BLOW-PIPE. This instrument, in the simple form in which it has long been em ployed by jewellers and others in soldering upon a small scale, is a metallic tube seven or eight inches long, about a quarter of an inch in diameter at one end, and gradually tapering to a fine point, pierced by an extremely mi nute orifice at the other. The tube is bent to a right angle about an inch or an inch and a half from its smaller extremity ; and, the larger end being inserted in the mouth of the operator, it is used to direct the flame of a lamp upon the solder or other substance to be heated. The substance thus operated upon is laid upon a piece of charcoal held in the left hand of the operator, and a steady gentle current of air is impelled through the pipe by contracting the muscles of the cheek, the mouth having been previously inflated with air. The power of thus producing a blast without the aid of the lungs, and of respiring during the operation, is an important accom. plishment, as without it the health may be injured by the use of the blow-pipe ; and ex perience is necessary to enable the operator to regulate the strength of the blast, which if too great will diminish the heat by throwing too much air into the flame, and if too weak will produce a feeble flame.
In the simplest form of blow-pipe, the col lection of water from the condensed moisture of the breath prevents the continuance of the blast for any length of time. This inconven ience is avoided by making the blow-pipe in two pieces, and interposing between them a receptacle for retaining the water, and prevent ing its entrance to the finer portion of the pipe.
The application of the blow-pipe to scien tific purposes appears to have originated about 1738, when Antony Swab, a Swedish bergrath, or counsellor of mines, employed it in the ex amination of ores and minerals. Cronstedt, whose system of mineralogy, based upon the chemical composition of the minerals, was published in 1758, by the employment of fluxes in the experiments performed with this instrument, may be considered the founder of a new department of chemical science ; Berg man published a Latin treatise embodying the results of his researches with it in 1770 ; and Gahn, though he left no work on the subject, far exceeded any of his predecessors in expe riments with this instrument, the results of which were subsequently given to the world by J. J. Berzelius, in a treatise, of which Eng lish, French, and German translations have appeared.
Modifications of the common blow-pipe have been contrived with jets of hydrogen or oxy gen, or of the two gases combined in definite proportions. By the oxyhydrogen blow-pipe, which, though highly dangerous in the form in which it was originally contrived by Dr. Hare, of Philadelphia, early in the present century, has by successive improvements, been rendered a safe apparatus, the hardest and most refractory substances, including all kinds of jewels and other stones, metals, rock crys tal, and every description of porcelain, may be fused or sublimed, and the most brilliant effects of combustion may be produced.