Weidel's reaction

Weidel's reaction may refer to either a chemical reaction showing the presence of uric acid or xanthine bodies, or to a test (now considered obsolete) based on that reaction (invented by the Austrian chemist Hugo Weidel).

A solution of the suspected substance in chlorine water with a little nitric acid is evaporated in a water bath, and then exposed to the vapor of ammonia; the presence of xanthine is indicated when a red or purple color develops.