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XV. — Contributions to the Chemical History of Archil and of Litmus. By Robert 
Kane, M.D., M.R.I.A. Communicated by Francis Baily, Esq. V.P.R.S . , Sfc.fyc.fyc. 
Received April 30, — Read June 4, 1840. 
Among the numerous and complex questions as to the constitution of organic 
substances, which have latterly attracted the attention of chemists, there is scarcely 
one possessed of more interest to the manufacturer, as well as to the philosopher, and 
the elucidation of which might better be expected to lead to improved processes in 
the arts, or to throw more light on difficult points of abstract theory, than the study 
of the nature and mode of origin of those remarkable colouring materials which form 
the basis of the archil and litmus of commerce, and which are obtained from lichens 
of various genera and species, themselves totally devoid of colour. 
Although the problem of the origin and nature of these bodies has never been con- 
templated by chemists in the general point of view, by which alone consequent and 
satisfactory results could have been arrived at, yet from a very early period in 
organic chemistry, attention had been directed to isolated portions of it, particularly 
with regard to litmus, which from its general use as a reagent excited curiosity, and 
became the subject of frequent, though incomplete examination. Indeed, the nature 
of litmus appears to have been to many chemists peculiarly obscure, as notwithstanding 
the researches ofFouRCROY and Vauquelin, of Tennant, Chevreul,Peretti,Desfosses, 
and many others, Berzelius declared in the last year that the chemistry of litmus 
remained yet to be created. Regarding archil, still less knowledge has been obtained. 
I am not aware of any writer who has occupied himself directly with its examination; 
and, indeed, it is only incidentally that Heeren mentions, in his admirable memoir 
of the lichen products, any facts belonging to the substance found in commerce. 
The origin of those beautiful colouring materials from the different kinds of colour- 
less lichens has, however, formed the subject of extensive and connected investiga- 
tion, for which we are indebted to Heeren and to Robiquet; and it will be found 
useful in the subsequent portions of the present paper, to notice briefly the results to 
which those eminent chemists arrived. Heeren analysed particularly the lichens 
Parmelia Roccella, and the Lecanora Tartarea. He found therein a peculiar body 
which he termed Erythrine, as being the basis of the red substances. This erythrine 
appeared by boiling in alcohol to be changed into another Pseudo-erythrine, and by 
exposure to the air, into a material soluble in water, which he called Erythrine-bitter. 
By acting on erythrine or erythrine-bitter with ammonia and exposure to air, there 
were produced in his experiments three substances, one, yellow, which he did not 
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