new inflammable Air or G-afs , &c. 379 
animal ceconomy which is fo important, that without its 
conftant influence an animal, once born, has but a few 
moments to live. 
The criterion of the degree of goodnefs of refpirable 
air, by the quantity which is abforbed or deftroyed by 
the addition of nitrous air, is one of thofe ufeful difco- 
veries of Dr. Priestley’s from which mankind will, 
perhaps, hereafter reap a confiderable benefit. 
The difcovery of the various kinds of inflammable 
airs or gaffes becoming powerfully explofive, when they 
are mixed with a fufficient quantity of common air, and 
flill more fo when they are combined with dephlogi fticated 
air, is one of thofe improvements in natural philofophy 
which, giving occafion to various amufing and intereft- 
ing experiments, have call: at the fame time a new light 
upon fome powerful agents, whofe milchievous force 
was known, though their nature was flill in the dark. 
As thofe inflammable airs have been of late years one 
of the principal philofophical amufements, I intend to 
lay before the Royal Society an eafy method of produc- 
ing, without any trouble or particular apparatus, fuch 
quantity of an inflammable air or gafs as may be re- 
quired; to which I ill all fubjoin fome confiderations 
which have occurred to me about the nature of that won- 
derful fubftance gunpowder, which conveys death at fuch 
an immenfe diftance by its almoft irrefiftible explofive 
force, 
