On two new Classes of Galvanic Conductors. 297 

 rubbing it on the skin, we feel an efiect similar to that pro- 

 diiceii by a resin dissolved in alcohol. 



It is not without difiiculty, as may well be supposed, 

 that we succeed in ascertaining correctly the nature oi the 

 gallic acid. Does this acid exi*t completely formed in gall- 

 nuts ? May we regard it as a particular acid ; or rather, is 

 it not the result of the combination of a vegetable acid 

 with tannin, with extractive matter, or with other sub- 

 stances existino- in gall-nuts ? These are questions which 

 still remain to be resolved. I endeavoured, by a course 

 of exper'ments, to add some facts to those already known; 

 .and if they do not as yet lead to a complete solution, I think 

 that we shall find in them some new results, ar least, which 

 will serve to ascertain the nature and properties of the gallic 

 acid. \ 



[To be continued.] 



XLI. Extract of a Memoir tipon two new Classes of Gal- 

 vanic Conductors. By M. Erman, of Berliri*. 



Xhe anomalies of the conductory faculty arc so strongly 

 evinced in galvanic electricity, that they have furnished ar- 

 gunjents to those who have attempted to refer phaeno- 

 mena of this kind to a principle essentially different from 

 electricity. The examination to which I submitted a great 

 number of substances relatively to the phenomena they pre- 

 sent, when we employ them to close the galvanic circle from 

 one pole to the other of the pile, has furnished nie with an- 

 swers to some of these arguments; but I obtained from tliem 

 a nmch more precious result ; since I convinced myself that, 

 in this kind uf effects, all possible combinations are realised, 

 A given substance being applied to the two poles of the 

 pile, there constantly happens one of five things : 



1 . This substance, not acting separately upon any of the 

 poles, leaves them therefore perfectly insulated, when we try 

 to put them in conflict by its intermedium; whence it results 



• From /!„„;ln ilc Chimie, tom. 1x1. p. Vlfi. Thh memoir gained the an- 

 nual prize on ^.ilvanisnn given liy the French Institute. 



