Page:The fairy tales of science.djvu/54

32 Everybody is familiar with the fact, that a considerable amount of heat is evolved when water is poured upon quicklime, a fact which illustrates the great chemical law, that no union of two bodies can take place without a change in their temperature.

The intense heat emitted by the flame of a candle may be traced to chemical action. If we cover a lighted candle with a glass shade, the flame will soon begin to languish, and in a few minutes it will expire. The flame seems to rob the confined air of a certain virtue which is essential to its continued existence. This is the true interpretation of the phenomenon. The air contains a wonderful gas called oxygen, which combines with the vaporized tallow, just as water combines with quicklime, and their union is attended by a development of heat.

The phenomena presented by a burning candle may now be easily understood. The tallow is melted and sucked up to the top of the wick, where it is boiled and converted into vapour. This vapour combines rapidly with the oxygen of the surrounding atmosphere, and the heat evolved is such as to render the vapour luminous. To bring about the combustion of the candle it is necessary to apply heat to the wick, but afterwards the heat which is liberated is more than sufficient to sustain the action.

We have now arrived at a tolerably clear conception of Flame; it is merely volatile combustible matter heated to whiteness. Fire is simply a