A. The intensity of fire-light depends upon the whiteness to which the carbon is reduced, by combustion. If the carbon be white hot, its combustion is perfect, and the light intense; if not, the light is obscured by smoke.
Q. Why will not cinders blaze, as well as fresh coals?
A. The flame of coals is made chiefly by hydrogen gas. As soon as this gas is consumed, the hot cinders produce only an invisible gas, called carbonic acid.
Q. Where does the hydrogen gas of a fire come from?
A. The fuel is decomposed (by combustion) into its simple elements, carbon and hydrogen gas. (see p. [33])
Q. Why does not a fire blaze on a frosty night, so long as it does upon another night?
A. The air (being very cold) rushes to the fire so rapidly, that the coals burn out faster, and the inflammable gas is sooner consumed.
Q. Why does a fire burn clearest on a frosty night?
A. Because the volatile gases are quickly consumed; and the solid carbon plentifully supplied with air, to make it burn bright and intensely.
Q. Why does a fire burn more intensely in winter than in summer time?