140 BbTTER-MAKINO. 



effect the different degrees of agitation of milk has upon the 

 efficiency of separation : 



Av. Fat 

 No. of Per Cent 

 Experi- in 

 ments. Skim- 

 milk. 



Milk heated in vat, not pumped 10 .117 



Milk heated in Pasteurizer, 200 revolutions of agitator per minute 8 .115 



250 " " " " " 3 .118 



300 " " " " " 8 .134 



350 " " " " " 2 .143 



400 " " " " " 7 .198 



500 " " " " " 4 .225 



Milk pumped by the turbine pump at 122° F 3 .129 



" " " " " 64° F 3 .119 



" " with the pump, effective at 122° 3 .117 



" " " " " 64° 3 .115 



In the above experiments the diameter of the agitator in 

 the Pasteurizer was 14 inches. The speed at the periphery, 

 at 250 revolutions per minute, was 5 feet per second. 



It will be seen from the above table that the higher the 

 speed of the agitator, the greater the difficulty in getting a 

 complete separation. Besides the speed of the agitator in 

 the heating apparatus, undoubtedly the shape of the Pas- 

 teurizer is a factor in determining the efficiency of the 

 subsequent separation. For instance, the milk in most hori- 

 zontal Pasteurizers is, even at low speed, exposed to con- 

 siderable agitation. 



If the milk is suddenly heated from a low temperature to 

 about 80° or 90° F. and then skimmed, the heating does not 

 facihtate the skimming process very much. It is essential 

 that the milk should be exposed to this temperature for a 

 considerable time. The fat-globules do riot warm as rapidly 

 as the milk-serum. This diminishes the difference between the 

 specific gravity of the two substances, consequently complete- 

 ness of separation becomes more difficult. If milk is heated 

 to a high temperature, say, for instance, 170° F., then the 

 separation will be sufficiently complete without exposing the 

 milk for any length of time to that temperature. 



