Ellagic acid C_{14}H_{8}O_{9}, when pure, is a sulphur-yellow crystalline body almost insoluble even in boiling water, and only slightly so in alcohol and ether, though by agitation with the latter, small quantities may be completely removed from aqueous solution. In hot alcohol it dissolves with a yellow colour, and crystallises on cooling. Solid ellagic acid gives with ferric chloride at first a greenish, and then a black coloration. In strong nitric acid it is soluble with a deep crimson coloration: that from divi-divi gives a crimson liquid on dilution with water, but from other sources it is rather orange. Ellagic acid may be obtained in considerable quantity by pouring a concentrated alcoholic extract of divi-divi into water, when it separates and may be filtered off and recrystallised from hot alcohol. It may also be obtained by boiling the aqueous extracts of divi, myrabolans, pomegranate rind, &c., with dilute hydrochloric acid, and purified by the same means. It may be prepared from gallic acid by heating the latter with dry arsenic acid to 320° F. (160° C.), but is difficult to purify from traces of arsenic. Ellagic acid has not been reconverted into gallic acid. Its constitutional formula is, according to Schiff, {CO.OH {OH C_{6}H_{2}{ {O────┐ {O } │ } │ {CO} │ {O────┘ C_{6}H_{2}{ {OH {OH differing from gallotannic acid only by the loss of two atoms of hydrogen. Air-dried ellagic acid, C_{14}H_{8}O_{9} + OH_{2}, contains 1 mol. of water, which it loses at 212° F. (100° C.) but reabsorbs in moist air. When heated to 392°-410° F. (200°-210° C.) it forms an anhydride, C_{14}H_{6}O_{8}, losing another molecule of water, which it does not recover from moist air, but is slowly reconverted to ellagic acid by boiling with water.