Journal of the Chemical Society Abstracts
A n a l y t i c a l C h e m i s t r y . Thompson's Calorimeter. By SCHEURER-KESTNER (Compt. rend., 106, 941--%&4) .-The proportion of oxidising mixture necessary for complete combustion varies with the nature of the coal and the proportion of ash which it contains. The author employed from 10.5 t o 12.5 times the weight of the coal ; with only 10 parts of oxidising mixture, the combustion is usually incomplete. The correction of 10 per cent. usually added to the results is much too low.
... ch too low. Experiments with ignited wood charcoal showed that for the author's apparatus 15 per cent. was the true correction. This was used for samples of coal, the heat of combustion of which had previously been determined by Favre and Silbermann's method; the maximum difference was 1.25 per cent. The heat of combustion of 20 coals was determined by Thompson's calorimeter, and afterwards by Favre and Silbermanu's appRratus. The variations were sometimes on the one side, sometimes on tjhe other, the maximum difference being 3.5 per cent. In 11 cases, the difl'erence was less than 2 per cent. Although Thompson's calorimeter gives results of practical value, when an error of 2 o r 3 per cent. is negligible, it is only worthy of limited confidence. Berthelot's calorimetric bom b would be much better. The main sources of error, as Stohmann has pointed out, are the heat of decomposition of the oxidising mixture and the heat of dissolution of the salts after combustion, since tLe proportion of each salt varies with each coal. Some finely powdered samples of coal which had been exposed to diffused light for 20 years in bottles not very tightly closed, were found to be completely unaltered.