After a review of the physical foundations of bomb calorimetry, a bomb calorimeter is described which can be heated electrically or by combustion. The evaporation of water is prevented by sealing the vessel completely. Other modifications in the normal technique are introduced after consideration of (
a
) the difference in temperature between the outer surface of the calorimeter and the thermometer immersed in it, (
b
) the effective ‘boundary’ of the calorimeter in electrical and combustion experiments, and (
c
)variation with temperature of the constants of the apparatus. The heat of combustion of samples from a batch of thermochemical quality benzoic acid is found to be 26436 J/g under ‘standard bomb conditions’. The standard error of the determination, a combination of errors in reproducibility of electrical and combustion experiments and in measurement of the corrections, is estimated to be 2.2 J/g.
Heat of combustion of benzoic acid, with special reference to the standardization of bomb calorimeters
