84 BRIDGMAN. 



values of A// and AE in Figure 14, and the numerical values in Table 

 \l. The marked upward concavity of the transition line is unusual. 



There are no other results for comparison. The data are too 

 inaccurate to justify any attempts to estimate Aa, AjS, or ACp. 



No new form was found to 12000 at .30° or 60°. 



Carbon Trichloride. — -This was Kahlbaum's purest, used with- 

 out further purification. The powder was hammered cold into an 

 inverted steel shell, and the pressure transmitted to it by mercury. 

 Four fillings of the apparatus were made, two for the points at high 

 pressures, and two for the points at low pressures (80 to 400 kgm.) 

 About 21.5 gm. were used for the high pressure determinations, and 

 33 gm. for the low pressures. 



C2CI6 is known to have three modifications at atmospheric pressure, 

 and hence two transition lines. These have already been investi- 

 gated by Tammann "^ up to 3000 kgm. The substance promised to 

 be an interesting one, because the transition lines diverge at atmos- 

 pheric pressure, a phenomenon not shown by any other substance 

 of which I know. It was of interest to see whether these lines would 

 tend to come together again at high pressures. It is unfortunate, 

 however, that this question could not be answered, because at the 

 higher pressures on the transition line above 3000 kgm. the substance 

 decomposes. The first run gave four points on the II-III curve to 

 177°. The transition runs cleanly on this line with no perceptible 

 rounding of the corners. There is, howe\'er, some lag on both sides 

 of the line. This lag, combined with the small change of ^■olume, 

 once or twice resulted in the pressure limits from above and below 

 being as wide as 200 kgm., one phase being all exhausted before pres- 

 sure could be restored to the equilibrium value. The lag at other 

 points was not so great, and the pressure range was only 40 to 60 kgm. 

 wide. The effects were very different on the I-II curve. The first 

 point attempted on this curve was at 177°. Above the proper value 

 of the transition pressure, the pressure l)egan to rise slowly with time, 

 just as it does with premature melting due to impurity. In the sup- 

 position that the effect was really due to impurity, the work was 

 hastened so as to minimize as far as possible the effect. On arriving 

 at the transition point, however, the rise of pressure continued at a 

 nearly constant rate to nearly 1200 kgm. beyond the supposed point. 

 On increasing pressure again, the automatic rise of pressure continued 



7 G. Tammann, " Kristallisieren und Schmelzen," 298. 



