CREAM SEPARATORS
In the matter of separating the fatty from the watery elements of milk machinery also plays a part. The custom of allowing the cream to "rise" in open pans suffices for small dairies where speed and thoroughness of separation are not of primary importance. But when cream is required in wholesale quantities for the markets of large towns, or for conversion into butter, much greater expedition is needed.
The mechanical cream separator takes advantage of the laws of centrifugal force. Milk is poured into a bowl rotating at high speed on a vertical axis. The heavier—watery—portions climb up the sides of the bowl in their endeavour to get as far away as possible from the centre of motion; while the lighter particles of cream, not having so much momentum, are compelled to remain at the bottom. By a simple mechanical arrangement, the—very—skim milk is forced out of one tube, and the cream out of another. An efficient separator removes up to 99 per cent. of the butter fat. Small sizes, worked by hand, treat from 10 to 100 gallons of milk per hour; while the large machines, extensively used in "creameries," and turned by horse, steam, electric, or other power, have a capacity of 450 gallons per hour. The saving effected by mechanical methods of separation is so great that dairy-farmers can now make a good profit on butter which formerly scarcely covered out-of-pocket expenses incurred in its manufacture.