24 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



Amagat are found for the changes of volume at low pressures (which 

 indeed is already the case for those liquids measured by Richards), 

 then the results given here may be corrected by adding a constant to 

 the volumes throughout the tables, except of course at atmospheric 

 pressure. The addition of such a constant to the volumes will not 



alter the behavior of any of 

 the thermodynamic proper- 

 ties at high pressures; it can 

 at most affect those which 

 involve integrations by a very 

 small constant corrective 

 term. 



That it was possible to 

 represent the approximate 

 behavior of these twelve liq- 

 uids by similar formulas is 

 itself a somewhat surprising 

 and significant fact. It seems 

 to suggest that at extremely 

 high pressures all licfuids be- 

 come alike. The greatest 

 differences between different 

 liquids are at the low pres- 

 sures. The use of a separate 

 formula in the case of ethyl 

 chloride, which might appear 

 to be an exception, was 

 necessitated in fact only by 

 its abnormal compressibility at low pressures. 



It was necessary to compute the thermal dilatation also by a method 

 slightly different from that used for water, because only one piston 

 displacement was read at each temperature instead of two. The 

 piston displacements were plotted against pressure on the same dia- 

 gram as the isothermal compressibility at 40°. (See Figure 2.) 

 Through each of the points a curve was drawn of the same general 

 slope as the curve of pressure and volume at 40°. The slight changes 

 necessary in the slope of this curve at different temperatures could 

 be made graphically with sufficient accuracy. The difference of the 

 piston displacement for every interval of 20° at the mean of the two 

 pressures involved was now read from these curves. Thus in Figure 2, 

 the line AB represents the piston displacement at constant pressure 



Pressure 



Figure 2. Shows a portion of the dia- 

 gram for determining the compressibihty 

 and thermal expansion from the piston dis- 

 placements. The piston displacements are 

 plotted against pressure. The heavy points 

 are the readings with increasing and de- 

 creasing pressure at 40° for the isothermal 

 compressibility. The discrepancy between 

 these points is due to hysteresis. The open 

 circles show the readings at constant volume 

 with changing temperature. The dotted 

 lines, AB for example, show the piston 

 displacement which would have been found 

 if the temperature had been changed at 

 constant pressure. 



