producer gas, fuel gas consisting chiefly of carbon monoxide and nitrogen. It is prepared in a furnace or generator in which air is forced upward through a burning fuel of coal or coke. Although the fuel is introduced through the top, no air is admitted there. The carbon of the fuel is oxidized by the oxygen of the air from below to form the carbon monoxide. The nitrogen of the air, being inert, passes through the fire without change. When steam is introduced with the air, the final gaseous product contains hydrogen also. Producer gas has a low heating value because it is about 60% inert nitrogen. It is widely used in industry because it can be made with cheap fuel. When producer gas contains hydrogen, it is also a source material for the manufacture of synthetic ammonia.