108 



BRIDGMAN. 



calculated values of latent heat and the change of internal energy in 

 Figure 10, and the numerical values are collected in Table VI. 



There are three modifications of the solid, but it was possible to 

 make observations on only two of the transition lines because of the 

 unusual volume relations. At lower temperatures there is only one 

 transition line, I-III, but at 102.3° there is a triple point, and the line 

 splits in such a way that almost all the change of volume remains with 

 one of the lines, I-II, and almost all the heat of transition with the 

 other. The change of volume between II and III is so small that it 

 w^as not possible to measure points on this line, the motion of the 

 piston accompanying this transition being only 0.001 of an inch. 

 Apart from the e^^dence afforded by the sharp change of direction of 

 I-III, the existence of the line II-III was verified by direct observa- 



80° 



Temperature 

 Carbamide 



Figure 10. Carbamide. The calculated latent heats and the changes of 

 internal energy. 



tion, by varWng temperature at constant volume and plotting the 

 resulting change of pressure. A discontinuity in this curve of the 

 appropriate order of magnitude was found, but of course this method 

 does not give accurately the coordinates of the transition line. 



Along with an abnormally small change of volume and a fairly high 

 latent heat goes, of course, a very small slope for the line II-III. 

 This slope was found by calculation from the data for the other lines 

 at the triple point to be only 0.7° per 1000 kgm., by far the smallest 

 slope yet found. It should be pointed out, however, that this calcu- 

 lated value was found from the difference of two very nearly equal 

 quantities, so that it may be in error by a rather high percentage. 

 The relation of the curves for the change of volume makes it perfectly 

 certain, however, that the slope is positive. 



