438 PROCEEDINGS OF THE AMERICAN ACADEMY. 



minatioiis. The wide deviations between the individual determinations 

 illustrate the uncertainty of a voltameter in which the anode is merely 

 wrapped in filter paper. 



When to this difference is added the amount (0.018 per cent) caused 

 by the included mother liquor, it is obvious that the weight of silver 

 observed in the experiments upon Faraday's law made by Richards 

 and Collins must have been 0.059 per cent too heavy. This would 

 cause the ol)served electro-chemical atomic weight of copper (63.563 *) to 

 be too small by the same percentage. Correcting for this error, the 

 atomic weight of copper calculated from the results of the experiments 

 upon Faraday's law becomes 63.601, while the most probable value 

 found in purely chemical ways is 63.604. f 



The agreement is as close as the probable accuracy of the electrolytic 

 determinations. Thus good experimental evidence is furnished, showing 

 that Faraday's law holds rigorously true in aqueous solution at ordinary 

 temperatures. Apparent deviations are simply due to the disturbing 

 effect of side reactions. 



V. The Electrochemical Equivalent of Silver. 



It becomes now an important matter to determine, if possible, a cor- 

 rection which miglit be applied to tlie methods of earlier physical ex- 

 periments iqion the electrochemical equivalent of the ampere. Such 

 correction must at best be an unsatisfactory expedient; the only really 

 satisfactory method of proceeding would be to repeat the work wholly, 

 using the new voltameter as a chemical measure of the current. But 

 such a proceeding involves an expenditure of time not now at our dis- 

 posal ; hence it seems not wholly fruitless to attempt the correction of 

 the older results. 



The series of comparisons of the standard with the filter paper voltam- 

 eter just given (p. 422) will hardly serve for the purpose, since the 

 latter voltameter changes in its indications with every change of form ; 

 and the two comparisons with Lord Rayleigh's form, given in the 

 previous paper, form too small a basis upon which to make so serious a 

 correction. Hence another series of these experiments was made, in 

 which the porous cup voltameter was compared directly with a voltameter 



* This result was obtained by extrapolation for a copper katliode of zero area. 

 It had a " probable error " of 0.004, and possibly contained a source of error tending 

 to make it slightly too large. 



t Kichards, These Proceedings, 26, 293 (1891). 



