POLYMORPHISM AT HIGH PRESSURES. 



105 



value much too large, 0.001 against 0.0005. This indicates that at 

 least the initial values of Aa are a little too high. 



A number of measurements have been made on acetamide at atmos- 

 pheric pressure by other observers. For the melting point of the 

 stable variety there is 82° to 83° by Hofmann,^^ 81.5° by Block/i and 

 80.1° by Korber.-^'^ The value for the specimen used above was 81.5°. 

 The change of volume has been found to be 0.1507 cm.Vgm- at atmos- 

 pheric pressure by Block/ ^ which is in inexplicable disagreement with 



TABLE V. 



Acetamide. 

 Difference of Compressibility between the Liquid and the Two Solids. 



the value found above. The effect of pressure on the melting point 

 has been measured by Korber/^ who used the comparatively ^inaccu- 

 rate method of varying temperature at constant volume. His melting 

 curve shows considerably more curvature than mine, starting at a 

 temperature lower by 1°.4, it is 3°.8 higher at 1600 kgm., and l°.l 

 higher at 3000. This must have been a result of his method; the 

 lower initial melting point and much premature rounding of his curves 

 shows that his specimen must have been the impurer of the two. It 



20 Hofmann, Bar. D. Chem. Ges., 14, 2729. 



