( 607 ) 



tiires coincides almost witli llic ciirxc Liiveii l)_v llio observations; 

 according as we approach the critical Icinperaliirc the calcnhited 

 cnrve shows a (lisi)hice!nciit towards the small densities with regard 

 to the observed curve. That this displacement is much larger than 

 follows from the calcnlation of Snppl. N". 14 mentioned above must 

 be ascribed at least partly to the circumstance that Amagat probably 

 did not derive the licpiid and vapour densities from his equation of 

 state by means of the criterium of Maxwell, but for shortness' sake 

 calculated by means of his equation of state the densities for which 

 p has the value for the saturation pressure furnished by experiment. 

 I). In Comm. N". 75 Nov. '01 attention was directed to the difterence 



T fbp 

 between the (7, = 



and the (/, 



resulting from his detei-minations of the 



derived from Amagat's net of isothermah 

 _p \oT 



T dpcoi'x 



_p dT 



saturated vapour pressure, which values must be ecpial for the 



undisturbed equation of state ^). One of the reasons to undertake 



the observations about carbon dioxide of Oomm. N". 88, Jan. '04, 



was the wish to obtain more certainty about these peculiarities 



in the behaviour of the substance in the neighbourhood of the 



critical point (comp. I.e. p. 566). The same difference viz. C^ = 7.12, 



Cj = 6.71 followed from these determinations. Brinkman (Thesis 



for the doctorate, Amsterdam 1904, p. 43) con tinned this difference 



not only for carbon dioxide, but he also found it for methyl 



chloride," while Mills (Journ. pliys. Chem. 8 (1904) p. 594, 685; 



éomp. also 9 (1905) p. 402) for ethyl oxide (Ramsay and Young), 



isopentane and normal pentane (Young) finds differences of 10 



percent between C^ dej'ived by means of the formula of Biot 



for the saturated Napour pressures and C'j which with regard paid 



to the regular variation of h with temperature "), follows from the 



data collected by Ramsay and Young (ethyl oxyde), Young (isopentane) 



and Rose-Innes and Young (normal pentane) in order to judge of the 



equation of isochors p = hT — a. 



c. In Comm. N". 88, Jan. '04, p. 575 table XXII the saturated 



vai)Our pressures of carbon dioxide between 25^.55 C. and the 



critical temperature (30\98 C.) are compared with the formula 



log — = / which was obtained by keeping in the develop- 



~Vm. Planck, Wied. Ann. 15 (1882) p. 457; comp. also Comm. N». 75 § 3. 

 The quantities C- and Gp, are both obtained by an extrapolation, 65 at v = Vh of 

 a liigher temperature to 2'/.- , Cq along the vapour pressure curve of lower T to Tk . 

 •V S. Young, Proc. Piiys. Soc. London 1894/95, p. 602; comp. also Comm. 

 Phys. Lab. Leiden No. 88 p. 54 note 1, Keesom Thesis p. 86. 



