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.
Fig. 2
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 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.
