LICHENS AS DYE-PLANTS 



413 



British species), in R. Montagnei and R.peruensis 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 

 forming a blue solution with alkalies. 



• Ronceray 1904. ^ Zopf 1907. 



' Zahlbruckner (1905, p. 109) quotes from Czapek a statement that orchil fermentation is brought 

 about by an obligate aerobic bacillus. 



F'g' 133- Roccella tinctoria Ach. 

 the Cape of Good Hope. 



From 



