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,
Acidophiles in acid mine drainage economically and from a conservation perspective. Control of these acidophiles and their harnessing for industrial biotechnology shows their effect need not be entirely negative. The use of acidophilic organisms in mining is a new technique for extracting trace metals through bioleaching, and offers solutions for the phenomenon of acid mine drainage in mining spoils. Upon exposure to oxygen (O) and water (HO), metal sulfides undergo oxidation to produce metal-rich acidic effluent. If the pH is low enough to overcome the natural buffering capacity of the surrounding rocks (‘calcium carbonate equivalent’ or ‘acid neutralising capacity’), the surrounding area may become acidic,