CHAPTER VIII CARBON AND THE HYDROCARBONS

molecule of methane is brought about by the faculty of mutual combination which exists in the atoms of carbon, and, as a consequence of the most detailed study of the subject, much that might have been foreseen and conjectured from the law of substitution has been actually brought about in such a manner as might have been predicted, and although this subject on account of its magnitude really belongs, as has been already stated, to the sphere of organic chemistry, it has been alluded to here in order to show, although only in part, the best investigated example of the application of the law of substitution. According to this law, a molecule of methane, CH 4 , is capable of undergoing substitution in the four following ways:—(1) Methyl substitution, when the radicle, equivalent to hydrogen, called methyl CH 3 , replaces hydrogen. In CH 4 this radicle is combined with H and therefore can replace it, as (OH) replaces H because with it it gives water; (2) methylene substitution, or the exchange between H 2 and CH 2 (this radicle is called methylene), is founded on a similar division of the molecule CH 4 into two equivalent parts, H 2 and CH 2 ; (3) acetylene substitution, or the exchange between CH on the one hand and H 3 on the other; and (4) carbon substitution—that is, the substitution of H 4 by an atom of carbon C, which is founded on the law of substitution just as is the methyl substitution. These four cases of substitution render it possible to understand the principal relations of the hydrocarbons. For instance, the law of even numbers is seen from the fact that in all the cases of substitution mentioned the hydrogen atoms increase or decrease by an even number; but as in CH 4 they are likewise even, it follows that no matter how many substitutions are effected there will always be obtained an even number of hydrogen atoms. When H is replaced by CH 3 there is an increase of CH 2 ; when H 2 is replaced by CH 2 there is no increase of hydrogen; in the acetylene substitution CH replaces H 3 , therefore there is an increase of C and a decrease of H 2 ; in the carbon substitution there is a decrease of H 4 . In a similar way the law of limit may be deduced as a corollary of the law of substitution. For the largest possible quantity of hydrogen is introduced by the methyl substitution, since it leads to the addition of CH 2 ; starting from CH 4 we obtain C 2 H 6 , C 3 H 8 , and