80 PROFITABLE DAIRYING 



principle. In this plaything a stone is placed in 

 a little hole cut in a piece of leather to which 

 are attached two strings. The "shot" is then 

 whirled rapidly around the head and one of the 

 strings suddenly loosened, when the stone flies off 

 in a straight line. The boy who is able to whirl 

 his sling-shot with the greatest speed succeeds 

 in throwing the farthest; that is, he gives it the 

 greatest force. Now, in the cream separator the 

 builders have figured out just how rapidly the 

 bowls must rotate in order to throw all the skim- 

 milk to the outside and force the fat globules 

 to the center. The separator must, therefore, be 

 kept up to this calculated speed if the separation 

 is to be complete. This speed is usually plainly 

 marked on the machine and the operator should 

 see to it that the indicated speed is maintained. 

 The effect of temperature in separation. An- 

 other condition which affects the completeness 

 of the separation is temperature. The best 

 machines will not do close work on cold milk. 

 The most favorable temperature for the farmer 

 to use is from 90 degrees F to 100 degrees F., or 

 the temperature of milk when it is first drawn 

 from the cow. In no case should the milk be 

 allowed to cool or the cream to rise before sep- 

 aration. If the milk is cold the fat losses are 

 large and the machine is easily clogged. If the 

 cream has risen it may be churned in the machine 



