Testing Milk on the Farm. 151 



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 of ordinary quality at the latter 

 temperature. While the temperature has therefore prac- 

 tically no importance, the air incorporated in the milk 

 during the milking process will introduce an appreci- 

 able error in the testing, and samples of milk should 

 therefore be left for an hour or more after milking be- 

 fore the milk is measured into the test bottles. By this 

 time the specific gravity of the samples can also be cor- 

 rectly determined (113). 



171. Size of the testing sample. Four ounces is a 

 sufficient quantity for a sample of milk if it is desired 

 to determine its per cent, of fat only ; if the milk is to 

 be tested with a lactometer, when adulteration is sus- 

 pected, a pint sample is needed. If this sample of milk 

 is put into a bottle and carried or sent away from the 

 farm to be tested, the bottle should be filled with milk 

 clear up to the neck to prevent a partial churning of 

 butter in the sample during transportation (30). 



172. Variations in herd milk. While considerable 

 variations in the quality of the milk of single cows are 

 often met with, a mixture of the milk of several cows, 

 or of a whole herd, is comparatively uniform from day 

 to day; the individual differences tend to balance each 

 other so that variations, when they do occur, are less 

 marked than in case of milk of single cows. There are, 

 however, at times marked variations also in the test of 

 herd milk on successive days ; the following figures from 

 the dairy tests conducted at the World's Columbian Ex- 

 position in Chicago in 1893 illustrate the correctness of 



