ON THE SILVER VOLTAMETER. 547 



of a solution, and that the nature of the deposit also varied with the solution 

 employed. In 1892 SCHUSTER and CROSSLEY* discovered that the mass of silver 

 deposited was related to the pressure and also to the size of the silver anode ; the 

 pressure effect was verified by KAHLE,! RICHARDS,! and MYERS, and the latter 

 observer found an increase when the liquid was saturated with nitrogen, but a 

 decrease when the dissolved gas was carbon dioxide. MERRILL || repeated the pressure 

 experiments and found no effect due to change of pressure alone. Lord UAYLEIOH 

 and Mrs. SIDOWICK observed an increase of deposit with increase of temperature ; 

 RICHAHDS, COLLINS, and HEIMROD obtained greater deposits at 60 C. and at C. 

 than at 20 C. LfiDucIT found a decrease with increasing temperature, aud MKI:I:I i.i. 

 suggests that the mass is independent of the temperature. 



In more recent years GUTHK** and VAN DiJKtt have made a special study of 

 various forms of voltameters. The form suggested by RICHARDS was found by him 

 to give a smaller deposit of silver than the form originally devised by Lord 

 RAYLEIOH. The difference between the two forms found by RICHARDS in 1899 was 

 80 parts in 100,000; in 1902 he found 44 parts in 100,000; WATSON,}} in 1901, 

 obtained a difference of 26 ; GUTHE, in 1904, found 48, and in the same year 

 VAN DIJK ol>served a difference of 23. VAN DIJK also compared the syphon and 

 Rayleigh types and found a mean difference of 8 parts in 100,000, the latter form 

 giving the heavier deposit ; if a very doubtful observation is excluded, the mean 

 difference is 18 parts in 100,000. In addition, VAN DIJK observed a difference due to 

 the size of the platinum bowls, the smaller one invariably containing the lighter 

 deposit for the same form of voltameter. There are many other interesting differences 

 which need not now be enumerated ; sufficient has been written to show that the 

 silver voltameter could not be regarded as an instrument of high precision. The 

 international ampere is, however, defined in terms of the deposit of silver, and the 

 Conference on Electric Units at Charlottenburg in October, 1905, reaffirmed this 

 definition, but expressed the opinion that the information before it was not sufficient 

 to enable it to lay down exact directions in respect to the silver voltameter to be 

 employed. Hence the necessity for an enquiry to ascertain the possibility of specifying 

 a voltameter which is easily reproducable and in which an ampere-second always 

 deposits the same mass of silver. 



* SCHUSTER and CROSSLEY, ' Roy. Soc. Proc.,' 50, p. 344, 1892. 

 t K.UII.K, 'Brit. Assoc. Report,' Section A, 1892. 

 I RICHARDS and HEIMROD, 'Proc. Am. Ac.,' 37, p. 415, 1902. 

 MYERS, ' WIED. Ann.,' 55, p. 288, 1895. 

 || MERRIIX, 'Phys. Rev.,' 10, p. 167, 1900. 

 f LEDUC, ' Journ. de Phys.,' 1, p. 561, 1902. 



** GITIIK, 1'hys. Rev.,' 19, p. 138, 1904. 'Bull. Bureau of Stands.,' vol. 1, No. 1, p. 28, 1906. 

 tt VAN DIJK and KUNST, 'Ann. der Phys.,' 14, p. 569, 1904. VAN DIJK, 'Ann. der Phys.,' 19, 

 p. 249, 1906. 



tt WATSON, ' Phil. Trans.,' 1898, p. 445, 1902. 



4 A 2 



