98 



Proceedings of Indiana Academy of Science 



there is a steeper rise than is customary aided by the ever increasing 

 amount of heat required to transform the dihydrol into monohydrol, or 

 dissolved steam. Steam, also, has an abnormal specific heat curve. 

 Over the range 250-300° it increases with the temperature as all gases 

 do. Below this range the curve rapidly becomes nearly horizontal at 

 a specific heat of about 0.5. The reason for this is because of the extra 

 amount of heat energy required to overcome the intermolecular attrac- 

 tion, which is abnormally high in proportion to its molecular weight, 

 because of the polar nature of the molecule. 



From the compressibility curve (figure 1) some information about 

 the molecular aggregation of water may be obtained. Since the com- 

 pressibility of any substance decreases with its compression or density 

 that region of minimum compressibility of water corresponds to a 

 preponderance of denser aggregates, which would be dihydrol in this 



FiK. 7. The ice crystal consists of tetrahcdral oxygen atoms surrounded each by 

 four hydrogens. Each hydrogen is between two oxygens. There is no residual i)olarity. 

 This arrangement is responsible for the hexagonal shape of snow crystals ; cf. Natio7ial 

 Geographic Magazine, January, 1923. 



case. The compressibility curve reaches a minimum at about 45°, and 

 gives us, probably the best guide as to the relative proportions of these 

 three kinds of aggregates in liquid water. The molecular weight of 

 water dissolved in other solvents approximates 36 which gives us an- 

 other reason for speaking of water as chiefly dihydrol. 



The high latent heat of vaporization is required to complete the 

 change of the compact complex molecule, dihydrol, into monohydrol as 

 well as to separate the monohydrol molecules from each other and to 

 do the work of expansion against the atmosphere. According to 

 our method of reasoning ammonia should also have a high latent heat 

 of vaporization, as it does. This property, together with its high 

 specific heat has a great deal to do with the value of ammonia as a 

 refrigerating agent. The magnitude of their values is caused, in large 

 part, by the polarity of the ammonia molecule. 



As a solvent, water is extremely important. Bring it into contact 

 with a crystal of ordinary salt and, according to the orthodox method 

 of expressing what happens, the salt dissolves and then breaks up into 



