74 CARBURETTED HYDROGEN. 



131. Although when carbon burns in the air it 

 onlj combines with oxygen, it can, under some cir- 

 cumstances, combine with nitrogen and also hydro- 

 gen. Thus when vegetable matters decay under 

 water, we find that a gas is given off in bubbles 

 which consist of hydrogen and carbon, and is there- 

 fore called carburetted hydrogen. 



132. This gas is, as may be supposed, inflamma- 

 ble; burning in the air with a tolerably bright flame, 

 and forming, by the combustion of its two elements, 

 water and carbonic acid. This gas is found in very 

 large quantity in coal mines, where it is called fire- 

 damp, and occasions violent explosions, when a light 

 is incautiously brought into a mixture of it and com- 

 mon air. 



133. In these cases the gas is mixed with a quantity 

 of atmospheric air, but the affinity of the carbon and 

 hydrogen, of which it consists, for the oxygen of the 

 air, is not powerful enough to cause combination. 

 When, however, a lighted candle or lamp is brought 

 into the mixture, that part is immediately raised to 

 the temperature at which combination can take place, 

 the mixture takes fire, the flame spreads with very 

 great rapidity, and in a few seconds the mixed gases 

 are changed from air and carburetted hydrogen, into 

 carbonic acid gas, steam, and nitrogen. At the mo- 

 ment of explosion the gases are very greatly expanded 

 by the heat of the flame, and subsequently they are 

 suddenly condensed, as the steam is cooled and con- 

 verted into water. Carbonic acid and nitrogen alone 



