302 Royal Society. 



III. Roccella Montagnei. 

 By similar treatment yielded — 



1 . Erythric acid C;,, Hjo Og + HO. 



This acid gives a blood-red colour with hypochlorite of lime. 



2. Erythric ether Coo H,o O, +C, H^ O. 



3 . Erythric methylic ether C^, H ,„ O.j + C, H3 O . 



This ether crystalhzes in longer and narrower prisms than erythric 

 ether. 



4. Erythrelesic acid is analogous to alpha- and beta-orsellesic acids. 



5. Picro-erythrine. — By neutralizing erythric acid with lime or 

 baryta, and throwing down erythrelesic acid with muriatic acid, a 

 mother-liquid is obtained containing picro-erythrine, from which that 

 substance may be separated in the form of yellowish crystals ; and 

 these may be purified and decolorized by repeated crystallization from 

 hot water aided by the use of animal charcoal. Picro-erythrine gives 

 a blood-red colour with hypochlorite of lime. 



Its empirical formula is C34 H-j Ojo- 



6. Pseudo-orcine, of which the empirical formula is Cio H,3 0,„. It 

 is obtained by boiling the lime solution of R. Montagnei till it is re- 

 duced to one-fourth of its bulk, passing carbonic acid in excess 

 through the liquid, and evaporating the filtered liquid to the consist- 

 ence of a syrup ; this is introduced into a flask and digested with a 

 laro-e quantity of ether, which dissolves orcine and leaves pseudo- 

 orcine. On being ciystallized two or three times from strong spirit, 

 it is obtained in large shining colourless crystals. Still larger cry- 

 stals may be obtained from an aqueous solution. Hypochlorite of 

 lime has no action upon it. 



The author then gives a mode of extracting the colouring princi- 

 ples of the lichens, so as to make them portable for commercial pur- 

 poses. The extraction might be performed in the country where the 

 lichens grow, by cutting them up into small pieces, macerating in 

 milk of lime, neutralizing with muriatic or acetic acid, collecting 

 the gelatinous precipitate on cloths, and drying it at a gentle heat. 



He also suggests two modes of estimating the quantity of colour- 

 ing matter in the lichens. 



1, By macerating a known quantity of the lichen in milk of lime, 

 and adding bleaching powder of known strength from an alkalimeter 

 till all colour disappears from the liquid, and noting the quantity of 

 solution required. It is thus found that — 



Angola lichen requires 200 measures 1 -00 



American lichen requires 120 . . O'GO 



Cape lichen requires. 35 . . 0'17 



Lecanora Tartarea (from Germany, "I ^^ q.j^2 



near Giessen) requires J 



2. By extracting the lichen with milk of lime, precipitating with 

 acetic acid, collecting the precipitate on a weighed filter, drying and 

 weighing it. 



