The Romance of Modern Chemistry

FLAME: WHAT IS IT? effect, and a similar result is obtained by introducing into the flame some body which is a good conductor of heat. Indeed the temperature may be so much lowered by this latter device that the flame is extin- guished. If, for example, a coil of copper wire is care- fully placed over the wick of a burning taper, the flame goes out immediately. In order to understand the possibility of this pheno- menon, we must remember that every inflammable vapour has a certain ignition temperature. That is to say, for each vapour there is a point to which it must be heated in presence of air before it will catch fire and give a flame. Once it has been ignited, the heat given out by the flame as the result of the chemical action raises the incoming gas above the ignition tempera- ture, and so the combustion continues. Different substances have very different ignition tem- peratures. The vapour of carbon disulphide can be ignited by contact with a glass rod which has been heated only to 250° Fahrenheit, a little higher than the temperature of boiling water. A current of hydrogen issuing from a tube is ignited by sparks from a flint and steel, whereas marsh gas is quite indifferent to such treatment. The possibility of cooling an inflamed vapour below its ignition temperature may be demonstrated in a very simple manner. If, as shown in Fig. 7, a, a piece of copper wire gauze is pressed down on a flame of burning coal gas (which, as we have already seen, contains a large proportion of marsh gas), no combustion takes place above the gauze, although it is easy to show that there is inflammable vapour there by bringing up a lighted match. Again, if we hold the gauze an inch 161 L