ORCIN 2Aq.) .Alphaorcin. It has already been stated [LicHENs, colouring matters of] that this peculiar crystalline principle exists to a small extent iu the free state in many of the lichens. It is largely produced, however, when lichens are exposed to the joint influence of heat and alkalies, conditions that always exist in the manufacture of archil, litmus, cudbcar and other colour derivatives of the lichens. Under these circumstances, some acid substances that occur naturally in the lichens are split up into secondary acids and orcin, the latter immediately undergoing further alteration by absorb ing oxygen and nitrogen, and becoming converted into a deep purple or red-coloured body termed orcein. By skilful management the operation may be arrested at any stage, various tints being thus obtained, or orcin itself may be extracted.
Stenhouse gives the following directions for isolating orcin : exhaust the lichens with water containing lime, boil the strained liquor till it is concentrated to about one-fourth its original bulk, separate lime by a current of carbonic acid, filter, evaporate to a syrupy consistence, treat with boiling absolute alcohol, and set aside to crystallise. The orcin thus obtained is usually of a red colour, but may be perfectly decolorised by two or three rccrystallisations from ether.
Pure orcin crystallises in colourless quadrangular prisms, and is very soluble in water, alcohol, or ether. It is neutral to test paper, has a mawkish Aweet taste, loses its two equivalents of water when moderately heated, or when exposed in vacuo, or even when crystallised from anhydrous ether. It sublimes in needles on being slowly
heated in flat vessels; is precipitated white by acetate of lead, and red by perehloride of iron ; is converted first into a resin, and finally into oxalic acid by nitric acid; and gives an Intense purple-red colour, quick!) chang,uig to yellow, with chloride of lime.
Brosissirvia iC„11,11r,0,) was discovered by Stenhouse. It is formed on adding bromine to a concentrated aqueous solution of °rein, and may be obtained in silky needles by crystallisation from dilute alcohol. It Is very fusible, insoluble in water, but soluble in alcohol or ether.
CAlur-orein Ls produced in the same way, and much resembles brom-orcin Ita exact composition has not yet been ascertained.
In the presence of ammonia orcin rapidly absorbs oxygen, and is converted into omits Orcin may be precipitated from its dilute ammoniacal solution by the addition of acetic acid ; it then falls in red flocks, almost insoluble in water, readily so in alcohol and sparingly so in ether. It is very soluble in alkalies, forming rich purple solutions. Its solutions are deodorised by nascent hydrogen and again become coloured by exposure to air, but If ammonia is added before exposure, an abundant white precipitate of kocorcein is thrown down. Leueorcein becomes purple in contact with air.
is n yellowish-brown substance, formed on passing chlorine through water containing orcein. It is insoluble in water, but soluble in alcohol or ether.