Hydrazoic acid was originally prepared by the reaction of aqueous hydrazine with nitrous acid. Other oxidizing agents, such as hydrogen peroxide, nitrosyl chloride, trichloramine or nitric acid, can also be used. In its properties hydrazoic acid shows some analogy to the halogen acids, since it forms poorly soluble (in water) lead, silver and mercury(I) salts. The metallic salts all crystallize in the anhydrous form and decompose on heating, leaving a residue of the pure metal. It is a weak acid (p"K" = 4.75.) Its heavy metal salts are explosive and readily interact with the alkyl iodides. Azides of heavier alkali metals (excluding
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