arsenic; and the residues, when moistened with hydrochloric acid, evolve sulphuretted hydrogen, recognisable by its smell and action on lead paper. Orpiment and realgar are not dissolved by boiling hydrochloric acid, but disappear more or less completely in nitro-hydrochloric acid, forming solutions from which arsenic acid may be obtained by evaporating to dryness. They also dissolve in sulphide of ammonium, and are redeposited on evaporating the liquid to dryness. 3. Scheele's green. an impure arsenite of copper. yields a crystalline sublimate of arsenious anhydride, and a black residue of oxide of copper, which may be dissolved in hydrochloric acid, and tested by the usual reagents. Arsenite of copper dissolves in dilute hydrochloric acid, forming a solution in which, after precipitation of the copper by excess of oxalate of ammonium, arsenic may be detected by sulphuretted hydrogen, or by Marsh's or Reinsch's tests. This well-known green pigment is (140.) IN ORGANIC MIXTURES. a. A hydrochloric acid decoction may be prepared as already described and tested by Reinsch's process. Or the organic substance may be distilled to dryness with hydrochloric acid, the residue redistilled with fresh hydrochloric acid, the two distillates collected in water, and the product examined by sulphuretted hydrogen, or by Marsh's or Reinsch's process. Or the tissue, &c., may be destroyed with hydrochloric acid and chlorate of potassium, the solution submitted to the prolonged action of sulphuretted hydrogen, and the resulting precipitate further examined (vide par. 116 B). § IX. ANTIMONY. a. Tartar emetic. This compound usually occurs as a white powder, or in ill-defined crystalline masses. It becomes charred by heat, and when ignited with a little carbonate of sodium on charcoal before the blowpipe, yields a bead of brittle metal and an abundant white incrustation. It is turned of an orange colour, and finally dissolved by sulphide of ammonium. Its solution in Fig. 49. water when carefully evaporated yields beautifully polarising crystals (fig. 49), chiefly tetrahedral, but here and there cubical and octahedral. When acidified by nitric or hydrochloric acid, it furnishes a white precipitate soluble in excess of either acid. 6. Chloride of antimony. This is a highly corrosive fuming liquid, usually having a yellow or orange colour from the presence of chloride of iron. Poured into water, it gives rise to an abundant white precipitate, which, after thorough washing with water, is turned of an orange colour and finally dissolved by sulphide of ammonium. The precipitate is also readily soluble in tartaric acid. Mixed with carbonate of sodium and heated on charcoal before the blowpipe, it yields a bead of brittle metal and an abundant white incrustation. (142.) IN SOLUTION. a. Precipitation of trisulphide of antimony. A current of sulphuretted hydrogen gas passed into an antimonial solution acidified with tartaric acid, throws down an orange precipitate, which after washing with water, is insoluble in carbonate, but soluble in sulphide of ammonium, forming a solution from which it may be reprecipitated on the addition of an acid. B. Precipitation of oxichloride of antimony. Precipitated trisulphide of antimony dissolves completely in hot hydrochloric acid with evolution of sulphuretted hydrogen gas. The resulting trichloride of antimony, freed from excess of hydrochloric acid by evaporation to a small bulk, gives when poured into water an abundant white precipitate of oxichloride of antimony, soluble in tartaric acid. γ y Metallic precipitation on tin. A piece of tin foil or bar immersed in the above tartaric acid solution, becomes speedily covered with a pulverulent black deposit of metallic antimony. (143.) MARSH'S TEST. The antimonial solution, acidulated with tartaric acid, may be introduced into the original or modified form of Marsh's apparatus, previously charged with pure zinc and dilute sulphuric acid, and the resulting gas examined as follows: a. Appearance of flame, &c. Hydrogen contaminated with antimonetted hydrogen produces a black discolouration on paper moistened with nitrate of silver solution. It burns with an opaque bluish white flame, and evolves a white smoke of teroxide of antimony, which, unlike the arsenical smoke, does not produce a yellow turbidity with ammonio-nitrate of silver. B. Characters of deposit. When a piece of talc, porcelain, or glass is depressed upon the flame, a dark stain or deposit is produced, distinguishable from the arsenical stain by the following properties :-a, by its comparative want of metallic lustre; b, by its smoky black colour; c, by its non-volatility save at a heat approaching redness; d, by its insolubility in chloride of lime; e, by its ready solubility in yellow sulphide of ammonium, so as to form a solution which on evaporation to dryness leaves a bright orange stain; and f, by its yielding after treatment with nitro-muriatic acid and evaporation to dryness, a residue which does not give a red precipitate with nitrate of silver solution. 7. Decomposition by heat. Instead of burning the antimonetted hydrogen, it may be transmitted through a tube heated to redness, and finally through a solution of nitrate of silver. The deposit of antimony produced in the tube is characterised by its position, just before and beyond the exact spot where the heat is applied, by its want of volatility, by its non convertibility into arsenious anhydride or arsenic acid, and by its ready solubility in yellow sulphide of ammonium to form a solution which leaves a bright orange stain on evaporation. 8. Reaction with nitrate of silver. Antimonetted hydrogen produces in nitrate of silver solution a black deposit of antimonide of silver, from which, after washing with water, the antimony may be dissolved away by a boiling solution of cream of tartar, and precipitated from the resulting solution by sulphuretted hydrogen. (144.) REINSCH'S TEST. a. Deposit on copper. The deposition of antimony upon copper foil or gauze boiled in a hydrochloric acid decoction of organic matter contaminated with antimony, or in a weak acidulated solution of some antimonial salt, takes place exactly as does the deposition of arsenic under similar circumstances. The highly lustrous deposit of antimony differs from that of arsenic in having a marked violet colour, and in being less easily dissipated by heat. When a piece of the coated foil or gauze is strongly heated in a reduction tube, it either does not afford any sublimate at all, or else a very slight white deposit situated close to the heated end of the tube, not having a crystalline character, and being practically non-volatile. B. Solution of deposit. When boiled for a few minutes in a weak feebly alkaline solution of permanganate of potassium, the antimonial coating is dissolved away from the copper, while the permanganate loses its colour and furnishes a slight turbidity of manganic hydrate. The filtered liquid acidulated with hydrochloric acid and treated with sulphuretted hydrogen, acquires a yellowish colour, and on standing deposits an orange precipitate, which may be further examined if necessary. Or, if the antimonial coating be not very thick, it will suffice to boil the copper for some time, with frequent exposure of its surface to the air, in a weak solution of caustic potash only, and to treat the resulting liquid, after acidification by hydrochloric acid, with sulphuretted hydrogen. (145.) IN ORGANIC Mixtures. The processes of precipitation by sulphuretted hydrogen and deposition on copper, are perfectly applicable to acidified organic liquids, and to the hydrochloric acid decoctions of organic tissues. Or the tissue may be destroyed by hydrochloric acid and chlorate of potassium, the solution after evaporation treated by sulphuretted hydrogen, the resulting precipitate dissolved in boiling hydrochloric acid, and the solution so formed tested in Marsh's apparatus, or by the process of Reinsch. § X.-PRUSSIC ACID. (146.) IN AQUEOUS SOLUTION. a. Appearance, &c. Prussic or hydrocyanic acid CNH, occurs in the state of aqueous solution as a colourless, perfectly volatile, feebly acid, mobile liquid. Its vapour, which is given off at all ordinary temperatures, is invisible, has an odour said to be like that of bitter almonds, and when inspired even in minute quantity causes a peculiar sensation in the fauces. 6. Formation of Prussian blue. The turbid greenish liquid made by adding excess of potash to solution of ordinary sulphate of iron, does not undergo any visible alteration when mixed with aqueous prussic acid; but, on acidifying the mixture with hydrochloric acid, a bright blue, or sometimes a greenish blue colour is developed, due to the production of finely divided Prussian blue, which gradually separates as a distinct precipitate. Or the potash and sulphate of iron may be added separately to the suspected liquid, and the mixture be afterwards acidulated with hydrochloric acid. Aqueous y. Formation of sulphocyanate of iron. prussic acid, mixed with a drop or two of yellow sulphide of ammonium solution and evaporated to dryness at a low temperature, leaves a residue of sulphocyanate of ammonium, which, when moistened with water and tested with a drop of per |