l
remain in the water, though it should be kept uncorked for any length of
time.

CAROLINE.

I have often heard of people drinking soda-water. Pray what sort of
water is that?

MRS. B.

It is a kind of artificial Seltzer water, holding in solution, besides
the gaseous acid, a particular saline substance, called soda, which
imparts to the water certain medicinal qualities.

CAROLINE.

But how can these waters be so wholesome, since carbonic acid is so
pernicious?

MRS. B.

A gas, we may conceive, though very prejudicial to breathe, may be
beneficial to the stomach. --But it would be of no use to attempt
explaining this more fully at present.

CAROLINE.

Are waters never impregnated with other gases?

MRS. B.

Yes; there are several kinds of gaseous waters. I forgot to tell you
that waters have, for some years past, been prepared, impregnated both
with oxygen and hydrogen gases. These are not an imitation of nature,
but are altogether obtained by artificial means. They have been lately
used medicinally, particularly on the continent, where, I understand,
they have acquired some reputation.

EMILY.

If I recollect right, Mrs. B., you told us that carbon was capable of
decomposing water; the affinity between oxygen and carbon must,
therefore, be greater than between oxygen and hydrogen?

MRS. B.

Yes; but this is not the case unless their temperature be raised to a
certain degree. It is only when carbon is red-hot, that it is capable of
separating the oxygen from the hydrogen. Thus, if a small quantity of
water be thrown on a red-hot fire, it will increase rather than
extinguish the combustion; for the coals or wood (both of which contain
a quantity of carbon) decompose the water, and thus supply the fire both
with oxygen and hydrogen gases. If, on the contrary, a large mass of
water be thrown over the fire, the diminution of heat thus produced is
such, that the combustible matter loses the power of decomposing the
water, and the fire is extinguished.

EMILY.

I have heard that fire-engines sometimes do more harm than good, and
that they actually increase the fire when they cannot throw water enough
to extinguish it. It must be owing, no doubt, to the decomposition of
the water by the carbon during the conflagration.

MRS. B.

Certainly. --The apparatus which you see here (PLATE XI. fig. 3.), may
be used to exemplify what we have just said. It consists in a kind of
open furnace, through which