176 
succeeded in getting quantitative data about the homogeneous equi. 
librium by a colorimetrie method, which data accord well with the 
determinations from the vapour densities. As the colour of the liquid 
and the vapour gets darker and darker towards the critical temperature, 
the degree of dissociation will probably be great at 7. 
In order to get a criterion about the degree of the dissociation 
we have calculated the values of a and 5 from the equation of 
state (as the result of a discussion of one of us with prof. VAN DER 
ae By substitution of 7),= 481.2 and Pr = 100, we find: 
AT Sie 
= 0,0105 and 
ETT Di Pi 
i Ti 
000107: 
T 8.273 273 Pz 
If to get an approximative estimation we now consider the 5 as 
an additive quantity, we can calculate the theoretical 5 for NO, 
resp. V,Q, from the tables of the J-values, and compare them with 
the values found above. 
From the values for nitrogen and oxygen we find in this way 
for NO, and N,O, resp. 0,00226 and 0,00452. 
Calculation with the aid of the data about nitrogen oxide and 
oxygen, resp. nitrogen mon-oxide and oxygen, yields for NO, and 
N,O, 0,00186 and 0,00372, resp. 0;00200 and 0,00400. 
So we draw the conclusion from these values, that the fluid phase 
for the critical circumstances consists for by far the greater past of 
split molecules. 
7. The complex behaviour of the nitrogen tetroxide leads us to 
expect an intricate equation for the P7*-line. Caloric data, which 
can be of use to us to find the vapour tension equation, are not 
sufficiently known. For this we must of course know the heat of 
evaporation and the specific heats along the border-line. The specific 
heats which are known, refer to unsaturate vapours as far as the 
vapour state is concerned. Accordingly they would have to be corrected | 
in accordance with the change of the degree of dissociation with the 
pressure. The heat of dissociation in the homogeneous vapour is 
known pretty accurately, and so this correction might be applied 
at those temperatures for which the degree of dissociation in the 
saturate vapour is known (see preceding communication Table IV). 
The specific heat of the liquid is almost quite unknown. So even if 
the heat of evaporation at one temperature were known with sufficient 
accuracy, the unknown dependence of the specific heats on the 
