138 
DE. WALTER WAHL: PHYSICO-CHEMICAL DETERMINATIONS 
Table IV. 
Observations at falling 
temperatures, about 
Constant pressures, Pp. 
Series A. 
°c. 
71 
970 kg./cm.- 
63-5 
700 „ 
54-5 
385 „ 
Series B. 
73-2 
1,000 kg./cm. 2 
67-8 
760 „ 
61-3 
510 „ 
55-0 
299 „ 
51-9 
200 
The pressures Pg, P 4 , P^, and P,., given in the Tallies IT, III., and IV., Series A, are 
plotted in the diagram, fig. 6 , and foim the lower group of curves in this. The 
curve P 3 intersects with the temperature axis of the diagram at 47°‘8 C. and the 
curve P 4 at 46°'6 C. 
The significance of these transition-point curves Pg, P 4 , P 5 , and Pg, may be explained 
in the following manner ;— 
Pg represents the temperatures and pressures at which the growth of the anisotropic 
modification just attains a noticeable velocity when both modifications coexist. 
P 4 again the pressures and temperatures at which the isotropic modification is formed 
with noticeable speed under these same conditions. In the small strip between these 
two curves the two modifications of carbon tetrabromide will thus coexist without 
changing one into the other. The true equilibrium curve must lie between these two 
curves of “false equilibrium,” probably nearer to the curve P 4 than to Pg, as the 
velocity of transition seems to increase more rapidly in directions at right angles to 
this curve than to the curve Pg. 
If we work by a volumetric method we may, according to these curves, expect to 
find that the transformation takes place at a lower temperature when working at 
descending temperature than when working at rising temperature, and the horizontal 
distance (40 kg./cm.^) between the curves would represent the pressure values 
obtainable by the method at constant temperature which has been employed by 
Tammann in his transition-point determinations. 
The curves P 5 and P^ again represent the temperatures and pressures at which 
each modification is at first spontaneously formed from the other. The much greater 
distance at which tliese run from the true equilibrium curve shows to what a much 
