RICHARDS AND HEIMROD. — THE IMPROVED VOLTAMETER. 433 



on one of platinum by the same current when only filter paper is used 

 to protect the kathode. The results of Kahle and others seem to indi- 

 cate that the presence of acid, which prevents the formation of the simple 

 oxycomplex, is fiivorable to the formation of the ion Agg + . This is 

 not surprising, since the oxycomplex is probably formed at the expense 

 of some of the silver which would otherwise remain in the polymerized 

 condition. The fact that the kathode deposit in the common voltameter 

 consists of comparatively few I.arge crystals, while the porous cup voltam- 

 eter yields a host of evenly distributed small crystals, is also explained 

 by this interpretation. Solutions having a tendency to supersaturation 

 always tend to deposit large crystals, for obvious reasons. When 

 the absence of acid increases the number of available hydroxy! ions, 

 the formation of the silver-complex is less considerable ; but the oxide- 

 complexes then begin to affect the result. In concentrated solutions of 

 the nitrate, this ion also enters into the irregularities. Thus the various 

 irregularities are not necessarily coexistent ; circumstances determine 

 which one shall play the most important part. 



There seems, then, to be concordant evidence of conflicting tendencies 

 at work, some oxidizing and some reducing ; some tending to cause the 

 dissolving of too much silver at the anode, and some to cause the dissolv- 

 ing of too little. It seemed worth while to test the complicated conclu- 

 sion by determining accurately the loss of weight of silver at the anode, 

 in order to obtain a last ray of light upon the question. The disintegration 

 of the anode renders the determination of the loss somewhat difficult ; 

 but by carefully collecting all the silver powder left in the porous cup 

 (when no filter paper is used) on a Gooch crucible, and adding this 

 weight to the weight of the coherent part of the anode, fairly good 

 results may be obtained. The following table records a series of such 

 determinations. In each case the current strength amounted to about 

 0.25 ampere. The experiments are arranged below in the order of cur- 

 rent density. 



In some cases the anode loses more than the ideal amount, in other 

 cases less. Such results can only be explained by the assumption of 

 several causes of inaccuracy, and the four which we have discussed seem 

 capable of explaining all the changes, l^ut it is not worth while to 

 trace out every possible variation ; enough has been said to emphasize 

 the great complexity of the side reactions which interpenetrate a 

 process apparently so simple, and at the same time to permit those 

 readers who are especially interested to work out the combinations for 

 themselves. 



VOL. xxxvii. — 28 



