And it is probably from this circumstance that it has been called an oil, for it can have no real claim to that name, as it does not contain either hydrogen or carbon, which are the essential constituents of oil. MRS. B. Certainly; and therefore it would be the more absurd to retain a name which owed its origin to such a mistaken analogy. Sulphuric acid, in its purest state, would probably be a concrete substance, but its attraction for water is such, that it is impossible to obtain that acid perfectly free from it; it is, therefore, always seen in a liquid form, such as you here find it. One of the most striking properties of sulphuric acid is that of evolving a considerable quantity of heat when mixed with water; this I have already shown you. EMILY. Yes, I recollect it; but what was the degree of heat produced by that mixture? MRS. B. The thermometer may be raised by it to 300 degrees, which is considerably above the temperature of boiling water. CAROLINE. Then water might be made to boil in that mixture? MRS. B. Nothing more easy, provided that you employ sufficient quantities of acid and of water, and in the due proportions. The greatest heat is produced by a mixture of one part of water to four of the acid: we shall make a mixture of these proportions, and immerse in it this thin glass tube, which is full of water. CAROLINE. The vessel feels extremely hot, but the water does not boil yet. MRS. B. You must allow some time for the heat to penetrate the tube, and raise the temperature of the water to the boiling point-- CAROLINE. Now it boils--and with increasing violence. MRS. B. But it will not continue boiling long; for the mixture gives out heat only while the particles of the water and the acid are mutually penetrating each other: as soon as the new arrangement of those particles is effected, the mixture will gradually cool, and the water return to its former temperature. You have seen the manner in which sulphuric acid decomposes all combustible substances, whether animal, vegetable, or mineral, and burns them by means of its oxygen? CAROLINE. I have very unintentionally repeated the experiment on my gown, by letting a drop of the acid fall upon it, and it has made a stain, which, I suppose, will never wash out. MRS. B. No, certainly; for before you can put it into water, the spot will become a hole, as the acid has literally burnt the muslin. CAROLINE. So it has, indeed! Well, I will fasten the stopper, and put the bottle away, for it is a dangerous substance. --Oh, now I have done worse still, for I have spilt some on my hand! MRS. B. It is then burned, as well as your gown, for you know that oxygen destroys animal as well as vegetable matters; and, as far as the decomposition of the skin of your finger is effected, there is no remedy; but by washing it immediately in water, you will dilute the acid, and prevent any further injury. CAROLINE. It feels extremely hot, I assure you. MRS. B.