Humphry Davy and the Elements He Pulled From Ancient Compounds, 1807 to 1810

Potassium is where it begins. In October 1807 Davy passed a current through molten potash and obtained the metal, the first element ever isolated by electrolysis. Potash, leached from wood ash, had served soap and glass makers for centuries, and it gives the element its English name.

Sodium followed within months. Davy electrolysed molten caustic soda in 1807, a method the page says soon gave him more metals. Its compounds were ancient, common salt and the natron of Egyptian mummification among them, but the metal itself had never been seen before him.

In 1808 the same approach reached calcium. Burning limestone to quicklime is one of the oldest chemical processes known, and lime mortar built the Roman world, yet nobody had suspected a metal inside lime until Davy isolated it that year.

Strontium was named for Strontian, a Highland village where its mineral turned up in lead workings. Adair Crawford recognised the new earth in 1790, and Davy isolated the metal in 1808. Its salts give the deep red of fireworks and warning flares.

Magnesium shows how long an earth could be known before its metal was. Joseph Black distinguished magnesia from lime in 1755, and Davy isolated the metal in 1808. The element sits at the centre of the chlorophyll molecule, so every green plant depends on it.

Barium takes its name from the Greek for heavy, after the dense mineral barite. Carl Wilhelm Scheele identified the earth in 1774 and Davy isolated the metal in 1808. The page also records the Bologna Stone, a barium sulfide that glowed after sunlight and puzzled natural philosophers for decades.

Boron is the stop where Davy was not alone. Gay-Lussac and Thenard in France and Davy in England all obtained impure boron in 1808. Its salt borax had been traded from Tibetan lake beds along the Silk Road and used as a soldering flux long before anyone knew the element.

Chlorine closes the path with a different kind of discovery. Scheele prepared the gas in 1774, but it was long thought to be a compound of oxygen until Davy showed in 1810 that it was an element and named it for its colour, from the Greek chloros.