CENTRIFUGAL FORCE. 155 



Centrifugal Force. When milk is passed through a sepa- 

 rator for the separation of the cream there is deposited upon 

 the drum of the machine a thick slimy mass which contains 

 a considerable quantity of dirt. This has suggested that cen- 

 trifugal force may be used to free milk from its impurities. 

 Recognizing that the bacteria find their entrance into the 

 milk with the various kinds of filth, it is natural to expect 

 that centrifugal force, in removing the filth, will, at the same 

 time, remove many of the bacteria. The plan of passing 

 milk through a centrifugal machine for its purification has 

 been adopted in many places and great claims have been made 

 for special machines used for this purpose. 



In such a purification of milk it is, of course, not desired 

 that the cream should be separated from the milk. Conse- 

 quently the machines devised for this purpose are run at a 

 speed lower than that of the ordinary separator, but sufficient 

 to remove the heavier particles of dirt. 



Such machines quite effectually remove the dirt and filth 

 particles from the milk. A long series of tests, for example, 

 has shown that the milk drawn directly into an open pail may 

 contain as much as .4 gm. per liter of various kinds of dirt 

 (183). Nearly all of this dirt is removed from the milk by 

 passing it through an ordinary cream separator, and, the 

 larger part of it at least, is removed by passing it through 

 the machines with a lower rate of revolution. The removal 

 of the dirt improves the quality of the milk. It takes away 

 the so-called animal. odors, and both the taste and the odor 

 of the milk is benefited by the treatment. A device which 

 will thus remove most of the filth and improve the taste is 

 certainly a useful device for the dairyman. 



But the effect of the treatment upon the bacterial content 

 is very slight (180183). Experimental tests have, indeed, 

 shown that the number of bacteria in milk which has passed 

 through such a centrifugal is sometimes slightly reduced, or 

 occasionally quite materially reduced. Other tests, and these 



