An automatic micro-injection system and its use in the microcalorimetry of cation-exchange sorption

Details are given of a remote-control device which can deliver known microlite volumes of solutions simultaneously to the 'control' and 'reaction' cells in the LKB calorimeter, and can do so accurately, automatically and at preset intervals. The device incorporates Hamilton microsyringes. The facility for injection at preset intervals is designed to allow the heat change after each addition of reacting solution to be recorded completely before the next addition, the interval for a reaction being predetermined in a pilot scale experiment. A method is described for measuring different enthalpies of potassium-calcium exchange in soils and clays using an LKB microcalorimeter incorporating this device. This achieves a considerable economy in time over the method of deriving information from the thermodynamic treatments of cation-exchange isotherms. The degree of cation-saturation is interpolated from a parallel 'isotherm' experiment on a macroscale in which several consecutive additions in the 'calorimeter' experiment are telescoped into single steps.