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 forces team to investigate, but the team is obliterated by armed resistance. With no other options and time running out, the US government calls Solid Snake to infiltrate the laboratory, discover the nature of Pythagoras, and to rescue Senator Hach. According to an interview originally published by "Electronic Gaming Monthly" with the game's producer, Masahiro Hinami, the 'Acid' part of the title actually has three different meanings. The first meaning refers to "Acid's" departure from the previous "Metal Gear" games in terms of style, which is an analogue to acid's ability to dissolve metal. The second is a reference to