Chemistry. — *'The mutual influence on the electrolytic conductivity 

 of yallic tannic acid and boric acid in connection nnth the 

 composition of the tannins". By Prof. J. Böesekkn and W. M. 

 Dekrns. 



(Communicated in the meeting of November 30, 1918). 



By the researclies of Emil Fischkr ') and others on the poljdepsides, 

 it is now verj probable that the tannin of the gall-nut principally 

 consists of a mixture of the pentadigalloylethers of u- and ji-glucose, 

 in which the two galloyi groups are coupled in such a manner 

 that the carboxyl group of the one tannic acid molecule has been 

 esterified with one of the OH groups in the meta position of the 

 other tannic acid radical, thus: 



HO COO 



H0<^ \ COO <^ \ 

 HO HO OH 



C,H,0 



\i this conception be the right one, then the influence of the con- 

 ductivity of this substance on that of boric acid should be consider- 

 able, viz. should agree with that of five mol. pyrogallol -|- five mol. 

 pyrocatachol per molecule of the tannin. 



Here however two circumstances ought to be consideied. In the 

 first place a solution of the tannin, because of the high molecular 

 weight (db 1700) has the character of a collpidal solution and a 

 priori it is not certain that it will behave like an ordinary solution. 



However a qualitative experiment showed that the increase of 

 the conductivity was considerable, so that tJie solution of the tannin 

 behaved quite normally as regards that phenomenon. 



In the second place the tannin must not be compared with pyro- 

 gallol and pyrocatechol, but with the esters of gallic acid and of 

 protocatechuic acid. 



Therefore we have first measured the influence, which the con- 

 ductivity of the gallic acid methylester exercises on that of boric 

 acid. 



1) Berichte 45, 915 (1912). 



