37°

DYEING AND CALICO PRINTING.

split up, / 3 -orcine, we may admit that it might produce / 3 -orsellic orevernic acid.

6. Roccellic acid, Ci 7 H 32 0 4 .

7. Roccelline, CisHjgOy.

8. Parelline, or parellic acid, C9H6O4: the two last-named bodies are not

very well known.

Erythric acid, or Erythrine, C 20 H 22 Oio, was discovered by M. Heeren, andfully investigated by Drs. Schunck, Stenhouse, Hesse, and De Luynes. Itoccurs in most of the orchil lichens, and especially in the species known asRoccella tinctoria,fuciformis, and Montagnei. This acid is insoluble in coldwater, soluble in 240 parts of boiling water, whence, on cooling, it is depositedin the crystalline state. It is more readily soluble in alcohol and ether,boiling alcohol being its best solvent. On cooling, the solution depositsgroups of crystals. The alcoholic solution is neutral to test-paper, colourless,inodorous, and tasteless. Erythrine is dissolved by strong sulphuric acid inthe cold, and by hot hydrochloric acid ; the former solution is precipitated bycold water. Caustic and carbonated alkalies, and the hydrates of baryta andlime, dissolve erythrine readily, whilst acids precipitate the substance unal-tered, in the shape of a white, bulky, gelatinous mass ; but if the alkalinesolutions have been boiled, or kept for a long time, this precipitation does nottake place, since erythrine is then altered in a peculiar manner, which weshall presently describe. The ammoniacal solution reddens on exposure toair; with perchloride of iron a purplish colouration is produced. Themagnesia-solution of erythrine {erythrite of magnesia) is precipitated by neu-tral acetate of lead, but the alcoholic solution of erythrine is not precipitatedby that reagent; it is, however, thrown down by basic acetate of lead. Whenerythrine is for a length of time boiled with water it fixes the elementsthereof, giving rise to the formation of picroerythrine, carbonic acid, andorcine. This readtion is performed in two periods, during the first of whichpicroerythrine and orsellic acid are generated, while during the second theorsellic acid is split up into carbonic acid and orcine. If, instead of water,alcohol or wood spirit (pure methylic alcohol) is taken, orsellate of ethyl andorsellate of methyl are produced. Alkalies, especially if aided by heat andlime, greatly favour the transformations of erythrine.

Dr. Schunck prepares erythrine by exhausting the lichens with boilingwater; the crystalline powder deposited on cooling is purified by the re-crystallisation from alcohol. By this method a portion of the produdt ismodified, and converted into orcine and picroerythrine, whence it is preferableto treat the lichens with milk of lime in the cold. The calcareous solutionthus obtained is treated with carbonic acid, whereby carbonate of lime anderythrine are thrown down. This mixed precipitate is next treated with tepidalcohol, and the solution first purified by means of animal charcoal, and,when decolourised and still hot, so much water is added to the alcoholicsolution as to produce a permanent turbidity : on cooling, the erythrine isthrown down in a crystalline form.* The calcareous solution may also beprecipitated by hydrochloric acid. When the lichens are exhausted with coldweak ammonia a yellow liquor is obtained, containing erythrine and roccellicacid, the latter being a kind of fatty matter, insoluble in water, but soluble in

* Hesse, “ Annalen der Chemie und Pharmacie,” vol. cvii., p, 297.