Hermann Sicius presents the elements of the sixth subgroup (chromium group) in detail in this essential work. He demonstrates that the elements of this group are generally relatively unreactive and exhibit regular gradations in their properties. For instance, from chromium to tungsten, density, melting points, and boiling points increase, while reactivity slightly decreases. Chromium, molybdenum, and tungsten were discovered in the late 18th century, while seaborgium, which can only be produced artificially, was discovered about 200 years later. Molybdenum, for example, is a component of very hard steels, and tungsten was used for the filaments of light bulbs.