Monitoring the chemical composition of a fluid

Apparatus for monitoring the chemical composition of a fluid eg liquid having at least two components comprises sensors such as temperature probe, pressure dip tubes for density measurement, and conductivity probe for measuring at least two physical parameters dependent on the relative proportions of the components. The electrical measurements are processed by a micro processor using a series of polynomial equations relating the parameters with concentration and which are solved simultaneously by an iterative technique to derive values of the concentrations of the different components in the fluid. Control means may receive feedback signals so that any drift from a desired concentration can be corrected. The apparatus may be used in a plant for dissolving uranium ore in nitric acid, the components being acid and water, or in reprocessing irradiated nuclear fuel. (author)