Period 6 element also dissolves in alkaline solutions of cyanide, which have been used in mining. Gold dissolves in mercury, forming amalgam alloys. Gold is insoluble in nitric acid, which dissolves silver and base metals, a property that has long been used to confirm the presence of gold in items, giving rise to the term "the acid test." Gold has been a valuable and highly sought-after precious metal for coinage, jewelry, and other arts since long before the beginning of recorded history. Gold standards have been a common basis for monetary policies throughout human history, later being supplanted by fiat currency starting in
Brønsted–Lowry acid–base theory to become its conjugate base, A. The base, B, can accept a proton to become its conjugate acid, HB. Most acid-base reactions are fast so that the components of the reaction are usually in dynamic equilibrium with each other. Consider the following acid–base reaction: Acetic acid, CHCOOH, is an acid because it donates a proton to water (HO) and becomes its conjugate base, the acetate ion (CHCOO). HO is a base because it accepts a proton from CHCOOH and becomes its conjugate acid, the hydronium ion, (HO). The reverse of an acid-base reaction is also an acid-base reaction, between the