Manganese (Mn) is a transition metal that presents complex chemistry, making its identification challenging for early scientists. Its isolation in the 18th century helped pave the way for a deeper understanding of metallic properties and their practical applications. The process of discerning this element from its minerals highlights the rigorous experimental work conducted by chemists in Sweden during that era.
The Element Manganese
Manganese is the twenty-fifth element on the periodic table. In its pure state, it is a hard, brittle metal with a silvery-gray color, often resembling iron. Although it is the twelfth most abundant element in the Earth’s crust, manganese is rarely found in its pure metallic form. It is predominantly found bonded within various minerals and ores, such as pyrolusite (manganese dioxide, MnO2). Its numerous oxidation states contribute to its diverse roles in industrial processes and biological systems.
Pre-Discovery History
Compounds containing manganese were used by ancient civilizations long before the element’s formal identification. Pyrolusite, the black manganese dioxide ore, served as a stable pigment in cave paintings dating back over 17,000 years. Egyptian and Roman glassmakers used manganese compounds, calling them “glassmakers’ soap,” to remove the greenish tint caused by iron impurities or to color glass deep purple. Early chemists struggled to distinguish manganese ores from those containing iron or magnesium due to their similar physical appearances. This confusion was compounded because the compounds behaved similarly in many early chemical tests, delaying its recognition as a unique element.
Isolation and Identification
The element was definitively recognized through the work of two Swedish chemists, Carl Wilhelm Scheele and Johan Gottlieb Gahn, in 1774. Scheele, an analytical chemist, first demonstrated that pyrolusite contained an unknown element distinct from any previously classified metal. He heated manganese dioxide with hydrochloric acid, a reaction that produced chlorine gas, and concluded the mineral’s metallic component was a new substance. Following Scheele’s theoretical work, his colleague, the mineralogist Johan Gottlieb Gahn, successfully isolated the metal later that same year. Gahn achieved this through an intense reduction process. He mixed the black pyrolusite ore with charcoal and subjected the mixture to very high temperatures within a furnace. This allowed the carbon to strip the oxygen atoms from the manganese dioxide, yielding a small, impure sample of hard, brittle, silver-white metallic manganese.
Immediate Impact and Application
After Gahn’s isolation, applications for the new metal were explored in both chemical and metallurgical fields. Scheele’s earlier work established that manganese dioxide was an effective agent for generating chlorine gas, which became a foundation for the industrial production of bleaching agents. In metallurgy, researchers observed that adding manganese to iron significantly enhanced the resulting alloy’s properties. By the end of the 18th century, patents were granted for utilizing manganese in steelmaking to improve the metal’s strength and hardness. This early recognition of manganese as an alloying agent laid the groundwork for its adoption in the steel industry during the Industrial Revolution.