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IV. Examination of the proximate Principles of some of the Lichens. 
By John Stenhouse, Esq., Ph.D., Glasgow. 
Communicated hy Thomas Graham, Esq., F.R.S., 8^c. 
Received January 27, — Read February 3, 1848. 
The examination of the proximate principles of the lichens, especially of those 
which yield red colouring matters with ammonia, attracted the attention of some 
very eminent chemists at a comparatively early period in the history of organic 
chemistry, and by the labours of Messrs. Robiquet, Heeren, Dumas and Kane, very 
considerable progress was made in their investigation. Within the last four or five 
years, Messrs. Schunck, Rochleder, Heldt and Knop have resumed the subject and 
greatly extended our acquaintance with this interesting but rather difficult depart- 
ment of organic research. It is but justice to Mr. Schunck to state that he has been 
by far the most successful cultivator of this field, and that he has done more to 
elucidate it than any of his predecessors. 
Nearly two years ago my attention was directed by Dr. Pereira to a kind of 
Orcella weed which had been recently imported into London from the Cape of Good 
Hope, but which had been rejected by the London archil manufacturers as unfit for 
their use, from the small quantity of colouring matter it yielded when subjected to 
the usual process. The lichen was of considerable size, from eight to ten inches 
long, and was pronounced by an eminent botanist. Dr. Scouler of Dublin, to whom 
I submitted it, to be merely a large variety of the Roccella tinctoria. I soon ascer- 
tained on a very cursory examination, why the lichen had been rejected by the archil 
makers, for it only contained a small portion of a crystalline principle which yields 
a red colour with ammonia ; I found in its stead, however, a considerable quantity of 
another crystalline body on which ammonia had no action, and which appeared to 
have been hitherto undescribed. As it seemed important to ascertain whether or 
not the red dyes obtained from the various lichens resulted from the action of am- 
monia on the same crystalline principle, described by Mr. Schunck under the name 
of Lecanorin, I procured quantities of the several lichens usually employed by the 
archil makers, and subjected them to investigation. These lichens consisted, — 1st, of 
a large species of Roccella tinctoria from the west coast of South America ; 2nd, of the 
R. tinctoria from the Cape of Good Hope ; 3rd, of the R. Montagnei from Angola ; 
and 4th, of the Lecanora tartarea. I had made considerable progress with the 
investigation of these lichens, and also with that of the Evernia primastri, when Mr. 
Schunck’s elaborate paper on the Angola lichen appeared, from which it was evident 
that at least two varieties of the red colouring principle existed in these liciiens. 1 
now therefore proceed to give a detail of the results of these examinations. 
