472 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



first tabulated values 



dp 



are obtained from this smooth curve. 



With these values of — , AZT was calculated. It was then necessary 



to adjust the values of A/iT slightly so as to satisfy the identical relations 

 at the triple point. These new values of AZTare tabulated. The change 



in the value of AZT demands a corresponding change in the values of -j- 



which are given in the sec- 

 ond column. These latter 

 values are to be taken as'the 

 most probable values. The 

 difference between the two 

 columns shows the amount 

 of adjustment necessary, 

 and gives an idea of the accu- 

 racy of the data. Of course, 

 as already explained, the 

 slope is very much more sen- 

 sitive to slight errors than 

 the observed values of jt?and 

 t themselves. This same 

 process of adjustment has 

 been used on all the equilib- 

 rium curves. In some cases, 



80 



75 . 

 70 £ 



S5< 

 o 



60 o 



55 



-25" 



-20" -15° -10° 

 TEMPERATURE 



-5° 



Figure 7. The latent heat and the change 



of internal energy on the I-L curve. -, dp . ,, 



where ~- is very small, no 



change has been necessary. The data of Table IX. are shown graphi- 

 cally in Figure 7. 



The data give some hold on the actual compressibility of the solid 

 at different points on the equilibrium curve. At 0° this may be cal- 

 culated without approximation from the observed data. The thermal 

 dilatation and compressibility of water at 0°, and the thermal dilata- 

 tion of ice at 0°, are already known. These present data give the 

 change of A F with temperature and pressure on the equilibrium curve. 

 These four quantities evidently suffice to determine the compressibility 

 of the solid at 0°, for we have for small changes of ^:> and t, 



where the subscript (1) denotes the liquid and (2) the solid. 



