Electromotive Forces in the Voltaic Cell. 167 
4. Meanwhile some experimenters, starting with a belief 
in the chemical origin of the Volta effect, had made experi- 
ments supposed to support this view. Mr. J. Brown, of Bel- 
fast, in 1878, 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 1l-centimetre deflection in the direction indicating 
iron + in air; while in SH, he obtained a 3-centimetre de- 
flection, 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. 
i 
(il 
appeared in the Journal de Physique, May 1880. Fig. 10 sufficiently 
exhibits Sir William’s arrangement. In a postscript are described a few 
additional experiments of the same kind as those published in 1881 by 
Schulze-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 im gas is more effective 
than electroplating it with the same gas with an E.M.F. of a volt. 
* J. Brown, Phil. Mag. August 1878, Feb. 1879, and March 1881; see” 
also Brit. Assoc. Trans. of Sect. 1881, and ‘ Electrician,’ vol. vii. p. 165. 
