MRS. B.
That is not a proof of its being pure, but only of the absence of oxygen, as it is that principle alone which can produce combustion, every other gas being absolutely incapable of it.
EMILY.
In the methods which you have shown us, for decomposing the atmosphere, the oxygen always abandons the nitrogen; but is there no way of taking the nitrogen from the oxygen, so as to obtain the latter pure from the atmosphere?
MRS. B.
You must observe, that whenever oxygen is taken from the atmosphere, it is by decomposing the oxygen gas; we cannot do the same with the nitrogen gas, because nitrogen has a stronger affinity for caloric than for any other known principle: it appears impossible therefore to separate it from the atmosphere by the power of affinities. But if we cannot obtain the oxygen gas, by this means, in its separate state, we have no difficulty (as you have seen) to procure it in its gaseous form, by taking it from those substances that have absorbed it from the atmosphere, as we did with the oxyd of manganese.
EMILY.
Can atmospherical air be recomposed, by mixing due proportions of oxygen and nitrogen gases?
MRS. B.
Yes: if about one part of oxygen gas be mixed with about four parts of nitrogen gas, atmospherical air is produced.[*]