BRIDGMAN. — WATER UNDER PRESSURE. 443 



tion of ice above 0° was not then suspected. When this was discovered 

 in the course of the compressibility measurements, the plan of the paper 

 was extended so as to take in the investigation of this new form of ice 

 over the same temperature range as the compressibility determinations. 

 The compressibility measurements were then completed and the inves- 

 tigation of this new form of ice taken up. This led into all the un- 

 suspected complications of the equilibrium conditions between the five 

 different forms of ice, which necessitated the expenditure of much more 

 time than had been anticipated. It then became necessary, for the sake 

 of completeness, to measure the compressibility of water in its region of 

 existence as a liquid below 0°. During this work with the various mod- 

 ifications of ice, experimental familiarity with the possibilities of high 

 pressure apparatus had been increasing, so that it became possible to ex- 

 tend the work on the ice first found to nearly twice the pressure range 

 reached in the compressibility measurements. This is the state of 

 the work as presented here. To be complete, the compressibility of 

 water should now be redetermined over an increased temperature range 

 corresponding to the increased pressure range, but this process of ad- 

 vancement might be continued indefinitely and a stop has to be made 

 somewhere. For instance, it would probably be possible with the means 

 now at hand to measure directly the compressibility and the dilatation 

 of these various forms of ice, and also the adiabatic compressibility of 

 the liquid. As it is, the pressures have been pushed far enough on 

 both the liquid and the solid to indicate what the general nature of the 

 effects for the highest pressures may be. The pressure required to in- 

 dicate this is higher for the solid than for the liquid, so that the lack 

 of complete parallelism between the results for the liquid and the solid 

 is partly justified. 



The order of presentation finally chosen arranges the subject matter 

 in two parts. The first deals with the compressibility of the liquid at 

 different temperatures. The second, by far the longer, gives the data 

 for the different modifications of the solid, including the quantities 

 involved in the transition solid-solid as well as in the transition solid- 

 liquid. The order of presentation in the second part will be the natural 

 order, proceeding systematically fi-om the lower to the higher pressures. 



This systematic order was not, as has been stated, the actual order 

 of the experiment. The existence of another form of ice stable at high 

 pressures and at temperatures above zero was first discovered by the 

 anomalous results of the compressibility determinations. The exist- 

 ence of this form was then made certain by the measurement of the 

 electrolytic conductivity of very dilute solutions, there being a change 

 in the conductivity when the transition occurs. Not until then was 



