CRUDE DRUGS. 



543 



principle resembling pyrocatechin ; upon fusion with potassium 

 hydrate a phenol similar to protocatechuic acid is formed; dilute 

 solutions are colored olive-brown with ferric chloride and possess 

 a slight fluorescence ; alkalies give a deep red color to the solutions 

 which also have a decided blue fluorescence. 



Fig. 238. 



Elm bark, the specimen to the right with the periderm removed 

 representing the official bark. 



Allied Plants. — Qnercus roher, indigenous to Europe, is 

 the source of the bark used in England and Continental Europe; 

 the bark closely resembles that of Quercus alba, but the periderm 

 is not removed; it contains from 10 to 16 per cent, of tannin, 

 besides gallic and ellagic acids. Qnercus velutina, or black oak, 

 yields the quercitron bark, which resembles that of Quercus alba 



