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
Chromotropic acid uses chromotropic acid. Chromotropic acid Chromotropic acid has the formula is (HO)CH(SOH). It can be used for as a reagent in the quantitative determination of the systemic herbicide, 2,4-dichlorophenoxyacetic acid. Chromotropic acid is also used for testing of presence of formaldehyde. The usefulness of this reagent in quantitative determination is the formation of a red colouration (peaking at 580 nm wavelength) when chromotropic acid in 50% sulfuric acid reacts with formaldehyde. The colouration is specific to this aldehyde and is not produced from other organic species such as ketones and carboxylic acids. The NIOSH Formaldehyde method #3500 is the reference