864 THE PEOPLE 'S FARM AND STOCK CYCLOPEDIA. 



whirling at about two thousand five hundred revolutions per 

 minute. The rapid revolutions causes the caseine and the min- 

 eral matters of the milk, by their greater specific gravity, to seek 

 the larger circumference of revolution, and this separation forces 

 the cream, which, at the natural temperature of milk, is several 

 degrees lighter in specific gravity, to the center of the cylinder, 

 where it is found perfectly separate from the rest of the fluid. 

 Experiments show that the cream thus obtained is perfectly 

 pure, for the separation has been secured by an agency that 

 discriminates between weights with exact precision, and that 

 the separation has resulted in a per cent of cream shown to be 

 9 per cent greater than by the most perfect cold system yet 

 invented, and 16 J per cent greater than by the open-pan system 

 of cream-raising. 



Why the cold system is superior to the open-pan plan is, 

 that the cream globules of the milk vary in size, and are forced 

 to the surface exactly in the same proportion. The larger glob- 

 ules, by their greater diameter and consequent cubical contents, 

 are quickly acted upon, but as the resistance is exactly inverse 

 to their diameters, that as the globules diminish in size their 

 cubical contents diminish faster than their surfaces, it will be 

 seen that the smaller ones meet with a resistance that they can 

 not overcome, and are thus held in suspension. The cold-set- 

 ting plan so contracts the serums that more are liberated than 

 by open-setting, and when acted upon by centrifugal forces, the 

 density is yet more pronounced, and another per cent escapes, 

 making the difference in one case 9 per cent, and in another 

 16 per cent. In cheese-making this would tend to make skim- 

 cheese still poorer by subtracting 16 i per cent more of fatty 

 matter; but if for feeding purposes, it could be fully and very 

 cheaply compensated for by feeding a ration of oil-meal, for the 

 saving of half a ton of butter by this method would buy ten 

 tons of oil-meal. 



Superiority of the Centrifugal. In brief, the superior- 

 ity of the centrifugal consists first, in a perfect separation of 

 the fats (for force is employed, rather than gravity) ; the cream 

 is longer-keeping, owing to its complete aeration; is uniform in 



