The tube D F has four-tenths of an inch internal diameter, and is pretty thick in the sides. You must commence by bordering and slightly widening one of its extremities, and then proceed to choke it at about two inches from its other extremity, taking care to give to the choked part a figure as perfectly conical as possible, in order that the valve may act well. We have described the valve at length at p. 6.
The tube d is as much narrower than the tube D F as is necessary to permit it to pass up and down within the latter. Its use is to lengthen or shorten the tube for the convenience of the blower. The lower end is wound round with waxed thread, to make it fit air-tight. The mouth-piece is executed by widening the end of the tube, and then, while the widened part is still soft, by pressing the two sides obliquely, one against the other. By this means you give to the mouth-piece a flattened form, which adapts it better to the lips. The tube is finished by slightly bending this extremity.
In order that the bladder, or air reservoir, may be conveniently and securely attached to the tube E, you must take care to widen the end of this tube, and to turn up the edges strongly, by pressing the soft end against a flat metallic surface.
Capsules.—These are very small mercury funnels, of which the opening or neck has been closed. To transform these funnels into capsules, you must cut the neck as close as possible, and then soften, close, and flatten the opening. In performing this operation, hold the capsule by the edge with your pincers, and employ a piece of metal to press the glass together and make it close the hole and form the flat bottom of the capsule. See [pl. 2], fig. 23.
Another Method.—After having blown a bulb at the end of a point, soften a narrow zone of the bulb, and then blow suddenly and strongly into it; by which means you separate the bulb into two capsules, which only need to be bordered. If you find any difficulty in presenting to the flame the capsule which forms the part of the bulb opposed to the point, you can attach to it a little rod of glass, which you can afterwards easily separate by a slight smart blow.
Occasionally you will have to make capsules with double sides, which will be described at the article Nicholson’s Hydrometer.
Cartesian Devils.—Blow a bulb at the extremity of a very small tube, and heat a portion of the bulb, for the purpose of prolonging it into a beak. This can be effected with the aid of an auxiliary tube, which, on being joined to the heated part of the bulb, carries away with it the portion of glass which adheres. This portion of the bulb becomes thus prolonged into a little point, which must be cut at its extremity, so as to leave a small opening. The principal tube must be cut at the distance of half an inch from the bulb, and the ends of it must be drawn out and twisted into a ring. Instead of forming laterally a little beak to the bulb, you may pierce the tail, after twisting it into the form of a ring, or you may manage in such a manner as not to obliterate the canal of the twisted part. In general, little enamel figures are suspended to the ring of these globes, as is represented by [pl. 2], fig. 22. A simple bulb, blown at the extremity of a small portion of tube, can supply the place of the Ludion or Cartesian devil. See [pl. 2], fig. 8.