40-1. M. R. Clausius on the Deportment of Vapour. 



drawn or communicated, so that the vapour may remain com- 

 pletely gaseous and quite saturated, and hence at the surface 

 KLM shall have the exact temperature /.,=100°, and the corre- 

 sponding volume Sr,. The question is, what quantity of heat 

 Q3 must be imparted to, or withdrawn from, the issuing steam so 

 that this condition shall be fulfilled. 



The interior work performed by the vapoiir during its issue in 

 the present instance is exactly the same as in the other cases. 

 With regard to the exterior work, however, an entirely new cir- 

 cumstance enters into the consideration, Avhich renders this 

 ease essentially different from the former ones. 



Let us examine the quantity of work produced at both the 

 surfaces GHJ and KLM. Through the surface GHJ the vapour 

 is driven with the volume s, and the pressure p^^, it therefore 

 produces the work 



This work proceeds from the vapour within the vessel, and more- 

 over only from that ])ortion of it which, during the time of issue, 

 is developed anew. To obtain room for itself, this presses the 

 neighbouring stratum forwards, this the next, and so on. The 

 intervening layers thus serve merely to transmit the force from 

 the surface of the water to the orifice. The quantity of heat 

 consumed in the production of this work is contained in the 

 latent heat of the developed steam, and need not in the present 

 consideration be further taken into account. 



If now in the surface KLi\I exactly the same work be pro- 

 duced as in GHJ, then in the interval between both sui-faces no 

 proper work is produced, inasmuch as in this case there would 

 be merely a transmission of work from one surface to the other. 

 If, on the contrary, the work accomplished at the surface KLIM 

 be different from that produced at GHJ, the difference must be 

 referred to the said interval. But through KLM the unit of 

 weight of steam with the volume Sg and the pressure j)^ is driven, 

 and hence produces the work 



P^.Sc^. 



The Mork performed in the intervening space is then 



lh'Sc,-p^.s^, 

 which is a negative quantity. This shows, that, during the 

 passage from surface to surface, a portion of the exterior work 

 already completed is again lost. 



The quantity p-i-Sc^—p^s^ must be treated as the quantity 



/ p^ds in the second case ; in this way we obtain the following 



equation, which corresponds to equation (2.) : 



