Abstract
A study of the partition function and of the equations of state of solid and liquid is made. By assuming a simple form of mutual potential energy function, we have obtained F-like curves as in the van der Waals' theory and determined the in- citing point by the condition of phase equilibrium. Lindemaun's formula is derived Change of density upon fusion is calculated. Further, thermal pressure in liquid is calculated and compared with the result which the author has got previously