Rural School Leaflet. 993 



Utensils. — A hand-power centrifugal tester, at least two skimmed 

 milk test bottles having double necks. The rest of the equipment 

 is similar to that used for testing whole milk, and described in the 

 Leaflet for December. 



Method. — Several pupils should bring from home a sample of skimmed 

 milk, separated by the gravity method. A pint of skimmed milk would 

 be sufficient for testing. A few others can bring samples of skimmed 

 milk, obtained by skimming the cream with a centrifugal separator. 



The value of the lesson, then, consists in demonstrating to the pupils • 

 the larger amount of fat in the skimmed milk separated by the old- 

 fashioned gravity method. The method for testing is exactly the same 

 as for testing the whole milk, apart from the use of the double-neck 

 bottle. The skimmed milk is run into the bottle through the larger 

 neck. When the fat rises it will be in the smaller of the two necks. 

 Each space on a double-neck bottle stands for .05 of i per cent of fat 

 in the skimmed milk. 



Millions of dollars are lost annually by the farmers of the United 

 States in separating cream from the milk by the old-fashioned gravity 

 methods. An excellent way of demonstrating the value of. centrifugal 

 separation to the pupils and to their parents is by the method suggested 

 in this lesson, and by doing the following problem: 



Problem. — Farmer A separates his milk by the gravity method. The 

 skimmed milk tests .2 per cent fat. Farmer B uses a centrifugal separa- 

 tor. The skimmed milk tests .01 per cent. Each farmer has 20 cows, 

 and each cow gives an average of thirty pounds of milk per day. A pound 

 of milk fat will make one and one-sixth pounds of butter. If butter 

 sells for 30 cents per pound, how much money does Farmer B receive 

 more than Farmer A in one year of three hundred days? 



Buttermilk. — The same method can be followed in testing buttermilk 

 obtained by churning at different temperatures and with different 

 makes of churns. 



THE BATTLE OF THE TREES 



HERBERT A. SMITH 



When trees take possession of any piece of ground, they soon begin 

 to contend with one another for the supply of what they must have to 

 live. No one can understand what forestry is until he has firmly grasped 

 this fact. 



The best time to find out what is happening among the trees is in the 

 winter when the branches are leafless. Go into the high woods and 

 32 



