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emptying them In the Grotto di cani, or other deadly 
caverns, thofe mephitic exhalations (of which fomany 
of theantients,as well as the moderns, have fo much and 
fo varioLifly written) may be colledled, and conveyed 
to a great diftance j and, when duly examined, will, 
doubtlefs, be found true, permanent, mineral air, of 
that kind known to our miners by the name of 
Choak-damp. Of which fort the air of the mi- 
neral water of Spa appears alfo to be, from the fol- 
lowing experiment. 
Experiment V. 
I took the air which, two days before, I had ex- 
trailed from the Pouhon water, as related in Expe- 
riment III. This air I emptied out of the vial into 
the receiver fixed in the ciftern, in the manner de- 
fcribed in the foregoing experiment. Into the fame 
receiver I alfo emptied a bladder of air, extraded: 
from the Pouhon water four days before. Which 
two parcels of mineral air filled as much of the re- 
ceiver as had before been filled with common air, in 
the laft-mentioned experiment. Into this mineral 
air, thus included in the receiver, the moufe was 
conveyed, which had been employed on the pre- 
ceding day in the foregoing experiment. On palling 
into this air, it immediately held up its head very high, 
and turned it on every fide ; and, in four or five le- 
conds, without any difficulty of breathing, or other 
ftruggle, fell down on one fide, and remained with- 
out motion. Half a minute after, it was taken out 
of'the receiver, and placed on a table before a win- 
dow in the open air, where it lay four hours with- 
VoL. LV. H h out 
