g only common air, I force a quantity of
nitrous air at random, out of a bladder, and instantly clap my finger on
the mouth of the bottle. I then immerse the neck of it into water, a
small quantity of which I suffer to enter, which squirts into it with
violence; and immediately replacing my finger, remove the phial. The
water contained in it is already _very_ acid, and it becomes more and
more so (if a sufficient quantity of nitrous air was at first thrown in)
on alternately stopping the mouth of the phial, and opening it, as often
as fresh air will enter.

Since I wrote the above, I have frequently converted a small portion of
water in an ounce phial into a weak _Aqua fortis_, by repeated mixtures
of common and nitrous air; throwing in alternately the one or the other,
according to the circumstances; that is, as long as there was a
superabundance of nitrous air, suffering the common air to enter and
condense it; and, when that was effected, forcing in more nitrous air
from the bladder, to the common air which now predominated in the
phial--and so alternately. I have wanted leisure, and conveniences, to
carry on this process to its _maximum_, or to execute it in a different
and better manner; but from what I have done, I think we may conclude
that nitrous air consists principally of the nitrous acid,
phlogisticated, or otherwise so modified, by a previous commenstruation
with metals, inflammable spirits, &c. as to be reduced into a durably
elastic vapour: and that, in order to deprive it of its elasticity, and
restore it to its former state, an addition of common air is requisite,
and, as I suspect, of water likewise, or some other fluid: as in the
course of my few trials, I have not yet been able to condense it in a
perfectly dry bottle.

NUMBER VI.

_A Letter from_ Dr. FRANKLIN.

Craven Street, April 10, 1774.

Dear Sir,

In compliance with your request, I have endeavoured to recollect the
circumstances of the American experiments I formerly mentioned to you,
of raising a flame on the surface of some waters there.

When I passed through New Jersey in 1764, I heard it several times
mentioned, that by applying a lighted candle near the surface of some of
their rivers, a sudden flame Would catch and spread on the water,
continuing to burn for near half a minute. But the accounts I received
were so imperfect that I could form no guess at the cause of such an
effect, and rather