410 



MR. V. F, SMITH OX THK NORMAL WESTOX CADMIUM CELL. 



" Ageing " of Cells. 



Lord RAYLEIGH observed that the electromotive force of Clark cells when originally 

 set up was invariably high, and in some cases the fall in E.M.F. in a few weeks was 

 0'02 volt. This fall in E.M.F. immediately after manufacture has been confirmed by 

 numerous observers, and in consequence Clark cells were supposed to require 

 " ageing." The same is true of Weston cadmium cells if set up with pastes prepared 

 similarly to those used by Lord RAYLEIUH, but such extreme changes as 2 per cent, 

 have not come under the author's notice. The mercurous sulphate prepared by any 

 of the four methods described in this communication does not require " ageing," or to 

 a very small extent only. 



Washing with Alcohol. 



The group of cells, of which N 23 to N 26 are types, were abnormal in their 

 behaviour. The E.M.F. was at first 3 parts in 10,000 low, but gradually increased 

 until it was normal, and since then it has remained approximately constant. The 

 mercurous sulphate for these cells was washed with absolute alcohol to free the salt 

 from acid, but no attempt was made to remove the alcohol by further washing the 

 sulphate with saturated cadmium sulphate solution. The salt was removed from the 

 filter and immediately made into paste. Table VI. gives the observations from the 



TABLE VI. 



date of preparation, September 20, 1905, to January 1, 1906; Cell N 17 contains 

 mercurous sulphate from the same sample, but which was freed from alcohol l>efore 

 making up the paste. 



GUTHE and v. ENDE* prepared some mercurous sulphate which was not 

 thoroughly free from alcohol and found the E.M.F. of some Clark cells 0'00040 volt 

 lower than normal when set up with this, and there was no appreciable change in the 

 course of time. Their observations extended over threl months. 



K. E. GITHE and C. L. v. ENDE, ' Phys. Rev.,' 24, pp. 214-221, February, 1907. 



