The principle behind capillary viscometry is the Poiseuille’s law, which states that the time of flow of a polymer solution (ps) through a thin capillary is proportional to the viscosity of the solution. The latter increases with increasing solution concentration. From Equation 17.6, the time of flow of the solvent (solv) or of the polymer solution will be proportional to the viscosity, and inversely proportional to the density: