Not quite: ashes, as you supposed, are a fixed product of combustion; but smoke, properly speaking, is not one of the volatile products, as it consists of some minute undecomposed particles of the coals that are carried off by the heated air without being burnt, and are either deposited in the form of soot, or dispersed by the wind. Smoke, therefore, ultimately, becomes one of the fixed products of combustion. And you may easily conceive that the stronger the fire is, the less smoke is produced, because the fewer particles escape combustion. On this principle depends the invention of Argand’s Patent Lamps; a current of air is made to pass through the cylindrical wick of the lamp, by which means it is so plentifully supplied with oxygen, that scarcely a particle of oil escapes combustion, nor is there any smoke produced.
EMILY.
But what then are the volatile products of combustion?
MRS. B.
Various new compounds, with which you are not yet acquainted, and which being converted by caloric either into vapour or gas, are invisible; but they can be collected, and we shall examine them at some future period.
CAROLINE.
There are then other gases, besides the oxygen and nitrogen gases.
MRS. B.
Yes, several: any substance that can assume and maintain the form of an elastic fluid at the temperature of the atmosphere, is called a gas. We shall examine the several gases in their respective places; but we must now confine our attention to those that compose the atmosphere.
I shall show you another method of decomposing the atmosphere, which is very simple. In breathing, we retain a portion of the oxygen, and expire the nitrogen gas; so that if we breathe in a closed vessel, for a certain length of time, the air within it will be deprived of its oxygen gas. Which of you will make the experiment?