890 Prof. A. W. Porter on the Inversion-Points for 



and that if A is plotted against T the inversion-points are 

 given by the same rule as before. The curves thus obtained 

 enable fairly accurate estimates of the inversion temperatures 

 to be made. At the same time the present writer has for 

 some years found them to be of great use in exhibiting the 

 properties of real gases in other respects. It is convenient to 

 take zero centigrade as the standard temperature ; the value 

 of A is then necessarily zero at that temperature. If the 

 origin be shifted to this temperature the tangents for finding 

 the inversion-points must be drawn from the centigrade tem- 

 perature corresponding to the absolute zero ; this has been 

 taken as — 273°"1. Since the pressure p is a constant for 

 each curve the product pA may be dealt with instead of A. 



The following table, based on Amagat's experiments [Ann. 

 de Chem. et de Phys. 1893), exhibits the data for nitrogen in 

 full :— 



Table I. — Nitrogen. 



Temp. 

 Cent. 



150 Atmos. 



200 Atmos. 



250 Atmos. 



300 Atmos. 



pv. 

 1-0085 

 1-0815 

 1-4500 

 1-8620 



pA X 10 4 . 





 133 



742 

 1186 



pv. 



pA X 10*. 



pv. 

 1-0825 

 1-1575 

 1-5376 

 1-9585 



pA X 10 4 . 

 



115 

 609 

 852 



pv. 

 1-1360 

 1-2105 

 1-5905 

 2-0145 



pA X 10 4 - 

 



78 

 409 



488 





 1603 

 99-45 

 199-5 



10390 

 1-1145 

 1-4890 

 1-9065 





 145 



717 

 1086 



Temp. 



Cent. 



350 Atmos. 



400 Atmos. 



450 Atmos. 



950 Atmos. 



pv. 



pAxlOK 



pv. 



pAXlOK 



pv. 

 1-3230 

 1-3940 

 1-7665 

 21940 



pA x 10 4 . 







-66 



-382 



-954 



pv. 

 2-0015 

 2-0690 

 2-4230 

 2-8380 



pAxlO 1 . 







-500 



-3064 



-6256 





 1603 

 99-45 

 199-5 



1-1950 

 1-2675 

 1-6465 

 20730 







24 



163 



50 



1-2570 

 1-3290 

 1-7060 

 21325 







-18 



-88 



-418 



The corresponding curves are shown in fig. 2; and from 

 these the inversion-points are found by drawing tangents 

 through the absolute zero. The values so found are given in 

 Table II. In the columns headed " reduced " the pressures 

 and temperatures are given as fractions of their critical values, 

 viz. :—p e = 27 atmos., T c =127° abs. C. 



