THE BABCOCK MILK TEST. 165 



4. Thorougly mix the milk and acid as soon 

 as measured into the test bottle. This is not 

 always necessary, but for the same reason just 

 mentioned a better separation of fat is some- 

 times obtained by mixing at once than by allow- 

 ing the two liquids to stand partially mixed in 

 the bottle, as often happens when the acid is 

 poured into the test bottle. 



5. Add the hot water in two portions and 

 run the centrifuge after each addition of water. 

 Use soft water for this purpose because many 

 hard waters contain so much carbonate of lime 

 that the carbonic acid set free by the sulphuric 

 acid makes considerable foam at the top of the 

 fat column. Some waters can be used to fill 

 the test bottles without causing any foam if 

 first boiled a short time or by adding a tea- 

 spoonful of acid to about one quart of the 

 water used for filling the test bottles. 



6. When the test bottles are taken from the 

 machine it is a good plan to put them into 

 water at 140 to 160 deg. Fah. The fat is kept 

 liquid at this temperature. Each end of the 

 fat column can be distinctly seen and its 

 amount measured. 



7. Too low results will be obtained if the 

 centrifuge does not have sufficient speed. The 

 machines have to be watched, as constant use 

 wears some of them so that the speed designed 

 by the manufacturer is not obtained. 



