CEXTRIFUG.'lL CRE-UIIXG 155 



cream and the skim-milk, and the force acts in a A'crtical direc- 

 tion. The force generated in the separator is se\-eral thousand 

 times greater than the natural force in tlie gra\"ity method. 

 For this reason the cream separates almost instantaneously after 

 the milk has entered the separator and is exposed to the cen- 

 trifugal force. 



Advantages. — The centrifugal separator has several advan- 

 tages over the gravit^- method, which are apparent without 

 detailed elaboration. In the hrst place, the range of tempera- 

 ture and condition of the milk at which the cream can be suc- 

 cessfully separated is much greater than that for successful 

 separation by the gravity method. Second, a much better 

 quality of cream can be obtained by the centrifugal s}stem, 

 as the separation can be done before the milk gets old, while 

 by the gravity method the time required for elTicient separation 

 is so long that the cream deteriorates more or less before it is 

 removed from the milk. Third, by the centrifugal method the 

 thickness of the cream can be regulated to suit reciuirements, 

 while by the gravity method the thickest cream that can be 

 obtained is about 20 per cent. Fourth, by the centrifugal method 

 man}' impurities and undesirable germs are removed, while in 

 the gra\'ity method the exposure to open air, more or less impure 

 is likely to contaminate the milk wdth taints, and also allows the 

 gemrs to fall into it. Fifth, b}- the centrifugal method the skim- 

 milk is left in a more natural condition. The milk can be 

 skimmed soon after milking, or after it has been deU\'ered to the 

 creamery, and thus be in the best possible condition for feeding 

 purposes. Sbcth, the centrifugal method pemiits of a more 

 thorough separation of the fat. Butter-fat, as a rule, is too 

 expensive to feed, when good and much cheaper substitutes can 

 be had. 



History of Centrifugal Separators. — The first centrifugal 

 separator was a very simple one. It consisted of buckets hanging 

 on the ends of arms, or on the periphery of a rotating horizontal 

 flat wheel which swung on a central axis. The milk was placed 

 in the buckets and whirled for a time, and then the machine (if 

 we mav call it such) was stopped, and the cream removed in the 



