FAVRE AND SILBERMANN'S CALORIMETER. 2$ 



5. Weight of carbon escaped unburnt in the gaseous 

 products; 



6. Elevation of temperature of calorimeter bath; 



7. Correction for heating and cooling caused by external 

 influences on the calorimeter cylinder. 



The combustion of the coal by this means is rarely com- 

 plete; there remain variable quantities of coke mixed with 

 the cinders formed. An uncertainty attends the calorimetric 

 value according as the combustion was slow or rapid, since 

 this small quantity of coke contains more or less hydrocarbons. 

 These differences, however, apply within very close limits, so 

 that no fear need be entertained of large errors therefrom. 

 When a coal, in pieces, has been burnt, there remains in the 

 capsule only a few milligrams of coke or unburnt carbon. 

 From this we calculate the calorimetric value, using 8080 as 

 coefficient (heat of combustion of charcoal according to Favre 

 and Silbermann); and in using that coefficient the hydrogen 

 which may exist in the coke is naturally neglected, but this 

 cannot be prevented. The carbon and hydrogen of the com- 

 bustible gases which escaped combustion are transformed into 

 water and carbonic acid, and weighed as such. The hydrogen 

 is calculated as in the free state (coefficient 34500) and the 

 carbon as carbonic oxide (coefficient 2435). 



It is evident that these are only approximations, since the 

 hydrogen is not disengaged in a free state, but as a hydro- 

 carbon; and its coefficient (34500) should be diminished by the 

 heat of formation of this compound, or, in other words, by the 

 heat of combustion of hydrogen and carbon. This correction, 

 however, is not possible; for neither the composition nor state 

 of molecular condensation of such hydrocarbon is known. 

 Similarly for the carbon, and its heat of combination in the 

 carbon compound. There are, then, some uncertainties, 

 but not of much importance, in the determination of the heat 

 of combustion of fuels uncertainties which the use of the 

 calorimetric bomb has entirely avoided. 



