278 Dr. G. Gore. Relations of Heat to Voltaic and 



The instances were selected because they were conspicuous ones. 

 The results are probably in some cases partly due to extremely thin 

 films of insoluble matter formed upon the metals (see pp. 255, 261, 

 270, 278) ; this assumption of the existence of films will not, however, 

 explain many of the cases in Tables I and IV, when non-corroded 

 metals were rendered negative by being heated. Fifty-six cases of 

 relative diminution of volta-electric potential by rise of temperature 

 are included in the cases of reversal in Table X (see p. 266). 



Similar results to the above were arrived at by a more direct 

 method. The chemico-electric potential of each pair of metals was 

 first determined (by the method of balance) at 60 and then at 160 F., 

 by suddenly immersing the pair in the previously prepared liquid. 

 The following were the results : 



Table XVI. Influence of Temperature on Voltaic Potential. 



Remarks. While each of these determinations except the last one 

 agrees with the former ones in being a case of decrease of electric 

 potential by equal rise of temperature, the amounts of decrease for 

 the corresponding pairs of metals differ very considerably in the two 

 tables, probably in consequence chiefly of the circumstance that in 

 each of the experiments of the former determinations the metals in 

 mutual contact were the same, but at different temperatures, whilst 

 in the latter they were dissimilar ones at the same temperature. 

 When heating a voltaic pair, the heat is applied to two metals, both 

 of which are previously electro-polar by contact with each other, as 

 well as by contact with the liquid; but when heating one junction of 

 a liquid and metal thermo-couple, the metal has not been previously 

 rendered electro-polar by contact with a different one, and is there- 

 fore in a somewhat different electric state. Faraday observed similar 

 cases ("Experimental Researches," 1923), viz., that by either 

 heating one or two pieces of silver or of platinum in a cold mixture of 

 1 part of sulphuric acid and 80 of water, little or no electric current 

 was manifest, but on heating the silver or platinum alone of a voltaic 

 pair of those metals in that liquid, in each case a current occurred. 

 Heating the platinum made it strongly negative, and heating the 

 silver made it weakly positive. These cases illustrate the necessity 

 of considering the effect of voltaic contact, as well as that of chemico- 



