Platinum is not attacked by fluorine at a low temperature, and advantage of this was taken by Moissan when he first isolated that element and by Moissan and Dewar when they first liquefied this gas. At higher temperature C) Moissan obtained two fluorides, and Platinum does not readily form stable salts with oxy-acids. A sulphate Pt(SO4)2 is said to have been produced by dissolving platinic hydroxide in sulphuric acid but no nitrate of platinum is known. A series of salts known as pla tino-nitrites having the general formula M,Pt(NO,), is well known, and another series, the platino-oxalates of the composi tion has also been recorded. Two sulphides of plat inum, PtS and PtS2, are definitely known, and the existence of various intermediate ones has been announced from time to time. PtS and PtS2 are produced by acting upon solutions of correspond ing platinum compounds with sulphuretted hydrogen. Both sul phides are black powders; must be dried without access of air as it readily undergoes oxidation.
Platinolis cyanide, Pt(CN),, is best produced by precipitating a solution of potassium platinochloride, with mercuric cyanide. It is of importance as it combines with cyanides of the alkali and alkaline-earth metals to produce a, series of salts known as platinocyanides which are remarkable for their wonderful col ours and for their use in radiography. They are derived from plat inocyanic acid, which can be prepared by decompos ing the mercury or copper salt with sulphuretted hydrogen. The acid crystallizes from water in deliquescent prisms but is better crystallized frcm an ether–alcohol mixture. Potassium platino
cyanide, is easily produced by dissolving spongy platinum in a solution of potassium cyanide, preferably in the presence of air, or by the interaction of a solution of platinous chloride with excess of potassium cyanide ; in the latter method recrystallization is necessary to remove the potassium chloride simultaneously produced. It crystallizes in rhombic prisms which are yellow by transmitted light but have a blue metallic lustre by reflected light. The magnesium salt, crystal lizes in beautiful red tetragonal prisms with metallic moss-green reflex. Its solution in water is colourless. Barium platinocyanide, is the compound used for X-ray screens. It occurs in citron-yellow monoclinic prisms with a green reflex.
Platinum salts combine with ammonia in various proportions to form two series of bases, platinous and platinic ammines (see AmmiNEs). In the platinous series there are two compounds hav ing the formula they are probably cis- and trans isomerides. A polymeride having the formula has long been known as the "green salt of Magnus," and is made by the action of ammonia upon platinous chloride. These corn pounds, although of great interest theoretically, are of little practical value. A complete account of these interesting com pounds may be found in Gmelin-Kraut's Handbuch. (F. E. M.) See L. Duparc and M. N. Tikhonovich, Le Platine et les gites plataniferes de l'Oural et die Monde (192o) ; C. Janin, World's Out look for Platinum (1928).