Chalk is, then, a compound salt! I never should have supposed that those immense beds of chalk, that we see in many parts of the country, were a salt.—Now, the white film begins to appear on the surface of the water; but it is far from resembling hard solid chalk.
MRS. B.
That is owing to its state of extreme division; in a little time it will collect into a more compact mass, and subside at the bottom of the glass.
If you breathe into lime-water, the carbonic acid, which is mixed with the air that you expire, will produce the same effect. It is an experiment very easily made;—I shall pour some lime-water into this glass tube, and, by breathing repeatedly into it, you will soon perceive a precipitation of chalk—
EMILY.
I see already a small white cloud formed.
MRS. B.
It is composed of minute particles of chalk; at present it floats in the water, but it will soon subside.
Carbonat of lime, or chalk, you see, is insoluble in water, since the lime which was dissolved re-appears when converted into chalk; but you must take notice of a very singular circumstance, which is, that chalk is soluble in water impregnated with carbonic acid.
CAROLINE.