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
Acid–base reaction When a weak acid reacts with a weak base an equilibrium mixture is produced. For example, adenine, written as AH can react with a hydrogen phosphate ion, . The equilibrium constant for this reaction can be derived from the acid dissociation constants of adenine and of the dihydrogen phosphate ion. The notation [X] signifies "concentration of X". When these two equations are combined by eliminating the hydrogen ion concentration, an expression for the equilibrium constant, "K" is obtained. An acid–alkali reaction is a special case of an acid–base reaction, where the base used is also an alkali. When an acid