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III. — Experiments on the Total Heat of Steam. 

 By J. P. Joule, LL.D., F.R.S., ^c. 



Eead November 29th, 1859. 



The total heat of steam is understood to mean that which 

 is evolved when the steam is condensed into water of the 

 freezing temperature. It is a mixed quantity, and consists 

 of: 1st, the heat due to the change of state from vapour 

 to water, or the true latent heat; and (as I showed long- 

 ago)* the heat arising from the work done on the vapour 

 in the act of condensation ; and 3rd, the heat evolved hy 

 the water during its descent from the temperature of con- 

 densation to the fixed temperature chosen, viz,, 0° centi- 

 grade. 



The importance of a correct determination of the total 

 heat can hardly be over estimated, and it is fortunate that 

 one of the most eminent physicists of modern times has 

 made it the object of long and elaborate research. It is 

 not my design to attempt to improve upon the experi- 

 ments of M. Regnault, but having had the opportunity of 

 making some determinations in a different manner from 

 that he employed, I think my results may not be thought 

 without interest. 



In Regnault^s experiments the steam was passed into 

 globes and a worm immersed in the water of a calori- 

 meter. By the use of an artificial atmosphere connected 



* Transactions of British Association, Birminghamj 1849. 



