1862.] 263 



VIII. " Additional Observations on the Proximate Principles of 

 the Lichens." By JOHN STENHOUSE, LL.D., F.R.S. Re- 

 ceived October 3, 1862. 



The Lichens on which I have recently been experimenting are two 

 in number, namely, the South American variety of Roccella tinctoria, 

 which is imported in considerable quantities from the neighbourhood 

 of Lima and Valparaiso, and is known in commerce as " Lima weed ;" 

 and the Roccella tinctoria var. fuciformis, the same which I had 

 formerly designated Roccella Montagnei ; it is the " Angola weed " 

 of commerce. 



Soon after the publication in 1848 of my first paper on this subject, 

 Dr.Schunck* threw out the hypothesis that the various compounds 

 produced by boiling lecanoric, erythric, alpha- and beta-orsellic 

 acids with alcohol were all one and the same ether the pseudo- 

 erythrin of Heeren. No further light was thrown upon this obscure 

 subject till the publication of Hesse's able paper in the March 

 Number of Liebig's ' Annalen' for 1861. The Archil-lichen which 

 Professor Hesse investigated was that from Angola. He extracted its 

 colour-yielding principle to which, from its feeble acid properties, 

 he restores the name of erythrin originally given it by Heeren by 

 treating it with milk of lime, arid precipitating either with carbonic 

 or hydrochloric acid. On drying and boiling the erythrin with strong 

 alcohol, he produced the ether which he terms orsellinic ether, the 

 composition and properties of which he found to correspond precisely 

 with those which Schunck and I had previously ascertained. Hesse's 

 formula for this ether is 



C 10 tH,(C 4 H,)0.. 



By treating it with chlorine and bromine, he succeeded in replacing 

 two equivalents of hydrogen by these elements, producing what 

 he termed the bichloro- and bibromo-orsellinic ethers. I have re- 

 peated Hesse's experiments, so far as the preparation ofthebibromi- 

 nated ether is concerned, and find, as will be seen by the subjoined 

 analyses, that his statements are perfectly correct. 



I. 0*7960 grm. substance, dried in vacua over sulphuric acid, 

 gave in the usual manner 0-8390 grm. Ag Br. 



* Philosophical Magazine, October 1848. f C=6 &c, et wq. 



