146 MANUAL OF MILK PRODUCTS 



acid has been added, and the solution filtered. A strip of tur- 

 meric paper moistened with the filtrate will be colored reddish 

 brown when dried at 100° C. on a watch glass, if boracic acid 

 is present. 



If a little alcohol is poured over the ash to which concentrated 

 sulfuric acid has been added, and fire is set to the alcohol, after 

 a little while this will burn with a yellowish green tint, especially 

 noticeable if the ash is stirred with a glass rod and when the 

 flame is about to go out. (Testing Milk and Its Products, 

 Farrington and Woll, p. 247.) 

 Test for salicylic acid (salicylates, etc.). 



Twenty c.c. of milk are acidulated with sulfuric acid and 

 shaken with ether; the ether solution is evaporated, and the 

 residue treated with alcohol and a little iron-chloride solution ; 

 a deep violet color will be obtained in the presence of salicylic 

 acid. (Testing Milk and Its Products, Farrington and Woll, 

 p. 248.) 

 Test for benzoic acid. 



Two hundred and fifty to 500 c.c. of milk are made alkaline 

 with a few drops of lime or baryta water, and then evaporated 

 to about a quarter of the bulk. Powxlered gypsum is stirred 

 into the remaining liquid until a paste is formed, which is then 

 dried on the water bath. The gypsum only serves to hasten 

 the drying, and powdered pumice stone or sand can be used 

 equally well. When the mass is dry, it is finely powdered and 

 moistened with dilute sulfuric acid and shaken out three or 

 four times with about twice the volume of 50 per cent alcohol, 

 in which benzoic acid is easily soluble in the cold, the fat only 

 being dissolved to a very slight extent or not at all. The acid 

 alcoholic liquid from the various extractions, which contains 

 milk-sugar and inorganic salts in addition to the benzoic 

 acid, is neutralized with baryta water and evaporated to a 

 small bulk. Dilute sulfuric acid is again added, and the 

 liquid shaken out with small quantities of ether. On evapora- 



