(1) The solution, poured into a large volume of warm distilled water, gives a crystalline precipitate of subnitrate of bismuth. The only metal giving a similar reaction is antimony, and this is excluded by the method employed.
(2) The filtered fluid gives on addition of sodic chloride a precipitate of oxychloride. This, again, is distinguished from oxychloride of antimony by its insolubility in tartaric acid.
(3) Any bismuth precipitate, fused with soda on charcoal, gives a brittle bead of bismuth; the coal is coated whilst warm a dark orange-yellow, on cooling citron-yellow.
(4) The bead may be identified by powdering it, placing it in a short subliming tube, and passing over it dry chlorine. The powder first turns black, then melts to an amber-yellow fluid, and finally, by prolonged heating, sublimes as terchloride of bismuth.
(5) A very delicate test proposed by Abel and Field, in 1862,[894] specially for the detection of bismuth in copper (but by no means confined to mineral analysis), utilises the fact that, if iodide of lead be precipitated from a fluid containing the least trace of bismuth, instead of the yellow iodide the scales assume a dark orange to a crimson tint. A solution of nitrate of lead is used; to the nitric acid solution ammonia and carbonate of ammonia added; the precipitate washed, and dissolved in acetic acid; and, finally, excess of iodide of potassium added. It is said that thus so small a quantity as ·00025 grm. may be detected in copper with the greatest ease, the iodide of lead becoming dark orange; ·001 grain imparts a reddish-brown tinge, and ·01 grain a crimson.
[894] Journ. Chem. Soc., 1862, vol. xiv. p. 290; Chem. News, vol. xxxvi. p. 261.
(6) A solution of a bismuth salt, which must contain no free HCl, when treated with 10 parts of water, 2 of potassium iodide, and 1 part of cinchonine, gives a red orange precipitate of cinchonine iod.-bismuth.[895]