The original osmometer described by Goyan and Johnson was improved, resulting in a 10-fold increase in sensitivity and greater convenience in use. A concentration change of 0.001 molal is easily detected in aqueous solutions; however, the instrument may be used without modification for nonaqueous solvents. A new measuring circuit and a new temperature control system are described. The original features for introduction and removal of samples are retained. Solutions contact only glass and platinum. Valuable compounds may be recovered unchanged by evaporation. The instrument may be used in various analytical applications, ranging from the study of complex formation to the determination of concentrations of known solutes. It is useful for the determination of molecular weights and for direct measurement of osmotic properties of solution.