FLAME, in chemistry, a shell of in candescent matter surrounding a mass of combustible vapor. To produce flame it is therefore necessary that the burning body should be capable of volatilization just below the temperature at which it undergoes combustion. Charcoal or iron will burn with a steady glow, more or less luminous according to the medium in which they are burnt, neither of these substances being susceptible of volatili zation at the temperature at which com bustion takes place. A piece of wood or paper, on the contrary, burns with a large luminous flame, in consequence of the combustible matter of which it is composed rising in vapor or becoming converted into mixed gases at the tem perature required for kindling the sub stance. Flame is, in fact, produced when ever a continuous supply of inflammable vapor or gas is made to combine with a supporter of combustion, such as the atmosphere, at a sufficiently elevated temperature to cause ignition. The heat ing power of a flame is in direct propor tion to the energy of the chemical action that takes place, those flames being hot test and least luminous which proceed from gases containing no solid particles, as in the case of a mixture of oxygen and hydrogen in the proportion necessary to form water, which is one of the hottest flames we have at our command. The most luminous flames are from gases which contain just sufficient solid matter to give the maximum of incandescence without any of its particles passing away unburnt. Olefiant gas and the ordinary coal gas are good examples of this as compared with the oxyhydrogen flame, which contains no solid matter on the one hand, and the flame of pitch or turpentine on the other, which contains too much carbon, the excess passing off in the form of smoke. The flames used for illuminating purposes are all produced by the combustion of compounds con taining carbon and hydrogen. Besides
the proper proportions of gaseous and solid matter contained in illuminating substances, care must be taken to regu late the supply of air. The ARGAND LAMP (q. v.) and chimney, as applied to gas and camphene, are examples of this.
Flame has three distinct parts: The central or non-luminous part, where there is no combustion, but where the carbon begins to separate from the hydrogen; the second or luminous part, where the carbon is for a moment free and heated to a white heat; and the exterior part, which is the hottest, and where the combustion is complete. It is easy now to understand of what impor tance is the form of the burner, and how it may be modified accordingly as we desire light or heat. If we wish light the carbon must be protected for some seconds from contact with the air; but not long enough to allow it to pass off unconsumed. If, on the contrary, heat is desired, the carbon must be burned as quickly as possible. The German chemist Bunsen constructed a gas burner after this theory, which is perfectly adapted to the production of heat. Every mixture of gases requires a certain tem perature to inflame it; and if the tem perature be not reached, the mixture does not take fire; we may thus cool down a flame so much that it goes out by plac ing over it a small coil of cold copper wire, whereas if the coil be previously heated, the flame will tontine to burn. If a piece of wire gauze be held close over a jet of gas and the gas lit, the gauze may be removed several inches above the jet, and yet the inflammable gas below will not take fire, the flame burning only above the gauze. See