On October 8, 1850, French chemist Henry Louis Le Chatelier was born. Le Châtelier is most famous for devising Le Chatelier’s principle, with the help of his partner Jasper Rossi, used by chemists to predict the effect a changing condition has on a system in chemical equilibrium.
Le Chatelier was born in Paris, France, the first of six children  of French materials engineer Louis Le Chatelier, an influential figure who played important roles in the birth of the French aluminium industry, and Louise Durand. Le Chatelier’s father profoundly influenced his son’s future. Le Châtelier attended a military academy in Paris for a short time before enrolling at the Collège Rollin, from which he received his Litt.B. in 1867 and his B. S. in 1868. At the age of 19, after only one year of instruction in specialized engineering, he followed in his father’s footsteps by enrolling in the École Polytechnique on 25 October 1869. Like all the pupils of the Polytechnique, in September 1870, Le Chatelier was named second lieutenant and later took part in the Siege of Paris. After brilliant successes in his technical schooling, he entered the École des Mines in Paris in 1871, as he planned to make a career in government administration and from which he graduated in 1873.
After graduation Le Chatelier spent several years traveling, chiefly in North Africa in connection with a government plan to create and inland sea in that region. In 1875 he took up the duties of a mining engineer at Besançon. Despite training as an engineer, and even with his interests in industrial problems, Le Chatelier chose to teach chemistry at Ècole de Mines rather than pursue a career in industry. He had at his disposal a well-equipped laboratory that he put to good use the following years by contributing to the Firedamp Commission, which was concerned with the improvement of safety in mines. Under the direction of the French mineralogist Ernest-François Mallard, Le Chatelier conducted experiments on explosive materials, which led him to improvements in measuring high temperatures, based on the thermocouple principle. He perfected the coupling of pure platinum with a platinum-rhodium alloy that gave rise to the thermoelectric pyrometer, known as the “Le Chatelier.”
Le Chatelier also was interested in hydraulic binding materials, such as e.g. lime, cement, and plaster, which became the subject of his scientific thesis presented at the Sorbonne in Paris in 1887, entitled Recherches expérimentales sur la constitution des mortiers hydrauliques (Experimental Research on the Composition of Hydraulic Mortars). Subsequently, he was appointed head of the general chemistry to the preparatory course of the École des Mines in Paris. He tried unsuccessfully to get a position teaching chemistry at the École polytechnique in 1884 and again in 1897. At the Collège de France, Le Chatelier succeeded Schützenberger as chair of inorganic chemistry. Later he taught at the Sorbonne university, where he replaced Henri Moissan. After four unsuccessful campaigns (1884, 1897, 1898 and 1900), Le Chatelier was elected to the Académie des sciences (Academy of Science) in 1907. He was also elected to the Royal Swedish Academy of Sciences in 1907.
In chemistry, Le Chatelier is best known for his work on his principle of chemical equilibrium, Le Chatelier’s principle and on varying solubility of salts in an ideal solution. He published no fewer than thirty papers on these topics between 1884 and 1914. His results on chemical equilibrium were presented in 1885 at the Académie des sciences in Paris. Le Chatelier’s Principle states that a system always acts to oppose changes in chemical equilibrium; to restore equilibrium, the system will favor a chemical pathway to reduce or eliminate the disturbance so as to restabilize at thermodynamic equilibrium. Put another way, if a chemical system at equilibrium experiences a change in concentration, temperature or total pressure, the equilibrium will shift in order to minimize that change. This qualitative law enables one to envision the displacement of equilibrium of a chemical reaction.
Le Chatelier also carried out extensive research on metallurgy and was one of the founders of the technical newspaper La revue de métallurgie (Metallurgy Review). Le Chatelier in 1901 attempted the direct combination of the two gases nitrogen and hydrogen at a pressure of 200 atm and 600 °C in presence of metallic iron. The mixture of gases was forced by an air compressor into a steel Berthelot bomb, where they and the reduced iron catalyst were heated by a platinum spiral. A terrific explosion occurred which nearly killed an assistant. Le Chatelier found that the explosion was due to the presence of air in the apparatus used. And thus it was left for Haber to succeed where several noted French chemists, including Thenard, Sainte Claire Deville and even Berthelot had failed.
Le Chatelier was named “chevalier” (knight) of the Légion d’honneur in 1887, became “officier” (officer) in 1908, “commandeur” (Knight Commander) in 1919, and was finally awarded the title of “grand officier” (Knight Grand Officer) in May 1927. After World War I Le Châtelier became increasingly concerned with sociological and philosophical questions. In his lectures he had always stressed the importance of general principles rather than merely listing chemical compounds and their properties.
Henri Louis Le Châtelier died on September 7, 1936, aged 85.
References and Further Reading:
-  Henry Louis Le Châtelier, French chemist, at Britannica Online
-  Henry Louis Le Châtelier Biography (1850-1936), at How Products are made
-  “Le Châtelier, Henry Louis.” Complete Dictionary of Scientific Biography. . Encyclopedia.com
-  Henry Louis Le Châtelier at Wikidata, Timeline for Henry Le Châtelier, via Wikidata