Barium

Although dissolved barium is toxic, the medical 'barium meal' taken before a digestive test contains barium sulfate, a practically water and gastric juice insoluble compound. It passes through the stomach and intestines without being absorbed by the body. Because barium is a heavy atom that blocks X-rays, it draws with enormous contrast the relief of the organs in the images.

During drilling of natural gas or crude oil wells at thousands of metres deep, ground barite (with a density of 4.5 g/cm³) is added to the drilling fluid. This dense mixture exerts a colossal hydrostatic pressure at the well bottom that exceeds the geological pressure of underground gas and oil pockets. This fluid weight confines the hydrocarbons in the reservoir, preventing uncontrolled gas eruptions to the surface that would cause explosions.

Barium titanate (BaTiO₃) is a ceramic that exhibits ferroelectricity with an enormously large dielectric constant at room temperature, exceeding by thousands of times that of traditional insulators such as mica or glass. When an electric field is applied, titanium and barium ions move within the crystal cell generating a reversible spontaneous polarisation. This property allows the manufacture of microscopic multilayer ceramic capacitors (MLCCs) capable of storing great electrical charge in smartphones and computers.

In old cathode-ray tubes for televisions and radio valves, it was essential to maintain an almost perfect vacuum for electrons to travel without colliding with gas molecules. At the end of the tube's manufacture, a small barium pellet volatilised by radio frequency induction, depositing a bright metallic mirror on the inner glass. This highly reactive barium film chemically captured any residual oxygen, nitrogen or water molecule for years.

In the early 17th century in Italy, the amateur alchemist Vincenzo Cascariolo collected dense nodules of barite on Mount Paderno and calcined them with coal in his forge. The process reduced the barium sulfate to impure barium sulfide, creating an insoluble material that, after exposure to daylight, shone intensely in the dark for hours. That 'Bologna phosphorescent stone' fascinated European scientists, inaugurating the formal study of inorganic luminescence.

The divalent Ba²⁺ cation has an ionic radius very similar to that of potassium (K⁺). When it enters the bloodstream from ingested soluble salts, it fits perfectly into the selectivity filter of voltage-gated potassium channels in muscle and cardiac cells, lodging there and blocking potassium exit. This inhibition prolongs cell depolarisation, triggering severe hypokalaemia, involuntary tetanic muscle contractions, flaccid respiratory paralysis and fatal cardiac arrests.

The brilliant green colour of pyrotechnics is due to compounds such as barium nitrate or barium chloride. When the gunpowder detonates and heats the mixture to over a thousand degrees, barium electrons are excited and, when returning to their original state, release excess energy by emitting light at a very pure emerald green wavelength highly visible in the night sky.