104 GIBBS. 



SEPARATION AND DETERMINATION OE SALICYLIC ACID AND METHYL 

 SALICYLATE IN FOODS AND DRUGS. 



The suljstance under investigation, containing salicylic acid and methyl 

 salic3date, is made strongly alkaline to C'ongo red with an approximately 

 normal solution of pure sodium acid carbonate, free from normal car- 

 bonate^" and, if not liomogeneous, the aqueous solution is separated and 

 the process repeated with the residue until it is thorouglily extracted 

 by the sodium acid carbonate solution. All of the salicylic acid has now 

 passed into the acid carbonate solution in the form of sodium salicylate 

 together with small amounts of methyl salicjdate. This solution is 

 extracted repeatedly, not less than three times, with small amounts of 

 chloroform^^ until all traces of methyl salicylate have been removed. The 

 sodium acid carbonate solution is now made acid with sidphuric acid 

 (1 to 3) and extracted in the usual way to remove and determine the 

 salic3dic acid.^^ ■ i 



This method has been successfully applied to emulsions of cod-liver oil 

 which are usually veiy difficult to separate. The sodium acid carbonate 

 layer, carrying the salicylic acid and small amounts of methyl salicylate, 

 can be separated in a rapidly revolving centrifuge. AVith non-alcoholic 

 beverages and soda-water flavors, the method is especially easy of manip- 

 ulation. During the process of extraction, while the methyl salicylate 

 is still in the solution with the salicylic acid salts, the temperature should 

 not be unduly raised for the reason that the rate of hydrolysis of methyl 

 salicylate is accelerated with increase in temperature. During the manip- 

 ulation in this laboratory, where the temperature is always high, the 

 solutions have been kept below 35°, which temperature has been found 

 to be a fairly safe limit. Lower working temperatures are, of course, 

 to be desired. 



The ester, separated by chloroform extraction,^^ is saponified by heat- 



'" Solutions of sodium acid carbonate lose carbon dioxide and therefore should 

 be freshly prepared and kept in well-stoppered bottles. The loss of carbon 

 dioxide, the increase of normal sodium carbonate, and consequent increase of 

 sodium hydroxide in the solution is in most cases counterbalanced by the acidity 

 of the substance under examination. When this substance is very acid it is best 

 made alkaline by the addition of solid spdium acid carbonate in order to avoid 

 a great increase in the bulk of the solution. 



" Chloroform has been fowid to be better than ethei- for removing tlie methyl 

 salicylate from this solution, for the reason that it is less miscible with the 

 aqueous solution. 



'- Methods of Analysis, Loc. cit. 



"' In the case of oil emulsions and some other mixtures the ester is best 

 separated, after the removal of the salicylic acid, by steam distillation from a 

 sulphuric-acid solution. Since methyl salicylate is partially hydrolyzed on heat- 

 ing in a sulphuric-acid solution, it is necessary to carry on the distillation until 

 all of the salicylic acid formed has passed over into the receiver. 



