Oxides of I'latimum.—The protaride (Pt 0) Is a black precipitate, formed on digesting the protochloride in caustic) potash, and neutra lising with sulphuric acid. It forms unstable salts with acids. The tinoxide (Pt 0,) is precipitated as a bulky brown hydrate, on adding carbonate of soda to excess of nitrate of platinum. It forms crystalline compounds with the alkalies and with acids.
Sulphides of platinum are formed by the action of sulphuretted hydrogen on proto- and biasalta of platinum. The protosulphide (Pt S) is gray, the lusulpAide (Pt S,) black.
Iodides c f p/atintens are produced by acting upon the chlorides with iodide of potassium. The protoiodide (Pt I) is black ; the biniodide (Pt is deep wine-red.
Pitranide of platinum, (Pt Br,) is a brown insoluble powder.
Nitrate of platinum (Pt 0,,2N0,) remains in solution when nitrate of potash is added to bichloride of platinum Belong as potassio-chloride of platinum is deposited.
Compound platinaun and ammonia bases. Platosamine, platinamine, &e.—By the action of ammonia on protochloride and bichloride of platinum, and by the action of nitric, acid, rho., n the resulting pro ducts, a series of remarkable compounds have been produced by Gros, Relict, Gerhardt, and Raewsky. These bodies seem to be derivatives of hydrated oxide of ammonium, containing platinum in the place of hydrogen : they bear a striking resemblance to the ammonium onoaario oasts.
Spongy platinum; is a dull-gray, soft, porous form of platinum, having somewhat the appearance of sponge. It is produced on simply igniting the ainmonio-chloride of platinum. It possesses in a high degree that power of inducing the combustion of inflammable gases in the manner already alluded to. When freshly prepared, it causes the inflammation of a jet of hydrogen on the latter being impinged against a small pellet of it. By great pressure spongy platinum is condensed into
Laminas having the metallic lustre.
Platinum black differs from spongy platinum, not only in colour, but in being perfectly amorphous. It is also in a still finer state of division, and possesses in the highest degree the power of condensing gases upon its surface and of inducing the combustion of gases and vapours. It is prepared by adding to bichloride of platintim, first protosuiphate of iron, then caustic soda, and afterwards hydrochloric acid; or by precipitation from the chloride by means of metallic iron reduced by hydrogen from the oxide obtained on igniting the oxalate of iron.
Alloys of platinum.-11atinura forma an alloy with tin, which crystallises in cubes, and contains Pt, Sn,. With twenty-five per cent. of iridium, or with nineteen and a half per cent. of iridium and five per cent. of rhodium, platinum forms alloys that are perfectly malleable : they may be worked into vessels that are almost unacted upon by aqua regia, and which, from their greatly increased rigidity, retain their shape longer and better than if constructed of platinum alone.
Detectia of platinum.—The prodnction of the yellow crystalline precipitate with chloride of ammonium, which becomes converted into a spongy metal on ignition, is sufficiently characteristic of platinum.
Estimation of platinum.—This maybe effected in the Mato of spongy platinum produced as already directed; or, on a tared filter, as arnmonio-chloride of platinum which contains per cent. of metal; or as potasaio-chloride which contains 40.43 per cent. of platinum.