[ 60 ] 
of water perfe€tly infipid. Hence it would follow that too 
parts allum contain 41,66 of water of cryftallization, but having 
calcined 100 grs. of allum in a fand heat where the evapora- 
tion was freer, I found the lofs of weight to be 45,5, but then 
the laft drop was acid. Hence I conclude the water of cryftal- 
lization to amount to 44 per cent. 
Tue refiduum of too parts cryftallized allum, amounting to 
26,63 grs. muft therefore have been mere acid, or acid. ftill retaining 
a quantity of water not feparable by a heat of 465°. To refolve 
this doubt I made-a folution of 100 grs. cryftallized allum in 
1600 of water, heated it to 200°, and gradually added to it a 
folution of mild vegetable alkali, which contained mar of its 
si 
weight of mere alkali, being the fame I ufed in forming tartar 
vitriolate, &c. I continued adding this as long as any effer- 
vefcence appeared, making the mixture to boil; the quantity em- 
ployed -and neceffary to faturate the acid was go grs. that is 
aL ers. of mere alkali; Now we have already feen 
that 100 parts mere vegetable alkali’ take up 92 of the vitriolic 
flandard, ‘therefore 21,5 grs.of pure vegetable alkali take up 
| Bh 19,78 
When allum is decompofed by aerated alkalies without boiling, (and a fortiori 
in cold) a fmall part only of the acid is feparated, the greater part of the alkali unites 
without lofing its air to the precipitate, forming a falt compofed of aerated alkali, 
earth and vitriolic acid; when the earth is properly feparated it falls in a granular 
and not in a flaky ftate. 
