ON MILK AND MILK-TESTING 59 



1. Because with every change in the per cent of 

 fat in cream there is a change in the specific gravity, 

 so that a pipette that would hold the proper amount 

 of cream of one quality would not hold the right 

 amount of cream of another quality. 



2. Cream is viscous and a variable amount re- 

 mains in the pipette. 



3. Air bubbles become incorporated during the 

 mixing and gases from fermentation also cause 

 bubbles which are retained in the cream on account 

 of its viscosity, so that in measuring out such 

 cream too small a quantity would be secured. 



How should the per cent of fat be read? 



By counting the graduations between the bottom 

 of the fat column and the bottom of the meniscus 

 at the upper surface of the fat. 



Why do we not read to the top of the meniscus as 

 in the case of milk bottles? 

 Because the diameter of the neck is greater and 

 the space occupied by the meniscus is larger in 

 cream bottles and is altogether too large a quantity 

 to allow for the fat that does not rise. 



When the whole of the fat column has the clouded 

 appearance and color of muddy water, how may 

 it be corrected? 



I. It may be corrected by shaking the mixture of 

 cream and acid for several minutes before whirling, 

 in the meantime keeping the bottles hot. After 

 the whirling is completed the condition of the test 

 may be improved by allowing the fat to solidify. 



