174 
It will be clear from the table and the corresponding graphical 
„representation (fig. 3) that there is sufficient harmony between the 
results obtained by the two methods of observation. 
P 
atm. 
100 
90 
80 
10 
60 
50 
40 
ne 
0 20 40 60 80 100 120 140 160 7 
Fig. 3. 
By way of control of the pressure measurements we have exposed 
one of our manometer tubes, after being opened, in the copper tube 
to the same pressures and temperatures as occurred in our deter- 
minations. Then it appeared that in none of the observations a 
correction was required for a change of the zero position. 
5. As for the nitrogen tetroxide we have to do with a substance 
which is in dissociation, for which the values of the degree of the 
dissociation appreciably vary both in the liquid state and in the 
vapour state corresponding with it — for the vapour we already 
gave some values for the degree of dissociation in our preceding 
communication — it seemed desirable to calculate the value of f from 
VAN DER Waars’s empirical equation with the aid of our observations. 
If for this purpose in the equation: 
i ae TT 
VEE T 
