( 274 ) 
“It is proved by these experiments that the free energy of the 
two forms of the oxide is the same; since the same thing has been 
proved for the total energy by the experiments of Varer, the above 
conclusion, that the two forms are identical, follows of necessity.” 
2. In my researches on the difference in the free energy of the 
two isomeric forms of tin, the grey and the white !), of which I 
shall publish the details shortly, I had found that the difference 
between the forms is very small. Even at a considerable distance 
from the transition temperature (20° for example) the difference is 
only of the order of a few millivolts. 
If now, in a case such as that of tin where the isomerism is 
so clearly marked, only such small differences in the free energy 
of the modifications are to be found, it is natural to assume that 
the scale with which OsrwaLD measured in the case of the red 
and yellow mercuric oxides (1 to 2 Millivolts) was much too large 
to permit of the definite conclusion that there is no difference in 
the free energy of the two modifications. 
I decided therefore to determine the difference of free energy 
between red and yellow mercuric oxides, choosing a scale a thousand 
times smaller than OsTwALD’s (*/jo99 millivolt). 
3. In 1892 an investigation by GLAZEBROOK and SKINNER ap- 
peared 2) in which a number of observations is described which 
indirectly have an important bearing on the question with which 
we are here occupied. 
GLAZEBROOK and SKINNER investigated the E. M. F. of the 
Gouy normal cell 3), which is constituted as follows: 
Hg | HgO | 10 °/, solution of Zine sulphate | Zn, 
and found a great difference between the E.M.F. of elements con- 
structed with yellow and with red mercuric oxide. 
For the E. M.F. of the Gouvy cell containing red mercuric oxide 
they found 1,384 Volt, for that of the element with yellow oxide 
1,391 volt at 12° C. 
1) See Ernst Conen, A new kind of transition element (sixth kind). Proceed. Roy. 
Acad. Amsterdam. Vol. IT. 1899 p. 153. 
2) Phil. Trans. of the Royal Society 183. 367 (1892). 
3) Journal de Physique Tome VII (1888), p. 532. 
