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Joseph Louis Gay-Lussac.

Gay-Lussac and Biot ascend in a hot air balloon, 1804. Illustration from the late 19th Century.

Joseph Louis Gay-Lussac (December 6, 1778 – May 9, 1850) was a French chemist and physicist. He is known mostly for two laws related to gases, and for his work on alcohol-water mixtures, which led to the degrees Gay-Lussac used to measure alcoholic beverages in many countries.

Gay-Lussac was born at Saint-Léonard-de-Noblat, in the department of Haute-Vienne. He received his early education at home and in 1794 was sent to Paris to prepare for the École Polytechnique after his father was arrested, into which he was admitted at the end of 1797. Three years later he transferred to the École des Ponts et Chaussées, and shortly afterwards was assigned to C. L. Berthollet as his assistant. In 1802 he was appointed demonstrator to A. F. Fourcroy at the École Polytechnique, where subsequently (1809) he became professor of chemistry. From 1808 to 1832 he was professor of physics at the Sorbonne, a post which he only resigned for the chair of chemistry at the Jardin des Plantes. In 1831 he was elected to represent Haute-Vienne in the chamber of deputies, and in 1839 he entered the chamber of peers.

In 1809 Gay-Lussac married Geneviève-Marie-Joseph Rojot. He had first met her when she worked as a linen draper's shop assistant and was studying a chemistry textbook under the counter. He was father of five children, of whom the eldest (Jules) became assistant to Justus Liebig in Giessen. Some publications by Jules are mistaken as his father's today since they share the same first initial (J. Gay-Lussac). Some of his descendants live in Brazil, South America (de Salusse Lussac/Lussac Do Coutto/Do Coutto Monni) and in Ontario, Canada.

In 1802, Gay-Lussac first formulated the law that a gas expands linearly with a fixed pressure and rising temperature.

In 1804 he made a hot-air balloon ascent with Jean-Baptiste Biot to a height of 6.4 kilometres in an early investigation of the Earth's atmosphere. He wanted to collect samples of the air at different heights to record differences in temperature and moisture.

In 1805, together with his friend and scientific collaborator Alexander von Humboldt, he discovered that the basic composition of the atmosphere does not change with decreasing pressure (increasing altitude). They also discovered that water is formed by two parts of hydrogen and one part of oxygen (by volume).

In 1808, he was the co-discoverer of boron.

In 1810, in collaboration with Louis Thenard, he developed a method for quantitative elemental analysis by measuring the carbonic acid and oxygen evolved by reaction with potassium chlorate.

in 1811, Gay-Lussac recognized iodine as a new element, described its properties, and suggested the name iode.^[1]

In 1824 he developed an improved version of the burette that included a side arm, and coined the terms "pipette" and "burette" in an 1824 paper about the standardization of indigo solutions.^[2]

In Paris, a street and a hotel near the Sorbonne are named after him as are a square and a street in his birthplace, St Leonard de Noblat. His grave is at the Père Lachaise cemetery in Paris.

1. ^ See p. 133 (Appendix 2) of The Chemical Elements: A Historical Perspective by Andrew Ede, Greenwood Press, 2006.
2. ^ Louis Rosenfeld. Four Centuries of Clinical Chemistry. CRC Press, 1999, p. 72-75.

• Gay-Lussac, L. J. and A. von Humboldt (1805) Expérience sur les moyens oediométriques et sur la proportion des principes constituents de l'atmosphère. J. Phys.-Paris LX.
• Maurice Crosland. Gay-Lussac, Scientist and Burgeois, Cambridge University Press, Cambridge, 1978, 333p., ISBN 0521219795