. Lichens. Lichens. LICHENS AS DYE-PLANTS 413 British species), in R. Montagnei and the acid present is erythrin; in R. tinctoria, R. portentosa and R. sinuensis it is lecanoric acid. In R. tinctoria (Fig. 133), according to Ronceray', the acid is located chiefly in the gonidial layer and the soredia but is absent from the cortex and centre. In R. portentosa it is abundant in the cortex and central layer, while scarcely to be detected in the gonidial layer, and it is wanting altogether in the soredia. In R. Montagnei it is chiefly found in the cortex and the gonidial layer, and is
. Lichens. Lichens. LICHENS AS DYE-PLANTS 413 British species), in R. Montagnei and the acid present is erythrin; in R. tinctoria, R. portentosa and R. sinuensis it is lecanoric acid. In R. tinctoria (Fig. 133), according to Ronceray', the acid is located chiefly in the gonidial layer and the soredia but is absent from the cortex and centre. In R. portentosa it is abundant in the cortex and central layer, while scarcely to be detected in the gonidial layer, and it is wanting altogether in the soredia. In R. Montagnei it is chiefly found in the cortex and the gonidial layer, and is absent from the soredia and from the medulla. c. Purple dyes: Orchil, Cudbear AND Litmus. Orseille or orchil is formed not only from erythrin and lecanoric acid (orseillic acid), but also from erythrinic, gyrophoric, evernic and ramalic acids^ and may be obtained from any lichen contain- ing these substances. By the action of ammonia the acids are split up into orcin and carbonic acid. In time, under the influence of ammonia and the oxygen of the air^, orcin becomes orcein which is the colouring principle of orchil; the perfecting of the process may take a month. The dye is used for animal fibres such as wool and silk; it has no effect on cotton. There are several different preparations on the market, chiefly obtained from France and Holland; orchil or orseille in the form of a solution, cudbear (persio of Germany) almost the same, but manufactured into a violet-reddish powder, and litmus (tournesol of France) which is prepared in a slightly different manner. At one time the lichen, broken into small pieces, was soaked in urine; a fermentation process was set up, then lime and potash with an admixture of alum were added. The mass of material when ready was pressed into cubes and dried in the air. Commercial litmus contains three substances, erythrolein, erythrolitmin and azolitmin ; the last named, which is the true litmus, is a dark brown amorphous powder soluble in water, and
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