On Substances contained in the Roccella tinctoria. 26 1 



but since/ 6 must be periodical, a and b will be imaginary; 

 let therefore a = m + n */ — 1 and b=m—n V—l. Then 



/^^'{AcosMfl + Bsinwfl} ; 

 and that this may be periodical m must = 0. Also, since 



/«+/(« + «) = <>, 

 n is restricted to be an odd integer. 



Also when 0=0/0 = 1, .-. A= 1 ; and when = | /0 = 0. 



But n being odd cos n — = sin w - = ± 1. Hence B=0, 



and therefore 



/ = cos w ; 



but cos w =0 when w = -, or = — - ; but/0 cannot=0, 

 for < -. Hence n is restricted to be = 1, and therefore, 



35 



finally, 



/0 = COS0. 



XLIII. Ow Me Substances contained in the Roccella 

 tinctoria. By Edward Schunck, Esq.* 



f I TIE Roccella tinctoria derives its interest from the fact of 

 ■*■ its being that species of lichen from which the finest 

 kind of archil is prepared. It has been examined by Heeren 

 and Kane. The former discovered in it a peculiar substance, 

 which he called Erythrine, and a fat acid named by him jRoc- 

 cellic acid. The latter extracted from the plant a substance 

 which he called Erythriline, similar in properties to Heeren's 

 erythrine, and a body to which he applied the name of Ery- 

 thrine, but which possesses all the properties of the substance 

 called by Heeren Pseuderythrine, and supposed by him to be 

 a product of the action of boiling alcohol on his erythrine 

 My results do not agree entirely with those of either of these 

 chemists. 



The lichen which I employed for my investigation was ob- 

 tained from Angola and Madagascar, and was pronounced by 

 a distinguished botanist, to whom I submitted it, to be the 

 Roccella tinctoria var. fuciformis. In order to extract the 

 various substances contained in it, I submitted it to the fol- 

 lowing operations : — 



Communicated by the Chemical Society; having been read April 6, 

 1846. 



