liUlDG.MAN. — TIIEUMODYNAMIC PROPERTIES OF WATER. 323 



coefficient could l>c round for the four lower temperatures, but be- 

 tween 85° and 110° there is a very perceptible chatiffc of 1%. But 

 since the range of temperature of the actual e\j)criment flid reach 

 over 80°, no correction was applied to the observations for this effect. 

 It is to be noticed that this result is valid only for this one coil, since 

 previous work, both by Lisell ^ and by the author, liave shown that 

 different pieces from the same spool of wire may show slight \ariations 

 in the temperature coefficient, which is sometimes positive and 

 sometimes negative. 



In addition to this special calibration for slight relative changes 

 in the pressure coefficient with temperature, the absolute value of the 

 pressure coefficient has been checked from time to time during the 

 course of the experiments. This could be done conveniently with the 

 apparatus as used for the compressibility determinations by determin- 

 ing the transition point of ice VI, or of mercury at known temperatures. 

 These calibrations have shown no change whatever in the pressure 

 constant of the coil. 



It has already been stated that the actual measurements involve 

 two sets of readings, one with the apparatus filled with water, kerosene 

 and a small amount of bessemer steel, and a second set with additional 

 steel replacing the water. By subtracting the piston displacement at 

 any given pressure for these two sets of experiments a value is obtained 

 which gives approximately the piston displacement for the water alone, 

 and from which the effect of the distortion of the vessel has in large 

 measure been eliminated. But a moment's consideration will show 

 that the effect of distortion has not been entirely eliminated, and it 

 is necessary to apply a correction for the slight residual effect. The 

 correction comes because of the fact that the position of the piston 

 at corresponding pressures is not the same in the two sets of experi- 

 ments, so that the subtraction leaves still uncorrected the distortion 

 due to the part of the cylinder exposed to pressure in the one set of 

 experiments and not so exposed in the other. This correction can- 

 not be determined directly, and the only way seems to be to calculate 

 it by the ordinary theory of elasticity, taking for the constant of the 

 steel the values under ordinary conditions, which are known not to 

 vary much even for the most different varieties of steel. There is 

 undoubtedly some error in the correction as so determined, but the 

 total value of the correction is at best small, and any such error is 

 relatively unimportant. 



7 Lisell, Om Tryckets Inflytande pk det Elektriska Ledingsmotst&ndet 

 hos Metaller samt en ny Metod att Mata Hoga Tryck (Diss. Upsala, 1903). 



