mon air by the mixture of
nitrous air was sensibly increased by the presence of the volatile
alkali. It is possible, however, that, by assisting the water to take up
the acid, something less of it may be incorporated with the remaining
diminished air than would otherwise have been; but I did not give much
attention to this circumstance.

When the phial in which I put the alkaline salts contained any kind of
noxious air, the opening of it in nitrous air was not followed by any
thing of the appearance above mentioned. This was the case with
inflammable air. But when, after agitating the inflammable air in water,
I had brought it to a state in which it was diminished a little by the
mixture of nitrous air, the cloudy appearance was in the same
proportion; so that this appearance seems to be equally a test of the
fitness of air for respiration, with the redness which attends the
mixture of it with nitrous air only.

Having generally fastened the small bag which contained the volatile
salt to a piece of brass wire in the preceding experiment, I commonly
found the end of it corroded, and covered with a blue substance. Also
the salt itself, and sometimes the bag was died blue. But finding that
this was not the case when I used an iron wire in the same
circumstances, but that it became _red_, I was satisfied that both the
metals had been dissolved by the volatile alkali. At first I had a
suspicion that the blue might have come from the copper, out of which
the nitrous air had been made. But when the nitrous air was made from
iron, the appearances were, in all respects, the same.

I have observed, in the preceding section, that if nitrous air be mixed
with common air in _lime-water_, the surface of the water, where it is
contiguous to that mixture, will be covered with an incrustation of
lime, shewing that some fixed air had been deposited in the process. It
is remarkable, however, as I there also just mentioned, that this is
the case when nitrous air alone is put to a vessel of lime-water, after
it has been kept in a _bladder_, or only transferred from one vessel to
another by a bladder, in the manner described, p. 15. fig. 9.

As I had used the same bladder for transferring various kinds of air,
and among the rest _fixed air_, I first imagined that this effect might
have been occasioned by a mixture of this fixed air with the nitrous
air, and therefore took a fresh bladder; but still the effect was the
same. To satisfy mys