450 SCIENCE AND PRACTICE OF CHEESE-MAKING 



removed and placed in a rack in an upright position 

 and then read after lo minutes or more. The chloro- 

 form and fat should be at the bottom and on top of 

 this a white, cylindrical mass of casein. The end 

 surfaces of this casein cylinder, which should be flat, 

 are read on the scale directly, the result being the 

 per cent of casein in the milk, if the test is successful. 

 While fresh milk is desirable for best results, it is said 

 that seven-day composite samples may be used by 

 taking one-ounce samples of milk each day in a brown 

 or amber-colored glass receptacle, adding on the first 

 day and again on the third day one-fourth of an or- 

 dinary potassium bichromate tablet (equal to i^ or 

 2 grains). The mixture is gently agitated daily by a 

 rotary motion, and kept well stoppered in a dark, cool 

 place. 



Conditions affecting accuracy of results. — (i) Use 

 of sour milk. (2) Use of milk containing preserva- 

 tives, except bichromate. (3) Too strong or too dilute 

 solution of acetic acid. (4) Poor quality of chloro- 

 form. (5) Temperature of acid and milk below 65° 

 or above 75° F. (6) Shaking mixture of acid, chloro- 

 form and milk too short or too long a time, too hard or 

 not hard enough. (7) Allowing shaken mixture to 

 stand too long before whirling. (8) Running centri- 

 fuge too slow or too fast, or for a longer or shorter 

 time than 7^ or 8 minutes. (9) The use of a revolv- 

 ing wheel greater or less than 15 inches without a cor- 

 responding change in the number of revolutions. ( 10) 

 Reading the results in less than 10 minutes after whirl- 

 ing. (11) Any condition which disturbs the distinct 

 flatness of the upper or lower surface of the cylindrical 

 column of compacted casein. 



