1032 FOODS AND FOOD ADULTERANTS. 



The test finally used to identify the salicylic acid is preferably that 

 with ferric ehlorid, though the methyl ester reaction can also be used. 

 The solution of ferric chlorid employed should contain about 5 ing 

 to the cc and about 2 or 3 drops should be employed for each test. 



In the ethereal extract obtained in the method for salicylic acid just 

 given, saccharin if present may be identified by evaporating off the 

 ether from a portion and tasting the residue. Should saccharin be 

 present in the original sample in quantities sufficient to communicate 

 to it a sweet taste, and it would hardly be worth while to add less, an 

 unmistakable sweet taste will be obtained. There is no better method 

 than this for saccharin, though many have been proposed. It is prac- 

 tically that used by the French customs officers. 



Benzoic acid may be tested for by taking the unused portion of the 

 distillate from the canned food sample, making alkaline with caustic 

 soda, after adding a little silver sulphate, transferring to a porcelain 

 dish and evaporating to dryness. Next heat on a sand bath to a fairly 

 high, temperature for about fifteen minutes. While still hot a little 

 sulphuric acid is added, and the benzoic acid which is liberated, if pres- 

 ent, recognized by the smell, or rather by its irritating effect on the 

 nose. Considerable practice is necessary to use this test, but with pure 

 chemicals as little as half a milligram can be recognized. Mohler's 

 test 1 may also be used on the dried residue obtained after the evapora- 

 tion. The reaction given by this test, however, is not characteristic 

 for benzoic acid being also given by salicylic acid. 



Besides the method already given for sulphurous acid, another was 

 used frequently which is very convenient. In this method a portion of 

 the liquid obtained by mixing the contents of the can with acid and 

 straining off is mixed with hydrochloric acid, placed in a test tube, and 

 powdered zinc added. It is then covered with a layer of ether and a 

 piece of lead paper (paper moistened with lead acetate) laid above the 

 mouth of the tube. In the presence of sulphurous acid, hydrogen sul- 

 phid is evolved and its presence shown by the paper assuming a 

 brown color. The object of the ether is to keep down any frothing. 

 Results obtained by this method agree very well with those furnished 

 by the distillation method. 



SULPHUROUS ACID. 



This preservative, in the form of the fumes from burning sulphur, has 

 been used from time immemorial as a general disinfectant and antisep- 

 tic. It exercises a bleaching as well as an anti-putrefactive action, and 

 it is therefore greatly favored by corn canners. 



Sulphurous acid, although not a normal constituent of food, is prob- 

 ably not directly harmful in itself. Its use, however, for foods put up 

 in tin cans is to be deprecated for the reason that it attacks the tin and 

 brings it into solution. 



1 Sec page 11G7. 



