268 



Nature-Study Agriculture 



Making the 

 test 



in the milk of each cow. 

 To do this, Professor 

 Babcock of the Uni- 

 versity of Wisconsin in- 

 vented an instrument 

 that shows how much 

 butter fat any sample 

 of milk contains (Fig. 



215)- 



About a tablespoon- 

 ful of milk is measured 

 into one of the long- 

 necked bottles shown 

 in Figure 215, and a 

 tablespoonful of strong 

 sulfuric acid is added. 

 The acid destroys the 

 curdy part of the milk 

 and' so sets the butter 

 fat free. (Butter fat 

 consists of very small 

 drops of oil that float 

 all through the milk.) 



The bottle is now placed in one of the containers of the 

 machine, and the crank is turned rapidly for five min- 

 utes. Centrifugal force causes the containers to swing 

 outward till they are in a horizontal position. The 

 heavy mixture of milk and acid is driven to the bottom 

 of the bottle, which is now on the outside of the circle, 

 and the oil drops, being light, come to the top. After 

 this turning, warm water is poured into the bottle till 



FIG. 214. More of the fine particles of 

 dirt can be removed from milk by using a 

 cloth strainer than by using a wire strainer. 



