The colouring principle of logwood, which is obtained by digesting alcohol for a day on the aqueous extract of logwood; then filtering the solution, evaporating partially, and leaving the liquid to rest, hematin will be deposited in small crystals, which, after washing with alcohol, are brilliant, and of a whitish red colour, having a bitter, acrid and slightly astringent taste. Hematin forms an orange-red solution with boiling water, becoming yellow as it cools, but recovering with increase of heat its former hue. Excess of alkali converts it first to a purple, then to violet, and lastly to brown. Metallic oxides combine with hematin, forming blue-coloured compounds. Gelatin throws down reddish floculi; peroxide of tin and acid redden it.