Barium

Category: alkaline earth metal Atomic number: 56 Colour: silvery gold Melting point: 729°C (1,344°F) Boiling point: 1,845°C (3,353°F) First identified: 1808

If you’ve ever been unlucky enough to have a barium meal or enema, you probably won’t have very happy memories of it. As a heavy element, it shows up clearly on X-rays, so it is often used to diagnose diseases that affect the intestine or the oesophagus. A suspension of barium sulphate (barite) in fluid is administered, with flavouring such as strawberry or peppermint added in a vain attempt to make it palatable. The advantage of barium sulphide is that it is insoluble in water, so it will completely leave the digestive system afterwards. Soluble barium salts are quite poisonous, so this is crucial. Barium carbonate has been used as rat poison, while barium acetate, stolen from a chemistry classroom, was employed as a murder weapon by Texas teenager, Marie Robards, who used it in 1993 to kill her father.

Barium sulphate is naturally found as a white, slightly transparent ore, an unusually heavy rock. In the seventeenth century, a shoemaker from Bologna called Vincenzo Casciarolo discovered a rock that would glow in the dark if it were heated sufficiently during the day. He was excited by the idea that this stone (called lapis solaris or Bologna Stone) might somehow be a way to manufacture gold, but it turned out merely to be barite.

Barium is only found in compounds, as it is highly reactive in air – it can, for instance, be found in the ore, witherite (barium carbonate). Attempts to extract the element from these ores by smelting it with carbon failed, but Humphry Davy succeeded in isolating the soft, greyish metal in 1808 by electrolysing barium hydroxide. It is named after the Greek barys, meaning ‘heavy’. Also known as ‘heavy spar’, barite is used in the petroleum industry as a weighting agent in the drilling mud used in creating oil wells.

It has a few other uses, such as in making paint and in glassmaking, and barium nitrate is used for the green colour in fireworks. The fascinating compound YBCO (yttrium barium copper oxide; see here), which can be used as a superconductor at relatively high temperatures, is attracting a lot of scientific interest. And barite has an interesting role for scientists studying the ocean: because it is insoluble and remains stable for millions of years, the accumulation of this ore in ocean sediments can give us crucial information about how productive marine phytoplankton were in particular periods of the planet’s past.