Testing Milk on the Farm. 141 



manner. The result of this test shows the average qual- 

 ity of the milk produced by the cow during the time the 

 milk was sampled. 



166. As the amounts as well as the quality of the milk 

 produced 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 (180), or by a 25 cc. 

 pipette divided into ^ cc. ; in using the latter apparatus as 

 many cubic centimeters and tenths of a cubic centimeter 

 of milk are conveniently taken each time for the compos- 

 ite sample as the weight of milk in pounds and tenths of 

 a pound produced by the cow. 



The opinion is often expressed that a considerable 

 error is introduced by measuring out milk warm from 

 the cow for the Babcock test, since milk expands on being 

 warmed, and a too small quantity in this manner is 

 obtained. By calculation of the expansion of milk 

 between different temperatures it is found that 1 cc. of 

 milk at 17.5 C. (room temperature) will have a volume 

 of 1.006289 cc. at 37 C. (blood-heat), i. e., an error of 

 less than .03 per cent, is introduced by measuring out 

 milk at the latter temperature. While the temperature 

 has therefore practically no importance, the air incorpo- 

 rated in the milk during the milking process will intro- 

 duce an appreciable error in the testing, and samples of 

 milk should therefore be left for an hour or more after 

 milking before the test samples are taken. By this time 



