[3] That is, a substance having a wave-length equal to 0·0005875 millimetre.
[4] He maintains (on p. 309) that the periodic law requires two new analogous elements, having atomic weights of 48 and 64, occupying positions between sulphur and selenium, although nothing of the kind results from any of the different readings of the law.
[5] It is noteworthy that the year in which Lavoisier was born (1743)—the author of the idea of elements and of the indestructibility of matter—is later by exactly one century than the year in which the author of the theory of gravitation and mass was born (1643 N.S.). The affiliation of the ideas of Lavoisier and those of Newton is beyond doubt.
[6] I foresee some more new elements, but not with the same certitude as before. I shall give one example, and yet I do not see it quite distinctly. In the series which contains Hg = 204, Pb = 206, and Bi = 208, we can imagine the existence (at the place VI-11) of an element analogous to tellurium, which we can describe as dvi-tellurium, Dt, having an atomic weight of 212, and the property of forming the oxide DtO3. If this element really exists, it ought in the free state to be an easily fusible, crystalline, non-volatile metal of a grey colour, having a density of about 9·3, capable of giving a dioxide, DtO2, equally endowed with feeble acid and basic properties. This dioxide must give on active oxidation an unstable higher oxide, DtO3, which should resemble in its properties PbO2 and Bi2O5. Dvi-tellurium hydride, if it be found to exist, will be a less stable compound than even H2Te. The compounds of dvi-tellurium will be easily reduced, and it will form characteristic definite alloys with other metals.
[7] 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.
[8] I pointed them out in the Liebig's Annalen, Supplement Band., viii. 1871, p. 211.
[9] Thus, in the typical small period of
Li, Be, B, C, N, O, F,
we see at once the progression from the alkali metals to the acid non-metals, such as are the halogens.
[10] Liebig's Annalen, Supplement Band., vii. 1870.