Anhydrous uric acid: nature and occurrence of a new form of urinary calculi.

A second form of anhydrous uric acid has been found in urinary calculi; it is probably derived as an artifact from uric acid dihydrate during storage. It has been prepared in the laboratory by desiccation of uric acid dihydrate. Mixtures of these two substances sometimes give x-ray powder patterns that resemble that of xanthine on weak photographs, but are distinguishable by their infrared spectra.