contained in the Roccella tinctoria. 267 



The decomposition of erythric acid by means of alkalies is 

 therefore as follows : — 



1 equivalent of erythric acid . =0^ H 19 15 

 — 2 equivalents of carbonic acid . = C 2 4 



-f 3 equivalents of water . . . =H 3 3 , gives 



2 equivalents of crystallized orcine = Cg2 H 22 14 . 



Erythric JEther, 



This body has all the properties ascribed to pseuderythrine 

 by Heeren and Kane, and as I found its composition to differ 

 very little from that given by Liebig for Heeren's pseudery- 

 thrine, and by Kane for his erythrine, it can hardly be sup- 

 posed that it is a different body. It is easily prepared by the 

 action of boiling alcohol on erythric acid, in the same way as 

 lecanoric aether from lecanoric acid. Indeed its formation 

 takes place so easily and rapidly in this way, that it is almost 

 impossible to extract erythric acid from the plant by means 

 of boiling alcohol, nothing being obtained by endeavouring 

 to obtain it in this way but erythric aether. In its appearance 

 and properties erythric aether can hardly be distinguished 

 from lecanoric aether, and as its composition in 100 parts 

 happens to be almost the same, the one may easily be mis- 

 taken for the other. Erythric aether is at first tasteless, but 

 after being kept for some time in the mouth, it produces a 

 burning sensation on the tongue. It is soluble in boiling 

 water. If more of the substance be taken than the water 

 can dissolve, the excess melts, forming drops like oil, which 

 sink to the bottom. On cooling the solution becomes milky, 

 and a great part of the aether crystallizes out in needles and 

 plates. It is easily soluble in alcohol and aether. On allow- 

 ing the alcoholic solution to evaporate spontaneously, it is 

 obtained in prismatic crystals. When heated in a tube it 

 melts, and is almost completely volatilized, the vapour con- 

 densing in the colder parts of the tube to a fluid which soon 

 crystallizes. It is soluble in caustic and carbonated alkalies, 

 and in lime and baryta water. From these solutions it is 

 precipitated unchanged by acids, unless they have previously 

 been boiled for a length of time. It reduces nitrate of silver 

 on the addition of ammonia and boiling, and chloride of gold 

 without the addition of any alkali. It gives a precipitate with 

 basic acetate, but none with neutral acetate of lead. On 

 dissolving a quantity of it in caustic potash and subjecting 

 the fluid to distillation, I obtained in the receiver a fluid, 

 from which, on the addition of dry carbonate of potash, a 

 thin layer of alcohol separated, which was easily recognised 

 by its peculiar spirituous smell and its burning with a blue 



T2 



