of air. The air to which I
refer was kept about a fortnight in a bladder, through which the
peculiar smell of the nitrous air was very sensible for several days. In
a day or two the bladder became red, and was much contracted in its
dimensions. The air within it had lost very little of its peculiar
property of diminishing common air.

I did not endeavour to ascertain the exact quantity of nitrous air
produced from given quantities, of all the metals which yield it; but
the few observations which I did make for this purpose I shall recite in
this place:

dwt. gr.

6 0 of silver yielded 17-1/2 ounce measures.
5 19 of quicksilver 4-1/2
1 2-1/2 of copper 14-1/2
2 0 of brass 21
0 20 of iron 16
1 5 of bismuth 6
0 12 of nickel 4

FOOTNOTES:

[6] I have since found, that nitrous air has never failed to escape from
the water, which has been impregnated with it, by long exposure to the
open air.

[7] This suspicion has been confirmed by the ingenious Mr. Bewley, of
Great Massingham in Norfolk, who has discovered that the acid taste of
this water is not the necessary consequence of its impregnation with
nitrous air, but is the effect of the _acid vapour_, into which part of
this air is resolved, when it is decomposed by a mixture with common
air. This, it will be seen, exactly agrees with my own observation on
the constitution of nitrous air, in the second part of this work. A more
particular account of Mr. Bewley's observation will be given in the
_Appendix_.

SECTION VII.

_Of AIR infected with the FUMES of BURNING CHARCOAL._

Air infected with the fumes of burning charcoal is well known to be
noxious; and the Honourable Mr. Cavendish favoured me with an account of
some experiments of his, in which a quantity of common air was reduced
from 180 to 162 ounce measures, by passing through a red-hot iron tube
filled with the dust of charcoal. This diminution he ascribed to such a
_destruction_ of common air as Dr. Hales imagined to be the consequence
of burning. Mr. Cavendish also observed, that there had been a
generation of fixed air in this process, but that it was absorbed by
sope leys. This experiment I also repeated, with a small variation of
circumstances, and with nearly the same result.

Afterwards, I endeavoured to ascertain, by what appears to me to be an