C 170 3 
of fixed air; and 1 66 x grains of it iaturated as 
much acid as iooo grains of marble. 
One thoufand grains of marble were found to 
contain 4074. grains of air, and 1661 grains of vola- 
tile fal ammoniac contain 885 grains. Therefore this 
parcel of volatile fal ammoniac contains more fixed 
air, in proportion to the quantity of acid that it can 
laturate, than marble does, in the proportion of 885 
to 4074, or of 217 to 1 00. 
N. B. It is not unlikely, that the quantity of fixed 
air may be found to differ confiderably in different 
parcels of volatile fal ammoniac; fo that any one, 
who was to repeat thefe experiments, ought not to be 
lurprized if he was to find the refult to differ confi- 
derably from that here laid down. The fame thing 
may be laid of pearl allies. 
Experiment XII. 
This ferves to account for a remarkable phenome- 
non, which I formerly met with, on putting a folution 
of volatile fal ammoniac in water into a folution of 
chalk in fpirit of fait. The earth was precipitated 
hereby, as might naturally be expeded: but what 
lurprized me, was, that it was attended with a con- 
fiderable eftervefcence ; though I was well affured, 
that the acid in the folution of chalk was perfedly 
neutralized. This is very eafily accounted for, from 
the above-mentioned circumflance of volatile fal 
ammoniac containing more fixed air in proportion to 
the quantity of acid that it can faturate, than calca- 
reous earths do. For the volatile alcali, by uniting 
to the acid, was neceffarily deprived of its fixed air. 
Part of this air united to the calcareous earth, which 
^was 
