Physics. — "On the Critical Temperature and Pressure of Mercury 

 and Phosphorus." By Dr. J. J. van Laar. (Communicated by 

 Prof. H. A. LoRENTZ). 



(Communicated in the meeting of April 27, 1917). 



A. Mercury. 



1. In a previous paper ') I calculated tlie value 1 260° abs. 

 (987° C.) for the critical temperature of mercury, and 192 at m. for 

 the critical pressure. 



We namely calculated as most probable value from the densities 

 of the compounds HgCl,, HgBr, and Hgl, (loc. cit. p. 7— 8jfor bk 

 for mercury per Gr. atom the value J50.10— ^ and further i'ovl^ajc 

 fiom the values of Tk, found by Rotinjanz (Z. f. ph. Ch. 87, p. 153) 

 for these compounds, the mean value (likewise per Gr. atom) 

 11,0 . 10-'^. (loc. cit. p. 8). With these values of Y^ak and bk we 

 further calculate from the formulae 



S ak 1 , at 



'''^' = 2l'Vk^'' ' ""'^ri'b^^^ 

 with R=\ : 273,1, / = ^7,3 = 0,964, n = '2, the values 

 7'a:= J260 ; PA: = 192 atm. 

 All this on the supposition that (saturated) mercury vapour at 

 7\ is /^/molecular {n = 2); a supposition, to which the course of 

 the vapour tensions between 0° and 500° C. leads us necessarily. 

 (Cf. also loc. cit. p. 12—16). 



2. Since then the vapour pressure observations of Cailletet, 

 CoLARDEAU and Riviere (1900) have become known to me, which 

 go up to 880° C. With 



log^ ^fl^ — l\ or ƒ + log pic = logp + ^ 



we calculate for /Tk the values 3004, 2979, 3233, 3107 (mean 3080) 

 from the values* 8,0, 22,3, 50, 102, 162 atm. at resp. 500°, 600°, 

 700°, 800°, and 880° C. ; always from a corresponding couple of 



M On the Fundamental Values of the Quantities b and i-^a etc. II. These Proc. 

 of March 25, 1916, p. 4 and 9. 



