36 Testing Milk and Its Products. 



The fat obtained should form a clear yellowish liquid 

 distinctly separated from the acid solution beneath it. 

 There should be no black or white sediment in or below 

 the column of fat, and no bubbles or foam on its surface. 

 The bottles must be kept warm until the readings are 

 made, so that the column of fat will have a sharply de- 

 fined upper and lower meniscus. 



The readings should be made when the fat has a tem- 

 perature of about 140 P., although the results obtained 

 will not be appreciably affected if the temperature falls 

 below 120. The fat separated in the Babcock test solid- 

 ifies at about 100 P. No reading should be attempted 

 if the fat is partly solidified, as it is impossible to get an 

 accurate reading in this case. 1 



Eeadings of tests of milk made in turbine testers with 

 tightly closed covers which prevent the free escape of 

 the exhaust steam (71) will come .2 to .3 per cent, too 

 high if the temperature of the fat is allowed to rise to 

 that of the exhaust steam during the process of whirling. 

 In such cases the test bottles must be allowed to cool to 

 about 140 (by placing them in water of this tempera- 

 ture for a few minutes) before readings are taken. 2 



1 The effect of differences in the temperature of the fat on the readings 

 obtained will be seen from the following: If 110 and 150 F. be taken as the 

 extreme temperatures, at which readings are made, this difference of 40 

 F. (22.3 C.) would make a difference in the volume of the fat column ob- 

 tained in case of 10 per cent, milk, of .00064 x 2 x 22.3=. 028514 cc., or .14 per 

 cent., .00064 being the expansion coefficient of pure butter fat per degree 

 Centigrade between 50and 100 G.(Zune, Analyse des Beurres,l, 87), and 2, the 

 volume of the fat in cc. contained in 17.6 cc. of 10 per cent. milk. On 5 per 

 cent, milk this extreme difference would therefore be about .07 per cent., 

 or considerably less than one-tenth of one per cent. 



2 See Wis. Experiment Station Rep. XVII, p. 76. 



