298 



PROCEEDINGS OP THE AMERICAN ACADEMY. 



It will be observed that in every case the loss of heat capacity has the 

 same sign as the excess of heat evolved ; and in general, where one is 

 large the other is also large. This relationship is illustrated by the 

 accompanying diagram. In comparing differences between such large 

 numbers one could hardly expect exact parallelism; but the two phe- 

 nomena run so closely together that one is forced to infer the existence 

 of a fundamental connection between them. 



Mg-Fc 



Mg-Zn 



Diagram Illustrating Parallelism of Change of Heat 

 Capacity and " Bound Energy." 

 Note. The left-hand zigzag line depicts change of heat capacity in the ten 

 cells given in the previous table, and the right-hand zigzag line depicts the " bound 

 energy " or the difference between the heat of reaction and the available free 

 energy of the reaction. In order to avoid confusion, these curves are referred to 

 different ordinate axes, indicated by the two vertical zero lines. 



A few more similar cells with other anions might have been added 

 to this list from the data of Wright and Thompson, Marignac, and Julius 

 Thomsen. The following exhibit relationships similar to those already 

 given in detail: zinc-copper nitrate; zinc-lead nitrate; zinc-magnesium 

 nitrate ; lead-copper nitrate ; * le^ul-magnesium nitrate ; copper-magne- 

 sium nitrate ; zinc-magnesium chloride. Unfortunately the great bulk 



* The heat value for this cell, calculated from the results of Jahn (Wied. Ann., 

 17, 593 [1882]), do not at all agree with the results of Thomsen. For the Ag-Cu- 

 nitrate cell Jahn gives 10.6 Cal. per gram equivalent, while Thomsen gives 17.8 

 Cal. ; and for the Ag-Pb-nitrate cell Jahn gives 21.5 Cal., while Thomsen gives 

 25.6 Cal. The value for the Pb-Cu-nitrate cell would then be 10.9 Cal. according 

 to Jahn, and 7.8 according to Thomsen. I selected the latter value. 



