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 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 G, 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 contracted 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 F, 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 the 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 respectively 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 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 ascertained 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 purchased 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 a single lever-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.