CAKIJON AND TIIK HYDROCARBONS 353 



anything, whilst the other hydrocarbons which contain less hydrogen 

 than expressed by the formula C M H 3/l+2 are capable of combining with 

 hydrogen, chlorine, certain acids. Arc. 



Marsh gas is the only hydrocarbon which contains one atom of 

 carbon in its molecule, 36 and stands, therefore, to that element in the 

 same relation as water does to oxygen or ammonia to nitrogen. The mul- 

 titude of hydrocarbons which carbon has the power of forming must be 

 derived from this unique and simplest hydrocarbon. By arranging the 

 molecules (and consequently equal volumes) in the following order 



HH ; OH, ; NH 3 ; CH $ ; 



HC1 ; SH 2 - ; PH 3 : SiH 4 ; 



it is evident that hydrogen and chlorine are univalent, oxygen and 

 sulphur bivalent, nitrogen and phosphorus trivalent, carbon and sili- 

 con quadrivalent. And if the law of substitution gives a very simple 

 explanation of the formation of hydrogen peroxide as a compound con- 

 taining two aqueous residues (OH) (OH), then on the basis of this 

 law all hydrocarbons ought to be derived from methane, CH 4 , as being 

 the simplest hydrocarbon. The increase in complexity of a 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 of that which might be foreseen and 

 conjectured from the law of substitution has been actually brought 

 about in such manner as might have been predicted. Although this sub- 

 ject, on account of its magnitude, appertains, as has been already stated, 

 to the sphere of organic chemistry, yet it has been touched on 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 mole- 

 cule of methane, CH 4 , is capable of undergoing substitution in the four 

 following ways : (1) Methyl substitution, when the radicle equivalent 

 to hydrogen CH 3 , called methyl, replaces the hydrogen. In CH 4 this 

 radicle is combined with H, and therefore can replace it, as (OH) re- 

 places 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 equiva- 

 lent 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 similarly to the methyl 

 substitution. These four cases of substitution render it possible to 

 understand the principal relations of the hydrocarbons. For instance, 



36 Methylene, CHo, does not exist. When attempts are made to obtain it (for 

 example, by removing X.> from CEUXo), C 2 H 4 or C 3 H 6 are produced that is to say, it 

 undergoes polymerisation . 



VOL. I. A A 



