32 



Testing Milk and Its Products. 



a specific gravity of 1.82-1.83. This amount of acid is 

 carefully poured into the test bottle containing the milk. 

 In adding the acid, the test bottle is conveniently held 

 at an angle (see fig. 7), so that the acid will run down 

 the wall of the bottle and 

 not run in a small stream into 

 the center of the milk, the 

 bottle being slowly turned 

 around and. the neck thus 

 cleared of adhering milk. By 

 pouring the acid into the 

 middle of the test bottle, 

 there is also a danger of com- 

 pletely filling this with acid, 

 in which case the plug of 

 acid formed will be pushed 

 over the edge of the neck by 

 the expansion of the air in 

 the bottle, and may be spilled 

 on the hands of the operator. 

 The milk and the acid in 

 the test bottle should be in 

 two distinct layers, without 

 much of a black 

 band of partially 

 mixed liquids be- 

 tween them. Such FlG 8 The W rong way of emptying pipette 



a dark layer is of- 

 ten followed by an indistinct separation of the fat in 

 the final reading. The cause of this may be that a par- 

 tial mixture of acid and milk before the acid is diluted 



