The D retort, line the rotary furnace, was used to recover mercury from cinnabar ore. Whereas the rotary furnace was a continuously-operating system, the D retort was loaded with ore, fired for a period of time (usually 8 to 24 hours), then allowed to cool before emptying the burnt ore (calcines) and recharging with more ore. Burning fuel in a fire box under the retort heated [the] ore to dissociation temperature (1095 degrees F). Vapors driven from the ore by heat, including mercury, sulphur [sic], and water vapor, were condensed in external air-cooled or water-cooled metal pipes attached to the top of the retort.
The retort was most often used to process relatively small amounts of ore and to perform a second processing of calcines and dust from the rotary furnace.
This retort and condenser were used in the Guadalupe mine from 194-s until the mine closed in the 1970s. The Guadalupe Rubbish Company donated the D retort to NAQCPA in 1987.