io6 GUIDE TO DAIRYING IN SOUTH AFRICA 



know from experience to be very necessary, as I 

 have often observed good types of machines that 

 frequently go wrong owing to their having been 

 bolted down direct, on either a stone or concrete 

 base. 



The Principle of Separation. Before coming to 

 the main issue as to why cream tests vary, it will 

 be as well to explain briefly the principal factors 

 which actually cause the cream to separate from the 

 milk, as when these factors are known, the reasons 

 for variations in cream tests will be the more easily 

 understood. 



Generally speaking, the law of gravity as applied 

 by centrifugal force is the principle on which all 

 cream separators work. This law of gravity, when 

 applied to milk in conjunction with centrifugal force, 

 causes the cream to separate from the skim milk, 

 owing to the former being lighter than the latter. 

 Thus, when new milk is admitted to the bowl of a 

 separator which is revolving at a great speed, the 

 skim milk being the heaviest portion of the milk is 

 immediately thrown to the most distant part of the 

 circumference of the bowl, i.e. against the outer 

 walls of the bowl, and the cream being the lightest 

 portion cannot possibly be thrown so far, conse- 

 quently it remains nearer the centre of the bowl. 

 To make this point quite clear, take a cork in place 

 of the cream and a stone in place of the skim milk, 

 and exactly the same effect will be obtained, as no 



