COLOURING MATTERS OF LICHENS.

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upon a sieve; a whitish starch-like powder is thus obtained, which, on beingtreated with ammonia, yields a colour far purer and more beautiful than thatobtained by the maceration of the whole weed.

Before we can further enter into the details of the orchil manufacture, wehave to turn our attention to the remarkable discoveries made by chemists inthis field, since upon these the improved methods of applying the lichens asdye-materials are based.

Chemical History of the Colouring Matters of Lichens.

M. Robiquet succeeded, in 1849, in extracting from the Variolaria dealbata acolourless, crystalline, saccharine, yet astringent, substance, which he termedorcine. He found, also, that orcine, under the influence of air and ammonia,fixes nitrogen, and becomes converted into a violet-coloured matter. Thecomposition of orcine and of the orceine thence derived were investigated byDumas, who also found the clue to the precise reaction which accompaniesthe formation of orceine from orcine. Kane proved that orceine is not theonly colouring substance formed by the transformation of orcine/ The re-searches on this subject carried out by Heeren, Schunck, Stenhouse, Rochleder,Hesse, De Luynes, Menschukine, Grimaux, and others, have led to the dis-covery and examination of several acids pre-existing in the lichens, which,under varying conditions, split up into orcine and other substances of no in-dustrial moment.- From these researches we learn that the existence ofready-formed orcine in the lichens is the exception, since it is only formedwhen the lichens are treated, and as soon as developed it is furthermodified.

Although the chemical history of these acids is not fully elucidated,they have been sufficiently studied to admit of their rational formulae beingestablished and their relations indicated. The acids are—

1. Erythric acid, or erythrine, C20K22O20, yielding, as immediate deriva-

tives,—(a), picroerythrine, C^H^O;; ( b ), orsellic acid, CsH80 4 : picro-erythrine splits up into—(«), erythrite or erythromannite, C 4 H io 0 4 ;(b), orsellic acid, which in its turn is split up into carbonic acid, C0 2 ,and orcine, C 7 H 8 0 2 .

2. Lecanoric acid, lecanorine, a or /3 orsellic acid, di-orsellic acid, C^H^O/;'

it is decomposed into orsellic acid, C8H 8 0 4 , without production oferythrite- or picroerythrine.

3. /3-Erythrine or /3-erythric acid, C 2 iH 24 O io , a higher homologue of

erythrine: its products of decomposition are — (rt), orsellic acid;(6), /3-picroerythrine, C13H16O6, which differs from its homologue, picro-erythrine, C^H^O;, by having H 2 0 less: it (viz., the /3-picroerythrine)is split up into erythrite and a mixture of carbonic acid, and /3-orcine,C 8 H 10 0 2 , which, by combining together, form ( 3 - orsellic acid,—that isto say, a higher homologue of the orsellic acid : /3-orcine is a homologueof orcine.

4. Evernic acid, Ci 7 Hi 60 7 , the superior homologue of lecanoric or diorsellic

acid ; it is decomposed into orsellic and evernic, or /3-orsellic acid, thehomologue of the first, CgHj 0 0 4 .

5. a and (3 Usnic acids, isomeric with and homologues of evernic acid,

Ci 8 H'r80 7 ; it is also called di-/3-orsellic acid. Since it yields, when