51J 



lower than this temperaliire ; e.g. 7\- = 2000° (extrapolated 1997°). 

 A second test is furnished b}' the vapour pressure determinations. 

 We owe the following data to Hackspilt, (1912). 



t^ 350 355 365 390 397 | 883^ C. 



T= 623 628 638 663 670 j 1156°abs. 



i 

 p= 0,08 0,12 0,15 0,21 0,26 760 mm. 



logio p= 0,903(— 2) 0,079(— 1) 0,176(— 1) 0,322(— 1) 0,415(-1) 2,881 



According as 7';t = 1970° is assumed or 1730° abs., we find 

 /c(/^" Pi = 2,532 or 2,499 (see above), and we have therefore, this 

 being in mm. = 5,413 or 5,380: 

 Pk 



logXQ'L^ = 6,509 6,333 6,236 

 P 

 or = 6,477 6,301 6,204 



^ -1 = 2,162 2,137 2,088 



or = 1,777 1,755 1,712 



■ 1 

 Hence ƒ lO = 3,02 2,96 2,99 3,09 3,09 3,60 -►4,67 



or = 3,64 3.59 3,62 3,76 3,77 5,03 -*• 4,48 



We see, therefore, from this that the vapour pressure factor ƒ is 

 pretty well constant at the lower temi^eratures 350 to 400° C, but 

 at the boiling point (the values of the last column on the righthand 

 side of the vertical line refer namely to the boiling point) it has 

 considerably increased in both cases : from 3,1 to 3,6, and from 3,8 

 to 5,0. The latter increment is much too great, the more so as the 

 /hititmg value at 7\, viz. f\ = 8y = 10,74 or 10,32, so /k^° = 4,67 

 to 4,48, would be smaller in the latter case than the value at y.\, 

 viz. 5,03, which in view of the great increase. of ƒ at higher tem- 

 peratures is quite impossible. 



We see from the above how exceedingly sensitive the method of 

 the vapour pressures is, especially at higher temperatures. This is 

 owing to this, that then (7^: T) — 1 is exceedingly variable on only 

 a slight variation in the value of Tk- In our example from 0,70 to 

 0,50 for a decrease from 1970 to 1730. And in consequence of this 

 also the value of ƒ is changed in the same degree (from 3,6 to 5,0). 

 We can therefore conclude from the vapour pressure determina- 

 tions for Na with great certainty that 7\=:1730° will be out of 

 the question, and that 7\- = 1970° will be near the truth. 



dt 

 Heijcock still gave — := 0,153 (p. in mm.) at the boiling point 

 dp 



temperature 882°, 9 C Now follows from 



