CHAPTER III. 

 CALORIMETRY. 



CALORIMETERS for rapid combustion are invariably com- 

 posed of a combustion-chamber and a calorimetric bath, 

 usually a cylinder, surrounding it and containing a known 

 quantity of water, the elevation in temperature of which is 

 measured. The combustion is made in oxygen, pure or 

 diluted. 



Combustion-chambers are either under a constant pressure, 

 as in the calorimeters of Rumford, Favre and Silbermann, 

 etc. ; or with a constant volume, as in the calorimeters of 

 Andrews, Berthelot, etc. With solids the difference of results 

 obtained under constant volume and constant pressure is so 

 small that we. shall not consider it. With gases, however, it 

 is different, and we will state under which conditions the 

 results have been obtained. 



The first calorimetric experiments date from Lavoisier and 

 Laplace. In 1814 Count Rumford replaced the ice calorim- 

 eter of Lavoisier by an apparatus in which the heat devel- 

 oped during the combustion was absorbed by water. It was 

 some time after, 1858, that Favre and Silbermann discovered 

 the causes of , the great errors of their predecessors, and pub- 

 lished methods for correcting some while avoiding others. 

 We owe to them, above all, the observation that, even when 

 supplied with pure oxygen, combustion may be only partial, 

 on account of the formation of combustible gases. They 

 determined that this occurs generally, and gave a method of 

 estimating the unburnt gases, so as to make allowances in the 

 calculation. 



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