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
Phosphorous acid concentrating the solution and precipitations with alcohols, the pure acid can be separated from the salt. Phosphorous acid is a strong acid with a p"K" in the range 1.26–1.3. It is a diprotic acid, the hydrogenphosphite ion, HP(O)(OH) is a moderately strong acid: The conjugate base HP(O)(OH) is called hydrogen phosphite, and the second conjugate base, , is the phosphite ion. (Note that the IUPAC recommendations are hydrogen phosphonate and phosphonate respectively). The hydrogen atom bonded directly to the phosphorus atom is not readily ionizable. Chemistry examinations often test students' appreciation of the fact that "not" all three hydrogen atoms