History of Technology in India, Vol. I: From Antiquity to c. 1200 A.D. v1.c13.s2.t4.192

v1.c13.s2.t4.192

Zinc is one of the few metals produced by the reduction distillation technique even today because the commercially viable reduction of ZnO by ‘C’ is obtained only above 1200-1300°C while the boiling point of zinc is 930°C only. Hence, the metallic vapour produced after reduction has to be cooled at a fast rate below 500°C to produce liquid metal and prevent its reoxidation to ZnO (blue dust). Craddock (1885) has recently published a comprehensive review on the distillation technology and the apparatus used in ancient times in various countries, and he has concluded that in India the process of distillation of water, wine (*Somarasa*) and probably mercury were known even in the Vedic period (Yajurveda). The distillation apparatus found near the ancient Taxila (Needham) was unique and much advanced. This system uses a separate condenser tube fitted to the mouth of the distill to carry the vapours to the condenser vessel which was water cooled.