Chemistry History (DL) By amlindberg Period: 1750 to 1800 The invention of the Volta Pile 1772 The discovery of Oxygen 1801 Davy: employed by Royal Institution 1807 Discovery of Sodium and Potassium 1814 Fraunhofer lines discovered 1859 Invention of the spectroscope 1860 The discovery of Caesium 1867 Periodic Law (Mendeleev) Mendeleev starts forming the periodic table by listing elements according to their atomic weight 1870 60 elements had been discovered. Period: 1880 to 1890 Rayleigh's work with gases Rayleigh begins to conduct experiments in order to find the accurate densities of various gases by simplifying them into their pure form