but Mr. Hey, who made the
trial, found that, after some months, various animal substances were
shriveled, and did not preserve their natural forms in this kind of
air.

FOOTNOTES:

[13] The result of several of these experiments I had the pleasure of
trying in the presence of the celebrated Mr. De Luc of Geneva, when he
was upon a visit to Lord Shelburne in Wiltshire.

[14] I have not repeated this experiment with that variation of
circumstances which an attention to Mr. Bewley's observation will
suggest.

SECTION IV.

_Of MARINE ACID AIR._

In my former experiments on this species of air I procured it from
spirit of salt, but I have since hit upon a much less expensive method
of getting it, by having recourse to the process by which the spirit of
salt is itself originally made. For this purpose I fill a small phial
with common salt, pour upon it a small quantity of concentrated oil of
vitriol, and receive the fumes emitted by it in a vessel previously
filled with quicksilver, and standing in a bason of quicksilver, in
which it appears in the form of a perfectly _transparent air_, being
precisely the same thing with that which I had before expelled from the
spirit of salt.

This method of procuring acid air is the more convenient, as a phial,
once prepared in this manner, will suffice, for common experiments, many
weeks; especially if a little more oil of vitriol be occasionally put to
it. It only requires a little more heat at the last than at the first.
Indeed, at the first, the heat of a person's hand will often be
sufficient to make it throw out the vapour. In warm weather it will
even keep smoking many days without the application of any other heat.

On this account, it should be placed where there are no instruments, or
any thing of metal, that can be corroded by this acid vapour. It is from
dear-bought experience that I give this advice. It may easily be
perceived when this phial is throwing out this acid vapour, as it always
appears, in the open air, in the form of a light cloud; owing, I
suppose, to the acid attracting to itself, and uniting with, the
moisture that is in the common atmosphere.

By this process I even made a stronger spirit of salt than can be
procured in any other way. For having a little water in the vessel which
contains the quicksilver, it imbibes the acid vapour, and at length
becomes truly saturated with it. Having, in this manner, impregnated
pure water with acid air,