120 MILK AND DAIRY PRODUCTS PART 



Soxhlet-Scheibe use another method, which is based upon 

 the quantitative determination of the carbon dioxide in the ash 

 of the milk. The normal amount of carbon dioxide in milk 

 does not exceed 2 per cent. 



2. Boracic Acid and Borax. 



E. Meissl l has given the following method for detecting 

 boracic acid or its salts in milk: 100 c.c. of milk are made 

 alkaline with milk of lime evaporated to dryness and then ignited. 

 Lime is preferable to the alkalies because the ignition is much 

 easier. The ash is dissolved in the smallest possible quantity 

 of concentrated hydrochloric acid, the carbon filtered off, and 

 the liquid evaporated to dryness, care being taken to drive off 

 all the acid. The residue is then moistened with a little very 

 dilute hydrochloric acid, the mass completely soaked with 

 tincture of curcuma, and evaporated down on the water-bath. 

 In the presence of the smallest trace of boracic acid, the residue 

 is coloured red, varying between vermilion and cherry-red. 

 This test is extremely sensitive : 1 mg. to 0*5 mg. of boracic acid 

 in the ash or O'OOl to 0'002 per cent, in the milk can be 

 detected with certainty. 



Concentrated hydrochloric acid also gives a cherry-red colour 

 with tincture of curcuma, but it disappears at once on the 

 addition of water. The ash which has been tested with 

 curcuma can, if required, be used for the flame test. To carry 

 out this test, the material is brought along with methyl alcohol 

 into a flask provided with inlet and outlet tubes. Hydrogen 

 gas is then passed through the flask and lighted, and the flame 

 will have a green colour in the presence of boracic acid, 



3. Salicylic Acid. 



Ch. Girard 2 uses the following method in testing for salicylic 

 acid in milk : 8 drops of acetic acid and 8 drops of mercuric 

 nitrate are added to 100 c.c. of milk and 100 c.c. of water at 

 60 C., and well shaken. The precipitate is filtered off and the 

 filtrate shaken out with ether, which extracts the salicylic acid, 

 the ethereal solution being filtered through a dry filter. After 



1 Zeitschrift fur analytische Chemie, 1882, p. 531. 

 a Ibid., 1883, p. 277. 



