on the fpeclfc Gravities , &c. of Saline Subfances. 195 
rco gr. of this pure earth take up as far as I can judge 1 5 3 of 
the mere nitrous acid. The folution fiill reddened vegetable 
blues ; but after the addition of this quantity of pure earth, I 
think it was, that an infoluble fait came to he formed. The 
folution, when cold, grew turbid, and could not be wholly 
diflolved by 500 times its weight of water. 
The fame quantity of pure earth requires 1 y q, 45 of the 
mere marine acid for its folution ; but the folution fiill red' 
dens vegetable blues. After this an infoluble fait was formed ; 
but the beginning of its formation is difficultly difcovered both 
in this and in the former cafes. 
The fpecitic gravity of argillaceous earth, containing 25 
per cent, of fixed air, I found to be 1,9901. 
OF PHLOGISTON. 
Before I proceed to inveftigate Its proportion in various com' 
pounds, and particularly in phlogifiicated acids, it will be ne- 
ceflary to laylomething of its nature. 
It is allowed on all hands, that fixed air, or the Aerial Acid, 
as it is more properly called, is capable of exifting in two 
Bates ; the one fixed, concrete, and unelaflic, as when it is 
actually combined with calcareous earth, alkalies, or magnolia ; 
the other, fluid, elafiic, and aeriform, as when it is actually 
difen gaged from all combination. I11 its concrete and un elafiic 
ftate it can never be produced fiiiglc and difengaged from other 
fubfiances ; for the moment it is feparated from them, it 
afiumes its aerial and elafiic form. The fame thing may be 
laid of phlogifion : it can never be produced in a concrete fate, 
lingle and uncombined with other fubfiances ; for the inftant it 
C c 2 is 
