The Babcock Test. 57 



The bottles are, therefore, under the conditions given, sub- 

 jected to a pressure of about 30.65 pounds. In order to calcu- 

 late the speed required for obtaining this force in case of ma- 

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

 found from 



32 - 2 



Substituting the values for F and w, we have 



/32.2X30.65r / 

 v= ]/ j =i/o264r 



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

 are substituted in each case ( T 5 .,, ^ / f , . . . JJ 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 = 7 r- -, v being as before 



2 Trr 



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, 24 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. 



