64 CANDLES AND LAMPS. 



that come in contact with it, and so stop their combustion, 

 and then their true character is at once revealed. 



Very often a portion of the particles of carbon escape 

 from the flame themselves without being burnt, and go up 

 the chimney in the form of a blue smoke. The white vapors 

 which are seen arising sometimes from a fire are vapors of 

 water or steam, but the blue fumes are composed of parti- 

 cles of carbon, some of which escape out of the chimney 

 into the air, while a portion of them lodge upon the sides 

 of it, forming soot. 



Some substances give out a much greater quantity of 

 carbon in burning than others, as, for example, birch bark, 

 pitch-pine knots, and the "light-wood," so called, of the 

 Southern States. A great portion of this carbon is made 

 incandescent in the flame, and gives out great light. That 

 is the reason why those substances make such excellent 

 torches. Of the carbon which is thus made incandescent 

 in these flames, some is burned that is, it finds oxygen 

 enough to combine w r ith it in the flame and so disappears 

 as carbon, and forms another substance. But some of the 

 particles which are made incandescent that is, red hot 

 in the flame, and so help to emit light, are not burned, be- 

 cause there is not oxygen enough for all. This portion, 

 then, escapes into the air, where it cools and becomes black 

 again that is to say, each separate particle becomes black ; 

 but generally, when it comes from a common fire, being 

 more or less mingled with a certain portion of watery va- 

 por, which is white, the mixture assumes a bluish hue. 

 When, however, it is not so modified as, for instance, 

 sometimes when issuing from the smoke-pipe of a steamer 

 it shows, by its very dark bluish color, what its true 

 character is. 



The cause of this escape of carbon unconsumed is that 

 the supply of oxygen for the flame is insufficient ; for, 



