224 MILNE art. f 



and so > 



Ax = Ae + pAv 



= Ae + ATF = AQ. 



Thus the increase in the heat function between any two states is 

 equal to the heat communicated when the same change is 

 effected (reversibly or irreversibly) at constant pressure and no 

 other external work is done. This property gives rise to the term 

 "heat function," (Gibbs, I, 92, equation [119].) The change 

 in the heat function is the quantity measured by any constant- 

 pressure calorimeter. If dt is the increase in temperature in an 

 infinitesimal change conducted at constant pressure when no 

 other external work is performed, then 



dx ^dQ^ 

 dt ~ dt* 



whence 



\dt)^ 



7. The Heat Function in General. In any change, we have 



Ax = Ac + A(pv), 



whence 



Ax = AQ - AF + A(pv). 



It may happen that some of the intrinsic energy e is converted 

 into kinetic energy during the process, as in the expansion of a 

 fluid through a nozzle. If q is the velocity of a typical element, 

 then for unit mass the first law of thermodynamics must be 

 written in the form 



AQ = A(ig2) + Ae + ATF, 



whence 



Ax = [AQ - A(ig2) _ AW] + A{pv) 



