parate, and this I can show you by an easy experiment.

This phial, which contains some salt, I shall fill with water, pouring
it in quickly, so as not to dissolve much of the salt; and when it is
quite full I cork it. --If I now shake the phial till the salt is
dissolved, you will observe that it is no longer full.

CAROLINE.

I shall try to add a little more salt. --But now, you see, Mrs. B., the
water runs over.

MRS. B.

Yes; but observe that the last quantity of salt you put in remains solid
at the bottom, and displaces the water; for it has already melted all
the salt it is capable of holding in solution. This is called the point
of _saturation_; and the water in this case is said to be _saturated_
with salt.

EMILY.

I think I now understand the solution of a solid body by water
perfectly: but I have not so clear an idea of the solution of a liquid
by caloric.

MRS. B.

It is probably of a similar nature; but as caloric is an invisible
fluid, its action as a solvent is not so obvious as that of water.
Caloric, we may conceive, dissolves water, and converts it into vapour
by the same process as water dissolves salt; that is to say, the
particles of water are so minutely divided by the caloric as to become
invisible. Thus, you are now enabled to understand why the vapour of
boiling water, when it first issues from the spout of a kettle, is
invisible; it is so, because it is then completely dissolved by caloric.
But the air with which it comes in contact, being much colder than the
vapour, the latter yields to it a quantity of its caloric. The particles
of vapour being thus in a great measure deprived of their solvent,
gradually collect, and become visible in the form of steam, which is
water in a state of imperfect solution; and if you were further to
deprive it of its caloric, it would return to its original liquid state.

CAROLINE.

That I understand very well. If you hold a cold plate over a tea-urn,
the steam issuing from it will be immediately converted into drops of
water by parting with its caloric to the plate; but in what state is the
steam, when it becomes invisible by being diffused in the air?

MRS. B.

It is not merely diffused, but is again dissolved by the air.

EMILY.

The air, then, has a solvent power, like water and caloric?

MRS. B.

This was formerly believed to be the case. But it appears from more
recent enquiries that the solvent power of the atmosphere depends solely