the heavy inflammable Air. 53 
much was difengaged during the operation, it is not eafy to 
determine. Neither are we acquainted with any fubftance 
which will feparate the two kinds of inflammable air by com- 
bining with the one and leaving the other : but we know that 
dephlogifticated air will combine, in certain proportions, with 
each of them, either mixed or feparate ; that with one of them 
it forms fixed air, with the other water. Therefore, by in- 
flaming dephlogifticated air with a mixture of thefe two airs, 
and obferving the quantity of dephlogifticated air confumed, 
and the quantity of fixed air produced, we difcover the excefs 
of dephlogifticated air confumed above what is fufficient for 
the production of the fixed air ; and may conclude, that this 
excefs of dephlogifticated air has combined with light inflam- 
mable air. This conclufion is further confirmed by attending 
carefully to the contraction which takes place upon inflaming 
thefe airs, which is much greater in piopoition to the quantity 
of fixed air produced, when a mixture of the two inflammable 
airs is inflamed, than when the heavy inflammable air is burnt 
alone. It is well known, tnat in all experiments of this kind, 
what remains after the combuftion of the aus mixed together 
in due proportion, and after the ieparation of the fixed air, is 
chiefly phlogifticated air. From a confiderable number of ex- 
periments, conduded with great care and attention to all thefe 
circumftances, I have endeavoured to appioximate to tne quan^ 
titles of the phlogifticated and light mflammable airs difen- 
gaged, when a given quantity of the heavy mtlammable an was 
decompoled. But all that can be attained to, is only an ap- 
proximation to truth. The quantity of air decompofed by 
this method is fo fmall, and the feparation of tne different 
parts into which it is refolved is attended with fuch difficulties, 
