This sparkling, or effervescence, as it is called, is always occasioned by the action of an elastic fluid escaping from a liquid; in the artifical Seltzer water, it is produced by the carbonic acid, which being lighter than the water in which it was strongly condensed, flies off with great rapidity the instant the bottle is uncorked; this makes it necessary to drink it immediately. The bubbling that took place in this bottle was but trifling, as the water was but very slightly impregnated with carbonic acid. It requires a particular apparatus to prepare the gaseous artificial mineral waters. EMILY. If, then, a bottle of Seltzer water remains for any length of time uncorked, I suppose it returns to the state of common water? MRS. B. The whole of the carbonic acid gas, or very nearly so, will soon disappear; but there is likewise in Seltzer water a very small quantity of soda, and of a few other saline or earthy ingredients, which will 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.