History of Chemistry in Ancient and Medieval India, Incorporating the History of Hindu Chemistry by Acharya Prafulla Chandra Ray c37.s1.15

c37.s1.15

"Most of the saltpetre, which is sold in Guzuratta, comes from Ajmer, sixty leagues from Agra, and they get it out of land that hath lain long fallow. The blackest and fattest ground yields most of it, though other lands afford some, and it is made thus : they make certain trenches which they fill with their saltpetrous earth, and let into them small rivulets, as much as will serve for its soaking, which may be the more effectually done, they make use of their feet, treading it till it becomes a brooth (broth). When the water has drawn out all the saltpetre which was in the earth, they take the clearest part of it, and dispose it into another trench, where it grows thick, and then they boil it like salt, continually scumming it, and then they put into earthen pots, wherein the remainder of the dregs goes to the bottom ; and when the water begins to thicken, they take it out of these pots, to set it adrying in the sun, where it grows hard, and is reduced into that form wherein it is brought into Europe."
@H pp. 66-67.