stroyed by
the explosion, which was again fired, and the operation continued till
almost the whole of the mixture was let into the globe and exploded.
By this means, though the globe held not more than a sixth part of the
mixture, almost the whole of it was exploded therein without any fresh
exhaustion of the globe."

At first this condensed matter was "acid to the taste and contained
two grains of nitre," but Cavendish, suspecting that this was due to
impurities, tried another experiment that proved conclusively that his
opinions were correct. "I therefore made another experiment," he says,
"with some more of the same air from plants in which the proportion of
inflammable air was greater, so that the burnt air was almost completely
phlogisticated, its standard being one-tenth. The condensed liquor was
then not at all acid, but seemed pure water."

From these experiments he concludes "that when a mixture of inflammable
and dephlogisticated air is exploded, in such proportions that the burnt
air is not much phlogisticated, the condensed liquor contains a little
acid which is always of the nitrous kind, whatever substance the
dephlogisticated air is procured from; but if the proportion be such
that the burnt air is almost entirely phlogisticated, the condensed
liquor is not at all acid, but seems pure water, without any addition
whatever."(2)

These same experiments, which were undertaken to discover the
composition of water, led him to discover also the composition of nitric
acid. He had observed that, in the combustion of hydrogen gas with
common air, the water was slightly tinged with acid, but that this
was not the case when pure oxygen gas was used. Acting upon this
observation, he devised an experiment to determine the nature of this
acid. He constructed an apparatus whereby an electric spark was passed
through a vessel containing common air. After this process had been
carried on for several weeks a small amount of liquid was formed. This
liquid combined with a solution of potash to form common nitre, which
"detonated with charcoal, sparkled when paper impregnated with it was
burned, and gave out nitrous fumes when sulphuric acid was poured on
it." In other words, the liquid was shown to be nitric acid. Now, since
nothing but pure air had been used in the initial experiment, and since
air is composed of nitrogen and oxygen, there seemed no room to doubt
that nitric acid is a combination of nitrogen and oxygen.