Grafts et al. — 14 — Water in Plants 



rangements in the liquid form. Properties are explained on the basis mainly 

 of internal geometrical structure. 



Katzoff (1934) made x-ray studies on water and arrived at a mole- 

 cule having essentially the same electron distribution as postulated by Ber- 

 NAL and Fowler (Figure 5). He also agreed on the arrangement of 

 molecules in the liquid where each molecule has four others around it. He 

 found no evidence for the quartz-like structure (water II) nor for the 

 degree of close packing described by Bernal and Fowler in water at high 

 temperatures. If in ice each oxygen is tetrahedrally surrounded by four 

 others with the hydrogens on or near the center lines between adjacent 

 oxygens, then water appears to have a broken down ice structure with less 

 regularity of arrangement but still maintaining the tetrahedral order char- 

 acteristic of ice. Hot water also maintains the fundamental four-coordina- 

 tion but has more randomness of arrangement than that of cold. 



The Second Faraday Symposium: — A symposium of the Faraday 

 Society on the structure and molecular forces in pure liquids and solu- 

 tions, in 1936, brought together many workers in this field and accumu- 

 lated in one publication (Trans. Faraday Soc. Vol. 33) the current views. 

 Kendall (1937) commented on the changing opinion regarding the na- 

 ture of liquids. The hard and fast distinction between the solid, liquid, 

 and gaseous states has largely disappeared. Dififerences do exist; the 

 close packing of molecules in the liquid state renders intermolecular forces 

 much greater than those between gaseous molecules. In contrast to the 

 older belief that such forces were essentially similar in nature (ordinary 

 van der Waals attractions or valence forces) the modern view involves the 

 stresses caused by dipole structure, the coulomb forces in electrolytes, and 

 the metallic cohesive forces in metals. Association into definite groups 

 (polyhydrol concept) has been largely abandoned, most scientists subscrib- 

 ing to the view of Langmuir that a liquid consists of one loose molecule. 



If the solute in a solution were in the gaseous state the heat of solution 

 of a gas would be zero, those for a liquid and solid respectively should ap- 

 proximate the heats of vaporization and sublimation. This is not the case. 

 In the ideal case, the heat of solution of a gas is equal to its heat of con- 

 densation, the heat of solution of a liquid is zero, and the heat of solution 

 of a solid is equal to its heat of fusion. In other words, any substance dis- 

 solved in a liquid, itself assumes the liquid state. 



Ideal solutions are rare; solutions deviating from Raoult's law have 

 been studied in detail and their behavior explained on the basis of the mag- 

 nitude of forces between solute and solvent molecules. Whereas most 

 positive deviations were at one time explained in terms of association of the 

 solvent, they are now considered to result from differences in internal pres- 

 sure. Negative deviations which Longinescu (1929) states have been 

 "timidly assumed" to be non-electrolytic dissociation, Kendall explains as 

 resulting from molecular attractions that, in the extreme case, result in com- 

 pound formation. This is in agreement with Hildebrand (1924). 



The simple concept of intermolecular forces exemplified by van der 

 Waals force was expanded by London (1937) to account for orientation, 

 induction, and dispersion effects and MacLeod (1937) proposed a com- 

 pressional effect to cover the forces of molecules under high pressure. 



Bernal (1937) postulated points of abnormal coordination in liquids 

 to explain their properties. His theory pictures the liquid as like an or- 

 dered solid containing a number of holes. Water, he concluded, is a liquid 



