82 ANIMAL CHEMISTRY LECTURE IY. 



into acetic acid, vinic alcohol into propionic acid, propyl-alcohol 

 into butyric acid, and so on ; but until very lately we could 

 not step from acetic to propionic acid, or from propionic to butyric 

 acid, that is to say, we could obtain butyric acid C 4 H 8 2 , from 

 certain members of the 3 -carbon group, but not from those mem- 

 bers which we had ourselves produced from the 2 -carbon group ; 

 and, similarly, we could produce propionic acid C 3 H6O 2 , from cer- 

 tain members of the 2 -carbon group, but not from those members 

 which we had ourselves produced from the I -carbon group. The 

 series of synthetic operations by which it would be possible to 

 pass from any group not merely to the next, but to the next 

 but one, and so on ad libitum, was incomplete through our 

 ignorance of the metamorphic relation subsisting between the 

 acid and its associated alcohol. The alcohol, and not the acid, 

 being the plastic member of the group, we could convert the 

 I -carbon alcohol into the 2 -carbon acid, and the 2 -carbon alcohol 

 into the 3 -carbon acid, and so on; but being unable to convert 

 the 2 -carbon acid into the 2-carbon alcohol, we could not by any 

 means pass from the I -carbon to the 3 -carbon group. Very 

 recently, however, this difficulty has been overcome by the sepa- 

 rate researches of "Wurtz and Mendius, who have shown us how 

 to transform any acid into its corresponding alcohol ; whereby a 

 continuous series of synthetic processes may now be carried on as 

 far as we please. Without entering into purely chemical details, 

 I may say that the process of Wurtz consists in transforming the 

 aldehyd of the acid into the normal form of the alcohol ; while 

 that of Mendius consists in transforming the nitrile of the acid into 

 the ammoniated form of the alcohol, by means of nascent hydro- 

 gen, as illustrated below in the case of ethylic alcohol, thus: 



Aceto-nitrile Ethyl-amine 



C,H 3 N + H 4 C 3 H 7 N or C,H 5 .H,N 



Acet-aldehyd Ethyl-hydrate 



C a H 4 + H 3 C 3 H 6 or C 2 H 5 .HO 



Ethyl-chloride 



C,H 5 C1 or C 3 H 5 .C1 



