Let me consider. --The receiver was full of atmospherical air; the taper, in burning within it, must have combined with the oxygen contained in that air, and the caloric that was disengaged produced the light of the taper. But when the whole of the oxygen was absorbed, the whole of its electricity was disengaged; consequently no more caloric could be produced, the taper ceased to burn, and the flame was extinguished. MRS. B. Your explanation is perfectly correct. EMILY. The two constituents of the oxygen gas being thus disposed of, what remains under the receiver must be pure nitrogen gas? MRS. B. There are some circumstances which prevent the nitrogen gas, thus obtained, from being perfectly pure; but we may easily try whether the oxygen has disappeared, by putting another lighted taper under it. --You see how instantaneously the flame is extinguished, for want of oxygen to supply the negative electricity required for the formation of caloric; and were you to put an animal under the receiver, it would immediately be suffocated. But that is an experiment which I do not think your curiosity will tempt you to try. EMILY. Certainly not. --But look, Mrs. B., the receiver is full of a thick white smoke. Is that nitrogen gas? MRS. B. No, my dear; nitrogen gas is perfectly transparent and invisible, like common air. This cloudiness proceeds from a variety of exhalations, which arise from the burning taper, and the nature of which you cannot yet understand. CAROLINE. The water within the receiver has now risen a little above its level in the bason. What is the reason of this? MRS. B. With a moment’s reflection, I dare say, you would have explained it yourself. The water rises in consequence of the oxygen gas within it having been destroyed, or rather decomposed, by the combustion of the taper. CAROLINE. Then why did not the water rise immediately when the oxygen gas was destroyed? MRS. B. Because the heat of the taper, whilst burning, produced a dilatation of the air in the vessel, which at first counteracted this effect. Another means of decomposing the atmosphere is the _oxygenation_ of certain metals. This process is very analogous to combustion; it is, indeed, only a more general term to express the combination of a body with oxygen. CAROLINE. In what respect, then, does it differ from combustion? MRS. B. The combination of oxygen in combustion is always accompanied by a disengagement of light and heat; whilst this circumstance is not a necessary consequence of simple oxygenation. CAROLINE. But how can a body absorb oxygen without the combination of the two electricities which produce caloric? MRS. B.