into water, nitric
peroxide, and oxygen; in others he heated nitrates. His conclusion
is: “_Atmospherical air_, or the thing we breathe, _consists of the
nitrous acid and earth_, with so much phlogiston as is necessary to
its elasticity; and likewise so much more as is required to bring it
from its state of perfect purity to the mean condition in which we find
it.”[7]

When such experiments were made by heating nitrates in a gun-barrel,
“phlogisticated air” was obtained. This was nitrogen, for the iron had
reduced the oxides of the latter, and combining with their oxygen, had
formed nitrogen; moreover, it had absorbed to a greater or less extent
the oxygen simultaneously produced.

Having concluded that respirable air was a compound of nitrous acid,
phlogiston, and earth, Priestley endeavoured to ascertain what was the
nature of this earth. He concludes “that the _metallic earths_, if free
from phlogiston, are the most proper, and next to them the _calcareous
earths_.”

“Dephlogisticated air may be procured from any kind of earth with which
the spirit of nitre will unite.” A few quantitative experiments would
surely have refuted this erroneous conclusion. Those which he attempted
to make were very crude. A bladder (of which he does not give the
capacity) was filled with

  Phlogisticated air, and weighed 7 dwts. 15 grs.
  Nitrous air          "     "    7   "   16  "
  Common air           "     "    7   "   17  "
  Dephlogisticated air "     "    7   "   19  "

He concludes (taking into consideration that inflammable air is
very light) “that the less phlogiston any kind of air contains, the
heavier it is; and the more phlogiston it contains, the lighter it
is.”[8] Strange that this should not have led to the rejection of the
phlogistic hypothesis!

Priestley had the curiosity to breathe his “good” air. He says: “My
reader will not wonder that, after having ascertained the superior
goodness of dephlogisticated air by mice living in it, and the other
tests above mentioned, I should have t