GERHARDT'S NOTATION. On certain theoretical grounds, Gerhardt doubled the numbers that had hitherto been current, expressing the atomic weights of certain of the chemical elements—oxygen, carbon, sulphur, selenia, and tellurium ; the other num bers remaining unaltered. We give in the following table the earlier system and Ger hardt's numbers: .
Old Equivalent. , Gerhardt's Equivalent.
0, 8 16 C, 6 12 S, 16 32 Se, 39.75 Te, 129 The examination of a few formulm will readily enable the reader to translate from one system into the other: Compounds. Old Formuhe. Gerhardt's Formula.
Water HO Potash.... • KO K, 0 Hydrate of potash KO,HO K110 Hydrated nitric acid HO,NO, NO,Il Hydrated sulphuric acid. HO,S0, Hydrated acetic acid HO, Alcohol..... 110, C411,0 C,I160 In Gerhardt's formulm the symbols whose equivalents are changed are printed in italics. Each system of notation seemed to have its-advantages; and until the original publication of this work was far advanced, most British chemists adhered to the old, which for the sake of uniformity was maintained to the end of the eneyelopmdia. In the end, however,
the new atomic weights gained the day-• and in the SUPPLEMENT a further account is given of the change and of the reasons by which it is justified. The general principle on which it is grounded is, "that the atomic weights of an element and of its combina tions should be selected so as to express the entire series of combinations by the simplest series of formula; so as best to accord with the chemical propertiesiind metamorphoses of the bodies; so as best to illustrate their analogies with other bodies; and so as to be in relation with their physical properties, such as their specific volumes, specific heats, isomorphism, &e."