16 
Though both values, as well Ts as px, are supposed to be unknown, 
yet we find for these quantities (and that for an abnormal substance, 
for which the state of association continually varies with the tem- 
perature) values, which differ only little from the values calculated 
in the other way. Those that were calculated between 357° and 
400°, come very near, indeed, to the latter (viz. 1260° and 192 atm.). 
We see from what precedes, that for many substances with as 
yet unknown pj or even unknown pj and 7).. these quantities can 
be calculated with some approximation from a few vapour pressure 
observations; in the last mentioned case (p, and 7% unknown) by 
the aid of the probable value of Wa,. But the molecular state in 
the critical point must then be accurately known. 
«) Calculation of Ti, from the temperature of the boiling port. 
If the foundation of the calculation of the foregoing paragraph 
is wanting, in consequence of the molecular state at Tj, hence also 
Va,, being unknown, the equation (4) is still valid. We can, there- 
fore, always determine « and y from two vapour pressure obser- 
vations, ie. (7% and f + log pz. If the observations are made in 
the neighbourhood of the boiling point, we can sull determine the 
values of 7; and p, with some approximation from the approximated 
value of f at this point (determined from the mean value for a 
number of analogous substances). 
Besides 7, can be determined directly from 7’, when the mean 
value of the ratio 7: 7, is used as first approximation. 
We will, therefore, in the first place consider the values of Sh 
and 7}: 7, more closely. 
In the following table, besides 7} and p;, the triplepoint tem- 
perature 7, and the boilingpoint temperature T, of a great number 
of substances have been given, and also the ratios TT and 
T,: T,. Further log ps: and f… The ratio T.: T, will depend on 
log p‚ according to the relation (ps == taim) 
Pk (ae 
log —=fsl ——1 }, 
og 1 Js be ) 
so that: 
Ty log ph 
wh a SOE ee, en ee 
Ts Ts 
Now — at least for ordinary substances, where the critical tem- 
peratures are not excessively low — the values of fs (for normal 
substances) will not diverge very much, so that 7%: 7, would have 
about the same value for all such substances, if log p‚ had the same 
