Physics. — ''On the Fundamental Values of the Quantities b and 

 V^'a for Different Elements, in Connection luith the Periodic 

 System. V. The Elements of the Carbon and Titanium Groups." 

 By Dr. J. J. van Laar. (Communicated by Prof. H. A. Lokentz). 



(Communicated in the meeting of May 26, 1917). 



A. The Carbon Group. 



1. For the calculation of the critical data and the values of a 

 and b following from them the elements of this group offer very few 

 data indeed. Even the situation of the melting point is still insuffi- 

 ciently known for carbon ; of other elements the accurate knowledge 

 of the boiling point is wanting. Yet it is exactly this group — though 

 we have often to be satistied with a rough estimation — that gives 

 a fine confirmation of the fact set forth by me in the preceding 

 papers that the values of Va. for elements, which (at least for high 

 temperatures) occur as separate atoms and not as molecules (either 

 partially dissociated or not), will suddenly become very much higher 

 than the normal (rest) values for compounds. 



We alread}^ found a first example for Antimonium and Bismuth, 

 where S/ajc (per gramme atom) present instead of the normal rest 

 values 9, resp. 11 .10"^ the greatly increased values 32,5 and 

 36 . 10—2. Ti^g value of Vak was only partially increased for other 

 elements, as Arsenic, Selenium and Tellurium, owing to the fact 

 that these elements are only partially dissociated to separate atoms 

 at the critical temperature. 



For the carbon group we find values for V^ak which lie between 

 32 and 40 . 10~2^ so that all these elements appear in the form of 

 separate atoms, as the rest values for \/ak, which would hold for 

 compounds, lie much lower, viz. between 3 and 11 . 10-^, 



2. Carbon. The melting point lies very high, viz. at 4200° 



absolute. Probably this is only the sublimation point at 1 atm. pres- 

 sure. According to Lummer's interesting experiments, described in a 

 paper published by Vieweg : '' VerflUssigung der Kohle" ^), the carbon 



1) Sammlung Vieweg, Heft 9/10, 1914. 



