20 
LABORATORY MANUAL 
EXERCISE NO. 12 
Object: To determine the effect of speed of the centrifuge on the reading of 
the fat column. 
Procedure: “It is vitally important that the required speed be always 
kept up;.if the speed is slackened, the results obtained 
are too low; it may be a few tenths, or even more than one per 
cent.” (F. & W. If 67.) 
A. Make a duplicate test of a sample of milk with the centrifuge 
operated at the prescribed rate of speed. 
B. Make a duplicate test of the same sample of milk when the 
tester is being operated at one-half the correct rate of speed. 
Note: The correct rate of speed for testers of various diam¬ 
eters is given in F. & W. H 66. 
Observations: 
Sample 
Diameter 
of tester 
Speed 
% fat 
Condition 
Color 
1 
a 
b 
2 
a 
b 
Conclusions: 
Questions: (1) Explain the distribution of the components of milk in 
buttermaking, cheese making, and ice cream making. Write 
the answer in the form of a table. 
(2) What causes souring of milk? Explain. 
(3) Discuss the condition of the casein as found in normal cow’s 
milk. 
(4) What is meant by the term viscosity of milk, and how may 
the relative viscosity be determined? 
References: F. & W. % 18, 19, 23-27 inclusive, 66, 67, 68; Van S. pp. 16, 
131-132; Jud. pp. 26-29, 102 111; St. pp. 23-37. 
