and other Substa?ices derived from Lichens. 499 



formula for lecanorin as ^iven above. If, however, the for- 

 mula Cjg Hg Oc, be taken for anhydrous orcin, and C,6 H,i O7 

 for crystallized orcin, then the decomposition which lecanorin 

 undergoes with alkalies may be expressed as follows: — 



1 atom of anhydrous orcin . . Cig Hg O^ 



2 atoms of water H2 Oj 



2 atoms of carbonic acid . . . Cg O4 



1 atom of lecanorin C,8 Hg O3 



Two atoms of water are furnished by the decomposition of the 

 lecanorin itself, and three more by the fluid, to form from 

 C,e Hg Oo one atom of crystallized orcin, C^g Hj, O7. The 

 combustions which I have made of this substance agree per- 

 fectly with these formulas, but Dumas's analyses of the lead 

 compound of orcin, which I have myself not yet examined, do 

 not coincide with them, unless it be supposed that this com- 

 pound contains acetate of lead, either in chemical combina- 

 tion or mechanically mixed. 



In regard to the numerical results from which the above 

 formulas have been deduced, I shall reserve them for a future 

 occasion, when, having completed the investigation of the 

 whole class of substances of which those here described are 

 only a part, I shall be able to enter more minutely into de- 

 tails, and exhibit the facts and numbers brought to light in 

 their proper connexion and order. I have merely been de- 

 sirous of showing, on the present occasion, that our know- 

 ledge of this series of bodies is far from being complete. I 

 have shown above, that the action of alkalies on lecanorin is 

 twofold ; it consists, first, in abstracting from the substance 

 carbonic acid, a process not requiring the co-operation of the 

 oxygen of the atmosphere; secondly, in inducing in contact 

 with the air the formation of colouring matters. The first 

 action seems to have been overlooked in the case of all the 

 bodies nearly allied to lecanorin. I have found the most com- 

 plete analogy in the case of Heeren's pseuderythrin; and, if 

 I am not mistaken in the interpretation of his statements, his 

 erythrin also undergoes the same decomposition as lecanorin, 

 for the former is converted into erythrin-bitter by the very 

 same agencies by which lecanorin is converted into orcin, and 

 in fact there is the same relation in regard to all general pro- 

 perties between erythrin and erythrin-bilter as between leca- 

 norin and orcin. This circumstance is of some importance, 

 for in order to arrive at a knowledge of the exact composition 

 of such complex bodies as the colouring matters formed by 

 the action of alkalies on these substances, and to understand 

 2 L2 



