PROXIMATE PRINCIPLES OF SOME OF THE LICHENS. 
89 
both a tedious and a costly method. Messrs. Rochleder and Heldt extracted it by 
macerating the lichens with a mixture of ammonia and spirits of wine. This latter 
method succeeds very well, but is also costly, especially in England, where alcohol 
is so dear. I have found that the method already so often described, viz. macc’ating 
the lichens in milk of lime and precipitating with muriatic acid, answers perfectly 
well, and is much to be preferred to either of the preceding methods. It is not ad- 
visable to employ e\t\iev Evernia Prunastri or any of the species of Ramalinea for the 
preparation of usnic acid, as the acid obtained from these lichens is always accom- 
panied with a good deal of resinous brownish colouring matter, which adheres to the 
acid so pertinaciously that it is very diflScult to purify it completely. The lichens I 
prefer for the preparation of usnic acid are the Cladoma Rangiferinu, but especially 
the Usnea Jlorida. The lime solution of these lichens is deep yellow, and the preci- 
pitate thrown down either by muriatic or acetic acid has a bright yellow colour. 
By crystallizing this precipitate repeatedly out of alcohol, aided by a little anitnal 
charcoal, the usnic acid is obtained in large flat crystals of a pale-yellow colour. 
Usnic acid is not readily combustible. 
0 2955 grm. acid dried at 212 °Fahr. and burned with oxide of copper and a stream 
of oxygen gas, gave 0-688 carbonic acid gas and 0-134 water. 
Calculated. 
38 C 2854-56 63-90 
17 H 212-16 4-75 
14 0 1400-00 31-35 
Found numbers. 
63-62 
5-03 
31-35 
4467*00 100-00 
100-00 
Potash Salt. 
The potash salt was prepared in the way indicated by Mr. Knop, by boiling the 
acid with carbonate of potash. The salt crystallizes readily in large plates. 
I. 0-407 grm. salt dried at 212 °Fahr., gave 0-087 sulphate of potash =0-047 Ko 
= 11-55 per cent. 
II. 0-212 grm. salt gave 0-0453 KoSo 3 = 0-0244 Ko= 11-50 per cent. 
The calculated quantity of potash in the salt is 1T66 per cent. 
Usnic acid is oxidized and converted into a dark brown uncrystallizable resin 
when it is boiled for a considerable time with an excess of either potash or baryta. 
The action of chlorine upon usnic acid produces a somewhat similar result. 
Glasgow, January 25, 1848. 
MDCCCXLVIII. 
N 
