Who discovered potassium and sodium?

	Vocabulary
	alkali metal electrolysis hydroxide reduction

Alkali metals are so reactive that they never occur in uncombined form in nature. Many metals can be isolated from their minerals by reduction with carbon or hydrogen, but alkali metal ions are extremely difficult to reduce. A more powerful technology for metal reduction was needed before alkali metals could be isolated in pure elemental form.

Sir Humphry Davy believed that chemical union was electrical in nature- and so, a strong electric current might be able to overcome the forces binding compounds together, and lead to the isolation of new elements. In 1807 he tested this hypothesis on caustic potash (potassium hydroxide, KOH) and caustic soda (sodium hydroxide, NaOH), which had previously been suspected to be oxides of unknown metals.

Davy fired a small piece of KOH in a furnace and placed it on a platinum plate. He connected the plate to the negative terminal of an enormous battery made of 250 stacked cells made of 6" x 4" copper and zinc plates. The positive terminal was connected to a platinum wire and touched to the top of the KOH. The results were spectacular. Davy wrote:

"The potash began to fuse at both its points of electrization. There was a violent effervescence at the upper surface; at the lower, or negative surface, there was no liberation of elastic fluid (gas), but small globules having a high metallic lustre, and being precisely similar in visible characters to quicksilver, appeared, some of which burnt with explosion and bright flame, as soon as they were formed, and others remained, and were merely tarnished, and finally covered with a white film which formed at their surfaces."

According to Davy's brother, when Davy saw the globules of potassium metal break through the potash and burst into flame, "he could not contain his joy- he actually bounded about the room in ecstatic delight". A few days later, the experiment was repeated with sodium hydroxide, and sodium metal was discovered.

References and Web Links

A Short History of Chemistry, J. R. Partington, Macmillan, London (1937).

Author: Fred Senese senese@antoine.frostburg.edu

General Chemistry Online! Who discovered potassium and sodium?

Who discovered potassium and sodium?

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References and Web Links