The other special reagents of the present and three preceding subdivisions give no characteristic reactions with solutions of bismuthic salts. The chief means employed for the detection of bismuth in its salts is the precipitation of the oxychloride, which is formed whenever a solution of bismuthic chloride is mixed with a large quantity of water. This (and so are the precipitates produced in a similar way with other salts of bismuth) is a salt which may be distinguished from the precipitates formed under the same circumstances in solutions of antimony, by being insoluble in tartaric acid. The other chief insoluble salts by which bismuth is recognized are the chromate, the hydrate, and the sulphide; the blowpipe reactions on charcoal are also characteristic. The insoluble bismuth salts, as the chromate, hydrate, or carbonate, may be easily distinguished from the analogous salts of lead or silver by their being insoluble either in hydrate of potassium or hydrate of ammonium. SALTS OF PALLADIUM. The metal palladium being of far rarer occurrence than the previously described members of the present group, its salts have not been so completely studied. The characteristics which these salts present differ from those of the salts already given, and more closely resemble those exhibited by tin and platinum compounds. Palladium forms two series of combinations with acidradicals, the palladious and the palladic: of the former, palladious chloride (PdCl) and palladious oxide (Pd, O) may be considered typical, while, of the latter, palladic chloride (PdCl) and palladic oxide (Pd, O2) are representatives. Palladic salts have a great tendency to form compounds the acidradical of which contains palladium united with chlorine, iodine, &c.; they yield these definite saline combinations with the chlorides and iodides of the metals of the first subdivision, as in the following instance: PdCl2+KCl=KPdCl2. When heated before the blowpipe, palladium salts are reduced with the greatest ease either in the oxidizing or reducing flame, the heat alone being sufficient to decompose them with formation of metal; owing to the difficult fusibility, however, of this element, no globules are seen, but only a black powder: they impart no colour to the blowpipe flame, nor do they give any reaction with nitrate of cobalt; when fused with borax, they are readily reduced in either flame. Palladium salts are reduced by the same metals as effect the reduction of silver salts, and also by ferrous sulphate. PALLADIOUS SALTS, OR PROTO-SALTS OF PALLADIUM. Solution for the reactions:-palladious chloride (PdCl) in water. The principal insoluble salts of this series are the iodide, the cyanide, the chromate, the hydrate, the sulphide, the oxalate, the ferrocyanide, the ferricyanide, and the phosphate. THE CHLORIDE is soluble. The Iodide is produced by the action of hydriodic acid or of iodide of potassium on solutions of palladious salts: in very dilute solutions a brownish red colour at first appears; but after some time a black precipitate separates, which is the iodide. Its formula is PdI. It is insoluble in water, alcohol, or ether; neither is it dissolved by hydriodic acid. THE CYANIDE is produced by the action of cyanide of potassium, or mercuric cyanide, on solutions of palladious salts: it is a yellowish-white precipitate. Its composition is said by some to be PdCy; when precipitated by mercuric cyanide the formula 2(PdCy, HgCy)+aq has been assigned to it. It is extremely soluble in cyanide of potassium and in hydrate of ammonium. It is soluble in hydrochloric acid unless very dilute. THE CHROMATE is produced by the action of chromate of potassium, but is not accurately known. The Hydrate is produced by the action of the hydrates of the alkaline metals on solutions of palladious salts; it is also produced by the carbonates of potassium and sodium. Its composition is that of a basic salt. It is soluble in the hydrates of potassium or ammonium; it also dissolves in strong acids with the aid of heat. The action of hydrate of ammonium on palladious salts varies: with some, as the nitrate, it produces no precipitate; with others, especially the chloride, it gives a flesh-coloured precipitate, which is but slightly soluble in water, and less so in alcohol, but soluble in excess of its precipitants. This precipitate is NH, PdCl, or NaCl, as it may be written,-i. e. the chloride of pallad ammonium. H The Sulphide is produced by the action of hydrosulphuric acid on alkaline, neutral, or acid solutions of palladious salts: it is a brownish-black precipitate. Its formula is Pd, S. It is insoluble in sulphide of ammonium, but soluble in hydrochloric acid. THE SULPHATE is soluble. THE CARBONATE does not exist; for the soluble carbonates precipitate palladious hydrate. THE OXALATE is produced by the action of oxalate of potassium on solutions of palladious salts. PALLADIC SALTS, OR PER-SALTS OF PALLADIUM. 187 Its composition is not accurately known. When, however, oxalic acid is added to an ammoniacal solution of a palladious salt, a double oxalate is produced, having the formula PdNH, C2O+aq when crystallized in short rhombic prisms, and the formula PdNH, C2O+4aq when occurring in long needles. THE FERROCYANIDE is produced by the action of ferrocyanide of potassium on palladious salts, and is precipitated on standing: it is a yellowish brown precipitate. THE FERRICYANIDE is produced by the action of ferricyanide of potassium: it is a red-brown precipitate. THE PHOSPHATE is produced by the action of phosphate of sodium: it is a brown precipitate. This precipitate is said to be a basic phosphate. The other special reagents of the present and three preceding groups exert no characteristic action upon palladious salts. The formation of palladious iodide, hydrate, and sulphide, and the reduction of the metal before the blowpipe, are made use of in analysis to detect palladious salts: the blowpipe reaction is, of course, applicable also to the recognition of the palladium in palladic salts. PALLADIC SALTS, OR PER-SALTS OF PALLADIUM. Only a few representatives of this series exist; they are almost confined to the chloride (PdCl2) and the oxide (Pd, O2); the former gradually gives off chlorine, especially on heating, and even when its aqueous solution is boiled, and is reduced to palladious chloride (PdC1). When combined with chloride of potassium, palladic chloride gives a salt which is very stable; but the palladium in it probably exists in the form of a compound acid-radical (PdCl1): this salt crystallizes in brownish-red octahedra. The oxide (Pd, O) may be obtained by acting on palladic chloride with the hydrate of potassium. The sulphide (Pd, S2) cannot be obtained by passing hydrosulphuric acid into a solution of palladic chloride; for, if formed at all, it is immediately decomposed into palladious sulphide (Pd, S) and sulphur. On account of the large number of important metals included in this Subdivision, we have not deferred giving the Table of Reactions until the end of the group, but have placed a synopsis of the reactions of the 1st Section on the following page; and for the same reason, an Analytical Table will also be found appended. |