Acid test (gold) mark is tested by applying aqua fortis (nitric acid), which dissolves the mark of any item that is not gold. If the mark remains, it is tested by applying aqua regia (nitric acid and hydrochloric acid). If the mark is removed, then this test dissolves the gold, proving the item to be genuine gold. More accurate testing of the item for its fineness or purity can be done through the use of differing strengths of aqua regia and comparative testing of gold items of known fineness. The figurative meaning of the expression, where it is applied to tests of character,
Metal Gear Acid vecuronium bromide, the chemical used by Elsie and Frances to hijack Flight 326. The third is stated to be an acronym for Active Command Intelligence Duel, a reference to the game's mixture of turn-based tactics with card-based gameplay. The game's soundtrack was composed by Nobuko Toda, Shuichi Kobori and Akihiro Honda. The soundtrack was released on December 21, 2005, packaged with the "Metal Gear Acid 2" soundtrack. The album's title is "Metal Gear Acid 1 and 2 Original Soundtrack". "Metal Gear Acid" received generally positive reviews from critics. "Acid" was followed by a sequel for the PSP, "Metal Gear Acid