FLAME is a particular form of combustion (q,v,) or burning. .Ordinary combustion consists in the of the aimoiphere combining with some combiatible substance so rapidly as to give out light and heat. When the combustible is either originally a gas, or becomes 30 by the heat, the combustion takes the form of flame. F., then, is the burning of a gas. In most cases, the gas of F. is a compound of hydrogen and carbon, with minute, particles of solid carbon suspended in it, and is formed from the fuel (coal, tallow, etc.) being decomposed by the heat. The heat and light of F. vary with the gas; hydrogen produces great heat, but little light. The lighting power of a gas depends upon the proportion of carbon it contains, the particles of which become glowing hot before being consumed.
The F. of a lamp or candle, or simple gas-jet, consists of a hollow cone, in the center of which there is no combustion. The central space appears dark only by con trast with the luminous cone which surrounds R. It consists, in reality, of transparent invisible compounds of carbon and hydrogen, which are constantly rising in vapor from the wick. If a glass tube, open at both ends, be held obliquely in the F. of a candle, with its lower extremity in the dark central space above the wick, it will conduct away a portion of the combUstible vapor, which may be kindled like a gas-jet at its upper end. This dark portion of the F. may be called the area of no combustion.
The luminous cone which envelops the dark space is the urea of partial combustion. The oxygen of the atmosphere penetrates to this depth, but not in sufficient quantity to oxidize or burn both the carbon and the hydrogen; it therefore unites with the hydrogen, for which it has the stronger attraction, and leaves the carbon free. The outer cone is
named the area of complete combustion, because there the carbon meets with sufficient oxy gen to burn it entirely. The light is produced in the area of partial combustion, where the carbon inset free from the hydrogen in the form of solid particles, and is heated to whiteness by the combustion of the hydrogen. The combustion of the carbon in the outer cone, by which it is converted into carbonic acid gas, produces heat, but so little light as to be barely traceable. • That carbon exists in a solid state in the white part of a F., is readily shown by holding a piece of white earthen-ware. into it, which becomes coated with carbon in the form of soot. No soot is deposited in the dark or no-combustion area of the flame, because there the carbon is in chemical combination with hydrogen, forming a gas. The carbon becomes solid only when the hydrogen aeserts it, as it were, to unite with oxygen.
The highly illuminating power of compounds of hydrogen and carbon is thus traced to the fact, that their hydrogen and carbon do not burn simultaneously, but successively, and in such a way that the one heats the other white hot. It is quite possible to make them burn simultaneously; but when they do, the light evolved is very feeble. This takes place in the "Bunsen burner," in which air is allowed to mix with the gas before com bustion.