358 OllSELLIC ACID. 



cules water of crystallization ; fusing point above 220 ; 

 gives no reaction with iron chloride. 



2. Orsellic Acid. 



( (OH) 2 

 C 8 H 8 4 = C 6 H 2 \ CH 3 



( CO.OH. 



Is formed by boiling erythrin with baryta-water and 

 by heating a neutral solution of lecanoric acid in lime- 

 water. Colorless prisms, soluble in water, alcohol, and 

 ether; fuses at 176, undergoing decomposition into 

 carbonic anhydride arid orcin (p. 307). Its solution is 

 turned purple by iron chloride. 



Erythrin (Erythrite biorsellate), C 20 H 22 10 = 

 C 4 H 8 (C 8 H 7 3 ) 2 4 . Is contained in the lichen Eoccdla 

 fuciformis, which is employed in the manufacture of 

 archil (p. 308). It can be extracted from this by 

 means of cold milk of lime. The solution is decom 

 posed rapidly with carbonic acid ; and the erythrin ex 

 tracted from the precipitate with alcohol. Crystalline, 

 globular mass with 1J molecule water of crystalli 

 zation. Almost insoluble in cold water, difficultly so 

 luble in hot water, easily soluble in alcohol. When 

 boiled for a long time with water or baryta, it is de 

 composed into orsellic acid and picroerythrin (erythrite 

 monorsellate), C 12 H 16 7 + H 2 0, which forms colorless, 

 bitter tasting crystals, that are easily soluble in water 

 and alcohol. By continued boiling of erythrin with 

 baryta there are formed carbonic acid, orcin, and 

 erythrite (p. 180). 



Lecanoric acid (Diorsellic acid), C 16 H 14 7 + IPO. 

 Occurs in several lichens, belonging to the genera Roc- 

 cella, Lecanora, and Variolaria. It can be extracted 

 from these by means of ether or milk of lime, and is 

 then precipitated by hydrochloric acid. Crystallizes 

 from alcohol and ether in colorless prisms ; almost in 

 soluble in water. Dissolved in lime or baryta water 

 and boiled, it is at first converted into orsellic acid; by 



