. The principles of chemistry . carbon burns, and we imagine that a portion of the hydrogenis in a free state, then a portion of the carbon must also occurin the same form in the flame, because, other conditionsbeing unchanged, carbon burns after hydrogen, and thisis actually observed in the combustion of various hydro-carbons. Charcoal, or the soot of a common flame, arisesfrom the dissociation of organic substances contained in the flame. The majority ofhydrocarbons, especially those containing much carbon—for instance, naphthalene-burn, even in oxygen, with separation of soot. In that porti
. The principles of chemistry . carbon burns, and we imagine that a portion of the hydrogenis in a free state, then a portion of the carbon must also occurin the same form in the flame, because, other conditionsbeing unchanged, carbon burns after hydrogen, and thisis actually observed in the combustion of various hydro-carbons. Charcoal, or the soot of a common flame, arisesfrom the dissociation of organic substances contained in the flame. The majority ofhydrocarbons, especially those containing much carbon—for instance, naphthalene-burn, even in oxygen, with separation of soot. In that portion of the flame wherethe hydrogen burns the carbon remains unburnt, or at least partly so. It is thisfree carbon which causes the brilliancy of the flame. That the interior of the flamecontains a mixture which is still capable of combustion may be proved by the follow-ing experiment: A portion of the gases may be withdrawn by an aspirator fromthe central portion of the flame of carbonic oxide, which is combustible in air. N 2. Fic 36.—In the candle flamethe portion C contains thevapours ancl products of de-composition ; ill the brightzone A. the combustion hascommenced, and particlesof carbon are emitted ; andill the pale zone B tiie com-bustion is completed. For 180 PEINCIPLES OF CHEMISTRY The combination of various substances with oxygen may notpresent any signs of combustion—that is, the temperature may risebut inconsiderably. This may either proceed from the fact that thereaction of the substance (for example, tin, mercury, lead at a hightemperature, or a mixture of pyrogallol with caustic potash at theordinary temperature) evolves but little heat, or that the heatevolved is transmitted to good conductors of heat, like metals, or thatthe combination with oxygen takes place so slowly that the heatevolved succeeds in passing to the surrounding objects. Combustionis only a particular, intense, and evident case of combination with this purpose Deville passed water through
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