ations; but in distillations (the general
object of which is to evaporate, by heat, in closed vessels, the
volatile parts of a compound body, and to condense them again into a
liquid,) it serves to carry off the condensed fluid, which otherwise
would fall back into the cucurbit. But this is rather foreign to our
present subject. Let us return to the sulphur. You now perfectly
understand, I suppose, what is meant by sublimation?

EMILY.

I believe I do. Sublimation appears to consist in destroying, by means
of heat, the attraction of aggregation of the particles of a solid body,
which are thus volatilised; and as soon as they lose the caloric which
produced that effect, they are deposited in the form of a fine powder.

CAROLINE.

It seems to me to be somewhat similar to the transformation of water
into vapour, which returns to its liquid state when deprived of caloric.

EMILY.

There is this difference, however, that the sulphur does not return to
its former state, since, instead of lumps, it changes to a fine powder.

MRS. B.

Chemically speaking, it is exactly the same substance, whether in the
form of lump or powder. For if this powder be melted again by heat, it
will, in cooling, be restored to the same solid state in which it was
before its sublimation.

CAROLINE.

But if there be no real change, produced by the sublimation of the
sulphur, what is the use of that operation?

MRS. B.

It divides the sulphur into very minute parts, and thus disposes it to
enter more readily into combination with other bodies. It is used also
as a means of purification.

CAROLINE.

Sublimation appears to me like the beginning of combustion, for the
completion of which one circumstance only is wanting, the absorption of
oxygen.

MRS. B.

But that circumstance is every thing. No essential alteration is
produced in sulphur by sublimation; whilst in combustion it combines
with the oxygen, and forms a new compound totally different in every
respect from sulphur in its pure state. --We shall now _burn_ some
sulphur, and you will see how very different the result will be. For
this purpose I put a small quantity of flowers of sulphur into this cup,
and place it in a dish, into which I have poured a little water: I now
set fire to the sulphur with the point of this hot wire; for its
combustion will not begin unless its temperature be considerably raised.
--You see that it burns with a faint blueish flame; and as I invert