268 



THE CHEMICAL CONTROL OF THE DAIRY. 



It is impossible to test the specific gravity of a cream con- 

 taining more than 30 per cent, of fat with a hydrometer direct ; 

 but if it is diluted with an equal weight of separated milk the 

 hydrometer can be used as with a thinner cream. 



To calculate the specific gravity of a thick cream from that of 

 a mixture with an equal weight of separated milk, the following 

 formula may be used : — 



_ s X m 

 ~ 2s — m' 



c = specific gravity of cream. 

 .s = „ „ of separated milk, 



m = „ ,, of mixture. 



Cream containing 25 per cent, 

 gravity 0-00027 or 0-27° for each 1° 



Table LXV. shows the results 

 fat from the specific gravity. 



of fat decreases in specific 



F. above 60° F. 



obtained by calculating the 



TABLE LXV. — Calculation of Fat in Cream. 



The specific gravity of cream is affected by the state in which 

 the fat globules exist ; if they are in the solid state, the specific 

 gravity will be very appreciably higher than if liquid. The 

 formula given above assumes that they are solid ; if, however, 

 the cream has been separated at a temperature above the melting 

 point of the fat, the globules are liquefied, and do not at once 

 assume the solid state on cooling. For this reason the method 



