x] TESTING OF MILK 161 



not, as in a mixture of water and alcohol, merely two 

 factors determining specific gravity. In milk we 

 have water, fat, and solids not fat. The tendency of 

 the fat, since it possesses a lower specific gravity 

 than water, viz. *93, is to counteract the tendency of 

 the " solids not fat," which possess a higher specific 

 gravity, viz. 1/6. Two interpretations, therefore, of 

 a low specific gravity in a sample of milk are possible, 

 viz. the addition of water, or excessive richness in 

 fat. It is for this reason that the determination of 

 the specific gravity alone must not be overrated in 

 value. 



Formulae for Calculating Composition of Milk 

 from certain Data. In conjunction, however, with 

 a knowledge of the total solids of milk, the specific 

 gravity furnishes a most useful indication of the 

 percentage of fat ; and similarly, if the fat be known, 

 it permits us to calculate the percentage of total 

 solids. This can be effected by using the following 

 formulae (Fleischmann), in which 



T = percentage of total solids in milk. 

 F = percentage of fat in milk. 

 G = specific gravity at 15 C. 



(a) For calculating the percentage of fat from the 

 specific gravity and total solids : 



G 

 ii 



