EXTENDED FORMULA. 97 



It is occasionally useful to calculate the specific gravity of 

 the total solids of a milk, as the total solids of skimmed milk 

 have a considerably higher specific gravity than those of whole 

 milk. 



Instead of taking the solids not fat as one substance, we may 

 consider its constituents lactose, protein, and mineral matter 

 separately. 



Calling the percentage of fat F, lactose L, protein P, and 

 mineral matter A, we may write 



= 10& F + lOc L + Wd P + lOfi A 



by the same reasoning employed in deducing formula (5). 



The author has deduced from the mean of many analyses the 

 formula 



1= - 0-761 F + 4 L + 2-5714 P + 8-46 A. 



From these factors the following specific gravities are deduced, 

 as previously shown : 



Specific gravity of fat, ...... 0-93 



lactose, ..... 1-666 



protein, ..... 1-346 



mineral matter, . . . .5-5 



Using these specific gravities, together with Vieth's estimate 

 of the proportions of lactose, protein, and mineral matter 

 13 : 9 : 2 we can calculate what the specific gravity of solids 

 not fat should be. As Vieth's proportions are by weight, we 

 must transform specific gravities into specific volumes. 



Specific volume of lactose = - = 0'6 



I'6d6 



- - protein 



,, ,, mineral matter = = 0'182. 



5-5 



Then specific gravity of 



S ' n ' F> = 13 x 0-6 + 9 x 0-743 + 2 x 0*182 = (HUSS = ' 16> 



24 

 which agrees with that given above, 1-616. 



It is a useful check on an analysis to calculate the specific 

 gravity from the percentage of milk-sugar, protein, fat, and mineral 

 matter ; this should agree within small limits with that found. 



