46 



THE STORY OF MILK 



and more easily seen in raw milk than in pasteurized 

 milk and its absence is not always a sure sign of 

 lack of richness or purity of the milk. By cooling the 

 milk thoroughly so that it will keep, almost all the 

 cream will be at the top in forty-eight hours and can 

 be skimmed off. The cream can be used for coffee or 

 on cereals or fruits or puddings; the skim milk left 

 will still hold ]/2% 01* more of butter-fat and can be 

 used to drink or for cooking. 



The Separator. — On the farm or in the creamery the 

 cream is no longer raised by gravity, that is, by letting 

 the milk ''set" either in shallow pans on the kitchen 

 shelf or in deep cans in ice water, but the fresh, warm 

 milk is run through the separator in a continuous 

 stream. 



It was noticed that the rising of the cream due to the 

 difference in specific gravity between the butter-fat and 



the milk-' 'serum" (the watery 

 solution of the other constit- 

 uents) might be greatly hastened 

 by subjecting the milk to cen- 

 trifugal force. This physical phe- 

 nomenon was taken advantage 

 of in the first conception of the 

 separator where it was shown 

 that if a pail of milk was whirled 

 around like a stone in a sling the 

 heavier milk-serum would be 

 thrown towards the bottom of the 

 pail with so much greater force 

 than the lighter cream (butter-fat mixed with a small 

 part of the serum) that the separation which would take 

 48 hours in the milk at rest, could be accomplished in a 



Early conception of the 

 separator 



