( 460 ) 
If, now, we introduce into the equation 
Ez dm 
= —+7— 
k NE) + dT 
or 
da 
d 
the found values (T= 298; 7 = 0.685; Pe 0,0088 ) and express 
everything in caloric measure we find 
E, = — 2X 23,09 & 1,9374 = — 89.4 calories }) 
6. VARET has determined in 1895 the heat of reaction of red 
mercuric oxide with hydroeyanie acid. He finds this to be 31550 
calories, whilst BERTHELOT found 31600 for the yellow oxide. 
VARET then observed: “On voit que la transformation de l’oxyde 
“jaune de mercure en oxyde rouge ne donne lieu a aucun effet 
“thermique appréciable.”’ 
The difference of — 50 calories certainly does rot signify much 
considering it is a difference between two large figures and the 
ordinary caloricmetric determinations are subject to rather great errors. 
Still I cannot help pointing out that the calculated results of — 89 
calories and the experimental result obtained by VARET are of the 
same order, whilst our electrical measurements decidedly prove that 
there must exist a difference in chemical energy between the two 
varieties of mercuric oxide. 
It is moreover somewhat illogical on the part of VARET ?) 
to state that no appreciable thermic effect takes place when the 
yellow oxide changes into the red modification, when in his paper 
on the different modifications of mercury sulphide, real importance 
is attached to the caloric value of —60 calories obtained as a difference 
between 240 and 300 calories. 
Amsterdam, Chem. Lab. of the University. 
January 1900. 
Strictly taken we aught to pay attention to the difference of heat of solution of 
HgO in the solutions of KOH. 
*) Ann, de chimie et physique [VII] T. 8 p. 102. (1895). 
