T H E 

 LONDON, EDINBURGH and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[THIRD SERIES.] 

 OCTOBER 1848. 



XXXVIII. Some Remarks on the Siibstances discovered by Mr. 

 Stenhouse in the Roccella tinctoria and Evernia Prunastri. 

 By Edward Schunck*. 



IN a paper read some months ago before the Royal Society, 

 *■ Mr. Stenhouse has communicated the results of an elabo- 

 rate investigation of the proximate principles of some of the 

 lichens, especially the Roccella tinctoria and the Evernia Pru- 

 nastri. The multitude of new observations recorded by Mr. 

 Stenhouse in his valuable paper, and the accuracy with which 

 he has examined the composition of the various substances 

 obtained by him, would seem at length to confer on this part 

 of organic chemistry the degree of completeness required in 

 the present state of the science. Nevertheless, on comparing 

 his results with those of his predecessors on this field of in- 

 quiry, it may be asked how it is possible for so many persons 

 to examine the same subject and arrive at such widely differ- 

 ent results ; and some doubt may arise in the mind either as 

 to the skill of some of the investigators, or as to the accuracy 

 of the methods at present employed in organic chemistry. 

 The Roccella tinctoria has now been examined four times, and 

 the discrepancies between the several investigations are very 

 striking. Heeren discovered in it a substance which he called 

 erythrine. Kane obtained from it a substance differing in its 

 properties from Heeren's erythrine, and which he named ery- 

 thryline. In my examination of the plant I found a body 

 corresponding to Heeren's erythrine and Kane's erythryline, 

 but differing in properties from both, and in composition from 

 the latter. To this substance I gave the name of erythric acid. 

 Lastly, Mr. Stenhouse has obtained from different varieties of 

 the Roccella tinctoria no less than three different substances, 

 similar to, but not identical with, those discovered by Heeren, 

 Kane and myself. If, therefore, we are to believe all the 

 * Communicated by the Author. 

 Phil. Mag. S. 3. Vol. 33. No. 222. Oct. 1848. S 



