224 



Dr. J. Stenhouse on certain Lichens. 



[Feb. 24, 



insoluble), and recrystallized from boiling spirit to render them quite 

 pure. 



AYhen tbe quantity of acid operated on was but small, the best process 

 was to dissolve it, by means of caustic soda solution, in a large quantity of 

 boiling spirit, filter from the insoluble impurities, and strongly acidulate 

 with acetic acid. The nearly pure usnic acid, which crystallizes out in 

 laree needles when the solution cools, was collected, washed, and recrys- 

 tallized two or three times from spirit. 



L *130 grm. usnic acid gave *298 grm. carbonic anhydride and *060 

 grm. water. 



II. -245 grm. usnic acid gave "504 grm. carbonic anhydride aud *188 









I. 



II. 







= 216 



= 62-43 



62-53 



62 70 



62-80 





= 18 



= 5-20 



513 



4'00 



5-00 



o T 



= 112 



= 32-37 











346 



100-00 









L was purified by boiling with lime, and II. by repeated crystallization 

 of the crude acid from spirit. 



In the analyses published by W. Knop, Rochleder, and Heldt, and also 

 by myself in 1848, the carbon is about */5 per cent, higher than the above, 

 and the formula deduced from it was C i; H.,0_. Hesse* from his analyses 

 proposed the formula C H H i5 O., which I have adopted. 



Usnate of Sodium. 



This was best prepared by adding one part pure usnic acid to twenty of 

 boiling water, and then sufficient caustic soda solution to dissolve nearly 

 the whole of the acid, filtering, and setting aside to crystallize. 



After one recrystallization it was subjected to analysis. 



I. '598 grm. usnate of sodium gave '114 grm. sulphate of sodium. 



II. '864 grm. usnate of sodium gave * 168 grm. sulphate of sodium. 



I. II. Mean. 



C 1S = 216 = 58-70 

 H l7 = 17 = 4-61 



Na = 23 = 6-25 6-18 6'30 6*24 

 O. = 112 = 30-44 



368 100-00 



This salt crystallizes in pale yellow silky needles, is not very soluble in 

 cold water, but more so in spirit. It is readily decomposed by carbonic 

 anhydride ; so much so, that when pure sodium usnate is exposed for some 

 time to the atmosphere, it absorbs carbonic acid, and is no longer com- 

 pletely soluble in water. By passing a current of carbonic anhydride 

 through its aqueous solution, the usnic acid is entirely precipitated. 

 * Ann, der Chem. und Pkann. toL cxvii. p. 345. 



