410 CREAM. 



which expresses the time taken for a globule to pass from any point in the 

 separator to any other point, provided the serum is at rest and the globule 

 travels radially. 



This is not the case in modern separators where the milk runs in 

 continuously, and terms expressing the rate of flow of milk, and the 

 shape of the separator, must be introduced. The resulting equations 

 are so complex that it would serve no useful purpose to deduce a general 

 equation. 



Whatever the form of equation suited to any particular separator, the 

 time taken by a globule to pass through a given space will always be pro- 

 portional to the square root of the cube of the radius, and as the number 

 of gallons per hour passed through the separator will be inversely propor- 

 tional to the time, it follows that for each size of fat globule there will be 

 a limit where its velocity against the stream of milk will be equal to the 

 velocity of the stream itself, and all globules smaller than this will pass 

 out with the separated milk. If we assume that the total weight of fat 

 in globules of any size is equal to the total weight of fat in globules of any 

 other size, it follows that the amount of fat in the separated milk is pro- 

 portional to the cube root of the square of the number of gallons per hour. 

 The coefficient of viscosity, and also the value of the factor (ds df), vary 

 with the temperature, and consequently the viscosity of the fat globules 

 and the amount of fat in the separated milk. 



The relative proportions of the cream and skim milk will also affect the 

 percentage of fat in the separated milk, as not only is the rate at which 

 milk travels towards the separated milk outlet affected, but any resistance 

 to the exit of cream causes the fat globules to touch each other, and interferes 

 with their free motion. 



The author has, upon these considerations, worked out a formula to 

 give the percentage of fat in the separated milk 



where / = percentage of fat in separated milk, 

 F = ,, cream, 



t = temperature in degrees Centigrade, 

 m number of gallons per hour, 

 v = revolutions per minute. 



a, b, and c are constants for each separator. 

 b usually varies from 1-035 to 1-05. 

 c from 1-00 to 1-05. 



c is appreciable, chiefly with separators in which the adjustment of the 

 thickness of the cream is made at the cream outlet e.g., in the Alpha 

 separator, in which c has the value 1-04 to 1-05. 



The following results were obtained with a separator, for 

 which the following formula was applicable : 



OQ 2 



(40 "~ 



