THE OXIDES OF CARBON 107 



over water made alkaline with caustic potash. Does it now 

 turn blue litmus red and render lime water milky ? Is it com- 

 bustible? Is carbonic acid gas the product of combustion? 

 Observe that the charcoal in the tube has slowly burnt away. 



Irhe only possible explanation of this change is that the 

 carbon burns in the carbon dioxide, producing a lower oxide 

 of carbon. This lower oxide has no action on litmus or on 

 bases, and is therefore not an anhydride ; but it burns in the 

 air, producing carbonic acid gas. Analysis shows that its 

 composition is represented by the formula CO ; it is therefore 

 the monoxide of carbon, and has been produced thus : — 



C02 + C = 2CO. 



This experiment explains the occurrence of a blue flame over a coke fire. 

 The coke burns without flame at the bottom of the fire to carbonic acid 

 gas, but this, on passing over more heated coke, is reduced to carbon 

 monoxide, which burns at the top of the fire with a blue flame to carbon 

 dioxide. In a slow combustion stove, where insufiicient air is supplied for 

 complete combustion, the carbon monoxide escapes unburnt. As this gas 

 is very poisonous, care must be taken that no leakage occurs from the flues 

 of such a stove into the room. "Producer gas" is the product of the 

 action of air on excess of coke, and consists of carbon-monoxide and 

 nitrogen. *' Water gas" is the product of the action of incandescent coke 

 on steam, — HgO + C^CO + Hg, — and therefore consists of a mixture of 

 carbon monoxide and hydrogen. Both these mixtures are largely used as 

 fuels. 



Besides reducing carbon dioxide, charcoal can also be 

 employed to reduce the metallic oxides. Mix a little litharge 

 with sodium carbonate, and place the mixture in a small hollow 

 on a lump of charcoal. Now heat the mixture by means of a 

 mouth blow-pipe flame, so regulating the air that the flame 

 directed upon the mixture is luminous. Such a flame contains 

 free carbon, which assists the reduction. Note that in a few 

 minutes globules of metallic lead are produced. Mix together 

 a little oxide of arsenic and powdered charcoal. Place the 

 mixture at the bottom of a very small bulb tube made of a 



