But this cannot be the case with combustions in general; for when any substance is burnt in the common air, so far from increasing in weight, it is evidently diminished, and sometimes entirely consumed.
MRS. B.
But what do you mean by the expression consumed? You cannot suppose that the smallest particle of any substance in nature can be actually destroyed. A compound body is decomposed by combustion; some of its constituent parts fly off in a gaseous form, while others remain in a concrete state; the former are called the volatile, the latter the fixed products of combustion. But if we collect the whole of them, we shall always find that they exceed the weight of the combustible body, by that of the oxygen which has combined with them during combustion.
EMILY.
In the combustion of a coal fire, then, I suppose that the ashes are what would be called the fixed product, and the smoke the volatile product?
MRS. B.
Yet when the fire burns best, and the quantity of volatile products should be the greatest, there is no smoke; how can you account for that?
EMILY.
Indeed I cannot; therefore I suppose that I was not right in my conjecture.
MRS. B.