Justus von Liebig did not make his reputation with a single discovery or innovation, but rather with his tremendous versatility. He conducted research inorganic and inorganic chemistry, agricultural chemistry, physiology, and biochemistry and made significant contributions to the study of acids and bases,the chemistry of ether, the systematization of organic chemistry, and the production of industrial dyes as well as synthetic fertilizers. Liebig is considered to be one of the most important chemists of the nineteenth century.
Born in Darmstadt, Germany, on May 12, 1803, Liebig was the son of a merchantwho sold pharmaceuticals, dyes, and salts, so he developed a keen interest in chemistry early in his youth. By the time he was nineteen, he had earned his Ph.D. at Erlangen, and at the recommendation of Alexander von Humboldt (1769-1859) was hired to work in the laboratory of Joseph Gay-Lussac (1778-1850),where he remained for two years.
In 1825, he was appointed chairman of chemistry at the obscure University ofGiessen, where he proceeded to build an excellent chemistry program. He was among the first to focus on laboratory instruction as a means of educating chemists. He remained at Giessen for 27 years before he moved to the Universityof Munich, staying there until his death on April 18, 1873.
Liebig is probably best known to chemistry students as the inventor of the Liebig condenser, a distillation apparatus found in almost every chemical laboratory. It consists of a glass tube surrounded by a glass "jacket" through which cold water can be circulated. As a substance is boiled in a flask, vapor is directed from the mouth of the flask into the tube, and it is cooled and condensed by the water flow. The condensed vapor is free of any dissolved chemicals.
He played a part in numerous key discoveries as well. For example, in the early 1820s Liebig and Friedrich Wöhler had been conducting individual research on inorganic chemicals, and Gay-Lussac noticed that a compound Liebig called silver fulminate had the same chemical formula as a compound Wöhlercalled silver cyanate, though the compounds were different chemically. Informed of this peculiarity by Gay-Lussac, Jöns Berzelius was inspired to derive the theory of isomers. Liebig and Wöhler began working together inorganic chemistry, a field that lacked systematic theory at the time, and introduced a degree of methodical analysis to the field, including techniques todetermine the content of various elements such as carbon, hydrogen, and halogens in organic chemicals. Upon discovering the benzoyl radical (C6 H5 CO-), they also attempted to find a way to define allorganic chemicals as combinations of radicals (groups of molecules that tendto act as a unit). Though they failed, their efforts to present organizing principles in organic chemistry stimulated more successful attempts later.
Beginning in the late 1830s, Liebig pioneered the production and use of artificial fertilizers. At the time, it was believed that plants obtained carbon from organic chemicals in the soil and that they took in other essential nutrients in the form of organic compounds. Liebig showed that, in fact, plants receive all of their carbon in the form of carbon dioxide from the atmosphere.Furthermore, he found that in order to survive, plants required only water and minerals (such as calcium, phosphorus, and potassium) in the form of simplecompounds from the soil. This meant that inorganic compounds containing minerals alone could be used to fertilize fields; organic mulch or manure was unnecessary. Following Liebig's instructions, Muspratt and Co. of Liverpool, England manufactured an experimental batch of synthetic fertilizer in 1845.
The fertilizer was not effective for two reasons. First, fearing that the mineral content of a synthetic fertilizer would be rapidly leached out of the soil by rain, Liebig locked the minerals into molecules that would not readilydissolve in water. But this same insolubility prevented the roots of the plants from absorbing the minerals. Second, he held to a false belief that all plants obtained their nitrogen directly from the atmosphere, so he did not include nitrogen in his formula. Once Liebig corrected these errors, his experiments attained their promised result of improved plant growth.
Liebig wisely argued against fertilizing with only nitrogen, as this would ultimately result in depletion of other minerals from the soil, and correctly theorized that the least abundant mineral in a given expanse of soil will limit plant growth no matter how plentiful other minerals were. This hypothesis came to be called the law of the minimum.
The insights of Liebig helped to modernize the science of plant biochemistry,and served as a catalyst in the development of the modern agricultural industry. He made noteworthy contributions for studies on fermentation and the calorific content of food.