24 THE BUTTER INDUSTRY IN UNITED STATES [248 



separator. To Europe, therefore, belongs the credit for 

 finally crystallizing into a practical machine an idea which 

 had long been lingering in the minds of inventors. 



In 1873 a Dane separated cream by suspending two 

 pails from a stick which was revolved at a speed of 400 

 revolutions a minute. Machines were also constructed 

 having a series of buckets suspended from arms attached 

 to a vertical shaft. When the shaft revolved rapidly the 

 buckets containing the milk swung out to nearly a horizontal 

 position. The centrifugal force caused the skim milk to 

 be drawn toward the bottom of the pail while the fat was 

 forced to the surface. Whirling, therefore, caused the fat 

 and skim milk to separate into layers, and after the machine 

 was stopped the cream could be skimmed in the same way 

 as it is skimmed when it rises by gravity. 



In 1876 there appeared a machine with a vertical drum 

 into which the milk was poured and revolved at a speed of 

 800 or 900 revolutions. When the process of separation 

 was complete the machine was stopped and the skim milk 

 was siphoned out, after which the cream was removed 

 through a valve at the bottom of the drum. The drum 

 was then filled with milk and the operation was repeated. 



Another machine similar to the above showed a slight 

 improvement. The skim milk was removed by opening 

 valves in the periphery of the drum while in motion. To 

 remove the cream, however, is was also necessary to stop 

 the machine. 



After the advance that had been made prior to 1877, it 

 was comparatively easy to take the next step in the evo- 

 lution of the separator. Accordingly in 1877 and 1878 

 machines into which the milk could be fed continuously, 

 and which discharged at the same time cream and skim 

 milk, were developed. These machines embodied the basic 

 principles upon which all separators are constructed. 



