The Gould rotary furnace and condensing system recovered mercury from cinnabar ore at the Guadalupe mine from 1940 until the mine closed in the 1970s. Finely crushed ore from the fine ore bin entered the furnace through a feeder known as a shotgun or bump feeder, which periodically injected measured amounts into the rotary tube. There the ore was heated above the dissociation temperature of 1095 degrees F, while injected air from the burner blower also oxidized the sulphur within the ore. As the tube slowly rotated, the ore was constantly mixed, exposed to heat, and gradually moved toward the burner end, where spent ore dropped into the calcines bin. Gases produced by the heat, consisting of mercury, sulphur, and water vapor along with an unavoidable amount of dust, were drawn through a dust separator and then to the condenser. Mercury vapor condensed back into liquid form and, with a small amount of rock dust, was caught in rubber buckets, while sulphur vapor was exhausted into the air. Manufactured in 1940 by Mutual Engineering Co. of South San Francisco, California, the Gould Improved Quicksilver Furnace Condensing System had a capacity of 15 tons per day, used bunker oil for fuel, and was powered by a 4.98 HP electric motor that turned the rotary tube about once per minute.