Revolutionary Science – Lavoisier to Volta Rob Iliffe An Explosion of Gases • Note importance of Industrial Revolution in Britain: • In 1754, the chemist Joseph Black isolated ‘Fixed Air’ (CO2), so named as it could apparently be returned to or ‘fixed’ in the solids in which it was found. • In 1766 Henry Cavendish produced a highly ‘inflammable air’ (hydrogen), produced by bringing certain acids into contact with various metals, and which formed water on combustion. • It was increasingly understood that ordinary air was not homogenous but was composed of a number of different ‘gases’. Joseph Priestley (1733-1804) A Democratic Philosopher • Priestley born into a dissenting family and though largely self-taught, was unable to enter one of the two English universities. • Interested in chemistry and electricity from early 1760s – travelled regularly to London where he met Benjamin Franklin and others. • In late 1760s he worked near a brewery in Leeds, where he had ready access to ‘Fixed Air’ (CO2). • In 1767 he found a way to artificially impregnate water with the gas, producing the first account of soda water in 1772. • Published books aimed at educating a general audience on electricity (1767) and light (1772), which made him famous. The Theory of Phlogiston • A fiery element contained in combustible bodies and which was released by burning (‘dephlogistication’); • loss of weight of burning bodies demonstrated the loss of their phlogiston. • Combustion stopped in closed spaces as air was ‘saturated’ with phlogiston. • Metals contained phlogiston: • when a metal was corroded in air or heated it lost its phlogiston and formed a powdery metal ‘calx’ or metallic ash (oxide), • so metals were composed of phlogiston + calx. • Problem was that the calx weighed more than the original metal so perhaps phlogiston had negative weight?. Dephlogisticated Air • Joseph Priestley isolated Nitrous Oxide (‘laughing gas’, which he called “phlogisticated nitrous air”) in 1772. • In 1774 he focussed sunlight on mercuric oxide, finding that the gas emitted was “eminently respirable”, • “five or six times as good as common air” in terms of its support to breathing, while and allowed a flame to burn incredibly brightly: • He wrote: “Who can tell but that in time, this pure air may become a fashionable article in luxury”. • He called this air “dephlogisticated air” because it could apparently absorb vast amounts of phlogiston given off by burning objects. Priestley’s Later Life • Priestley met Antoine Lavoisier in Paris in 1774 and described his discovery • Lavoisier would come to understand that burning substances took on Oxygen and did not ‘give off’ phlogiston. • Priestley returned to England where he joined other philosophers and entrepreneurs (inc. James Watt and Erasmus Darwin) in Birmingham, at start of Industrial Revolution. • He was a strong supporter of the American and French Revolutions but his radical politics forced him to flee to Pennsylvania in 1794. • Became friends with Jefferson and isolated “heavy inflammable air” (CO) Antoine-Laurent Lavoisier (1743-94) • Lavoisier was trained in different sciences in the 1740s but studied law instead of going to university. • Returned to science, esp. field of geology, and analysed features of various rocks and elements with great precision. • Elected to Academy of Sciences in 1768, at same time buying a share in a private firm that collected taxes for the government (a fateful decision given his ultimate fate). • Married Marie-Anne Paulze in 1771, and she acted as a research assistant and collaborator. Jacques-Louis David, Portrait of Monsieur and Madame Lavoisier (Marie-Anne Pierrette Paulze), 1788 The ‘eminently respirable” part of the air. • Lavoisier was introduced to theory of phlogiston in 1772 but soon realized that the theory had a number of problems; • He performed exceptionally precise measurements in enclosed environments on Priestley’s airs, • and concluded that the masses of the elements were conserved after reaction – so Phlogiston theory (i.e. the idea it had negative weight) was wrong. • By 1777 he had determined that combustion was due to the reaction of a metal or organic substance with the “eminently respirable” part of air. • In 1779 he showed that most acids contained this air, and he called it ‘Oxygen’ (‘Acid generator’). Phlogiston was a fiction. Quantitative Chemistry • Lavoisier was the supreme quantitative chemist, proving his claims through meticulous measurements based on his commitment to the principle of the conservation of mass • His reform was not just in practice and theory but in nomenclature (calx became oxide, e.g.), which reflected the actual composition of the substance or compound. • New conception transformed chemistry in same year as the French Revolution, and it quickly became the dominant theory in Europe. Table of new substances with former names (where appropriate), but also including ‘calorique’ from Lavoisier, Traité Elémentaire de Chimie (1789), translated in to English as Elements of Chemistry. The End of Natural Philosophy in the Ancien Régime • With few exceptions, French science dominated period 1780-1830, spanning the end of Ancien Régime to the decade after Napoleon. • Towering figures in analytic mechanics and mathematical physics were Joseph-Louis Lagrange (originally from Turin) and Pierre Simon de Laplace. • Many Académiciens, like Condorcet, were fervent supporters of the Revolution, and used its aftermath to promote the metric system. • In the period of the Jacobin Reign of Terror (May 1793-July 1794), the Académie Royale des Sciences was abolished: • major figures were led away to the guillotine (e.g. Lavoisier and the astronomer Charles Bailly), with others (Condorcet) taking their own life. The Reorganization of Science • New institutions, and reorganized versions of older societies, emerged during this period. • Most significant of these were the Muséum d’Histoire Naturelle, the Société Philomatique, the Ecole Polytechnique (founded 1794), • and the successor to the Académie, the Institut de France (1796). • From 1799, the advent of the scientifically-obsessed Napoleon energized French science and a new generation of brilliant thinkers emerged with Laplace as inspirational leader – • Concerned both with ‘pure’ science but also with the application of science to technology and issues of social utility. Luigi Galvani (1737-98) • Born in Bologna, attending medical school where he studied surgery and anatomy (and later took up university positions in both subjects). • Galvani became interested in medical electricity in late 1770s, and made his famous observation of the twitching of a frog’s leg in 1780. • This happened when the crural nerve of a dissected frog was touched with a scalpel, with sparks being produced at the same time by a nearby electric machine. • After further experiments Galvani inferred that muscles were activated by an electric fluid that was secreted by the brain and which entered the muscles via the nerves. Galvanism • Galvani believed that the metals created a circuit that revealed the existence of innate animal electricity. • Galvani realized that the phenomenon required the use of two different metals as electrodes - • The publication of his short Latin text "De Viribus Electricitatis in motu musculari commentarius" in 1791, announcing the discovery of the electrical power in all animate bodies, caused a sensation. • Numerous natural philosophers successfully repeated and extended Galvani’s work by making various circuits in their own bodies. Electrodes (C and Z are two different metals – iron and bronze or silver) link sciatic nerve N to exposed leg of frog, thereby creating a circuit and causing them to twitch upwards. Alessandro Volta (1745-1827) • Performed many experiments on electricity in 1770s and 80s, discovering proportionality between electrical potential (V) and charge (Q), • the unit of electrical potential being named after him. • Became prof. of Experimental Physics at Pavia in 1779 • Astounded by Galvani’s (1791) discovery of “animal electricity”, Volta initially agreed that it was a different kind of electricity (and named the phenomenon ‘Galvanism’) • But soon showed that the frog’s leg could be replaced by an inanimate object (e.g. paper soaked in saltwater or ‘brine’ – the electrolyte) • This produced similar effects, so ‘animal electricity’ was a fiction. The Battery • Volta announced invention of the battery (cell) in 1800, and it was immediately used to effect the electrolysis of water (into O2 and 2H2) • It was recognised as a revolutionary device, serving as a continuous power source, an unparalleled scientific instrument, and a model for understanding natural phenomena. • Volta was praised across Europe, and scientists like Humphry Davy and Johann Wilhelm Ritter took great pride in building bigger and longer-lasting batteries. • Problems with leaking of the electrolyte (due to weight of the metals) led to many different designs for the battery in the next half century. Volta addressing the Institut de France on the battery, in presence of Napoleon Bonaparte, 18 November 1800 Giovanni Aldini (1762-1834) • Nephew of Galvani and professor of Physics at Bologna, • Aldini was concerned for many years with proving the existence of ‘animal electricity’ (against views of Volta). • Used Peace Treaty of Amiens (1802-3) as opportunity to tour Europe with experiments on the phenomenon of ‘galvanism’; • Did experiments with decapitated dogs and bulls, making parts of their bodies move by passing