No. «. DEPARTMENT OF AGRICULTURE. 177 



the general pi-inciples applying to their use and the results secured. 

 There are on the market many dill'erent forms of these machines, 

 aod between many of them there is very little choice in respect to 

 their relative efficiency. If any one, not vi^ell informed about sepa- 

 rators, plans to purchase one, it is suggested that it would be de- 

 sirable to correspond with the Experiment Station at State College 

 and obtain authoritative advice in regard to the qualities of different 

 machines rather than to rely wholly upon the persuasive statements 

 of agents who are ambitious to sell machines. 



All centrifugals designed for separating cream from milk are 

 based upon the same general principle. The milk enters a rapidly 

 whirling bowl and at once partakes of the centrifugal motion, being 

 thrown by the centrifugal force to the extreme wall of the bowl. 

 As the milk continues to flow in, the bowl fills from the outside 

 toward the center. The centrifugal force acts more strongly upon 

 the heavier portion of the milk, that is, the milk serum or all the 

 milk except the fat. Hence, the milk-serum is forced to the outside 

 wall of the bowl, while the lighter portion of the milk, the fat with 

 some adhering serum, is forced to the center. Tubes connect with 

 the skim-milk laver at the outer wall and with the cream laver at 

 the center of the bowl to carry away these products as they accu- 

 mulate. The outer walls of the separator bowl gradually become 

 covered with some of the solid, heavier constituents of the milk, 

 including solid dirt present in the milk, forming what is known as 

 "separator slime," the composition of which we will notice later. 



(1.) Conditions Affecting Creamiog Efficiency of Separators. — The 

 efficiency with which separators remove cream from milk depends 

 upon several different conditions, some of which we will briefly con- 

 sider. 



(a.) The intensity of centrifugal force affects the efficiency of a 

 separator. This increases as the diameter of the bowl increases 

 and also when the bowl whirls rapidly. So, the larger the bowl, and 

 the greater the speed of the bowl, the greater is the centrifugal force 

 and also the creaming efficiencv. 



fb.) The rate at which the milk flows into the separator bowl af- 

 fects the creaming efficiency. The more slowly the milk flows in, the 

 longer it is under the action of the centrifugal force and the more 

 completely is the fat removed from the milk. 



(c.) The temperature of the milk when run through the separator 

 affects the creaming efficiency. The warmer the milk, the more 

 easily the fat separates. The temperature commonly employed is 

 from 76 to 98 degrees F. In producing cream for butter-mak- 

 ing, the milk should be separated at as low a temperature as 

 possible without diminishing the creaming efficiency, because heating 



37—6—1902 



