COMMON THINGS FIRE. 



luminous nor visible, the carbon disappears. But in the case of 

 hydrogen, the heat produced by the combustion is so intense as to 

 render the gas itself luminous, just as intense heat will render a 

 mass of iron red hot or white hot. When gas becomes thus 

 luminous it is called flame. 



12. Flame, therefore, must be understood to be nothing more 

 than matter in the aeriform, gaseous, or vaporous state, rendered 

 so intensely hot as to be incandescent, and to emit light, just as 

 would a bar of iron taken from a furnace. 



13. It is easy to show that, comforrnably with what has been 

 already demonstrated in our Tract on Water, the product of the 

 combustion of hydrogen is the vapour of water, which by exposure 

 to cold can be reduced to the liquid state. 



If a glass jar be held over a jet of inflamed hydrogen, as repre- 

 sented in fig. 2, the aqueous vapour formed by the combination of 

 the hydrogen with the oxygen of the surrounding air, will be con- 

 densed upon the inside of the jar, and will appear first as a 

 cloudy dew upon it, and, as the process is continued, it will 

 increase in quantity, and, trickling down the side of the jar, may 

 be received in drops by a dish placed beneath it. 



Fig. 2. 



14. As we have stated above, the principal constituents of every 

 species of combustible, whether used for heating or lighting, are 

 carbon and hydrogen, and the products of their combustion are 

 therefore carbonic acid and water, the latter being evolved in the 

 form of vapour. 



15. It happens, however, rarely that the hydrogen is evolved in 

 the pure state. It is more generally combined with a certain dose 

 of carbon, forming a compound gas called CAEBTJEETTED HYDEOGEJT . 

 This gas burns with a much whiter and more luminous flame than 

 that of pure hydrogen, and it is therefore much better fitted for 

 the purpose of illumination. 



16. That the flame owes its whiteness and illuminating power 

 to the carbon with which the gas is charged, is proved by the fact, 



198 



