Liebig, Justus, Baron von (1803-1873)

German chemist, a major contributor to agricultural chemistry. He introduced the theory of compound radicals and discovered chloroform and chloral. Many new methods of organic analysis were introduced by Liebig, and he devised ways of determining hydrogen, carbon, and halogens in organic compounds. He demonstrated that plants absorb minerals (and water) from the soil and postulated that the carbon used by plants comes from carbon dioxide in the air rather than from the soil. Liebig was born in Darmstadt, Hesse, and studied at Bonn (where he was arrested for his liberalist political activity), Erlangen, and Paris. At the age of 21 he became professor at Giessen, moving to Munich 1852. In the 1820s Liebig began a long collaboration with Friedrich Wöhler. In 1832, from a study of oil of bitter almonds (benzaldehyde; phenylmethanal), they discovered the benzoyl radical (C6H5CO-). Based on study of related compounds, they introduced the idea of compound radicals in organic chemistry. Liebig studied fermentation (but would not acknowledge that yeast is a living substance), and analysed various body fluids and urine. He calculated the calorific values of foods, emphasizing the role of fats as a source of dietary energy, and even developed a beef extract - long marketed as Liebig extract.