70 CENTRIFUGAL SEPARATION 



The Deep-setting Method. The milk, preferably fresh from 

 the cow, is poured into a can of the "shot-gun" type, about 8 

 to 10 inches in diameter and 18 to 25 inches deep. This can is 

 placed in cold water and held at as low a temperature as possible. 

 Temperatures between 45 degrees F. and the freezing point of 

 water are preferable. At the end of 24 hours the separation is 

 usually as complete as it is possible to secure by this method of 

 separation. The removal of the cream thus separated is most 

 conveniently accomplished by drawing the skim milk from a 

 faucet at the bottom of the can, leaving about one inch of skim 

 milk in the can. The skim milk should be drawn off slowly in 

 order to avoid currents which cause a portion of the cream to be 

 drawn into the skimmilk. In the case of cans without faucets the 

 cream is removed with a dipper from the top. The skim milk, 

 under proper conditions of creaming, averages about .2 to .3 per 

 cent fat. 



The Water-Dilution Method. The milk is diluted with equal 

 parts of clean water, usually at about 100 degrees F. and set in 

 a cool place for 12 hours, when it is ready to be skimmed. 

 The skim milk is drawn from the bottom of the can. The 

 great rapidity of the separation by this method is due to the 

 lesser viscosity of the diluted milk which permits the fat globules 

 to rise more readily to the surface. The skim milk generally 

 contains from .3 to .4 per cent fat, but since it is diluted to twice 

 its volume with water, the actual loss of fat in the original skim 

 milk is .6 to .8 per cent. 



CENTRIFUGAL SEPARATION 



Definition. In centrifugal separation the centrifugal force 

 generated in a rapidly revolving bowl takes the place of the 

 gravity force acting on milk in a vessel at rest. By centrifugal 

 force, in the sense used here, is understood the force which 

 causes a body, revolving around a center point, to fly from the 

 center. As a simple illustration of this may be mentioned the 

 pull which is felt when a weight attached to a string is whirled 

 about the hand. The pull is caused by the tendency of the con- 

 centrally moving weight to fly outward and the pull increases in 

 force, the longer the string and the faster the weight is whirled. 



