924 NEUTRAL COLOURING MATTERS. 



spaniolitmm C 18 H 7 O 16 . It is of a bright red colour, insoluble 

 in alcohol and in ether, and very sparingly soluble in water, 

 which it tinges bright red. 



The blue liquors which are obtained in the first place by 

 digesting litmus cakes in water contain but a small quantity of 

 colouring matter, considering their depth of tint. It is gene- 

 rally azolitmin nearly pure ; with occasionally a small portion 

 of spaniolitmin. 



By the action of chlorine upon orcein, chlororcein is formed, 

 C 18 H 10 NO 8 ,C1, which possesses a yellowish brown colour. With 

 azolitmin a similar compound of chlorine is produced, 

 C 18 H 10 NO 10 ,C1. By the action of nascent hydrogen upon 

 orcein, a colourless body is formed, leucorcein, C 18 H 10 NO 8 ,H. 

 For all these facts we are indebted to Dr. Kane (Phil. Trans. 

 1840, p. 298). 



Cudbear, in German persio, is prepared from the Leconora 

 tar tarea, Parmelia omphalodes, and probably other lichens. 

 The lichen is steeped and left for some time in open vessels 

 covered by ammonia, till the purple .colour is sufficiently de- 

 veloped, and then the whole is dried in the open air and reduced 

 to a fine powder. 



Mr. Schunk has lately obtained by extraction with ether from 

 the Leconora tartarea and other lichens employed in the manu- 

 facture of cudbear a white crystalline substance leconorin, which 

 is dissolved by alkalies and precipitated again unaltered by acids. 

 But if the alkaline solution is allowed to stand for an hour, no pre- 

 cipitate is afterwards obtained, the new substance having resolved 

 itself into carbonic acid and orcin. When the solution of the 

 new substance in barytes-water is heated to the boiling point, 

 carbonate of barytes precipitates and the solution yields by 

 evaporation large crystals of orcin. It is probable therefore 

 that orcin does not exist ready formed in any lichen, but is 

 always the product of the action of an alkali, a circumstance 

 which has hitherto been overlooked. 



Litmus is much used as a re-agent from its susceptibility to 

 the action of acids and alkalies, being reddened by the former 

 and having its blue colour restored by the latter. In preparing 

 litmus paper an infusion is made of commercial litmus, filtered, 

 concentrated by a water bath, and a very small quantity of 

 carbonate of soda added. Good letter paper cut into slips of 



