and other Substances derived from Lichens. 497 



off and the residue treated with boiling water, which dissolved 

 all the pseuderythrin and deposited it on cooling. The mass 

 left undissolved was washed with sther, which dissolved all 

 the chlorophyll and left behind the fatty substance mentioned 

 above, which was purified by re-dissolving in alcohol. 



1 will now proceed to a more minute description of the 

 properties of these several bodies. 



Leca7iorin. 



This substance, when pure, is perfectly white. If prepared 

 in the manner described above, it has the appearance of a 

 white mass composed of acicular needles. When its solutions 

 are slowly evaporated, it crystallizes in silky needles grouped 

 together in star-shaped masses. It is insoluble in boiling 

 water, but soluble easily in alcohol and aether. Its solutions 

 redden litmus paper. It is soluble in alkaline liquors, from 

 which it is precipitated unchanged by acids, provided the so- 

 lutions be not boiled and be not left to stand too long. It is 

 insoluble in all weak acids, with the exception of acetic acid. 

 Strong nitric acid converts it ultimately into oxalic acid. It 

 combines with metallic oxides by double decomposition. 

 Heated on platinum foil it melts, emits a dense vapour, and 

 burns off, leaving but little carbonaceous residue. When 

 heated in a tube closed at one end, it melts, and, under violent 

 ebullition, gives off a dense vapour, which condenses in the 

 upper part of the tube into a thick liquid, which after some 

 lime solidifies, forming a crystalline mass. The nature of this 

 sublimate will be explained further on. 



The action of the alkalies on this substance is of course the 

 most interesting point connected with its history. A solution 

 of lecanorin in ammonia when exposed to the air, acquires 

 after some time a beautiful deep purple colour: from this 

 solution acids precipitate a red colouring matter. A solution 

 in potash, under the same circumstances, becomes of a deep 

 red colour. Being desirous of ascertaining whether the leca- 

 norin was immediately converted into the red colouring mat- 

 ter, or whether it passed first through any intermediate state, 

 which was not improbable, I dissolved some of the substance 

 in ammonia, excluding the solution from contact with the air. 

 After a lapse of some hours, the solution, though perfectly 

 colourless, was found no longer to contain any lecanorin ; for 

 acids, instead of producing a thick gelatinous or flocculent 

 precipitate, as they do when applied immediately after solu- 

 tion has been effected, merely caused a brisk effervescence of 

 carbonic acid, plainly showing that the substance had been 

 completely decomposed without a colouring matter having 



Phil. Maii. S. 3. Vol. 20. No. 133. June lbl-2. 2 L 



