Some Further Experiments on the Rate of Decomposition of Calcium Carbonate

JSGT 1932 V16 T080-T093

 The importance of the rate of diffusion away of CO₂ on the rate of decomposition of calcite at constant temperature in air is exemplified by the effect of free space round the containing crucible and by the mass and depth of the charge. Alternative methods of measuring the rate of decomposition are described, in the best of which a continuous flow of CO₂-free air at a controlled rate passes through the tube containing the charge of calcite and the CO₂is absorbed in one of a series of absorbing tubes. It is shown that grains of pure limestone or of calcite of upwards of 3 mm diameter usually disintegrate at an early stage of the heating, so that the rate of decomposition rises after a certain interval to a value corresponding with that of much finer grains. Quantitative relationships are derived between amount of decomposition and time and temperature, respectively. Despite the fact that the dissociation CaCO₃CaO+CO₂+Q cal. is heterogeneous, the rate of decomposition can be expressed by the equation of the first order for homogeneous reactions, with a temperature coefficient of approximately 2. The critical increment of energy is calculated as 95,000 cals., a value in agreement with that determined by other methods.

William Maskill & W. E. S. Turner