The Art of Glass-Blowing / Plain Instruction for the Making of Chemical and Philosophical Instruments Which are Formed of Glass

by T.-P. Danger

BLOWPIPE WITH CONTINUED CURRENT.

It is after having, during a long period, made use of the instruments of which we have spoken, and fully experienced their inconveniences, that, aware of the indispensable necessity for such instruments in the arts and sciences, we have thought it our duty to make known to the public a New Apparatus, which is, not only calculated to fulfil the same purposes, but presents advantages which it is easy to appreciate. The price of it is only the sixth part of that of the glass-blower’s table[1]. It is very portable, and capable of being attached to any table whatever. It unites the advantages of not fatiguing the workman, of leaving his hands free, and of rendering him absolute master of the current of air, which he can direct on the flame either of the lamp or the candle,—advantages which are not offered in the same degree even by the table of the glass-blower.

[1] In Paris, the blowpipe which is here described is sold for six francs (five shillings English); or, with the improved lamp and candlestick, twelve francs.

The instrument which we have presented is, properly speaking, nothing but a simple blowpipe, C, ([pl. 1], fig. 19) communicating with a bladder, or leather bag, fixed on E, which is kept full of air by means of a bent tube, D, through which the operator blows occasionally with the mouth. This tube is closed at its inferior extremity, F, by a valve, which permits the passage of air into the reservoir, but not of its return, so that the air can only escape by the beak of the blowpipe.

The valve at F is constructed in the following manner:—At about two inches from the end of the tube a contraction is made, as represented at a, [pl. 1], fig. 24. This reduces the internal diameter of the tube about one-third. A small conical piece of cork or wood is now introduced into the tube in the manner represented by c. The base of the cone must be large enough to close the tube at the point where it is contracted; it must, however, not be so large as to close the tube at the wide part. A brass pin is inserted in the point of the cone, as is shewn in the figure. Between the cone and the end of the tube, the piece of wood, b, is fixed; the shape of this piece of wood is best shewn by figure 25, on the same plate. There is a hole in the centre, in which the pin of the cork cone can move easily. The cone or valve is therefore at liberty to move between the contraction a, and the fixture b. Consequently, when air is blown into the tube at e, the valve is forced from the contraction, falls into the position indicated by the dotted lines d, and allows the air to pass by its sides. When, on the contrary, the operator ceases to blow, the valve is acted upon by the air in the bladder, which, pressing back at f, drives the valve close against the contraction, and effectually closes the aperture. A slight hissing is heard, but when the contraction is well made, and the cork is good, an extremely small quantity of air escapes.

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.