38 Mr. kirwan’s Experiments , Sec. on the fpecific Gravities 
OF FIXED VEGETABLE ALKALI. 
As the manner of conducing the experiments I made on this 
fait was nearly the fame as that I ufed in the foregoing (except 
that to f nd its fpecific gravity I weighed it in aether inflead of 
■ water), I lhall content myfelf, to avoid the repetition of tedious 
calculation, with relating the refult of thefe experiments. 
• rib I found that 100 gr. of this alkali contain about 6,7 gr. 
of earth, which, according to Mr. bergman, is fliceous : this 
earth paftes the filter with it when the alkali is not faturated 
* with fixed air, fo that it feems to be held in folution as in liquor 
Jilicum. 
2-dly. I found, that the quantity of fixed air in oil of tartar 
i*and dry vegetable fixed alkali is various at various times and 
in various parcels of the fame fait ; but that at a medium in the 
purer alkalies it may be rated at 2 1 gr. in 1 00 ; and hence 
the quantity of this alkali in any folution of it may be very 
nearly guefi'ed at, by adding a known weight of a dilute acid to 
a given weight of fuch folution, and then, weighing it again ; 
for as 21 is to 100, fo is the weight loft to the weight of mild 
alkali in fuch folution. 
The fpecific gravity of mild and perfectly dry four times cal- 
cined fixed alkali, free from filiceous earth, and containing 21 
per cent, of fixed air, I found to be 5,0527. 
When it contains more fixed air, its fpecific gravity is proba- 
. bly higher, except it were not perfectly dry: from whence I 
inferred the fpecific gravity of this alkali, when cauftic and 
free from water, to be 45234. 
6 
From 
