THE THERMAL PROPERTIES OF STEAM 



seems to be no valid reason for 

 below both sets of points. 



a curve, like curve C t lying 



Latent Heat of Saturated Steam. The Clapeyron relation 



gives a means of calculating the latent heat. It is convenient to write 



the equation in the form 



in u hie h the second mt mUr is made up of two factors. From the char* 

 acteristic equation, the first is expressed !> 



Ap(v" -r') - ABT- Ap(i + 3a*) -; 



Upon differentiating equation (A) connecting the pressure and tempera- 

 ture of saturated steam, namely 



log/> - A - | - Clog r- DT+ EP- A, 

 the second factor is obtained in the form 



For the range 32-212 degrees, within whit h the heat of the liquid b 

 n accurately by the exp -rinu -nts of Barnes and Callendar, a second 

 independent method of calculating tin- latent heat U available. Satura- 

 tion values of i are calculated from the formula for heat content and 

 from these are subtracted the corresponding known values of the heat 

 of the H<jui(l. Tin- ditYi rvnce gives, of course, the latent heat. The 

 following table gives values of r obtained by the two methods. 



LATENT HEAT, ji*-au* P. 



Tmp.'P. 



:- | r. , D 



t Ban 



r byMbtnctioo 





O 



..-- 



' M 



Alx\( 212 degrees the heat of the liquid b so uncertain that the 

 method of determining r by subtraction is hardly justified. Hence 

 values of r are calculated from the Clapeyron relation, and subtracted 

 from corresponding values of i". The result is a set of values of i' that 

 may be compared with the Regnault and Dieterici experimental values. 

 The following table exhibits the details of the calculation. 



