Page:Popular Science Monthly Volume 33.djvu/268

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THE little yellow candle-flame, which, is gradually disappearing from our households to give place to brilliant gas and electric lights, still plays a considerable part in the labors and researches of physicists, chemists, and astronomers. The former find in it a source of heat capable of melting and oxidizing or reducing the most refractory metals. The last employ it as a photometric unit, both to measure the most considerable lights and to determine the luminosity of stars so faint that they can hardly be seen in the great telescopes. But the most curious and interesting thing about this little flame is the fact that the optical study of it has contributed very largely to our knowledge of the elementary composition of the celestial bodies.

Carefully examined with the naked eye, the flame of a candle is composed of three distinct layers or envelopes, viz., a dark central part, the dark cone around the wick, formed of gaseous products of low temperature, and holding in suspension carbon in a state of fine division, but not yet incandescent; a luminous part, surrounding the dark part, and composed of carbon raised to a bright incandescence; and a thin external envelope, only faintly luminous and faintly colored, yellow toward the top, where the carbon is completely burned, and bluish toward the base, where the primary products of the decomposition of the matter of the candle are burning in contact with the air.

Analyzed by the aid of the spectroscope, the luminous cone gives a brilliant and continuous spectrum—that is, one having the appearance of a ribbon exhibiting all the colors of the rainbow, while the exterior, faintly luminous envelope gives a discontinuous spectrum formed of three bright bands—one yellow, one green, and one blue.

As only solid incandescent bodies are capable of giving a continuous spectrum, we conclude that carbon in the solid state is incandescent in the luminous envelope of the flame. But, the spectrum of the exterior envelope being discontinuous, we conclude that it is composed entirely of gaseous products.

The flame of illuminating gas presents, both to the naked eye and in the spectroscope, the same aspect as the flame of the candle, whence it is concluded that its lighting and heating powers are derived from the same cause—the more or less complete combustion of carbon.

By blowing air or injecting oxygen through the blow-pipe into a candle-flame or a gas-light, its aspect is greatly changed.