AbstractAn adiabatic calorimeter has been developed for the measurement of the heat of solution. By means of a thermistor temperature changes of about 0.04°C can be measured with a precision better than 4 × 10−5°C, hence only small amounts of solute are required. As a check of accuracy the integral heat of solution of KCl in H2O at 25°C up to a concentration of 2 × 10−4molar was directly determined as 17.24±0.03 kj per moleFor the “uncertainty interval” is used twice the standard deviation of the mean, i.e., as recommended bij F. D. Rossini and W. E. Deming, J. Wash. Acad. Sci. 29, 416 (1939). The probability that the measured quantity lies within this l