Humphry Davy

Sir Humphry Davy, (17 December 1778 – 29 May 1829) was a Cornish chemist and inventor, who is best remembered today for isolating, using electricity, a series of elements for the first time: potassium and sodium in 1807 and calcium, strontium, barium, magnesium and boron the following year, as well as discovering the elemental nature of chlorine and iodine. Davy also studied the forces involved in these separations, inventing the new field of electrochemistry.

In 1799, he experimented with nitrous oxide and was astonished at how it made him laugh, so he nicknamed it "laughing gas" and wrote about its potential anaesthetic properties in relieving pain during surgery. He also invented the Davy lamp and a very early form of arc lamp. He joked that his assistant Michael Faraday was his greatest discovery.

Discovery of new elements

Davy was a pioneer in the field of electrolysis using the voltaic pile to split common compounds and thus prepare many new elements. He went on to electrolyse molten salts and discovered several new metals, including sodium and potassium, highly reactive elements known as the alkali metals. Davy discovered potassium in 1807, deriving it from caustic potash (KOH). Before the 19th century, no distinction had been made between potassium and sodium. Potassium was the first metal that was isolated by electrolysis. Davy isolated sodium in the same year by passing an electric current through molten sodium hydroxide.

Discovery of calcium, magnesium, strontium and barium

During the first half of 1808, Davy conducted a series of further electrolysis experiments on alkaline earths including lime, magnesia, strontites and barytes. At the beginning of June, Davy received a letter from the Swedish chemist Berzelius claiming that he, in conjunction with Dr. Pontin, had successfully obtained amalgams of calcium and barium by electrolysing lime and barytes using a mercury cathode. Davy managed to successfully repeat these experiments almost immediately and expanded Berzelius' method to strontites and magnesia. He noted that while these amalgams oxidized in only a few minutes when exposed to air they could be preserved for lengthy periods of time when submerged in naphtha before becoming covered with a white crust. On 30 June 1808 Davy reported to the Royal Society that he had successfully isolated four new metals which he named barium, calcium, strontium and magnesium which were subsequently published in the Philosophical Transactions. The observations gathered from these experiments also led to Davy isolating boron in 1809.

Discovery of chlorine

Chlorine was discovered in 1774 by Swedish chemist Carl Wilhelm Scheele, who called it "dephlogisticated marine acid" and mistakenly thought it contained oxygen. Davy showed that the acid of Scheele's substance, called at the time oxymuriatic acid, contained no oxygen. This discovery overturned Lavoisier's definition of acids as compounds of oxygen. In 1810, chlorine was given its current name by Humphry Davy, who insisted that chlorine was in fact an element.The name chlorine, chosen by Davy for "one of obvious and characteristic properties - its colour", comes from the Greek χλωρος (chlōros), meaning green-yellow.

Laboratory accident

Davy seriously injured himself in a laboratory accident with nitrogen trichloride. French chemist Pierre Louis Dulong had first prepared this compound in 1811, and had lost two fingers and an eye in two separate explosions with it. In a letter to John Children, on 16 November 1812, Davy wrote: "It must be used with great caution. It is not safe to experiment upon a globule larger than a pin's head. I have been severely wounded by a piece scarcely bigger. My sight, however, I am informed, will not be injured". Davy's accident induced him to hire Michael Faraday as a co-worker, particularly for assistance with handwriting and record keeping. He had recovered from his injuries by April 1813.

Acid-base studies

In 1815 Davy suggested that acids were substances that contained replaceable hydrogen ions;– hydrogen that could be partly or totally replaced by reactive metals which are placed above hydrogen in the reactivity series. When acids reacted with metals they formed salts and hydrogen gas. Bases were substances that reacted with acids to form salts and water. These definitions worked well for most of the nineteenth century.