HISTOCHEMICAL RECOGNITION OF CALCIUM OXALATE

Of the workers applying the von Kossa test to calcium oxalate crystals in animal tissue, about half reported blackening in silver nitrate on exposure to light. We found that "pure" calcium oxalate crystals, produced in rats by the administration of ammonium oxalate or ethylene glycol, gave a negative von Kossa reaction. These crystals, however, were blackened when treated with a solution of silver nitrate in concentrated hydrogen peroxide. Other von Kossa negative salts, such as CaF2 or CaSO4·2H2O, do not respond to the H2O2 and AgNO3 test.