Lavoisier's Elements of Chemistry from which Humphry taught himself chemistry as a young lad made it quite clear that both potash and soda were compounds and likely to be decomposed into their true constituent elements in the future. It had been suspected for a while that this substance was not elemental, but its exact nature unknown. It was to caustic potash that Humphry focussed his attention. In his notebook in August 1800, Humphry records 'I cannot close this notice without feeling grateful to Volta, Nicholson, and Carlisle, whose experience has placed such a wonderful and important instrument of analysis in my power.' Humphry's younger brother John Davy stated that this experiment 'immediately impressed powerfully the mind of my brother.' Such a voltaic pile had been used in spectacular fashion at the turn of the century by English chemists William Nicholson and Anthony Carlisle to decompose – or electrolyse – water into its constituent elements hydrogen and oxygen. This device consisted of alternating plates of two different metals, such as copper and zinc, sandwiched with cloth soaked in a solution of brine. His fellow countryman, Alessandro Volta, recognised the electrical origin of these observations, and went on to develop the so-called Voltaic pile. After further experiments, he found that combinations of different metals gave even stronger effects. It was from this pure hydroxide that Davy first isolated the metal potassium.To do this he used the relatively new force of electricity.Īlmost twenty years earlier, the Italian physician Luigi Galvani noticed that when he touched the central nerve of a dead frog with a metal knife, the muscles in the frog's leg violently contracted. The potassium carbonate and calcium hydroxide solutions react with a bit of chemical partner-swapping: insoluble calcium carbonate or chalk precipitates out, leaving a solution of potassium hydroxide. The crude potash can be made more caustic or 'pure' by treating a solution of it with lime water, calcium hydroxide. However, it is from the herb kali, that we owe the word that describes both – al-kali or alkali the 'al' prefix simply being Arabic – the definite article 'the'. The salty herbs giving more sodium carbonate: Soda. The wood ash method yielding more potassium carbonate: Potash. His method of production of this 'salt of alkali' is pretty similar to that described by Boerhaave with both processes actually yielding an impure mixture of what we would now call potassium and sodium carbonates. Potash mountains near Soligorsk City, Belarus This, then, is immediately put into large copper pots, and is there boiled for the space of three days, by which means they procure the salt they call potas, (which signifies pot-ashes) on account of its being thus made in pots.'Įven earlier in the 16th Century, Conrad Gesner tells us that 'of the hearbe called kali, doe certayne prepare a salt.' He describes this plant, kali whose Latin name is Salsola kali but is more commonly known as saltwort: 'Kali is of two cubits of height, having no prickles or thorns, and is sometimes very red, salty in taste, with a certain ungratefull smell, found & gathered in salty places, out of which, the salt of Alkali may be purchased.' freed from impurities, 'by standing quiet, it is poured-off clear. These ashes are then dissolved in boiling water, and when the liquor at top, which contains the salt, is depurated,' i.e. It is prepared there from the wood of green fir, pine, oak and the like, of which they make large piles in proper trenches, and burn them till they are reduced to ashes. 'Potas or pot-ashes is brought yearly by the merchant's ships in great abundance from Coerland' now part of Latvia and Lithuania, 'Russia, and Poland.
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