Starkweather — Thermodynamic delations for Steam. 139 



80° C. There will now be developed a formula for j? from the 

 latent heats. 



We have from Clausius for the saturation line 



from which follows 



JL dT 



V - W =T-d P > 



dp d log p 



JL 



pdT 



dT Tp(v-w) 



Let us denote this by D. We have already obtained p (v—w) 

 with great accuracy (page 134) for temperatures below 100° C. 

 For L we take the values from the assumed equation for /(T), 

 which seem to be the best obtainable. Thus D is found for 

 various values of T. 

 Next the writer has assumed that D is represented by 



D 



rp2 > rp3 



c 



This is Rankine's form, with the addition of the term — . 



Determining A, B and C from the values of D at 273°'7, 323°'7 

 and 373°% there are found 



log A = 3*539061 



B = 5-826374 log C = 7-556878 



How well this represents D is shown by the following com- 

 parison. Under I) is given the value as first found from the 

 latent heats, and under D' that according to the formula. 



T 



D 



D' 



T 



D 



D' 



273-7 



0-0724625 



0-0724626 



333-7 



0-0462057 



0-0462064 



283-7 



0-0667980 



0-0667857 



343-7 



0-0432180 



0-0432188 



293-7 



0-0617441 



0-0617298 



353*7 



0-0405067 



0-0405049 



303-7 



0-0572187 



0-0572100 



363-7 



0-0380399 



0-0880322 



313-7 



0-0531516 



0-0531546 



373-7 



0-0357738 



0-0357738 



323-7 



0-0495038 



0-0495037 









Integrating, there is obtained 



_ A _K C^ 



+ K 



where 



log A' = 3-176848 

 logC = 6-717544 



logB' = 5-163131 

 K = 7-844259 



K is determined by makings equal to 760 mm when T is 373°*7. 

 In the following table the values of jp according to this formula 

 are given in the second column, in the third are Regnault's 



