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

 mother-liquid is obtained containing picro-erythrin, 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-erythrin gives 

 a blood-red colour with hypochlorite of lime. 

 Its empirical formula is C34 Ho^ OgQ. 



6. Pseudo-orcin, of which the empirical formula is Cio Hjg Oiq. 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 

 large quantity of ether, which dissolves orcin and leaves pseudo- 

 orcin. On being crystallized 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 .. 0'60 



Cape lichen requires 35 . . 0'17 



Lecanora Tartarea (from Germany, 

 near Giessen) requires 



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

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

 weighing it. 



IV. Evernia Pj^iinastri. 



1 . Evernic acid is obtained by extracting the lichen with milk of 

 lime, precipitating with muriatic acid, dr}'ing the precipitate, and 

 digesting in weak spirit till nearly two-thirds are dissolved. The 

 solution yields crystals of evernic acid. The insoluble part is usnic 

 acid. Evernic acid yields only a slight yellow colour with hypo- 

 chlorite of lime. 



Formula of hydrated evernic acid , . C34H15O13 + HO 

 Formula of everniate of potash .... C34 H15 O13 + KO 

 Formula of everniate of baryta .... C34 H15 Oi3 + BaO + Aq. 



2. Evernesic acid is obtained by dissolving evernic acid in a slight 



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