[ r 59 3 
ing the common air unchanged ; whereby the end of 
the tube would be filled with common air only ; by 
which means the vapours, contained in the refi of the 
tube and bottle A, teem to have been defended from 
the adion of the water. But when almofi: all the 
common air was driven out of the bottle, then the 
proportion of common air contained in the vapours, 
which pafifed through the tube, feems to have been 
too fmall to defend them from the adion of the water. 
In the fecond experiment, the narrow fpace left be- 
tween the neck of the inverted phial and the tube 
would anfwer much the fame end, in defending the 
vapours within the inverted phial from the adion of 
the water, as the bent tube in the firft experiment did 
in defending the vapours within the bottle from the 
adion of the water. 
Experiments on Factitious Air. 
PART II. 
Containing Experiments on Fixed Air , or that Species of 
FaBitious Air, which is produced from Alcaline 
Sub/lances , by Solution in Acids or by Calcination. 
Experiment I. 
T he air produced, by diffolving marble in fpirit 
of fait, was caught in an inverted bottle of water, 
in the ufual manner. In lefs than a day’s time, much 
the greateft part of the air was found to be abforbed. 
The water contained in the inverted bottle was found 
to precipitate the earth from lime-water ; a lure fign 
that it had abfor bed fixed air *. 
* Lime, as Dr. Black has lhevvn, is no more than a calcarious 
earth rendered ioluble in water by being deprived of its fixed 
Experi- 
