310 SCIENCE AND PRACTICE OF DAIRYING. 



The actual yield of butter obtained may be easily tested, as soon as the 

 average percentage of fat of the milk treated is known, by means of a for- 

 mula, to see whether it may be regarded as satisfactory or not. If the 

 quantity of butter-milk obtained from 100 kilos, of milk be indicated by 

 the letter B, and the percentage of fat of the milk, the skim-milk, and the 

 butter by/, f\ and F, and the quantity of cream yielded per 100 parts by 

 weight by the letter K, and the yield of butter by the letter A, the follow- 

 ing formula will be obtained : 



A 



= F \-J 100 



Thus, if to A, F, and f l the values of 97 per cent, 84 per cent, and -25 

 per cent be given, which may be regarded as what should be easily obtained 

 in practice by careful work, and which, therefore, should be regarded as 

 satisfactory, and to R the value of 15 per cent, we find the following: 



(I.) B = 1-155 x/- 0-245. 



For / will be found 3-30 per cent, and for B 3-57 per cent; that is, one 

 must obtain from 100 kilos, of milk 3 '57 kilos, of butter. If, then, the 

 calculated quantity of butter is found to be more than that actually obtained 

 by '1 or more per cent, there is a mistake made somewhere, either in the 

 creaming or in the churning. In order to discover where this mistake is, 

 the percentage of fat in the skim-milk and in the butter-milk must be 

 determined, so that the correct measure obtained in proper working should 

 not be exceeded. 



If the common formula (1) for/ be worked out, the result is as follows : 



If, again, the values for A, F, f 1 , and E, be again the same, as given above, 

 the following will be the result: 



(II.)/=0'866xB + 0-2125. 



From this formula, provided the work be carefully and properly carried 

 out, it is possible to calculate, with approximate accuracy, the average per- 

 centage of fat in the milk, when the yield of butter is known. 



Finally, if we indicate the percentage of fat in the cream by the letter 

 f 2 , the following formula will be obtained: 



