64 MILK HYGIENE 



considered injurious. On this account its use should be 

 prohibited. 



The presence of salicylic acid in milk is determined 

 in the following ways : 



To 20 c.c. of milk add 2 to 3 drops of sulphuric acid 

 and about the same amount of ether, then shake the 

 mixture. The ether dissolves the fats and the salicylic 

 acid that is present. The ether solution is evaporated 

 and the residue is extracted with 40 per cent, solution of 

 alcohol and filtered. The addition of a few drops of 

 ferric chloride solution to the filtrate gives a violet color 

 if salicylic acid be present. (Bemont.) 



Girard mixes 100 parts milk with 100 parts water at 

 60° C, and then adds a few drops of acetic acid and a 

 few drops of a solution of mercuric nitrate, the mixture 

 is then shaken vigorously and filtered. The filtrate is 

 shaken with ether, which dissolves the salicylic acid. 

 The ether layer is then filtered and is evaporated in the 

 air; if salicylic acid be present it remains behind as a 

 white crystalline mass, which, after solution in alcohol, 

 is colored violet by a weak solution of ferric chloride. 



c. Benzoic acid possesses very powerful antiseptic 

 properties, but is difficult of solution, and is little used 

 as a preservative of milk. Benzoic acid appears to be 

 somewhat harmful to man, and may be poisonous in 

 large doses; there is little definite knowledge as to its 

 special effect on young children. 



The tests for benzoic acid in milk are more compli- 

 cated. 400 c.c. to 500 c.c. of milk is made alkaline by 

 the addition of lime water and evaporated to about 

 one-fourth its volume ; this is then mixed with pulverized 

 pumice stone until it forms a thick pap, which is evap- 

 orated to dryness over a water bath. The mass is pul- 

 verized, moistened with diluted sulphuric acid and 

 shaken with a double quantity of 50 per cent, alcohol. 



