The heat capacity of water adsorbed on cellulose has been measured by means of a new type of adiabatic calorimeter and a new experimental technique. Measurements have been made with 2, 4, 8, and 12% adsorbed water over the temperature range − 35° to + 25 °C. with considerable accuracy. A mechanism, that of a change in the amount of bound water with the temperature, has been suggested to explain the high values obtained for the apparent specific heats of adsorbed water.