497 



becomes = 3730 : 505 = 7A which is very high ; with Tk = 4100° 

 or still higher this ratio would even become 8 or 9. 



Greenwood's vapour pressure determinations gave the following 

 result. 



T= 2243 

 p= 0,133 



2373 I 2543 abs. 

 0,345 I 1 atm. 



From the well-known formula log —^^=/l — — 1 J or log p 



= (ƒ + ^09 P*) TFT we find : 



/ + ^09 Pk = ^F~~T ' 



every time from two successive observations (between which / is 

 supposed constant), after which f7\ can further be calculated from 

 /Tk= T{f-\-logpTc)— Tlogp. Thus we find from 



log^op= 0,12385(— 1) I 0,53782(— 1) | 



Tlog^op= 277,8—2243 | 1276—2373 | 



resp. /'" 4- log'' Pk = 6,681 and 6,453; /^"Tj^ 16950 and 16410. 

 (Greenwood calculates for this the too low values 29 : 4,571 = 6,344 

 and 73900 : 4,571 = 16167). 



Hence ƒ ^° becomes resp. =3,868 and 3,640 with jy^ = 650 atm., 

 log"> pk=z2,S\S, from which 4380, resp. 4510, mean 4450° would 

 follow for Tjc. And a modification, even a considerable one, in the 

 assumed value of pk has little influence on this. 



The value of y^'" lies here, therefore, in the neighbourhood of 3,75, 

 i.e. fs in that of 8,6. This value seems too low to us, as 2y = 3,44 

 already corresponds with the critical temperature 7\ = 3730°, so 

 that /;. tlien would be = 13,8 . And 2y would be = 3,7 with 4500°, 

 i.e. //: = 14,8. Everything points therefore to the fact that the boiling 

 point determined by Greenwood is too high, or rather that the 

 vapour pressures determined by him, have been given too low. 



If we retain the value T^ = 3730°, calculated by us, the real 

 boiling point temperature 7s would be = 2330° abs. with 7^: Tg = 1,6, 

 instead of 2543° abs. as Greenwood gives, and the value /s^" would 

 then be = 4,69, i. e. /, = 10,8 . 



6. Lead. If we assume here I ak — 40 . 10 -\ and bk = 320. 10-^ 

 again 55 units higher than tin, though this cannot be ascertained 

 in default of compounds, the critical temperature and pressure of 

 which are known), we get with 2y = 3,35, X = 0,855 : 



