~ Chemical Affinity in terms of Electromotive Force. 119 
minutes after setting up. The readings during this period did 
not always exhibit constancy, especially with the weaker solu- 
tions; but the extreme alteration usually only amounted to a 
few millivolts, concurrently with a visible alteration in the 
surfaces of the plates. Strength of solutions, mM(NO;). 
100 H,0. 
m=°25. m=1°0. m=2:0. m=8'0, 
Maximum......... 1:087 1:104 1112 1:095 
Minimum ......... 1:053 1-073 1:108 1-087 
Average............ 1:066 1-089 1-109 1-091 
Probable error ... +0035 +0034 +0005 +0009 
These figures correspond with the following thermovoltaic 
constants, the values of Eq being deduced from the experi- 
ments of Julius Thomsen, including his valuations of the 
heats of dilution of zinc- and copper-nitrate solutions. The 
difference between the heats of formation of mM(NO3)o 
100H,0 are given by the formula 
102510—h, — (52410 — hy) =50100— (hy — he), 
where Zn, 0, NO; aq. =102510, and Cu, O, N,O; aq. =52410 
for solution-strengths ‘25 M(NO3)., 100 H,O; whilst 2, and hy 
are the heats of dilution of solutions of zinc and copper 
nitrate respectively from the strength mM(NO3;),. 100 H,O to 
"25 M(NOQ3). 100 H,0. 
MM, h,. feo SOTO =e, h.)..\ ngs | ES | Bae 
25 0 0 50100 1105 | 1-066 | —-039 
1:0 ar AQ) | 2s 47 50098 1105 | 1-089 | —-016 
2-0 —132-| —175 50057 1104 | 1:109 | +-005 
8:0 +439 | +214 49875 1100 | 1-091 | —-009 
J 
It is here noticeable that the thermovoltaic constant for 
electro-copper in nitrate solution has in no case any large 
value ; whilst of negative sign for low-solution strengths, it 
becomes positive for stronger fluids, and again negative with 
highly concentrated solutions, following the variations in the 
voltaic constant, which has a maximum value for fluids of 
medium strength. 
