The Babcock Test. 57 



the speed required for obtaining this force in case of machines 

 of other diameters, the value of v in formula (I) is found from 



Substituting the values for F and w, 



r _ /32.2 X 30.65 r 



V 3 



= V/5264 r 



In this equation the values r = 5, 6, 7, 8, 9, 10, 11, 12 inches 

 are substituted in each case (^ r \, j 7 ^, . . . }| feet), and the 

 velocity in feet per second then found at which the bottles are 

 whirled when placed in wheels of diameters 10 to 24 inches, and 

 subjected in each case to a centrifugal force of 30.65 Ibs. As the 



number of revolutions per minute = , v being as before 



2 TT r 



the velocity in feet per second, and r the radius of the wheel, 

 the speed at which the wheel must be turned, is found by sub- 

 stituting for v the values obtained in the preceding calculations 

 in case of wheels of different diameters. The results of these 

 calculations are given in the following table: 



Diameter Velocity in feet Number of revolutions 



of wheel, d. per second, v. of wheel, per minute. 



10 46.84 1074 



12 51.31 980 



14 55.43 909 



16 59.26 848 



18 62.84 800 



20 66.24 759 



22 69.47 724 



24 72.56 693 



These figures show that a tester, for instance, 25 inches in 

 diameter, requires less than 700 revolutions per minute for a 

 perfect separation of the fat in Babcock bottles, while a ten- 

 inch tester must have a speed of nearly 1100 revolutions, in 

 order to obtain the same result. 



The speed at which testers of different diameters should be 

 run to affect a complete separation has been calculated by Prof. 

 C. L. Beach in the following manner 1 . The same standard as 



i Private communication. 



