The four Gould Rotary Furnaces at Idria are contained within an approximately 80-foot by 100-foot building consisting of the ore feeders, ore bins, rotary kilns, calcine bins, dust collectors, steel condensers, exhaust system, hoeing tables, and bottling room. Except for two-years between 1920 and 1922, the facility was used continuously between 1918 and 1972 as a mercury ore reduction facility for the New Idria Quicksilver Mine. While various portions of the building and facility have been remodeled over the intervening years, the original four rotary kilns have remained in place.
Each furnace, or kiln, is a cylindrical tube formed from 5-foot rolled 1-inch iron plates riveted together to make a 5-foot diameter by 56-foot long horizontal tube. The 5-foot section at the ore-feed end of the kiln is tapered to form a 3½-foot opening.
The first successful commercial application of a rotary kiln was for Portland cement production. This was accomplished by David O. Saylor in 1889 in Coplay, Pennsylvania and this marked an important technological step that contributed to increased material production. However, the initial use of rotary kilns was restricted to wood and coal fired cement production until 1918 when Henry Gould, the mine superintendent and engineer for the New Idria Quicksilver Mining Company, adapted the kiln's fuel, air draft and exhaust system to mercury ore reduction. The innovative design of the Gould Rotary Furnace led to worldwide use of this technology in metallurgical and mineral processing, pulp and paper drying, waste regeneration, and drastic improvements in environmental quality.
Successful adaptation of the rotary kiln began at New Idria in 1917 during the height of World War I when mercury production was a critical component of munitions needed to support United States victories during the war. Mr. Gould installed a 4'X50' experimental rotary kiln and solved the technical issues that led to the failure of two pervious attempts to introduce rotary kilns to mercury ore reduction. Mr. Gould's experimental unit was fully operation in production mode by March 1918 and his rapid success was quickly followed by the installation of four 5'X56' production kilns.
By 1907, Idria had already introduced electrical generators and fuel oil to their mining facility. "Bunker-C" fuel oil was being delivered from Coalinga and Mendota and electricity was generated locally from an oil-operated generator and a stream driven waterwheel. Mr. Gould already had at least ten years experience using these energies, so it was a natural step to adapt the rotary kiln to fuel oil and electric drive during their development stage.
The five kilns operated continuously until June 1920 when a disastrous oil fire caused extensive damage to the town of Idria and much of the company's mining equipment. The fire and the low price of mercury following the war forced the company into receivership. The mine reopened in January 1923 as New Idria Quicksilver Mines, Incorporated. The new company decommissioned the experimental kiln, rebuilt the furnace building, returned the four production kilns to service, and produced a $642,522.89 profit during that year. Coast Valleys Gas and Electric Company ran a fifty-six mile long power line from King City to the mines in 1924. The furnaces continued producing mercury through the Great Depression, but because of low demand, the company focused on recovery mining and reclaimated the grounds under and around the old Scott furnace-a side benefit of this is that we have a much cleaner environment at Idria than at other quicksilver mining operations.
The New Idria Quicksilver Mines, Incorporated sold all of its mining property in June 1936 to William Moorehead. That same year former-president Herbert Hoover, who had a degree in mine engineering from Stanford University, inspected the property for his brother, who soon became one of the owners of the mines. The new owners included Theodore Hoover, California State Senator Sanborn Young, and Henry Gould. The new owners installed new firing heads, dust chambers and blowers.
The firing heads were redesigned in 1944 to include new muffle blocks, and at the same time, the furnace building got a major face-lift. The front retaining wall was extended to include the calcine ore bin, which previously dumped directly into ore cars, and a fresh concrete overlay was added to the foundation. The building was also reclad with corrugated sheet metal. The condensing chambers were upgraded from wood to cast-iron, and the first automated hoeing tables were installed.
Ore production during World War II earned the company the Army-Navy "E" Production Award. In 1946, the furnaces were used to recycle 363,000 pounds of war surplus mercury batteries, and another 253,000 pounds were recycled in 1948. However, by the end of 1948, the demand for mercury plummeted and the company became idle. With a reduced workforce, the company once again focused on recovery mining by processing mercury-contaminated soil from 2-miles of the San Carlos Stream basin.
The Korean War increased the market for mercury and the market remained profitable through the 1950s. However, the market was again declining by 1964 and Idria once again turned to low-cost recovery mining by processing mercury-contaminated soil between the furnace area and San Carlos Creek. The company continued to maintain profit until 1972 when declining value of mercury and new environmental regulations finally caused production cost to exceed market value and the company decided to close.
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Idria Furnace Building Floor Plan
Idria Furnace Facility Map