 His evening lectures were among the most popular in the history of the College.With Thomas Sterry Hunt, Douglas was involved with many experiments in the hydrometallurgy of coppers and devised what is known as the "Hunt-Douglas" process (first patented 1869) for extracting copper from its ores.Douglas was also the inventor of several other improvements in the mining industry, consisting of the invention for calcining ores (1884), a furnace for calcining ores (1898), a process for extracting copper from cupriferous nickel ore (1892), a process for separating and recovering copper (1896), and an improved smelting furnace in 1897.