and of the temperature T at which the gaseous pressure is equal one atmosphere is Q/T = 32. This law can be applied to such cases as sublimation and dissociation of calcium carbonate and can predict whether a chemical reaction will proceed and whether it will be reversible. At the Sorbonne, Matignon mostly worked on rare-earth elements. He was heating the metal oxide with magnesium to produce the pure metal in an atmosphere of a certain gas, and demonstrated that most rare earths easily react with nitrogen and absorb hydrogen. He also studied the chemistry of numerous rare-earth salts and revealed that samarium can have the valence of two in addition to the common 3+ state. For other metals, Matignon showed that technical-grade zinc, aluminium and ferromanganese powders always contain some nitrogen (e.g. 0.2–0.4% for zinc). World War I urged most chemists to work on urgent technological problems, and Matignon had studied the water-sodium sulfate-ammonium system aiming for the production of sulfuric acid. He also worked on the stability of the ammonium carbonate-urea system, which was important for fertilizers, and discovered an iron-alumina catalyst for the synthesis of ammonia. By applying an oxidation reaction to a cargo of sugar spoiled by seawater he managed to convert it into oxalic acid. Matignon also tried to design recycling procedures for waste products of grape processing and brandy distillation. Major publications (with multiple re-editions) References 1867 births 1934 deaths 20th-century French chemists Lycée Condorcet alumni Members of the French Academy of Sciences Rare earth scientists People from Yonne 19th-century French chemists