so 



coalesce, forming butter. Changes also occur in the milk, 

 sugar, casein and fats, more or less quickly, according to the 

 higher or lower temperature to which the milk is exposed. 

 The milk sugar becomes converted, apparently through the 

 agency of a ferment, into lactic acid. This gives the milk 

 an acid reaction, and precipitates the casein, causing the milk 

 to curdle. The coagulum or curd, incloses the fat globules. 

 The liquid from which it is separated, a solution of milk sugar, 

 and salts, is known as whey. The curd, when completely 

 separated from the whey, is called cheese. 



The average composition of human and cow's milk and 

 of the cream from cow's milk is given in the following table : 



174. Test the reaction of milk. Fresh cow's milk may 

 often be neutral or even acid or amphoteric i. e., will color 

 blue litmus red or red litmus blue. Sour milk is acid. The 

 reaction of fresh human milk is always alkaline. Free lactic 

 acid is present in the fresh milk of carnivora. 



175. Determine the specific gravity of unskimmed milk 

 with an accurate lactometer or urinometer. Allow some milk 

 to stand until the next day. Remove the cream and again 

 take the specific gravity, then add from 10% to 25% of water 

 and take the specific gravity once more. 



The laws of New York require milk to have a density of 

 not less than 1.029, and total solids of not less than 12%, of 

 which 3% must be fats. 



Various forms of apparatus for testing milk are on the 

 market. A convenient apparatus is sold by the Whitall Tatum 

 Co. of New York. (Apparatus No. 2). The following sug- 

 gestions and directions accompany each apparatus : The lac- 

 tometer is intended to show the specific gravity or density of 

 milk at the temperature of 60° Fahrenheit. On the scale 

 represents a specific gravity of 1.000, which is that of water, 

 and 100 represents a specific gravity of 1.029, which has been 



