BLOW-PIPE, an instrument for directing the flame of a lamp or candle horizontally, so as to com municate an intense heat to small bodies placed in the flame. This is effected by impelling through a small aperture, against the flame, a stream of air moved with velocity, by means of the muscles of respiration and the mouth, or by a bellows. The Blow-pipe is used in soldering, by the jeweller and goldsmith, and other artists, who fabricate small objects of metal ; by the glass-blower, in making thermometers and barome ters, and other instruments made from the -tubes which are got from the glasshouse; by the enamel ler ; and in glass-pinching, which is the art of forming glass in a mould fixed on a pair of pincers, into the ornamental pendants for glass lustres. This is one of the.many ingenious processes carried on at Birming ham. The glass-blower, the enameller, and the glass-pincher, work their blow-pipe with the blast from a pair of bellows. As the process of soldering requires a shorter continuance of the blast, the blow-pipe for this purpose is blown by the mouth. By the mineralogist and chemist, the blow-pipe is used as an instrument for extemporaneous analysis in the du way.
Fig. 1Mate XXX 1V. is the common blow-pipe used in soldering ; it is of brass. Fig. 2. is Dr Wollaston's blow-pipe, which is composed of three tubes of brass, of an elongated conical form, which are made to fit stiff and air-tight into each when in use, and the two smaller pack into the largest ; so that the instrument, when not in use, occupies a very small space, and may be carried in the pencil-case of a common pocket-book. This, with a piece of platina foil, two or three inches long, to hold the object of experiment to the flame, constitutes a commodious docimastic apparatus for the travelling mineralogist. The three parts of the tube are represented, packed the one within the other, at A, separate at B, and put together ready for use at C, fig. 2.
A second division of blow-pipes consists of those which have a cavity for the purpose of retaining the humidity of the breath, which, without this precau tion, collects into drops when the blowing is con tinued long, and is at last driven upon the matter under operation so as to cool it. They are of various forms ; see figures 3, 4, 5, 6, 7 ; and have been contri ved for the purposes of the chemist and mineralogist. Fig. 3. is of glass or of metal. Fig. 4. is of brass or
of silver, containing no alloy of copper, so that it may not be subject to green rust. This is the form recommended by Bergman in his treatise on the application of the blow-pipe to the purposes of the mineralogist, which is contained in the collection of his works. (See Bergmani Opuscula, Vol. II.) For the facility of cleaning, it is in three pieces, which fit in stiff at A and B. Fig. 5. is of tin, that is to say, tinned iron ; the small pipe A is of brass, and has two or three caps that fit on stiff; each cap is pierced . with a hole of a different diameter, and es NINe bleu issues through This hole, the force of the blast may be varied by chaiiging the cap : this is called Dr Black's Blow-pipe. Fig. 6. is of.silver ; the adjutage, which is of platina, turns on an axis at right angles to the main tube at A, so that it may be made to form different angles with the main tube ; the pro longation B, serves to receive the condensed vapour of the breath. Fig. 7. is of brass ; A is cylindrical, the axis of the cylinder being at right angles to the axis of the blow-pipe. A consists of two pieces, one of which fits air-tight into the other, and may be turned on its axis, so that the pipe of issue may be made to form different angles with the axis of the blow-pipe, us the position of the matter under experi ment may require.
Flame consists of vapour in a state of incandescence. Many substances, both of the vegetable, animal, and mineral kingdoms, have the quality of giving out this incandescent vapour. For domestic uses, and for the arts, organized bodies of the vegetable and ani mal kingdom alone are employed to produce it ; such as oils, some of which are solid, others fluid, at the usual temperature of the air, alcohol, ether, wood, and pit-coal. This latter, though found amongst minerals, is of organized matter, changed and rendered bituminous by a particular process of decomposition. The blow-pipe, by directing the in candescent particles of which the flame consists, so aS to strike against and surround a small body, pro duces the effect of heating the body considerably. The flame used with the blow-pipe, mayiither be the flame of an oil or spirit lamp, or of a candle ; the flame of the carbonated hydrogen gas proceeding from the distillation of pit-coal, is also found advan tageous for this purpose.