[ 161 ] 
any alteration would be made in the conftitution of 
fixed air, by this mixture of iron filings and brim- 
ftone. I therefore put a mixture of this kind into a 
quantity of as pure fixed air as I could make, and 
confined the whole in quickfilver, left the water 
fhould abforbe it before the effiedts of the mixture 
could take place. The confequence was, that the 
fixed air was diminifhed, and the quickfilver rofe in the 
veffel, till about the fifth part was occupied by it ; and, 
as near as I could judge, the procefs went on, in all 
refpedts, as if the air in the infide had been common 
air. 
What is moft remarkable, in the refult of this ex- 
periment, is, that the fixed air, into which this mix- 
ture had been put, and which had been in part di- 
minifhed by it, was in part alfo rendered infoluble 
in water by this means. I made this experiment 
four times, with the greateft care, and obferved, 
that in two of them about one fixth, and in the 
other two about one fourteenth, of the original 
quantity, was fuch as could not be abforbed by wa- 
ter, but continued permanently elaftic. Left I fhould 
have made any miftake with refpedf to the purity of 
the fixed air, the laft time that I made the experi- 
ment, I fet part of the fixed air, which I made ufe 
of, in a feparate veffel, and found it to be exceed- 
ingly pure, fo as to be almoft wholly abforbed by 
water j whereas the other part, to which I had put 
the mixture, was far from being fo. 
In one of thefe cafes, in which fixed air was made 
immifcible with water, it appeared to be not very 
noxious to animals ; but in another cafe, a moufe 
died in it pretty foon. 
Vol. LXII. 
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As 
