It is easy to estimate its weight, by separating it from the manganese, and finding how much the latter has lost.
EMILY.
But if you can take the oxygen from the metal, shall we not then have it in its palpable simple state?
MRS. B.
No; for I can only separate the oxygen from the manganese, by presenting to it some other body, for which it has a greater affinity than for the manganese. Caloric affording the two electricities is decomposed, and one of them uniting with the oxygen, restores it to the aëriform state.
EMILY.
But you said just now, that manganese would attract oxygen from the atmosphere in which it is combined with the negative electricity; how, therefore, can the oxygen have a superior affinity for that electricity, since it abandons it to combine with the manganese?
MRS. B.
I give you credit for this objection, Emily; and the only answer I can make to it is, that the mutual affinities of metals for oxygen, and of oxygen for electricity, vary at different temperatures; a certain degree of heat will, therefore, dispose a metal to combine with oxygen, whilst, on the contrary, the former will be compelled to part with the latter, when the temperature is further increased. I have put some oxyd of manganese into a retort, which is an earthen vessel with a bent neck, such as you see here. ([Plate VII.] Fig. 2.)—The retort containing the manganese you cannot see, as I have enclosed it in this furnace, where it is now red-hot. But, in order to make you sensible of the escape of the gas, which is itself invisible, I have connected the neck of the retort with this bent tube, the extremity of which is immersed in this vessel of water. ([Plate VII.] Fig. 3.)—Do you see the bubbles of air rise through the water?
CAROLINE.