Section III, 1919 [171] Trans. R.S.C. 



The Effects of Ageing in Standard Weston Cells of a Modified Type 

 By A. Norman Shaw, D.Sc, and H. E. Reilley, M.Sc. 



Presented by Dr. L. V. King, F.R.S.C. 



(Read May Meeting, 1919.) 



§1. Introduction 



The investigations on standard cells at the Macdonald Physics 

 Building, McGill University, were commenced by Prof. H. L. Cal- 

 lendar, F.R.S., and Prof. H. T. Barnes, F.R.S., in 1896, and a large 

 number of the older types of cells were constructed and examined.^ In 

 1908, the investigation was resumed by Dr. H. L. Bronson and one 

 of the present writers (A.N.S.), at the suggestion of Prof. Barnes, in 

 order to equip the laboratory with a set of modern standards, and to 

 provide means of completing some experiments which were in progress 

 at that time. The opportunity was taken to consider thoroughly the 

 general questions of reproducibility and constancy of standard cells 

 and the relationship to one another, of the various existing types^. In 

 1910 and 1911, an investigation was conducted by one of the writers 

 on the absolute measurement of the electromotive force of 

 the international normal Weston standard celF, and at this time 

 further observations were made on the behaviour of the various cells. 



The present notes refer to the continuation of these tests in the 

 summer of 1912 and during the winter of 1918-19. They deal especi- 

 ally with the effects of ageing in Weston standard cells of various 

 types. It has been found that the constancy and accuracy of certain 

 types of Weston cell, which may be constructed in any laboratory, 

 compare favourably with those made according to elaborate and more 

 costly specifications. The assurance with which an absolute value of 

 voltage may be determined from a batch of old cells is discussed, and 

 some objectionable characteristics of old cells are noted, together with 

 simple methods of treatment for their improvement. 



It should be pointed out that this laboratory is in a fortunate 

 position to discuss the international mean value of the e.m.f. of the 



* Callendar and Barnes, Proc. Roy. Soc, Vol. 62; p. 117 (1897); also Barnes, 

 Phil. Trans. A, Vol. 199, p. 159 (1902). 



'^ Bronson and Shaw, British Association Report, Vol. 79, p. 396, (1909); Bronson 

 and Shaw, The Electrician, Vol. 66, p. 698, (1911). 



» A. N. Shaw, Phil. Trans. A, Vol. 214, pp. 147-198. 



