The Romance of Modern Chemistry

FLAME: WHAT IS IT? The luminosity of flame varies very remarkably with the nature of the combustible substance and with the conditions under which the combustion takes place. A hydrogen flame is quite non-luminous, carbon' monoxide burns with a pale blue flame, while a candle or coal gas gives a bright white illumination. One cause of lumin- osity has been already referred to in a previous chapter, namely, the presence of solids which are made incandescent by the heat of the flame. A coal-gas flame contains in its luminous zone a host of unbumt carbon particles which are raised to a very high temperature and so give out a strong light. By mixing the gas with air before it comes to the nozzle of the burner these carbon particles are completely oxidised, and the flame becomes non-luminous. Such a non-luminous flame may, however, again be rendered useful for purposes of illumination by the artificial intro- duction of incombustible solids which are made incandes- cent by the heat of the flame. This is what is done in the ordinary incandescent gas burners and in the lime light. There are other causes which determine the luminosity of a flame besides the presence of solid particles. There are some flames known which are characterised by very high illuminating power, and in which at the same time there cannot possibly be any solid particles present. For example, phosphorus burning in oxygen produces a dazzling light; but the oxide of phosphorus which results from the combustion is converted into a vapour at a red heat, and it is therefore impossible that it could exist in the solid state in the phosphorus flame, the temperature of which is far above the melting-point of platinum. The well-known English chemist Frankland, who made many experiments on the nature of flame and the cause of 158