Electromotive Force to Pressure SfG. 107 



produce the currents. In all these experiments, and in the 

 previous ones in which a diaphragm was employed (see fig. 2), 

 the latter manifestly diminished the amount of the current. 



Influence of Titer moelectric Action. 



It might be supposed that the stronger pressure at the 

 lower electrode, by giving rise to greater chemical heat, is 

 attended by a thermoelectric current from that electrode to 

 the electrolyte ; and this view is apparently supported by the 

 circumstances : — 1st, where the chemical energy is greatest 

 the current is usually the strongest ; 2nd, the full strength 

 of the current is developed gradually ; and, 3rd, the current 

 is a continuous one. But it does not agree with the fact, 

 established by numerous and varied experiments, that whilst 

 heat usually makes metals more electropositive in solutions of 

 alkaline salts and alkalies, it makes them more negative in those 

 of acid salts and acids (see " The Thermoelectric Properties 

 of Liquids," Proc. Roy. Soc. 1878, vol. xxvii. p. 513) . If heat 

 therefore was the cause, downward currents would have 

 occurred in the latter group of liquids, instead of which no 

 currents occurred in dilute acids, and upward ones were pro- 

 duced in solutions of acid salts. 



In order to finally settle this point, I made the following 

 experiments : — Two vertical metal wires, 2 inches long, coated 

 with shellac over about an inch of their length at about half 

 an inch from their ends, were immersed three-fourths of an 

 inch in two portions of the electrolyte contained in two small 

 glass beakers placed about 3 inches asunder, the two portions 

 of liquid being connected together by a piece of cleau linen 

 tape previously soaked in the solution and laid upon a strip 

 of sheet-glass connecting the edges of the two vessels ; each 

 beaker contained a thermometer, and the wires were connected 

 with the usual galvanometer. After the needles of the gal- 

 vanometer had settled at zero, heat was applied to one of the 

 beakers until the temperature of the liquid had risen about 3 

 or 4 Centigrade degrees, and the effect was then noted. 



With zinc and the solution of KHS0 4 of exp. 29, no per- 

 ceptible current occurred, but in that of NaC10 3 of exp. 39 

 a deflexion of 20° was produced, the warm metal being nega- 

 tive. With platinum in the KHS0 4 solution, and in that of 

 KHO, no current was perceptible (compare exps. 87, ^). 

 These results together with those previously mentioned clearly 

 prove that the currents obtained were not due to thermo- 

 electric action. 



