THE PRINCIPLES OF ORGANIC CHEMISTRY 61 



the other and joined to nitrogen, and so reappears as methyl- 

 amine. Bearing in mind the underlying assumption that the 

 hydrogen atoms are always monovalent, the carbon atoms 

 always tetravalent, and the nitrogen either trivalent or penta- 

 valent, the above reactions find satisfactory explanation in the 

 following formulae and equations : 



OK 



H 3 C f|=N + KOH + H 2 = H 3 C-C=0 + NH 3 



Cyanide. 



OK 

 H 3 C-N=C + KOH + H 2 = H 3 C N=H 3 + HC=0 



Iso-cyanide. 



The first compound is termed a cyanide, the other an iso~ 

 cyanide. 



Another simple but important instance of isomerism may 

 be referred to in illustration, viz., the case of the lactic_acid$. 

 Ordinary lactic acid is produced by the fermentation of milk 

 sugar or lactose ; it has the molecular formula C 3 H 6 3 . Another 

 acid of the same molecular formula exists whose chemical 

 properties are quite different from those possessed by the 

 fermentation lactic acid. The difference between these two 

 acids finds an explanation in the reactions by which they 

 have been artificially prepared, and in the products to which 

 they give rise on oxidation, etc. An acid having chemical 

 properties identical with the fermentation acid is obtained 

 from acetaldehyde by the following typical reactions. By 

 the action of hydrocyanic acid on aldehyde a cyanhydrin 

 is formed : 



CH 3 



CH 3 | 



0=0 CN 



