Pur. The antimony of commerce generally contains a little arsenic, with variable quantities of iron, lead, sulphur, and tin. These impurities may be thus detected:—
1. (Arsenic.) By fusing the sample, in powder, mixed with about an equal weight of tartrate or bitartrate of potassium, in a covered crucible, for 2 or 3 hours, and placing the resulting button, which is an alloy of antimony and potassium, in a ‘Marsh’s apparatus’ along with a little water, when the disengagement of hydrogen gas will commence, and may be tested in the usual manner. See Arsenic.
2. (Iron.) Dissolve the powdered sample in nitrohydrochloric acid, dilute the solution with a large quantity of cold water, filter, and pass a current of sulphuretted hydrogen through the filtrate as long as it produces a precipitate; again filter, boil the filtered liquor for a few minutes to drive off the sulphuretted hydrogen, and then test it with ferrocyanide of potassium, which will give a blue precipitate if iron be present; or supersaturate the last filtrate with ammonia, and then add hydrosulphydrate of ammonium, when, under like conditions, a black precipitate will be formed.
3. (Lead.) Digest the powdered sample in hot nitric acid, which will dissolve out the LEAD but leave the antimony behind. The whitish powdery residuum may be washed, dried, ignited, and weighed, as above; the clear decanted liquor may now be mixed with the first washings, evaporated to dryness, the residuum re-dissolved in water, and the solution submitted to reagents (see Lead). If lead is found to be present, a solution of sulphate of sodium may be added until it ceases to disturb the liquid, and the resulting precipitate (sulphate of lead) washed, dried, and gently ignited (alone) in a porcelain crucible; the weight of the ignited residuum furnishes a number which, multiplied by ·683, gives the weight of the LEAD sought.
4. (Sulphur.) The solution in nitrohydrochloric acid, when tested with either nitrate or chloride of barium, gives a white precipitate of sulphate of barium, insoluble in both water and acids, which when dried, ignited, and weighed, and the weight multiplied by ·136, gives the quantity of SULPHUR as before. In this case, as with the sulphides (see above), free sulphur maybe removed by digesting and washing the powdered sample in bisulphide of carbon, previous to its solution in the acid, by which the violence of the subsequent reaction will be lessened.
5. (Tin.) Two samples of equal weight are taken; the one is tested for ANTIMONY, as described above; the other is dissolved in a mixture of equal parts of hydrochloric and nitrohydrochloric acid, and a blade of zinc immersed in the solution (see above); the mixed precipitate of tin and antimony which forms is collected on a weighed filter, washed, dried, and weighed. The weight of antimony in the first sample subtracted from that now obtained, leaves a remainder which indicates the quantity of TIN in the original sample.
Phys. eff., &c. Nearly all the salts and preparations of antimony are emetic and cathartic, and in large doses poisonous—occasioning vomiting, profuse alvine dejections, acute colic, and inflammation of the stomach and bowels, often serious, though rarely resulting in death. Tartar emetic and BUTTER OF ANTIMONY are those from which accidents have principally occurred.—Ant., &c. Copious vomiting, if it has not already occurred, should be promoted, and the recently prepared hydrated sulphide of iron administered in considerable doses, followed or accompanied by mucilaginous drinks and diuretics. If much prostration follows, wine and stimulants may be had recourse to. In the absence of hydrated sulphide of iron, a solution of tannin, or decoction of galls; cinchona, or oak bark, or even powdered cinchona, mixed with tepid water, may be administered.
Uses. In the arts, antimony enters into the composition of several useful alloys, as TYPE-METAL, PEWTER, BRITANNIA-METAL, MUSIC-PLATE METAL, &c. It is added to the alloy for concave mirrors, to give them a finer texture; to bell metal, to render it more sonorous; and to various other metals to increase their hardness and fusibility; for the latter purpose it is employed in the casting of cannon balls.
Concluding Remarks. In ‘roasting’ or oxidising the native sulphide of antimony on the bed of the reverberatory furnace, as in the common method before referred to, care must be taken to regulate and gradually raise the heat, which, until towards the end of the process, need not be extreme, and then only should it approach dull redness. Without this precaution much of the undecomposed sulphide will be lost by volatilisation. During the whole time the ‘charge’ should also be well stirred with an iron spatula, to ensure the constant exposure of every part of it to the atmosphere. The process is complete when
the whole mass assumes a greyish-white appearance. Earthen crucibles are commonly employed for the subsequent reduction, and after being charged and covered over with ground charcoal, are heated in a reverberatory furnace. The product is the crude metallic antimony of commerce. It is generally REFINED by smelting it with about 1-8th of its weight of the refined sulphide, and about 1-4th of its weight of carbonate or sulphate of soda; but if there be much iron present, more of the sulphide—even 1-4th—may be required; for unless there be sufficient sulphur to combine with the whole of the iron, the arsenic will not be oxidised, but remain as a contamination. When cold, the metal is carefully separated from the slag, and is frequently re-fused with a little fresh carbonate of soda (1 to 11⁄2 part); after which it is cast into pigs, lumps, or ingots. The crude metal, thus treated, commonly yields 94% of REFINED METAL of tolerable purity.