800 CYCLOPEDIA OF LIVE STOCK AND COMPLETE STOCK DOCTOR. 



and the milk is gmdually arranged in layers, the lighter portion at the 

 top and the heavier portion at the bottom. The force acting in the sepa- 

 rator has precisely the same action on the milk, but acts outward from the 

 center of the bowl the same as gravity acts downward from the surface, 

 only many thousand times stronger, accomplishing in a few moments and 

 far more completely what it takes gravity several hours to do. 



As the milk goe» into the bowl it is at once thrown to the outermost 

 parts and fills the bowl completely until an opening is reached where it 

 will flow out again. The surface of the milk is on a line parallel with the 

 center, or axis, of the \yo\\\, and is exactly in line with the cream outlet. 

 A cross section througli the bowl from this surface to the outside presents 

 much the same appearance as would a pan of milk after the cream has 

 raised by gravity. The cream is on the surface, which might be called the 

 top, and the heavier portions of the milk at the point farthest from the 

 center, which would represent the bottom. 



With this understanding of the arrangement of the milk in the bowl 

 there are a number of things to be observed which influence the separa- 

 tion. The difference in length of time it takes to separate cream by 

 gravity and by centrifugal force shows plainly that the time varies with 

 the amount of force applied. The shorter the time the greater the force 

 must be. Skim milk from the separator contains less fat than that secured 

 by the gravity system, showing that the greater force causes more perfect 

 separation. 



From the above statements the following conclusions regarding the 

 ues of the separator may be drawn : (1) If the amount of milk that passes 

 through the separator in a given time is a fixed quantity, any increase in 

 the speed of the machine will tend to cause closer skimming because of 

 the greater force exerted; (2) if the amount of milk that passes through 

 in a given time is increased and the speed remains the same the skimming 

 will not be so perfect, for the centrifugal force is not exerted on the milk 

 so long a time. It is evident, therefore, that the closeness of skimming 

 is the result of two factors — time and force. If either of these is de- 

 creased, the result will be poorer work. If either is increased, better work 

 will result. 



Common Errors in Operating Separators. — Two errors are made in 

 operating separators because of ignorance of the facts just stated. The 

 f'rst consists in allowing too nmch milk to pass through the machine. As 

 theie is a limit to the practical speed at which the machine can be safely 

 run, it is not good practice to try to overcome the error referred to by 

 increasing the speed bej'Ond the safe point. The feed outlet is usually 

 fixed so that too much milk will not run through, but cases have been 

 known where operators, anxious to shorten the time of separation, have 

 enlarged the opening, allowing too much milk to pa=s. This error is not 

 so conmion as the second, which is to allow the speed of the machine to 

 become too slow. The slow speed does not generate enough force to skim 

 properly, and the result is loss of butter fat in the skim milk. The number 

 of revolutions per minute required by a machine is usually indicated on 



