256 Ice and its Natural History 



and it is made up of 901-49 c.c. ice and 90-154 c.c. water. 

 When this is warmed to -o*i, we may take it that the whole 

 of the ice is melted. Taking the latent heat per unit volume 

 of ice as 66*5 at o*i, and its specific heat per unit volume as 

 0-45, the heat required to raise the ice from - i to -o'i is 

 365' i gram-degrees (g.); that required to raise the tempera- 

 ture of the water by the same amount is 81*14 g., and the 

 heat required to melt the ice at o'i is 59,949 g., the total 

 heat used being 60,395 ' 2 S- ^ we ig nore the possibility of 

 partial melting, and assume that we have 999*84 c.c. solid ice 

 at i, and that its temperature is raised to o, at which tem- 

 perature it melts, we have the following expenditure of heat: 

 for rise of temperature 449-9 g., and for melting 66,489*3 g., 

 making together 66,939*2 g., as against 60,391*5 g.. If from 

 60,395*2 g. we deduct the heat calculated for warming the 

 ice in the second case, 449-9 g., we obtain 59,945*3 g. as 

 the heat required to melt 1000 c.c., or 916*7 grams, of ice 

 at o, whence the latent heat would be, per unit volume, 59*94, 

 and per unit weight 65-39. 



This example illustrates also the effect of impurity on the 

 apparent specific heat of ice. 



It will thus be seen how powerful is the influence of 

 medium on the behaviour of ice in the laboratory ; it will 

 now be shown that, in nature, this influence is equally power- 

 ful and much more far-reaching. 



The nature of the medium is responsible, in the case of 

 sea-ice, for depressions of freezing and melting temperature of 

 30, 40, and even more degrees of Celsius' thermometer, while 

 the greatest pressure to which fresh-water ice is exposed in 

 nature cannot well produce an alteration of freezing and 

 melting-point amounting to as many hundredths of a degree. 



The ice which surrounded the " Vega" during her winter's 

 imprisonment in the Arctic Ocean had a pasty semi-liquid 

 consistence, although the temperature of the air was at or 

 below 30 C. It remained stationary only because it was 

 on a level surface. Had it been shovelled up on an inclined 

 plane it would have quickly flowed down it until it reached 

 the lowest level again. If we pick up a piece of ice floating 



