Note 46 — Chapter XIX · PHOSPHORUS AND THE OTHER ELEMENTS OF THE FIFTH GROUP

With an excess of water a further quantity of acid is separated and a still more basic salt formed. The ultimate product, on which an excess of water has apparently no action whatever, is a substance having the composition BiO(NO3).BiO(OH). In the latter salt we see the limit of change, and this limit appears to show that the type of the saline compounds of bismuthic oxide is of the form Bi2X6, and not BiX3; but it is very probable, on the basis of the examples which we considered in the case of lead, that this type should be still further polymerised in order to give a correct idea of the type of the bismuthous compounds. If we refer all the bismuthous compounds to this type, Bi2X6, we shall obtain the following expression for the composition of the nitrates: normal salt, Bi2(NO3)6, first basic salt, Bi2O(OH)2(NO3)2, magistery of bismuth, Bi2(OH)4(NO3)2, and the limiting form Bi2O2(OH)(NO3).

The general character of bismuthous oxide in its compounds is well exemplified in the nitrate; bismuthous chloride, BiCl₃, which is obtained by heating bismuth in chlorine, or by dissolving it in aqua regia, and then distilling without access of air, is also decomposed by water in exactly the same manner, and forms basic salts—for instance, first, BiOCl, like the above salt of nitric acid. Bismuth chloride boils at 447° and probably its formula is BiCl₃. Polymerisation may take place in some compounds and not in others. A volatile compound of the composition Bi(C₂H₅)₃ is also known as a liquid which is insoluble in water and decomposes with explosion when heated at 130°. Double salts containing chloride of bismuth are: 2(KCl)BiCl₃2H₂O (from a solution of Bi₂O₃ and KCl in hydrochloric acid) and KClBiCl₃H₂O. Bigham (1892) also obtained KBr(SO₄)₂ in tabular crystals by treating the above-named double salt with strong sulphuric acid. The composition of this salt recalls that of alum.