pper in diluted spirit of nitre, in nitrous air, I
found there was a considerable addition to the quantity of it; upon
which I fired some of the same kind of paper in quicksilver and
presently observed that air was produced from it in great plenty. This
air, at the first, seemed to have some singular properties, but
afterwards I found that it was nothing more than a mixture of nitrous
air, from the precipitate of the solution, and of inflammable air, from
the paper; but that the former was predominant.

In the mixture of this kind of air with common air, in a trough of water
which had been putrid, but which at that time seemed to have recovered
its former sweetness (for it was not in the least degree offensive to
the smell) a phenomenon sometimes occurred, which for a long time
exceedingly delighted and puzzled me; but which was afterwards the means
of letting me see much farther into the constitution of nitrous air than
I had been able to see before.

When the diminution of the air was nearly completed, the vessel in which
the mixture was made began to be filled with the most beautiful _white
fumes_, exactly resembling the precipitation of some white substance in
a transparent menstruum, or the falling of very fine snow; except that
it was much thicker below than above, as indeed is the case in all
chemical precipitations. This appearance continued two or three minutes.

At other times I went over the same process, as nearly as possible in
the same manner, but without getting this remarkable appearance, and was
several times greatly disappointed and chagrined, when I baulked the
expectations of my friends, to whom I had described, and meant to have
shewn it. This made me give all the attention I possibly could to this
experiment, endeavouring to recollect every circumstance, which, though
unsuspected at the time, might have contributed to produce this new
appearance; and I took a great deal of pains to procure a quantity of
this air from the paper above mentioned for the purpose, which, with a
small burning lens, and an uncertain sun, is not a little troublesome.
But all that I observed for some time was, that I stood the best chance
of succeeding when I _warmed_ the vessel in which the mixture was made,
and _agitated_ the air during the effervescence.

Finding, at length, that, with the same preparation and attentions, I
got the same appearance from a mixture of nitrous and common air in the
same trough of water, I