A HEAT-CONDUCTION FLOW MICROCALORIMETER FOR SOLUTE TRANSFER ENTHALPY DETERMINATIONS - DESIGN AND CALIBRATION

The construction of a heat-Conduction now microcalorimeter of the twin type, that uses thermopiles to detect thermal changes in the referenc e and reaction cells, is described. For comparative purposes, gold and silver cells, with different geometric shapes, are used. The calorime tric set is immersed in a water thermostat at a temperature of 25.000 +/- 0.005 degrees C. The thermostat is placed in a room whose temperat ure is controlled to 25.0 +/- 0.2 degrees C by an air thermostat. The calibration constant of the apparatus is determined for several values of electric work and power, Values of 22 WV-1 and 14 WV-1 are obtaine d for the gold and silver cells, respectively. The influence of the no w rate on the potential signal is studied. Chemical calibrations are p erformed with HCl-NaOH, THAM-HCl (trihidroxymethylaminomethane), and u rea-water systems at different flow rates. The results are in good agr eement with those reported in the literature.