ity of it, I did not perceive that any sensible alteration was made
in it. A little inflammable air was produced, but not more than might
have come from the two iron nails which I made use of in taking the
sparks.

FOOTNOTES:

[9] It will be seen, in the second part of this work, that, in some of
these processes, I had afterwards more success.

SECTION X.

MISCELLANEOUS OBSERVATIONS.

1. As many of the preceding observations relate to the _vinous_ and
_putrefactive_ fermentations, I had the curiosity to endeavour to
ascertain in what manner the air would be affected by the _acetous_
fermentation. For this purpose I inclosed a phial full of small beer in
a jar standing in water; and observed that, during the first two or
three days, there was an increase of the air in the jar, but from that
time it gradually decreased, till at length there appeared to be a
diminution of about one tenth of the whole quantity.

During this time the whole surface of it was gradually covered with a
scum, beautifully corrugated. After this there was an increase of the
air till there was more than the original quantity; but this must have
been fixed air, not incorporated with the rest of the mass; for,
withdrawing the beer, which I found to be sour, after it had stood 18 or
20 days under the jar, and passing the air several times through cold
water, the original quantity was diminished about one ninth. In the
remainder a candle would not burn, and a mouse would have died
presently.

The smell of this air was exceedingly pungent, but different from that
of the putrid effluvium. A mouse lived perfectly well in this air, thus
affected with the acetous fermentation; after it had stood several days
mixed with four times the quantity of fixed air.

2. All the kinds of factitious air on which I have yet made the
experiment are highly noxious, except that which is extracted from
saltpetre, or alum; but in this even a candle burned just as in common
air[10]. In one quantity which I got from saltpetre a candle not only
burned, but the flame was increased, and something was heard like a
hissing, similar to the decrepitation of nitre in an open fire. This
experiment was made when the air was fresh made, and while it probably
contained some particles of nitre, which would have been deposited
afterwards. The air was extracted from these substances by heating them
in a gun-barrel, which was much corroded and soon spoiled by the
experiment.