Dr. R. D. Thomson on Parietin, a Yellow CdUmring Matter, 191 



disease which occurs in autumn. Iloflfmann states, that in Norway, 

 when boiled with milk, it is used as a remedy in jaundice. This idea 

 may have perhaps originated from the correspondence in colour of the 

 disease and cure, upon the principle so much in vogue at present, 

 " similia similihm curantur.'* Hoffmann aflBrms that he never could 

 obtain a yellow colour from this lichen, but that with wine vinegar he 

 obtained an olive-green or fawn colour ; and with true wine vinegar 

 (aceto vini vera) and copperas, a flesh or apricot shade. Of these 

 colours he has appended to his essay specimens, together with forty- 

 nine others, obtained from various species of lichens. Dr. John P. 

 Westring of Nordkoping, in Sweden, who prosecuted an extensive 

 inquiry into the colouring matter of lichens, describes the Lichen pari- 

 etinus (Wagglaf) as affording, with wool, by infusion for fourteen days, 

 and then boiling for half an hour, a fawn colour; by longer boiling a 

 yellow was produced, and this mixture became, by simple infusion and 

 extraction, similar to the red wool of Florence. With common salt 

 and nitre boiled for an hour, a beautiful straw colour was elicited. 

 Upon silk it gave similar colours, differing in their shade from red to 

 yellow, according to the methods employed in dyeing the goods.* 



Subsequently to those observations, which are perhaps interesting 

 in an economical point of view, the yellow parmelia was recommended 

 by Dr Sande, probably misled by the colour, as a substitute for Peru- 

 vian bark during the last French war. It has also been chemically 

 examined by Herberger,but not apparently with the same results afford- 

 ed by Scotch specimens, as he found no inorganic constituents which 

 amount to from 6 to 7 per cent., according to my trials, and obtained 

 a much larger quantity of colouring matter than existed in any plants 

 examined by me. He also found a red colouring matter, which did 

 not appear in the process of extraction as followed by me, and which 

 may therefore be a product of the oxidation of parietin. More lately 

 still. Dr. Gumprecht extracted yellow oil from the lichen, but in such 

 minute quantity as not to be susceptible of examination. I obtained 

 a quantity of sugar, by means of alcohol, in crystalline grains. 



Note. — Since the preceding paper was read, the yellow needles 

 described above have been analysed in the laboratory at Giessen, and 

 have been found to consist of C40 H,6 0,2, approaching one of the 

 analyses already detailed. So that we have now the following oxides : — 



Oil of parietin, C^ H,. 



Parietic acid, C40 H.e 0„ 



Parietin, C« H,^ Ou 



Oxide of parietin, C40 H.e 0,6 



• Kongl. Vetenakap, Acad. xii. p. 300, Ann. 1791. 



