ON THE SILVER VOLTAMETER. 57!) 



v 



'Hie Electrochemical Equivalent of Silver. 



The mean of the values for the mass of silver deposited by the passage of 1 coulomb 

 ot electricity through any of the normal voltameters described in this communication is 



1'11827 milligrammes. 



The quantity of electricity which passed through a voltameter in any experiment 

 was determined by a measurement of time, to which measure no appreciable error can 

 be attached, and by an evaluation of a current in absolute measure through the 

 medium of the Ayrton-Jones ampere balance. It is shown elsewhere* that the error 

 in such a determination of current is of the order of 2 parts in 100,000, and this also 

 is the probable error of the value stated above for the mass of silver deposited per 

 coulomb. 



The value has been obtained not from one solution, nor with one voltameter, but 

 with many solutions and many forms, as well as many voltameters. It has, moreover, 

 been shown that the value is the same whether a current of half an ampere is passed 

 through a voltameter, or a current of 8 amperes ; whether the pressure is atmospheric 

 or equivalent to that of a few centimetres of mercury ; and if the temperature is 

 90 C. instead of 15 C., it is probable that the value is still the same. 



The remarkable consistency of our results is probably due to the large kathode 

 bowls, the purity of our anodes, the small mass of filter paper in the Rayleigh form, 

 and most of all to the purity of the electrolyte. With very small bowls, a small 

 quantity of electrolyte, a small anode, a relatively large mass of filter paper, and 

 current densities which are very high or very low, the estimated mass of silver 

 deposited in the passage of 1 coulomb may be different from the value given by us. 

 Secondary reactions may then occur which never happened in our experiments, or 

 if they did the large volume of electrolyte masked their effects and rendered their 

 detection impossible by any means tried by us. 



Comparison of Results with those of oilier Observers. 



Professor VAN DIJK very kindly forwarded to Dr. GLAZEBROOK two of his 

 voltameters together with a considerable quantity of silver nitrate which he had 

 recrystallised, and which was comparable with that employed in his investigations. 

 We here express our hearty thanks to Professor VAN DIJK. Solutions were prepared 

 from the salt which was sent, and they were found to be abnormal. In one case the 

 value found for the electrochemical equivalent was 1 '11847 (526), and in a second 

 experiment 1 '1 1860 (76/>) resulted. The solutions, as originally prepared, were slightly 

 turbid and had to be filtered, and the deposits with a current of 1 ampere were 

 noticeably striated. If different quantities of an abnormal electrolyte are contained in 



* AYRTON, MATHER, and SMITH, 'Phil. Trans.,' A, vol. 207, p. 534, 1908. 



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