MKTHYL SALICYLATE L 



103 



presence of organic acids, as the latter do not ailect it." This has been 



found to be an error, as salicylic acid can be accurately titrated, the end 



point being ver}' sharp when either standard sodium hydroxide, carbonate 



or bicarbonate solutions are used, the carboxyl group only Ijeing affected. 



Walker and Wood '' have used Congo red for titrating salicylic acid against 



l)aryta. Erythrosin has also been found to give fairly good results, 



although Congo red has been used almost entirely throughout this work. 



In titrating the free acid in methyl salicylate, from 5 to 20 cubic 



centimeters of the ester are sliaken with an equal quantity of neutral, 



N 

 distilled water in a glass-stoppered flask, and standard alkali, — r , added 



50 



until the color indicating the end point remains permanent on shaking. 



Standard solutions of sodium acid carbonate'' are best used in this 

 titration, for reasons explained further on, although sodium hydroxide 

 solutions give accurate results. The titrations were carried out at the 

 room temperature, wliicli varied in this laboratory from 28° to 34°. 



In order, to show that the acidity of the samples was not due to acids 



other than salicylic, the following method was employed : Ten cubic 



centimeters of the ester or oil of gaultheria were extracted three times 



N 

 with 5 cubic centimeter 23ortions of — sodium acid carbonate. The acid 



carbonate solutions were united, extracted three times with chloroform 

 to remove the ester which was in solution, made acid with sulphuric acid 

 (1 to 3) and extracted three times with chloroform. The chloroform 

 extracts were united, filtered into a weighed dish, and evaporated sjDon- 

 taneoiisly in a vacuum desiccator. After weighing the residue, it was 

 dissolved in liot water and the salicylic acid determined colorimetrically.* 



Table I. — Amounts of salicylic acid in natural and artificial oil of gaultheria. 



Sample. 



Amount. 



Salicylic acid— 



By titrat- 

 ing. 



By weighing. ° 



1 

 Colorimet- 

 rically. 



Oil of gaultheria (genuine) 



10 

 10 



Per cenf. 

 0.025 

 0.0113 



5.5 mg. = 0.016 per cent__ 

 3.9 mg. = 0.033 per cent- 



Pa- cent 

 0.028 

 0.0113 





'J. Chem. Soc. (1898), 73, 619. 



' Standard solutions were made from Kalilbam's sodium acid carbonate, wliich 

 was found to be very pure. 



"Methods of Analysis, Bull. V. S. Dept. Agrie. (1907), 107, 180. 



" The weights of the salicylic acid are evidently too great for the reason that 

 drying was imperfect. Small quantities of the acid are so easily volatilized that 

 it was considered preferable to err in the opposite direction and rely upon the 

 colorimetric method for accuracy. 



