How very small, then, is the proportion of lime dissolved! MRS. B. Barytes is still of more difficult solution; it dissolves only in 900 times its weight of water: but it is much more soluble in the state of crystals. The liquid contained in this bottle is lime-water; it is often used as a medicine, chiefly, I believe, for the purpose of combining with, and neutralising, the superabundant acid which it meets with in the stomach. EMILY. I am surprised that it is so perfectly clear; it does not at all partake of the whiteness of the lime. MRS. B. Have you forgotten that, in solutions, the solid body is so minutely subdivided by the fluid as to become invisible, and therefore will not in the least degree impair the transparency of the solvent? I said that the attraction of lime for carbonic acid was so strong, that it would absorb it from the atmosphere. We may see this effect by exposing a glass of lime-water to the air; the lime will then separate from the water, combine with the carbonic acid, and re-appear on the surface in the form of a white film, which is carbonat of lime, commonly called _chalk_. CAROLINE. 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. It is very curious, indeed, that carbonic acid gas should render lime soluble in one instance, and insoluble in the other! MRS. B. I have here a bottle of Seltzer water, which, you know, is strongly impregnated with carbonic acid:-- let us pour a little of it into a glass of lime-water. You see that it immediately forms a precipitation of carbonat of lime? EMILY. Yes, a white cloud appears. MRS. B. I shall now pour an additional quantity of the Seltzer water into the lime-water-- EMILY. How singular! The cloud is re-dissolved, and the liquid is again transparent. MRS. B.