Direct reduction process invented by Adolphus Frederick Gurlt. The iron ore is charged un the chamber B. The chambers D make the daseification of (char?)coal. The b-b inlets bring air to induce a post-combustion, in order to increase the temperature of the reducing gas. This kind of furnace was used in Spain between about 1865 to 1884. It is pretty similar to Tourangin's furnace.