( 273 ) 



we find: 



dT 9 



3=_0,493-h — (—0,493- 0,0903)^ = —0,493^0,1914 =—0,302. 



Tdx^ '16 



The value found by Keesom for x = 0,1047 is AT = — 8,99. 

 Supposing this value of x small enough to be substituted for f/.i'o, we 



find = — 0,284. 



Td.v, 



For .1'=: 0,1994 this value of AT found by Keesom is equal 



dT 

 to — 18,47 ; with these data we should find -— — = — 0,304, so 



1 d.v^ 



perfectly equal to tlie value calculated by means of (1). We have here 

 not a molecular increase of the critical temperature, but a decrease, 

 as indeed, was to be expected, because we had to do with the 

 addition of a more volatile component. 



Though I derived formula (9), on which formula (11) of 1895 

 and formula (1) of this communication are founded, in more than 

 one way in my two communications of 1895, I will derive them 

 once more here in order to have an opportunity to discuss somewhat 

 more fully some questions which present themselves in the derivation. 



For the plaitpoint line the simple relation: 





dp XP'V^JpT 

 df' 





dh] 



holds, which, ^ — not being directly known, may be brought 

 under the following form : 



rpd^_ rjJdp\ K^^V" ) xT\dic ) pT \dxdvjT\dxJ,/f \d.v'- 



~Yr~ ydTJ, ~^ 



dT \dTj,r. fd 



d''v\ 

 dx^JpT 



The factors of — and — and also —- ) being finite 



\dxJpT \dxJpT \d'V JvT 



1 fdv\ 

 quantities, and on the other hand I — I being infinitely great, when 



\dxjpx 



the plaitpoint lies at x = 0, we may write for this case : 



/dvy 



19 



Proceedings Royal Acad. Aniblerdam. Vol. VIII. 



