[ ao8 ] 



imparted to it ; confequently to find the true quantity of acid we 

 mufl find out how much of the refiduary 360 grains were mere 

 earth, for by deducing this quantity from 428, the remainder 

 will exprefs the quantity of acid in the 428 grains. 



Then let the quantity of earth in the 360 grains = x, and the 



quantity of fixed air = j, then x -hjy = 360. and x: y:: 78 : 



78 y 

 21 * nearly; and therefore 21 x = ^8jy, and a- = — p, then 



J + 2__^ _ n^Q ^ 21 — 7560, and 21 y + 78 j = 7560 or 99 _y 



= 7560, and y = — — = 76,36 grains of fixed air ; and deduc- 

 ing this from 360, we have the quantity of mere earth = 360 

 — 76,36= 283,64; and deduding this quantity from 428, we 

 have the quantity of vitriolic acid = 144,36 grains; and laflly, 

 if 428 barofelenite contain 144,36 of vitriolic acid, 100 grains 

 barofelenite fliould contain 33,64. 



This laft quantity of acid fomewhat exceeds the ufual cente- 

 nary proportion obtained by chymifts, yet I believe the faturating 



proportion of acid to be ftill higher, for the following reafons : 



There are three ways of adding to each other an acid and earth or 

 metal, the one by dropping the acid to be combined into the fo- 

 lution of the earth in an acid to which the earth hath a weaker 

 aflinity, and the other by infer ting the earth immediately into 



the 



• I fay 21 rather than 22, as Dr. Withering himfelf ftatcs it at 20,8. 



i 



