POLYMORPHISM AT HIGH PRESSURES. 



93 



corners of the melting curve show somewhat more rounding, which 

 in any event is sHght, and on taking the apparatus apart a few 

 bubbles of gas are set free. To avoid error from this effect meas- 

 urements were begun about twice as far above the melting pressure 

 as usual, and the cylinder was kept in cold water over night between 

 runs. At the highest point attempted, 12000 kgm. and 165°, the 

 reaction becomes so much more rapid that it did not seem worth 

 while to make measurements. Runs were made with three fillings 

 of the apparatus, two at high pressures and one near atmospheric 

 pressure. 



The equilibrium values of pressure and temperature are shown in 



'0 



J3456789 10 

 Pressure, kgm. /cm. ^ x 10^ 

 Acetic Acid 



Figure 1. Acetic Acid. The observed equilibrium pressures and tempera- 

 tures. 



Figure 1, the observed changes of volume in Figure 2, the latent heat 

 and change of internal energy in Figure 3, and the numerical results 

 are collected in Table I. There is a second solid phase; the existence 

 of this phase was first discovered by Tammann. No peculiarities are 

 presented by the phase diagrams. It is to be noticed that the direc- 

 tion of curvature of the Av curves on both melting lines is the normal 

 one for solid-liquid. 



There are a number of measurements of the thermodynamic data 

 at atmospheric pressure. For the melting temperature there is 17.5° 



