of Atmospherical Air, Ge. 125 
at the end of the process, azotic gas or phlogisti- 
cated air, exceeding in quantity the pure air, in as 
much as the substance emitted amounted to. 
The mode in which the martial sulphuret operates 
on pure air, is illustrated by the operation of the 
calcareous and alkaline sulphurets. These also have 
a very strong smell, and the property of absorbing 
pure air. But when the diminution has arrived at 
its maximum, no increase of the bulk of the air en- 
sues.* But if the diminution were effected by the 
emission of some substance from the sulphuret, that 
emission would probably go on after the dimimu- 
tion: at least there is as much ground for this sup- 
position as there is for Dr. Priestley’s, namely, 
that it is probable that something is emitted from 
the martial sulphuret during the diminution of the 
air, because something is emitted afterwards. In all 
these’ cases, the air is diminished both in volume and 
_ in weight; and it is surely absurd to say, that this is 
caused by an addition of something. But the re- 
sult of the following experiment will remove every 
doubt on this subject. I kept a mixture of iron- 
* I know that thecontrary has been asserted by Dr.Priest- 
ley and some others; but I am convinced by my own experi- 
ments, that no increase of air takes place after the alkaline 
or calcareous sulphurets have absorbed the oxygen of air + 
exposed to the action of either of them. I constantly 
make use of liquid sulphuret of pot-ash as a test, but I have 
never found the least increase of air after‘the greatest di- 
minution of it had taken place. 
