Mercury.—Stain silvery: in closed tube gives a sublimate of metallic globules, made more visible by rubbing them together with a splinter of wood.
Bismuth, tin, silver, gold, platinum, palladium, &c., give black, grey or silvery deposits, but no sublimate in the tube. Gold gives a stain which is yellow on burnishing, and yields no sublimate.
Sulphur compounds in the organic matter may give a dull stain, which may even yield a kind of sublimate in the tube, but this sublimate will not conform to the tests for As or Sb.
If there is much As or Sb, the deposit sometimes peels off if boiled too long.
The process used by Prof. Maclagan in the Pritchard trial is also a good means of verification. Boil the stained foil in a solution of caustic potash, exposing it occasionally to the air (or boil with a weak, slightly alkaline solution of potass, permanganate, and filter—Odling). The Sb will be oxidized and dissolved. Add HCl and pass H2 S: an orange precipitate of Sb2 S3 will prove the presence of antimony.
If Sb has been found, remove the first piece of copper, and boil with another piece, and so on till the Sb is all removed. The coated slips, the sublimate, the Sb2 S3, and the copper in the second flask which has still remained bright, should be sealed up to be shown in court.
The previous treatment with sulphurous acid prevents any interference by oxidizing agents such as chlorate of potash, nitrates, iodine, &c.
Marsh’s Test is more delicate, but more liable to error, than Reinsch’s.
Two methods of applying Marsh’s test to antimony may be used.
A. By Edmund Davy’s process with sodium amalgam (see Arsenic, p. 388), only As H3 passes off, the Sb remaining behind. Hence, when the arsenic has finished coming over, if the remaining solution be acidulated with pure sulphuric acid,[189] pure zinc put in, and one or two drops of pure platinic chloride added to facilitate the evolution of hydrogen, the antimony will then come over as Sb H3.