[barnesJ 



THE PHYSICAL CONSTANTS OF ICE 



feeble electric current until tlie temperature was about 1°C. below zero. 

 A larger current was then supplied for a sufficient time to melt the ice 

 and raise the temperature of the water to half a degree above zero. Cor- 

 recting for the specific heat of the ice and water, the heat of fusion could 

 be obtained. The result thus found was 79.896 calories. This value, 

 however, should be somewhat lower since it was worked out in terms of 

 the Clark Cell =1.434: volts at 15°C. A closer value for the Clark cells 

 used by Smith would be 1.4333. This brings Smith's value down to 

 79.818. 



TABLE III. 



Heat of Fusion of Ice. 



Black 



Lavoisier & Laplace 



Regnault 



Regnault corrected by Guttmann . . 



La Provostaye & Desains 



Hess 



Person 



Bunsen 



A. W. Smith. 



79 . 7 calories 



75. 



79.24 



79.59 



79.25 



80.3 



80.0 



80. 02 



79.818 " 



Person calculated that the heat of fusion of a body is smaller the 

 lower the temperature becomes. Pettersson verified this in the case of 

 ice and found that for 1°C. lowering of the freezing point the heat of 

 fusion was reduced by 0.59 calorie. At — 6°C. observation gave a value 

 of 76.0 calories. 



Latent Heat of Vaporization of Ice. 



No direct determinations have been made of the heat of sublimation 

 of ice until very recently. This has always been assumed on theoretical 

 reasoning to be the sum of the latent heat of vaporization of water and 

 the latent heat of fusion of ice, i.e., 680 calories per gram. 



Direct measurements of this quantity were carried out by Barnes 

 and Vipond in 1909, who found that the heat of sublimation at 0°C. is 

 the same as that of water at the same temperature, which is 600 calories. 

 This is explained on the ground that ice vapourizes in the solid condition. 

 This polymeric ice vapour was found by experiment to be unstable even 



