CARBON AND HYDROGEN. 4<25 



In "By where the supply of air is insufficient for complete com- 

 bustion, it is the hydrogen principally which burns, the carbon 

 being liberated in solid particles, which are heated white-hot 

 from the combustion of that gas. The sphere B, indeed, is the 

 luminous portion of the flame, for the light depends entirely 

 upon the deposition of carbon, arising from the consecutive 

 combustion of the two elements of the vapour. Gaseous bodies, 

 however strongly heated, emit no light, or at most, not more than 

 a sensible glow, and luminous flame has justly been described by 

 Davy as always containing solid matter heated to whiteness. 

 The same sphere of the flame, possessing an excess of combus- 

 tible matter at a high temperature, takes oxygen from metallic 

 oxides, such as arsenious acid, placed in it, and developes their 

 metals. It is, therefore, often referred to as the deoxidizing or 

 reducing flame. In the external hollow cone, C, the deposited 

 carbon meets with oxygen, and is entirely consumed. The 

 hottest point in the whole flame is within this sphere, near the 

 summit of B. This part of the flame, possessing an excess of 

 oxygen, at a high temperature, is the proper place for kindling 

 a combustible, and is called the oxidizing flame \ its properties 

 are the opposite of those of B. 



When coal gas is mingled with an equal bulk of air before 

 being burned, it is found to lose half its illuminating power. It 

 may be conveniently mixed with a quantity of air sufficient for 

 its complete combustion, by placing over an argand burner, a 

 brass chimney of 5 inches in height, provided with a cap of 

 wire gauze ; when kindled above the wire-gauze, the gas burns 

 with a blue flame, .not more luminous than that of sulphur. 

 The flame is so feebly luminous because no deposition of carbon 

 occurs in it. The quantity of heat is the same, whether the 

 gas is burned so as to produce much or little light ; and where 

 the gas is burned for heat, this mode of combustion has the 

 advantage of giving a flame without smoke. The heat derived 

 from coal gas burned in this manner is not, however, so intense 

 as that of an argand spirit lamp. According to my own expe- 

 rience, the highest temperature is obtained from coal gas, when 

 burned from that form of the argand recently introduced, in 

 which the burner rises through a truncated brass cone. A 

 tangential current of air is thus occasioned, which sweeps the 

 outer surface of the flame, and produces a perfect combustion. 



