499 



A similar calculation as that for tin yields between each succes- 

 sive couple of observations : 



f\Q^log\Qp^= 6,301 6,672 4,965 3,573 



/lor^ = 11372 11996 i 8927 5944 



From the two last calculated values for f^" -\- log^° ]}k and/^°7i 

 appears the inaccuracy of Greknwood's vapour pressure determinations, 

 especially at temperatures higher than 2000° abs. (the same 

 therefore as for tin). For as /oi/^" p^^ 2,Qd to 2,57, hence on an 

 average about 2,63, it would follow from the last determinations 

 that ƒ ^^ is = 2,34 to 0,94, wlucli is quite impossible. And if reversely 

 we take the probable value 4 for /^', the much too low values 

 2200° to 1500° abs. would follow for Tk from the said determina- 

 tions. ■ Accordingly, both for tin and for lead, we must reject the 

 vapour pressure determinations above 2000' as quite erroneous, li 

 we only take into account those below 2000°, we find with 

 log'' })k = 2,63 the values ƒ '° = 3,67, resp. 4,04, yielding Tj, = 3100 

 to 2970°, mean 3035° abs.; in excellent agreement with the value 

 of 7\. computed by us, when 0^ = 375.10-5 is assumed (viz. 3000°). 

 Very little in agreement, however, with the calculated value of 7\ 

 on the assumption of è^ = 320.10 ~5, viz. 3460° abs. It is really 

 difficult to make a choice here-, we do not know in how far 

 Greenwood's observations below 2000° are reliable. That, however, 

 V. Wartenberg found an only slightly divergent value for the 

 boiling point, is a reason to assume the middle value 1825° for the 

 boiling point as pretty accurate. But then the critical temperature 

 can probably not be higher than 2900° or 3100°. (According as 

 Tjc : Ts is taken 1,6 or 1,7). If we, therefore, retain the value 

 3000^ abs. ^), which was obtained with 6^. = 375.10-5, 1\ ■ T' 

 becomes = 1,64. As log'" 370 = 2,57, ƒ/' becomes = 2,57 : 0,64 =4,0, 

 '\.e.fs=^^ while the value 12,8 is expected for /i- = 4 X 2y. 

 (With log'' pk = 2,57 the value"X73, resp. 4,10 follows for ƒ/" 

 from Greenwood's observations, which is in good harmony with the 

 above mentioned value 4,0). 



7. Recapitulation. Combining the values of V^ak, (n-, Tk, pk, etc., 

 found above for the elements of the carbon group, in acompiehen- 

 sive table, we get the following survey. For lead we have given 



^) GuLDBEKG (1887) gives also for lead the much too low value 2"^ = 2000" abs. 

 For mercury the same: 1000° abs., which is also loo low. 



