Up to the latter date the attempts to make and utilize water gas all met with failure; but about this time the subject began to be taken up in America, and the principle of the regenerator, enunciated by Siemens in 1856, having been pressed into service in the water-gas generator under the name of fixing chambers or superheaters, we find water gas gradually approaching the successful development to which it has attained in the United States during the last ten years.  Having now, by the aid of American skill, been brought into practical form, it is once more attempting to gain a foothold in Western Europe—­the land of its birth.

When carbon is acted upon at high temperatures by steam, the first action which takes place is the decomposition of the water vapor, the hydrogen being liberated, while the oxygen unites with the carbon to form carbon dioxide: 

Carbon.  Water. 
  C + 2H2O = CO2 + 4H2

And the carbon dioxide so produced interacts with more red-hot carbon, forming the lower oxide—­carbon monoxide: 

  CO2 + C = 2CO

So that the completed reaction may be looked upon as yielding a mixture of equal volumes of hydrogen and carbon monoxide, both of them inflammable but non-luminous flames.  This decomposition, however, is rarely completed, and a certain proportion of carbon dioxide is invariably to be found in the water gas, which, in practice, generally consists of a mixture of about this composition: 

  WATER GAS.

  Hydrogen 48.31
  Carbon monoxide 35.93
  Carbon dioxide 4.25
  Nitrogen 8.75
  Methane 1.05
  Sulphureted hydrogen 1.20
  Oxygen 0.51
                        ------
                        100.00

The above is an analysis of water gas made from ordinary gas coke in a Van Steenbergh generator.

The ratio of carbon monoxide and carbon dioxide present entirely depends upon the temperature of the generator, and the kind of carbonaceous matter employed.  With a hard, dense anthracite coal, for instance, it is quite possible to attain a temperature at which there is practically no carbon dioxide produced, while with an ordinary form of generator and a loose fuel like coke, a large proportion of carbon dioxide is generally to be found.

The sulphureted hydrogen in the analysis quoted is, of course, due to the high amount of sulphur to be found in the gas coke, and is practically absent from water gas made with anthracite, while the nitrogen is due to the method of manufacture, the coke being, in the first instance, raised to incandescence by an air blast, which leaves the generator and pipes full of a mixture of nitrogen and carbon monoxide (producer gas), which is carried over by the first portions of water gas into the holder.  The water gas so made has no photometric value, its constituents being perfectly non-luminous, and attempts to use it as an illuminant have all taken the form of incandescent burners, in which thin mantles or combs of highly refractory metallic oxides have been heated to incandescence.  In carbureted water gas this gas is only used as the carrier of illuminating hydrocarbon gases, made by decomposing various grades of hydrocarbon oils into permanent gases by heat.