t 176 ] 
I once imagined that, fince fixed and inflammable 
air are the reverfe of one another, in feveral remark- 
able properties, a mixture of them would make 
common air ; and while I made the mixtures in 
bladders, I imagined that I had fucceeded in my 
attempt ; but I have fince found that thin bladders 
do not fufficiently prevent the air that is contained in 
them from mixing with the external air. Alfo corks 
will not fufficiently confine different kinds of air, 
unlefs the phials in which they are confined be fet 
with their mouths downwards, and a little water lie 
in the necks of them, which, indeed, is equivalent 
to the air handing in veffels immerfed in water. In 
this manner, however, I have kept different kinds of 
air for feveral years. 
Whatever methods I took to promote the mixture 
of fixed and inflammable air, they were all ineffec- 
tual. I think it my duty, however, to recite the 
iffue of an experiment or two of this kind, in which 
«qual mixtures of thefe two kinds of air had flood 
near three years, as they leem to ihew that they had 
in part affe&ed one another, in that long fpace of 
time. Thefe mixtures I examined April 27, 1771. 
One of them had flood in quickfilver, and the other 
in a corked phial, with a little water in it. On 
opening the latter in water, the water inflantly rufhed 
in, and filled almofl half of the phial, and very little 
more was abforbed afterwards. In this cafe the water 
in the phial had probably abforbed a confiderabie part 
of the fixed air, fo that the inflammable air was 
exceedingly rarefied ; and yet the whole quantity 
that muft have been rendered non-elaffic was ten 
times more than the bulk of the water, and it has 
not 
4 
