Ten years after the development of the original equation for calculating the osmotic potential of aqueous inorganic and organic solutions a new revision was made. The revised “new”quation was based on a molecular model of the structure of water. Factors that affect the size of the structure of water and the consequent distance an individual molecule must travel to and fro across its “cage”, were considered to determine its direction and rate of flow. The formulation of the new equation involved a detailed revision from established physical principles. It was tested successfully by comparative calculations on a selection of inorganic and organic aqueous solutions.
The revised “new equation”, gave improved estimates of osmotic potential for both electrolytic and non-electrolytic compounds over wide ranges of solute concentrations, without the need for individual osmotic coefficients. It contained no subequations that could not be fully derived from established physical principles. -It is interesting to observe that the calculated “t” values recorded in Tables 2 and 3 of Cochrane (1994) are close to estimates of the structural relaxation times for water (Stillinger & Rahman 1972).
It may also be observed that the model on which the equation is based, provides an improved means of visualizing many osmotica processes. For example, the model provides unifying principles for visualizing the molecular role and movements of water throughout plants. -In this context, the leaf surface of plants may be envisaged as a mechanism for expanding the average size of the “cage” of a water molecule, and so increasing the distance a water molecule travels intermittently to and fro across its cage. This facilitates the evaporative loss of water and results in a reduction in pressure to speed the translocation of water and mineral ions via the plant xylem vessels, and eventually from the soil. The average size of the cage of a water molecule increases from the roots to the leaves.
The distribution of sugars produced in the leaves through photosysthesis, and the redistribution of water and mineral ions via the phloem tissue along increasing osmotic pressure gradients, is seen in the same context of increasing the distance travelled by water molecules to and fro across their increasingly expanded structural cages. The latter are affected by the amount, type and characteristics of solute particles in solution, and undoubtedly the characteristics of the surfaces and membranes of the conducting vessels.
It was clear that model on which the improved “new equation” was formulated could well enhance future research on many osmotic potential related phenomena in both biological and environmental sciences generally. It was also evident that the equation could be improved using variants of the model visualized for the structure of water, and by taking to account other factors of molecular forces.