A New High Precision Calorimeter for the Measurement of Heats of Combustion: And the Heat of Combustion of Succinic Acid

The construction, calibration and use of a high-precision bomb calorimeter of the aneroid type are described. It consists of a stainless-steel combustion bomb as designed by Garlton-Sutton (I933) in a mantle of aluminium alloy, the temperature of which is measured by a platinumresistance thermometer. A simple means of measuring the electrical ignition energy has been devised. Because the time required for the attainment of a thermal steady state is greater for this type than for the conventional water calorimeter, the theory underlying methods of allowing for heat loss from the calorimeter to its surroundings has been critically re-examined, and the limitations of the commonly used Dickinson method (1914) have been clearly stated. For high precision to be attained, it proves to be particularly necessary that the conditions under which calibrations and measurements are performed shall be as similar as possible. Working under optimum conditions, chosen after systematic trials, it is possible to reduce to 0.012 % the standard deviation of the values for the calibration constant, with benzoic acid as the standard substance. The heat of combustion of succinic acid has been redetermined as — A.US = 3020-57 +0-43 cal/g (vac.). This agrees very well with the high-precision determination by Huffmann (1938) 3020-47 ± 0.43. Succinic acid is suitable as a secondary standard for combustion calorimetry; and the best value is taken to be 3020.5 ± 0.5 cal/g (vacj