If a slip of pure tinfoil be suspended for six hours in a solution, which should not contain more than one-tenth of its bulk of ClH, and exhibit no stain or deposit, it is certain that antimony cannot be present. It may also conveniently be deposited on a platinum dish,[813] by filling the same with the liquid properly acidulated, and inserting a rod of zinc; the metallic antimony can afterwards be washed, dried, and weighed.
[813] According to Fresenius (Zeitschr. f. anal. Chem., i. 445), a solution which contains 1⁄10000 of its weight of antimony, treated in this way, gives in two minutes a brown stain, and in ten a very notable and strong dark brown film. When in the proportion of 1 to 20,000, the reaction begins to be certain after a quarter of an hour; with greater dilution it requires longer time, 1 to 40,000 giving a doubtful reaction, and 1 to 50,000 not responding at all to this test.
Reinsch’s and Marsh’s tests have been already described ([pp. 558] and [559]), and require no further notice. There is, however, a very beautiful and delicate means of detecting antimony, which should not be omitted. It is based upon the action of stibine (SbH3) on sulphur.[814] When this gas is passed over sulphur, it is decomposed according to equation, 2SbH3 + 6S = Sb2S3 + 3SH2, the action taking place slowly in diffused daylight, but very rapidly in sunshine. An ordinary flask for the evolution of hydrogen (either by galvanic processes or from zinc and sulphuric acid), with its funnel and drying-tubes, is connected with a narrow tube having a few fragments of sulphur, kept in place by plugs of cotton wool. The whole apparatus is placed in sunshine; if no orange colour is produced when the hydrogen has been passing for some time, the liquid to be tested is poured in gradually through the funnel, and if antimony should be present, the sulphur acquires a deep orange colour. This is distinct even when so small a quantity as ·0001 grain has been added through the funnel. The sulphide of antimony thus mixed with sulphur can, if it is thought necessary, be freed from the sulphur by repeated exhaustion with bisulphide of carbon. The stibine does not, however, represent all the antimony introduced, a very large proportion remaining in the evolution flask;[815] hence it cannot be employed for quantitative purposes. Moreover, the test can, of course, only be conveniently applied on sunny days, and is, therefore, in England more adapted for summer.[816] Often, however, as mentioned elsewhere, when the analyst has no clue whatever to the nature of the poison, it is convenient to pass SH2 in the liquid to saturation.[817] In such a case, if antimony is present (either alone or in combination with other sulphides), it remains on the filter, and must be separated and identified as follows:—The sulphides are first treated with a solution of carbonate of ammonia, which will dissolve arsenic, if present, and next saturated in situ with pure sulphide of sodium, which will dissolve out sulphide of antimony, if present. The sulphide of antimony will present the chemical characters already described, more particularly—
[814] See Ernest Jones on “Stibine,” Journ. Chem. Soc., vol. i., 1876.
[815] Rieckter, Jahresbericht, 1865, p. 255.
[816] The action of salts of cæsium with chloride of antimony might be used as a test for the latter. A salt of cæsium gives a white precipitate with chloride of antimony in concentrated ClH; it contains 30·531 per cent. of antimony, and corresponds to the formula SbCl3CsCl. Chloride of tin acts similarly.—E. Godeffroy, Berichte der deutschen Chem. Gesellschaft, Berlin, 1874.
[817] The solution must not be too acid.