io Mr. kirwan’s Experiments , &c. Jpecific Gravities 
this the exa£t proportion of acid in all other acid liquors ; for 
if a given quantity of pure fixed alkali were faturated, fir ft by 
a certain quantity of fipirit of fait, and then by determined 
quantities of the other acids, I concluded, that each of thele 
quantities of acid liquor muft contain the lame quantity of acid, 
and this being known, the remainder being the aqueous part, 
this alfo muft be known; but this conclufioti intirely refted on 
the fuppofition that the lame quantity of all the acids was requi- 
fite for the faturation of a given quantity of fixed alkali ; for 
if fuch given quantity of fixed alkali might be iatu rated by a 
fmaller quantity of one acid than of another, the conclufion 
fell to the ground. This point might, indeed, be in fome mea- 
fure determined by weighing the neutral falts, formed by thefe 
acids, when thoroughly dry ; but ftill a fource of inaccuracy 
remained ; for if they were expofed to a conliderable heat, part 
of the acid would neceflarily be expelled, and more of one acid 
than of another, and if the heat were not conliderable, much 
of the water of cryftallization would remain ; fo that if the 
weights were found to be equal, this equality could not be 
aferibed to equal quantities of acid, but might perhaps arife 
from a fmaller proportion of acid in one of them, and a larger 
proportion of water, and in another from a larger propor- 
tion of acid and a fmaller proportion of water ; and if the 
weights were unequal, no certain conclufion could be drawn. 
To obviate this difficulty I ufed the following expedient, ift. I 
fuppofed the quantities of nitrous and vitriolic acids, neceflary 
to faturate a given quantity of fixed alkali, exactly the fame as 
that of marine acid whofe quantity I determined ; and to prove 
the truth of this fuppofition, I obferved the fpecific gravity of 
the fpirit of nitre and oil of vitriol I madeufe of, and in which 
t fuppofed, from the trial with alkalies, a certain proportion of 
z acid 
