Gay Lussac

Gay-Lussac

Joseph Louis Gay-Lussac (1778–1850) grew up during both the French and Chemical Revolutions. His comfortable existence as the privately tutored son of a well-to-do lawyer was disrupted by political and social upheavals: his tutor fled, and his father was imprisoned. Joseph, however, benefited from the new order when he was selected to attend the École Polytechnique, an institution of the French Revolution designed to create scientific and technical leadership, especially for the military. There his mentors included Pierre Simon de Laplace and Claude Louis Berthollet, among other scientists converted by Antoine-Laurent Lavoisier to oxygen chemistry. Gay-Lussac’s own career as a professor of physics and chemistry began at the École Polytechnique

Law of Combining Volumes of Gases

In 1808 Gay-Lussac announced what was probably his single greatest achievement: from his own and others' experiments he deduced that gases at constant temperature and pressure combine in simple numerical proportions by volume, and the resulting product or products—if gases—also bear a simple proportion by volume to the volumes of the reactants. This conclusion subsequently became known as Gay-Lussac’s law.

Other Achievements

With his fellow professor at the École Polytechnique, Louis Jacques Thénard, Gay-Lussac also participated in early electrochemical research, investigating the elements discovered by its means. Among other achievements, they decomposed boric acid by using fused potassium, thus discovering the element boron.

When they heard of the English chemist Humphry Davy’s isolation of the newly discovered reactive metals sodium and potassium by electrolysis in 1807, they worked to produce even larger quantities of the metals by chemical means and tested their reactivity in various experiments. Notably they isolated the new element boron. They also studied the effect of light on reactions between hydrogen and chlorine, though it was Davy who demonstrated that the latter gas was an element. Rivalry between Gay-Lussac and Davy reached a climax over the iodine experiments Davy carried out during an extraordinary visit to Paris in November 1813, at a time when France was at war with Britain. Both chemists claimed priority over discovering iodine’s elemental nature. Although Davy is typically given credit for this discovery, most of his work was hurried and incomplete. Gay-Lussac presented a much more complete study of iodine in a long memoir presented to the National Institute on August 1, 1814, and subsequently published in the Annales de chimie. In 1815 Gay-Lussac experimentally demonstrated that prussic acid was simply hydrocyanic acid, a compound of carbon, hydrogen, and nitrogen, and he also isolated the compound cyanogen [(CN)2 or C2N2]. His analyses of prussic acid and hydriodic acid (HI) necessitated a modification of Antoine Lavoisier’s theory that oxygen was present in all acids.

The two also took part in contemporary debates that modified Lavoisier's definition of acids and furthered his program of analyzing organic compounds for their oxygen and hydrogen content.