Minerals and Metals in Ancient India v1.c26.s6.t3.5

v1.c26.s6.t3.5

Sodium in the spent charge could have been derived from gangue such as albite NaAlSi₃O₈, but high chlorine content (0.53 %, vide column 5 in Table 18.2) is less easy to explain. The fourteenth-century AD text Rasaratnasamuccaya (2.157) recommended the inclusion of salt in the zinc-smelting charge, an idea which was incorporated by William Champion in his AD 1748 British patent. Common salt would have served the zinc distillation process in two ways. Firstly, the soda vapour would help to sinter calcium and magnesium oxides and hence keep the charge within the retorts in a porous open texture. This Analysis of the Spent Charge from Zawar Zinc-Smelting Retorts