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,
Acid–base imbalance Any combination is possible, as metabolic acidosis and alkalosis can co exist together. The traditional approach to the study of acid–base physiology has been the empirical approach. The main variants are the base excess approach and the bicarbonate approach. The quantitative approach introduced by Peter A Stewart in 1978 is newer. There are numerous reasons that each of the four processes can occur (detailed in each article). Generally speaking, sources of acid gain include: Sources of acid loss include: The body's acid–base balance is tightly regulated. Several buffering agents exist which reversibly bind hydrogen ions and impede any change in