COLOURING MATTERS OF LICHENS.

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assumes gradually a violet-red. If boiled along with water and an excess oflime and baryta, first an orsellate is formed, which is, in its turn, when theprocess is continued, decomposed into carbonic acid and orcine. The sub-stance known as a-orcine, or simply, also, orcine, first discovered by Robiquet,is the colourable material of the lichens, or rather it is—among the ultimateprodudts of the splitting up of the acids just mentioned—the only substancecapable of conversion into a colouring matter. It is not proved, and does notappear probable, that the colouring matter which is the result of the simulta-neous adtion of air and ammonia upon orcine is identical with the colouringmatters which ensue by the ammoniacal oxidation of the colourable acids(viz., erythrine, lecanoric, orcellic, and picroerythrine). Indeed during themanufacture of orchil by the ordinary methods there are formed severalcolours, all exhibiting different tones.

Pure orcine forms colourless prismatic crystals, belonging to the monoclinicsystem.* It is very readily soluble in water and alcohol, and soluble in ether ;from its aqueous solutions it crystallises with one equivalent of water, but theethereal solution yields anhydrous crystals. Orcine has a sweetish, but atthe same time a disagreeable, taste. Its hydrate fuses at ioo°, losing its.water of crystallisation; but in the anhydrous state it may be distilled at 290°,and sublimes without decomposition when not submitted to this experimentin large quantity at once. The formula of orcine is C 7 H 80 2 + H 2 0 , the lattereliminable at ioo°, or over sulphuric acid in vacuo , being water of crystallisa-tion. Though orcine is neutral to test-paper, it behaves in some instances asan acid, so that in a state of fusion it decomposes alkaline carbonates, andprecipitates silica from alkaline silicates; orcine precipitates the quinine salts,entering into a peculiar combination with that base. Solutions of orcine arenot precipitated by bichloride of mercury, neutral acetate of lead, sulphate ofcopper, tannin, and gelatin, but yield with basic acetate of lead a white, andwith chloride of iron a deep red, precipitate. Orcine reduces salts of gold andsilver to the metallic state, if ammonia is simultaneously present. Orcinecombines with chlorine and bromine; if thrown into fuming nitric acid whichis kept cool, it dissolves therein without giving off nitrous vapours. Thissolution is precipitated by water, yielding a red substance soluble in alkalies.When crystallised orcine is placed under a bell-jar, close to a vessel containingnitric acid (sp. gr. 1-3S4), it becomes first brown, and then red. This changeproceeds for some days. The substance thus produced differs essentially fromorcine ; it dyes silk and wool red, without requiring any mordant. Ammoniachanges this colour temporarily to a violet; fixed alkalies do so permanently,but acids restore the original colour.! On treatment with a large excess ofconcentrated sulphuric acid, and exposure to a temperature of from 60° to 80°,orcine becomes black. If water is added to the acid after cooling, and theliquid saturated while cold with carbonate of lead, then filtered, andthe clear filtrate concentrated by evaporation, a crystalline mass is obtainedwhich, if treated with ether, yields orcine. On dissolving the residue inboiling water, re-treatment with carbonate of lead, filtering again, and settingaside the liquid, it yields brownish crystals of basic orcino-bisulphate of lead,

* Laurent and Gerhardt, “ Annales de Chimie et de Physique” f3], vol. xxiv., p. 317.Miller, 11 Ann. der Chem. und Pharm.,” vol. lxviii., p. gg.

t Le Luynes, " Comptes Rendus de l’Acaddmic des Sciences,” vol. lvi., p. 715.