es out its latent heat. The condensation of the gas more than
counterbalances the expansion of the water; therefore, upon the whole,
heat is produced. --But if you dissolve ammoniacal gas with ice or snow,
cold is produced. --Can you account for that?

EMILY.

The gas, in being condensed into a liquid, must give out heat; and, on
the other hand, the snow or ice, in being rarefied into a liquid, must
absorb heat; so that, between the opposite effects, I should have
supposed the original temperature would have been preserved.

MRS. B.

But you have forgotten to take into the account the rarefaction of the
water (or melted ice) by the impregnation of the gas; and this is the
cause of the cold which is ultimately produced.

CAROLINE.

Is the _sal volatile_ (the smell of which so strongly resembles
hartshorn) likewise a preparation of ammonia?

MRS. B.

It is carbonat of ammonia dissolved in water; and which, in its concrete
state, is commonly called salts of hartshorn. Ammonia is caustic, like
the fixed alkalies, as you may judge by the pungent effects of
hartshorn, which cannot be taken internally, nor applied to delicate
external parts, without being plentifully diluted with water. --Oil and
acids are very excellent antidotes for alkaline poisons; can you guess
why?

CAROLINE.

Perhaps, because the oil combines with the alkali, and forms soap, and
thus destroys its caustic properties; and the acid converts it into a
compound salt, which, I suppose, is not so pernicious as caustic alkali.

MRS. B.

Precisely so.

Ammoniacal gas, if it be mixed with atmospherical air, and a burning
taper repeatedly plunged into it, will burn with a large flame of a
peculiar yellow colour.

EMILY.

But pray tell me, can ammonia be procured from this Lybian salt only?

MRS. B.

So far from it, that it is contained in, and may be extracted from, all
animal substances whatever. Hydrogen and nitrogen are two of the chief
constituents of animal matter; it is therefore not surprising that they
should occasionally meet and combine in those proportions that compose
ammonia. But this alkali is more frequently generated by the spontaneous
decomposition of animal substances; the hydrogen and nitrogen gases that
arise from putrefied bodies combine, and form the volatile alkali.

Muriat of ammonia, instead of being exclusively brought from Lybia, as
it originally was, is now chiefly prepared in Europe, by chemical
processes. Amm