Influence of the temperature on the viscosity measurements of solutions of a soil fulvic acid

The influence of the concentration (ca. 45 to 300 mg L-1), the pH (3.0 to 8.0), the ionic strength (0.005 to 0.10 M), and the temperature (283 to 303 K) on the viscosimetric behaviour of solutions of a soil fulvic acid has been analysed, and their molecular parameters (length, thickness, and molecular volume) calculated. The results indicate that the polyelectrolytic behaviour of the fulvic acid is similar at all the temperatures, i.e., increasing the viscosity when reducing the ionic strength and to increase the temperature. With respect to the pH an initial decrease in the viscosity is obtained followed by a rise to the highest pH values. These variations have been interpreted by their molecular parameters as due to modifications of the structure of the molecules of the fulvic acid.Key words: fulvic acid, viscosity, temperature. </jats:p