The vaporisation heat of liquid helium from 0 to 5.2° K and the value of h, calculated from the thermodynamical behaviour of helium

Abstract

Summary The vaporisation later γ T was calculated by equalizing the thermic potentials in vapour and liquid. Below the λ-point we calculated γ T=0 , using our recent vapour pressure determinations. We found 14.24 ± 0.01 5 cal/mol, in good agreement with Bleaney and Simon's value 14.26. But using the scale 1937 we found an important inconstancy in the results obtained for γ T=0 . This shows that an error in the scale 1937 below as well as above the λ-point up to 3°K is probable. A formula for the vapour pressure as a function of T , in the helium II region, is given. The value of h , calculated from the chemical constant, is within 1% in agreement with Ohlin's experimental determination. The vaporisation heat from 0 to 3.5°K, which has been calculated from the difference in entropy between vapour and liquid, is within 1% in accordance with Dana and Kamerlingh Onnes' experimental values; this statement constitutes a reliable confirmation of all thermodynamical data available at this moment. Above 3.5°K an error of 6% in Dana and Kamerlingh Onnes' values seems probable.