"Calomel, corrosive sublimate, and vermilion have been manufactured for centuries at Hankow, China. Chemists of India prepared both chlorides of mercury as early as the twelfth century. A detailed description of the process was given in the thirteenth or fourteenth century . A mixture of common salt, brick dust, alum, Indian aloe, and mercury was heated for three days in a closed earthen pot. The Japanese and Chinese also prepared calomel by similar methods."