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Encyclopedia Britannica - Main :: BLA-BOS |
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BLOWPIPE , in the arts and chemistry, a tube for directing a jet of air into a fire or into the flame of a lamp or gas jet, for the purpose of producing a high temperature by accelerating the combustion. The blowpipe has been in common use from the earliest times for soldering metals and working glass, but its introduction into systematic chemical analysis is to beascribed to A. F. Cronstedt, and not to Anton Swab, as has been maintained (see J. Landauer, Bey. 26, p. 898). The first work on this application of the blowpipe was by G. v. Engestrom, and was published in 1770 as an appendix to a treatise on mineralogy
Berzelius
The simplest and oldest form of blowpipe is a conical brass tube, about 7 in. in length, curved at the small end into a right angle, and terminating in a small 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 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 Joseph Black's instrument consists of a conical tube of tin 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 o5 mm. A trumpet mouth-piece is recommended from the support it gives to the cheeks when inflated. The mode of blowing is peculiar, and requires some practice; an uninterrupted blast is kept up by the muscular action of the cheeks, while the ordinary respiration goes on through the nostrils.If the flame of a candle or lamp be closely examined, it will be seen to consist of four parts(a) a deep blue ring at the base, (b) a dark cone
cone
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 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 nucleus about the wick. The substance to be reduced is brought into the luminous portion, where the reducing power is strongest.Various materials are used as supports for substances in the blowpipe flame; the principal are charcoal, platinum and glass or porcelain
wood
The mouth blowpipe is unsuitable for the 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 mechanical means. The laboratory form in common use consists of a bellows worked by either hand or foot, and a special
supply of air and gas being regulated by stopcocks. The hot blast blow-pipe of T. Fletcher, in which the blast is heated by passing through a copper coil heated by a 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, Russell & Co., and have proved of 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: Analytical. End of Article: BLOWPIPE If you wish, you can link directly to this article.
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