The workman, seated before the table where he has fixed his instrument, blows from time to time, to feed the reservoir or bladder, which, being pressed by a system of strings stretched by a weight, produces an uniform current of air. The force of this current of air can be modified at pleasure, by pressing the reservoir more or less between the knees. (Fig. 22 represents a blowpipe complete, formed not of glass, but of brass tubes. Fig. 22, bis, represents the bladder or reservoir appertaining to this blowpipe.)
M. Gaultier de Claubry, who was charged by the Committee of Chemical Arts of the Society of Encouragement (of Paris) to make a report on this instrument, was astonished at the facility with which the author, in his presence, reduced the oxide of cobalt to the metallic state, and fused the metal to a globule; an experiment which even M. Berzelius could not perform with the simple blowpipe, since he expressly says, in his work on that instrument, that oxide of cobalt suffers no change when heated before the blowpipe. The results obtained with cast iron, oxide of tin, &c.—experiments which are exhibited every day at the public lectures given by the author—evidently prove the superiority of this apparatus over all the blowpipes that have hitherto been contrived.
A detailed account of the glass tubes belonging to this improved blowpipe will be found in the fourth part of this work, at the article Blowpipe.
THE LAMP.
While occupied in rendering popular, if we may so speak, the use of the blowpipe—an instrument which is so advantageous in a great number of circumstances—we have also endeavoured to improve the lamp, which has, until the present time, been used by all those who employ the glass-blower’s table. The lamp which we recommend ([pl. 1], fig. 23) is of a very simple construction. It possesses the advantages of giving much less smoke than the old lamp, and of being cleaned with the greatest facility. It also gives sensibly more heat; because the portion of flame which, in the common lamps, rises perpendicularly, and is not used, is, in this case, beaten down by a cap or hood, and made to contribute to the force of the jet. This cap also keeps the flame from injuring the eyes of the operator, and destroys the smoke to such an extent, that the large hoods with which glass-blowers commonly garnish their work table, to carry off the smoke, become unnecessary. This is a peculiar advantage in the chamber of a student, where a large hood or chimney can seldom be conveniently prepared.
THE CANDLESTICK.
For mineralogical researches, chemical assays, and the soldering of small objects, as in jewellery, we recommend the use of a little candlestick, which, by means of a spring fixed to the bottom, maintains the candle always at the same height. A reservoir, or shallow cup, formed at the top of the candlestick, to hinder the running away of the tallow or wax, allows the operator to consume the fragments of tallow or grease which are ordinarily lost in domestic economy. There is a little hole in the centre of the cup or upper part of the candlestick, through which the wick of the candle passes. o, [pl. 1], fig. 22, is a representation of this candlestick.
COMBUSTIBLES.
Oil, Tallow, &c.—Among the substances which have been employed to feed the fire of the glass-blower’s lamp, those to which the preference is to be given are wax, olive oil, rape oil, poppy oil, and tallow. Animal oils, such as bone oil and fish oil, are much esteemed by some glass-blowers, who pretend that with these substances they obtain better results than with other combustibles. Nevertheless, animal oils, generally speaking, do not give so much heat as purified rape oil, while they exhale an odour which is extremely disagreeable.
As to alcohol, which is sometimes used with the eolipyle, its combustion furnishes so feeble a degree of heat that its employment cannot be recommended.