the Disgregation of a Body. 29 



paper referred to, the following equation, 



dh=\dZ, (1) 



where Z is a quantity completely determined by the actual con- 

 dition of the body, and independent of the way in which the 

 body arrived at that condition. If the state of the body is 

 determined by two variable quantities, Z will be a function of 

 these variables. And it is this quantity Z which I have called the 

 disgregation of the body. 



The total quantity of work L, an element of which occurs in 

 equation (1), is made up of the internal work and the external 

 work, which I will denote respectively by J and W. The in- 

 ternal work J is a quantity which can be expressed, like the 

 disgregation, by a function of the two variables which determine 

 the actual condition of the body. The external work W, on the 

 contrary, depends not only on the actual condition of the body, 

 but also upon the way in which it came into that condition. 



If we suppose that the temperature T and the volume v are 

 the two variables which determine the condition of the body, 

 we may write 



dJ = - 1Fr .dT + -,- dv. 

 «T dv 



For the external work W, in case the only external force which 

 has to be overcome during the change of condition is a pressure 

 p acting on the surface of the body, we have the equation 



dW =pdv. 



By introducing these values of dZ, dJ, and dW into equation 

 (1), after substituting dJ -\-dW for dh, we obtain 



dJ jrp /dJ \ . T (dZ 7m dZ . \ 

 and hence we get 



T 

 A 



dZ dJ 

 ' dT " dV 



T 

 A 



dZ_dJ 

 dv dv 



(2) 



From these equations a very simple value of the differential 

 -7- can be deduced. For this purpose we must differentiate the 



