The steam becomes superheated in traversing the regenerators, B’, and in this state enters the bottom of the generator through the flue, E’.  In passing into the incandescent fuel that fills the generator, the steam is decomposed, and there forms carbonic oxide, while hydrogen is liberated.  The mixture of these two gases with the hydrocarburets furnished by the fuel constitutes water gas.  This gas on making its exit from the generator through the pipe, M’, passes through the chambers, B, and abandons therein the greater part of its heat, and enters the pipe, R, whence it passes through Q into the purifiers, and then into the gasometer.

As the production of water gas implies the absorption of a large quantity of sensible heat, it is accompanied with a rapid fall of temperature in the chambers, B’, and eventually also in the generator, A, while at the same time the chambers, B, are but moderately heated by the sensible heat of the current of gas produced.  When this cooling has continued so long that the temperature in the generator, A, is no longer high enough to allow the fuel to decompose the steam with ease, the valve, J’, of the pipe, P’, that leads the steam is closed, as is also the valve, K, of the pipe, Q, while the valves, L and H, of the pipes, R and N, are opened.  After this the valve, I’, is opened, and a current of air is let in through the pipe, O’.  This air, upon traversing the chambers, B’ and T’, is raised to a high temperature through the heat remaining in these chambers, and then enters at the bottom of the generator, through the flue, E’.  The air gas that now makes its exit from the pipe, M, in the chamber, T, meets another current of air coming from the pipe, N, and is thus burned.  The products resulting from such combustion pass into the chambers, B, and then into the chimney, through the pipe, R. The temperature then rapidly lowers in the chambers, B’, and rises no less rapidly in the generator, A, while the chambers, B, are soon heated to the same temperature that first existed in the chambers, B’.  As soon as the desired temperature is obtained in the generator, A, and the chambers, B, the air is shut off by closing the valve, I’, of the pipe, O’; the valve, F’, of the flue, E’, is also closed, the valves, G’ and K’, of the pipes, M’ and Q’, are opened, the valves, G, H, and L, of the pipes, M, N, and R, are closed, and the valve, F, of the flue, E, and the valve, J, of the pipe, P, are opened.  A current of steam enters the apparatus through the pipe, P, traverses the chambers, B, and enters the generator through the flue, E. The gas produced makes its exit from the generator, passes through the pipe, M’, and the chambers, T’ and B’, and the pipe, R, and enters the gasometer through the pipe, Q’.

[Illustration:  WATER-GAS APPARATUS.]