62 DETECTION OF PRESERVATIVES. 



compared with known unadulterated milk. Phenolph- 

 thalein solution may not be used, as an indicator in place 

 of rosolic acid in this test. By the method given 0.05 per 

 cent of these carbonates may be easily detected (Hilger, 

 E. Schmidt). 



III. SALICYLIC ACID. 



(a) Acidify 20 c. c. of milk with two or three drops of 

 sulphuric acid and shake with about an equal amount 

 of ether. The greatest possible part of the ether solu- 

 tion is drawn ofT and evaporated ; the residue extracted 

 with 40 per cent alcohol ; filtered ; and 5 c. c. of the fil- 

 trate treated with a few drops of ferric chloride. A violet 

 color shows the presence of salicylic acid. By comparison 

 with a solution of salicylic acid of known strength and 

 colored by treatment with ferric chloride the approximate 

 amount of acid present may be estimated. (Remont.) 



(b) 100 c. c. of milk are diluted with 100 c. c. of water 

 at 60 degrees and treated with eight drops, of mercuric 

 nitrate, thoroughly shaken, and the resulting precipitate 

 filtered off. The filtrate which will contain all of the sali- 

 cylic acid originally in the milk sample is shaken with 

 50 c. c. of ether ; the ether solution is drawn ofif, filtered 

 through a dry filter and allowed to evaporate spontane- 

 ously in the air. If the residue resulting be white and 

 crystalline, soluble in alcohol and produces a violet 

 color with a few drops of one per cent ferric chloride so- 

 lution the presence of salicylic acid is proved conclu- 

 sively. (Girard.) 



IV. BENZOIC ACID. 



A large quantity of milk (300-500 c. c.) is made alkaline 

 with calcium or barium hydroxide solution ; evaporated 

 to one-fourth its volume ; mixed with pure sea sand, 

 pulverized pumice stone or gypsum, to a thick paste and 



