520 Br. B. Mendelee^ [May 31, 



(OH). "Without investigating all the possible isomers, we will note 

 only that the hydrate CH(OH)'-CH(OH)- has the same composition 

 as CH-(OH)C(^OH)^, and although corresponding to glycol, and 

 being a symmetrical substance, it becomes on part'ng with its water 

 aldehyde of oxalic acid, or the glyoxal of Debus, CHOCHO. 



5. CH(OH)-C( OH^), from the tendency of all the preceding, 

 corresponds to glyoxylic acid, aldehyde acid, CHOC 0( OH), because 

 the g"oup CO(OH), or carboxyl, enters into the compositions of 

 organic acids, and the group CHO defines the aldehyde function. 



6. C(OHPC(OH)^ through the loss of 2H-0 yields the bibasic 

 oxalic acid C0( OH )C0^ OH), which generally crystallises with 

 2H'0, following thus the normal type of hydration characteristic of 

 ethane.* 



Thus, by applying the principle of substitution, we can, in the 

 simplest manner, derive not only every kind of hydrocarbon com- 

 pound, such as the alcohols, the aldehyde alcohols, aldehydes, alcohol 

 acids, and the acids, but also combinations analogous to hydrated 

 crystals which usually are disregarded. 



But even those unsaturated substances, of which ethylene, CH-CH-, 

 and acetylene, CHCH, are types, may be evolved with equal sim- 

 plicity. ^Vith respect to the phenomena of isomerism, there are 

 many possibilities among the hydrocarbon compounds containing 

 two atoms of carbon, and without going into details it will be 

 sufficient to indicate that the following formulae, though not identical, 

 will be isomeric substantially among themselves : — CH'^CHX- and 

 CH=^XCH-X, although both contain C=^H*X^ or CH-CX- and 

 CHXCHX, although both contain C'-H-X-, if by X we indicate 

 chlorine or generally an element capable of replacing one atom of 

 hydrogen, or capable of uniting with it. To isomerism of this kind 

 belongs the case of aldehyde and the oxide of ethylene, to which we 

 have already referred, because both have the composition C-H^O. 



* One more isomer, CH^CH (OH), is possible, that is secondary vinyl alcohol, 

 which ia related to ethylene. CH-CH-, but derived by the principle of substitution 

 from CH*. Other isomers of the composition C-H*0, such, for example, as 

 CHCH^ (OH), are impossible, because it would correspond to the hydrocarbon 

 CHCH^ = C-H*. which is isomeric with ethylene, and it cannot be derived from 

 metLane. If such an isomer existed, it would be derived from CH-, but 

 such products are up to the present unknown. In such cases the insufficiency of 

 the points of departure of the statical structural teaching is shown. It first 

 admits constant atomicity and then rejects it, the facts serving to establish either 

 one or the other view; and therefore, it seems to me, that we must come to the 

 conclusion that the structural method of reasoning, having done a service to 

 science, has outlived the age, and must be regenerated as, in their time, was the 

 teaching of the electro-chemists, the radicalists, and the adherents of the doctrine 

 of type:*. As we cannot now lean on the views above stated, it is time to abandon 

 the structural theory. They will all be united in chemical mechanics, and the 

 principle of substitution must be looked upon only as a preparation for the coming 

 epoch in chemistry, where such cases as the isomerism of fumaric and maleic 

 acids, when explained dynamically, as proposed by Le Bel and Van't Hoff, may 

 yield points of departure. 



