Best known for the eponymous Liebig condenser, the German chemist Justus von Liebig was the founder of agricultural chemistry. Indeed, he was one of the greatest chemists of the 19th Century.

Liebig was born in Darmstadt, Germany, on 12 May, 1803. His father sold drugs, dyes and other chemicals, and by playing with the chemicals in his father's laboratory, where pigments and varnishes were prepared, he acquired an early interest in chemistry. Liebig was later expelled from his gymnasium¹ for detonating an explosive device he'd made at home with chemicals obtained from his father's business.

At the age of 15, he was apprenticed to an apothecary in Heppenheim, but soon gave up this work to read chemistry in Bonn and Erlangen, where he studied under the famous chemist Karl Wilhelm Kastner. When Kastner moved to the University of Erlangen, Liebig accompanied him, receiving his doctorate there in 1822.

He then received a grant from the Hessian government to study in Paris. Through the influence of Alexander von Humboldt, Liebig was able to work in the private laboratory of the great French chemist Joseph Louis Gay-Lussac. He gained his PhD at the tender age of 19.

After two years (1822 - 1824) in Paris, Liebig became associate professor, and in 1825 (at the age of 22) professor of chemistry at the University of Gießen. In 1852, Liebig accepted an invitation to the University of Munich, where he remained until his death.

Liebig was an excellent teacher and a pioneer in chemical education. At Gießen, he established the first laboratory in which chemical research was taught systematically. The courses of instruction which he organised served as models for other universities.

Many of Liebig's students, including Friedrich Kekule, discoverer of the structure of benzene, went on to become famous chemists in their own right.

Isomers

Back in the 1820s, Liebig began a long collaboration with one of his students, Friedrich Wöhler. Liebig was investigating a class of compounds called 'fulminates', at the same time that Wöhler was working independently with cyanates. In 1826, Liebig prepared silver fulminate (modern formula AgCNO), while Wöhler made silver cyanate (AgNCO). When they reported their results they assigned the same formula to the two different compounds. This stimulated work by Berzelius that led him to the concept of isomers - compounds that share the same chemical composition (molecular formula) but have different chemical and/or physical properties.

Organic Chemistry and 'Compound Radicals'

From the late 1820s, Liebig's research began to focus on organic chemistry - the chemistry of the compounds of carbon. With Wöhler, he published research showing the persistence of groups of atoms in chemical reactions; that is, they introduced the idea that whole families of chemicals can be made from the same molecular unit, or radical².

In 1832, from a study of 'oil of bitter almonds' (benzaldehyde; phenylmethanal), the pair discovered the benzoyl radical C₆H₅CO-. They showed that benzaldehyde can be converted to benzoic acid and made a number of other related compounds, such as benzyl alcohol and benzoyl chloride. The benzene ring had, in fact, conferred unusual stability to the benzoyl grouping, allowing it to persist in the various reactions. Although they found no other radicals that supported their theory as convincingly, they had introduced a degree of systematization into the confused field of organic chemistry.

Liebig devised many new methods to determine the composition of organic compounds, specifically ways of determining the hydrogen, carbon and halogen content of organic compounds.

Biochemical Studies

From 1838, Liebig's work focused on what we now call 'Biochemistry'. He studied fermentation and analysed human tissues and body fluids.

In his studies of animal nutrition, Liebig showed that different types of food have different functions in the body. And he proved that body heat is produced from energy derived from food. Liebig calculated the energy content of foods, emphasising the role of fats as a source of dietary energy. He even developed the beef extract we now know as OXO. In 1865, he set up the Liebig Extract of Meat Company, which produced beef extract as a cheap, nutritious alternative to real meat.

He maintained that certain mineral substances are essential in plant nutrition and that the soil becomes barren unless these substances are returned to it in manure or by the natural decay of plant material. From this, he devised specific rules for fertilising, although some of his formulations lacked essential nitrogen compounds.

Liebig's Condenser

In chemistry, a condenser is a piece of laboratory glassware designed to cool hot vapours or liquids. It usually consists of a large glass tube containing a smaller glass tube running its entire length, within which the hot fluids pass. The Liebig condenser is the most basic water-cooled design, consisting of a straight inner-tube, making it cheaper to manufacture. Water is passed between the inner and outer tubes from bottom to top, to facilitate more efficient cooling. Although it carries Liebig's name, like Bunsen's burner, he's thought to have popularised rather than invented it.

A Prolific Author

Liebig was a prolific author and wrote 317 scientific papers, a book on organic chemistry, and an encyclopedia of all chemical sciences. The two books he wrote: Chemistry in its Application to Agriculture and Physiology(1840) and Organic Chemistry in its Application to Physiology and Pathology (1842) can be said to have laid the foundations for these important branches of study. The former gave great impetus to the more widespread study of chemistry in England.

Both works, together with the popular Chemical Letters, ensured Liebig's name received a wide audience. They gave him a supreme position of influence in scientific and economic chemistry fields. Later in his career, Liebig founded the Annalen der Pharmacie, now the Annalen der Chemie, which is still a respected research journal.

In 1842, Liebig embarked on a tour of England during which he gave both private interviews and public lectures. These helped to raise the profile of, and increase interest in, the chemical sciences. An immediate consequence was a general realisation of the importance of chemistry, particularly organic chemistry. Universities and colleges were stimulated into giving increased attention to laboratory teaching. Much of this teaching, however, was for professional purposes, including the training of doctors, engineers, and the like. It was realised that it was important to value and study chemistry for its intellectual merit. Taking advantage of the enthusiasm generated by a visit by Liebig, Sir James Clerk, court physician to Prince Albert and Queen Victoria, succeeded in founding the Royal College of Chemistry³ in London.

Liebig was also instrumental in founding the Chemical Society in 1841, the oldest society of its kind anywhere in the world⁴. Liebig died on 18 April, 1873.

Germany's high profile in chemistry and pharmaceuticals is due in no small part to a research and manufacturing tradition which Liebig helped to establish. One of his greatest students, Albert Wilhelm von Hofmann, wrote:

No other man of learning, in his passage through the centuries, has ever left a more valuable legacy to mankind.

On 22 May, 2003, Britain's Royal Society of Chemistry unveiled a 'landmark plaque' on the site of the former Royal College of Chemistry (1845 - 1872) on Oxford Street, London, to mark the 200th anniversary of the birth of the man who inspired the founding of the Royal College of Chemistry and Imperial College - Justus von Liebig.

Among his many honours, Liebig became Freiherr (Baron) in 1845. Today, the University of Gießen is officially named after him, as the Justus Liebig University, Gießen.