tag="{http://www.w3.org/1999/xhtml}a">Properties of Vitreous Silica—Preparing non-splintering Silica from Brazil Pebble—Apparatus—The Method of Making Silica Tubes—Precautions—Making Larger Tubes and other Apparatus of Silica—Quartz Fibres,

CHAPTER I.

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 operations 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 devote sufficient time to acquiring the necessary manipulative dexterity, to prepare such apparatus as test-tubes, distillation 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 appearance 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 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-blowing, 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, preferably 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 construction 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 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 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