152 Testing Milk and Its Products. 



be labeled with the number or name of the particular 

 cow. Composite tests are generally taken for two or four 

 days cr for a week. If continued for a week, the jars will 

 contain at the end of this time a mixture of the milk 

 of fourteen milkings. The composite sample is then 

 carefully mixed by pouring it gently a few times from 

 one jar to another, and is tested in the ordinary man- 

 ner. The result of this test shows the average quality 

 of the milk produced by the cow during the time the 

 milk was sampled. 



As the amounts as well as the quality of the milk pro- 

 duced by single cows vary somewhat from day to day 

 and from milking to milking, it is desirable in testing 

 single cows, especially when the test includes only a few 

 days, to take a proportionate part (an aliquot) of each 

 milking for the composite test sample. This is easily 

 done by means of a Scovell sampling tube, the use of 

 which is explained in another place (183), or by a 25 cc. 

 pipette divided into -^ cc. ; in using the latter appara- 

 tus as many cubic centimeters and tenths of a cubic 

 centimeter of milk are conveniently taken each time for 

 the composite sample as the weight of milk in pounds 

 and tenths of a pound produced by the cow. 1 



170. Testing warm milk. The opinion is some- 

 times expressed that a considerable error is intro- 

 duced by measuring out milk warm from the cow 

 for the Babcock test, since milk expands on being 

 warmed, and a too small quantity is obtained in 

 this manner. By calculation of the expansion of 

 milk between different temperatures it is found that 



1 Decker, Wis. experiment station, report 16, p. 155. 



