THE PLATINUM METALS 885 



R0 3 or hydrates, HaRO^ROafHO^ (the type o sulphuric acid) ; bu$ 

 they, like ferric and manganic acids, are chiefly known in the form of 

 salts of the composition K 2 R0 4 or K 2 R 2 7 (like the dichromate). These 

 salts are obtained, like the manganates and ferrates,, by fusing the oxides, 

 or even the metals themselves, with nitric, or, better still, with potassium 

 peroxide. They are soluble iji water, are easily deoxidised and do not 

 yield the acid anhydrides under the action of acids, but break up, either 

 (like the ferrate) forming oxygen and a basic oxide (indium and rhodium 

 react in this manner, as they do not give higher forms of oxidation), Or 

 passing into a lower and higher form of oxidation that is, reacting 

 like a manganate (or partly like nitrite 'or phosphite). Osmium and 

 ruthenium react according to the latter form, as they are capable of 

 giving higher forms of oxidation, Os0 4 and RuO 4 , and therefore their 

 reaction.^, of decomposition may be essentially represented by the equa- 

 tion 20sC>3=OsO a 



respects. In general, Eu has much in common with Mn, Joly (1889) also showed that 

 If KNO 5 be added to a solution of EuClj containing HC1, .the solution, becomes hot, and 

 ft salfr, EuCl 3 N02KCl, is formed, which enters into double .decomposition and is very 

 Btable. Moreover, if Eu.Cl 3 be treated with an excess of nitric acid, it forms a salt^ 

 EuCl 3 NOE a O, after being heated (to boiling) and the addition of HCL The vapour 

 density of Eu04, determined by Pebray and Joly, corresponds to that formula, 



10 Although palladium gives the same type.s of combination (with chlorine) as 

 platinum, its reduction to EX 3 is incomparably easier tnan that of platinic-chloride, and 

 (a the case of iridium iij is also very easy. Iridic chloride, IrCl 4 , ^ts as an oxidising 

 agent, readily parts with a fourth of its- chlorine to a number of substances, readily 

 evolves chlorine when heated, an,d it is only at low temperatures that chlorine and aqua 

 regia convert iridium into iridio chloride. In' .disengaging chlorine iridium more often 

 and easily gives the very* stable iridious chloride, IrCl 3 (perhaps this substance is 

 lr 2 Cle=IrCl 2 ,IrCl 4 , insoluble in water, but soluble in potassium chloride, because it 

 forms the double salt K 3 IrCl 6 ), than the dichloride, IrCl^. This compound, corresponding 

 to IrX 2 , is very stable, and corresponds with the basic oxide, Ir 2 3> resembling the 

 oxides Fe 2 3 , Co 2 3 . To this form there correspond ammoniacal compounds similar to 

 those given by cobaltic oxide. Although iridium also gives an acid in the form of the 

 salt K 2 Ir 2 07, it does not, like iron (and chromium),, form the corresponding chloride^ 

 IrC-l c . In general, in this as in the other elements, it is impossible to predict the chlorine 

 compounds from those of oxygen. Just as there is no chloride SC1 6> but only SC1 2 , so 

 also, although Ir0 3 exists, IrCl 6 is wanting, the only chloride being IrCl 4 ^ and this 

 is unstable, like SC1 2 , and easily parts >with its chlorine. In this respect rhodium, is 

 very much like iridium (as platinum is like palladium). For KhCl 4 decomposes with 

 extreme ease, whilst rhodium chloride, EhCl 3> is very -stable,.like many of the salts of 

 the type EhX 5) .although like the platinum elements these salts are easily reduced to 

 metal by the actjon of heat and powerful reagents. There 'is as close a resemblance 

 between osmium and ruthenium. Osmium when submitted to the riction of dry chlorine 

 gives osmic chloride, OsCl^ but the' latter is converted by water (as is osmium by moist 

 chlorine) into osmic anhydride, although the greater portion is then decomposed .into 

 Os(HO) 4 and 4HC1, like a chloranhydride of an acid. In general this acid character is 

 more developed in osmium than in platinum and iridium. Having parted with chlorine, 

 osmio chloride, OsCl 4 , gives the unstable trichloride, OsCl 3 , an.d the stable soluble 

 dichloride, OsCl 2> which corresponds with platinous chloride in its properties and 

 reactions. 'The relation of ruthenium to the halogens is of the ^amQ nature* 



