A new method for vapor liquid equlibrium determination without analytical determination of concentration is proposed.Based on the relation of material balance in a steady flow system
the method consists in measuring the dew point or bubble point temperature of a solution with gravimetrically determined concentration z by equal volume exchange of y region or x region inside the VLE still into a steady state where z equals to y or x. The equation of equal volume exchange method is deduced from the relation of material balance of the steady state. The technique of the application are discussed in detail. Two newly designed ebulliometers were used successfully. The bubble point of dilute solution and dew point line of some system were measured with good agreement with parallel measurement and thermodynamic consistecy test also gave good results.