Copper in Ancient India c10.s3.8

c10.s3.8

When the flame issuing from the molten calamine changes from blue to white, the crucible is caught hold of by means of a pair of tongs and its mouth held downwards and it is thrown on the ground, care being taken not to break its tubulure. The essence possessing the lustre of tin which is dropped is collected for use.” The chemical reaction that takes place in the above process is easily understood and is the same as takes place in the modern process of the extraction zinc. In the first place calamine is converted by heat into zinc oxide, which when heated with soot and carbon obtained by the destructive distillation of carbonaceous substances such as lac is converted into metallic zinc whilst carbon monoxide is evolved which burns at the mouth of the tubulure with the characteristic bluish flame. When the reduction is complete and the zinc vaporises, the bluish flame is replaced by the white flame of burning zinc vapour. At that time the molten zinc is poured out from the crucible by holding its mouth downwards.