156 SCIENCE AND PRACTICE OF DAIRYING. 



The quantity of phosphoric acid quoted includes that which has been 

 formed by the burning of the protein bodies containing phosphorus. 



The percentage composition of fat (x) of the cream may be found by 

 the following formula, in which (/) denotes the percentage of fat in the 

 milk, (/j) the percentage of fat in the skim-milk obtained, and R the 

 weight of cream expressed in percentage of the weight of milk, by the 



formula given in 74, viz. x= V? +/u an d the percentages of 



the quantity of cream R, which must be removed from the milk if the 

 percentage of fat of the cream is to be obtained as x per cent, is as 

 follows : 



100 (/-/,). 



-/, 



The money value which the cream possesses for the producer can be 

 easily ascertained. For example: If from 100 kilos, of milk there are 

 obtained 3 '75 kilos, of butter, valued at 2 marks, and the butter-milk is 

 valued at *02 marks; and it be estimated that 100 kilos, of milk yield 

 20 kilos, of cream, the following shows the method of calculation: 



3*75 kilos, of butter at 2 marks, 7 '5 marks. 



16-00 kilos, of butter-milk at '02 marks, ... '32 



0-25 loss. 



20 kilos of cream are worth ... ... ... 7 '82 ,, 



According to this calculation, 1 kilo, of cream is worth 39 '1 pfennig. 

 In order to calculate the net value, however, the expenses due to the 

 preparation of the butter, and the value of the butter-milk, must be 

 deducted. The market price, as a rule, considerably exceeds the true 

 value of cream. Cream with 14-20 per cent of fat may, on an average, be 

 valued at four times the same quantity of milk. 



81. Skim-milk. Skim-milk is a by-product of the dairy industry, 

 and the small quantity of fat it contains is chiefly in the form of the 

 smallest fat globules of the milk. In addition to the common con- 

 stituents of milk, it generally contains small quantities of free lactic 

 acid. Compared with milk, its composition is more watery, and its 

 colour appears at average and higher temperatures slightly bluish. 

 Skim-milk obtained in well-conducted dairies has a specific gravity, 

 which at 15 C. varies between T032 and T0365, on an average, 

 ] '0345, and contains, according to older methods of cream -raising, 

 8 per cent of fat, and when obtained in separators not more than 

 "3 per cent. It is used for the preparation of skim-milk cheeses for 



