck. 



PREPARING NON-SPLINTERING SILICA. 89 

should be thoroughly cleaned, heated in boiling water, and 
dropped into cold water, the treatment being repeated till 
the masses have cracked to such an extent that they may 
be broken easily by blows from a clean steel pestle %r 
hammer. 

The fragments thus produced must be hand-picked, and 
those which are not perfectly free from foreign matter 
should be rejected. The pure and transparent pieces 
must then be heated to a yellow-red heat in a covered 
platinum dish in a muffle or reverberatory furnace and 
quickly plunged into a deep clean vessel containing clean 
distilled water; this process being repeated, if necessary, 
till the product consists of semi-opaque friable masses, very 
much like a white enamel in appearance. After these have 
been washed with distilled water, well drained and dried, they 
may be brought into the hottest part of an oxy-gas flame 
safely, or pressed suddenly against masses of white hot silica 
without any preliminary heating, such as is necessary in 
the case of natural quartz. Quartz which has not been sub- 
mitted to the above preparatory process, splinters on contact 
with the flame to such an extent that very few would care to 
face the trouble and expense of working with so refractory 
a material. But after the above treatment, which really 
gives little trouble, all the difficulties which hampered the 
pioneer workers in silica disappear as if by magic. 

Apparatus. Very little special apparatus need be pro- 
vided for working with silica, but it is absolutely essential to 
protect the eyes with very dark glasses. These should be 
so dark as to render it a little difficult to work with them 
at first. If long spells of work are undertaken, two pairs of 
spectacles should be provided, for the glasses quickly become 
hot enough to cause great inconvenience and even injury to 
the eyes. 



90 CLASS-BLOWING. 

Almost any of the available oxy-gas burners may be 
wed, but they vary considerably in efficiency, and it 
is economical to obtain a very efficient burner. The 
'Wow-through' burners are least satisfactory, and I have 
long since abandoned the use of them. Some of the sa: 
'mixed-gas jets' have an inconvenient trick of burning-back, 
with sharp explosions, which are highly disconcerting, if tin 
work be brought too near the nozzle of the burner. I 
have found the patent burner of Mr. Jackson (Brin's Oxygen 
Company, Manchester) most satisfactory, and it offers the 
advantage that several jets can be combined in a group 
easily and inexpensively for work on large apparatus. The 
large roaring flames such as are used, I understand, for 
welding steel are very expensive, and not very efl 
the work here described. 

The method of making Silica Tubes. Before com- 
mencing to make a tube a supply of vitreous silica in rods 
about one or two millemetres in diameter must be prepared. 
To make one of these, hold a fragment of the non-splint^ -\ 
silica described above in the oxy-gas flame by means of forceps 
tipped with platinum so as to melt one of its corners, press 
a small fragment of the same material against the melted 
part till the two adhere and heat it from below upwards, 1 
till it becomes clear and vitreous, add a third fragment in a 
similar manner, then a fourth, and so on till an irregular 
rod has been formed. Finally reheat this rod in sections and 
draw it out whilst plastic into rods or coarse threads of 
the desired dimensions. If one works carefully the forceps 
do not suffer much. I have had one pair in almost constant 
use for several years ; they have been used in the training of 
five beginners and are still practically uninjured. 

1 This U to avoid bubbles in the finished glaa* 



PRECAUTIONS. 91 



The beginner should work with a gauge and regulator on 
the bottle of oxygen, and should watch the consumption of 
oxygen closely. A large expenditure of oxygen does not 
by any means necessarily imply a corresponding output of 
silica, even by one who has mastered the initial difficulties. 

When a supply of the small rods of vitreous silica has 
been provided, bind a few of them round a rod of platinum 
(diameter say, 1mm.) by means of platinum wires at the 
two ends and heat the silica gradually, beginning at one end 
after slightly withdrawing the platinum core from that end, 
till a rough tube about four or five centimetres in length 
has been formed. Close one end of this, expand it, by 
blowing, into a small bulb, attach a silica rod to the remote 
end of the bulb, reheat the bulb and draw it out into a 
fine tube. Blow a fresh bulb on one end of this and again 
draw it out, proceeding in this way till you have a tube 
about six or eight centimetres in length All larger tubes 
and vessels are produced by developing this fine tube 
suitably. 

Precautions. The following points must be carefully 
kept in mind, both during the making of the first tube and 
afterwards : 

(1) The hottest spot in the oxy-gas flame is at a point 
very near the tip of the inner cone of the flame, and silica 
can be softened best at this hot spot. The excellence of a 
burner does not depend on the size of its flame, so much as 
on the temperature of its "hot spot," and the success of the 
worker depends on his skill in bringing his work exactly to 
this part of the flame. Comparatively large masses of silica 
may be softened in a comparatively small jet if the hot spot 
is properly utilised. 

(2) Silica is very apt to exhibit a phenomenon resembling 



92 GLASS-flLOH'IHG. 

devitrification during working. It becomes covered with a 
white incrustation, which seems to be comparatively rich in 
alkali. 1 This incrustation is very easily removed by re- 
heating the whitened surface, provided that the material 
has been kept scrupulously clean. If the silica has been 
brought into the flame when dusty, or even after much 
contact with the hands of the operator, its surface is very 
apt to be permanently injured. Too much attention cannot be 
given 9 cdtmlinnt by the workman. 

(3) When a heated tube or bulb of silica is to be expanded 
by blowing, it is best not to remove it from the flame, for 
if that is done it will lose its plasticity quickly unless it be 
large. The better plan is to move it slightly from the " hot 
spot" into the surrounding parts of the flame at the moment 
of blowing. 

It is best to blow the bulb through an india rubber 
tube attached to the open end of the silica tube. At 
first one frequently bursts the bulbs when doing this, but 
holes are easily repaired by stopping them with plastic sili. ;i 
applied by the softened end of a fine rod of silica :m<l 
expanding the lump, after reheating it, by blowing. After 
a few hours' practice these mishaps gradually become rare. 

I find it a good plan to interpose a glass tube packed 
with granulated potash between the mouth and the silica 
tube. This prevents the interior of the tube from being 
soiled. The purifying material must not be packed so closely 
in the tube as to prevent air from passing freely through it 
under a very low pressure. 

- It may be mentioned here that a finished tube usually 
contains a little moisture, and a recognisable quantity of 
nitric peroxide. These may be removed by heating th< 

1 The rock crystal exhibits a yellow flame when first heated in the 
oxy-gaa flame, and moat samples contain spectroscopic quantities of 

lithium. 



MAKING LARGER TUBES AND APPARATUS. 93 

tube and drawing filtered air through it, but not by 
washing, as it is difficult to obtain water which leaves no 
residue on the silica. 

Making larger tubes and other apparatus of 
Silica. In order to convert a small bulb of silica into a 
larger one or into a large tube, proceed as follows : Heat 
one end of a fine rod of silica and apply it to the bulb 
so as to form a ring as shown in the figure. Then 
heat the ring and the end of the bulb till it softens, 
and expand the end by blowing. If this process 
is repeated, the bulb first becomes ovate and 
then forms a short tube which can be lengthened 
at will, but the most convenient way to obtain a 
very long tube is to make several shorter tubes of 
the required diameter, and say 200 to 250 mm. in 
length, and to join these end to end. It does not 
answer to add lumps of silica to the end of the 
bulb, for the sides of the tube made in this way 
become too thin, and blow-holes are constantly 
formed during the making of them. These can 
be mended, it is true, but they spoil the appearance 
of the work. 

Tubes made in the manner described above are 
thickened by adding rings of silica and blowing 
them when hot to spread the silica. If a combina- 
tion of several jets is employed, very large tubes 
can be constructed in this way. One of Messrs. Baird and 
Tatlock's workmen lately blew a bulb about 5 cm. in diameter, 
and it was clear that he could have converted it into a 
long cylindrical tube of equal diameter had it been neces- 
sary to do so. 

Very thin tubes of 1 '5 cm. diameter, and tubes of consider- 
able thickness and of equal size, are easily made after some 




94 GLASS-BLOWING. 

practice, and fine capilliaries and millimetre tube can be 
made with about equal readiness. 

If a very fine tube of even bore is required, it may be 
drawn from a small thick cylinder after a little practice. 

When a tube becomes so large that it cannot be heated 
uniformly on all sides by rotating it in the flame, it is con- 
venient to place a sheet of silica in front of the flame a little 
beyond the object to be heated, in order that the former may 
throw back the flame on those parts of the tube which are 
most remote from the jet A suitable plate may be made 
by sticking together small lumps of silica rendered plastic 
by heat. 

The silica tubes thus made can be cut and broken like 
glass, they can be joined together before the flame, and th \ 
can also be drawn into smaller tubes when softened by heat. 

In order to make a side connection as in a T piece, a rim: 
of silica should be applied to the tube in the position fixed 
upon for the joint This ring must then be slightly expanded, 
a new ring added, and so on, till a short side tube is formed. 
To this it is easy to seal a longer tube of the required dimen- 
sions. It is thus possible to produce Geissler tubes, small 
distilling flasks, etc. Solid rods of silica are easily made by 
pressing together the softened ends of the fine rods or thread! 
previously mentioned. Such rods and small mallei can be 
ground and polished without annealing them. 

Quartz Fibres. These were introduced into pli 
work by Mr. Boys in 1889. They may be made by attaching 
a fine rod of vitrified quartz to the tail of a small straw 
arrow provided with a needle point; placing the arrow in 
position on a cross-bow, heating the rod of silica till it is 
thoroughly softened and then letting the arrow fly from the 
bow, when it will carry with it an extremely fine thread of 
silica. A little practice is necessary to ensure success, l-ut 



QUARTZ FIBRES. 95 

a good operator can produce threads of great tenacity and 
great uniformity. Fuller accounts of the process and of 
the various properties and uses of quartz fibres will be 
found in Mr. Boys' lectures (Roy. Inst. Proc. 1889, and 
Proc. Brit. Assn. 1890), and in Mr. Threlf all's Laboratory 
Arts. 



VITREOUS SILICA. 



BAIRD & TATLOCK, LONDON, 
are Makers of Non-Splintering Silica, Silica 
Tubes, and Silica Apparatus generally, and 
supply all the Apparatus required for working 
Silica before the Blow-pipe. Method of making 
Silica can be seen at their Works. List, etc.. 
on application. 



BAIRD & TATLOCK 

flfcamifacturcrs ot CbcmicaU JSactcrtoIOfiical, 
and Hseap apparatus 



14 CROSS STREET 

HATTON GARDEN 

LONDON, E.G. 



No. 749 Hoi WORK. TJKAPHic AoDioww : ' Bcwrrnt, I 



INDEX. 



Air-traps, 69. 

Annealing, 23. 

Apparatus needed for Glass-work- 
ing, 11. 

Appendix, 82. 

Beginners, Failures of, 22. 

Bellows, Position of, 3. 

Various forms of, 7. See 

also Blower. 

Bending Glass Tubes, 28. 

Blower, Automatic, 8. 

Blow-pipe, Cheap form of, 4. 

Dimensions of, 4-5. 

Fletcher's Automaton, 6. 

Fletcher's Compound, C. 

Gimmingham's, 6. 

Herapath's, 6. 

Jets for the, 7. [Flames. 

Use of the, 8. See also 

Blow-pipes, Use of several m 
combination, 21. 

Brush Flame, 9. 

Oxidising, 20. 

Bulbs, Methods of blowing, 47. 

Calibrating Apparatus, 76-81. 

Camphorated Turpentine, 11. 

Cetti's Vacuum Tap, 66. 

Charcoal Pastils, 1 1 . 

Choking or Contracting the Bores 
of Tubes, 35. 

Combining the Parts of Compli- 
cated Apparatus, 61. [25. 

Combustion Tube, how to work it, 



Contracting theBoreof aTube, 35. 
Cotton Wool for Annealing, 24. 
Cutting Glass Tubes, 26, 27, 28. 
Dividing a Line into Equal Parts, 

75. 

Electrodes, 38, 55. 
Electrolysis, Making Apparatus 

for, 59. 

Files for Cutting Glass, 27. 
Flame, the Pointed, 8. 

the Brush, 9. 

the Oxidising Brush, 20. 

the Smoky, 10. 

Fletcher's Automaton Blow-pipe, 

6. 
Fletcher's Compound Blow-pipe, 

6. 

Funnels, Thistle-headed, 57. 
Gimmingham's Blow-pipe, 6. 
Gimmingham's Vacuum Tap, 68. 
Glass, Annealing, 23. 

Devitrification of, 15. 

Method of Working with 

Lead, 17. 
Method of Working with 

Soda, 22. 

Nature of, 12. 

Presenting to the Flame, 16. 

Glass Tubes, Bending, 28. 

Bordering, 31. 

Characters of good, 14. 

Choking, 35. 

Cleaning, 15. 



9 8 



INDEX. 



Olass Tubes, Cutting, 26, 27, 28 
Piercing, 37. 

Purchase of, 12. 

- Sealing, 32. 

Sealing Hermetically, 58. 

Sizes of, 82. 

Welding or Soldering, 39, 62. 

Widening the Ends of, 36. 

Graduating Apparatus, 70. 

Grinding Stoppers, 51. 

Herapath's Blow-pipe, 6. 

Hofuian's Apparatus for Electro- 
lysis, 59. 

Inside Joints, 43. 

Jets for Blow-pipes, 7. 

Joints, Air-tight, 64. 

Lead Glass, Method of Working 
with, 17. 

Lead Glass, Blackening of, 17. 

Light, Effect of, in Working, 3. 

Line, to Divide into Equal Parts, 
75. 

Mercury Joints, Various, 64. 

Non-splintering Silica, Prepara- 
tion of, from Quartz, 83. 

Ozone Generator, To Make an, 
44. 

Pastils of Charcoal, 11. 

Piercing Tubes, eta, 37. 

Platinum Electrodes, Sealing in, 
38, 55. 

Pointed Flame, the, 9. 

Quartz Fibres, 94. 

Rounding Ends of Tubes, 31. 

Sealing or Closing Openings in 
Tubes, 32. 

Side-tubes, Fixing, 41. 

Smoky Flame. 10. 

Soda Glass, Method of Working, 
22. 



Soldering or Welding, 39, 62. 

Spiral Tubes, 56. 

Stoppers, Making and Grinding, 

51. 

Table for Glass-blower, 3. 
Taps, Vacuum, 65. 
Thistle-headed Funnels, 57. 
Traps, Air, 69. 
Tube, Combustion, how to work 

it, 25. 
Tubes. 'e Glass Tubes. 

- T., 41. 
U-, 56. 

Turpentine, Camphorated, for 
Grinding, 11. 

U-Tubes, 56. 

Vacuum Taps, 65-68. 

Tube, To Make a, 60. 

Vitreous Silica, Apparatus re- 
quired for Making, 89. 

Behaviour under sudden 

changes of Temperature, 87. 

Bulbs, etc., Making Joints 

on, 93. 

Expansion of, 86. 

Hardness of, 85. 

- Insulating Power of, 85. 

- Melting Point of, 85. 

Permeability to Gases, 87. 

Properties of, 84. 

Rods, Making Joints on, 94. 

- Tube*, Method of Making, 
90. 

Tubes, Making Joints on, 

94. 

Welding or Soldering Tubes to- 
gether, 39, 62. 

White Enamel, Uses of, 39, 50. 

Widening the Ends of Tubes, 36. 

Working-place, 2. 



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at the Edinb 




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