Did you know that in most countries, gold is used as a standard for monetary exchange, in coinage and in jewelry? Pure gold is far too soft for ordinary use and is typically hardened by alloying with copper or other base metals such as iron. Gold is insoluble in nitric acid, which will dissolve silver and base metals, and is the basis of the gold refining technique known as inquartation and parting.

In 2006 to sell gold in Phoenix, the U.S. Mint began production of the American Buffalo gold bullion coin also at 99.99% purity. Modern industrial uses include dentistry and electronics, where gold has traditionally found use because of its good resistance to oxidative corrosion. Chemically, gold is a transition metal and can form trivalent and univalent cations upon solvation. At STP it is attacked by aqua regia, forming chloroauric acid and by alkaline solutions of cyanide but not by hydrochloric or even when you sell gold Phoenix, nitric or sulphuric acids. Gold dissolves in mercury, forming amalgam alloys, but does not react with it.

Nitric acid has long been used to confirm the presence of gold in items, and this is the origin of the colloquial term "acid test", referring to a gold standard test for genuine value. The popular issue Canadian Gold Maple Leaf coin has a purity of 99.99%. Several other 99.99% pure gold coins are currently available, including Australia's Gold Kangaroos (first appearing in 1986 as the Australian Gold Nugget, with the kangaroo theme appearing in 1989), the several coins of the Australian Lunar Calendar series, and the Austrian Philharmonic. The gold content when you sell gold Arizona, of gold alloys is measured in carats (k), pure gold being designated as 24k.
Special issue Canadian Gold Maple Leaf coin with the highest purity of any gold coin at a guaranteed 99.999% some of the time.

Modern collector/investment bullion coins (which do not require good mechanical wear properties) are typically 24k, although the American Gold Eagle, the British gold sovereign and the South African Krugerrand continue to be made at 22k, on historical tradition. A special issue Canadian Gold Maple Leaf coin contains the highest purity gold of any bullion coin, at 99.999% and that is a lot. Gold coins intended for circulation from 1526 into the 1930s were typically a standard 22k alloy called crown gold, for hardness and because they have a crown of gold on them.