142 



4. For the successive values of van der Waals' xapour pressure 

 factor / we now tind between 0° and 880° C. from the following 

 vapour pressure observations (at lower temperatures mean values) 



0° 100° 200^ 300° 400^ 500^ 550° 600° 650° 700^ 



/) = 24.10-5 0.2775 17,13 246 (mm.) 2,05 8,0 13,8 22,3 34 50 



750° 800° 850° 880° C. 

 72 102 137,5 162 (aim.) 



the following values. 



/o^^*z= 8,7534 5,6903 3,8998 2,7427 1,9410 1,3497 1,1129 



0,9045 0,7213 0,5538 0,3955 0,2442 0,1145 0,0433 



^ — 1 = 3,2930 2,1421 1,4778 1,0454 0,7415 0,5162 0,4241 



0,3425 0,2698 0,2045 0,1457 0,0923 0,0436 0,0165 



ƒ,0 = 2,66 2,66 2,64 2,62 2,62 2,61 2,62 



(min) 



2,64 2,67 2,71 2,71 2,65 2,63 2,62 



A =6,12 6,12 6,08 6,04 6,03 6,02 6,04 



6,08 6,15 6,24 6,25 6,09 6,05 6,04 



The value of p at 0° C. has probably been taken slill somewhat 

 too high; we assumed 0,00024 for it (Hertz gave 0,00019, v. d. 

 Plaats 0,00047). And especially for the values at the higher 

 temperatures the slightest error in the vapour pressure will make 

 itself greatly felt in the calculated values of /; the same thing 

 holds with respect to only an minimum error in the calculated 

 values of pjc and 2\-. If we assume e.g. p^- = 180atm. instead of 

 J 79 atra., log pk becomes 24 units in the last decimal greater, which 

 would cause the values of ƒ at the highest three temperatures to 

 rise immediately to 2,67, 2,68, and 2,77 (with nep. log. : 6,15,6,17, 

 6,38). Then bk would get the value 149.10-5 instead of 150.10-5, 

 and j/r/jf. would become 10,74 instead of 10,77. But in any case 

 the course of /' is pretty regular; this quantity decreases from about 

 2,66 at 0° C.'to 2,61 (the minimum value) at 500° C, after which 

 it increases again to 2,7 oi' 2,8 at the critical temperature. The 

 minimum lies at ^^0,66 7^:. 



The value of ƒ at the critical temperature might liave been ex- 

 pected higher than 6,4 or 6,5 (nep. log.), since ƒ^. is equal to 8y 

 according to our former considerations, when neither a nor h are 

 functions of the temperature. Now y is about = 1,2, hence 87 would 

 be = 9,6. But we should bear in mind that exactly in the case of 

 mercury a would be a temperature function in a high degree. For 

 only through the predominant influence of the volume does Hg 

 become Hg, at higher temperatures, whereas if the temperature 

 influence only could make itself felt, Hg, would dissociate to Hgi, 



