solution on the addition of a given quantity of acid depends indisputably on the amount (mass) of water (Muir). The solution, which is perfectly transparent with a small amount of water, becomes cloudy and deposits the salt of the type BiOX, when diluted. The white flaky precipitate of Bi(OH)_{2}NO_{3} formed from the normal salt Bi(NO_{3})_{3} by mixing it with five parts of water, and in general with a small amount of water, is used in medicine under the name of magistery of bismuth.[46] [46] 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(NO_{3}).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 Bi_{2}X_{6}, and not BiX_{3}; 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, Bi_{2}X_{6}, we shall obtain the following expression for the composition of the nitrates: normal salt, Bi_{2}(NO_{3})_{6}, first basic salt, Bi_{2}O(OH)_{2}(NO_{3})_{2}, magistery of bismuth, Bi_{2}(OH)_{4}(NO_{3})_{2}, and the limiting form Bi_{2}O_{2}(OH)(NO_{3}). The general character of bismuthous oxide in its compounds is well exemplified in the nitrate; bismuthous chloride, BiCl_{3}, 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 BiCl_{3}. Polymerisation may take place in some compounds and not in others. A volatile compound of the composition Bi(C_{2}H_{5})_{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)BiCl_{3}2H_{2}O (from a solution of Bi_{2}O_{3} and KCl in hydrochloric acid) and KClBiCl_{3}H_{2}O. Bigham (1892) also obtained KBr(SO_{4})_{2} in tabular crystals by treating the above-named double salt with strong sulphuric acid. The composition of this salt recalls that of alum.