FLAME, is the combustion of an ex plosive mixture of an inflammable gas or vapor with air. That it is not, as many suppose, combustion merely at the ex terior surface, is proved by plunging a fragment of burning phosinorus or sul phur into the centre of a large flame of alcohol. Either of these bodies will con tinue to burn there with its peculiar light ; thus proving that oxygen is mixed with the whole of the burning vapor. If we mix good coal gas with as much at mospheric air as can convert all its carbon into carbonic acid, the mixture will ex plode with a feeble blue light; but if we mix the same gas with a small quantity of air, it will burn with a rich white flame. In the latter case the carbona ceous particles are precipitated, as Sir H. Davy first showed, in the interior of the flame, become incandescent, and consti tute white light : for from the ignition of solid matter alone can the prismatic rays be emitted in that concentrated union. Towards the interior of the flame of a candle, a lamp, or a gas jet, where the air is scanty, there is a deposition of solid charcoal, which first by its ignition, and afterwards by its combustion, in creases in a high degree the intensity of the light. If we hold apiece of fine wire gauze over a jet of coal gas close to the orifice, and if we then kindle the gas, it will burn above the wire with its natural brilliancy ; but if we elevate the gauze progressively higher, so as to mix more and more air with it before it reaches the burning point, its flame will become fainter and less white. At a certain dis tance it becomes blue, like that of the above explosive mixture. Since the com bustion of all the constituents is in this case direct and complete, the heat be comes greatest in proportion nearly as the light is diminished. If a few platina wires be held in that dim flame they will grow instantly white hot, and illuminate the apartment. On reversing the order of this experiment, by lowering progres sively a flaimpiece of wire gauze from the summit towards the base of a as flame, we shall Bind no charcoal deposited at its top, because plenty of air has been intro duced there to convert all the carbon of the gas into carbonic acid, and therefore the apex is blue ; but as we descend, more and more charcoal will appear upon the meshes. At the very bottom, in
deed, where the atmospheric air impinges upon the gauze, the flame is again blue, and no charcoal can therefore be depo sited.
Time fact of the increase of the bril liancy and whiteness of flame by the de velopment and ignition of solid matter in its bosom illustrates many curious phenomena. We can thus explain why olefiant gas affords the most vivid illumi nation of all the gases ; because, being surcharged with charcoal, its hydrogen lets it go in the middle of the flame, as it does in an ignited porcelain tube, whereby its solid particles first get igni ted to whiteness, and then burn away. When phosphorus is inflamed it always yields a pure white light, from the igni tion of the solid particles of the snowy acid thus produced.
In the blowpipe the inner blue flame has the greatest heat, because there the combustion of the whole fatty vapor is complete. The feeble light of burning hydrogen, carbonic oxide, and sulphur, may, upon the principles now expound ed, be increased by simply placing in them a few particles of oxide of zinc, slender filaments of amianthus, or fine plating wire. By narrowing the top of a long glass chimney over an argand flame either from oil or coal gas, the light can be doubled at the same cost of material. The very tall chimneys used by the Pa risian lampists are very wasteful. The light of a flame may be increased by di minishing its heat, or the intensity of its combustion ; and conversely the heat of flame may be increased by diminishing its light.