BRIDGMAN. — THERMODYNAMIC I'liUl'liUTIES OF WATKK. 345 



factorily, and in which tlic accuracy was not very high. The curves 

 at the higher temperatures behave as one wouhl he prepared to expect 

 in the region of low pressiu'es. The curve for 40° sliows x'estiges of 

 the abnormal behavior at the low pressures, namely slight initial 

 rise of dilatation with rising pressure, followed by a fall, but the 

 curves at the higher temperatures, 60° and S0°, show the regular 

 initial decrease with rising pressure shown by all normal liquids. But 

 at higher pressures, the behavior of all three of these curves, for 40°, 

 00° and S0° is different from what might be expected. The unexpected 

 feature consists in the crossing of the curves, all in the vicinity of the 

 same pressure, 5500 kgm., so that at higher pressures the thermal 

 dilatation at the higher temperatures is lower than it is at the lower 

 temperatures. It has been already remarked that there are indica- 

 tions, both from the present work and from that of Amagat, that this 

 may be the beha\ior for any normal liquid at sufficiently high 

 pressures. The comparative constancy of the thermal dilatation at 

 the higher pressures, fs also a matter perhaps not to be expected. 

 Thus the expansion at 40° remains nearly constant over the entire 

 range of pressure, while the compressibility has in the same range 

 dropped from 44 to 9. It was distinctly expected, before these 

 measurements were taken, that the dilatation would show the greater 

 variation with pressure, so that the effect of temperature on the 

 volume would tend to disappear at the higher pressures, but such is 

 not the case. 



The relative thermal dilatation may be plotted against pressure, 

 as was the relative compressibility. The curve shows no striking 

 features. The curve plotting relative dilatation against volume has 

 also been plotted, and this is the same in general character as the 

 others. The slight differences consist in an accentuation of the ab- 

 normalities in the neighborhood of 5500 kgm., and the fact that at 

 the lower volumes, that is at the higher pressures, the dilatation 

 against volume increases with decreasing volume for 40° and 60°, 

 but decreases for 80°. 



These figures for the thermal dilatation and the compressibility 

 complete those which are obtainable directly from the table. Other 

 quantities of thermodj'namic interest may be obtained by combining 

 these, however. Perhaps the simplest of these quantities are those 

 connected with the absorption of energ}' when the pressure is changed 

 at constant temperature. The first of these is the actual mechani- 

 cal work done by the external pressure in compressing the liquid 

 at constant temperature. This of course is simply the expression 



