Catechin is a white crystalline substance, contained to the extent of some 30 per cent. in cube gambier, and in smaller proportion in block gambier and cutch, and very probably in all tanning materials yielding catechol-tannins. It melts at 422-1/2° F. (217° C.) and yields a sublimate of catechol on further heating. It is readily soluble in alcohol and in boiling water, but requires 1133 parts of cold water for its solution. Hence it separates on cooling from a hot solution of gambier, and may be purified by redissolving in hot water and treatment with animal charcoal, and subsequent crystallisation. It may also be extracted from its aqueous solution by agitation with ether. It possesses no acid properties, though some writers have incorrectly called it catechuic acid. The aqueous solution gives precipitates with lead acetate and mercuric chloride, and reduces ammonia-nitrate of silver; but, unlike tannins, it does not precipitate gelatin, alkaloids, or tartar emetic. It is oxidised by permanganate in presence of free acid, and hence, when in solution, is estimated by the Löwenthal method as "not tannin." It dissolves in concentrated sulphuric acid with a deep purple coloration. By fusion with caustic alkalies it yields protocatechuic acid and phloroglucol together with hydrogen. Its constitution is very uncertain, but it is probable that the phloroglucol stands in a somewhat similar relation to the protocatechuic acid that glycerin does to the fatty acids in natural fats; and that its decomposition by fused alkalies is a process much akin to saponification. This constitution is represented by the following formula:-- {O.C_{6}H_{3}(OH)_{2} C_{19}H_{18}O_{8} or C_{7}H_{8}O_{2}{ {O.C_{6}H_{3}(OH)_{2} When acted on by heat and dilute acids the following anhydrides are produced--the formulæ given must be taken as to some extent provisional. Catechin 2C_{19}H_{18}O_{8} = C_{38}H_{36}O_{16} Not acid; does not precipitate gelatin. Catechutannic acid C_{38}H_{34}O_{15}} } Acid, precipitate Dianydride C_{38}H_{32}O_{14}} gelatin. Trianydride C_{38}H_{30}O_{13}} Insoluble in water. Catechuretin C_{38}H_{30}O_{12}} Soluble in alcohol and alkalies.