I2O MODERN METHODS OF TESTING MILK 



curate results, the following precautions should be 

 observed: (i) The cup should be heated gradually, 

 since too rapid heating causes sputtering and loss. (2) 

 During the evaporation, the dish should be shaken 

 with a rotary motion in order to distribute the heat 

 more uniformly and facilitate escape of water-vapor. 

 (3) The butter must not be heated so high nor so long 

 as to cause decomposition and volatilization of the 

 butter-solids. 



GRAY'S TEST FOR WATER IN BUTTER 



This method was worked out in the Dairy Division 

 of the Bureau of Animal Industry, U. S. Dept. of 

 Agr. (Circular No. 100). It differs from the methods 

 already described in several respects: (i) The water 

 is evaporated from the butter in the presence of a 

 slightly volatile mixture of high boiling-point, which 

 does not mix with water. (2) The evaporated water 

 is recovered by distillation. (3) The distilled water 

 is caught in a graduated tube, which permits direct 

 reading of the results in percentage of water in 

 butter. 



The apparatus and reagents employed in the test, 

 aside from an accurate scale with a 5-gram and a 10- 

 gram weight, an alcohol lamp and a 6-cc. measuring- 

 graduate are (i) the special testing-apparatus, (2) 

 parchment paper, perfectly dry, (5 by 5 inches in size), 

 (3) rubber stoppers (one stopper lasts for about 100 

 tests), and (4) the amyl reagents (a mixture of 5 

 parts of amyl acetate and i part of amyl valerianate, 

 entirely free from water-soluble impurities). 



The special testing apparatus includes three essen- 



