Physics. — ''On the Fundamental Values of the Quantities h 

 and V^a for Dijferent Elements, in Connection with the 

 Periodic System. VI. The Alkali Metals". By Dr. J. J 

 VAN Laar. (Commnriicated by Prof. H. A. Lorentz). 



(Communicated in the meeting of June 30, 1917) 



1. After the group of the noble gases, the halogens, the elements 

 of the oxygen and nitrogen groups, and those of the carbon group, 

 we will, for praotical reasons, first treat the group of the alkali 

 metals, and not until after this can we treat the intermediate 

 Beryllium and Borium groups, and the remaining minor groups 

 with some certainty. 



The task undertaken by us to compute with some certainty the 

 values of the critical quantities, and those of bk and V^a^, with the 

 required accuracy, gets more and more difficult. For the alkali 

 metals e.g. compounds of which the boiling point or the critical 

 temperature are known, are entirely wanting, and thus we are deprived 

 of a valuable test. Nothing is known beforehand that could be 

 used in any way as a foundation; everything must be calculated 

 anew, estimated, weighed, and considered. For an element as 

 recalcitrant as e.g. Carbon or Silicium, the critical temperature of 

 which is quite inaccessible, we know at least the value of h-k from 

 compounds, from which — in connection with other data — the 

 values of ajc, 1\ and pi- can be calculated with almost mathematical 

 certainty. 



This is not the case for the alkali metals. Here nothing is known 

 beforehand concerning b]c, and in most cases we shall therefore 

 have to be satisfied with defining limits between which the required 

 values of hk and K<7;fc must lie. Fortunately these limits are com- 

 paratively narrow, particularly when the course of the vapour 

 tension curve is sufficiently known, so that the values calculated 

 by us can yet lay claim to a satisfactory degree of accuracy. 



It will appear that for the alkali metals we are very near the 

 truth with respect to the critical temperature, when we multiply the 

 absolute temperature of the melting point by 57», and that of the 

 boiling point by 1,7. Thus we have the following survey. 



33 



Proceedings Royal Acad. Amsterdam. Vol. XX- 



