28 DAIRYING 



obtained. One of the first applications of this principle to cream 

 separation was made by a Massachusetts man in about 1870. 

 He placed graduated glass tubes filled with milk in pockets some- 

 thing like those now used in the Babcock milk tester and whirled 

 these tubes in a machine constructed for the purpose. Aft^i- 

 whirling about 20 minutes the thickness of the cream was meas- 

 ured in each tube. This machine was designed to be used as a 

 cream tester for milk. It was, however, a pattern for the first, 

 commercial cream separators which were constructed on the same 

 plan excepting that pails holding fifty to sixty pounds of milk 

 were substituted for the glass tubes. These pails of milk were 

 whirled at a speed of 400 revolutions per minute and when they 

 were stopped the cream was skimmed from them in the same way 

 as gravity cream had been formerly skimmed from milk. This 

 operation required a great deal of time and power. It was of 

 no particular value except as a demonstration that cream could 

 be separated by centrifugal force. A number of machines of this 

 type were made, but they all had to be stopped after whirling 

 and the cream skimmed off as in the gravity methods. 



271. These so-called "pail" machines were followed by the 

 "drum" centrifuge, which was a revolving, vertical cylinder filled 

 with milk. Four wings extended from the walls to the about one- 

 half way to the center of the drum, in order to carry the milk 

 with the drum. After whirling for some time the drum was 

 stopped and the skim milk or the heavier part thrown toward 

 the circumference of the drum was drawn off by means of faucets 

 in its walls. The cream was then removed from the center, a new- 

 supply of milk added and the whirling process repeated. These 

 "drum" centrifuges were experimented with for some time. Dr. 

 Fleishman used one holding 200 pounds of milk, which was 

 whirled at about 900 revolutions per minute. The time required 

 for this heavy drum to stop after it had attained full speed was 

 about one-half hour, and this long time was a serious drawback 

 to its use. It was demonstrated, however, by the use of this 

 machine that 95.6 per cent, of the fat in normal whole milk could 

 be separated in this way and that the completeness of the cream 

 separation is influenced by the temperature of the milk and the 

 length of time it is whirled in the centrifuge at full speed. 



