oxide), PtO, -4H¢O, is obtained by adding an excess of caustic soda solution to a boiling solution of chlorplatinic acid, the hot solution being diluted and neutralized with acetic acid. It loses its water of hydration when heated, finally decomposing into platinum and oxygen. When freshly prepared it is soluble in dilute acids. Other hy drated forms of composition, PtO2'3HzO and PtO2-2H2O, have been described (E. Prost, Bull. soc. chcm., 1886, 46, p. 156; H. Topsoe, Bef, 1870, 3, . 462). The tetra hydrate may be considered as an acid, H2Pt(Ol-Igs, or salts are known (namely the palatinates) corresponding to it, those of the alkali metals being soluble in water, and possessing an alkaline reaction (M. Blondel, Amt. chzm. phys., 1905 [v1ii.], 6, p. 81). A similar set of chlorine-holding compounds is also known, the chlorine replacing one or more hyldroxyl rou s and iving rise to complexes of composition, ¢[Pt ljOHli. H2[Pt%l¢(OH)zl. H2[PtCl¢(OH)4] and H¢[PtCl(OH)5]. The platinic salts (derived from PtO¢) are yellow or brown solids, which are readily reduced to the metallic condition. They give with sulphuretted hydrogen a dark brown precipitate, soluble in excess of ammonium sulphide. Potassium iodide Fgives a brown solution with gradual formation of a precipitate. hey form characteristic precipitates with potassium and ammonium chlorides. The platinous salts are brown or colourless solids which, with sulphuretted hydrogen, give a dark brown preci itate of platinum sulphide, and with potassium iodide a graduai) precipitation of p atinic iodide, Pt12. Platmum trtoxtde, PtO3, is obtained as K¢O~3PtOs, by electrolysing a solution of platinic hydroxide in potash, this compound with acetic acid giving the oxide as a brown, easily decomp;>sable powder (L. Wohler and F. Martin, Bef., 1909, 42, P 3326 -

-Platinum bichlorule, PtCl2, is obtained by heating chlorplatinic acid to 300-350° C. (]. ]. Berzelius), or, mixed wit more or less platinic chloride, by assing chlorine over spongy platinum at a temperature of 250 (P. Schutzenberger, Comptes rendus, 1870, 70, pp. 1134, 1287). It may also be obtained by the decomposition of the compound HCl'PtCl2-ZHQO (see below) at 100° C., this method giving a very pure product (L. F. Nilson, Journ. prak. Chem., 1877 (2), 1 5, p. 260). It is a brown or greyish green coloured solid, which is soluble in hydrochloric acid. It decomposes into its constituent elements when heated. It combines with many chlorides to form characteristic double salts. Platinum bi chloride combines with carbon monoxide, yielding compounds of composition, PtClz. CO, PtCl¢-2CO, 2PtCl, ~3CO (P. Schutzenberger, Ann. chcm. phys., 1870 (4), 21, p. 350). Hydrogen platinochloride or chlorplatinous acid, H2PtCl¢, is only known in solution, and as such is obtained when platinum bi chloride is dissolved in hydrochloric acid, or by decomposing the banum salt with sulphuric acid, or the silver salt with hydrochloric acid. Its salts, the platinochlorides or chlorplatinites, are obtained by reducing the ch orplatinates or directly from the acid itself. They are mostly soluble in water giving red solutions. They are readily oxidized, and nascent hydrogen reduces them to metallic platinum Potassium platmorh orcde or chlorplatcmte, red by reducing hydrogen platinichloride with r potassium platinichloride with potassium oxalate iridium (Klason, Bef., If904, 37, p. 1360); or by chloride to a solution o platinum bi chloride in It crystallizes in dark red prisms, is readily but insoluble in alcohol. The solution of the concentrated m vacuo leaves a residue of

When the tree acid is reduced by alcohol, or passed into a solution of platinum bi chloride in PtCl, CZH4 is obtained as a brown amorphous mposes when heated. When the bi chloride is, heated in a current of carbon monoxide, a sublimate of platinomonocarbonyl dichloride, PtCl¢CO, dicarbonyl dichloride, PtCl2 (CO)¢, and tricarbonvl tetrachloride, Pt¢Cl¢(CO)a, is obtained The first forms bright yellow needles and the second white acicular cr(ystals. The bi chloride also combines with phosgene to form PtCl¢.z OCIZ. Platcmc chlurtde, PtCl4, is obtained when chlorplatinic acid is heated in a current of dry hydrochloric acid gas to 165° C. (W. Pulhnger, Joum Chem Soc., 1892, 61, p. 422) or in a current of dry chlorine at 275° C. (A. Rosenheim and W. Lowenstamm, Zeit. anorg. Chem, 1903, 37, p. 394). It forms a reddish brown crystalline mass which is very hygroscopic. Numerous hydrates are known. The chloride is characterized by the readiness with which it forms double salts with the metallic chlorides and with the hydro chlorides of most organic bases Chlorplatcmc amd, H2PtCl6-6H2O, is obtained bly dissolving platinum in aqua regia containing an excess of hlydro- loric acid, or by the action of chlorine (dissolved in hydroc loric acid) on platinum sponge It crystallizes in needles, which are very deliquescent and dissolve easily in water. It melts in its own water of crystallization at 70° C, and when heated m vacuo to 100° C. it leaves a residue of composition HCl PtCl4 ZHQO. The potassium and ammonium salts and the salts it lorms with organic bases are characterized by their exceedingly small solubility in water. The aqueous solution of the acid reddens litmus and decomposes the metallic carbonates lts salts may he prepared by the direct action of the acid on the metallic hydroxides or carbonates, and are usually of an orange or yellow colour and are mostly soluble in water Potassium chlorplatmate, K;»PtCl6, is obtained, in the form of a yellow crystalline precipitate, when a concentrated solution of a potassium salt K2P|;Cl., is prepa

sulphur dioxide, o

in the presence of

adding potassium

hy drochloric acid

soluble in water,

free acid when

PtCl¢ 2H¢O.

when ethylene is

hydrochloric acid,

mass which deco

is added to a solution of chlorplatinic acid. It crystallizes in octahedral which are scarcely soluble in water, and practically insoluble in absolute alcohol. It decomposes at a red heat into platinum, chlorine and potassium chloride. The corresponding sodium salt, Na2PtCl6.6H2O, is much more soluble in water and in alcohol. The ammonium salt, (NH¢)¢PtCl6, resembles the potassium salt in its solubility in water and in alcohol. Corresponding bromo- and iodo- compounds are known. Platmum bcfluorcde and tetrajiuortde, PtF2 and PtF4, were obtained simultaneously by H Moissan (Ann. chcm. phys., 1894 (6), 24, p. 282) by the action of Huorine on platinum at 500-600° C. They may be separated by taking advantage of their different solubilities in water. Platmum monosulphzde, PtS, is obtained by the direct union of platinum and sulphur; by heating ammonium c lorplatinate with sul phur; or by the action oi sulphuretted hydrogen on the chlorplatinites. It is a dark coloured powder which is almost insoluble in aqua regia. It decomposes when heated strongly leaving a residue of metallic platinum, the same reduction taking place at comparatively low temperatures when it is heated in a current of hydrogen. Platmtc sulphtde, PtS2, is formed when the chlorplatinates are heated with sulphuretted hydrogen to 60° C. The precipitate must be rapidly washed and dried m vacuo, since it oxidizes rapidly on exposure to air. It is a black powder, which when heated strongly in air decomposes and leaves a residue of platinum, but if heated in absence of air leaves a residue of the mono sulphide. It is scarcely aliected by acids and is little soluble in solutions of the alkaline sulphides. Sulphides of composition Pt¢S3 and Pt5S6 have been described (R. Schneider, Pogg. Ann, 1869, 138, p. 604; 1873, 148, p. 633; 1873, 149, p. 381). A salt of composition, Pt(OP)4.H2SO4.H¢O, has been prepared by M. Blondel (Arm. chcm. phys., 1805, (8), 6, p. 81) by the solution of the hydrate H2Pt(OH)6, ce. Pt 2-4H¢O, in dilute sulphuric acid (1.1) at 0° C. On the addition of cold concentrated sulphuric acid to the solution so obtained, the above salt is precipitated in the form of minute needles, which readily decompose in the presence of water. A platmum sulphate, Pt(SO¢)¢.2H, O, has been obtained by L. Stuchlik (Ben, 1904, 37, p. 2913) by the action of sulphuric acid (s.g. 1~84) on platinum under the influence of an alternating current. A crystal ine precipitate is obtained, which is soluble in water and is very hygroscopic.

The platmomtrctes of composition M2Pt(NO2)4 are mostly obtained by double decomposition from the potassium salt, which is formed rm aqueous solution of potassium nitrite to chlorplatinate. They are mostly colourless or which are more or less soluble in water (L. F. 9, p. 1722). The corresponding platino-oxalates first obtained by ]. W. Dobereiner (Pogg. Ann., and their constitution was determined by H. G. 1888, 21, p. 567 R; Zect. anorg. Chem., 1894, 6, um salt, from which the others are obtained by ion, is formed by adding a warm solution of oxalic palatinate. On recrystallization from alkaline by adding a wa

one of potassium

plale yel ow solids

ilson, Bef., 1876,

M2Pt(C¢O4)2 were

1833, 104, p. 180)

Soderbaum (Ben,

p. 45). The sodl

double decomposit

acid to sodium

solutions the salts are obtained in yellow or orange crystals (see M. Vezes, Bull. soc. chcm., 1898 (3), 19, p. 875). These salts are scarcely soluble in water and decompose explosively when suddenly heated. The free acid is obtained by decomposing the silver salt with hydrochloric acid, the indigo blue solution so obtained on concentration cn vacuo yielding a red crystalline mass, which dissolves in water with an indigo blue colour, changing to yellow on dilution.

Platmum cyamde, Pt(CN)¢, is formed by the addition of mercuric cyanide to a solution of a chlorplatinite, or by the decomposition of mercury or ammonium platinocyanide by heat. It is an amorphous powder which is insoluble in water, acids or alkalis, but is soluble in a solution of hydrocyanic acid. It burns when heated. The platinocyanides are derived from the acid H2Pt(CN)s, which is formed by the decomposition of the mercury or copper salt with sulphuretted hydrogen, or of the barium salt with sulphuric acid. It crystallizes from wafer in cinnabar-red prisms which contain five molecules of water of crystallization; in the anhydrous condition it is of a yellowish green colour. It decomposes carbonates. Its salts, which are characterized by the property of polychroism, may be prepared by the usual methods, or bv the solution of metallic platinum in the alkaline cyanides or alkaline earth cyanides under the influence of an alternating current (A. Brochet and ]. Petit, Arm. chtm. phys., 1904 (8), 3, . 460; M. Berthelot, Comptes rendus, 1904, 138, p. 1130). Tliose of the alkali and alkaline earth metals are soluble in water. Many combine with the halogen elements to form complex salts of the type M¢Pt(CN)4.Cl¢. oc HZO. By the decomposition of the barium salts of this tvpe, addition products of the free acid, of composition H¢Pt(CN)., Cl2.4H¢O and H2Pt(CN)4.Br2, have been obtained (C. Blomstrand, Bef., 1869, 2, . 202). They) are deliquescent solids which are exceedingly soluble in water otasstum platmocyamde, K2Pt(CN)4.3H2O, is obtained by dissolving platinum bi chloride in potassium cyanide; by heating potassium ferrocyanide with spongy platinum; or by heating ammonium chlorplatinaie with potassium cyanide. It crystallizes in needles which effloresce readily. The dry salt is exceedingly hygroscopic and is very soluble in

water. When boiled with aqua regia it forms the chlorine addition