Inorganic Constituents of Lichens. 47 



cumstances, which is a dirty brown. One of the principal re- 

 commendations of the liquid, not already noticed, is, the cir- 

 cumstance of its being capable of preservation without under- 

 going deterioration, while the test-papers, which have been 

 frequently recommended, although possessing most delicate 

 testing powers when freshly prepared, gradually lose their 

 value by preservation. I believe this to be the explanation of 

 the failure, in this country, of some continental test-papers 

 which have been recently recommended. It would therefore 

 appear that the best test-paper being that which is of fresh 

 preparation, the most convenient source for its production is 

 that from which the colouring substance can be most rapidly 

 procured in an efficient state. The observations which have 

 been made upon parietin, in reference to its colouring powers, 

 tend to show that it may be employed with advantage for the 

 most delicate purposes to which turmeric is applied. Parietin, 

 however, is not acted on by acids ; the natural yellow colour 

 merely becomes brighter, while turmeric, which contains a 

 blue and yellow colouring principle, has the former reddened 

 by acids and the latter converted to a brown by alkalies. 

 Moistened yellow parietin paper, on the other hand, becomes 

 red or purple when freshly prepared — reddish-brown, if long 

 prepared — by coming in contact with ammonia and other al- 

 kalies. The other reactions of parietin are simple. The alco- 

 holic solution is precipitated yellow by nitrate of silver, acetate 

 of lead and other metallic salts. A solution of permuriate of 

 iron renders the colour much darker. The precipitates with 

 silver and lead have not been analysed, from the minute quan- 

 tity of parietin at my disposal. 



The yellow colour of the Parmelia parietina early attracted 

 the attention of those persons interested in dyes. It was ac- 

 curately described by Hoffmann, Amoreux and Willemet, in 

 1786*. The latter informs us that the Swedes in the province 

 of Oeland obtained, by means of this lichen and alum, a yellow 

 dye for woollen stuffs, and that a flesh tint was also procured 

 from it fitted for linen and paper ; that goats eat this lichen, 

 and that Haller recommended it as a powerful tonic in diar- 

 rhoea. He adds, that he had himself used it in his practice as 

 a tisan, and had found it to prove beneficial in that form of the 

 disease which occurs in autumn. Hoffmann states, that in 

 Norway, when boiled with milk, it is used as a remedy in jaun- 

 dice. This idea may have, perhaps, originated from the corre- 

 spondence in colour of the disease and the remedy; upon the 



• Memoires couronnes en I'annee 1786 par 1' Academic des Sciences, 

 Belles Lettres et Arts de Lyon,sur TUtilite des Lichens dans la Medecine et 

 dans les Arts, 8vo, 1 787. 



