BRIDGMAN. — THERMODYNAMIC PROPERTIES OF WATER. 31 7 



not calculahlt' hy the theory of elasticity, because of the entrance of 

 such ofl'ects as hysteresis. To deteriuine the correction an auxiliary 

 set of experiments is necessary. Evidently if the true \alue of the 

 compressibility of some one substance were sufficiently well known, 

 then the apparent compressibility as determined bj' this method would 

 give the correction for the distortion of the cylinder. No such com- 

 pressibilities are known with any high percentage accuracy, but this 

 is not necessarv, T)rovide(l onlv that the uncertaintv in the standard 

 compressibility is small in comparison with the distortion of the 

 vessel. The substance which most readily suggests itself because 

 of its small compressibility is steel, but this is a solid, whereas the 

 method is applicable directly only to liquids, so that some modifica- 

 tion of the procedure is necessary. Such a modification readily sug- 

 gests itself, antl has been used by the author in the previous determi- 

 nations of the thernud dilatation of water at temperatures l)elow 0°, 

 and has also been used by Parsons and Cook. The modification is to 

 replace part of the liquid under investigation by a steel cylinder, and 

 determine the compressibility of the liquid and the steel together. 

 The difference of two determinations, the one for the liquid alone, 

 the other for the liquid and the steel, gives a value for the difference 

 of compressibility between the liquid and the steel from which the 

 effect of the distortion of the vessel has been almost entirely elimi- 

 nated. Furthermore, the compressibility of the steel is so small in 

 comparison with that of the liquid that the slight uncertainty in the 

 value for the steel is of no account, so that the compressibilit}' of the 

 liquid is given directly. 



The application of this method would demand, then, that the inte- 

 rior of the cylinder be filled first with water and the apparent compressi- 

 bility determined, and then part of the water replaced by steel and 

 the apparent compressibility determined again. But this demands 

 that the coil of manganin with which the pressure is to l)e measured 

 come directly in contact with the water, which evidently cannot be 

 allowed because of the short circuiting produced by the water. It 

 seemed to be necessary, then, to devise some sort of protection for the 

 coil, which should not occupy so much volume as to introduce a 

 serious correction, and which should at the same time transmit the 

 pressure readily to the innermost parts of the coil. Considerable 

 time was spent in trying to devise such a protection. The scheme 

 adopted was to surround the coil with a small mass of vaseline enclosed 

 in a flexible sac, formed from the finger of a silk glove, and rendered 

 impervious to water by painting it over with several coats of the col- 



