METHODS OF TESTING MILK FOR CASEIN 



faint but distinct pink color remains through the solu- 

 tion half a minute or longer. The same uniform shade 

 and duration of pink color should be obtained as near- 

 ly as possible in all cases. 



(5) Acid milk. Milk that is sour or that coagulates 

 on heating should not be used. 



(6) Use of preservatives. Milk treated, when fresh, 

 with a small amount of powdered mercuric chloride 

 and then kept in a cool place gives good results for 

 two or three weeks. 



CENTRIFUGAL TEST FOR CASEIN 



The following method has been devised at the Wis- 

 consin experiment station (Bulletin 156) by Hart: 



Apparatus and Reagents. (i) Testing-tubes with 

 neck so graduated that each division represents 0.2 per 

 cent, when a 5-cc. sample of milk is used. (2) Centri- 

 fuge of special form, run by hand, having a wheel 15 

 inches in diameter and geared to give a speed of 2000 

 revolutions a minute. (3) Pipette for measuring 5 cc. 

 of milk. (4) Cylinder for measuring 2 cc. of chloro- 

 form. (5) Dilute acetic acid containing 0.25 per cent. 

 prepared by diluting 10 cc. of glacial acetic acid to 100 

 cc. with water, and then diluting 25 cc. of this solu- 

 tion to 1000 cc. (6) Chloroform of the best quality. 



Method of operating test. In a testing-tube one 

 puts 2 cc. of chloroform and on top of this 20 cc. of 

 the dilute acid. Milk (65 to 75 F.) is then run in, 

 after which the thumb is placed over the opening of 

 the tube which is then inverted to bring the mixture 

 into the barrel-shaped portion ; then the whole is shaken 

 with considerable vigor for 15 to 20 seconds, accurately 



