122 SCIENCE AND PRACTICE OF DAIRYING. 



are every day displacing to a larger extent the older methods of 

 cream-raising. Up till 1886, the only kind of separators used were 

 the larger separators driven for the most part by steam-engines, or 

 horse-power, and in a few cases by other motors, and the application 

 of which only paid in large dairies. For the sake of simplicity the 

 larger machines driven by steam, &c., may be designated power- 

 separators, as distinguished from separators driven by manual power, 

 which may be called hand-separators. 



[The illustration in the preceding page of a section of the Alex- 

 andra cream-separator, with the explanation of parts, has been 

 inserted by the Translators to assist students in understanding and 

 describing the construction of the separator.] 



56. Milk in the Separator -drum. That portion of the separator 

 which is destined to hold the milk, and which is known as the drum, 

 forms the essential part of every separator, and revolves round a 

 horizontal or vertical axis. Whatever its shape, whether cylindrical 

 or bulbiform, round or pear-shaped, &c., it must always be a rotat- 

 ing body. 



When in motion, and filled with milk, the force of gravity acting 

 upon the separator-drum may be neglected, when compared with 

 the centrifugal force, which is several thousand times stronger; 

 indeed the force of gravity may be said to be replaced by centrifugal 

 force, and one may assume that the same action and conditions take 

 place in the milk, when shut up in the revolving separator-drum, as 

 take place when milk stands quietly at rest. 



Just as milk, which is poured in a slow, steady stream into a 

 milk-pan standing at rest, finds at once the lowest part of the can, 

 namely the bottom, and spreads itself over the bottom in a horizon- 

 tal layer, and gradually fills the vessel from the bottom to the top, 

 so does milk allowed to flow into a separator-drum, when revolving, 

 find its way with lightning-like rapidity to the most distant part of 

 the drum, and there spread itself out in a ring bounded by a free 

 and almost cylindrical surface, and the drum is thus gradually filled 

 from the outside to the inside, that is, in a direction exactly opposite 

 to that of the direction of the centrifugal force. All separator- 

 drums, without exception, when in motion, and when the milk is 

 allowed to flow in, are thus filled from the remotest part of the wall 

 to the axis round which the drum revolves. It is quite immaterial 

 what part of the drum the milk flows into. Any other method of 

 filling is inconceivable. 



