These four metals are all reduced easily from their oxides without any difficulty at all. All four likewise are perfectly stable at ordinary temperatures, while, at higher temperatures, they do not decompose carbon dioxide and therefore can be won by simple reduction with carbon at a red heat. That they are such expensive metals follows from their relative scarcity in nature and not at all from the trouble of winning them from their ores. Their low melting points, ease of reduction, and moderate chemical activities make their winning a simple task for the metallurgist; when they occur in small quantities with other metals, it may be quite a different matter to separate and to recover them efficiently.
Antimony is found chiefly as sulphide. This sulphide can be treated with metallic iron to yield metallic antimony directly. The operation can be carried out at moderate temperature in any suitable receptacle. The sulphide likewise can be roasted to oxide by the simplest means; the oxide then can be reduced to metal with carbon. Neither process offers particular metallurgical difficulty.
Considerable antimony always is recovered in lead refining; this is turned out as hard lead (12 to 14 per cent Sb) ready for use.
Antimony is used as metal chiefly in the minor alloys".
Bismuth occurs sometimes as metal, in which case it can be liquated from its gangue and recovered directly as metal. If an ore contains sulphide of bismuth, it can be roasted; this roasted ore as well as oxide ores are reducible directly to metal without difficulty, and they are reduced best in reverberatory furnaces.
Bismuth is recovered in electrolytic lead refining; in this case, any bismuth in the lead goes to the silver refinery in the tank slimes.
In the refinery it is separated from the silver by oxidizing fusions, is reduced to metal, and is refined electrolytically.
The metal goes into pharmaceutical preparations and into alloys with low melting points.
Mercury occurs in ore deposits mainly as its sulphide, cinnabar. An oxidizing roast of this compound frees the metal which is condensed in suitable receptacles or chambers. The literature contains abundant accounts of the devices for accomplishing this end. The metallurgy of the process is simple and most excellent results are reported wherever there is ore to treat.
Tin occurs chiefly as oxide in nature. This oxide is very heavy, and the mineral can be concentrated to a product high in tin. Concentration is effected by panning, by dredging, and by crushing and mill treatment. The concentrated mineral is reduced to the metal in either shaft or reverberatory furnaces.
It is rather necessary to have the concentrates as clean as possible to prevent the reduction of the other metals which might accompany. The furnaces used are all small, and the tin on the market is of surprisingly good grade. Tin is difficult to remove from other metals when it accompanies them, which, fortunately, is seldom suspected.