nsiderably lighter than oxygen gas, and only about half the
weight of atmospherical air. It possesses most of the properties of the
fixed alkalies; but cannot be of so much use in the arts on account of
its volatile nature. It is, therefore, never employed in the manufacture
of glass, but it forms soap with oils equally as well as potash and
soda; it resembles them likewise in its strong attraction for water; for
which reason it can be collected in a receiver over mercury only.

[Footnote *: This amalgam is easily obtained, by placing a globule
of mercury upon a piece of muriat, or carbonat of ammonia, and
electrifying this globule by the Voltaic battery. The globule
instantly begins to expand to three or four times its former size,
and becomes much less fluid, though without losing its metallic
lustre, a change which is ascribed to the metallic basis of
ammonia uniting with the mercury. This is an extremely curious
experiment.]

CAROLINE.

I do not understand this?

MRS. B.

Do you recollect the method which we used to collect gases in a
glass-receiver over water?

CAROLINE.

Perfectly.

MRS. B.

Ammoniacal gas has so strong a tendency to unite with water, that,
instead of passing through that fluid, it would be instantaneously
absorbed by it. We can therefore neither use water for that purpose, nor
any other liquid of which water is a component part; so that, in order
to collect this gas, we are obliged to have recourse to mercury,
(a liquid which has no action upon it,) and a mercurial bath is used
instead of a water bath, such as we employed on former occasions. Water
impregnated with this gas is nothing more than the fluid which you
mentioned at the beginning of the conversation--hartshorn; it is the
ammoniacal gas escaping from the water which gives it so powerful a
smell.

EMILY.

But there is no appearance of effervescence in hartshorn.

MRS. B.

Because the particles of gas that rise from the water are too subtle and
minute for their effect to be visible.

Water diminishes in density, by being impregnated with ammoniacal gas;
and this augmentation of bulk increases its capacity for caloric.

EMILY.

In making hartshorn, then, or impregnating water with ammonia, heat must
be absorbed, and cold produced?

MRS. B.

That effect would take place if it was not counteracted by another
circumstance; the gas is liquefied by incorporating with the water, and
giv