vin, a, i Gibbs and Pratt: Hydroxyl and Carboxyl 45 



of the absorption band of salicylic acid at 1/A=3300 and by a 

 shift of this band to 1/A==3400, a position which corresponds to 

 the same band shown by salicylic acid in the presence of 5 equiv- 

 alents of sodium ethoxide. In the latter case the salicylic acid 

 is almost entirely in the form of the mono-sodium salt (the 

 actual amount of the salicylic acid in the form of the di-sodium 

 salt is about 11 per cent of the whole), and the shift to the 

 shorter wave lengths may be due to the ionization phenomenon 

 previously mentioned. With 300 equivalents of alkali, the sali- 

 cylic acid in one-thousandth molar solution is approximately 9.2 

 per cent in the form of the mono-sodium salt and 90.8 per cent in 

 the form of the di-sodium salt for n X s/0.03=d where 



n= concentration of the free base, 



s= concentration of the mono-sodium salt, 



d= concentration of the di-sodium salt. 



These values are computed for aqueous solutions since the 

 hydrolysis constant in alcohol is not available. We believe the 

 error thus introduced has no bearing on the general consider- 

 ations. 21 



The absorption curve under these conditions is, therefore, 

 that of di-sodium salicylate. The absorption band is much 

 broadened ; and the shift toward the shorter wave lengths, found 

 in the presence of 5 equivalents of alkali, is more than counter- 

 balanced by the shift toward the red which is characteristic of 

 the enol-keto tautomerism. Since this absorption band has 

 almost entirely disappeared, it is evident that the free affinity 

 of the carbonyl group is approaching a minimum. 



The curve for methyl salicylate in the presence of a small 

 quantity of alkali, 1 equivalent, shows a shift toward the red 

 and a decrease in the persistence of the large absorption band. 

 In the presence of greater excess of alkali, the shift toward the 

 red is increased, while no further reduction in the persistence 

 is to be noted. The presence of acid causes no appreciable change 

 in the absorption spectrum of methyl salicylate. Since the 

 ionization constant of this compound 22 is very small ; namely, 

 1.2 XlO -11 , it appears probable that no measurable effect is to 

 be expected. All of the curves which have any significance are 

 plotted in fig. 4. 



" In one-thousandth molar alcohol solutions the addition of 10 per cent 

 of water was necessary to keep the salts in solution. 

 " This Journal, Sec. A (1913), 8, 1. 



