BRIDGMAN. — WATER UNDER PRESSURE. 465 



used in determining the change of vohime had to be modified with this 

 apparatus, since the reaction was so slow at the low temperatures. It 

 will be described in detail later. 



The third piece of apparatus for higher pressures and temperatures, 

 0° to 76° and 6000 to 20,500 kgm., consisted of only a single cylinder 

 containing the water, the measuring coil, and the advancing piston. 

 For these high pressures it was necessary to use only one piece of 

 apparatus because of the impossibility of getting tubing to stand these 

 high pressures over any extended time. The water was placed in a 

 steel shell surrounded by kerosene as before. The cylinder, together 

 with the lower part of the hydraulic press by which the piston was 

 advanced, was placed in a thermostat. In this third form, therefore, 

 the correction for the change of volume of the transmitting fluid on 

 passing from one temperature to another is avoided. But at the 

 higher pressures another correction is introduced because of the slow 

 yield of the steel. This will be described in its place. 



The data given for the ten equilibrium curves were all obtained in- 

 dependently of each other, at different times, with different fillings of 

 the apparatus, and in a number of cases with different pieces of ap- 

 paratus, either new pieces to replace those destroyed by explosions or 

 pieces of a different type. The consistency of the data obtained under 

 these various conditions is shown by the very close approximation 

 with which the identical relations are satisfied by the independent 

 data of the three curves at each of the three triple points. 



At each triple point there are three independent checks. In the 

 first place, the absolute values of the equilibrium pressures and tem- 

 peratures are checked by the necessity for the three curves running 

 together to a point. In the second place, the values of the change of 

 volume are checked by the obvious condition that at the triple point 

 I-II-III, for example, the change of volume I-II plus the change 

 II-III must be equal to the change I-III. The third check is given 

 by the condition for the latent heats analogous to that for the changes 

 of volume. This third check involves, besides the values already 

 given, the values of the slope of the three curves meeting at the triple 

 point. This third check is the most difficult to meet and the most 

 sensitive, as it is well known that the derivative of an experimental 

 curve is subject to much greater error than the curve itself. 



Such a triple check is afforded for the data of every one of the ten 

 equilibrium curves at at least one point : Five of the curves are rendered 

 still more secure by being tied down at both ends by a triple point, and 

 the other end of a sixth curve, I-L, is checked by the already known 

 data for 0°. 



VOL. XLVII. — 30 



