Copper in Ancient India c10.s3.5

c10.s3.5

In this process carbonated alkali and the carbon obtained by the destructive distillation of such carbonaceous substances as lac &c. supply the reducing agents in the extraction of zinc from calamine. In later alchemical treatises the covered crucible is provided with a tubulure so that the completion of the reaction may be ascertained when the blue flame at the mouth of the tubulure suddenly changes to white owing to the volatilisation of zinc. The description of the distillation of zinc in tubulated covered retorts or crucibles in *Rasaratna-samuchchaya*, *Rasaprakāsh-sudhākar* and other alchemical treatises of the 12th and 13th centuries is "so exact that it will bear repetition in any text-book of metallurgy." We give below the description of the process as given in *Rasaratna-samuchchaya*²:—"Rub calamine with turmeric, the chebulic myrobalans, resin, the salts, soot, borax and one fourth its weight of semicarpus anacardium and the acid juices. Smear the inside of a tubulated crucible with the above mixture and dry it in the sun and close its mouth with another inverted over it and apply heat..