THERMAL PROPERTIES OF CARBONIC ACID AT LOW TEMPERATURES. 373 



curves p^ and p 2 through A and B, OP is the limit curve, and CD the last I curve in 

 the saturation area. 



We assume that the points O and A are known and we require to find P where the 

 limit curve cuts p. 2 . Draw a horizontal line DP at 3 . Then P will be fixed when 

 0i = 0p 0n is found. 



Let - 3 = 9 m and JI be the difference of total heat between D and B. 



Zt 



Then 



But 



therefore 



_SI-o- 2 S9. 



(i) 



SI = 0.^ 



(ii) 



Similarly, selecting other pressure lines, we find a series of points P which all lie on 

 the limit curve. The same method is applicable for finding points P on pressure 

 curves above O, if O is not on the highest pressure curve. For checking our 6<f> chart 

 the point O was chosen on the 400-lb. pressure curve. 



APPENDIX VI. 



A Method of Correcting the Results of a Throttling Experiment for a Small 

 Departure from Standard Conditions. 



Let A (pA) be the standard starting point and p 2 the standard final pressure. 

 P and E are the actual starting point and finishing point. P and R lie on an I line 

 which cuts P! in Q and p 2 in S. The I line through A cuts the p 2 line in U. We 



