ANTIMONY.
Antimony occurs in the native state, but is rare; its common ore is antimonite, the sulphide (Sb2S3). Jamesonite and other sulphides of lead and antimony are frequently met with. Sulphide of antimony is also a constituent of fahlerz and of many silver ores.
Antimonite occurs generally in fibrous masses, has a lead-like metallic lustre, is easily cut with a knife, and melts in the flame of a candle.
Antimony itself has a very crystalline fracture, is brittle, and has a bluish-white colour. It is used in the preparation of alloys with lead and tin for the manufacture of type-metal. It is readily fusible, and imparts hardness and the property of taking a sharp cast to its alloys. It is practically insoluble in hydrochloric acid. On boiling with strong nitric acid it is converted into antimonic oxide (Sb2O5), which is a powder almost insoluble in this acid or in water, but which may be got into solution with difficulty by the prolonged action of hydrochloric and tartaric acids. Antimonic oxide is converted on ignition into the tetroxide (Sb2O4) with loss of oxygen. Antimony forms two series of salts, antimonious and antimonic; and advantage is taken of this in its determination volumetrically. Either sulphide of antimony yields antimonious chloride on boiling with hydrochloric acid, sulphuretted hydrogen being given off; and, in the case of antimonic sulphide, sulphur is deposited. Antimonious is converted into antimonic chloride by treatment with permanganate of potash in an acid solution. Antimonic chloride and potassium iodide react, forming antimonious chloride and free iodine. This latter may be got rid of by boiling. Sulphide of antimony is separated from the ore by liquation; this regulus is met with in commerce as "crude antimony."
DRY ASSAY.
An approximate determination of the amount of sulphide of antimony in an ore may be made by fusing and liquating in a luted double crucible in the manner described under bismuth. This is unsatisfactory. The determination of metallic antimony in an ore is made either by fusion with potassium cyanide or by fusion with iron, as in the galena assay. Both methods yield poor results; and, where iron is used, it must be added in quantity only sufficient for desulphurising; this amounts to about 40 per cent. in pure ores. If the iron is in excess it alloys with the reduced antimony. If, on the other hand, it is insufficient, the metal will contain sulphur; or sulphide of antimony will be lost in the slag.
The following note, for which we are indebted to Mr. Bedford McNeill, A.R.S.M., gives a description of the method adopted in the commercial valuation of a parcel of antimony ore:—
The antimony smelter, when he wishes to determine the value of any parcel of ore—usually the sulphide—that may be offered for sale, practically has recourse to the smelting operation. That is, a quantity of 2 or 3 cwts. taken by his sampler having been obtained, he treats it under the immediate supervision of the foreman smelter as if it formed part of the ore in process of daily reduction at his works. He thus determines by actual trial the output which it may fairly be anticipated will be yielded by the bulk, and upon the result of this trial or assay, and the knowledge gained of the actual behaviour of the ore under treatment, he bases his tender, knowing that, should he secure the parcel, he may confidently expect a similar return.
Briefly, the process consists of the three ordinary operations of—
(a) Singling or removing most of the antimony from the ore;
(b) Doubling;
(c) Refining or "starring."