The product shall be free from substances in suspension and crystallized salts. A choice of two pyknometers is provided: the Gay-Lussac pyknometer and the Reischauer pyknometer. The principle by using the Gay-Lussac pyknometer consists in determination of the capacity by measuring the mass of water at 20 °C and measuring the volume of sample at 20 °C. Principle of the Reischauer pyknometer: calibration by measuring the masses of water*introduced up to the different graduation lines. Measurement of the mass of the volume of sample at 20 °C up to a certain graduation line. Both of the types: calculation of the quotient which results from dividing the mass of the sample by the volume of the pyknometer corresponding to this mass.