The Babcock Test. 33 



sible; if the black specks occur in the fat column itself, 

 the readings are apt to be too high; if below it, the diffi- 

 culty conies in deciding where the column of fat begins. 

 38. Mixing milk and acid. After adding the acid, this is 

 carefully mixed with the milk by giving the test bottle a 

 rotary motion. In doing this, care should be taken that 

 none of the liquid spatters into the neck of the test bottle. 

 When once begun, the mixing should be continued until 

 completed; a partial and interrupted mixing of the liquids 

 will often cause more or less black material 

 to separate with the fat when the test is 

 finished. Clots of curd which separate at 

 first by the action of the acid on the milk, 

 must be entirely dissolved by persistent and 

 careful shaking of the bottle. Beginners 

 sometimes fail to mix thoroughly the milk 

 and the acid in the test bottle. As the acid 

 is much heavier than the milk, a thin layer 

 of it is apt to be left unnoticed at the bot- 

 tom of tlie bottle ? unless this is vigorously 

 acid cylinder, shaken toward the end of the operation. 

 The mixture becomes hot by the action of the acid on 

 the water in the milk and turns dark colored, owing to 

 the effect of the strong sulfur ic acid on the nitrogenous 

 constituents and the sugar of the milk. 



Colostrum milk or milk from fresh cows will form a 

 violet colored mixture with the acid, due to the action 

 of the latter on the albumen present in such milk in con- 

 siderable quantities (23). 



When milk samples are preserved by means of potas- 

 sium bichromate (188), and so much of this material has 

 3 



