460 Transactions. — Chemistry and Physics. 



Of the acids examined it is interesting to compare lactic 

 and mandelic with the compounds from which they are de- 

 rived. 



Propionic. Lactic. 



CH 3 • CH 2 • CO,H CH 3 • CH(OH) • CO,H 



18 23 



Pheuylacetic. Mandelic. 



C 6 H 5 • CH, • C0 2 H C 6 H 5 • CH(OH) • CO,H 



20 32 



The greater magnitude of the increase in the case of 

 mandelic acid is especially noteworthy when we remember 

 that all the disubstituted acetic acids containing a phenyl 

 radicle are characterized by their extremely low rate of 

 association. That the high value in the case of mandelic acid 

 is due to the remaining a hydrogen is evident from the fact 

 that benzilic acid, in which this hydrogen is replaced by 

 phenyl, has the low value of 7 for its rate of association. 

 Thus it seems that the oxy group protects the hydrogen from 

 the normalising influence of the phenyl ; other groups, how- 

 ever, have quite a different effect. Thus — 



Chlorpropionic. Chlorpkenylacetic. 



CH 3 • CHC1 • CO,H C 6 H 5 • CHC1 • COoH 



(13) 4 



Lactic. Mandelic. 



CH 3 • CH(OH) • C0 2 H C 6 H 5 ■ CH(OH) • COoH 



(23) 32 



When the hydroxyl occurs in the benzene nucleus of a sub- 

 stituted fatty acid its influence is only slight. This is shown 

 for othooxydiphenylacetic, which associates at about the rate 

 that we should expect in the case of diphenylacetic acid. 

 Nitrosovaleric acid possesses the constitution 



CH 3 • C • CH, • CH, • CO,H 



II 

 NOH 



It associates very rapidly, but it differs from most of the acids 

 with high association numbers in the fact that it possesses a 

 very low value for the initial molecular depression. Again, it 

 is the only acid of which the rate of association clearly 

 diminishes with the concentration. (See Plate XLIX.) Hence 

 it seems probable that the associating groups disappear in 

 the process of association. This favours the possibility of the 

 formation of complexes of the type 



CH 3 • C • CH, • CH 2 • C • OH 



;NOH HON x 



1/ ! 



HO • C ■ CH, • CH, • C • CH 3 



