THE BABCOCK TEST 57 



acid will follow the inside wall down to the bottom, 

 and the pouring should be slow and steady. Thus 

 handled, the acid, being much heavier than the milk, 

 forms a layer by itself at the bottom of the botUe, 

 while the milk forms a separate layer by itself on top 

 of the acid. While pouring in the acid, it is well to 

 turn the test-bottle around slowly so the acid may in 

 turn come in contact with different portions of the 

 inside walls of the neck and wash down any adhering 

 milk. Unless this is done, some milk may remain on 

 the wall of the neck, in which case it will not be prop- 

 erly acted on by the acid, and the fat-column will con- 

 tain particles of undissolved casein. 



If one attempts to pour the acid straight down the 

 neck of the bottle, two difficulties are liable to occur: 

 ( I ) The neck may easily choke up and the acid over- 

 flow on the operator's hands. (2) The acid may drop 

 into and partially mix with the milk, in which case 

 black particles may appear on the upper surface of the 

 acid layer and later, mixing in the fat-column, may 

 interfere with accurate reading of the results. 



Temperature of milk and acid. — It is directed to 

 have the milk and acid at a temperature of 60° to 

 70° F. before they are placed in the test-bottle. There 

 are good reasons for this precaution. If the milk or 

 acid is decidedly cold, as may easily happen in cold 

 weather, the action of the acid may not be vigorous 

 enough to redissolve comi:)letely the coagulated casein, 

 thus producing white specks or a cloudy appearance 

 in and below the fat-column at the end of the test. 

 On the other hand, if the milk or acid is at too high 

 a temperature, as may easily happen in hot weather, 



