Acid and Alkali
The concept of this basic chemical antithesis emerges clearly in the seventeenth century with the work of van Helmont and Robert Boyle. Early alchemists worked with lists of aquae (waters) (see Aqua) t and a familiar acid was aqua fortis or nitric acid, whose preparation is described in Geber, De inventione veritatis (On the discovery of the truth) (fourteenth century), Hoimyard traces preparation of nitric acid back to the tenth-century Jabirian corpus (see Jabir ibn Hayyan), During the thirteenth century, it was prepared by distilling nitrate with alum and ferrous sulphate. Alum and nitrate were also known to Ko Hung in fourth-century China ( see Chinese Alchemy), but no nitrate reagents were known in the early medieval West. Sulphuric acid from ‘oil of vitriol’ was familiar in the sixteenth century, however, and was popular with the Paracelsian iatrochemists. Hydrochloric add was known from 1640,
Acids were very important for purifying, separating and cleaning metals, and myth portrayed them as devouring metals. Nitric acid was used to separate silver from gold, dissolving the former and not the latter, while sulphuric acid was known from pseudo-Geber, prepared from vitriol, as dissolving all metals except gold.
Precipitation of silver from nitric acid solution baffled and fascinated alchemists, especially van Helmont Newton wrote a tract, Denatura aadorum (On the nature of acids), in which he uses his theory of particles, and experiments with nitric acid deeply impressed him: he dissolved many metals and obtained precipitates from solution. Aqua regia was famous as the only ‘water’ or add which would dissolve gold: this was prepared by adding sal ammoniac to nitric acid. In the mixture of hydrochloric and nitric acid, gold dissolves to a soluble chloride, silver to an insoluble one, thus aqua regia was ideal for separating gold from silver
‘Alkali’ belongs to the class of scientific words derived from Arabic: al-qaliy denotes calcined ashes of the plants ‘salsola’ and ‘salicorna’; qualay — to fry, or to roast. H Alcalay’ was originally a saline substance from calcined ashes of marine plants, soda-ash. Chaucer lists together ‘sal tart re, alcalay, and salt preparat’, Ripley in Compound of Alchemy lists ‘Sal Alkaly, Sal Alembroke, Sal Attinckari, and Ben Jonson gives ‘Alkaly* in company with + sal tartre , arsenic and vitriol as regular alchemical substances. The English Paracelsian surgeon John Woodall explains that Paracelsus ‘termeth every vegetable salt Alkaly*.