BRIDGMAN. — THERMODYNAMIC PROPERTIES OF WATER. 331 



tions were made were not exactly the e\'en temperatures desired, 

 namely 20°, 40°, and 00°, and 80°, but they were in all cases within 

 a few tenths of a degree of these temperatures. The results were 

 correcteil to these even temperatures by assuming the mean variation 

 with temperature over the whole temperature range to hold for the 

 few tenths of a degree on either side. The final result given by the 

 data is the total change of volume for an interval of 20°; from 20° 

 to 40°, from 40° to 60°, and from 60° to 80°. The mean of the results 

 of the two sets of experiments is shown with satisfactory accuracy in 

 Figure 2, on which are plotted all the values obtained by the different 

 methods. The results for the low pressures are shown in the full 

 black circles. These values are seen to extrapolate, without forcing, 

 to the values already found by other observers for atmospheric pres- 

 sure, and they also make fairly good connections with the values found 

 by the other method for the higher pressures. In view of this agree- 

 ment it did not seem to be necessary to make further determinations 

 of this quantity. 



Compressibility at High Pressure. 



The determinations of the isothermal compressibility at higher 

 pressures extended over a considerable interval of time and are more 

 numerous than any of the other determinations. In all, twelve deter- 

 minations of this quantity were made, at five different temperatures. 

 These determinations include those made during the early course of 

 the experiment, when the attempt was being made to find the thermal 

 dilatation directly from the difference of compressibility at different 

 temperatures. A little work with the method showed that it was not 

 sufficiently accurate for the purpose, but the results obtained then can 

 be used to give the compressibility at the standard temperature, 40°, 

 by applying the temperature correction found from the later more 

 accurate results. The temperature of 40° was chosen as the standard 

 because this is the lowest of the 20° intervals at which the water is 

 liquid up to 12000 kgm. 



The results of these twelve determinations, extending over a period 

 of three months, are shown in Table II. The results as given are 

 reduced to 40°, but the temperature at which the original measure- 

 ments were made is given also in the table. Two of these sets of 

 determinations differ considerably from the others, and were discarded 

 in taking the mean, although as it happens one of these discarded sets 

 is too high and the other too low, so that it makes very little difference 



