113,393. Gulck, L. van. June 23, 1917. Retort furnaces.-A reversible gas - heated retort or muffle furnace, more especially applicable for the treatment of zinc, comprises a number of compartments arranged in pairs on opposite sides of a central longitudinal wall reaching nearly to the roof, gas and air being supplied alternately to combustion chambers running longitudinally beneath each row of compartments, and regenerators for the air being arranged below. The flames from the combustion chamber in action rise between the retorts in the compartments on one side of the central wall and descend between those in the compartments on the other side to the regenerators on that side. As shown, each pair of compartments is divided by the central wall 3 into sections in which the muffles are arranged back to back. Gas flues 5<a>, 5<b> extend the length of the furnace, and communicate on the one hand through dampered upcast flues 6<a>, 6b with combustion chambers 7<a>, 7<b>, and on the other with a supply main through a single reversing-valve. The regenerators 8<a>, 8<b> similarly communicate with the combustion chambers through flues 9<a>, 9<b>, and with a reversing-valve for each pair of compartments through flues 10<a>, 10<b>. The air and combustion-product, reversing-valves 21, Fig. 4A, are connected for simultaneous operation by a rod 25, and are actuated by a weighted lever 26 through levers and rods. A passage 32 gives access to each combustion chamber for cleaning purposes. Any compartment can be cut out of action by closing the gas dampers 33, the air door or cover 23 of the reversing -valve, and a damper in the flue connecting the section to the chimney.