Mr. kirwan’s Experiments , See. on the fpecific Gravities 
of the compound. When this difference amounted to 2,2 gr, 
then I judged the whole of the fixed air expelled, and found it to 
be fo, as 100 gr. of this alkaline folution, being evaporated to 
drynefs in a heat of 300% left a refiduum which amounted to 
io| gr. ; which ioi gr. contained 2,2 gr. of fixed air, as will 
hereafter be feen. 
Hence 8,3 gr. of pure vegetable fixed alkali, free from fixed 
air and water, or 10*5 of mild fixed alkali, were faturated by 
2,55 gr. of pure marine acul, and confequently the refulting 
neutral fait fhould, if it .contained ho water, weigh u,85gr. ; 
but the falts refulting from this union (the folution being eva- 
porated to perfect drynefs in a heat of i6o J kept up for tour 
hours) weighed at a medium 12,66 gr. Of this weight 1 1,85 
gr. were. acid and alkali ; therefore the remainder, 'U/3. 0,81 of 
gr. were water; therefore 100 gr. of perfectly dry, digeftive 
lalt contain 28 gr. acid, 6,55 water, 65,4 of fixed alkali. - 
I was then curious to compare my experiments with thofe 
made by others, but could not find any made' with fufficient 
precifion but thofe of Mr. homberg in the Paris Memoirs for 
1699. However, as to fpirit of fait 1 did not think proper to 
.compare them, as he mentions that his could dilfolve gold, and 
therefore was probably impure. 
OF SPIRIT OF NITRE. 
l . - :• • . : r i : \'j: . ■ • _ • v 
.... The common reddifh brown, or greenifh fpirit of nitre con- 
taining, befides' acid and water, a certain portion of phlogifton, 
and being alfo mixed with lome portion of the acid of fea fait, 
I judged unfit for thefe trials, and therefore ufed only the de- 
phlogifticated fort, which is quite colourlefs, and refemblespure 
water in its appearance. This pure acid cannot be made to exift 
m 
