GEE AM. 117 



at which the milk has been kept having reduced chemical 

 change to a minimum. It occasionally happens that milk 

 will not yield its cream at low temperatures; this is 

 sometimes the case with the milk of cows several months 

 after calving, and especially when receiving a winter diet. 



A third plan of separating cream is by subjecting the 

 milk to extremely rapid horizontal revolution in a centri- 

 fugal machine; under these circumstances the fat globules 

 rise into the centre of the revolving mass. In Laval's 

 machine the new milk, at a temperature of 84, enters 

 in a continuous stream, and is immediately separated into 

 cream and skim-milk, the former leaving the apparatus 

 by a pipe at the top, the latter by another pipe from the 

 side. Both the cream and skim milk thus obtained are, 

 of course, perfectly sweet. The separation of cream in 

 the centrifugal machine is far more complete than in 

 either of the other processes. About 80 per cent, 

 of the milk fat is removed by the ordinary process of 

 shallow setting, and about 95 per cent, by a good machine. 

 A much larger quantity of butter can thus be obtained 

 with a machine than by any other mode of working. 



Cream varies considerably in composition according 

 to the manner in which it has been produced. The 

 volume of the cream obtained is always greater at a lower 

 temperature; this fact should be borne in mind when 

 comparing results given by the creamometer. Cream 

 raised in ice will contain about 20 per cent, of fat. Cream 

 obtained by ordinary shallow setting may contain 25 40 

 per cent, of fat. Cream separated by the centrifugal 

 machine will vary extremely according to the mode of 

 working; it may be quite poor, or it may contain 50 per 

 cent., or more, of fat. Casein, and the other constituents 



