The critical volume provides data which may be tested for additive relations.
Theoretically the critical volume is three times the volume at absolute zero, i.e.
It is found that isomers have nearly the same critical volume, and that equal differences in molecular content occasion equal differences in critical volume.
The critical volume of oxygen can be deduced from the data of the above table, and is found to be 29, whereas the experimental value is 25.
Experimentally (by extrapolation from the" law of the rectilinear diameter ") the critical volume is four times the volume at absolute zero (see Condensation Of Gases).
