464 PRINCIPLES Off CHEMISTRY 



oxygen substituted for two atoms of hydrogen. Exactly in the same manner 

 qut of CH(OH) 3 are formed water and formic acid, CHO(OH), and out of 

 C(OH) 4 is produced water an i carbonic acid, or directly carbonic anhydride, 

 CQ 2? which will therefore be nothing else than methane with the double re- 

 .placement of pairs of hydrogen by oxygen. As nothing leads to the supposi- 

 tion that the four atoms of hydrogen in methane differ one from the other, 

 so it does not matter by what means we obtain any one of the combinations 

 indicated they will be identical ; that is to say, there will be no case of 

 actual isomerism, although there may easily be such cases of isomerisui as 

 have been distinguished by the term metamerism. 



Formic acid, for example, has two atoms of hydrogen, dne attached to the< 

 Carbon left from the methane, and the other attached to the oxygen which 

 ha's entered in the form of hydroxyl, and if one of them be replaced by some 

 substance X it is evident that we shall obtain substances of the same composi- 

 tion, but of different construction, or of different orders of movement among 

 the molecules, and therefore endowed with other properties and reactions. If 

 X be methyl, CH 3 -that is to say, a group capable of replacing hydrogen 

 because it is actually contained with hydrogen hi methane itself then by 

 substituting this group for the original hydrogen we obtain acetic acid, 

 CCILjO(OH), out of formic, and by substitution of the hydrogen in its oxide or 

 hydroxyl we obtain methyl formate, CHO(OCH 3 ). These substances differ so 

 much from each Other physically and chemically that at first sight it is hardly 

 possible to admit that they contain the same atoms in identically the same 

 proportions. Acetic acid, for example, boils at a higher temperature than 

 water, and has a higher specific gravity than it, whilst its metameride, 

 methyl formate, is lighter than water, and boils at 80 that is {o say, it 

 evaporates very easily. 



Let us now turn to carbon compounds containing two atoms of carbon to 

 the molecule, as. in acetic acid, and proceed to evolve them from methane by 

 the principle of substitution. This principle declares at once that methane 

 can only be split up in the four following ways : 



1. Into a group CH 3 equivalent with H. Let us call changes of this 

 nature methylation. 



2. Into a group CBLj and H.J. We will call this order of substitutions 

 methylenation. 



3. Into CH and H 3 , which commutations we will call acetylenatioru 



4. Into C and H 4 , which may be called carbonation. 



It is evident that hydrocarbon compounds containing two atoms of carbon 

 can only proceed from, methane, CH 4 , which contains four atoms of hydrogen 

 by the first three methods of substitution ; carbonation would yield free carbon 

 if it could take place directly, and if the molecule of free carbon which is in 

 reality very complex, that is to say strongly polyatomic, as I have long since 

 been proving by various means could contain only C 2 like the molecules 

 O..,, H^; N 2 , and so on. 



By methylation we should evidently obtain from marsh gas, ethane, 



By methylenation that is, by substituting group CH,, for H, methane 

 forms ethylene, CHjCH., = C a H 4 . 



