§ 157. LICHEN ACIDS. 149 



plumhagin'^ (coloured cherry-red by small quantities of alkalies), 

 polygonic acid," quassin^ (whicH is soluble in water, can be removed 

 by shaking with benzene or chloroform. See also § 55), rottlerin^ 

 sicojpinn,^ tanacetin,^ ianghmin,'' taraxacin,^ xylostein,^ xanthosderotin, 

 or sderoxanthin}^ 



§ 157. Lichen Acids and allied Substances. — Amongst the consti- 

 tuents of plants that are soluble in ether a number occurring in 

 lichens may finally be mentioned here. Some of them possess 

 the characters of acids, as, for instance : 



Roccellic acid, which is itself insoluble in water, but forms soluble 

 alkaline salts. It can be detected in the gonidia by alkanna.^^ 



Others are characterized by yielding beautifully coloured com- 

 pounds when acted upon by alkalies, ferric chloride or chlorinated 

 lime, properties that would indicate some relation to orcin and 

 allied bodies. Others, again, possess the chemical characters of 

 ethereal salts, being resolved by alkalies into stronger acids and 

 alcohols. To the former group belong the following : 



Lecanoric acid (diorsellic acid), which is coloured deep red by 

 chlorinated lime (avoiding an excess), and is decomposed at 153" 

 into orcin and carbonic acid.^^ 



Orsellic acid, which undergoes a similar decomposition at 176°, 



^ Compare Dulong, Jahrb. f. Pharm, xiv. 441. 



" Compare Rademacker. 



3 Compare Wiggers, Annal. d. Chem. imd Pharm, xxi. 40, 1837; Gold- 

 schmidt und Weidel, Ber. d. Wiener Akad. Ixxiv. 389, 1877 (Journ. Chem. 

 Soc. xxxiv. 80). See also my 'Ermittelung d. Gifte,' 2nd ed., 300 et. seq. ; 

 and Jahresb. f. Pharm. 619, 1878. Also Christensen, Archiv d. Pharm, xvii. 

 481, 1882. 



* Compare Anderson, Chem. Centralblatt, 372, 1855 (Amer. Journ. Pharm, 

 xxxii. 325) ; Groves, Jahresb. f. Pharm. 161, 1873 (Pharm. Journ. Trans. [3], 

 iii. 228). 



^ Compare Peckolt, Zeitschr. d. Oesterr. Apotheker-Ver. 289, 1876 (Pharm, 

 Journ. Trans. [3], vü. 69). 



^ Compare Leroy, Journ. de Chim. med. xxi. 357 ; Leppig, ' Chem. Unters, 

 d, Tanacetum vulgare,' Diss Dorpat, 1882, 



'' Compare Henry, Journ. de Pharm, x. 52 (Amer. Journ. Pharm, viii. 102). 



8 Compare Kromayer, 'Die Bitterstoffe,' 97 ; and Polex, Archiv d. Pharm, 

 xix. 50, 1840. 



** Compare Hübschmann, Pharm. Vierteljahresschr. v. 197 ; and Enz, ibid. 

 196, 1856. 



1" Compare Dragendorff and Podwissotzki, loc. cit. 



^1 Compare Schunck, Annal. d. Chem. und Pharm. Ixi. 66, 78 ; also Hesse, 

 cxvii. 332, 1861 (Journ. Chem. Soc. iii. 153). 



1* Schunck, Annal. d. Chem. und Pharm, xli. 157, 1842 (Journ. Chem. Soc. 

 i. 71) ; liv. 261, 1845 ; Ixi. 64, 1847 ; Stenhouse, ibid. Ixviii. 57, 1848 ; cxxv. 

 353, 1863 (Journ. Chem. Soc. xx. 221) ; Hesse, cxxxix. 22, 1866. 



