180 



R< Clausius on the Application of the 



Akt, XV. — On the Application of the Mechanical Theory of Heai 

 to the Steam Engine ; by R Clausius, 



[Translated for this Journal from Pogg. Ann. xcviii, 441, by W. G.]* 



1. As the change in our views on the nature and relations of 

 heat which is now comprised under the name of the " mechan- 

 ical theory of heat," had its origin in the recognized fact that 

 heat may be employed in producing mechanical work, we might 

 a priori expect that, conversely, the theory which was originated 

 in this way would contribute to put this application of heat in a 

 clearer light. In particular the more general points of view ob- 

 tained in this way should render it possible to form a certain 

 judgment on the particular machines which serve for this appli- 

 cation, whether they already perfectly answer their purpose, or 

 whether, and how far, they are susceptible of improvement. 



To these principles, which hold good for all thermodynamic 

 machines, there are to be added for the most important of them — • 

 the steam engine — some particular ones which incite us to submit 

 it to a new investigation deduced from the mechanical theory of 

 heat. Some important deviations from the laws which were 

 formerly assumed as correct, or at least applied in calculation, 

 have been found to hold good precisely for steam at its maximum 

 density. 



2. In this particular I believe that I must first remind the 

 reader that it has been proved by Eankine and myself, that when 

 a quantity of steam, originally at its maximum density, expands 

 in a shell which is impermeable to heat, by pushing back with its 

 lull expansive force a movable portion of the shell, as for in- 

 stance a piston, a portion of the steam must be precipitated as 

 water, while in most previous writings on the steam engine, and 

 among others in the excellent work of de Pambour,f the princi- 

 ple of Watt, that under these circumstances the steam remains 

 precisely at its maximum density, is assumed as the basis of the 

 reasoning. 



Furthermore, in the want of accurate knowledge, it was for- 

 merly assumed, in determining the volume of the unit of weight 

 of saturated steam at different temperatures, that steam even at 

 its maximum density still obeys the laws of Mariotte and Gay 

 Lussac. In opposition to this I have already shewn in my first 

 memoir on this subject,^ that we may calculate the volumes which 

 a unit of weight of steam assumes at different temperatures at its 

 maximum density, from the fundamental principles of the me- 

 chanical theory of heat, by means of the collateral assumption, 

 that a permanent gas when it expands at a constant temperature ab- 



* The importance of this memoir induces us to give it in extenso instead of at- 

 tempting an abstract, which would scarcely do it justice. — w. g. 



f Theorie des machines a vapeur, par le Oonte F. M. G. de Pambour. Paris, 1844. 

 \ Pogg. Ann., lxxix, 368. 



