I. 



GRAPHICAL METHODS IN THE THERMODYNAMICS 



OF FLUIDS. 



[Transactions of the Connecticut Academy, II., pp. 309-342, April-May, 1873.] 



ALTHOUGH geometrical representations of propositions in the thermo- 

 dynamics of fluids are in general use, and have done good service 

 in disseminating clear notions in this science, yet they have by no 

 means received the extension in respect to variety and generality 

 of which they are capable. So far as regards a general graphical 

 method, which can exhibit at once all the thermodynamic properties 

 of a fluid concerned in reversible processes, and serve alike for the 

 demonstration of general theorems and the numerical solution of 

 particular problems, it is the general if not the universal practice to 

 use diagrams in which the rectilinear co-ordinates represent volume 

 and pressure. The object of this article is to call attention to certain 

 diagrams of different construction, which afford graphical methods co- 

 extensive in their applications with that in ordinary use, and prefer- 

 able to it in many cases in respect of distinctness or of convenience. 



Quantities and Relations which are to be represented by the 



Diagram. 



We have to consider the following quantities : 

 v, the volume, 

 p, the pressure, 



t, the (absolute) temperature, 

 e, the energy, 

 r\, the entropy, 



> of a given body in any state, 



also W, the work done, 1 by the body in passing from one state 

 and H, the heat received,* J to another. 



* Work spent upon the body is as usual to be considered as a negative quantity of 

 work done by the body, and heat given out by the body as a negative quantity of heat 

 received by it. 



It is taken for granted that the body has a uniform temperature throughout, and that 

 the pressure (or expansive force) has a uniform value both for all points in the body and 

 for all directions. This, it will be observed, will exclude irreversible processes, but will 

 not entirely exclude solids, although the condition of equal pressure in all directions 

 renders the case very limited, in which they come within the scope of the discussion. 

 G. I. A 





