The German chemist Baron Justus von Liebig (1803-1873) was one of the pioneers in the field of organic chemistry and introduced the science of agricultural chemistry.

Justus Liebig was born in Darmstadt on May 12, 1803, the son of a druggist and dealer in chemicals. His early interest in chemistry may possibly be attributed to the fact that as a boy he was permitted to play with the chemicals in his father's laboratory. He was at first apprenticed to an apothecary, but after his experiments had blown out all the windows in the attic of the shop, this career came to a sudden end. He was then 15 and determined to study chemistry and devote his life to it.

Liebig was a student in chemistry at both Bonn and Erlangen and received his doctoral degree from the latter university in 1822. However, he was not satisfied with his knowledge and training and went to Paris, which was then an important center for chemical research. He worked first in the private laboratory of a chemist, and from there he was taken into the laboratory of the discoverer of gas laws, Joseph Gay-Lussac. Liebig worked there from the summer of 1823 until the spring of 1824.

When he returned to Darmstadt carrying impressive letters of recommendation from Gay-Lussac and Alexander von Humboldt, the Hessian government immediately appointed Liebig as assistant professor of chemistry at the small University of Giessen. Two years later he was made professor, but in 1852 he moved to Munich, where he remained for the rest of his life.

Years at Giessen

When Liebig arrived at Giessen, he found the small school poorly prepared for instruction in chemistry. He changed all of this and made Giessen the chemical studies center of the world during his stay of 28 years. He was described as one of the greatest chemistry teachers of all time.

Not the least of Liebig's accomplishments at Giessen was the elimination of practical chemistry training, that is, in methods for making soap, distilling spirits, manufacturing paints and varnishes, and other industrial procedures. He contended that no progress in chemical technology could be made until there had been established a firm theoretical foundation which was thoroughly understood by a new generation of chemists. Liebig predicted that the German chemical industry would gain great benefits from the scientific study of chemistry, and the latter half of the 19th century proved him to have been right.

The Giessen years were also marked by Liebig's close association with Friedrich Wöhler. Their partnership proved to be one of the soundest and most productive in the history of science. They became personally acquainted in 1824, when Liebig paid a visit to Berlin, and from that point on their partnership and friendship were confirmed. In 1832 they discovered the "benzoyl radical" (C₇H₅O), the importance of the discovery being its demonstration that in organic substances there are groups of atoms which hold together and in reactions act like elements. From this discovery Liebig was led to the discovery of the ethyl radical (C₂H₅), which is found in such compounds as alcohol and ether. Wöhler and Liebig published their results on experiments with uric acid in 1838.

At Giessen, Liebig produced chloroform and chloral, discovered hippuric acid, studied the alkaloids and the amino acids, and began his work in agricultural chemistry and in the chemistry of life itself. He was the editor of Annalen der Pharmacie (1832-1839), which was continued as Annalen der Chemie und Pharmacie after 1840. He developed a method of organic analysis which is still used today. Although many of his theories were modified by later research and increased knowledge, he did more than any other individual to raise chemistry to a preeminent position in 19th-century Germany.

Theories in Biochemistry

About the midpoint in his career Liebig turned his attentions to biochemistry, literally, the chemistry of living organisms. He began by making analyses of such tissue fluids as blood, urine, and bile, and he went on from those studies to a consideration of body metabolism in animals. Out of his researches he proposed the theory that body heat and the ability of muscles to do work came from the energy which the oxidation of foodstuffs such as fats and carbohydrates provided.

Liebig also turned his attention to the process of fermentation. Here he fell into error, for he believed that fermentation resulted from the transmission of vibration from the particles in the mixture, which he thought were in a state of violent motion. This theory regarded fermentation as being independent of living organisms, that is, as purely a chemical reaction. In the case of yeast, for example, he denied that it was living and became involved in a long dispute with Louis Pasteur on the question. In this controversy Liebig was the loser, as Pasteur was able to offer incontrovertible proof that fermentation depends upon the presence of living organisms such as yeast cells.

Agricultural Chemistry

Liebig inaugurated the study of plant chemistry and its relationship to agriculture. In his view, green plants supported all life, and they derived their life from inorganic elements found in the soil and in the air. Green plants, he stated, receive from the air carbon from carbon dioxide, and nitrogen from ammonia. He believed that ammonia was also a component of rainwater, so that plants had an ample supply. In this concept, he was later proved to be wrong, and eventually he advised the use of some ammoniacal salts in plant fertilization.

Liebig also found, through the analysis of hundreds of samples of plant ash, that plants contain elements such as sodium, potassium, calcium, and phosphorus. They were the mineral content of plants and must come from the soil itself. Liebig said that the mineral content of soils could become exhausted, rendering the land unproductive for agricultural purposes. It was known that soil could replenish itself; that is, if no crops were grown on a piece of land for a time, eventually it would regain its productivity. Liebig suggested that this natural process of replenishment be supported through the use of mineral fertilizers.

To this end, Liebig began to compound mineral "manures," fertilizers that contained phosphates and potash, and he added them in an insoluble state so that rainwater would not wash them away. It was later realized that plants need these minerals in a soluble state and are quite capable of holding them in the soil regardless of rainfall. In spite of his lack of pronounced success with chemical fertilizers, Liebig showed the way for other reseachers, and the modern chemical fertilizer industry may be said to be his offspring. Much of his work in this field is described in Chemistry in Its Application to Agriculture and Physiology (1840).

His Place in Chemistry

Liebig, who received many honors during the course of his life, stands out as perhaps the most influential of the many German chemists of his age. He was a pioneer in chemical education, a discoverer in the realm of organic chemistry, and the first chemist to give serious consideration to the application of chemical science to food, nutrition, and agriculture. He also began basic research in the highly complicated field of biochemistry. At the time of his death on April 18, 1873, in Munich, one of his students, A. W. Hofmann, wrote, "No other man of learning, in his passage through the centuries, has ever left a more valuable legacy to mankind."

Further Reading

• The biographical literature on Liebig is mostly in German. W. A. Shenstone, Justus von Liebig: His Life and Work (1895), is a comprehensive biography in English. See also James R. Partington, A History of Chemistry (4 vols., 1961-1964); Aaron Ihde, The Development of Modern Chemistry (1964); Isaac Asimov, Short History of Chemistry (1965); and Eduard Farber, The Evolution of Chemistry: A History of Its Ideas, Methods, and Materials (2d ed. 1969).