molecules. When water is cooled to 4°, the first of these processes is the more intensive, with 

 further cooling, the second. The greatest density is attained at 4°, the equilibrium point of the two 

 processes. During ice formation the number of ice molecules increases sharply, which involves a 

 sharp decrease in density. 



With a rise in temperature, the heat acquired from without is expended 1) on increasing the 

 kinetic energy of motion and increasing the potential energy (by separation of the molecules) and 2) 

 on decreasing the number of ice molecules. The higher the temperature, the smaller the influence 

 of the second process and thermal capacity will decrease. The usual increase in thermal capacity 

 begins to appear when the temperature rises above 30°. 



Thus, the transformation of molecules of one structure into molecules of another structure 

 which takes place with every change in temperature (requiring an additional expenditure of energy) 

 explains the high thermal capacity, heat of fusion and heat of vaporization of water. 



LITERATURE: 62, 132. 



Section 2. The Composition of Sec Water 



One of the most remarkable properties of water is its capacity to dissolve all kinds of sub- 

 stances; no other liquid can compare with it in this respect. Strictly speaking, there are no sub- 

 stances in nature that are completely insoluble in water. Water itself, however, does not enter 

 easily into chemical compounds, in the literal sense of the word. 



Sea water is a dilute solution (not more than 4 per cent by weight of solid substances are dis- 

 solved in it). Evidently, all known elements are found in sea water; if some elements have not as 

 yet been found in sea water, the inadequacy of measuring methods is at fault rather than the actual 

 absence of the elements. 



The main elements comprising sea water are (in order of weight): chlorine, sodium, mag- 

 nesium, sulfur, calcium and potassium. Besides solid substances, water contains dissolved gases: 

 oxygen, nitrogen, carbon dioxide (and in some stagnant zones, hydrogen sulfide as well) . Further- 

 more, the presence of inert gases in sea water has also been established qualitatively. 



Some organic matter, of oceanic origin and from shore run-off, is also dissolved in sea 

 water. Finally, sea water contains some slime and suspended matter of organic and inorganic ori- 

 gin, which give sea water the properties of colloidal solutions. 



There are physical-chemical, biological and geological processes going on continually in sea 

 water, causing a change in its total salt content (concentration) and in the ratios between the dis- 

 solved substances. These processes may be divided into two groups according to their effect: 



processes which change, chiefly, the total concentration of the solution; this group includes: 

 the influx of shore waters, evaporation, precipitation, formation and melting of sea ice; 



processes which change the content of the gases and individual solid matter in sea water and 

 the ratios between them; to this group belong: the vital activities of marine organisms, the forma- 

 tion and disintegration of bottom deposits. 



Changes in the total concentration of sea-water solution in the individual parts of the ocean 

 may be very great and can easily be revealed by the simplest observations, e. g. , by density 



