If we know the salinity of the solution, using this table we can determine the temperature at 

 which ice formation begins. Conversely, given some temperature below 0°, we can derive the 

 salinity to which (by production of pure ice) the salinity of any sea-water solution can be raised. 



Complex phenomena analogous to ice formation also take place during evaporation of sea 

 water. Actually, if there is only one salt in a solution, it begins to precipitate out in the form of 

 crystals as soon as the solution becomes saturated at a given temperature due to evaporation. If 

 there are several salts in the solution, usually the least soluble ones precipitate first. It has been 

 found that during evaporation calcium carbonate precipitates first, then glauber salt, while potas- 

 sium chloride precipitates only with great difficulty. 



LITERATURE: 62, 73, 77, 168. 



Section 8. Thermo! Copocity, Heat of Fusion 

 and Heat of Vaporization 



The thermal capacity of sea water decreases from 1. 009 to 0. 925 cal/g/°C with an increase 

 in temperature and salinity. The thermal capacity of water is higher than that of any other sub- 

 stance on earth except for hydrogen (3.4 cal/g/°C) and liquid ammonia (1.2 cal/g/°C). 



The latent heat of fusion of distilled water, according to the most reliable determinations of 

 many researchers, is 79. 67 cal/g/°C at 0°. This heat of fusion is the highest of all substances on 

 earth, with the exception of ammonia, for which it is 108 cal/g/°C. 



The heat of vaporization of water decreases from 596 cal/g/°C at 0° to 540 cal/g/°C at 100°. 

 The heat of vaporization of water is higher than that of any other substance on earth. The heat of 

 vaporization of ice or snow is usually considered the sum of the heat of fusion of ice and the heat of 

 vaporization of water. 



The high values of the specific heat, heat of fusion and heat of vaporization of water for the 

 thermal regime of the earth are easily explained by the following calculation. 



When one volume of water is cooled 1° an amount of heat is released sufficient to heat 3100 

 volumes of air by 1°; when ice is formed an amount of heat is released from one volume of water 

 that is sufficient to heat about 250, 000 volumes of air by 1°; when one volume of water is con- 

 densed, enough heat is generated to heat about 1, 800, 000 volumes of air by 1°. 



LITERATURE: 62, 73. 



Section 9. Vapor Pressure 



If a small amoimt of water is placed in the Torricelli vacuum of a barometer, the water will 

 vaporize and the vacuum will become saturated with water vapors; there will be as much water vapor as 

 can exist in the gaseous state at the given temperature. These vapors will exert a certain pressure 

 on the mercury, whose level will decrease correspondingly. Vapor pressure is measured by the 

 fall of the mercury column in mm. The pressure of saturated sea-water vapor, as in the case with 

 any solution, is somewhat less than that of pure water. Actually, in sea water the molecules which 

 escape from the liquid during evaporation must overcome not only the attraction of the water mole- 

 cules, but also the attraction of the molecules of the dissolved substances, which remain in solution 

 during evaporation. 



18 



