over
it this receiver, white fumes arise from the sulphur, and fill the
vessel. --You will soon perceive that the water is rising within the
receiver, a little above its level in the plate. --Well, Emily, can you
account for this?

EMILY.

I suppose that the sulphur has absorbed the oxygen from the
atmospherical air within the receiver, and that we shall find some
oxygenated sulphur in the cup. As for the white smoke, I am quite at a
loss to guess what it may be.

MRS. B.

Your first conjecture is very right: but you are mistaken in the last;
for nothing will be left in the cup. The white vapour is the oxygenated
sulphur, which assumes the form of an elastic fluid of a pungent and
offensive smell, and is a powerful acid. Here you see a chemical
combination of oxygen and sulphur, producing a true gas, which would
continue such under the pressure and at the temperature of the
atmosphere, if it did not unite with the water in the plate, to which it
imparts its acid taste, and all its acid properties. --You see, now,
with what curious effects the combustion of sulphur is attended.

CAROLINE.

This is something quite new; and I confess that I do not perfectly
understand why the sulphur turns acid.

MRS. B.

It is because it unites with oxygen, which is the acidifying principle.
And, indeed, the word _oxygen_ is derived from two Greek words
signifying _to produce an acid_.

CAROLINE.

Why, then, is not water, which contains such a quantity of oxygen, acid?

MRS. B.

Because hydrogen, which is the other constituent of water, is not
susceptible of acidification. --I believe it will be necessary, before
we proceed further, to say a few words of the general nature of acids,
though it is rather a deviation from our plan of examining the simple
bodies separately, before we consider them in a state of combination.

Acids may be considered as a peculiar class of _burnt_ bodies, which
during their combustion, or combination with oxygen, have acquired very
characteristic properties. They are chiefly discernible by their sour
taste, and by turning red most of the blue vegetable colours. These two
properties are common to the whole class of acids; but each of them is
distinguished by other peculiar qualities. Every acid consists of some
particular substance, (which constitutes its basis, and is different in
each,) and of oxygen, which is common to them all.

EMILY.

But I do not clearly see the difference between ac