The Romance of Modern Chemistry

CHAPTER XIV FLAME: WHAT IS IT? THE reader will by this time have become fairly familiar with the conception of combustion, and he may be under the impression that, knowing what combustion is, he has nothing more to learn about flame. This would be a somewhat rash conclusion, for, to begin with, the one thing does not always accompany the other; there are cases of undoubted combustion in which there is no real flame. A little piece of charcoal, for example, burning in air or oxygen gives out no flame; it only glows. As a matter of fact, it is only when the burning sub- stance is in the form of gas or vapour that we get flame produced. It is true that many liquid and solid substances give a flame when they burn, but the production of the flame is preceded by their conversion into vapour. By holding a match to the wick of a candle we first melt and then vapourise the wax which is in the wick; the vapour catches fire and the candle is lit. Once this has been done, the heat of the flame keeps the wax round the base of the wick melted, the melted wax is sucked up the wick by capillary action, and at the top it is vapourised and ignited. Flame, then, is something different from combustion, and may be defined as gaseous matter which has been raised to such a high temperature that it is obvious to 154