a, Flask containing the suspected fluid, dilute sulphuric acid, and zinc.
b, Small tube, at the one end having an almost capillary orifice, where the gas is inflamed.
c, Spirit-lamp.
d, Support.
Estim. Antimony is generally WEIGHED under the form of tersulphide; but sometimes as antimonious anhydride, and—though more seldom—as pure metal:—
1. A solution being obtained as above, if necessary, it is strongly acidulated with tartaric acid, and the antimony thrown down as a sulphide by a stream of sulphuretted hydrogen. After warming the solution and allowing it to cool, the precipitate (TERSULPHIDE) is collected on a filter, dried, and weighed. A small portion digested in strong hydrochloric acid will completely dissolve if it be the pure sulphide; in which case the quantity of ANTIMONY sought will be equal to 711⁄2% (71·5%) of the weight of the sulphide found (very nearly).[72] Should only part of the precipitate be soluble, a known weight of it may be introduced into a flask, and a considerable quantity of fuming nitric acid added, drop by drop, and afterwards, a little hydrochloric acid, the mixture being digested, at a gentle heat, until the reaction is complete, and the whole of the sulphur is dissolved. The resulting solution diluted with water, strongly acidulated with tartaric acid, and solution of chloride of barium added as long as it disturbs the liquid, yields a precipitate, of which the weight, after it has been thoroughly washed, dried, and gently ignited, multiplied by 136, gives the quantity of SULPHUR in the sample; and which, deducted from the weight of the sulphide first found, gives the quantity of pure ANTIMONY, as before.
[72] Tersulphide of antimony dried at 212° Fahr. still retains traces of water, which is not wholly expelled until the heat reaches 390-392°, when it acquires a black colour and a crystalline appearance.
2. The quantity of PURE ANTIMONY in commercial samples may be determined by treating them (in powder) with nitric acid, which oxidises the antimony and leaves it in an insoluble state, whilst it dissolves the other metals. The resulting oxide is collected on a filter, washed, dried, ignited in an open porcelain crucible, and weighed—its weight multiplied by ·7898 gives the quantity of pure metal sought.
3. Dissolve a known weight of the sample in hydrochloric acid, immerse a blade of pure metallic tin in the solution, and keep the liquor acidulous, and in a state of gentle ebullition by the heat of a sand bath, when the whole of the ANTIMONY will be precipitated under the form of a black powder, and may be collected, washed, dried, and weighed. This is particularly adapted to alloys of antimony and tin. See Tests (above) and Pur. (below).