concluded that it could not depend upon any
thing peculiar to the precipitate of the _copper_ contained in the
_paper_ from which the air was procured, as I had at first imagined, but
upon what was common to it, and pure nitrous air.

Afterwards, having, (with a view to observe whether any crystals would
be formed by the union of volatile alkali, and nitrous air, similar to
those formed by it and fixed air, as described by Mr. Smeth in his
_Dissertation on fixed Air_) opened the mouth of a phial which was half
filled with a volatile alkaline liquor, in a jar of nitrous air (in the
manner described p. 11. fig. 4.) I had an appearance which perfectly
explained the preceding. All that part of the phial which was above the
liquor, and which contained common air, was filled with beautiful
_white clouds_, as if some fine white powder had been instantly thrown
into it, and some of these clouds rose within the jar of nitrous air.
This appearance continued about a minute, and then intirely disappeared,
the air becoming transparent.

Withdrawing the phial, and exposing it to the common air, it there also
became turbid, and soon after the transparency returned. Introducing it
again into the nitrous air, the clouds appeared as before. In this
manner the white fumes, and transparency, succeeded each other
alternately, as often as I chose to repeat the experiment, and would no
doubt have continued till the air in the jar had been thoroughly diluted
with common air. These appearances were the same with any substance that
contained _volatile alkali_, fluid or solid.

When, instead of the small phial, I used a large and tall glass jar,
this appearance was truly fine and striking, especially when the water
in the trough was very transparent. For I had only to put the smallest
drop of a volatile alkaline liquor, or the smallest bit of the solid
salt, into the jar, and the moment that the mouth of it was opened in a
jar of nitrous air, the white clouds above mentioned began to be formed
at the mouth, and presently descended to the bottom, so as to fill the
whole, were it ever so large, as with fine snow.

In considering this experiment, I soon perceived that this curious
appearance must have been occasioned by the mixture of the nitrous and
common air, and therefore that the white clouds must be _nitrous
ammoniac_, formed by the acid of the nitrous air, set loose in the
decomposition of it by common air, while the phlogiston, which mus