The Babcock Test. 33 



with the water of the milk may bring about too strong 

 an action of the acid on this small portion of the milk, 

 and thus char the fat contained therein. The appear- 

 ance of black flocculent matter in or below the col- 

 umn of fat which generally results, in 

 either case renders a correct measurement' 

 difficult and at times even impossible; if 

 the black specks occur in the fat column 

 itself, the readings are apt to be too high; 

 if below it, the difficulty comes in decid- 

 ing where the column of fat begins. 



38. Mixing milk and acid. After add- 

 ing the acid, this is carefully mixed with: 

 the milk by giving the test bottle a rotary 

 motion. In doing this, care should be 

 acid cyiinde?.' taken that the liquid is not shaken into 

 the neck of the test bottle. When once begun, the mix- 

 ing 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 continued and careful shaking of the bot- 

 tle. 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 bottom of the bottle, unless this 

 is vigorously 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 sulfuric acid on the nitrogenous 

 constituents and the sugar in the milk. 



3 



