A History of Hindu Chemistry from the Earliest Times to the Middle of the Sixteenth Century A.D. v1.c18.s5.18

v1.c18.s5.18

An examination into the nature of the chemical actions that take place during the operation clearly shows that Au₂O is the compound formed. We have seen in investigating the chemical changes during the third stage of colouring that KNO₃ and NaCl being heated together, yield free chlorine together with KOH and NaOH. This chlorine after being liberated in the fourth stage attacks the gold and a small amount of auric chloride is formed. But at this point sulphur is added, and the nascent chlorine, instead of going to attack the gold any more, combines with the sulphur to form one or more of the sulphur chlorides. The supply of fresh chlorine being thus cut off, the heated auric chloride decomposes into aurous chloride and chlorine. The chlorine thus liberated combines with the sulphur, while the aurous chloride is acted on by the KOH and NaOH with the result that Au₂O is formed.¹ This is partly deposited on the surface of the gold producing the required colour and partly mixed with the saline solid matter present in the solution.