Carbonic acid gas is found very abundantly in nature; it is supposed to form about one thousandth part of the atmosphere, and is constantly produced by the respiration of animals; it exists in a great variety of combinations, and is exhaled from many natural decompositions. It is contained in a state of great purity in certain caves, such as the _Grotto del Cane_, near Naples. EMILY. I recollect having read an account of that grotto, and of the cruel experiments made on the poor dogs, to gratify the curiosity of strangers. But I understood that the vapour exhaled by this cave was called _fixed air_. MRS. B. That is the name by which carbonic acid was known before its chemical composition was discovered. --This gas is more destructive of life than any other; and if the poor animals that are submitted to its effects are not plunged into cold water as soon as they become senseless, they do not recover. It extinguishes flame instantaneously. I have collected some in this glass, which I will pour over the candle. CAROLINE. This is extremely singular--it seems to extinguish it as it were by enchantment, as the gas is invisible. I never should have imagined that gas could have been poured like a liquid. MRS. B. It can be done with carbonic acid only, as no other gas is sufficiently heavy to be susceptible of being poured out in the atmospherical air without mixing with it. EMILY. Pray by what means did you obtain this gas? MRS. B. I procured it from marble. Carbonic acid gas has so strong an attraction for all the alkalies and alkaline earths, that these are always found in nature in the state of carbonats. Combined with lime, this acid forms chalk, which may be considered as the basis of all kinds of marbles, and calcareous stones. From these substances carbonic acid is easily separated, as it adheres so slightly to its combinations, that the carbonats are all decomposable by any of the other acids. I can easily show you how I obtained this gas; I poured some diluted sulphuric acid over pulverised marble in this bottle (the same which we used the other day to prepare hydrogen gas), and the gas escaped through the tube connected with it; the operation still continues, as you may easily perceive-- EMILY. Yes, it does; there is a great fermentation in the glass vessel. What singular commotion is excited by the sulphuric acid taking possession of the lime, and driving out the carbonic acid! CAROLINE. But did the carbonic acid exist in a gaseous state in the marble? MRS. B. Certainly not; the acid, when in a state of combination, is capable of existing in a solid form. CAROLINE. Whence, then, does it obtain the caloric necessary to convert it into gas? MRS. B.