198 Dr Thomson on Parietin^ ^c. 



(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 be- 

 came, 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 these observations, which are perhaps in- 

 teresting in an economical point of view, the yellow parmelia 

 was recommended by Dr Sande, probably misled by the co- 

 lour, as a substitute for Peruvian bark, during the last French 

 war. It has also been chemically examined by Herberger, 

 •but not apparently with the same results afforded 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 ex- 

 tracted yellow oil from the lichen, but in such minute quan- 

 tity 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 Qo Hig Ojg, ap- 

 proaching one of the analyses already detailed. So that we 

 have now the following oxides : — 



Oil of Parietin, C40 Hie 



Parietic acid, C40 Hie O12 



Parietin, C40 Hie Ou 



Oxide of Parietin, C40 Hie Oie 



Glasgow College, Dec, 1843. 



* Kongl. Vetenskap, Acad. xii. p. 300, Ann. 1791. 



