The apparent partial specific volume, phi, of a protein (or other macromolecule) and the absolute concentration, c, can be determined from the densimetry of solutions and diffusates in 1H2O , 2H2O and 1H2O/2H2O mixtures if the ratios of concentrations (relative concentrations) are known. The densimetry method allows a non-destructive check on total macromolecule concentrations without prior kno...