8 
LABORATORY MANUAL 
EXERCISE NO. 3 
Object: To determine the proper speed of the Babcock centrifuges 
Procedure: Dr. Babcock, in his early work with the tester, found that with 
a diameter of 18", the optimum separation was obtained at a 
speed of 700-800 R. P. M. This gives a centrifugal force 
of approximately 30.65 pounds. (F. & W. If 66. 
A. If 800 R. P. M. is used as the correct figure for an 18-inch 
tester, then the speed of any other tester can be calculated by 
using the formula. 
R. P. M. = /-=radius of tester studied. 
V r 
B. With a speed indicator determine the steam pressure neces¬ 
sary to operate the tester when empty, when half filled, and 
when full. 
Note. In obtaining the diameter of a tester, it should be 
measured with the cups extended. 
Observations: 
Tester 
Diameter 
Speed 
lbs. pressure 
empty 
lbs. pressure 
H full 
lbs. pressure 
full 
1 
2 
3 
; 
Conclusions: 
Questions: (1) Give the table of speeds for testers having a diameter 
of from 10-24 inches, progressing by 2. 
(2) Describe a method for determining the necessary speed of 
testers when no speed indicators or formulas are available. 
(3) What advantages are claimed for a steam tester over a belt, 
water motor, or hand power tester. 
(1) Give the average composition of normal cow’s milk. 
References: F. & W. 15-22, inclusive; 64-71, inclusive: Van S. p. 
15, 38-43; Jud. 69; Si. 16-20. 
