The Romance of Modern Chemistry

FLAME: WHAT IS IT? depends; the pressure under which the flame is burning has a decided influence. We must recognise also another factor which has a bearing on the luminosity of a flame, and that is its temperature; the hotter a particular flame is, the higher is its luminosity as a general rule. One way of raising the temperature of a flame is to feed it with oxygen instead of air, and the result of doing this is some- times surprising. The temperature, for instance, of a hydrogen flame in air is about 3600° Fahrenheit, while the same flame in an atmosphere of oxygen is some 1400° hotter. It is true that in the case of hydrogen no increase in luminosity results from this very remark- able rise of temperature, but the behaviour of hydrogen is exceptional. If a candle burning in air is transferred to a jar of oxygen, the flame shrinks in size but becomes distinctly more luminous, owing to the higher tempera- ture. We may get a hotter flame also by heating the air and the gas which are supplied to the burner, and such a rise in the temperature of the flame leads to increased luminosity. This was the principle applied in the so- called “ regenerative ” burners, in which the usual glass chimney was surrounded by a wider one closed at the bottom; the air, therefore, which fed the flame had to pass down between the chimneys, and was very con- siderably heated by contact with the inner one. Such devices, however, for securing increased luminosity have disappeared before the incandescent burner. Not only may a flame be made hotter in various ways; it is possible also to lower its temperature. Ad- mixture of an indifferent gas—that is, one which takes no part in the combustion—produces a marked cooling 160