1908] 



on Ice and its Natural History. 

 Table V. 



259 



Lowering of freez 

 ing-point 



Surface' of water 

 exposed to pres- 

 sure of 14,000 

 kilograms 



Volume of ice con- 

 taining 1 • 5105 

 gram NaCl 



o 



21-72 



cm.2 

 6-13 



4-55 



c.c. 

 5-50 



temperatures below 0° C, possessed by a given absolute pressure 

 and by a given mass of a particular salt, we see that the following 

 law holds : The surface of the water exposed to the pressure and 

 the volume of the water which holds the salt in solution are 

 approximately proportional. 



It was shown in mv paper On Steam and Brines,* that the eleva- 

 tion of the boiling-point of water bj pressure, and by dissolved salt, 

 follows the same law : there is the same approximate propor- 

 tionality between the surface which supports the pressure 

 and the volume which holds the salt. 



Influence of Impurity on the Apparent Latent Heat of Ice. — This 

 is illustrated by the numbers in Table II. Thus, at - 1° C, the 

 apparent volume of the block of ice is 991*644 c.c, and it is made 

 up of 901*49 c.c. ice and 90- 154 c.c. water. When this is warmed 

 to -0°.*1, we may take it that the whole of the ice is melted. 

 Taking the latent heat per unit volume of ice as G6*5 at -0°*1, 

 and its specific heat per unit volume as 0*45, the heat required to 

 raise the ice from - 1' to -0°*1 is 865*1 gram-degrees (g/) ; that 

 required to raise the temperature of the water by the same amount 

 is 81*14 g.°, and the heat required to melt the ice at -0°*1 is 

 59,949 g.°, the total heat used being 60,395*2 g.°. If we ignore 

 the possibility of partial melting, and assume that we have 999*84 

 c.c. solid ice at - 1°, and that its temperature is raised to 0°, 

 at which temperature it melts, we have the following expenditure of 

 heat : for rise of temperature 449*9 g.°, and for melting 66,489*3 



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*4 g.° as the heat 

 required to melt 1000 c.c, or 916*7 grams, of ice at 0°, whence the 

 latent heat would be, per unit volume, 59*94, and per unit weight 

 65*39. 



* On Steam and Brines, by J. Y. Buchanan, F.R.S., Transactions of the 

 Boyal Society of Edinburgh (1899), xxxix. p. 549. 



s 9. 



