338 SMITH'S INTERMEDIATE CHEMISTRY 



The coke is first set on fire in a brick-lined cylindrical structure 

 and brought to vigorous combustion by blowing in air for ten 

 minutes. Then steam is substituted for the air. 



The interaction, as the equation shows, takes place with absorp- 

 tion of heat. Hence, at the end of a few minutes, the coke be- 

 comes too cool. It is then necessary to turn the steam off and to 

 turn the air on again, and so on alternately. The mixture of 

 carbon monoxide (40 to 50 per cent) and hydrogen (45 to 50 

 per cent), containing also some carbon dioxide (4 to 7 per cent), 

 nitrogen (4 to 5 per cent), and oxygen (1 per cent), is known as 

 water gas. It is almost wholly combustible, burning with a blue 

 flame, and is used as a source of heat and, by driving internal com- 

 bustion engines, to furnish power. It is used also in manufactur- 

 ing illuminating gas (see p. 356). 



If both air and steam are driven together over the burning coke, 

 the ah 1 enables the coke to burn continuously, and a fuel gas 

 which is a cross between producer gas and water gas is obtained. 



Fuel gases are employed on a large scale in steel works, and 

 other industrial plants. They give a uniform and eacily regulated 

 heat, they leave no ash, and their use involves no labor for stoking. 



Industrial Hydrogen from Water Gas. Hydrogen is 

 required in large quantities in chemical industry for the manu- 

 facture of ammonia (p. 300) and for hydrogenating oils (p. 433). 

 It is essential that this hydrogen should be carefully purified 

 from traces of other gases, such as carbon monoxide and sulphur- 

 etted hydrogen, which act as poisons on the catalysts employed in 

 the above processes. The cheapest source of industrial hydrogen 

 is water-gas, and much work has been done to devise a method for 

 eliminating the undesirable carbon monoxide from this. 



When a mixture of water-gas (substantially H 2 + CO) and 

 superheated steam is passed over a suitable catalyst, such as 

 iron oxide, a reaction occurs as follows. 



CO + H 2 ^ CO 2 + H 2 + 9,800 calories. 



