ent to evaporate the water only.

I should not omit also to mention that bodies, in crystallising from
their watery solution, always retain a small portion of water, which
remains confined in the crystal in a solid form, and does not reappear
unless the body loses its crystalline state. This is called the _water
of crystallisation_. But you must observe, that whilst a body may be
separated from its solution in water or caloric simply by cooling or by
evaporation, an acid can be taken from a metal with which it is combined
only by stronger affinities, which produce a decomposition.

EMILY.

Are the perfect metals susceptible of being dissolved and converted into
compound salts by acids?

MRS. B.

Gold is acted upon by only one acid, the _oxygenated muriatic_, a very
remarkable acid, which, when in its most concentrated state, dissolves
gold or any other metal, by burning them rapidly.

Gold can, it is true, be dissolved likewise by a mixture of two acids,
commonly called _aqua regia_; but this mixed solvent derives that
property from containing the peculiar acid which I have just mentioned.
Platina is also acted upon by this acid only; silver is dissolved by
nitric acid.

CAROLINE.

I think you said that some of the metals might be so strongly oxydated
as to become acid?

MRS. B.

There are five metals, arsenic, molybdena, chrome, tungsten, and
columbium, which are susceptible of combining with a sufficient quantity
of oxygen to be converted into acids.

CAROLINE.

Acids are connected with metals in such a variety of ways, that I am
afraid of some confusion in remembering them. --In the first place,
acids will yield their oxygen to metals. Secondly, they will combine
with them in their state of oxyds, to form compound salts; and lastly,
several of the metals are themselves susceptible of acidification.

MRS. B.

Very well; but though metals have so great an affinity for acids, it is
not with that class of bodies alone that they will combine. They are
most of them, in their simple state, capable of uniting with sulphur,
with phosphorus, with carbon, and with each other; these combinations,
according to the nomenclature which was explained to you on a former
occasion, are called _sulphurets_, _phosphorets_, _carburets_, &c.

The metallic phosphorets offer nothing very remarkable. The sulphurets
form the peculiar kind of mineral called _pyrites_, from which certain
kinds of mineral waters, as those of H