42 MODERN METHODS OF TESTING MILK 



is made to turn 60 times a minute. The proper speed 

 once attained should be kept up during the testing of 

 a sample. The efficiency of whirling can be further 

 tested by treating different samples of the same milk 

 at different rates of speed, the highest per cent, of 

 fat beyond which there is no increase, showing the 

 right speed. 



KIND OF ACID USED IN BABCOCK TEST 



The acid used in the Babcock test is commercial sul- 

 phuric acid, commonly known as oil of vitriol. It 

 should not be quite as strong as the strongest com- 

 mercial acid. While the strong acid has a specific 

 gravity of about 1.84, the acid used in the test should 

 be between 1.82 and 1.83 at 60 F. 



Effect of weak acid. If the acid is weaker than 

 that indicated by specific gravity 1.82, there is danger 

 that some of the coagulated casein may not be com- 

 pletely redissolved and this, mixing with the fat, 

 makes the fat-column in the test-bottle more or less 

 pale and cloudy, when it should be clear and usually 

 golden yellow in color. In addition, there is apt to 

 be a collection of cloudy matter at the foot of the fat- 

 column, obscuring the line of division and making 

 sharp reading difficult. The use of more than 17.5 cc. 

 of acid not too weak may give good results. 



Effect of too strong acid. When the acid is too 

 much above specific gravity 1.83, the fat-column is 

 dark in color. There is a layer of black material be- 

 low it, and the amount of fat is difficult to read with 

 accuracy. When the acid is too strong, it is possible 

 to secure accurate results by using less than 17.5 cc. 



