pears in the form of
blueish black crystalline scales, such as you see in this tube.

CAROLINE.

They shine like black lead, and some of the scales have the shape of
lozenges.

MRS. B.

That is actually the form which the crystals of iodine often assume. But
if we heat them gently, by holding the tube over the flame of a candle,
see what a change takes place in them.

CAROLINE.

How curious! They seem to melt, and the tube immediately fills with a
beautiful violet vapour. But look, Mrs. B., the same scales are now
appearing at the other end of the tube.

MRS. B.

This is in fact a sublimation of iodine, from one part of the tube to
another; but with this remarkable peculiarity, that, while in the
gaseous state, iodine assumes that bright violet colour, which, as you
may already perceive, it loses as the tube cools, and the substance
resumes its usual solid form. --It is from the violet colour of the gas
that iodine has obtained its name.

CAROLINE.

But how is this curious substance obtained?

MRS. B.

It is found in the ley of ashes of sea-weeds, after the soda has been
separated by crystallisation; and it is disengaged by means of sulphuric
acid, which expels it from the alkaline ley in the form of a violet gas,
which may be collected and condensed in the way you have just seen.
--This interesting discovery was made in the year 1812, by M. Courtois,
a manufacturer of saltpetre at Paris.

CAROLINE.

And pray, Mrs. B., what is the proof of iodine being a simple body?

MRS. B.

It is considered as a simple body, both because it is not capable of
being resolved into other ingredients; and because it is itself capable
of combining with other bodies, in a manner analogous to oxygen and
chlorine. The most curious of these combinations is that which it forms
with hydrogen gas, the result of which is a peculiar gaseous acid.

CAROLINE.

Just as chlorine and hydrogen gas form muriatic acid? In this respect
chlorine and iodine seem to bear a strong analogy to each other.

MRS. B.

That is indeed the case; so that if the theory of the constitution of
either of these two bodies be true, it must be true also in regard to
the other; if erroneous in the one, the theory must fall in both.

But it is now time to conclude; we have examined such of the acids and
salts as I conceived would appear to you most interesting. --I shall not
enter into any particulars respecting the metallic acids, as they offer
no