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
Metal Gear Acid a trading card-based system to control the main character's movements and actions. "Acid" in the name stands for "Active Command Intelligence Duel". The cards are not truly collectible, as the game is complete with a single purchase. However, the game does feature deck design and deck optimization elements. The game allows for multiplayer gameplay by wireless ad-hoc connections of two PSPs. Before each round, the player can customize the deck of cards used by the main characters. The majority of the cards are based upon elements spanning the entire "Metal Gear" series, such as weaponry, characters, and even the Metal