^ 2 Dr. Austin’s Experiments on 
air, as foon ns I fufpecled that it contained the lighter air ns a 
con flit uen t part. Agreeably to my expe&ation, this experi- 
ment immediately detected the light inflammable air ; for fuch 
an expanfion took place as could not arife from any other 
known fubftance. Thus the heavy inflammable air was fome- 
times expanded to twice its original volume ; and yet, upon 
examining the air fo expanded, not a fixth part of the whole 
was found to have undergone a decompofition : for inftance, 
when two meafures and three quarters were expanded to fix, it 
appeared by experiment, that nearly two meafures and a half 
remained in their original ftate. 
After the inflammable air has been expanded to about double 
its original bulk, I do not find that it increafes further by con- 
tinuing the fhocks. Conceiving that the progrefs of the de- 
compofition was impeded by the mixture of the other airs with 
the heavy inflammable, I palled the Ipark through a mixture 
of the heavy inflammable air and of the light inflammable air, 
obtained from diluted vitriolic acid and iron filings ; but the 
expanfion fucceeded nearly as well as when the heavy inflam- 
mable was ele£trified alone. This is an almoft infurmountable 
obftacle to this mode of inveftigation : yet it has fuch advan- 
tages in other refpe&s, the air to be analyfed being unmixed 
with other fubltances, and only in contafl with the glafs and 
quickfilver by which it is confined, that I determined toprofe- 
cute the fubjeft in this manner as well as I could. 
From this partial decompofition of the heavy inflammable air 
we obtain a mixture of the two inflammable airs with phlo- 
gifticated air ; that is, of the heavy inflammable air not de- 
compofed, of the light inflammable air difengaged by the 
fpark, and of phlogifiicated air. How much of this phlogifti- 
cated air pre-exifted in the heavy inflammable air, and how 
much 
