146 Dr. G. Gore on the Relations of Surface-resistance 



In a previous investigation on ci transfer-resistance" (Proc. 

 Royal Soc. vol. xxxviii. p. 209) I also found " that a species 

 of electric resistance distinct from that of polarization and of 

 ordinary conduction-resistance, varying greatly in amount in 

 different cases, exists at the surfaces of mutual contact of 

 metals and liquids in electrolytic and voltaic cells. That this 

 resistance varies largely in amount with different metals in 

 the same solution, and with the same metal in different solu- 

 tions," " and is usually small with easily corrodible metals 

 which form readily soluble salts, and large with those which 

 are not corroded ;" and " that the same voltaic current was 

 resisted in different degrees by every different metal when 

 employed as an anode, and when used as a cathode ;" " and 

 that the resistance at the anode was usually smaller than 

 that at the cathode;" and " that by rise of temperature 

 ' transfer-resistance ' was usually and considerably reduced." 

 This " transfer- resistance " differs essentially from electric 

 potential, because it is incapable of producing a current. 



The present experiments were made for the purpose of 

 examining some relations of this " surface-resistance " to 

 various electrical phenomena. I call it " surface-resistance " 

 in the present case, because, in consequence of omission of 

 stirring, it includes other forms of resistance besides that of 

 " transfer " at the surfaces of mutual contact of the metals 

 and liquids employed. 



First. — In cases of thermoelectric currents produced by 

 heating the junction of a metal and electrolyte. We know 

 that when heat is applied to one of the two ends of a piece 

 of non-corrodible metal in contact with opposite parts of an 

 electrolyte, an electric current is usually produced, and we 

 infer from the principle of conservation of energy that when 

 such a current occurs heat is absorbed and disappears at or 

 near the heated junction, and is converted into and produces 

 the current. 



In order to determine whether the relative amounts of 

 " surface-resistance " at the junctions of such a thermo-couple 

 vary with temperature, and also whether the direction of 

 current produced by such a couple is influenced by the rela- 

 tive total amounts of such " resistance " in the two directions 

 in the circuit, I made the following experiments : — 



The liquids employed were dilute sulphuric and nitric acids, 

 each being composed of one volume of strong acid and ten 

 volumes of water; and the electrodes were two perfectly 

 similar sheets of platinum, each having a total immersed area 

 of surface of about 24*0 sq. cm. 



The thermoelectric apparatus consisted of a vertical glass 



