Chemical Affinity in terms of Electromotive Force. 35 
with water either at or near 0° or at or near 30°, as the 
case might be ; the masses of fluid (agitated from time to 
time with a peculiar stirrer) were so large that the tempera- 
ture of the chamber-spaces varied but little during the pro- 
gress of the series of readings ultimately made. The mean 
temperatures indicated by the thermometers during the series 
were taken as the mean temperatures of the cells (placed in 
the chambers some time before the readings were commenced, 
so as to attain sensibly the temperatures of the chamber-spaces). 
The readings were carried out in systematic order; so that the 
average reading for each cell should be exactly comparable 
with that of any other, notwithstanding any possible running- 
down of the electrometer-scale during the progress of the 
readings. For instance, if in the first chamber two cells (A 
and B) were placed, and in the second two others (C and D), 
the readings were alternately taken in the orders A, B, C, I) 
and D, C, B, A, or C, D, A, B and B, A, D, C ; so that the 
average reading for each cell was identical with that which 
would have been observed had the electrometer-scale value 
been absolutely constant throughout at its mean value (the 
actual variation of the electrometer-scale during any set of 
readings was considerably under 1 per cent.). 
Thus, for instance, the following numbers were obtained in 
two experiments, in each of which the same two cells A and B 
were placed in the first chamber, and the same two (C and D) 
in the second: — 
1st experiment. 
h 16°-84 
t 2 l°-08 
t 3 9°-72 
26°-02 
Average scale-reading for A 
and B taken together at 
Average reading for C at t 2 
Average reading for A an' 
B taken together at t 3 . 
Average reading of C at t± 
161 
t) 
159-94 
2nd experiment. 
17°-04 
3°-30 
10°-98 
25°-12 
161-00 
153-00 
152-25 
a. 2 
159-94 
152-25 
153 
= 1-0066 
= -9951 
<L\ — % 
a x {ti — 1 2 ) — aa(*s— *i) 
Mean value of x 
D2 
. -000358 
159-62 
160-75 
152-56 
152-00 
160-75 
159-62 
152 
152-56 
= 1-0071 
= -9963 
•000386 
•000372. 
