III. Picrorocellin

Through the kindness of Mr. C. Lavers Smith, the eminent orchil manufacturer of Spitalfields, we were furnished with a quantity of a lichen which he had observed to have a very bitter taste, and which came into the market through a Portuguese house. It is believed to have been brought from the West Coast of Africa; but our endeavours to ascertain the exact locality have hitherto been unsuccessful. From the appearance of the lichen it seems to grow on limestone rocks; and Mr. W. Carruthers, of the British Museum, and the Rev. J. Y. Crombie, to whom we submitted it, pronounced it to be a variety ofRocella fuciformis , the ordinaryRocella usually growing on trees. This lichen is remarkable for its intensely bitter taste; and the preliminary experiments showed that this is due to the presence of a crystalline compound which is but slightly soluble in water.Picrorocellin . The lichen was accordingly first treated with water and hydrate of lime, in the usual manner, to extract the erythrin which it contains in common with other varieties ofRocella , and the residue, after being dried at the ordinary temperature, was extracted by boiling spirit. The alcoholic solution, which contained the bitter substance together with chlorophyl and various fatty and resinous impurities, was concentrated by distillation until almost the whole of the alcohol was removed. When cold, the dark-coloured pasty mass was pressed in a cloth, boiled up with a small quantity of strong spirit, and allowed to cool, pressed, and again treated in the same manner. By this means much of the chlorophyl and almost the whole of the oily matters were dissolved out, leaving a dark green-coloured crystalline product. In order to remove the last traces of chlorophyl from this, it was boiled up twice or thrice with benziue, in which the crystals are only slightly soluble.