226 



Dr. J. Stenhouse on certain Lichens. 



[Feb. 24, 



extent from that impurity. The solution of calcium cremate is decom- 

 posed by a long-continued current of carbonic anhydride, which precipi- 

 tates calcic carbonate and unaltered eTernic acid. 



On theoretical grounds it has been stated* that, by the action of potassic 

 or baric hydrate, evernic acid should be resolved into orsellinic and ever- 

 ninic acids. This prediction, however, is incorrect, as I find, as formerly 

 stated*, that everninic acid is the only fixed product. 



Tefrabrom-erernic Acid. 

 Perfectly dry and finely powdered evernic acid was treated in the cold 

 with a slight excess of dry bromine, large quantities of hydrobromic acid 

 were given off, aud a brominated compound produced. In order to prevent 

 any portion of the acid escaping bromination, the product was finely pow- 

 dered and again treated with bromine. After standing some time to allow 

 the excess of bromine to volatilize, the finely powdered compound was well 

 washed with bisulphide of carbon, to remove the last traces of bromine, 

 aud a small quantity of a resinous body which is produced at the same 

 time. Two or three crystallizations from boiling spirit render it quite pure. 

 When subjected to analysis, it gave the following results : — 



I. *312 grin, acid gave *362 grm. carbonic anhydride and -067 grm. water. 



II. *32l grm. acid gave '373 grm. bromide of silver. 





■ 





I. 



EL 





= 204 = 



31-48 



31-64 





H * 



= 12 = 



1-SG 



203 





Br i 



= 320 = 



49-48 





4944 



0 T 



= 112 = 



17-28 









648 



100-00 







This analysis agrees very well with the formula C. H : , Br 4 O., four 

 equivalents of hydrogen in evernic acid being replaced by bromine. 



Tetrabrom-evemic acid is rather soluble in hot alcohol, from which it 

 crystallizes on standing some time in small colourless prisms. It is inso- 

 luble in water and bisulphide of carbon, slightly soluble in hot benzol, and 

 readily in ether, which when quickly evaporated leaves it as a transparent 

 colourless resiu ; it melts at 161° C. The acid is rery soluble in alkaline 

 solutions, which on evaporation dry up to a gummy mass. When heated 

 with concentrated sulphuric acid it decomposes. 



Usnic Acid from Evernia prunastri. 

 The usnic acid left undissolved in the preparation of evernic acid usually 

 retained traces of that acid even after repeated treatment with alcohol ; but 

 this was entirely removed by boiling with lime, as described in the first 

 part of this paper. This decomposed and removed the evernic acid and 

 other impurities, leaving the usnic acid in the form of an insoluble calcium 



* Wattes Diet. Chem. voL ii. p. 611.; 



f Ann, der Chem. und Pharm, vol. lxviiL p. 86. 



