188 THE ANALYSIS OF MILK PRODUCTS. 



expressing the relation between specific gravity, fat, and total 

 solids in milk. 



T = 0-2625^ + 1-2 F. 



Assuming that the solids not fat (S) are in the ratio to the 

 water as 10-2 : 100, 



then 10 ~ F - S 



10-804 - 



100 F 100 + 9-804 F 

 10-804 = 10-804 ' 



Substituting in the formula 



3-161 F = 100 2-836 



F = 31-6 -0-897?. 



The approximation formula 



F = 32-5 - 0-91 G 



is not only easier to use but gives better results. 



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 



~ 2T^n- 



c = specific gravity of cream. 

 s = of separated milk. 



m = of mixture. 



Cream containing 25 per cent, of fat decreases in specific 

 gravity 0-00027 or 0-27 for each 1 F. above 60 F. 



Table XXXI. shows the results obtained by calculating the 

 fat from the specific gravity. 



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 



