1879.] Ml' Shaw, On experiments with mercury electrodes. 811 



ing 2 p. c. by volume of Sulphuric acid), lying above the mercury 

 and the funnel in A. The funnels F and E and the India-rubber 

 tube contained similar mercury, the level of which could be 

 altered by raising or lowering the funnel T, or if T were so placed 

 that it was filled with mercury to *he cork, by raising or lowering 

 as a piston the tube E, which fitted sufficiently loosely in the cork. 

 The wires EE' were connected with the electrodes of a high-resist- 

 ance astatic galvanometer. An electromotive force was applied 

 by means of the Meidinger cell B acting through the resistance 

 R, which could be varied at pleasure, and the magnitude of the 

 E, M. F. was regulated by the resistance of the shunt is!'. 



Currents through the galvanometer will be denominated posi- 

 tive when they pass through the" fluid from the mercury in the 

 funnel F to the external mercury, and negative for the opposite 

 direction. 



Whenever the apparatus just described was freshly filled, with- 

 out applying any E. M. F. there was always on making contact a 

 current through the galvanometer which varied in intensity, and 

 was generally negative. This current disappeared when the elec- 

 trodes were left in contact for several hours. When this state was 

 arrived at, the raising of the funnel threw th^ galvanometer needle 

 against its stops in the positive direction, and the reverse effect 

 took place in lowering. 



Pushing down the piston E gave a mean throw of + 35", and 

 raising it a mean throw of — 32°. A varying electromotive force 

 was then applied in the negative direction so as to charge the 

 movable electrode with Hydrogen, time being allowed for the 

 opposing force of polarization to attain its maximum. 



The E. M. F. was gradually increased up to one quarter of the 

 Meidinger element, and the throws of the galvanometer needle on 

 raising and lowering the piston were in the same direction as 

 when there was no electromotive force impressed, and increased 

 very slightly in magnitude. 



These experiments accordingly confirm the result obtained by 

 Lippmann and Quincke as to the direction of the current, namely 

 that a current flows from an increasing mercury electrode through 

 the fluid to a fixed one. 



The battery was then thrown out of the circuit and the elec- 

 trodes connected until the polarization current was reduced to 

 zero. The throws on raising and lowering the piston were now 

 much smaller than originally, being approximately equal to 5° each 

 way only. An E. M. F. was then applied in the reversed direction, 

 i. e. making the movable mercury surface the positive pole. The 

 opposing E. M. F. of polarization was as before allowed to attain 

 approximately its maximum and the needle, which was permanently 

 deflected even for small electromotive forces, was reduced to its 



