86 
CHEMISTRY: }. H. ELLIS 
of this conductance-ratio at 18° at the other concentrations, enabhng 
a comparison of it to be made with the values of the activity-coefficient. 
It will be seen from Table 2 that with increasing concentration the 
activity-coefficient first falls more rapidly than the conductance-ratio, 
being about 10% smaller than the latter at concentrations 0.1 to 
0.5 molal. This shows that at these concentrations there is an error 
of this magnitude in the common practice of employing in mass-action 
expressions the conductance-ratio as a measure of the activity of the ions 
of the acid. The activity-coefficient, moreover, unlike the conduct- 
ance-ratio, passes through a minimum at about 0.50 molal, and then 
increases rapidly with the concentration, becoming about equal to that 
TABLE 2 
Energy-Effects Attending the Transfer of Hydrochloric Acid and Value of its 
Activity-Coefficient 
MOLS HCl 
PER 1000 G. WATER 
FREE-ENERGY DECREASE AT 
HEAT 
AcnviTy- 
CONDUCTANCE- 
DECREASE 
COEFFICIENT 
RATIO AT 
18" 
25° 
35° 
AT 25" 
AT 18" 
18° 
4.484 
23184 
23544 
24037 
8474 
2.23 
1.9278 
15454 
15744 
16143 
3591 
1.063 
1.0381 
11449 
11679 
12003 
1937 
0.864 
0.841 
0.7714 
9775 
9971 
10250 
1619 
0.823 
0.868 
0.5095 
7596 
7757 
7978 
999 
0.795 
. 0.889 
0.3376 
5730 
5856 
6021 
684 
0.816 
0.901 
0.1000 
0 
0 
0 
0 
0.844 
0.925 
0.03332 
-5053 
-5167 
-5331 
-300 
0.892 
0.955 
0.01668 
-8224 
0.926 
0.966 
0.01115 
-10084 
0.943 
0.971 
0 008324 
-11447 
0.953 
0.976 
0.006683 
-12472 
0.960 
0.978 
0 005569 
-13325 
0.967 
0.980 
0.003334 
-15717 
0.985 
0.985 
0.001667 
-19031 
0.988 
0.988 
ratio at 1 molal, and attaining at 4.5 molal a value 2\ times as great as 
that at zero concentration. This large increase is in correspondence 
with the rapid increase of the vapor-pressure of the acid at high con- 
centrations. 
Other exact electromotive force investigations from which ion-activ- 
ities can be derived have been published by Jahn^ on potassium chlor- 
ide and sodium chloride at concentrations between 0.00167 and 0.033 
molal and by Maclnnes and Parker^ on potassium chloride between 0.001 
and 0.5 molal. The results of the last-named investigators give for the 
activity-coefficient of potassium chloride the values 0.653 at 0.5 molal, 
0.738 at 0.1 molal, and 0.885 at 0.01 molal. The corresponding values 
