ELECTROMOTIVE FORCES IN THE VOLTAIC CELL. 



475 



4. Meanwhile some experimenters, starting with a belief in the chemi- 

 cal origin of the Yolta effect, had made experiments supposed to support 

 this view. Mr. J. Brown, of Belfast, in 1878, 1 repeated Thomson's divided 

 ring experiment, as well as Kohlrausch's condenser experiment, in other 

 gases than air ; and found a very decided difference, and even a reversal 

 of sign, when sulphuretted hydrogen was substituted for air. The metals 

 Brown used were copper and iron, and he obtained a one centimetre 

 deflection in the direction indicating iron + in air, while in S H., he 

 obtained a 3 centimetre deflection indicating that iron was — . On 

 readmitting air the deflection again reversed, and so on, until the copper 

 coated itself with a blue film of sulphide, when the deflection became 

 undecided, owing, as Brown supposes, to 'the cessation of chemical 

 action.' 



Fig. 8.— Mr. J. Brown's Arrangement for observing the Volta Effect in different 

 Gases by Sir William Thomson's Method of a bimetallic ring with an electrified 

 needle hanging over it. 



In 1881 he observed a time change (decrease) of the Volta effect at a 

 copper-zinc junction, and reckoned that at the first instant after cleaning 

 the potential difference would be as high as -9 Daniell, 'which,' he says, 

 ' agrees with J. Thomsen's determination of the difference of the heats of 

 combustion of zinc and copper and oxygen.' He here gives a hint of holding 



paper had appeared in the Journal de Physique, May 1 880. Fig. 10 sufficiently exhibits 

 Sir William's arrangement. In a postscript are described a few additional experi- 

 ments of the same kind as those published in 1881 by Schultze-Berge, in which a 

 platinum plate is soaked for a certain time in dry hydrogen or oxygen, and then 

 used in the Volta condenser. The observation is made that "merely soaking a plate in 

 gas is more effective than electroplating it with the same gas with an E.M.F. of 

 a volt. 



1 J. Brown : Phil. Mag., August 1878, Feb. 1879, and March 1881 ; see also Brit. 

 Assoc, Trans, of Sects., 1881, and Electrician, vol. vii. p. 165. 



