The discovery of fine-grained gold ores on the Witwatersrand in South Africa in 1886 highlighted the importance of finding a new method to extract the gold, because the losses with the amalgamation process used at the time were excessive. Chemists had known for 100 years that gold could be dissolved in potassium cyanide. A patent was taken out on the cyanide process in the United States in 1867, but neither the process that was the subject of that patent nor others taken out up to 1885 were used on a commercial scale. Recovering all the gold from the solution was a difficult problem to overcome.
In 1887, J. S. McArthur and R. and W. Forrest, working in a laboratory in Glasgow, Scotland, observed that a cyanide-leaching process followed by a zinc-precipitation process dissolved the gold from ores and ensured that there was a high recovery of gold from the pregnant solution (Wilson 1908). The cyanide process proved to be satisfactory on a small scale in Ravenswood, Queensland, Australia (Lougheed 1985), but its real test came when it was used to extract the gold from tailings on the Rand. It was very successful, as indicated by the value credited to the cyanide process by the South African gold industry, which increased from $6,000 in 1890 to $6 million in 1893 (Dorr 1936).