( 648 ) 
(» SE 5) BRD 
5 
where 6 will be regarded as independent of v and 7, then we 
find for @: 
wo = RT log (v—b) + oe = PU wen ENEN) 
5 
: REE a 5 : 
If we write now — | Al for v—b, and omit p, then we obtain: 
pt the 
in which vaN per Waats further wrote 4 for v, whereas for illustrating 
B a fs . . lanl a 5 
several properties 5 was brought in connexion with 7, and = with pa. 
) ) 
This is consequently a complete set of approximations, and 
with good reason Prof. Lormnrz remarked to me, that in such 
cases we must be carefull, whether these approximations are 
not in contradiction, and up to what temperatures the results, 
dw 
Ow 
Van per Waats himself considered therefore the deduced expression 
merely as a more or less rough approximation, but which is at all 
z ; dw 0 (a 0 fa 
events better than the former expression — =—|{— |= —[—}], 
deduced with the above-mentioned expression for —, can be used. 
Ow Ox 
a fp 
where the term with — log — was omitted. 
U v 
Now, I showed in my preceding communication, that at low tem- 
peratures, and in the case of normal substances, where the critical 
pressures rarely differ much, this omitted term has in the greater 
part of cases a very small value, and is of entirely the same order as 
v—b 
v 
Only at higher temperatures the term has a large value, but then 
Ow 
the deduced expression for Er is not exact enough by far, for then 
de 
, which is constantly neglected. 
; : a : v—b 
neither p can be neglected against —, nor terms of order 
v 
can 
be omitted in that case. 
The matter is consequently this: at sufficiently low temperatures 
