air of my study, after a few
persons have been with me in it, and the air on the outside of the
house. Also a phial of air having been sent me, from the neighbourhood
of York, it appeared not to be so good as the air near Leeds; that is,
it was not diminished so much by an equal mixture of nitrous air, every
other circumstance being as nearly the same as I could contrive. It may
perhaps be possible, but I have not yet attempted it, to distinguish
some of the different winds, or the air of different times of the year,
&c. &c. by this test.

By means of this test I was able to determine what I was before in doubt
about, viz. the _kind_ as well as the _degree_ of injury done to air by
candles burning in it. I could not tell with certainty, by means of
mice, whether it was at all injured with respect to respiration; and yet
if nitrous air may be depended upon for furnishing an accurate test, it
must be rather more than one third worse than common air, and have been
diminished by the same general cause of the other diminutions of air.
For when, after many trials, I put one measure of thoroughly putrid and
highly noxious air, into the same vessel with two measures of good
wholesome air, and into another vessel an equal quantity, viz. three
measures of air in which a candle had burned out; and then put equal
quantities of nitrous air to each of them, the latter was diminished
rather more than the former.

It agrees with this observation, that _burned air_ is farther diminished
both by putrefaction, and a mixture of iron filings and brimstone; and I
therefore take it for granted by every other cause of the diminution of
air. It is probable, therefore, that burned air is air so far loaded
with phlogiston, as to be able to extinguish a candle, which it may do
long before it is fully saturated.

Inflammable air with a mixture of nitrous air burns with a green flame.
This makes a very pleasing experiment when it is properly conducted. As,
for some time, I chiefly made use of _copper_ for the generation of
nitrous air, I first ascribed this circumstance to that property of this
metal, by which it burns with a green flame; but I was presently
satisfied that it must arise from the spirit of nitre, for the effect is
the very same from which ever of the metals the nitrous air is
extracted, all of which I tried for this purpose, even silver and gold.

A mixture of oil of vitriol and spirit of nitre in equal proportions
dissolved iro