74 0N GALVANIC BATTERIES. 



ploy next a slip of copper of a conical shape; and on re- 

 versing it, a very striking difference will be observed. When 

 the small end of it is placed in the glass containing the zinc 

 wire, no greater effect will be apparent, if it present nearly 

 the same surface, than when the copper wire was used as 

 the connecter ; but, when the broad end occupies the same 

 situation, the effect in decomposing water will be found in- 

 creased to a very considerable degree. This experiment 

 appears to prove, that the copper surface, in galvanic bat- 

 teries, ought to be greater than the zinc surface, in order to 

 produce the greatest possible effect. 

 Eflcets of a I shall conclude my present letter by mentioning a curi- 



rv interacted ous anoma ty w * tn respect to the agency of mercury in gal- 

 ley a coating of ranic combinations, which I do not recollect to have before 

 JJJJy ' & e seen noticed. For the purpose of showing the decomposi- 

 tion of water by galvanism, I have been accustomed to 

 employ wires of various metals connected with zinc, using 

 dilute muriatic acid as the oxidating medium ; and have 

 found silver, copper, bismuth, cobalt, arsenic, as well as 

 many others, answer the purpose extremely well. In mak- 

 ing the experiment at one of my lectures some time ago, 

 however, I was surprised to find, that the usual effects were 

 not produced, and was very long at a loss to conceive, what 

 could be the cause of so curious a circumstance. By an 

 attentive examination of the phenomena, I perceived, that 

 the wire which ought to have furnished the hidrogen had 

 become coated with a white matter, which, on subsequent 

 research, proved to be mercury, and had been obtained 

 which arose from the reduction of corrosive sublimate, which entered, 

 fio** *e »«»- as an impurity, into the composition of the muriatic acid 

 contaminated I had employed. Since that period, the accident has hap- 



by corrosive pene( j to me twice, in distant places, from the same cause ; 



sublimate. p . ' r . , 



^ v . .. a fact, which seems to point out corrosive sublimate as a 



This impurity * ... 



wore common more frequent ingredient in marine acid, than might be at 



t*an:suspccted. first suspected. This experiment contributes to the support 

 of an opinion, that galvanic effects are not entirely depend- 

 ent upon the relative oxidubility of the metals employed, as 

 has been hitherto generally supposed; for although, in the 

 ab*>vc case, the quicksilver was nearly as oxidable as the 



metal 



