The Romance of Modern Chemistry

FLAME: WHAT IS IT? a b Fig. 6.—The hollow nature of a flame may be shown in various ways. A match- head suspended in the centre is not ignited by the flame, and with a piece of glass tube the unburnt gai from the centre of the flame can be led off and set alight at the end of the tube. sketch, is confined to a certain zone or sheath in which the combustion is going on, and this cone-like sheath is hollow. That the cone of flame is hollow may be very easily and prettily shown by suspending the head of a match just above the end of the tube before lighting the gas. In spite of the burning gas the matchin the inside remains unaffected (see Fig. 6, d). But we can go a step further and show that this hollow part of the flame contains unbumt gas by carefully putting one end of a narrow tube in the centre of the cone and applying a light to the other end some distance away. We get a flame there (see Fig. 6, b) simply because with the tube we have succeeded in leading off some of the unbumt gas from the centre of the cone. A candle flame and a coal-gas flame differ from a hydrogen flame only in that their structure is a little more complicated; their general characteristics are similar. In these two cases the dark hollow cone in which is the unbumt vapour is surrounded by a white, luminous zone, and this again by an outer envelope of flame which is non- luminous and very difficult to see. This outermost sheath is obviously the one for which there is an unlimited supply of oxygen, and anything which has escaped combustion in the luminous zone is there completely burned to carbon dioxide and water.