94 BRIDGMAN. 



quantities easily so that the A// values shoukl check, and the values of 

 the tables are left with this error. This is the only substance for 

 which the values have not been so adjusted as to check at the triple 

 point. In the case of other substances the amount of necessary adjust- 

 ment is so slight and is indicated so unambiguously, that the probable 

 accuracy of the individual curves can only be increased by demanding 

 that the necessary conditions at the triple point be accurately satisfied ; 

 but here the error is great enough so that the precise direction in 

 which the adjustment should be made is not indicated unambiguously 

 and hence the adjusted values would be likely to have as much or 

 more error than the unadjusted ones. The amount of adjustment 

 is not so very large even here; an increase of one value of Ai/ by 

 3.5 % and a decrease of another by the same amount would satisfy 

 the conditions. 



The experimental results are shown in Figures 18 and 19, the com- 

 puted values of hH and I^E in Figure 20, and the numerical values are 

 collected in Table IX. In the figures the values of A I' are not given 

 which are obviously in error because of decomposition. In the phase 

 diagram the initial direction of the melting curve is indicated. This 

 is taken from the work of Wahl, who found that because of decomposi- 

 tion, the melting curve could be followed only about 10° above the 

 normal melting point. The initial slope of the melting curve is un- 

 usually high ; in this work no attempt was made to obtain any of the 

 data of the melting curve. 



Other results for comparison are as follows. For the transition 

 point at atmospheric pressure Schwarz ^ gives 46.1° by an optical 

 method, and Rothmond ^^ gives 46.91° by a thermometric method. 

 Wahl ^^ seems to have been the only previous experimenter on the 

 effects of pressure. His transition curve extrapolates to 47.3° as 

 the transition point at 1 kgm. The extrapolated value found above 

 from the second purer lot was 46.2°. The specimens of Rothmund 

 and Wahl were, therefore, probably purer than those used above; 

 in particular, Wahl's specimen seems to have been purified with very 

 great care. Wahl also followed the transition line I-II up to 1500 

 kgm. At 1500 his transition temperature is 2.8° higher than mine, 

 whereas it starts 1.1° higher at atmospheric pressure. The difference 

 of slope, which amounts to about 3.5%, may be an effect of impurity. 

 One point investigated with especial care by Wahl was that of the 



11 V. Rothmund, ZS. phys. Chem. 24, 705-720 (1897). 



12 \V. Wahl, Trans. Roy. Soc. 212, 117-148 (1912). 



