Purpurates, salts of purpuric acid. Scheele in 1776 found that a solution of uric in nitric acid produced a beautiful deep red dye. Prout in 1818 obtained this coloring matter in a crystalline form, and regarded it as purpurate of ammonia. By double decomposition he obtained metallic purpurates having a similar color. The colorless substance which separated from purpurate of ammonia by the action of strong acids, he regarded as purpuric acid; but Liebig and Wöhler showed that this did not possess the property of forming colored salts, and therefore held that Prout's compound was not an ammonium salt, but an amide, which they called murexide. (See Murex.) Later researches by Freitzsch and Beilstein indicate that it is a true ammonium salt; still the purpuric acid has never been isolated, because it is decomposed when its salts are treated with a stronger acid. The formula of purpurate of ammonia or murexide is C8H8N6O6= NH4C8H4N5O6; therefore the acid is represented by the formula C8H5N5O6. Murexide is the principal salt, and is a beautiful purple, but is becoming superseded by rosaniline.