Note 7 — APPENDIX II

Let me mention another proof of the bivalency of beryllium which may have passed unnoticed, as it was only published in the Russian chemical literature. Having remarked (in 1884) that the density of such solutions of chlorides of metals, MCln, as contain 200 mols. of water (or a large and constant amount of water) regularly increases as the molecular weight of the dissolved salt increases, I proposed to one of our young chemists, M. Burdakoff, that he should investigate beryllium chloride. If its molecule be BeCl2 its weight must be = 80; and in such a case it must be heavier than the molecule of KCl = 74·5, and lighter than that of MgCl2, = 93. On the contrary, if beryllium chloride is a trichloride, BeCl3 = 120, its molecule must be heavier than that of CaCl2 = 111, and lighter than that of MnCl2 = 126. Experiment has shown the correctness of the former formula, the solution BeCl2 + 200H2O having (at 15°/4°) a density of 1·0138, this being a higher density than that of the solution KCl + 200H2O (= 1·0121), and lower than that of MgCl2 + 200H2O (= 1·0203). The bivalency of beryllium was thus confirmed in the case both of the dissolved and the vaporised chloride.