Letter from Earl of Berkeley, Berkeley Castle, to AW Porter Stating that he has "recently found an equation (mostly empirical) connecting osmotic pressure with the physical properties of the solutions" and makes reference to Porter's paper 'On the Osmotic Pressure of Compressible Solutions of any Degree of Concentration. Part II. Cases in Which Both Solvent and Solute are Volatile', 'Proceedings of the Royal Society of London. Series A', Vol. 80, No. 541, Jun. 10, 1908. July 1931