759 



0,97 (cf. also New Relations I, loc. cit.). As far as <( is concerned, 

 we saw that this quantity is := 1,044 for H,. This renders the 

 product hp = \M^ for H„ and the ratio Tb' 7\ = 3,236. But for 

 other substances, with higher critical temperatures, for which f/^' gets 

 in the neigiibourhood of Vj^, Tb'- Tk will get into the neighbour- 

 hood of 3. 



V. The value of B = RTh^ — a for 20° C. 

 Schalkwijk ') found lately that his experiments at 20° C. can be 

 represented by the relation 



jou= 1,07258 + 0,000667* (/ + 0,0„98 cZ' (8 — 60 atm.). 



Kamerlimgh Onnes and Hyndman (Comm. 78'), however, nioditied 

 the virial coefficients B and C of the above formula in 667 MO"^ 

 and 993.10-9, to facilitate a comparison of their observations at 0° 

 and 20° with those of Schalkwijk. 



Later on Walstra (These Proc. Vol. XVII p. 217) calculated from 

 KoHNSTAMM and Walstra's later experiments (These Proc. XVII p. 203) 

 at 220° C. (125-2200 atm.) the relation 



py=1.07258-f 674,0. 10-6 (i+856, 9. 10-9 c/M 665,9.10-i5,/4(200-800atm.), 

 valid only from 200 to 800 atm., in good harmony with the cor- 

 rected formula of Schalkwijk, which according to Walstra would 

 be valid up to =t 120 atm. 



By addition of a term with r/* Walstra could derive a formula, 

 which comprises all the observations — also those of Schalkwijk at 

 lower pressures, and which is valid up to 1000 atm. 



It runs : 

 pv = 1,07258 + 676,3. 10-6r/ + 882,15 . 10-9 o'^ + 669,54.10-15^4 — 

 - 0,ir.l . 10-21 d' (up to 1000 atm.). 



Finally K. Onnes. Crommklin, and Smid (Comm. 146^) gave the 

 equation : 



pv = 1,07261 + 657,12 . 10-6 ,/ ^ 1292, 6 . IQ-a (up to 100 atm.) , (6) 



in connection with their definitive determination of the isotherm of 

 20° C. from 60 — 100 atm.; instead of Schalkwijk's formula (which 

 only holds from 4 to 60 atm.). 



When from this we calculate the value of pv at 100 atm., it 

 deviates only 0,1 7o fi'om that which can be calculated from the 

 values found by Amapat at 0° and 100° C. The term A = RT has 

 evidently been calculated from (1 + 0,0036618 x 20) x 0,999416 = 

 = 1,07261, so that for 0° C. the virial coefficient B was put at 



1) Thesis for the Doctorate. 



