52 



Dr. G. Gore. 



[Nov. 22,. 



solution of sodic diphosphate, was 0*66 volt for 100 F. degrees 

 difference of temperature, or about 100 times that of a bismuth and 

 antimony couple. 



Heating one of the metals, either the positive or negative, of a 

 voltaic couple usually increased the electric difference, making most 

 metals more positive and some more negative, whilst heating the 

 second one also usually neutralised to a large extent the effect of heat- 

 ing the first one. The electrical effect of heating a voltaic couple was 

 nearly wholly composed of the united effects of heating each of the 

 two metals separately, but was not, however, exactly the same, 

 because whilst in the former case the metals were dissimilar and 

 heated to the same temperature, in the latter they were similar but 

 heated to different temperatures : — also, when heating a voltaic pair,, 

 the heat was applied to two metals, both of which were previously 

 electro-polar by contact with each other as well as by contact with 

 the liquid, but when heating one junction of a metal and liquid 

 thermo-couple, the metal had not been previously rendered electro- 

 polar by contact with a different one, and was therefore in a some- 

 what different electric state. When a voltaic combination in which 

 the positive metal was thermo-negative and the negative one was 

 thermo-positive was heated, the electric potential of the couple 

 diminished, notwithstanding that the internal resistance was decreased. 



Magnesium in particular, also zinc and cadmium, were greatly 

 depressed in elect ro-motive force in electrolytes by elevation of tem- 

 perature. Reversals of position of the two metals of a voltaic couple 

 in the tension series by rise of temperature, were usually due to one of 

 the two metals increasing in electro-motive force faster than ther 

 other, and in many cases to one metal increasing and the other 

 decreasing in electro-motive force, but only in a few cases was it 

 a result of simultaneous but unequal diminution of potential of the- 

 two metals. With eighteen different voltaic couples, by rise of tem- 

 perature from 60° to 160° F., the electro-motive force in twelve cases 

 was increased, and in six decreased; and the average proportions of 

 increase for the eighteen instances was 0*1 volt for the 100 F. degrees 

 of elevation. 



A great difference in chemical composition of the liquid was attended 

 by a great change in the order of the volta tension series ; and the 

 differences of such order in two similar liquids, such as solutions 

 of hydric chloride and potassic chloride, were much greater than in 

 those produced in either of those liquids by a difference of 100° F. 

 of temperature. Difference of strength of solution, like difference 

 of composition or of temperature, altered the order of such series with 

 nearly every liquid, and the amount of such alteration produced by an 

 increase of four or five times in the strength of the liquid was rather 

 less than that caused by a difference of 100 F. degrees in temperature- 



