History of Technology in India, Vol. I: From Antiquity to c. 1200 A.D. v1.c12.s1.t4.32

v1.c12.s1.t4.32

The extraction of fine gold was carried out by adding mercury to a mixture of black sand and gold ore. They would rub the black sand mixture by adding a little common salt. In a little time the gold and mercury would form an amalgam and adding a little water to the mixture and agitating the dish, the particles of amalgam would come together and form a lump and black sand would be washed off. This lump of amalgam was rolled in a damp rag and after the superfluous mercury was squeezed off the rag, it was burned in a fire and a button of gold recovered. If the gold was found alloyed with silver or other base metals, it was hammered out between the two stones into a sheet. This sheet was coated with salt and with a little nitre (if copper was thought to be present). The plate was then laid between two layers of cow-dung and burned, the ash of the dung acted as a cupel and absorbed the base metals and left the pure gold (Bharat Gold Mines Ltd, notes, 1979).