FOOD PRESERVATIVES. 



1. SALICYLIC ACID, 

 (a) QUALITATIVE DETECTION. 



If the material be a solid or semisolid, macerate from 200 to 300 grams in a mortar with 

 about 400 cc of water made slightly alkaline and strain through a cotton bag or separate by 

 means of a centrifuge. Acidify the liquid (or the original sample if it be a liquid) with dilute 

 (1 : 3) sulphuric acid and extract with ether or chloroform. If an emulsion is formed it may 

 be broken up by the addition of more ether or by whirling in a centrifuge. The ether or 

 chloroform should be washed twice with about one-tenth its volume of water to remove the 

 least trace of sulphuric acid, transferred to a small porcelain dish, and allowed to evaporate 

 at a low temperature. The residue is taken up with a small volume of hot water. It may be 

 divided into several portions, some of which may be used for the detection of other preserva- 

 tives. A small amount of salicylic acid occurs naturally in many fruits and the portion of 

 the extract used for its detection should represent not more than 50 cc of wine or 50 grams 

 of fruit. A reaction obtained with this amount is due to added salicylic acid.. 



In testing for salicylic acid two or three drops of a one-half per cent solution of ferric 

 chlorid or of a 2 per cent ferric alum solution are added to the solution of the residue from 

 the ether in a small porcelain dish. In case of the presence of a considerable amount of 

 tannin or other bodies giving a precipitate or color with ferric salts the residue left on the 

 evaporation of the ether when perfectly dry may be extracted with gasoline of low boiling 

 point, the gasoline extract allowed to evaporate, and salicylic acid detected by ferric solution, 

 as indicated above. 



In the case of materials containing large amounts of extractive matter and those from 

 which the aqueous solution can not be separated from the solid matter by straining or cen- 

 trifuging, it may be found necessary to separate the salicylic acid by distillation. This is 

 especially true with foods rich in fat. In such cases acidify the macerated material with 

 phosphoric acid and transfer to a distilling flask with a very short neck and wide mouth. An 

 Erlenmeyer flask with inside diameter of mouth 1J inches is a good shape. The tube con- 

 necting the flask with condenser should be very short, with an inside diameter of not less 

 than three-eighths of an inch. 



Conduct steam through a small tube passing through the stopper and dipping deeply 

 into the material in the flask. The distillation of the salicylic acid is facilitated by sub- 

 merging the distilling flask almost to the stopper in an oil bath and distilling with the tem- 

 perature of the oil at from 120 to 130 C., or by adding about 20 grams of sodium chlorid to 

 the contents of the flask, for each 100 cc of the substance, to raise the boiling point. Care 

 must be taken not to let the contents of the flask get too low, as the heat will decompose the 

 organic matter. 



Distill 500 to 600 cc, make alkaline, evaporate to small volume, acidify with dilute sul- 

 phuric acid, extract with about 50 cc of ether, and proceed as directed above. In the 

 presence of a considerable amount of salicylic acid a reaction can usually b.e obtained by add- 

 ing a few drops of the ferric solution directly to the first 200 cc of the distillate. 



Salicylic acid may often be separated from fat extracted with the ether by washing the 

 ether solution with dilute ammonia. The aqueous liquid is then evaporated almost to dry- 

 ness and tested with ferric solution, as directed above. 



In the case of foods which yield to the gasoline solution of the ether residue a color that 

 obscures the ferric chlorid reaction (e. g., tomatoes) the ether solution may be evaporated, 

 the residue dried in a desiccator or in a current of dry air, sublimed, and collected on a 

 watch glass cooled with ice. The sublimate is then dissolved in hot water and tested with 

 ferric alum, as described above. 



The same difficulty may often be avoided, and in fact the extraction with gasoline of the 

 dry residue from the ether extraction may be obviated, by precipitating before extraction 



(3) 



