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



Cd, 154; Al and Fe, 110 ; Al and Sn, 100; Al and Pb, 68; Pt 

 and An, 185. Sodic tulphate: Fe and Pb, 62; Ag and Cn, 176. 

 Nitric add : Al and Cd, 140 ; Al and Fe, 116 ; Al and Pb, 86; Au 

 and Pt, 130; Ag and Pt, 64. Chloric acid: Al and Cd, 144; Al 

 and Fe, 120 ; Pb and Fe, 184. Magnesic sulphate: Fe and Pb, 65; 

 Ag and An, 182. Potassic alum: Al and Cd, 140 ; Al and Fe, 132; 

 Al and Pb, 130 ; Sn and Pb, 182 ; Ag and Pt, 70. Ammonic alum : 

 Sn and Pb, 102. The cases of chemico-electric reversal in which 

 both metals diminished in potential were : Au and Pd in potassic sul- 

 phate, also in oxalic acid ; Fe and Sn in chloric acid ; An and Ag in 

 magnesic snlphate ; and Pb and Al in potassic alum. As visible 

 chemical corrosion of metal is not necessary to thermo-electric action 

 of metals in liquids, reversals occurred with non-corroded, as well 

 as with corroded metals. 



Very slight circumstances altered the position of a chemico-electric 

 reversal point in the scale of temperature, and even caused it to pass 

 beyond the limits of the scale and of observation. A different 

 sample of metal or of salt, and other circumstances, often produced 

 this effect ; the results are therefore very variable. 



Out of the total 83 cases of reversal obtained by sudden immersion 

 of the pairs of metals, first at 60 and then at 160 F. (see Table X), 

 only 54 were reobtained on heating the metals gradually in the 

 liquids, and 11 of those so obtained occurred at temperatures higher 

 than those employed when the metals were suddenly heated. Gradu- 

 ally heating the metals appeared therefore to cause in some cases the 

 reversals either to disappear or to occur at a higher temperature (pro- 

 bably in consequence partly of polarisation). This effect was more 

 common in a solution of potassic cyanide than in dilute sulphuric or 

 nitric acids. 



It may be observed also with regard to some of these cases that the 

 temperatures at which the reversals took place were usually lower the 

 weaker the electromotive force ; this was the case with aluminium in 

 relation to cadmium, iron, tin, and lead in dilute sulphuric acid ; also 

 with that metal in relation to cadmium, iron, and lead in nitric acid ; 

 and less distinctly in solution of potassic alum and other liquids. 



The influence of heat upon the chemico-electric series of Table X 

 was further examined by measuring the degrees of electric potential, 

 both at 60 and 160 F., of the extreme top and bottom metals in the 

 respective liquids of that table. The results are given in Table XI. 



Remarks. In 12 cases the voltaic potential was increased, and in 

 6 decreased ; the total amount of increase was 5 times that of de 

 crease, and the average proportion of increase for the 18 instances 

 was '10 volt for 100 F. rise of temperature. By comparing these 

 cases with the thermo-electric positions of the same metals caused bj 

 the same difference of temperature in Table I, the two were found 



