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LXXIV. On some of the Substances contained in the Lichens 

 employed for the preparations of Archil and Cudbear. By 

 Edward Schunck, Esq., Majichester^. 



/^UR knowledge concerning that department of organic 

 ^-^ chemistry which embraces the colouring matters, and 

 other principles nearly allied to them, is of the most imperfect 

 kind. Though many other branches of organic chemis- 

 try have been so thoroughly and accurately investigated, 

 that little or nothing remains to be known concerning them, 

 this may be called an unexplored field. Most of the co- 

 louring matters are so little known, as I'egards even their 

 most essential characters, as not to allow us either to justify 

 or to question the propriety of throwing them together into 

 one general class ; a class distinguished from those nearly 

 allied to it merely by the (as far as we know) adventitious cir- 

 cumstance of the substances belonging to it being endowed 

 with certain more or less vivid colours. Among all the co- 

 louring matters there are none, the study of whose properties 

 and reactions is calculated to throw more light on the nature 

 of the whole class, than those which are prepared by an arti- 

 ficial process from certain kinds of lichens, and on this account 

 it is desirable that they should be carefully examined. It was 

 the circumstance of these substances being prepared artificially 

 from plants perfectly devoid of colour that first attracted to 

 them the attention of chemists, and led to a series of investi- 

 gations by which a number of highly interesting substances 

 was brought to light, and a process elucidated which belongs 

 to the most remarkable and unparalleled in the whole range 

 of organic chemistry. 



Robiquet first discovered a colourless crystallizable sub- 

 stance in them (orcin), capable of being converted by the 

 joint action of ammonia and oxygen into a true colouring mat- 

 ter, which contains neither the original substance nor ammo- 

 nia as such. This interesting discovery was followed by 

 others. The researches of Heeren made us acquainted with 

 a series of substances contained in the Roccella titictoria, pos- 

 sessed of the same property, and another substance, phlorid- 

 zin, was shown by Stas to bear a complete analogy to orcin 

 in this respect. The subsequent labours of Dumas, who sub- 

 jected orcin and the bodies derived from it to an accurate 

 examination, and of Kane, who has determined the compo- 

 sition of the substances discovered by Heeren, and of the co- 

 louring matters contained in archil and litmus, seemed to have 



* Communicated by the Clicmical Society, having been read January 4, 



