568 



MR. F. E. SMITH, MR. T. MATHER, AND DR. T. M. LOWIIY 



than that on one of platinum when the Rayleigh form of voltameter was used, but 

 that the masses were equal for the porous pot form. GUTHE* confirmed the latter 

 result. 



Influence of Pressure. 



In testing for a pressure effect, one of the voltameters was placed under a glass 

 bell jar in which the gaseous pressure could be varied from 2 '5 centims. of mercury to 

 atmospheric pressure. The voltameter was supported on a cast-iron plate through 

 which the leads passed, the latter being well insulated from the plate by ebonite and 

 rubber, and tests made before and after each experiment proved the efficiency of the 

 insulation. In two cases the solution under diminished pressure was made with silver 

 nitrate and distilled water which was boiled a few minutes before setting up the 

 voltameter ; in the remaining cases the solution was prepared in the ordinary way. 

 For obtaining a continuous low pressure a large filter pump was used and proved satis- 

 factory. The mass of silver deposited per coulomb is practically the same as before and 

 there is, therefore, no pressure effect in the Rayleigh form of voltameter if set up and 

 used in the manner specified in this communication. SCHUSTER and CnosSLEYt found 



TABLE VIII. Pressure Effect. Rayleigh form of Voltameter used. 



ft Absolute determinations. 



\\ Rayleigh voltameter at atmospheric pressure taken as the standard (1-11827). 



that the amount of silver deposited, when their voltameter was subjected to a gaseous 

 pressure of about 2'8 centims. of mercury, was 4 parts in 10,000 greater than when in 

 air, and Dr. KAHLE| verified this result. MYERS, who repeated these experiments, 

 found the difference between deposits in air and in vacito to be as much as 1 part 

 in 1000, and also found an excess of 5 parts in 10,000 if the deposit was made in an 



* GUTHE, 'Phys. Rev.,' 19, p. 138, 1904; ' Bull. Bureau of Stands.,' vol. 1, p. 34, 1904. 

 t SCHUSTER and CROSSLEY, 'Roy. Soc. Proc.,' 50, p. 344, 1892. 

 J KAHLE, 'Brit. Assoc. Report,' Section A, 1892. 

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



