SOME IMPROVEMENTS IN THE HEAT-EXCHANGE CALORIMETER FOR ESTIMATION OF SMALL HEAT-EFFECTS

In heat exchange calorimetry, sample and reference vessels are fixed in a temperature-controlled water-bath. Heat evolved in the sample vessel is exchanged freely with ambient water. Therefore, the measuring temperature can be easily selected by changing the temperature of the bath water. In the estimation of small heat effects, the measurement of temperature via a thermistor used as a sensor must be accurate and precise. Some improvements in the water-bath of the heat exchange calorimeter are reported. To find the influence of close agreement between B constants on the thermal fluctuation range of the bath water, a pair of thermistors with B constants of 3396 and 3342 K, used in the sample and reference vessels respectively, were compared with thermistors with B values of 3404.09 and 3404.07 K, respectively. A hand-made heater block was introduced into the temperature control system of the water-bath, and was found to shorten the delay time of heat evolution. The heat evolution from an area instead of a point source was effective in mixing the water throughout the water-bath. To demonstrate the proposed improvements, the total heat effects by electric heating were compared in the range 0.5-0.05 J. On the whole, reasonable repeatability and simple handling of the vessels were obtained.