or ‘battery’ of alternating zinc and silver discs gave chemists a powerful new analytical tool. As Davy said later, its use caused great excitement and it acted as ‘an alarm-bell to experimenters in every part of Europe’. Almost immediately it was found that the battery would decompose water into its elements. While there was nothing extraordinary about this further confirmation of Lavoisier’s chemistry, the puzzling fact was that hydrogen and oxygen were ejected from the water at different poles – the hydrogen at what Volta designated as the negative pole, and the oxygen at the positive pole. Two chemists who particularly concerned themselves with this galvanic phenomenon (the term ‘electrolysis’ was not coined by Faraday until 1832) were Davy and Berzelius.
Humphry Davy (1778–1829) was born at Penzance in Cornwall and educated locally. Intending to qualify as a doctor, he was apprenticed to a surgeon in 1795 and began to read Lavoisier’s Elements of Chemistry in French in his spare time. Though ignorant and completely self-taught, like Priestley before him, Davy began to repeat, correct and devise new experiments. Apart from this growing interest in chemistry, he wrote poetry (for this was the era of Romanticism when young men poured forth their individual feelings in verse), he admired the rich Cornish scenery and he fished. Through a friendship with Gregory Watt, the tubercular son of James Watt, Davy came to the attention of Thomas Beddoes, a pupil of Joseph Black and a former lecturer in chemistry at the University of Oxford, who had resigned from ‘that place’ because of his support for the French Revolution and his suspiciously radical politics. In 1798 Beddoes, convinced that the many gases that Priestley had discovered might prove beneficial in the treatment of tuberculosis (TB) and other urban diseases, founded a subscription-based Pneumatic Institute in Bristol. He persuaded Davy, whom he recognized as a man of talent, to join him as a research assistant. Davy probably still expected to qualify as a doctor, perhaps by saving sufficient money to enter Edinburgh University as a result of this experience. In the event, he became a chemist.
Davy’s risky and foolhardy experiments at Bristol, in which he narrowly escaped suffocation on several occasions, brought him fame and notoriety in 1800 when he published his results in Researches, Chemical and Philosophical; Chiefly Concerning Nitrous Oxide … and its Respiration. None of his inhalations demonstrated chemotherapeutic benefits – though his results with nitrous oxide (laughing gas) were to be the cause of regular student ‘saturnalia’ in chemical laboratories throughout the nineteenth century. Not until 1846 was the gas used as an anaesthetic. This inhalation research, and some further essays published in 1799, which included an attack on Lavoisier’s notion of caloric and the substitution of light for caloric in gaseous oxygen (phosoxygen), brought Davy’s name to the attention of another patron, Benjamin Thompson, who had also denied that heat was an imponderable fluid.
Count Rumford, as he is better known, had founded the Royal Institution in London in 1799 as a venue for publicizing ways in which science could help to improve the quality of life of the deserving poor and for the rising middle classes. By 1801 Rumford needed a new Professor of Chemistry. Davy’s appointment coincided with the wave of contemporary interest in electrolytic phenomena and, although he lectured, dazzlingly, on many other subjects at the Royal Institution, it was his research on electrochemistry that captured the public’s imagination and ensured the middle-class success of the Institution.
By building bigger and more powerful batteries, and by using fused electrolytes rather than electrolytes in solution, Davy confirmed Lavoisier’s hunch that soda and potash were not elementary by isolating sodium and potassium in 1807. In the next few years he demonstrated that Lavoisier’s alkaline earths were also compounds and prepared calcium, strontium and barium electrolytically. Later still, Davy argued convincingly against the view that muriatic acid contained oxygen, and for the opinion that oxymuriatic acid, which he renamed chlorine, was an undecompounded elementary body – a point supported by his isolation of its conjoiner, iodine, in 1813.
This succession of corrections to Lavoisier’s chemistry has led some historians to feel that Davy set out systematically to destroy French chemistry. Indeed, by 1815 he had critically and effectively questioned most of the assumptions of the antiphlogistic chemistry – that acidity was due to oxygen, that properties were due to ‘principles’ rather than arrangement, that heat was an imponderable fluid rather than a motion of particles, and that Lavoisier’s elements were truly elementary. Although Davy was often bold in his speculations and use of analogical reasoning, in stripping Lavoisier’s system to its empirical essentials he did not replace it with any grand system of his own, except to suggest that chemical affinity was, in the final analysis, an electrical phenomenon.
In the early 1800s there were two different opinions on the cause of electrolysis. According to the ‘contact theory’ advocated by Volta, electricity arose from the mere contact of different metals; an imposed liquid merely acted as a conductor. Since this theory did not easily account for the fact that the conducting liquid was always decomposed, the alternative ‘chemical theory’ argued that it was the chemical decomposition that produced the electric current. Davy found fault with both theories and as so often in the history of science, he drew a compromise: the contact theory explained the ‘power of action’ of, say, zinc becoming positively charged when placed in contact with copper; this power then disturbed the chemical equilibrium of substances dissolved in water, leading to a ‘permanent action’ of the voltaic pile. As to the cause of the initial ‘power of action’, Davy was in no doubt that it was chemical affinity5:
Is not what has been called chemical affinity merely the union or coalescence of particles in naturally opposite states. And are not chemical attractions of particles and electrical attractions of masses owing to one property and governed by one simple law?
If Davy was the first chemist to link chemical reactivity with electrolytic phenomena, it was the Swede, Berzelius, who created an electrical theory of chemistry. Davy had concluded from his long and accurate work on electrolysis that, in general, combustible bodies and bases tended to be released at the negative pole, while oxygen and oxidized bodies were evolved at the positive pole6:
It will be a general expression of the facts in common philosophical language, to say, that hydrogen, the alkaline substances, the metals, and certain metallic oxides, are attracted by negatively metallic surfaces [i.e. electrodes]; and repelled by positively electrified metallic surfaces; and contrariwise, that oxygen and acid substances are attracted by positively electrified metallic surfaces, and repelled by negatively electrified metallic surfaces; and these attractive and repulsive forces are sufficiently energetic to destroy or suspend the usual operation of elective affinity.
Berzelius, with his patron-collaborator, William Hisinger, had reached the same conclusion independently in 1804, but only developed the important and influential electrochemical theory, which was to leave a permanent mark on chemistry, in 1810 after he had learned of Dalton’s atomic theory. Jöns Jacob Berzelius (1779–1848), after being brought up by his stepfather, studied medicine at the University of Uppsala. Here he read Fourcroy’s Philosophie chimique (1792) and became convinced of Lavoisier’s new system. A competent reader and writer of English, French and German, and alert to the latest developments outside Sweden, his graduation thesis in 1802 was on the medical applications of galvanism. This brought him to the attention of Hisinger, a wealthy mine owner, who invited Berzelius to use the facilities of his home laboratory in Stockholm. Together they not only drew important conclusions about electrolysis, but discovered a new element, ‘ceria’, in 1803, which later turned out to be the parent of several ‘rare-earth’ elements (see chapter 9).
By 1807 Berzelius had become independent of Hisinger’s patronage when he was elected to a Chair of Chemistry and Pharmacy at the Carolian Medico-Chirurgical Institute in Stockholm. His light lecturing duties allowed him plenty of time to research in the Institute’s modest laboratory. Elected a member of the Swedish Academy of Sciences in 1808, in 1818 he became one of its joint secretaries. The appointment included a grace-and-favour
