550 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



The data obtained for the liquid are sufficient to enable us to calcu- 

 late certain other quantities of thermodynamic interest. Two of these, 

 the difference of the specific heats and the change of internal energy 

 along an isothermal, may be calculated directly from the given data. 

 Two others, the adiabatic compressibility and the rise of temperature 



rp 



e 

 PRESSURE, KGIvj/CM^XIO"? 



Figure 41. The mean difference of the specific heats of the liquid for 

 the temperature range 0°-22°. 



produced by compression, may be computed roughly, merely indicating 

 the direction in which these quantities change under pressure. 

 The difference of the specific heats is given by the formula 



c„ 



Cp — 



Xdr)^ 



{'A 



The quantities entering this equation have been determined directly. 

 The computed values for 22° are shown in Table XXXIIL, and graphi- 

 cally in Figure 41. The general behavior is a rise to a maximum at 

 5000 and then a decrease. For a normal liquid Cp — Cp probably de- 

 creases continuously with rising pressure. This has been shown to be 

 the case for mercury in the previous paper. The significance of the 

 maximum is, then, merely a repetition of the old story that at high 

 pressure water loses its abnormality and becomes normal. The meas- 

 urements have not been made to high enough pressures to show the 

 reversal of curvature on the descending branch of the curve, which 

 would show complete attainment of normality. The values of Cp — Cp 



