( 280 ) 
measurements, it appeared to me to be of importance to obtain 
further pound of this result. 
The red and yellow oxides from Merck were shaken with water, 
of conductivity 1 X 10%, for some days in sealed tubes in order 
to remove all traces of soluble matters which might possibly still 
be present. The specimens, after filtration, were then dried for a 
week in vacuo over sulphuric acid. 
A few grams of each material were placed in steamed glass tubes, 
a few ce. of potash lye added and the tubes, which had long necks 
in order to avoid warming the liquids in sealing them, sealed up 
before the blowpipe. They were then shaken in the thermostat at 
25°0 for 14 days and nights in order to saturate the lye with HgO 
and bring about equilibrium. The cell was then put together and 
placed in the thermostat at 25°.0. 
In the following table the results obtained are given in the same 
way as in table II. 
TABLE IIL. 
t (hours) E (Millivolts). 
0 0,686 
24 0,685 
70 0,685 
96 0,685 
120 0,685 
168 0,685 
The potential difference found here is therefore the same as in 
the first series of experiments, which proves that the materials were 
quite pure before they were shaken with water and that in the 
first experiment equilibrium was obtained (by diffusion). 
10. Between the free energies of red and yellow mercuric oxides, 
therefore, a sensible difference exist, viz. 0,685 millivolt at 25°.0, 
a difference at least 700 times greater than the difference which I 
was able to detect with the apparatus used between red and red or 
yellow and yellow oxide. 
OsTWALD’s statement, that the capillary electrometer employed, 
which was capable of detecting potential differences of 1 to 2 milli- 
volts, showed no deflection, agrees completely with my result that 
the difference of potential in question is only 0.685 millivolt. 
(OstTWALD does not state at what temperature MARK's measurements 
were made.) 
