256 EXPERIMENTS ON ASTRINGENT VEGETABLES. 



Negative galvs- The fame philofopher has alfo obferved a fingular coin- 

 nifm gives the cidence between thefe effects and thofe of galvanifm. He 



fcnfation of red ; . «? 



pofitive of blue, nrj ds that when the eye is placed m contact with the negative 

 conductor of the pile, it fees every object red, bat if placed 

 againft the pofitive conductor it fees them blue : whence-there 

 appears to refult an analogy between the action of the negative 

 electricity and that of the red light, and of the pofitive and 

 the violet light. 



IX. 



An Account of fome Experiments and Obfervations on the Conjli- 

 tuent Parts of certain AJlringent Vegetables ; and on their Ope~ 

 ration in Tanning, By Humphry Davy, Efq. Fro* 

 ftjfor of ' Chemiftry in the Royal Injiitution*. 



S * • difco- ■"■ ^^ difcovery made by M. Seguin, of a peculiar vege- 

 very of the tan- table matter which is eflential to the tanning of fkin, and which 

 nmg matter j j s p (f e fTed of the property of precipitating gelatine from its 

 folutions, has added confiderably to our knowledge of the con- 

 flituent parts of aftringent vegetables, 

 extended by Mr. P rou< ^ nas inveftigated many of the properties of 



Prouftj this fubftance ; but, though his labours, and thofe of other 



chemifts, have led to various interefting obfervations, yet they 

 are far from having exhaufted the fubject. The affinities of 

 tannin have been hitherto very little examined ; and the man- 

 ner in which its action upon animal matters is modified by 

 combination with other fubftances, has been fcarcely at all 

 ftudied. 



„ , , , At the defire of the Managers of the Royal Institution, I 



purfuedbythe . r-r ■ 77. 



author at the began, in September 1801, a ieries or experiments on the lub- 



«kfire of the fiances employed in the procefs of tanning, and on the chemi- 



Royalinftitu- , 7 J , . . ._. r . . , 



^ 0J ^ cal agencies concerned in it. J hele experiments nave occu- 



pied, ever fince, a confiderable portion of my leifure hours; 

 and I now prefume to lay before the Royal Society an account 

 of their general refults. My chief defign was, to attempt to 

 elucidate the practical part of the art; but in purfuing it, I 

 was necelfarily led to general chemical inquiries concerning 

 the analyfis of the different vegetable fubftances containing 

 tannin, and their peculiar properties. 



* From the Philofophical Tranfa&ions, 1803. 



3 I. OBSER- 



