British industrial chemist who developed the process of manufacturing potassium cyanide by passing ammonia over a heated mixture of charcoal and potassium carbonate. This process helped meet the increased demand for cyanide for use in extracting gold from low-grade ores.

After graduating from the University of Edinburgh, Beilby entered the oil-shale industry in 1869 and greatly increased the yield of paraffin and ammonia by introducing the continuous retort. In 1890 he turned his attention to the production of cyanide. Becoming interested in the destruction of metals by ammonia at high temperatures, Beilby undertook research on the flow of solids. He inferred that when a solid is caused to flow, as in polishing, the crystalline surface is broken down to a harder and denser layer. Although much criticized, this theory explained the hardening of metals under cold working and gave valuable stimulus to further research. Beilby was director of the Fuel Research Board from 1917 to 1923. He was president of the Institute of Chemistry (1909–12) and of the Institute of Metals (1916–18), was a fellow of the Royal Society of London (1906), and was knighted in 1916.