BLOWPIPE. A con ical tube of metal ter minating in a small opening, and used in the arts for soldering metals.
and in mineralogy and analytical chemistry for determining the nature of substances. According to Berzelius. Anton von Swab, a Swedish counsel or of mines, first used the blowpipe in 1738 to test minerals and ores, Its use extended from Sweden to Germany, and t hence throughout the Continent of Europe and to England. Cronstedt, Bergman, Galin, and Berzelius have successively introduced valuable improvements in the form of the blowpipe. The present form, however, is due to Plattner and his successors in the Royal Saxon 1Nlining Acade my in Freiberg.
The blowpipe most commonly used in doing analytical work consists of a conical brass tube about S inches long, terminating at the wider end in a convenient mouthpiece made of horn or rubber, while at the lower end a small tube with a finely perforated nozzle and a platinum tip is inserted at right angles to the larger tube slightly above its end, the space below being in tended as a chamber for the moisture from the breath.
When the nozzle of the blowpipe is placed within an ordinary flame and a somewhat strong current of air is blown through it, the flame is projected in a lateral direction as a long, point ed cone; the air thus supplied being sufficient for complete combustion, the flame is colored blue and is very hot. If the point of this flame is directed against metals, the latter are rapidly transformed into their oxides, and hence the flame is called an oxidizing flame. On the other hand, when the nozzle of the blowpipe is placed near but outside a flame, and a gentle current of air is blown through it, the flame retains its luminosity, and. owing to the presence in it of incandescent carbon, is capable of reducing oxides to the metallic state: whence the name, reducing flame. See also FLAME.
In certain tests the substance is heated before the blowpipe on a piece of charcoal, the forma tion of colored coatings often indieating the nature of the compound; thus, lead deposits on the charcoal a yellow coating of its oxide. In
other tests the substance examined is mixed with reagents, usually borax, sodium carbonate, mi crocosmic salt, and cobalt nitrate. The first four of these form, with metallic oxides, colored glass-like heads which serve to determine the eomposition of the substance. With borax, a bottle-green glass bead is obtained when iron salts are present: an amethyst-colored bead in dicates manganese, and a blue-colored bead, co balt. Sodium carbonate and mieroeosmic salt also yield characteristic colored beads that serve to indieate the presence of certain ingredients. The solution of cobalt nitrate, when applied to a powder on a piece of charcoal, yields charac teristic colors for certain compounds that are distinctive, notably the blue coloration for alu minium salts.
Blowpipe analysis is generally used for quali tative determinations, and finds its greatest ap plication in fieldwork as an easy means for determining the composition of minerals. In certain cases, it is possible to make also a quan titative estimation of ores, especially those of silver and lead, by the use of the blowpipe. But the insignificant quantity of the indterial that is employed renders the result scarcely precise enough even for the purposes of technical analy sis.
The blowpipe is the common instrument used by goldsmiths and jewelers for soldering metals. It is also ivied by.,01ass-blowers in their work, hut in their manipulations the form of the blow pipe is usually the Bunsen blast-lamp, in which the heat of the gas-flame is increased by a cur rent of air that is supplied front a bellows.
Consult: H. B. Cornwall, Manual of Blow pipe Analysis, Qualitative and Quantitative, with a Complete System of Determinative Min eralogy (New York, 1801) : C. F. Plattner, Manual of Qualitative and Quantitative Analysis with the Blowpipe, trans. Cornwall (New York, 1S92) : W. A. Ross, The Blowpipe in Chemistry, Mineralogy, and Geology (London, 1889) ; and Moses and Parsons, Elements of Mineralogy, Crystallography, and Blowpipe Analysis from a Practical Standpoint (Ne• York, 1895). See ANALYSIS, CHEMICAL.