FLAME REACTIONS BY JACOB PAPISH
I n an attempt to explain the chemistry of some flames, Smithellsl proved that carbon ‘is set free in a hydrocarbon flame. He also showed2 that metallic copper can be made to precipitate from the flame of a Bunsen burner which had been charged with a copper salt. Bancroft and W e i ~ e r ,independently ~ of the work of Smithells, have arrived a t the conclusion that it is impossible to account for the flame spectra of copper salts without postulating the existence of free copper in some flames. Experiments with copper chloride confirmed the soundness of this conclusion. Extending their experimental work to other metallic salts, Bancroft and Weiser4 proved that many of these salts dissociate at the temperature of the Bunsen flame, of the hydrogen-air flame, or of the oxyhydrogen flame, the metals being set free. The authors obtained metallic mirrors from the following compounds : Copper chloride, cadmium chloride, stannous chloride, silver nitrate, bismuth nitrate, lead nitrate, zinc chloride, arsenious oxide, antimony trichloride, molybdenum oxide and tungsten oxide. Mercuric oxide, when subjected to similar treatment, yielded drops of mercury. Dull red phosphorus was precipitated from phosphorus trichloride in a hydrogen flame, while yellow flowers of sulphur were obtained from sulphur dioxide in a hydrogen flame. Hodgkinson succeeded in precipitating sulphur on a cold object from a moderate-sized sulphur flame. He concluded that this sulphur precipitated because it escaped combustion: it vaporized and condensed on the cold object before igJour. Chem. SOC., 61, 223 (1892). *Phil. Mag., (5) 39, 127 (1895). Jour. Phys. Chem., 18, 252 (1914). Ibid., p. 261. Chem. News, 61, 96 (1890).
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niting. Hodgkinson “does not consider the possibility of free sulphur coming from sulphur dioxide.”l Sulphur, selenium and tellurium, in addition to their numerous properties in common, each imparts to the Bunserl flame a characteristic color. The precipitation of sulphur from a sulphur flame, and from a flame charged with sulphur dioxide, suggests the extension of the experiment to selenium . and tellurium. For this purppse the material; were prepared as follows: Selewiuwz Dioxzde.-Commercial selenium was dissolved in nitric acid with the aid of hydrxhloric acid, and the solution was evaporated to dryness. The residue was sublimed, and the sublimate was dissolved in water. The filtered solution was strongly acidified with hydrochloric acid and saturated with sulphur dioxide gas. The precipitated selenium was removed, washed with water, fused and cast in blocks. Selenium dioxide was prepared by dissolving these blocks, previously pulverized, in nitric acid with the aid of heat. Careful evaporation with repeated portions of water, and heating to dryness, yielded a product free from nirtic acid. Tellurium Dioxide.-Pulverized commercial tellurium was dissolved in aqua regia with the aid of heat. The white maSs was heated to dryness, fused in a porcelain crucible and poured in water. The granular mass was collected, dissolved in the least amount of hot strong hydrochloric acid, and this solution was diluted with a large excess of cold water. The white precipitate was filtered and washed with cold water with the aid of a suction pump. The washed product was fused in a porcelain crucible and allowed to solidify. The oxides of selenium and tellurjum thus obtained weie considered pure enough for the experimental work undertaken. These oxides were introduced ;tl the Bunsen flame in a manner similar to the one employed by Bancroft and Weiser : ? “A small hole was bored in the tube of the Bunsen burner about two inches from the top. A hard glass tube Bancroft and Weiser. Jour. Phys. Chem., 18,248 (1914). Ibid , p. z j 3 .
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of small diameter was drawn out to a jet that would fit this hole. Some of the dry salt (in this case, oxide) was placed in the glass tube. The tube was then heated, and a very slow current of air passed through it. The fumes of the volatilized salt (oxide) were thus carried into the burner and up into the flame. This secures a fairly uniform distribution OF the salt (oxide) throughout the flame.” A four-inch porcelain evaporating dish containing cold water was used as the cold object, and it gave satisfactory results. Selenium Dioxide.-This substance volatilizes very readily, coloring the flame intensely blue. Elementary selenium was easily precipitated on the cold object in the form of a dark red stain surrounded by an area of brighter red, which terminated in yellow. Tellurium Dioxide.-The vapors from tellurium dioxide imparted to the flame a blue color slightly modified by green. The uppermost part of the flame was distinctly green. A bright metallic mirror was easily produced on the cold object when the latter was held in the hottest portion of the flame.
Conclusions It was proved by different experimenters that metallic salts and other compounds are dissociated or reduced in the flame, and that this dissociation or reduction is the cause of a characteristic luminescence or spectrum. To this list of compounds the oxides oi selenium and tellurium should be added, since elementary selenium and tellurium can be easily precipitated from a Bunsen flame charged with their oxides. Selenium precipitates as the red variety, while tellurium yields a bright metallic mirror. Indiana Uniuersity
