CENTRIFUGAL SEPARATION 71 



The discus throw of the athlete is a concrete example of the cause 

 and effect of the centrifugal force. The centrifugal force acts on 

 liquids as well as on solid bodies. 



The Theory of Centrifugal Separation. The separation of 

 the cream from milk in the centrifugal separator is based on the 

 well known physical law that when liquids of different specific 

 gravities revolve around the same center, at the same distance, 

 and with the same speed, the greater force is generated by the 

 heavier liquid than by the lighter. Milk, as already stated, con- 

 sists of two liquids of different specific gravities, the fat particles 

 and the milk serum. The milk enters the rapidly revolving bowl 

 either at the top, middle or at, the bottom of the bowl. In most 

 separators it runs first through a central tube which carries it 

 to the middle or bottom before it is discharged into the bowl. In 

 the case of a bowl not in motion the milk fills the bowl from, 

 the bottom up due to the force of gravity. When the bowl is 

 rapidly revolving the force of gravity is overcome by the cen- 

 trifugal force which is over a thousand times greater than the 

 gravity force. The milk is therefore thrown immediately to the 

 periphery or side of the bowl, filling the bowl from the side to 

 the center. 



While both liquids, the fat particles and the milk serum, are 

 forced to the bowl wall, the heavier liquid, which is the skim 

 milk, is driven from the center with greater force than the 

 lighter liquid which is the fat particles. The skim milk thus 

 forms a vertical wall enveloping the side of the bowl. As the 

 result of this separation the fat globules, which are uniformly 

 distributed in the milk before it is subjected to the centrifugal 

 force, separate .from the skim milk and, through a recurrent 

 motion, are crowded toward the center of the bowl, where they 

 accumulate in a vertical layer of cream, in a similar way as 

 they gather on the surface of the milk by gravity creaming. It 

 is obvious, therefore, that the least fat is found near the periphery 

 of the bowl and the most fat is found near the center of the bowl. 



As more milk flows into the bowl, the vertical wall of skim 

 milk and cream expands in thickness, filling up the larger por- 

 tion of the bowl. In most types of bowls, operated under normal 

 conditions, the milk never fills the entire bowl, a vacant space 



