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BLOWPIPE
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BLOWPIPE , in the arts and See also:chemistry, a See also:tube for directing a See also:jet of See also:air into a See also:fire or into the See also:flame of a See also:lamp or See also:gas jet, for the purpose of producing a high temperature by accelerating the See also:combustion. The blowpipe has been in See also:common use from the earliest times for soldering metals and working See also:glass, but its introduction into systematic chemical See also:analysis is to beascribed to A. F. Cronstedt, and not to Anton Swab, as has been maintained (see J. Landauer, See also:Bey. 26, p. 898). The first See also:work on this application of the blowpipe was by G. v. Engestrom, and was published in 1770 as an appendix to a See also:treatise on See also:mineralogy. Its application has been variously improved at the hands of T. O. See also:Bergman, J. G. Gahm, J. J. See also:Berzelius, C. F. See also:Plattner and others, but more especially by the two last-named chemists. The simplest and See also:oldest See also:form of blowpipe is a conical See also:brass tube, about 7 in. in length, curved at the small end into a right See also:angle, and terminating in a small See also:round orifice, which is applied to the flame, while the larger end is applied to the mouth. Where the blast has to be kept up for only a few seconds, this See also:instrument is quite serviceable, but in longer chemical operations inconvenience arises from the condensation of moisture exhaled by the lungs in the tube. Hence most blowpipes are now made with a cavity for retaining the moisture. Cronstedt placed a bulb in the centre of his blowpipe. Dr See also:Joseph See also:Black's instrument consists of a conical tube of See also:tin See also:plate, with a small brass tube, supporting the nozzle, inserted near the wider end, and a mouth-piece at the narrow end. The sizes of orifice recommended by Plattner are 0.4 and o•5 mm. A See also:trumpet mouth-piece is recommended from the support it gives to the cheeks when inflated. The mode of blowing is See also:peculiar, and requires some practice; an uninterrupted blast is kept up by the See also:muscular See also:action of the cheeks, while the See also:ordinary respiration goes on through the nostrils. If the flame of a See also:candle or lamp be closely examined, it will be seen to consist of four parts—(a) a deep See also:blue See also:ring at the See also:base, (b) a dark See also:cone in the centre, (c) a luminous portion round this, and (d) an exterior See also:pale blue envelope (see See also:llama). In See also:blow-See also:pipe work only two of these four parts are made use of, viz. the pale envelope, for oxidation, and the luminous portion, for reduction. To obtain a See also:good oxidizing flame, the blowpipe is held with its nozzle inserted in the edge of the flame See also:close over the level of the See also:wick, and blown into gently and evenly. A conical jet is thus produced, consisting of an inner cone, with an See also:outer one commencing near its apex—the former, corresponding to (a) in the See also:free flame, blue and well defined; the latter corresponding to (d), pale blue and vague. The See also:heat is greatest just beyond the point of the inner cone, combustion being there most See also:complete. Oxidation is better effected (if a very high temperature be not required) the farther the substance is from the See also:apex of the inner cone, for the air has thus freer See also:access. To obtain a good reducing flame (in which the combustible See also:matter, very hot, but not yet burned, is disposed to take See also:oxygen from any See also:compound containing it), the nozzle, with smaller orifice, should just See also:touch the flame at a point higher above the wick, and a somewhat weaker current of air should be blown. The flame then appears as a See also:long, narrow, luminous cone, the end being enveloped by a dimly visible portion of flame corresponding to that which surrounds the free flame, while there is also a dark See also:nucleus about the wick. The substance to be reduced is brought into the luminous portion, where the reducing See also:power is strongest. Various materials are used as supports for substances in the blowpipe flame; the See also:principal are See also:charcoal, See also:platinum and glass or See also:porcelain. Charcoal is valuable for its infusibility and See also:low conductivity for heat (allowing substances to be strongly heated upon it), and for its powerful reducing properties; so that it is chiefly employed in testing the fusibility of minerals and in reduction. The best See also:kind of charcoal is that of close-grained See also:pine or See also:alder; it is cut in See also:short prisms, having a See also:flat smooth See also:surface at right angles to the rings of growth. In this a shallow hole is made for receiving the substance to be held in the flame. Gas-See also:carbon is sometimes used, since it is more permanent in the flame than See also:wood charcoal. Platinum is employed in oxidizing processes, and in the See also:fusion of substances with fluxes; also in observing the colouring effect of substances on the blow-pipe flame (which effect is See also:apt to be somewhat masked by See also:char-See also:coal). Most commonly it is used in the form of See also:wire, with a small See also:bend or See also:loop at the end. The mouth blowpipe is unsuitable for the See also:production of a large flame, and cannot be used for any lengthy operations; hence recourse must be made to types in which the air-blast is occasioned by See also:mechanical means. The laboratory form in common use consists of a See also:bellows worked by either See also:hand or See also:foot, and a See also:special type of gas burner formed of two concentric tubes, one conveying the blast, the other the gas; the See also:supply of air and gas being regulated by stopcocks. The hot blast blow-pipe of T. See also:Fletcher, in which the blast is heated by passing through a See also:copper coil heated by a See also:separate burner, is only of service when a pointed flame of a fairly high temperature is required. Blowpipes in which oxygen is used as the blast have been manufactured by Fletcher, See also:Russell & Co., and have proved of See also:great service in conducting fusions which require a temperature above that yielded by the air-blowpipe. For the applications of the blowpipe in chemical analysis see CHEMISTRY: See also:Analytical. Additional information and CommentsThere are no comments yet for this article.
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