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Charles Washington Merrill​
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Charles W. Merrill was a pioneering consulting metallurgist who made truly significant contributions to the mining industry through his own numerous inventions and discoveries, as well as by improving, developing, and marketing many processes, mechanisms, and devices initially developed by others.​

Charles Merrill received his B.S. in metallurgy and mining from the University of California in May 1891. Cyanide recovery of gold from its ores was the subject of his graduate thesis. His first significant work was to improve the existing cyanidation process. He met with early successes at mines in California, Arizona, and Montana, which led to an invitation to improve gold recoveries from the Homestake Mine in Lead, South Dakota.​

Charles Merrill so strongly believed in his process that he asked for no compensation for his work. If he succeeded, he would be entitled to a share of the profits. His process focused on extraction of residual gold in sands and slimes from existing Homestake processing plants. Homestake accepted the process and gave Merrill a ten-year contract to perfect it and oversee the building of treatment plants. His work resulted in an increase in Homestake gold recoveries from 75% to 94%--and it made him rich. While at Homestake, Merrill’s many process developments included the Merrill-Crowe zinc dust precipitation process, improved leaching vats, and filter presses for treatments of slimes. Around Homestake operations he was known as Cyanide Charlie.​

In 1908, Charles Merrill left Homestake to form his own company, The Merrill Company, to supply processing expertise and equipment to the mining industry. A few among the many processes developed and marketed by The Merrill Company were the Merrill Cyanide Recovery Process, the Merrill-Crowe Deaeration Process, the Merrill-Mills-Crowe Precoat Clarification Process, and the Merrill Cyanidation-Flotation Process.​

In 1916, a Merrill Company subsidiary, The Alloys Company, was founded to supply the expanding market for zinc dust required for Merrill’s gold precipitation process. A partnership—Merco Nordstrom Valve Co.—was formed with a Mr. Nordstrom to improve and market a special-applications valve invented by Nordstrom. Later, this company joined with the inventors of a centrifugal classifier to form another subsidiary, Merco Centrifugal, which in time merged with Dorr-Oliver.​

Even though Charles Merrill was fully engaged in managing his companies, he devoted additional energy to the wider industry as a member of professional societies in the United States, England, Australia, and South Africa. A far from complete list of his civic activities includes service as a Trustee of the California School of Mechanical Arts, as a Director of the Oakland Children’s Hospital, and as Vice President of the California Conference School of Social Work.​

Of all the honors and compliments Charles Merrill received in his life, the one he treasured most was from an old Homestake associate, who said, “Whatever Charlie Miller touched, he always made it better.”​