ON ELECTKOLTSIS IN ITS PHYSICAL AND CHEMICAL BEARINGS. 325 



the experiment lasts. The following tahle shows the weights of copper as thus 

 corrected : — • 



An examination of this table shows that, with some few exceptions, the results, 

 as corrected, are very fairly concordant. That no value of k' could be found 

 which would apply equally to all the observations is obvious from the discordance 

 in the values of a k' tabulated above. A striking feature of the table is that the 

 numbers under the heading of ' 2 wires' seem now to be the minimum values of 

 the table ; the ' 1 wire ' values are all greater ; and the numbers in the other columns 

 are very rarely less, and then only by very small quantities. This shows that the 

 correction applied is probably too large, though it is sometimes very successful. 

 It is probable that the correction ought not to be applied when the current-density 

 is very great, as the diflerence between the ' 1 wire ' and ' 2 wires ' is increased by 

 the correction, though not entirely due to it. This, as already pointed out, is probable 

 a priori, since the more rapid deposition of copper woidd weaken the solution in the 

 immediate neighbourhood of the cathode. The correction may, however, be fairly 

 adopted for the smaller current-densities. It appears on examination of the current- 

 densities that the exceptional cases do not arise when the current-density is below 

 •02 ampere per square centimetre, so that the weights of copper deposited with 

 currents of current-density less than -02 ampere per square centimetre may be cor- 

 rected by multiplication by a factor 1 + t-, where d is the current-density, and k' a 



ct 



constant not differing much from 00002.^ 



CHEiricAi Equivalent of Coppee. 



We have now to compare the results obtained for the ratio of the chemical 

 equivalent of silver to that of copper with those obtained by purely chemical 

 methods, in order to ascertain whether or not Faraday's law is strictly applicable 

 in the case of silver and copper. If we take the results given in Landolt and 

 Bernstein's ' Physikalisch-Chemiscbe Tabellen.'we find the atomic weight of silver 

 given as 107-66 by Meyer, and 107-675 by Clarke, and the accuracy is stated as 

 being within -05 ; that of copper is quoted as 6.3^18 from Meyer, and 6.3^17 from 

 Clarke, with a possible error of + -5. This would give a value for the ratio of the 

 chemical equivalents of silver and copper equal to 3-4086 ; or, allowing the fullest 

 margin for error, the value lies between 3-38 and 3-44 ; so that the values obtained 

 by the deposition of silver and copper seem to be-all within the limits of error thus 

 assigned ; and we cannot, therefore, test the accuracy of Faraday's law until the 



' The values obtained by Lord Eayleigh with copper bowls (Phil. Tr. Pt. II. 

 1884, p. 458) are : 



Current-density, about -012 ; ratio of equivalent, 3-405 

 •026 „ „ 3-408 



3-404 



