510 C. Bancs — Fluid Volume, Pressure, and Temperature. 

 Constructing the isometric for Y„ =Y rt ,, rt =1, it will "be 



n dip 29,100 y 



seen that the 310° point may be looked for in the region above 

 2000 atm. Hence, these observed results substantiate the 

 computed isometric in figure 4, which predicts the correspond- 

 ing point at 2300 atm. Nevertheless it cannot be too carefully 

 noted, that if the isometrics for Y„ =1*2, 1'3, 14, ... . be 



constructed tbe break between 185° and 310° remains in full 

 force, quite in conformity with the other data (alcohol, par- 

 affine, etc.). 



The full interpretation of these discrepancies is of great 

 importance and will therefore be made the subject of my sub- 

 sequent work. The isometric, curved as above, introduces 

 certain interesting conditions of maximum volume. 



The chief observational discrepancy remaining in the results 

 is the expansion error encountered in case of substances which 

 solidify between observations at different temperatures. Hence 

 the effect of different volumes on the slope of the isometrics 

 cannot be satisfactorily discussed. Since the compression 

 measurements retain their value independent of the thermal 

 expansion, and since the method pursued is such that all nec- 

 essary measurements for thermal expansion can be made under 

 atmospheric pressure, the difficulties may easily be rectified. 

 For by using a bulb and stem arrangement, the purely thermal 

 data can be supplied with any desired accuracy. This I con- 

 ceive to be the advantage of the mode of investigation set 

 forth in the present paper. 



Among the important results of the above tables is the fact 

 that compressibility moves in the even tenor of its way quite 

 independent of normal boiling points and melting points, pro- 

 vided of course the conditions are not such that boiling or 

 melting can actually occur. For this reason compressibility is 

 particularly adapted for exploring the nature of the environ- 

 ment of the molecule in its relations to temperature, i. e. for 

 exhibiting the character of the thermal changes of the molecu- 

 lar fields of force. 



The above work though confined to relatively low ranges of 

 pressure was believed to have a more general value for reasons 

 such as these : instead of tracing the isothermals of a single 

 substance throughout enormous ranges of pressure, similarly 

 comparable results may possibly be obtained by examining 

 different substances, conceived to exist in as widely different 

 thermal states as possible. For in such a case, since the actual 

 or total pressure is the sum of the pressures externally applied 

 and the internal pressure, the total pressure in question vir- 

 tually varies enormously. This calls to mind the remarks 

 made in §§ 2S, 34, relative to observations confined to a limited 

 part of the isothermal. 



