A calorimeter for the determination of the heat developed by fruit

Abstract

A calorimeter for measuring the heat evolved by apples during the senescence stage is described. A differential arrangement is used, one container being filled with apples and the other with dummy apples of the same thermal capacity, made of thin-walled glass spheres filled with moistened glass wool. These containers are enclosed in a metal box thermally insulated, and set up in a constant temperature room. Resistance thermometers composed of 80 yards of nickel wire in glass tubes are disposed among the apples and the dummies. They are connected differentially to a slide wire, on which a difference of one thousandth of a degree causes a movement of the contact maker of 3 millimetres. The air circulation is controlled so as to maintain at will atmospheres containing from 2 to 10 per cent. of CO2 around the apples. The moisture content of the air before and after circulation is determined by a dew-point apparatus, and a correction applied for the heat absorbed in evaporating water from the apples. The results show that at a temperature of 20°C. sound apples generate heat at the rate of about 0.012 calorie per second per kilogram of apples. Or for an apple of average size (2½ inches in diameter) the rate of heat generation per second is one and a half thousandth calories.