Note 25 — Chapter VIII · CARBON AND THE HYDROCARBONS

My article on this subject appeared in the Journal of the St. Petersburg Academy of Sciences in 1861. Up to that time, although many additive combinations with hydrocarbons and their derivatives were known, they had not been generalised, and were even continually quoted as cases of substitution. Thus the combination of ethylene, C2H4, with chlorine, Cl2, was often regarded as a formation of the products of the substitution of C2H5Cl and HCl, which it was supposed were held together as the water of crystallisation is in salts. Even earlier than this (1857, Journal of the Petroffsky Academy) I considered similar cases as true compounds. In general, according to the law of limits, an unsaturated hydrocarbon, or its derivative, on combining with rX2, gives a substance which is saturated or else approaching the limit. The investigations of Frankland with many organo-metallic compounds clearly showed the limit in the case of metallic compounds, which we shall constantly refer to later on.