itting fever, which seized
me a few days after, to my breathing too much of that foul air which I
stirred up from the bottom, and which I could not avoid while I stooped
in endeavouring to kindle it.--The discoveries you have lately made of
the manner in which inflammable air is in some cases produced, may throw
light on this experiment, and explain its succeeding in some cases, and
not in others. With the highest esteem and respect,

I am, Dear Sir,

Your most obedient humble servant,

B. FRANKLIN.

NUMBER VII.

_Extract of a Letter from_ Mr. HENRY _of_ Manchester.

It is with great pleasure I hear of your intended publication _on air_,
and I beg leave to communicate to you an experiment or two which I
lately made.

Dr. Percival had tried, without effect, to dissolve lead in water
impregnated with fixed air. I however thought it probable, that the
experiment might succeed with nitrous air. Into a quantity of water
impregnated with it, I put several pieces of sheet-lead, and suffered
them, after agitation, to continue immersed about two hours. A few drops
of vol. tincture of sulphur changed the water to a deep orange colour,
but not so deep as when the same tincture was added to a glass of the
same water, into which one drop of a solution of sugar of lead had been
instilled. The precipitates of both in the morning, were exactly of the
same kind; and the water in which the lead had been infused all night,
being again tried by the same test, gave signs of a still stronger
saturnine impregnation--Whether the nitrous air acts as an acid on the
lead, or in the same manner that fixed air dissolves iron, I do not
pretend to determine. Syrup of violets added to the nitrous water became
of a pale red, but on standing about an hour, grew of a turbid brown
cast.

Though the nitrous acid is not often found, except produced by art, yet
as there is a probability that nitre may be formed in the earth in large
towns, and indeed fossile nitre has been actually found in such
situations, it should be an additional caution against the use of leaden
pumps.

I tried to dissolve mercury by the same means, but without success.

I am, with the most sincere esteem,

Dear Sir,

Your obliged and obedient servant,

THO. HENRY.

_FINIS._

FOOTNOTES:

[15] See Dr. Falconer's very useful and ingenious treatise on the Bath
water, 2d edit. p. 313.

[16] May, 1772.

[17]