30 DAIRYING 



over the bowl. From these covers or pans the skim milk and 

 the cream are conducted into cans or vats by the side of the 

 machine. The required speed of this bowl is 8000 revolutions per 

 minute and about 1200 pounds of milk are skimmed per hour. 



274. These two machines were in use from 1879 to 1892. 

 They had nearly the same skimming efficiency ; approximately 

 0.2% of fat was left in the skim milk. Since then the separator 

 bowl has been considerably changed, but the construction of the 

 frame which supports the bowl and the method of attaching 

 power to it, together with some other features, are practically 

 the same today as they were in those old machines which possess 

 the distinction of being the first successful power cream separators 

 invented. 



At the present time some of the largest cream separators will 

 skim 300 pounds of milk per hour so that not more than one-tenth 

 of one per cent, of the butter fat is left in the skim milk, and in 

 addition to this the sweet milk from cows of any breed or in any 

 part of their lactation period may be efficiently skimmed. 



275. The power cream separators were the first ones used 

 extensively. These may be divided into two general classes, the 

 "hollow bowl" and those having the bowls filled with discs or 

 plates of some sort. 



In both types, milk enters at either the top or the bottom 

 of the bowl and by whirling in the bowl it is separated into three 

 layers, first, the dirt, ash and precipitated albumen, and casein 

 of the milk, which being the heaviest, flies to the walls of the 

 bowl and is deposited as "slime ;" second, the layers of skim milk, 

 and third, the cream which increases in richness towards the center 

 of the bowl. 



276. Both the cream and the skim milk are discharged near 

 the center of the bowl and the nearer the center these openings 

 are placed, the easier the bowl runs. If the skim milk discharged 

 at the circumference of the bowl considerable more power would 

 be required to run it. The size of the skim milk tubes in the 

 bowl are also regulated by the size of the milk inlet and the 

 speed of the bowl. 



