142 Starkweather — Thermodynamic Relations for Steam. 



Below 273°-7 we can set 



pv —p(v—w) = RT . 

 Then, since 



we have 



RT a ^o|^ __ j K (273-7 -T) — JG-RT-/(T) = 



Now first suppose that determinations of L below 0° C. are 

 made, or that those above 0° C. are so accurate that an expres- 

 sion for f(T) is obtained for that region which will bear extra- 

 polation below 0° C. Then J? is known and a relation 



between p and T determined. Conversely, if the relation 

 between p and T below 0° C. is known, f(T) is at once deter- 

 mined, and thence the latent heats. 





