BRIDGMAN. — WATER UNDER PRESSURE. 



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PRESSURE 



Figure 31. Shows the sharp 

 change of volume during freezing. 



experiments was published in the Physical Review, vol. 31, 1910, 

 p. 606. The values as found by these measurements lie on a straight 

 line, and agree with the possible limits found with the compressibility 

 measurements, except that at the highest temperature, 22°, freez- 

 ing had once been found to take place during the compressibility 

 measurements at a pressure lower 

 than that found here. This was 

 disconcerting. 



The transition curve as found in 

 this way did not give all the in- 

 formation needed for a complete 

 statement of all the quantities 

 involved in the change. A com- 

 plete statement thermodynamically 

 could be made if it were possible 

 to measure also the change of 

 volume during the change. This 

 seemed at first sight of doubtful 

 possibility. Tammann had made 

 such measurements up to 2000 

 kgm., but had not been able to go 



much higher because of leak. As it was, even at 2000, a correction 

 had to be applied for the leak, which was furthermore made as small 

 as possible by the use of a heavy oil, such as castor oil. In the 

 present work it was necessary to go to many times this pressure, 

 the equilibrium pressure even at 0° being 6400 kgm. The difficulty 

 was furthermore increased by the necessity for using some very light 

 and mobile oil to transmit pressure, the castor oil freezing absolutely 

 solid under such pressures as were to be used here. It was felt, there- 

 fore, to be a real step when it was found that the packing used in the 

 previous high pressure work was entirely satisfactory -when used for 

 this purpose. It is possible with it to retain liquids as mobile as ether, 

 CS2, pentane, or mercury, absolutely without leak, up to the highest 

 pressures attainable. Measurements of the change of volume have been 

 made up to 15,500 kgm., and this limit was set by yield of the steel 

 cylinders and not by failure of the packing. The readings of the piston 

 obtained were consistent to a few ten thousandths of an inch. The 

 only troublesome effect found with the packing was a slight wearing 

 away by abrasion, owing to the enormous friction. This effect was 

 troublesome only over a wide pressure range ; for the limited motion 

 of the piston during freezing or melting the effect was negligible. 



It was also a part of the preliminary work to show that the freezing 



