History of Chemistry in Ancient and Medieval India, Incorporating the History of Hindu Chemistry by Acharya Prafulla Chandra Ray c37.66

c37.66

The heap of dust and the refuse matters are ground fine by the *neharwalas*. The crushed materials are soaked in water in a big earthen pot for several days. They are then agitated with a large amount of water, when the lighter earthy materials float and remain in suspension, whereas the heavy metallic particles settle at the bottom. The supernatant water with its earthy suspension is then allowed to run out. The process is repeated till the solid matter is reduced to a small bulk. The residue is then dried up either in the sun or on fire The dried remnants of several washings are mixed together, and the mixture is washed once again. The metals present in the washed mixture generally include iron, which is removed by picking out with fine pincers. In later days, the use of magnet for the purpose has come into vogue. The mixture is then melted in a large crucible. The earthy matter sticks to the sides of the crucible, while the metallic portion melts and falls to the bottom. A button of gold, silver, copper and zinc is thus obtained. Gold is then extracted in a pure state from this alloy. For this purpose, the alloy is beaten into thin leaves Each leaf is then covered with a thin layer of a paste of brick dust and common salt. The leaves are finally arranged one above another and exposed to the heat of a fire. After a certain number of days, depending on the nature of the alloy and the temperature of the fire, the gold is found to be very nearly pure. This method has in the later ages been entirely superseded by the far easier and more economical process of treating the alloy with strong nitric acid. For this operation, however, the alloy must be reduced to a fine state of division. This is effected rather ingeniously by melting the alloy and then suddenly dropping the molten metal into water. By this means the metal is at once reduced to a fine powder