459 



II! fiict, something is to be said in favour of this. In § 17 we 

 namely calculated the value of P^ from 2y z= A/,, -. h^ = /?^. : ,?^, so 

 that /?., = /?^.: 27 = 0,429:1,5 became = 0,286. But in this it is 

 assumed that the direction of the straight diameter remains the same 

 down to the absolute zero point — which (as we already observed 

 at the conclusion of § 14 (III p. 1051) cannot be the case. On the 

 contrary the coefficient of direction will aj)proach to about 0,5 for 

 all substances at low temperatures. It follows from this that the 

 value of the liquid density at T=zO, viz. q^, which is extrapolated 

 from the direction of the so-called straight diameter {at the critical 

 point), will always be too great, hence v,, too small, and also b^ = i\ 

 too small. Accordingly also the value of P^ = b^ : Vk will be found 

 too smalL when the inadmissible extrapolation is performed. 



The real value of /?„, occurring in our formtila (SO^i for b=zfOv), 

 will therefore be always greater than that which occurs in our 

 relations found in I (which are valid at the critical temperature). 

 For the calculations of the real /?„, in order to test our formula 

 (30) by the observations, the calculation from P^ = P^. : 2y]c (which 

 is based on this extrapolation) has therefore to be rejected. 



The above table need, therefore, give no occasion to conclude to 

 any deviation with respect to the calculated and the found values 

 of P ; the more so as the cour.<;e is perfectly the same, in consequence 

 of the fact that in the relation (30) not b, but b — b^ occurs, so that 

 through simple increase of 3 to 0,305 the found values of b — b^ , 

 resp. i?— /?o ^vill agree perfectly with the values of ji — ^^ calculated 

 from our formula. 



Remark. We saw that the found values of ^i,, from the unsaturated 

 gas state (§ 17) were all found too great for values of ;/z ^ 1 ; for 

 values of m <^ 1 all too small i. e. larger or smaller than the values 

 of ^g or ^k' calculated from our formulae. Also in the region of 

 coexistence {m <^ 1) w^e found values for ^^ which are all too small, 

 nay even negative, hence impossible. Now the too small values may 

 be easily accounted for either by association in the vapour at low 

 temperatures, or through a faulty method of calculation of /?, from 

 the law of Boylk (see above). But the too large \alues of j^^ at 

 m^l cannot be accounted for in this way. 



It is, however, remarkable, that those too large values of j?^ at 

 m<^i, combined with the liquid values at ni<^l, seem to obey 

 the relation 



^ =r 0,4 l/m 



pretty well, as appears from the table on the next page. 



