BRIDGMAN. — THERMODYNAMIC PROPERTIES OF LIQUIDS. 95 



of the curves for Q, give us an idea of what we might expect to be 

 the relative values of Q if the liquids preserved over the entire 

 pressure range their relative initial behavior. Table XX shows this. 

 It gives the initial dilatation and its ratio to the average, the total 

 heat given out at 12000 kgm. and its ratio to the average. The 

 dilatation tabulated for the low boiling liquids was obtained by a 

 linear extrapolation, which gives values too small. Larger values 

 for these liquids would only increase the force of the argument. It is 

 obvious that the two ratio columns show only a general rough agree- 

 ment; large values of one corresponding to large values of the other. 

 There seems to be no correspondence in the small variations in the 

 ratio column. This shows that the initial behavior of a liquid with 

 respect to the heat of compression does not fix its behavior at the 

 higher pressures. Furthermore, the magnitude of the variations in 

 the ratios of the dilatation are greater than the variations of the heat 

 ratios; a maximum variation in the one column of 1:1.8 against 1:1.3 

 in the other. This shows again that the liquids become more alike 

 at the high pressures than we should expect from their initial behavior 

 at atmospheric pressure. 



The magnitude of the heat of compression is of interest. For the 

 average liquid this is about 17 kgm. m. at 12000 kgm. If we take as a 

 fair average for C^ 25 kgm. cm. this means that the amount of heat 

 flowing out of the average liquid as it is compressed isothermally to 

 12000 kgm. would raise it through 68° at atmospheric pressure. 



Change of Internal Energy. — This quantity is shown on 

 Folder V; for the twehe liquids separately at four temperatures 

 in Figures 73 to 84, and the average results for the twelve liquids 

 plotted against pressure in Figure 85 and against volume in F'igure 

 86. The change of energy plotted in these figures is the internal 

 energy at atmospheric pressure minus the internal energy at the 

 pressure in question. A positive value for the change means, there- 

 fore, that the internal energy is less at the higher pressure than it is 

 at atmospheric. The origins of the curves for the separate tempera- 

 tures have been displaced with respect to each other, so as not to 

 confuse by over lapping. In the cases where the liquid boils at low 

 temperatures the origin of the curve for the higher temperatures has 

 been taken at 500 or 1000 kgm. 



The change of internal energy was found by taking the difference 

 between the heat and the work of compression. The curves show 

 nothing, therefore, not already given. 



The different substances show irregularities which cannot be dwelt 



