Page:Treatise on poisons in relation to medical jurisprudence, physiology, and the practice of physic (IA treatiseonpoison00chriuoft).pdf/374

 When heated it decrepitates and then chars; and if the heat be increased the oxide of antimony is reduced by the carbonaceous matter, and little globules appear, like those of quicksilver in point of colour. The best way of reducing tartar-emetic is to char it in a porcelain vessel or watch-glass, and then to increase the heat till the charred mass takes fire. Or the charred mass may be introduced into a tube and heated strongly with the blowpipe, after which globules of antimony will be found lining the bottom of the glass where the material has been. None of it is ever sublimed. It is not easy to procure distinct globules by heating tartar-emetic at once in a small tube.

According to Dr. Duncan, tartar-emetic is soluble in three parts of boiling and fifteen of temperate water. The solution presents the following characters with reagents.

1. Caustic potass precipitates a white sesquioxide, but only if the solution is tolerably concentrated. The first portions of the test have no effect. The precipitate is redissolved by an excess of potass.

2. Nitric acid throws down a white precipitate, and takes it up again when added in excess.

3. The Infusion of Galls causes a dirty, yellowish-white precipitate; but it will not act on a solution which contains much less than two grains per ounce.

4. The best liquid reagent is Hydrosulphuric acid. In a solution containing only an eighth part of a grain per ounce, it strikes an orange-red colour, which, when the excess of gas is expelled by heat, becomes an orange-red precipitate; and if the proportion of salt is greater, the precipitate is thrown down at once.—The colour of the precipitate is so peculiar as to distinguish it from every other sulphuret; but if any doubt regarding its nature should occur, it may be known by collecting it, dissolving it with the aid of gentle heat in hydrochloric acid, and adding water to the solution; which will then yield a white precipitate, the sesquioxide of antimony in union with a little chlorine.

5. When the solution is put into Marsh's apparatus for detecting arsenic [p. 211], the flame yields a dark brownish-black, obscurely shining crust on a surface of porcelain held across it, and a white crystalline powder if the porcelain be held just above the flame. The dark crust is antimony, the white one its oxide. The former has only a distant resemblance to the brilliant stain of arsenic, notwithstanding all that has been said of their similarity. It is well, however, to use some other test for distinguishing the two metals besides their appearance; and the most convenient is a solution of chloride of lime, which instantly makes an arsenical crust disappear, but does not affect an antimonial one.

Tartar-emetic, like the soluble salts of mercury and copper, is decomposed by various organic principles. All vegetable substances that contain a considerable quantity of tannin have this effect; of which an example has been already mentioned in the action of infusion of galls. Decoctions of cinchona bark decom