Chapter III 



23 



Solutions 



The force of attraction between water molecules is equal to the product of 

 their dipole moments divided by the fourth power of the distance between 

 centers. This is great enough to bring about a quasi-crystal lattice as men- 

 tioned in the previous chapter. The energy of the O-H-O bond of water 

 is assigned a value of 4.5 K cal. Electronic theories of valence have in- 

 dicated that all types of bonds result from mutual potential energies of 

 atomic nuclei and their associated electrons. 



Bateman also considers van der Waals forces as active in the deter- 

 mination of the molecular volume of liquids. They are brought into cal- 

 culations to explain the discrepancies between the observed and calculated 

 values of the osmotic pressures of concentrated solutions, possibly because, 

 here too, they afifect the partial molal volume of the solvent. London 

 (1942) has treated systems containing long-range van der Waals forces 

 that may be of biological significance. Such long-range forces acting in 

 conjugated chains may account for the elasticity of rubber. In hydro- 

 philic systems these forces may even be visualized as affecting the properties 



Z 4 ^ 6 10 /Z Af J6, /6 20 22 Jif 26 2S^ 



Gram J water per wo gram^ of soil 



Fig. 9. — Typical vapor pressure-water content curves for sand and clay- 

 showing the values of the permanent wilting percentage (PWP) and field 

 capacity for each. (From Veihmeyer and Edlefsen, 1936). 



of whole molecules and molecular aggregates. Eley (1944) discusses the 

 effects of ions upon the heat capacity of water from the standpoint of hydra- 

 tion shells and long-range structure. Thus we perceive how, starting with 

 nuclear atoms, and utilizing the directive forces of electrons, it is possible 

 to build a picture of morphological organization conditioned largely by the 

 geometry of molecules and restriction of their random motion by bonding 

 forces. And dominating this picture, as it applies to biological systems, 



