THE CHEMICAL GAZETTE. No. CCCXCIX.—June 1, 1859. SCIENTIFIC AND MEDICINAL CHEMISTRY. On a Yellow Colouring Matter obtained from the Leaves of the Polygonum Fagopyrum, or Common Buckwheat. By Edward Schunck, Ph.D., F.R.S. Among the many plants which have been supposed to contain or yield indigo-blue, the Polygonum Fagopyrum or common buck wheat, a plant extensively cultivated in some countries for the sake of its seed, which is used as an article of food, is mentioned by some authors. In the ‘ Mechanics’ Magazine’ for November 1830, for instance, the following directions are given for obtaining a blue colour from this plant:—“ Take the buckwheat out of the ground before the seed has become quite hard, and lay it on the ground in the sun until it is dry. Then throw the plant into heaps, moisten it and allow it to ferment until decomposition commences, when it will assume a blue colour. It must now be formed into cakes, which may be dried either in the sun or in a stove. It imparts to boiling water a blue colour, which is not changed either by acetic or sulphuric acid. A durable blue may be dyed with it.” Though it does not follow from this that the blue colouring matter thus obtained was really indigo-blue, still it seemed not improbable that it might be identical with the latter, since another species belong ing to the same genus, the Polygonum tinctorium, is remarkable for the large amount of indigo-blue which it affords. Nevertheless, on submitting the leaves of the plant to the same process as that pre viously employed in the case of the Isatis tinctoria and other plants producing indigo, I was unable to obtain a trace of that or any other blue colouring matter. The examination led, however, to the discovery of a crystallized yellow colouring matter, the method of preparation and properties of which I shall now proceed to describe. The plant, which is one easily cultivated and will grow in the poorest soils, having been allowed to attain its full size, the leaves Chem. Gaz. 1859. m