COMMON THINGS FIRE. 



mil rise from the water in bubbles and will collect in the upper 

 part of the bottle or glass. 



The manner of performing this experiment is shown in fig. 3. 



When the gas is thus collected its inflammable nature may be 

 ascertained by applying a light to it as it issues from the bottle. 



22. Heavy carburetted hydrogen burns with a much whiter and 

 more luminous name. Its weight is very nearly equal to that of 

 common air, and, therefore, nearly double that of the light car- 

 buretted hydrogen ; hence it has acquired the epithet " heavy." 



The products of the combustion of both sorts of carburetted hy- 

 drogen are carbonic acid and water, the former proceeding from the 

 combination of the carbon, and the latter from that of the hydrogen 

 with the oxygen of the air. 



These points being understood it will be easy to render intel- 

 ligble the effects which are developed in all ordinary cases in which 

 PIEE or COMBUSTION takes place. 



23. The species of combustible used as fuel with which we 

 are most familiar in this country is TIT COAL. 



This mineral, exclusive of some extraneous and incombustible 

 ingredients which it contains in very small proportions, consists of 

 carbon and carburetted hydrogen of both kinds. 



The proportion of carbon varies in different sorts of coal from 

 80 to 90 per cent., the hydrogen varying from 3 to 6 per cent., 

 and the remainder consisting of oxygen and azote. 



In tLv heavy coal of Wales, called anthracite, the proportion of 

 carbon is aoove 90 per cent., while that of the hydrogenous gases 

 is only 3 or 4 per cent. In the bituminous coal of Northumber- 

 land the proportion of carbon is about 87 per cent., and that of 

 hydrogen from 5 to 6 per cent. 



24. When a fire composed of such fuel is properly kindled and 

 supplied with a draught of air necessary to sustain the combustion, 

 the carbon will continue to combine with its proper proportion of 

 oxygen, producing the corresponding quantity of heated carbonic 

 acid, and rendering the solid part of the fuel red and luminous ; 

 and the hydrogenous gases will at the same time combine with their 

 respective proportions of oxygen, producing carbonic acid and 

 watery vapour, and rendering the gases as they issue from the 

 fuel luminous, or, what is the same, converting them into flame. 



The flame will be faintly luminous and bluish if any part of 

 the gases be pure hydrogen, it will be yellowish and a little more 

 luminous if they be light carburetted hydrogen, and it will be 

 very white and very luminous if they be heavy carburetted 

 hydrogen. 



Thus all the phenomena exhibited by a common coal-fire, 

 the red unflaming fuel the faint blue flames occasionally seen, 

 200 



