217 



Physics. — ''The hydrogen isotherms of 20° C. and <?ƒ 15^5 C. hdioeen 

 1 and 2200 atmsr By Dr. K.W. Walstra. Van der Waals' 

 fund resetirclies N". 8. (Comniunicated by Prof. J. D. van 



DER Waals). 



(Communicated in the meeting of May 30, 1914). 



T = 20°. 



§ 1. Agreement of the observations below 1000 atms. loith 

 Schalkwuk's isotherms. 



For each of the series of observations given in the preceding 

 Communication we iiave determined an empiric equation of the form: 

 PV= a-^b D^cB'-^dB\ 



As only sei-ies of observations below 1000 atms. can be represented 

 by this equation with 4 virial coefficients, only these series come 

 into consideration for the present. The obtained observation material 

 above 1000 atms. will have to be considerably extended to enable 

 us to calculate the following virial coefHcients with the same 

 certainty. 



If of the above equation we wish to determine a, b, c, and d, 

 we get a number of equations equal to the number of obser- 

 vations, and consequently then with 4 unknown quantities. To 

 solve these equations according to the method of least squares 

 is not feasible, as then the normal equations become practically identical, 

 which may already be seen beforehand. We have been able to apply 

 Prof. E. V. D. Sande Bakhuijzen's method successfully, which was also 



7 = 20°. 5/6 November 1912. 



r=20°. 21 November 1912. 



PV{0) 



PV{C) {0).{C) 



579.72 

 378.48 

 283.02 

 132.69 

 129.26 

 124.90 



1068.76 1068.76 

 963.11 963.11 



0.00 

 0.00 

 0.00 



+0.03 

 0.00 



+ 0.03 



PF= 770.50 + 371.45/) + 

 + 272.26 Z)2-f 192.62 Di 



PI/=829.71 + 

 -f 353.40D2_^ 



445.08Z) + 

 197.28 £>-*. 



