This jar is full of that acid in its gaseous state--it is inverted over mercury instead of water, because, being absorbable by water, this gas cannot be confined by it. --I shall now raise the jar a little on one side, and suffer some of the gas to escape. --You see that it immediately becomes visible in the form of a cloud. EMILY. It must be, no doubt, from its uniting with the moisture of the atmosphere, that it is converted into this dewy vapour. MRS. B. Certainly; and for the same reason, that is to say, its extreme eagerness to unite with water, this gas will cause snow to melt as rapidly as an intense fire. This acid proved much more refractory when Sir H. Davy attempted to decompose it than the other two undecompounded acids. It is singular that potassium will burn in muriatic acid, and be converted into potash, without decomposing the acid, and the result of this combustion is a _muriat of potash_; for the potash, as soon as it is regenerated, combines with the muriatic acid. CAROLINE. But how can the potash be regenerated if the muriatic acid does not oxydate the potassium? MRS. B. The potassium, in this process, obtains oxygen from the moisture with which the muriatic acid is always combined, and accordingly hydrogen, resulting from the decomposition of the moisture, is invariably evolved. EMILY. But why not make these experiments with dry muriatic acid? MRS. B. Dry acids cannot be acted on by the Voltaic battery, because acids are non-conductors of electricity, unless moistened. In the course of a number of experiments which Sir H. Davy made upon acids in a state of dryness, he observed that the presence of water appeared always necessary to develop the acid properties, so that acids are not even capable of reddening vegetable blues if they have been carefully deprived of moisture. This remarkable circumstance led him to suspect, that water, instead of oxygen, may be the acidifying principle; but this he threw out rather as a conjecture than as an established point. Sir H. Davy obtained very curious results from burning potassium in a mixture of phosphorus and muriatic acid, and also of sulphur and muriatic acid; the latter detonates with great violence. All his experiments, however, failed in presenting to his view the basis of the muriatic acid, of which he was in search; and he was at last induced to form an opinion respecting the nature of this acid, which I shall presently explain. EMILY. Is this acid susceptible of different degrees of oxygenation? MRS. B. Yes, for though we cannot deoxygenate this acid, yet we may add oxygen to it. CAROLINE. Why, then, is not the least degree of oxygenation of the acid called the _muriatous_, and the higher degree the _muriatic_ acid? MRS. B.