219 

 T=20<'. 4 June 1913. 



PF=596.07 + 207.24Z)4- 

 + 147.31 Z)2 + 34. 13Z>+. 



To find out whether these series of observations are in harmony 

 with each other, they can be brought in correspondence directly. 

 We did so before, and found only a sligiit deviation between them. 

 Besides it is also possil)le to try and make ail the series of obser- 

 \ations agree with Schai,kwijk's isotherm, and then compare them 

 also inter se. But then there must first be a reason to suppose that 

 it was possible to make these observations agree with Schalkwijk's, 

 and this had soon appeared. When in December 1912 only three 

 series of observations had been found, we calculated from that 

 which contained the greatest number of observations (Dec. ^Vi2 ^912) 

 an empiric equation from four of the observations,, viz. at 787,15, 

 401,68, 320,29, 276,70 atms. 



The other observations of this series appeared to be in good 

 agreement with the found equation : 



PV= 841.70 + 415.09 D + 414.J0 D' + 198.16 D\ 



Also the two series of observations of Nov. 1912 appeared to be 

 in harmony with this. Then a comparison with Schalkwi.ik's obser- 

 vations was attempted by reduction of the above equation to one 

 with the same virial coefficient : a as Schalkwijk, viz. a = 1.07258. 

 This reduced equation then becomes: 



Pr= 1.07258 + 0.0,6740 D + 0.0„8569 B' -|- 0.0^,6659 D\ 

 Schalkwijk giving: 



jP r = 1 .07258 + 0.0,6671 U + 0.0,993 B\ 



This equation holds from 8 to 60 atms., ours from 200 to 800 

 atms., but we are now going to try to extrapolate with respect to 

 the region of the lower pressures in order to compare these exti-a- 

 polations with Schalkwijk's. 



The difïerences are most apparent when the product P F is deter- 



