A rough assay of lichens for colouring matter may be made by going through the above process on the small scale, a known weight of the lichen being taken, and the precipitated acids being dried at 212' Fahr. and weighed.
A list of the lichens used in the production of pigments, and a woodcut illustrating their general appearance, will be found under LICHENS, in NAT. HIST. DIV.
the acid and other bodies derived from the lichens are numerous, and as a whole have formed the subject of elaborate investigations by Stenhouse and Schunck. Their relations to each other, however, are at present not very well ascertained ; and although Gerhardt has pro posed formulae calculated from the analyses and the provisional empi rical formulae given by the chemists who have examined theni, he admits that those formula still require verification, and indicates that fact by placing a note of interrogation after the formula.
1. Chroophanic acid Vulpinie .—This acid is contained in wolves' lichen (Evernia vulpine), in vilely moss (Parmelia pavietino), as well as in the different Varieties of rhubarb. [CURTSOPIIANIO Am.] 2. Usnic kcid ; Csuein ; body is obtained on treating the Jupiter's-beard, Tree-beard, and other hair-like members of the Usnea,gOnud of lichens, with thin milk of lime, in the manner already described: The precipitated acid may be obtained in crystals from solution in warm (but not boiling) alcohol. Alkalies convert it into beta-mein. One equivalent of hydrogen in naade acid may be replaced by one of a metal. and aunties. formed.
3. &yank arid and its derivatives, 4, 5, 6, and 7, will be found described In a separate article, [Emsrunic Am.] It exists in largo quantity in many lichens, and ms therefore of more importance than wane other of the lichen acids.
S. Lemnos-in Acid Lecansodes.—Thia acid may be extracted from the
Roma., anemia and Leonora tartarat, in the ammo way as described for usnie acid, or by direct treatment of the lichen with other and evaporation of the ethereal liquid. It crystallises in starlike groups of needlea. By long boiling with alkalies, or with lime. lecanoric acid is converted into carbonic acid and orcin; but if ebullition be continued for a short time only, the acid assimilates two equivalents of water, and a new add is formed, to which the name corset& or orsellecie acid (9) has been given. braworates and orsellates have a constitution similar to the mutate& The mediate of ethyl is formed when lecanoric add is boiled for some time in alcohol ; it crystallises in plates or needlea, and when first discovered was called psetiderythrin (10). Amarythrin (11) is a non-crystalline substance resulting from the action of air upon eradiate of ethyL When exposed for many mouths to the air, it IS changed into a granular body, (12) tnlerythrin.
Alp1ia-mm.11in arid, and beta-orsellic add, were obtained by Stenhouse from the INVC114 riactoria ; but their composition and properties are en similar, that Gerhardt thinks them identical, and notices them as ecanoric acid.
13. ParrIlic add, Partllin, is described by Schunk as being met with In the preparation of lecanoric acid. It is slightly soluble in water, and very soluble in alcohol or ether. By slow evaporation it is obtained in colourless, brilliant, and heavy needles. Boiling alcohol does not act upon it, as upon lecanoric or erythric acids, and on this fact depends its isolation and purification. It forms pinnate: with bases.
11. lloccrilinin is also contained in the floccella tinctoria. It very much resembles parellic acid, hut appears to be insoluble in water.