412 



the question, why the values of "/,.5 will not diffei' much in manj' 

 cases, as Katz thinks he has observed. 



10. Some remarks on the values of «^,,2. 



In the first place it may be stated that in w = AP-\- a/,jt Av, AF 

 is, of course, only negligible when in consequence of great volume 

 contraction in associating components fchietly water) the term with 

 "/v"-Av greatly preponderates. Only then lo/Aiy may, of course, be 

 put = ^'/,;i in approximation. 



But in the second place "/„n = "/^a is not yet always constant 

 within narrow limits. A look at a table') of critical pressures is 

 enough to convince one of this. In water 2^, = 217,5 atm. ; in many 

 elements (metals e.g.) still much higher. In n)any "ordinary" sub- 

 stances, however, especially organic ones), the critical pressures will 

 be about between 30 and 60 atm., as extreme values And in many 

 only between 40 and 50 atm. 



All this is the consequence of the fundamental atomistic values 

 of V'^a and b, from which the values of l-^a and b for the molecule 

 can be calculated additatively in all compounds according to fixed 

 rules (see my papers on this subject already cited in 1). 



As an example let us take the following principal elements, of 

 which organic substances are built up. 



And as the values of ^jy/a do not differ so very much, this will, 

 of course, not be the case either for the compounds built up of 

 these elements, since — as was already mentioned — the values of 

 b and V^a can be additatively calculated from the fundamental values 

 recorded above. 



Before concluding I will just draw attention in this connection 

 to the fundamental values of \/a in carbon. In four single bonds 

 the (7-atom is towards the outside quite shaded as regards its attract- 



') Gf. e.g. p. 7 of my first Paper on the additivity cf h and \^a in the J. d. 

 Gh. ph. (1916) or These Proc. Vol. XVlll WK 8 p. 1220 et seq. 



