Note 22 bis — Chapter XVI · ZINC, CADMIUM, AND MERCURY

Calomel (in Japanese ‘Keyfun’) has been prepared in Japan (and China) for many centuries, by heating mercury in clay crucibles with sea salt, which contains MgCl2 and gives HCl. The vapour of the mercury reacts with this HCl and the oxygen of the air and forms calomel: 2Hg + 2HCl + O = Hg2Cl2 + H2O. The calomel collects on the lid of the crucible in the form of a sublimate (Divers, 1894).