BRIDGMAN. — THERMODYNAMIC PROPERTIES OF WATER. 



347 



of the luiuul for a given increment of pressure decreases almost at 

 the same rate that the pressure itself increases. 



The total heat given out during an isothermal compression may be 



derived from the formula 



dp 



dT 



This quantity is shown 



in Figure 7. The figure does not call for especial comment. The 



Pressure, ksrm. / cm. 



Figure 7. The heat given out by water during an isothermal compression. 



rapid change in the direction of the isothermal lines in the vicinity of 

 the origin due to the abnormal behavior at low temperatures and pres- 

 sures is manifest from the figure, as also the slight abnormalities at 

 the upper ends of the 0° and the 20° curves, already commented upon 

 in other connections. Beyond 5000 kgm. the curves for all tempera- 

 tures tend to become linear and parallel to each other. 



These two quantities, the heat liberated in compression and the 

 mechanical work, combine to give the change of internal energy along 

 an isothermal, this change of energy being equal to the difference of 

 the heat and the mechanical work. The change of energy so calcu- 

 lated is shown in Figure 8. The change is a decrease, which continues 

 at all temperatures up to the highest pressures. In the previous 

 paper a value of this quantity was given, confessedly inaccurate, 

 since in the computation the mean thermal dilatation between 0° and 

 20° had been used instead of the actual dilatation at 0° or 20°. The 



