Gold parting valens") could be made by the distillation of saltpetre (KNO) with alum (KAl(SO)) or vitriol (FeSO) with water. 2KNO + HO + FeSO → FeO + KSO + 2HNO Nitric acid, after distillation to increase the acid strength, is capable of dissolving the silver but it will not (by itself) dissolve the gold. However, nitric acid is not able to (fully) extract silver and other impurities from an alloy with a high content of gold. Therefore, one part of scrap gold was typically alloyed with three parts of copper (quartering) before parting with nitric acid. Another method uses Sterling silver
Solid acid Solid acid Solid acids are acids that do not dissolve in the reaction medium. They are often used in heterogeneous catalysts. Most of the acids solid in state are generally organic acids that includes oxalic acid,tartaric acid,citric acid,maleic acid,etc Examples include oxides, which function as Lewis acids including silico-aluminates (zeolites, alumina, silico-alumino-phosphate), and sulfated zirconia. Many transition metal oxides are acidic, including titania, zirconia, and niobia. Such acids are used in cracking. Many solid Brønsted acids are also employed industrially, including sulfonated polystyrene, solid phosphoric acid, niobic acid, and heteropolyoxometallates. Solid acids are used in catalysis in many industrial chemical