Specifies two methods for the determination of density. The method using pyknometer is to be preferred in the case of dispute or of high viscosity solutions. The principle of the method using a density hydrometer is based on pouring the test sample into a measuring cylinder and inserting the hydrometer selected from the test of density hydrometers, waiting for its return to the equilibrium position and recording of the graduation mark. The principle of the method using a pyknometer consists in measurement of the mass of the volume. The volume*is determined by measuring the corresponding mass of water at 20 °C, and calculation of the ratio of the mass of the sample to its volume.