250 Dr. E. Schunck on the Substances discovered in 



statements of those who have examined the subject, the same 

 plant, according to its varieties and the places of its growth, 

 produces sometimes one, sometimes another, of six different 

 bodies, each of which may entirely supply the place of any 

 one of the others. This circumstance is contrary to analogy ; 

 since it is more common to find plants^differing totally from 

 one another produce the same substance, than to find the same 

 plant in different circumstances secrete different substances. 

 From the Evemia Prunastri, again, Messrs. Rochleder and 

 Heldt obtained lecanoric acid, while to Mr. Stenhouse the 

 same plant afforded evernic acid. There can of course be 

 no doubt that the Roccella tinctoria does in reality produce 

 substances very different from one another according to the 

 place in which it grows. I shall, however, endeavour to show 

 in the following pages that it is possible, by comparing these 

 substances, to find a link by which to bind them together and 

 bring them into harmony with one another. 



Now on comparing together the various colour-giving sub- 

 stances found at different times in the Roccella tinctoria, we 

 shall find that all or several of them have certain properties 

 in common. They all give red colouring matters when dis- 

 solved in ammonia and exposed to the air. In the next place, 

 erythrine, erythryline and erythric acid, all produce, under 

 certain circumstances, a bitter substance; but these circum- 

 stances are not the same with all three, and the bitter sub- 

 stance itself is also different in each case. Erythric acid and 

 the two orsellic acids of Mr. Stenhouse are decomposed by 

 alkalies into carbonic acid and orcine, accompanied in the case 

 of erythric acid, according to Mr. Stenhouse, by another body, 

 viz. pseudo-orcine. Lastly, all these substances agree with 

 one another and with lecanoric acid, in giving, when treated 

 with boiling alcohol, crystallized bodies soluble in boiling 

 water, which have been proved to be aethers. 



It is to the latter circumstance that I wish in the first place 

 to draw attention. Lecanoric acid, erythrine, erythryline, 

 erythric acid, alpha-orsellic and beta-orsellic acid, all give, 

 when treated with boiling alcohol, solid crystallizable aethers. 

 The aether produced in this way from erythrine was called 

 by Heeren, who was ignorant of its true nature, pseudo-ery- 

 thrine. Let us now compare together the composition of these 

 various aethers, as determined by Kane, Rochleder and Heldt, 

 Stenhouse and myself. 



The aether from erythrine consists, according to Kane, of — 



I. II. 



Carbon . . 60'33 60*43 



Hydrogen . 6*20 6*31 



Oxygen . . 33*47 33*26 



