128 FLAME. 



Again ; if we allow the gas which issues from the jet to be 

 intimately mixed with atmospheric air before combustion, no 

 charcoal will be given off by the flame, the light of which will 

 be feeble, though the heat will be very intense. In this case the 

 combustion is perfect, every portion of the carbon being brought 

 into contact with sufficient oxygen for its saturation before under- 

 going combustion : but here, perhaps, it may be asked, Is not the 

 charcoal ignited ? and, if so, Why does it not give out light ? 

 This may be easily explained. In the case of the simple jet, the 

 carbon is ignited in an atmosphere of hydrogen, »and does not 

 come immediately into contact with the oxygen of the atmosphere, 

 except in the outer red casing, where it immediately enters into 

 combustion, gives out much heat, and looses its light. 



If in the combustion of carburetted hydrogen gas, we supply 

 the gas too quickly, or the air too slowly, the combustion will be 

 imperfect, the hydrogen of the compound will by its superior 

 attraction, seize on the oxygen ; but the temperature produced 

 by its combustion will be insufficient to ignite the whole of the 

 charcoal; part of it will therefore fly off unconsumed, producing 

 smoke. This may be easily shown by an argand gas burner; in 

 this instrument the cylindrical flame of gas, being supplied 

 within and without with a current of atmospheric air, is burning 

 under the most favorable conditions; but, if the aperture which 

 admits air to the inner surface be stopped, the flame immediately 

 becomes smoky ; the quantity of air supplied to the outer surface 

 being insufficient for the entire combustion of the whole of the 

 charcoal, which consequently flies off in smoke. 



Tliat the liglit of flame is derived from the solid substance 

 combined with it, is further shewn by the colour of the light vary- 

 ing with the nature of the substance used : for example, lime and 

 strontian communicate a red or crimson colour to flame; barytes, 

 a green; soda, yellow; copper and borax, green. 



Now as the light given out b} the substances held in solution 

 entirely depends upon the degree of ignition capable of being sup- 

 ported by those substances, without their entering into combus- 

 tion, it is evident that in these cases the intensity of the light can 

 never exceed a certain point : it is not, however, absolutely ne- 

 cessary that the solid matter employed to produce the light should 

 be held in solution in the flame : it is quite sufficient that flame 

 at a high temperature should be caused to act upon solid matter. 

 Here tlien we have an endless variety of substances for experiment ; 



