CURVE OF ACTUAL AND THEORETICAL PRESSURES. 13 



11. The true pressures will therefore always be greater, except 

 at the commencement, than those calculated from the quantity 

 of heat actually disengaged at the moment of maximum 

 temperature. 



On the other hand they will be at first less than the pressure 

 calculated from the quantity of heat observed in the calorimeter 

 at the ordinary temperature. But this latter difference 

 diminishes, and finally disappears altogether in proportion as 

 the volume increases, the reactions becoming more complete. 

 The curve of the true pressures, expressed as a function of the 

 volumes, is at first more drawn out than the curve of the 

 theoretical pressures with which it finally coincides, when 

 the state of combination of the elements has become the same 

 as at the ordinary temperature. 



12. To sum up, the quantity of heat and consequently the 

 maximum work which explosive substances can develop while 

 burning in a constant volume, may be calculated independently 

 of the phenomena of dissociation, provided the final state of 

 combination of the elements be exactly defined. 



Thus the knowledge of the initial composition, and that of 

 the products determine the potential energy, whilst pressure and 

 expansion are subordinates to dissociation. 



