FLAME. Newton and others have considered flame as an ignited vapour, or red-hot smoke. This, in a certain sense; may be true, but, no doubt, it contains an inaccurate comparison. Simple igni tion never exceeds in intensity of light the body by contact of which it was pro duced. But it appears to be well ascer tained, that flame always consists of vo latile ihflammable matter, in the act of combustion, and combination with the oxygen of the atmosphere. Many me tallic substances are volatilized by heat, and burn with a flame, by the contact of the air in this rare state. Sulphur, phos phorus, and some other bases of acids, exhibit the same phenomenon. But the flames of organized substances are in general produced by the extrication and ascension of hydrogen gas with more or less of charcoal. When the circum stances are not favourable to the perfect combustion of these products, a portion of the coal passes through the luminous current unburned, and forms smoke. Soot is the condensed matter of smoke.
As the artificial light of lamps and candles is afforded by the flame they ex hibit, it seems a matter of considerable importance to society, to ascertain how the most luminous flame may be produc ed with the least consumption of com bustible matter. There does not appear to be any danger of error in concluding, that the light emitted will be greatest when the matter is completely consumed in the shortest time. It is, therefore, ne cessary, that a stream of volatilized com bustible matter, of a proper figure, at a very elevated temperature, should pass into the atmosphere with a certain deter minate velocity. If the figure of this
stream should not be duly proportioned ; that is to say, if it be too thick, its inter nal parts will not be completely burned, for want of contact with the air. If its temperature be below that of ignition, it will not burn when it comes into the open air. And there is a certain veloci ty, at which the quantity of atmospheri cal air which comes in contact with the vapour will be neither too great nor too small : for too much air will diminish the temperature of the stream of com bustible matter so much, as very consi derably to impede the desired effect ; and too little will render the combustion languid.
We have an example of a flame too large, in the mouths of the chimneys of furnaces, where the luminous part is merely superficial, or of the thickness of about an inch or two, according to cir cumstances, and the internal part, though hot, will not set fire to paper passed into it through an iron tube, the same defect of air preventing the combustion of the paper, as prevented the interior fluid it self from burning. And in the limp of Argand, we see the advantage of an in ternal current of air, which renders the combustion perfect by the application of air on both sides of a thin flame. So like wise a small flame is whiter and more lu minous than a larger ; and a short snuff of a candle, giving out less combustible matter in proportion to the circumambi ent air, the quantity of light becomes in creased to eight or ten times what a long snuff would have afforded.