Nitric acid Nitric acid can oxidize non-active metals such as copper and silver. With these non-active or less electropositive metals the products depend on temperature and the acid concentration. For example, copper reacts with dilute nitric acid at ambient temperatures with a 3:8 stoichiometry: The nitric oxide produced may react with atmospheric oxygen to give nitrogen dioxide. With more concentrated nitric acid, nitrogen dioxide is produced directly in a reaction with 1:4 stoichiometry: Upon reaction with nitric acid, most metals give the corresponding nitrates. Some metalloids and metals give the oxides; for instance, Sn, As, Sb, and Ti are oxidized into SnO,
Acid test (gold) or definitive tests to other materials, became popular during and after the California Gold Rush, but was current before then, as shown by this quote from the Wisconsin paper "The Columbia Reporter", November 1845: "Twenty-four years of service demonstrates his ability "to stand the acid test", as Gibson’s Soap Polish has done for over thirty years." Other examples of the figurative use of the phrase are the web sites Acid1, Acid2 and Acid3, which are designed to test web browsers for compliance with current web standards. Another example is the quick ratio method, nicknamed "acid test", used by financial analysts