Note 1 bis — Chapter XXIII · THE PLATINUM METALS

Some light is thrown upon the facility with which the platinum compounds decompose by Thomsen's data, showing that in an excess of water (+ Aq) the formation from platinum, of such a double salt as PtCl2,2KCl, is accompanied by a comparatively small evolution of heat (see Chapter XXI., Note 40), for instance, Pt + Cl2 + 2KCl + Aq only evolves about 33,000 calories (hence the reaction, Pt + Cl2 + Aq, will evidently disengage still less, because PtCl2 + 2KCl evolves a certain amount of heat), whilst on the other hand, Fe + Cl2 + Aq gives 100,000 calories, and even the reaction with copper (for the formation of the double salt) evolves 63,000 calories.