History of Chemistry in Ancient and Medieval India, Incorporating the History of Hindu Chemistry by Acharya Prafulla Chandra Ray c37.s1.26

c37.s1.26

"The shale is excavated from pits and is exposed for four months, a slow combustion taking place owing to the decomposition of the pyrites. It is then spread in squares resembling salt pans and sprinkled with water. After about twelve days it consolidates into efflorescing mamillated crystalline plates or crusts, called *phūlhāri-kā-bīj* or seed of alum. These crusts are boiled in large iron vessels (luted inside with lime), together with saltpetre (or other potash salt), in the proportion of 15 of alum seed to 6 of the latter; when it has settled, the liquor is placed in small earthen vessels, somewhat the shape of flower-pots, and crystallisation takes place in three days. The crystals are again boiled one or more times to concentrate the solution, which is finally ladled into large thin bladder-shaped earthen *muthas* or *gharras* with small mouth; these are sunk into the ground to prevent their breaking, and in five days the alum is found crystallised in masses. The vessels are then broken, and the alum is stored.