498 



Tic 



69,16 X 1600 

 32vÓ 



= 3460° abs. 



The value of 2/ is then 



for A: 



3,35 X 207,2 694,2 



1 _[_ O 04 X 58,8 = 3.35, and we find 



= 9,68. (calculated) 



320.10-5X22412 71,72 



D has been found = 11,4 at the ordinary temperature, so that 9,7 

 would be about 15% too low — unless lead, like tin, is converted 

 to a less dense modification at lower temperature. Cohen and Hel- 

 derman's researches (cf. among other things Z. f. ph. Chem. 74, 202 

 (1910) and 89, 733 (1915)) suggest already tlie existence of even 

 more than two allotropic forms. 

 We find for the critical pressure: 



0,0317 X 1600.10-4 



Pk = 



= 490 atm. 



1024.10-8 



For the boiling point Greenwood (1911) found 1525° C. =1798° 

 abs.; V. VVartenberg (1908^ found 1580° C. = 1853° abs. The two 

 values do not differ much. If we assume the mean value Tg = 1825° 

 abs. as correct, Tk. Ts becomes := 1 ,90, which is very high, and 

 /,'' becomes = 2,69: 0,9 = 2,99, i. e./, = 6^, whereas/fc = 8y = 13.4 

 is expected. The value of ƒ,. would, therefore, be much too low. 

 And as To- = 327°,3 C. = 6"oO°,4 abs., 11: 7;. would become 5,76. 

 Possibly the critical temperature has been assumed soniewhat too 

 high. From Greenwood's vapour pressure determinations a tempe- 

 rature would follow for Tk somewhat below 3000°. But then hjg 

 must not be assumed to be = 320. 10— ^^ but e. g. again 55 units 

 higher, hence hk = 375 . 10 ^. In virtue of the Cerium-Tantalium 

 period, inserted after the tin, this may not be improbable. With 

 2y = 3,19, X = 0,868 we should then have obtained for Tk the value 

 70,23 x"l 600: 37,5= 3000° abs., in perfect agreement with Green- 

 wood's experiments. But a still lower value would then be calcula- 

 ted for D„ viz. 660,9:84,05 = 7^. The value of /;/,. would be 

 = 0,0321 X 1600.10-4; 1406,25.10^^8^ 370 ^tm., and the two ratios 

 Tk: Ts and T^: 7V would be found resp. = 1,64 and 5. 



Greenwood's determinations now gave what follows 



1798 

 1,0 





 



