COMBUSTION AND ILLUMINATION. 63 



there which have very little illuminating power. These 

 are usually flames of hydrogen, and are produced in places 

 where, for some accidental reason, hydrogen only for a few 

 minutes happens to issue. They would be found to be very 

 hot if we had any way of testing their temperature, but 

 they would afford but a very feeble light to write by if 

 by anv means we could bring one of them to the table. 



The flame of an alcohol lamp is almost entirely a hydro- 

 gen flame, and, though it is very hot, it gives very little 

 light, on account of there being no solid particles of car- 

 bon in it to be intensely heated by it and to emit their 

 superior light. 



It is all the better, on this account, for the purposes that 

 the alcohol lamp is used for namely, for producing heat; 

 for, if there were solid particles of carbon in the flame, just 

 so far as the force of the heat should be expended in heat- 

 ing them so as to give light, there would bo less heat for 

 the water, or the coffee, or the blowpipe, or for any of the 

 other heating purposes for which the flame was used. 



And then, besides, the floating particles of carbon in the 

 flame, if intercepted by any substance before they are con- 

 sumed, blacken it, or, as AVC say, smoke it. If you hold a 

 piece of cold iron or any other such substance in the flame 

 of a candle or lamp, it becomes smoked, as we say. The 

 philosophy of this is, that a great many of the floating par- 

 ticles of carbon are intercepted by the cold substance be- 

 fore they are consumed, and so become attached to it, and 

 blacken it. This proves that the particles of carbon are 

 really in the flame all the time, though we do not see them, 

 nor see any indications of their presence, except in the in- 

 creased brightness of the flame, in consequence of their be- 

 ing themselves heated intensely hot in it and in process 

 of being consumed. But by holding the iron, or any cold 

 substance, in the flame, w r e at once cool all the particles 



