A History of Hindu Chemistry from the Earliest Times to the Middle of the Sixteenth Century A.D. v1.c13.s1.13

v1.c13.s1.13

"Each charge of shale is exposed to three changes of water and the water itself is changed from one *ghara* to another till it has taken up the sulphates from seven different steepings. It is then of a thick dirty-bluish colour and is taken to the boiling house, where it is boiled in earthen *gharas*; when sufficiently concentrated it is left to cool, and thin sticks being introduced the blue vitriol crystallizes on them. The mother liquor is then poured off and again boiled, and on the addition of saltpetre, the alum crystallizes at the bottom of the vessel. The residual sulphates still in solution, are allowed to crystallize out by exposing the mixture to the sun.
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