the Theory of Luminous Flames. 17 



observed vacant space, it follows that heating the object placed 

 in the flame should cause a decrease in the extent of this space. 

 The following experiments prove that this actually takes place. 



A cold iron wire held in a non-luminous flame which has 

 been diluted with an excess of indifferent gas, causes extinction 

 of the flame throughout a considerable space around itself; but 

 as the wire becomes hotter, this space gradually decreases in 

 extent, until when the wire is raised to a red heat (either by 

 the heat of the flame or by an extraneous source of heat), the 

 flame is observed to rest upon the wire without any interve- 

 ning space. Again, a mixture of coal-gas and carbon dioxide 

 may be burned at the orifice of a platinum tube, so that a non- 

 luminous flame, separated from the upper rim of the tube by 

 a vacant space, is produced. If the platinum tube be now 

 heated by means of a Bunsen's lamp near its orifice, the non- 

 luminous flame spreads down throughout the formerly appa- 

 rently empty space until it touches the platinum tube. 



These experiments not only confirm the explanation already 

 given, but they also completely exclude the possibility of any 

 such cause as that suggested by Blochmann taking part, even 

 to a subordinate extent, in the production of the space observed 

 between the flame and the burner. For the experiments prove 

 that a flame, even w T hen largely diluted with indifferent gases, 

 burns in contact with a heated burner; whereas an effect such 

 as Blochmann imagined, tending to produce separation be- 

 tween flame and burner, although it might possibly be decreased, 

 yet certainly could not be removed by heating the burner. 



I therefore look on the following conclusion as perfectly 

 just: — The fact that a gas-flame does not touch the ring of the 

 burner, nor a candle-flame the wick — further, that a flame does 

 not actually impinge upon a cold body placed within it, is 

 caused by the withdrawal of heat from the glowing gas. The 

 flame is cooled below its ignition-temperature ; it ceases to glow 

 and becomes invisible: the flame in the neighbourhood of a 

 cold body is extinguished. 



The experiment just described, which proved that a greatly 

 diluted gas may be caused to burn in contact with the metallic 

 burner when the latter is heated, leads us to inquire whether 

 the action of the upper part of the burner in causing a separa- 

 tion between itself and the burning gas is not aided by the 

 cold gas issuing from the centre of the burner, or, indeed, 

 whether this cold gas is not of itself sufficient, under certain 

 conditions, to produce the observed effect. 



The temperature of the lower part of the flame is certainly 

 not so high as that of the middle portions; and the cause of 



Phil. Mag. S. 5. Vol. 3. No. 15. Jan. 1877. C 



