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CHAPTER II. 



CALORIMETRIC APPARATUS. 



1. GENERAL REMARKS. 



1. THE author has carried out almost all the measurements of 

 the quantities of heat liberated or absorbed in his experiments 

 with the water calorimeter. It is very well adapted for deter- 

 minations concerning explosive substances. This instrument, 

 employed by Dulong and Regnault, and also by Thoinsen, 

 appears to offer the guarantees of the greatest accuracy. In 

 fact, the quantities determined by it approach as closely as 

 possible the theoretical definition of the " calorie " ; whilst 

 the ice calorimeter of Lavoisier and Laplace, as well as that of 

 Bunsen, and the mercury calorimeter of Favre and Silbermann, 

 determine different quantities, such as the weight of water 

 liquefied, or the expansions of certain liquids. The relation of 

 these quantities to the calorie must be found separately, by a 

 system of special experiments, and it is liable to incessant 

 variation, according to the conditions of the surrounding 

 medium. In the use of these instruments, therefore, all the 

 uncertainties of indirect measurements occur. 



2. The conditions under which the calorimeter is employed 

 are very simple, and capable of being easily reproduced by all 

 chemists and physicists who desire to carry out similar experi- 

 ments. The measurements are, moreover, more promptly 

 executed, and the calculation easier than by any other method. 

 For the complete discussion of the process, the verification of 

 the thermometers, and the arrangements special to certain ex- 

 periments, the reader is referred to the author's "Essai de 

 Mecanique Chimique," where these subjects are more fully 

 treated. 



2. DESCRIPTION OF THE CALORIMETER. 



1. The apparatus consists of three fundamental parts, viz. a 

 calorimeter; a thermometer; an envelope. The annexed 



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