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 extraction pH range. The order of the step is not important and the process can be repeated to increase the separation. However, it is often convenient to have the compound dissolved in the organic phase after the last step, so that the evaporation of the solvent yields the product. The procedure works only for acids and bases with a large difference in solubility between their charged and their uncharged form. The procedure does not work for: Alternatives to acid-base extraction including: Acid-base extraction Acid-base extraction is a procedure using sequential liquid–liquid extractions to purify acids and bases from mixtures based on