Density determination by pycnometer is a very precise method. It uses a working liquid with well-known density, such as water. We will use distilled water, for which temperature dependent values of density ρH2O are shown in Table 1. The pycnometer (Fig. 1) is a glass flask with a close-fitting ground glass stopper with a capillary hole through it. This fine hole releases a spare liquid after closing a top-filled pycnometer and allows for obtaining a given volume of measured and/or working liquid with a high accuracy.