DAIRY MANAGEMENT, THE MILK TRADE, ETC. 95 



flavour, keeping longer, and showing a much better per-centage 

 to the milk than sweet cream. For this reason, where a 

 separator is used, a small quantity of sour buttermilk should 

 always be added to the cream in such quantity as will produce 

 the proper degree of ripeness or sourness in twenty -four hours, 

 the most convenient time in a large dairy. Although we 

 have seen no less than eight different cream separators at 

 work on the Continent — all the inventions of foreigners — there 

 are only two which are in general use : Petersen's, made in 

 Copenhagen, and the Swedish, or Laval, both of which are sold 

 in London, and extensively used in this country. The system 

 of the Danish machine is that the milk caused to revolve in a 

 horizontal drum, at a speed of 3000 revolutions a minute, is 

 divided by centrifugal force into two portions. The lighter 

 portion, the cream, comes to the surface, i.e., the face of the 

 vertical liquid body. A skimming tube is fitted to plough this 

 face, with the result that the whole of the cream passes through 

 it to the outside of the machine. The skim milk is behind this 

 cream column, and, to reach it, a flange encircles the drum near 

 the top, space being left behind to enable the milk to escape 

 upwards, between the flange and the periphery. This it is 

 compelled to do by the pressure of the constantly entering new 

 milk. Above this flange is another ploughing tube, which 

 takes off the milk in the same way as the cream, with this 

 difference, that it can be moved to take as much or as little as 

 required. This regulates the thickness of the cream skimmed. 

 When the skim milk tube is skimming as much as is entering 

 the machine — no cream is being skimmed — it is, however, 

 collecting, and comes off when permitted unusually thick. The 

 Laval machine works by similar force, but, although neither 

 milk nor cream are actually skimmed, both find their way out 

 of the machine after division by the pressure of the new milk 

 which is constantly entering. This machine is made in only 

 one size, and revolves at a speed of 6000 to 7000 revolutions a 

 minute, skimming 30 to 45 gallons an hour. The Danish 

 machine is made in three sizes, revolving at from 2000 to 3500 

 a minute, and skimming from 20 to 120 gallons. It has two 

 other advantages, the small machine can be worked by a pony 

 with great ease, and the milk can be elevated to a considerable 



