Of Ashes and Alkalis

The name azote, proposed by Lavoisier and his colleagues, did not gain wide acceptance; nitrogen, meaning ‘nitre-former’, is the name now familiar to us. Modern chemists understand ‘nitre’ to mean ‘potassium nitrate’, one of the key ingredients of gunpowder, containing the elements potassium, oxygen, and nitrogen. However, although it dates back to antiquity, the name nitre initially referred to a completely different compound containing no nitrogen at all. It is the Latinized name, natrium, derived from this original use, that gives us the modern chemical symbol Na, for the element Humphry Davy named sodium. Travellers to modern-day northern Egypt may find themselves in a region known as the Nitrian Desert, or the Natron Valley—Wadi El Natrun. Here, ancient Egyptians would collect crude salt mixtures from certain lakes and use them for a variety of purposes, such as cleaning, making glass, embalming, and the preparation of medicines. The Egyptian word for the salt may be written ‘nṭry’ or ‘ntr’ (‘neter’), and it has survived for over three thousand years through variations including ‘neter’ (Hebrew), ‘nitron’ (Greek), ‘nitrum’(Latin), and more modern modifications ‘nether’, ‘niter’, ‘nitre’, ‘natrun’, and ‘natron’. Bartholomeus Anglicus, the thirteenth-century monk and author of De proprietatibus rerum (‘On the Properties of Things’), quotes Isidore of Seville from five hundred years earlier saying: ‘Nitrum hath ye name of the countrey of Nitria that is in Aegypt. Thereof is medicine made, & there with bodies and clothes be cleansed and washed.’ Whether the salt was actually named after the region or vice versa is not clear. Although its composition varied enormously, what distinguished nitre from common salt was the presence of significant proportions of sodium carbonate and sodium bicarbonate (sodium hydrogen carbonate). In addition to these carbonates, analyses of ancient samples, including that used in the embalming of the pharaoh Tutankhamun, who died in 1352 BC, also reveal large proportions of common salt (sodium chloride), sodium sulfate, and silica (silicon dioxide), with smaller proportions of calcium and magnesium carbonates and other minor impurities.