Water Gas is produced by forcing steam through a network of very hot fire bricks, on the principle of the blast stove, and immediately, while at a high temperature, through a bed of incandescent fuel. The hot fuel decomposes the steam, consuming the oxygen, liberating hydrogen and giving off CO. In this way no nitrogen is introduced. The blowing of steam through the fire is intermittent as it soon cools the fire and must be shut off to allow the fire to regain heat by ordinary combustion. Water gas produces a more intense heat than does producer gas, but is used only for special needs as its cost is greater than that of producer gas.