History of Technology in India, Vol. I: From Antiquity to c. 1200 A.D. v1.c13.s2.t4.194

v1.c13.s2.t4.194

The process used for the distillation of zinc by the Indians around Zawar mines is unique in the sense that it is designed on the principles of down draft distillation. Fig. 42 shows a picture of this distillation apparatus as described in Rasa Ratna Samuccaya. In this ‘Yantra’ the solid charge was held in the upper inverted pot by sealing its mouth with clay and fixing a reed stick in the centre for the escape of gases etc. at high temperature. Another matching earthen pot was luted to the mouth of the inverted pot as shown in figure and the bottom pot was kept into a trough full of water. During the processing the upper inverted pot was heated by building a fire on a platform around it. On reaching the cherry red temperature (600°C) the reed was charred and burnt off and the reduced metal vapour Zn or Hg was forced downwards in the condenser where it got converted into liquid or solid metal. A similar but advanced method was used by the Zawar smelters. The process used by them consisted of the following steps: