94 PROCEEDINGS OF THE AMERICAN ACADEMY. 



deposited silver upon contact with the silver surface. This is a crucial 

 experiment, and the result is purely a question of fact, not of inter- 

 pretation. Clearly for some reason or other the anode irregularities 

 were less prominent in the experiments of Smith, Mather and Lowry 

 than in other cases, and one is inclined to refer the difference in this 

 respect between the results which they obtain and the Harvard results 

 to other causes as yet unknown. Possibly the fact that they used 

 electrically deposited silver for their anode may not only account for 

 their inability to deposit silver from the heavy anode liquid, but also 

 contribute toward the constancy of their results with Lord Rayleigh's 

 voltameter. Electrically deposited silver, being arranged in definite 

 crystals, may dissolve with less irregularity than a fused lump. Fur- 

 ther experiments must decide the uncertainty. For the present, until 

 this question has been settled, it would seem to be advisable to use 

 electrically prepared silver as the anode, if a porous cup is not 

 employed. 8 



It is to be hoped in view of these points still remaining unsettled that 

 the International Congress on Electrical Standards will not define too 

 positively the true electro-chemical equivalent. It is equally obvious 

 that with the exception of these disputed points the matter is in a much 

 more definite state than it was twenty-five years ago. There can be no 

 doubt that the final result of Lord Rayleigh and Mrs. Sidgwick was the 

 best of all the early absolute determinations, all things considered, be- 

 cause of their having taken account of the inclusion of mother liquor. 

 In this respect this pioneer work is better even than some of the most 

 recent work. Probably it was not over 0.05 per cent in error — a 

 remarkable degree of accuracy for that time. 



In brief, the contents of this note may be summarized as follows. 

 While it is clear that Smith, Mather and Lowry have done good service 

 in showing that large volumes of liquid, taken in connection with the 

 electrically prepared anodes, will give good uniform results with the 

 silver coulometer, and that the results thus obtained are like those ob- 

 tained with clean porous cups and siphons between the electrodes, 

 there are still a few minor points of detail left to be decided, especially 

 the question as to the amount of included liquid in the silver. 



8 I am glad to hear from Professor Smith that the National Physical 

 Laboratory of England proposes to test this and other doubtful points in the 

 near future. 



