Note 13 — Chapter XXIII · THE PLATINUM METALS

Subsequently, a whole series of such compounds was obtained with various elements in the place of the (non-reacting) chlorine, and nevertheless they, like the chlorine, reacted with difficulty, whilst the second portion of the X's introduced into such salts easily underwent reaction. This formed the most important reason for the interest which the study of the composition and structure of the platino-ammonium salts subsequently presented to many chemists, such as Reiset, Blomstrand, Peyrone, Raeffski, Gerhardt, Buckton, Clève, Thomsen, Jörgensen, Kournakoff, Verner, and others. The salts PtX4,2NH3, discovered by Gerhardt, also exhibited several different properties in the two pairs of X's. In the remaining platino-ammonium salts all the X's appear to react alike.

The quality of the X's, retainable in the platino-ammonium salts, may be considerably modified, and they may frequently be wholly or partially replaced by hydroxyl. For example, the action of ammonia on the nitrate of Gerhardt's base, Pt(NO₃)₄,2NH₃, in a boiling solution, gradually produces a yellow crystalline precipitate which is nothing else than a basic hydrate or alkali, Pt(OH)₄,2NH₃. It is sparingly soluble in water, but gives directly soluble salts PtX₄,2NH₃ with acids. The stability of this hydroxide is such that potash does not expel ammonia from it, even on boiling, and it does not change below 130°. Similar properties are shown by the hydroxide Pt(OH)₂,2NH₃ and the oxide PtO,2NH₃ of Reiset's second base. But the hydroxides of the compounds containing 4NH₃ are particularly remarkable. The presence of ammonia renders them soluble and energetic. The brevity of this work does not permit us, however, to mention many interesting particulars in connection with this subject.