Friedrich Stromeyer, a chemist and physician, officially identified cadmium, a soft, silvery-white metal, in 1817. This discovery, rooted in early 19th-century German chemistry, marked the element’s formal addition to the periodic table. Its identification was closely tied to pharmaceutical quality control during that era.
The Circumstances of Discovery
The discovery of cadmium arose from an investigation into the purity of medicinal zinc compounds in Germany. Friedrich Stromeyer, serving as the Inspector General of Apothecaries for Hanover, was examining zinc carbonate used in medicines like ointments and antacids. He noticed that certain batches of the zinc carbonate turned a distinct yellow color when heated, a reaction pure zinc carbonate should not exhibit.
Stromeyer isolated the new metal from the discolored ore by converting the impurity to a sulfide, then roasting and reducing the resulting compound. Simultaneously and independently, Karl Samuel Leberecht Hermann was investigating similar purity issues in medicinal zinc oxide, leading him to identify the same element.
The new element was ultimately named cadmium, a designation proposed by Stromeyer himself. The name originates from the Greek word kadmeia, an ancient term for calamine or zinc ore. This naming is logical, as cadmium naturally occurs as a minor component within most zinc ores.
Fundamental Properties of the Element
Cadmium is classified as a transition metal, occupying position 48 on the periodic table. It is a soft, malleable, and ductile metal with a distinctive silvery-white appearance. It has a relatively low melting point compared to many other metals.
Chemically, cadmium shares similarities with both zinc and mercury. Like zinc, cadmium exhibits an oxidation state of +2 in its compounds. It is found in the Earth’s crust at a low concentration, generally between 0.1 and 0.5 parts per million. As a bulk metal, it is insoluble in water and resists corrosion.
Modern Uses and Health Implications
Despite its toxic nature, cadmium has several important applications in modern industry.
- It is widely used as an electrode material in rechargeable nickel-cadmium (NiCd) batteries.
- It is employed as a corrosion-resistant coating for steel and other metals through electroplating.
- Cadmium compounds create brilliant yellow, orange, and red pigments used in paints and plastics.
- The element acts as a stabilizer in some plastic formulations.
Cadmium is a highly toxic heavy metal with considerable health risks. Chronic human exposure most often occurs through consuming contaminated food and water, or inhaling tobacco smoke, which contains high levels of the element. Industrial workers in areas like battery manufacturing or welding are also at heightened risk of exposure.
Cadmium is classified as a human carcinogen and has no known beneficial biological function in the human body. Long-term exposure primarily targets the kidneys, leading to significant damage and dysfunction. It also negatively affects the skeletal system, potentially causing bone degradation and conditions like Itai-Itai disease, first observed in Japan due to environmental contamination. Breathing high levels of cadmium fumes can cause severe lung damage.