RICHARDS, COLLINS, AND HEIMROD. COPPER AND SILVER. 141 



The latest work which has corae to our notice is that of Patterson and 

 Guthe.* In this paper the authors give the lion's share of their attention 

 to an admirably worked out treatment of the physical methods necessary 

 for fixing the electrical units, and pay little heed to the chemical side of 

 the question. Since they obtained constant results by treating their 

 electrolyte with argentic oxide, they recommend this method for general 

 use, in spite of the fact that both Rodger and Watson and Kahle have 

 shown that such treatment probably yields too high results. 



The essence of all these investigations, as far as they concern the 

 irregularities of the silver voltameter, may be summed up in the follow- 

 ing words. 



A substance which causes the deposition of too much silver seems to 

 be formed around a large anode. Oxygen tends to eliminate this sub- 

 stance, hence the substance must be a reducing agent. All the phenom- 

 ena agree with this interpretation. A very small anode (which causes 

 another irregularity, namely, the formation of argentic peroxide) may 

 result in the appearance of a lower weight of silver; perhaps argentic 

 peroxide may oxidize the reducing substance and thus remove it. The 

 formation of the reducing substance is accompanied by the liberation of 

 hydrogen ions in dilute solutions of argentic nitrate; but in stronger 

 solutions small amounts of acid may be neutralized. In warm solutions 

 the reducing agent is somewhat more active than in cold. 



An important point is left in doubt : — Does the acid appear at the 

 anode or the cathode ? Nothing could be easier than to answer this 

 question ; and a large number of trials in which the anode was enclosed 

 in a porous cup showed conclusively that the acid was always formed at 

 the positive pole. The solution around the cathode remained wholly 

 neutral to methyl orange, while the liquid within the cup gave a strongly 

 acid reaction. 



In marked contrast with the case of copper, the chief disturbing re- 

 actions seem then to exist at the point at which the positive electricity 

 enters the solution ; and the obvious remedy for the irregularity is to 

 enclose this positive electrode in a cell which will permit conductivity 

 but will shut out convection. 



Experimental Details. 



Small cylinders of Pukal's porous ware (Berlin), such as are used for 

 osmotic pressure experiments, were found to serve admirably as the 



* Physical Review, 7, 251 (1898). 



