[ 1 75 ] 
faturate, than marble does, in the ratio of 21 1 to 
100. 
Experiment XVI. 
As thefe cryftals contain about as much fixed air in 
proportion to the quantity of acid, that they can 
faturate, as volatile fal ammoniac does, it was natural 
to exped, that they fhould produce the fame effeds 
with a folutionof Epfom fait, or a folution of chalk 
in fpirit of fait ; as thofe effeds feemed owing only to 
the great quantity of fixed air contained in volatile fai 
ammoniac. This was found to be the real cafe: for a 
folution of thefe cryftals in five times their weight of 
water, being droptinto a folution of chalk in fpirit of 
fait, the earth was precipitated, and an effervefcence 
was produced. No precipitate was made on dropping 
fome of the fame folution into a folution of Epfom 
fait, though the mixture was kept upwards of twelve 
hours. But, upon heating this mixture over the fire, 
a great deal of air was difcharged, and the magnefia 
was precipitated. 
Experiments on Factitious Air. 
PART III. 
Containing 'Experiments on the Air , produced by Fer- 
mentation and Putrcfaffion. 
M R. M'Bride has already fhewn, that vegetable 
and animal fubftances yield fixed air by fer- 
mentation and putrefadion. The following experi- 
ments were made chiefly with a view of feeing, whe- 
ther they yield any other fort of air befldes that. 
Experi- 
