442 PROCEEDINGS OF THE AMERICAN ACADEMY. 



A few more points may be touched upon here, which follow directly 

 from the new value of the equivalent. A great number of physical 

 instruments have been standardized on the basis of a somewhat higher 

 electrochemical equivalent of silver, 0.001118. "Will they be affected 

 by the lowering of this number ? Evidently not, since if the value cor- 

 responding to a given mode of deposition is applied throughout, when- 

 ever this method is used, no constant error can result. Thus our low 

 value cannot be employed when the anode is unprotected, and the de- 

 posit not heated to redness. 



Therefore, as was shown in our last paper, the discovery of a constant 

 error in the silver voltameter cannot help the discrepancy which exists 

 between the electrical and mechanical methods of determining Joule's 

 equivalent. 



It is to be hoped that in the future, however, all experimenters will 

 use some method, such as ours, in which the anode complications are ex- 

 cluded. Obviously even the present condition of electrical science de- 

 mands a more precise electrochemical definition of the ampere than that 

 now prescribed. 



The present research seems to define the practical unit of current 

 strength no less accurately than the practical unit of electro-motive force 

 has been defined. Thus in a laboratory provided with pure chemicals, 

 each of these units may be established without outside help, and with 

 their assistance a standard ohm may be produced without comparison 

 with any other standard ohm. 



VI. Summary. 



The results of the prolonged investigation may be summed up as 

 follows : — 



1. The electrochemical equivalent of silver as determined by the 

 Lord Rayleigh voltameter is too high by at least 0.05 per cent. 



2. The true rate of deionization of silver can be determined by the 

 use of a porous cup which prevents the solution at the anode from reach- 

 ing the kathode. Results of great consistency and accuracy are then 

 obtainable. 



3. The porous cup does not introduce any new source of error, for 

 without it the same low results may be obtained when the anode is placed 

 below the kathode. 



4. At higher temperature the complications grow larger. 



5. The main disturbing factor is a complex silver ion formed at the 

 anode and carried over to the kathode, where it decomposes, thereby 



