16 



equally distributed about the wheel or disk so that the 

 equilibrium of the latter is not disturbed. An even 

 number of bottles should always be whirled. Should an 

 odd number of tests be made a test bottle filled with water 

 may be used to balance the machine. When the bottles 

 are in place, the tester is covered in order to keep the bottles 

 from getting cold and to protect the operator from flying 

 glass and acid should any of the bottles break. The tester 

 is now set in motion and the bottles whirled 4 to 5 minutes 

 at proper speed. This will be sufficient to bring prac- 

 tically all the fat to the surface. In cold weather, if a 

 hand tester is used, it may be necessary to pour hot water 

 into the jacket of the tester to keep the bottles warm. 



Speed of centrifuge. Farrington and Woll have calcu- 

 lated the proper speed of testers with wheels of different 

 diameters to be as follows: 



Revolutions 



of wheel 

 Diameter of wheel in inches: per minute. 



10 1, 074 



12 980 



14 909 



16 848 



18 800 



20 759 



22 724 



24 693 



Adding the water. With the pipette or with the device 

 for the purpose attached to some steam testers, or in any 

 other convenient manner, hot water is added to the bottles 

 until the contents come nearly to the lower part of the 

 neck. The cover is now replaced on the tester and the 

 whirling repeated for two minutes. Hot water is again 

 added until the fat reaches a point below the highest 

 graduation mark on the neck. It must never reach the 

 top mark, or some of the fat may be lost. This time the 

 water should be dropped directly into the fat in order to 

 clear the fat of the light, flocculent material which may be 

 entangled in it and which would later interfere with the 

 reading of the test. The whirling is repeated for another 

 minute. The temperature at which the readings are taken 

 is between 130 and 140 F., and this should be borne in 



