464« Royal Society. 



turers of archil, though the quantity of colouring matter contained 

 in it is by no means considerable, being little more than a twelfth 

 of that in the Roccella Montagnei. The Gyroplwra pustulata, on 

 which the author operated, was brought from Norway, where it is 

 annually collected in considerable quantity for the manufacture of 

 archil. The colouring principle was extracted by maceration with 

 milk of lime, and was precipitated in a gelatinous state by neutral- 

 izing the lime solution by muriatic acid precisely in the way so fre- 

 quently described in the author's former paper (Phil. Trans. 18i8). 

 The precipitate was gently dried, and then dissolved in hot spirits 

 of wine. On the cooling of the liquid, the colouring principle was 

 deposited in small soft crystals, which by digestion with animal 

 charcoal and repeated crystallizations were rendered quite colour- 

 less. This principle, to which the author has given the name of 

 Gyropfioric acid, is almost insoluble in either hot or cold water, and 

 is also much less soluble in hot spirits of wine than either orsellic, 

 erythric, or any of the analogous colouring principles. It is neutral 

 to test-paper, and possesses no saturating power, as the smallest 

 quantity of an alkali gives its solutions an alkaline reaction. Gyro- 

 phoric acid strikes a bright red fugitive colour with hypochlorite of 

 lime; and when macerated with a solution of ammonia, it is slowly 

 converted into a purplish-red colouring matter, similar to that 

 yielded by the analogous acids under the same circumstances. When 

 subjected to analysis, the formula of gyrophoric acid was found to 

 be C36 His O15. 



Gyrophoric acid when boiled for some hours in alcohol yields an 

 ether similar in appearance and properties to the erythric and leca- 

 noric ethers ; its formula is C4 H5 O -|- C.,6 H,8 O15. 



Gyrophoric acid unites with the alkalies and metallic oxides, but 

 the compounds which it forms possess little stability and cannot be 

 procured of an uniform composition. 



Lecanora tartarea. 

 This lichen, like the Gyrophora pustulata, has been employed 

 from an early period in the manufacture of archil. It is found in 

 considerable abundance in the hilly districts of the northern parts 

 both of Scotland and Ireland. The lichen on which the author 

 operated came from Norway. He found it also to contain gyro- 

 phoric acid, in much about the same quantity as the Gyrophora 

 pustulata. This fact was established by the analysis of the acid 

 itself and of its ether compound. 



Brom-orcine. 

 In the author's former paper on the proximate principles of the 

 lichens, read before the Royal Society on the 3rd of February 1848, 

 he described a crystalline body obtained by cautiously adding bro- 

 mine to an aqueous solution of orcine. In this second part he 

 states that, in the ' Comptes Rendus' for August of the same year, 

 Messrs. Laurent and Gerhardt describe the very same compound 

 obtained in precisely the same way, without even hinting that it had 

 been previously discovered. These gentlemen however give a dif- 

 ferent formula for the compound, viz. CnHaBrjO^, or orcine ia 



