of; in consequence of which
the acid fumes could act upon it only in a slow succession, so that part
of them, as well as of the fixed air, had an opportunity of forming
another union with the diminished air.

This, as I have observed before, was so much the case when the process
was made in quicksilver, without any volatile alkali, that when water
was admitted to it, after some time, it was not capable of dissolving
that union, tho' it would not have taken place if the process had been
in water from the first.

In diversifying this experiment, I found that it appeared to very great
advantage when I suspended a piece of volatile salt in the common air,
previous to the admission of nitrous air to it, inclosing it in a bit
of gauze, muslin, or a small net of wire. For, presently after the
redness of the mixture begins to go off, the white cloud, like snow,
begins to descend from the salt, as if a white powder was shaken out of
the bag that contains it. This white cloud presently fills the whole
vessel, and the appearance will last about five minutes.

If the salt be not put to the mixture of these two kinds of air till it
has perfectly recovered its transparency, the effervescence being
completely over, no white cloud will be formed; and, what is rather more
remarkable, there is nothing of this appearance when the salt is put
into the nitrous air itself. The reason of this must be, that the acid
of the nitrous air has a nearer affinity with its phlogiston than with
the volatile alkali; though the phlogiston having a nearer affinity with
something in the common air, the acid being thereby set loose, will
unite with the alkaline vapour, if it be at hand to unite with it.

There is also very little, if any white cloud formed upon holding a
piece of the volatile salt within the mouth of a phial containing
smoking spirit of nitre. Also when I threw the focus of a burning mirror
upon some sal ammoniac in nitrous air, and filled the whole vessel with
white fumes which arose from it, they were soon dispersed, and the air
was neither diminished nor altered.

I was now fully convinced, that the white cloud which I casually
observed, in the first of these experiments, was occasioned by the
volatile alkali emitted from the water, which was in a slight degree
putrid; and that the warming, and agitation of the vessels, had promoted
the emission of the putrid, or alkaline effluvium.

I could not perceive that the diminution of com