BLOWPIPE ANALYSIS, a branch of chemical analysis in which the composition of the substance under examination is inferred from its behavior when subjected to certain flame tests. The blowpipe itself commonly con sists of a tapering brass tube about eight inches long, provided with a bell-shaped mouthpiece at one end, and at the other with a nozzle that is turned at right angles to the general length of the instrument. The nozzle should be tipped with platinum, and provided with a very minute perforation through which the operator blows a tiny blast of air that drives the flame of his lamp against the object to be analyzed. The flame used in blowpipe work should not be round and colorless, like those of spirit lamps and Bunsen burners, but should be flat and luminous, containing plenty of free, incandes cent carbon. A large candle-flame serves very well, although it is not flat. Usually a gas flame is employed, in connection with a burner formed by flattening a piece of brass tubing, and then cutting it off at the top, at an angle. When the blowpipe is in service its tip is in troduced into the flame of the lamp, which the air-blast deflects laterally in the form of a long, almost non-luminous cone, which consists of two visibly different portions. The inner part is somewhat brighter, and is richer in unoxidized gases. The outer layer, being more plentifully supplied with oxygen, consists almost entirely of completely oxidized gases. The outer por tion of the blowpipe flame is called the 'oxi dizing flame," since this part, when directed against the specimen under examination, heats it while it is in contact with the air, and causes it to oxidize, if it is capable of doing so at the temperature that is attainable by the blow pipe. The inner portion of the flame is called the "reducing flame," from the fact that when the specimen is exposed to this part, it is heated, not in contact with the air, but while surrounded with an atmosphere of partially unoxidized hydrocarbon gases. Under these circumstances many metallic oxides give up their oxygen to the hot hydrocarbon gases in which they are bathed, and are themselves reduced to the metallic form. If a flame still richer in free carbon and unconsumed hydrocarbons is de sired, the tip of the blowpipe is held just out side of the lamp-flame, and a jet of flame with a luminous tip containing particles of solid carbon can easily be thrown down upon the specimen.
In blowpipe analysis there is no recognized to be followed out. The method is oftenest used for the determination of minerals, and in such cases the analyst usually has some sort of idea, in advance, of the elements that may possibly be present. The substance to be
examined is usually first pulverized, and a por tion of it heated in a tube that is open only at the upper end. If it carbonizes, it contains organic matter of some kind, and the odor that is produced is often a good indication as to whether the organic matter is of an animal or vegetable nature. If the substance, when heated in the closed tubes, gives off water which con denses in the upper part of the tube, the moist ure so condensed should be tested with litmus paper. If it is neutral, the substance is a hy drated compound, or a hydroxide. An acid re action indicates acid salts, and an alkaline one may usually be taken to indicate the presence of compounds of ammonia. If the substance melts but does not change its color, it is an alkaline or a hydrated salt. If it melts and turns yellow, remaining yellow even after cool ing, it contains oxide of bismuth; while if it melts to a yellow color, but turns red upon cooling, it contains oxide of lead. If it does not melt, but changes color, the indications are as follows : Yellow, both hot and cold, indi cates stannic oxide; if yellow while hot, but white when cold, zinc oxide; if black while hot, and reddish-brown when cold ferric oxide; if black while hot, but bright red when cold, mer curic oxide. If gas is evolved, its nature should be determined. Oxygen may be detected by the kindling of a glowing splinter of wood inserted into the tube; carbon dioxide by its extinguish ing such a spark promptly; carbon monoxide by the gas burning with a bluish flame when ignited at the mouth of the tube; sulphur dioxide, ammonia and cyanogen, by the odor. Oxygen indicates chlorates, peroxides, etc.; carbon diox ide indicates carbonates or oxalates; carbon monoxide indicates oxalates or formates; sul phur dioxide indicates certain sulphites or sul phates • cyanogen indicates cyanides ; and ammo nia indicates some compound of that substance. If the gas is reddish-brown in color, bromides, nitrates or nitrites, are probably present; if it is violet, an iodide is indicated. A sublimate may also be deposited upon the tube. If the sublimate is black, or nearly so, selenium or mercuric sulphide are indicated; if yellow, sul phur or a sulphide; if white, a salt of ammo nia or mercury, a volatile organic acid or an oxide of antimony or arsenic. Gray metallic globules indicate mercury, and a metallic mir ror may represent either antimony or arsenic.