CHAPTER VI. 



FORMULAE FOR CALCULATIONS. 



As stated above, the specific gravity is raised by the solids 

 not fat, and lowered by the fat. This fact is not only true quali- 

 tatively, but also, as the following demonstration will show, 

 quantitatively. 



By our definition that specific gravity (S) is the weight (W) 

 of the unit volume (V), we get the equation 



Let us suppose we have a mixture (having the specific gravity 

 S) of two substances, A and B, of differing specific gravities S A 

 and S B . 



Let us suppose that the respective weights are A and B, and 

 let A + B = 100. 



Then by (1) 



Volume of A = ^-, volume of B =or, and volume of mixture =-- 



Then 1 _?=^ + B = A+ 1 2Z A 



100_A(S B -S A ~) 100 



100 100 



S ,S - 



i rr~ = 



rn 



Now in the same way 



-S, 



As both S A and S a are constants, we may write 



o Q |^ TlQ NX T^" \ 



and S I S^ + AS X K A i K B and K A bein constants. ... (2) 



Now, as A + B = 100, A is the percentage by weight of this 

 substance ; and as 100 X S expresses the total number of grammes 



34 



