BRIDGMAN. — WATER UNDER PRESSURE. 545 



independent of the pressure until the maximum entirely disappears at 

 higher pressures. 



Figure 40 shows the results only to 3000 kgm. Up to this point the 

 dilatation at 0° has been increasing with rising pressure. But the fact 

 that the curves of Figure 4 pass through a maximum at about 3200 

 kgm. indicates a return to normal behavior. From here on the di- 

 latation decreases with rising pressure. The position of this maxi- 

 mum evidently corresponds to the position of the maximum of the 

 dilatation at 3700 kgm. found between 0° and 22°. One would expect 

 some change in the position of the maximum toward lower pressures 

 at lower temperatures, but even if there were none, the agreement is 

 perhaps as good as could be expected when one considers how very 

 small the experimental quantities are which are involved below 0°. 



As far as 4000 kgm., the curves of Figure 4 have been in perfect 

 accord with the manner of transition shown in Figure 40. Above 

 4000, however, if the curves are extrapolated in the direction in which 

 they are heading, there will be new abnormalities. This extension is 

 not actually possible physically, for the same reason that the h3rpo- 

 thetical curve connecting volume and temperature at atmospheric 

 pressure was not possible, namely because the water freezes. But the 

 extension may be made, nevertheless, for the purposes of speculation. 

 It is seen that this new abnormality at high pressures and low temper- 

 atures consists in a crossing of the lines again, so that at 5000 kgm., 

 for instance, water would expand on passing from -15° to -20°, just as 

 for water at 0" and atmospheric pressure. The explanation suggests 

 itself that this new abnormality is due to the new variety of ice which 

 is about to separate out, either V or VI. At any rate, the idea seems 

 perfectly plausible that each of the forms III, V, and VI is a solid form 

 of water in a different state of polymerization, and that this polymeri- 

 zation should be shown by anomalous effects in the liquid. There cer- 

 tainly seems to be a strong presumption raised for this possibility by 

 the present data. A more accurate experimental investigation would 

 be well worth making, but would require new methods and apparatus. 



We now have enough material in the behavior of the curves both 

 above and below 0° to see what the role of pressure in wiping out the 

 abnormalities must be. The one significant fact is that the pressure 

 wipes out the abnormalities where they stand, without any percepti- 

 ble shifting of their temperatures. Thus above 0°, the temperature of 

 minimum compressibility is very nearly constant at 50°, independent 

 of the pressure. Increasing pressure merely makes this minimum at 

 50° less and less pronounced until it has entirely disappeared. And 

 below 0° the abnormalities remain confined to the 15° or 20° below 0°, 



VOL. XLVII. — 35 



