Justus von Liebig

Transforming chemistry education

Liebig and several associates proposed to create an institute for pharmacy and manufacturing within the university.^[8]: 42 The Senate, however, uncompromisingly rejected their idea, stating that training "apothecaries, soapmakers, beer-brewers, dyers and vinegar-distillers" was not the university's task.^[8]: 43 As of 17 December 1825, they ruled that any such institution would have to be a private venture. This decision worked to Liebig's advantage. As an independent venture, he could ignore university rules and accept matriculated and unmatriculated students.^{[8]: 42–43} Liebig's institute was widely advertised in pharmaceutical journals and opened in 1826.^{[8]: 44–45} Its classes in practical chemistry and laboratory procedures for chemical analysis were taught in addition to Liebig's formal courses at the university.

From 1825 to 1835, the laboratory was housed in the guardroom of a disused barracks on the edge of town. The main laboratory space was about 38 m² (410 sq ft) in size and included a small lecture room, a storage closet, and a main room with ovens and work tables. An open colonnade outside could be used for dangerous reactions. Liebig could work there with eight or nine students at a time. He lived in a cramped apartment with his wife and children on the floor above.^[8]: 47

Liebig was one of the first chemists to organize a laboratory in its present form, engaging with students in empirical research on a large scale through a combination of research and teaching.^[11] His methods of organic analysis enabled him to direct the analytical work of many graduate students. Liebig's students were from many of the German states, as well as Britain and the United States. They helped create an international reputation for their Doktorvater. His laboratory became renowned as a model institution for the teaching of practical chemistry.^[8]: 47 It was also significant for its emphasis on applying discoveries in fundamental research to the development of specific chemical processes and products.^[12]

In 1833, Liebig convinced chancellor Justin von Linde to include the institute within the university.^[8]: 47 In 1839, he obtained government funds to build a lecture theatre and two separate laboratories designed by architect Paul Hofmann. The new chemistry laboratory featured innovative glass-fronted fume cupboards and venting chimneys.^[8]: 58 By 1852, when he left Giessen for Munich, more than 700 students of chemistry and pharmacy had studied with Liebig.^[8]: 57

Instrumentation

A significant challenge facing 19th-century organic chemists was the lack of instruments and methods of analysis to support accurate, replicable analyses of organic materials. Many chemists worked on the problem of organic analysis, including French Joseph Louis Gay-Lussac and Swedish Jöns Jacob Berzelius, before Liebig developed his version of an apparatus for determining the carbon, hydrogen, and oxygen content of organic substances in 1830. It involved an array of five glass bulbs, called a Kaliapparat, to trap the oxidation product of the carbon in the sample following its combustion. Before reaching the Kaliapparat, the combustion gases were conducted through a tube containing hygroscopic calcium chloride, which absorbed and retained the oxidation product of the hydrogen of the sample, namely water vapor. Next, in the Kaliapparat, carbon dioxide was absorbed in a potassium hydroxide solution in the three lower bulbs and used to measure the weight of carbon in the sample. For any substance consisting only of carbon, hydrogen, and oxygen, the percentage of oxygen was found by subtracting the carbon and hydrogen percentages from 100%; the remainder must be the percentage of oxygen. A charcoal furnace (a sheet steel tray in which the combustion tube was laid) was used for the combustion.^[13] Weighing carbon and hydrogen directly, rather than estimating them volumetrically, significantly increased the method's accuracy of measurement.^{[8]: 48–51} Liebig's assistant, Carl Ettling, perfected glass-blowing techniques for producing the Kaliapparat and demonstrated them to visitors.^[8]: 50 Liebig's kaliapparat simplified the method of quantitative organic analysis and rendered it routine.^[14] Brock suggests that the availability of a superior technical apparatus was one reason why Liebig was able to attract so many students to his laboratory.^[8]: 50 His method of combustion analysis was used pharmaceutically, and certainly made possible many contributions to organic, agricultural and biological chemistry.^{[8]: 76–77 [15]}

Liebig also popularized the use of a counter-current water-cooling system for distillation, still referred to as a Liebig condenser.^[8]: 84 Liebig himself attributed the vapor condensation device to German pharmacist Johann Friedrich August Gottling, who had made improvements in 1794 to a design discovered independently by German chemist Christian Ehrenfried Weigel in 1771, by French scientist P. J. Poisonnier in 1779, and by Finnish chemist Johan Gadolin in 1791.^[16]

Although it was not widely adopted until after Liebig's death, when safety legislation finally prohibited the use of mercury in making mirrors, Liebig proposed a process for silvering that eventually became the basis of modern mirror-making. In 1835, he reported that aldehydes reduce silver salts to metallic silver. After working with other scientists, Carl August von Steinheil approached Liebig in 1856 to see if he could develop a silvering technique capable of producing high-quality optical mirrors for use in reflecting telescopes. Liebig developed blemish-free mirrors by adding copper to ammoniated silver nitrate and sugar. An attempt to commercialize the process and "drive out mercury mirror-making and its injurious influence on workers' health" was unsuccessful.^{[8]: 136–139} Liebig's mirrors struggled commercially due to poor glass, which produced an off-color, greenish-yellow reflection. Rudely, Liebig commented that Frenchwomen especially hated his mirrors because Frenchwomen already looked yellow and sickly, and the mirrors just reminded them how ugly they were.^[17]

Organic chemistry

One of Liebig's frequent collaborators was Friedrich Wöhler. They met in 1826 in Frankfurt, after independently reporting on the preparation of two substances, cyanic acid and fulminic acid, that apparently had the same composition, but very different characteristics. The silver fulminate investigated by Liebig was explosive, whereas the silver cyanate found by Wöhler was not. After reviewing the disputed analyses together, they agreed that both were valid. The discovery of these and other substances led Jöns Jacob Berzelius to suggest the idea of isomers, substances that are defined not simply by the number and kind of atoms in the molecule, but also by the arrangement of those atoms.^{[8]: 72 [18][19]}

In 1832, Liebig and Friedrich Wöhler published an investigation of the oil of bitter almonds. They transformed pure oil into several halogenated compounds, which were further transformed in other reactions.^[20] Throughout these transformations, "a single compound" (which they named benzoyl) "preserves its nature and composition unchanged in nearly all its associations with other bodies."^[8]: 79 Their experiments proved that a group of carbon, hydrogen, and oxygen atoms could behave like an element, take the place of an element, and can be exchanged for elements in chemical compounds. This laid the foundation for the doctrine of compound radicals, which can be seen as an early step in the development of structural chemistry.^[19]

The 1830s were a period of intense investigation of organic compounds by Liebig and his students, and of vigorous debate about the theoretical implications of their results. Liebig published on a wide variety of topics, personally averaging 30 papers per year between 1830 and 1840.^[8]: 76 Liebig not only isolated individual substances, but also studied their interrelationships and the ways in which they degraded and metamorphosed into other substances, looking for clues to the understanding of both chemical composition and physiological function. Other significant contributions by Liebig during this time include his examination of the nitrogen content of bases;^[8]: 77 the study of chlorination and the isolation of chloral (1832);^[8]: 83 the identification of the ethyl radical (1834);^[8]: 82 the oxidation of alcohol and formation of aldehyde (1835);^[8]: 84 the polybasic theory of organic acids (1838);^{[8]: 86–87} and the degradation of urea (1837).^{[8]: 88–89}

Writing about the analysis of urine, a complex organic product, he made a declaration that reveals both the changes that were occurring in chemistry over a short time and the impact of his own work.^[8]: 89 At a time when many chemists such as Jöns Jakob Berzelius still insisted on a hard and fast separation between the organic and inorganic, Liebig asserted:

"The production of all organic substances no longer belongs just to living organisms. It must be seen as not only probable, but as certain, that we shall be able to produce them in our laboratories. Sugar, salicin, and morphine will be artificially produced. Of course, we do not yet know how to do this, because we do not yet know the precursors from which these compounds arise, but we shall come to know them."

— [Liebig and Woehler (1838)]

Liebig's arguments against any chemical distinction between living (physiological) and dead chemical processes proved a great inspiration to several of his students and others who were interested in materialism. Though Liebig distanced himself from the direct political implications of materialism, he tacitly supported the work of Carl Vogt (1817–1895), Jacob Moleschott (1822–1893),^[21] and Ludwig Büchner (1824–1899).^[22]

Plant nutrition

By the 1840s, Liebig was attempting to apply theoretical knowledge from organic chemistry to real-world problems of food availability. His book Die organische Chemie in ihrer Anwendung auf Agricultur und Physiologie (Organic Chemistry in its Application to Agriculture and Physiology) (1840) promoted the idea that chemistry could revolutionize agricultural practice, increasing yields and lowering costs. It was widely translated, vociferously critiqued, and highly influential.^[8]

Liebig's book discussed chemical transformations within living systems, both plant and animal, outlining a theoretical approach to agricultural chemistry. The book's first part focused on plant nutrition; the second was on chemical mechanisms of putrefaction and decay.^[8]: 148 Liebig's awareness of both synthesis and degradation led him to become an early advocate of conservation, promoting ideas such as the recycling of sewage.^{[8]: 250–270}

Liebig argued against prevalent theories about role of humus in plant nutrition, which held that decayed plant matter was the primary source of carbon for plant nutrition. Fertilizers were believed to act by breaking down humus, making it easier for plants to absorb. Associated with such ideas was the belief that some sort of "vital force" distinguished reactions involving organic as opposed to inorganic materials.^[23]

Early studies of photosynthesis had identified carbon, hydrogen, oxygen, and nitrogen as important, but disagreed over their sources and mechanisms of action. Carbon dioxide was known to be taken in and oxygen released during photosynthesis, but researchers suggested that oxygen was obtained from carbon dioxide, rather than from water. Hydrogen was believed to come primarily from water. Researchers disagreed about whether sources of carbon and nitrogen were atmospheric or soil-based.^{[23]: xv–xxi} Nicolas-Théodore de Saussure's experiments, reported in Recherches Chimiques sur la Végétation (1804), suggested that carbon was obtained from atmospheric rather than soil-based sources. It also indicated that water was a likely source of hydrogen. He also studied the absorption of minerals by plants, and observed that mineral concentrations in plants tended to reflect their presence in the soil in which the plants were grown. However, the implications of De Saussure's results for theories of plant nutrition were neither clearly discussed nor easily understood.^{[23]: xxii–xxvii}

Liebig reaffirmed the importance of De Saussure's findings, and used them to critique humus theories, while regretting the limitations of De Saussure's experimental techniques. Using more precise methods of measurement as a basis for estimation, he pointed out contradictions such as the inability of existing soil humus to provide enough carbon to support the plants growing in it.^[23]: xxix By the late 1830s, researchers such as Karl Sprengel were using Liebig's methods of combustion analysis to assess manures, concluding that their value could be attributed to their constituent minerals.^[8]: 106 Liebig synthesized ideas about the mineral theory of plant nutrition and added his own conviction that inorganic materials could provide nutrients as effectively as organic sources.^[8]: 148

In his theory of mineral nutrients, Liebig identified the chemical elements of nitrogen (N), phosphorus (P), and potassium (K) as essential to plant growth. He reported that plants acquire carbon (C) and hydrogen (H) from the atmosphere and from water (H₂O). In addition to emphasizing the importance of minerals in the soil, he argued that plants feed on nitrogen compounds derived from the air. This assertion was a source of contention for many years, and turned out to be true for legumes, but not for other plants.^[8]: 181

Liebig also popularized Carl Sprengel's "theorem of minimum" (known as the law of the minimum), stating that plant growth is not determined by the total resources available, but by the scarcest available resource. A plant's development is limited by the one essential mineral that is in the relatively shortest supply. This concept of limitation can be visualized as "Liebig's barrel", a metaphorical barrel in which each stave represents a different element. A nutrient stave that is shorter than the others will cause the liquid contained in the barrel to spill out at that level. This is a qualitative version of the principles used for determining the application of fertilizer in modern agriculture.

Organic Chemistry was not intended as a guide to practical agriculture. Liebig's lack of experience in practical applications, and differences between editions of the book, fueled considerable criticism. Nonetheless, Liebig's writings had a profound impact on agriculture, spurring experiment and theoretical debate in Germany, England, and France.^[8]: 165

One of his most recognized accomplishments is the development of nitrogen-based fertilizer. In the first two editions of his book (1840, 1842), Liebig reported that the atmosphere contained insufficient nitrogen, and argued that nitrogen-based fertilizer was needed to grow the healthiest possible crops.^[8]: 120 Liebig believed that nitrogen could be supplied in the form of ammonia, and recognized the possibility of substituting chemical fertilizers for natural ones (animal dung, etc.)

He later became convinced that nitrogen was sufficiently supplied by precipitation of ammonia from the atmosphere, and argued vehemently against the use of nitrogen-based fertilizers for many years. An early commercial attempt to produce his own fertilizers was unsuccessful, due to lack of nitrogen in the mixtures.^{[8]: 121–124} When tested in a farmer's field, Liebig's manure was found to have no appreciable effect.^[24]

Liebig's difficulties in reconciling theory and practice reflected that the real world of agriculture was more complex than was at first realized. By the publication of the seventh German edition of Agricultural Chemistry he had moderated some of his views, admitting some mistakes and returning to the position that nitrogen-based fertilizers were beneficial or even necessary.^[8]: 179He was instrumental in the use of guano for nitrogen.^[25] In 1863 he published the book "Es ist ja die Spitze meines lebens" in which he revised his early perceptions, now appreciating soil life and in particular the biological N fixation. Nitrogen fertilizers are now widely used throughout the world, and their production is a substantial segment of the chemical industry.^[26]

Plant and animal physiology

Liebig's work on applying chemistry to plant and animal physiology was especially influential. By 1842, he had published Chimie organique appliquée à la physiologie animale et à la pathologie, published in English as Animal Chemistry, or, Organic Chemistry in its Applications to Physiology and Pathology, presenting a chemical theory of metabolism.^[8]: 185 The experimental techniques used by Liebig and others often involved controlling and measuring diet, and monitoring and analyzing the products of animal metabolism, as indicators of internal metabolic processes. Liebig saw similarities between plant and animal metabolism, and suggested that nitrogenous animal matter was similar to, and derived from, plant matter. He categorized foodstuffs into two groups, nitrogenous materials which he believed were used to build animal tissue, and non-nitrogenous materials which he believed were involved in separate processes of respiration and generation of heat.^[8]: 184

French researchers such as Jean-Baptiste Dumas and Jean-Baptiste Boussingault believed that animals assimilated sugars, proteins, and fats from plant materials and that animals could not synthesize complex molecules. Liebig's work suggested a common ability of plants and animals to synthesize complex molecules from simpler ones. His experiments on fat metabolism convinced him that animals must be able to synthesize fats from sugars and starches.^[8]: 187 Other researchers built upon his work, confirming the abilities of animals to synthesize sugar and build fat.^{[8]: 189–190}

Liebig also studied respiration, at one point measuring the "ingesta and excreta" of 855 soldiers, a bodyguard of the Grand Duke of Hessen-Darmstadt, for an entire month.^[8]: 191 He outlined an extremely speculative model of equations in which he attempted to explain how protein degradation might balance within a healthy body and result in pathological imbalances in cases of illness or inappropriate nutrition.^{[8]: 191–193} This proposed model was justifiably criticized. Berzelius stingingly stated that "this facile kind of physiological chemistry is created at the writing table".^[8]: 194 Some of the ideas that Liebig had enthusiastically incorporated were not supported by further research. The third and last edition of Animal Chemistry (1846) was substantially revised and did not include the equations.^{[8]: 195–197}

The third area discussed in Animal Chemistry was fermentation and putrefaction. Liebig proposed chemical explanations for processes such as eremacausis (organic decomposition), describing the rearrangement of atoms as a result of unstable "affinities" reacting to external causes such as air or already decaying substances.^[8]: 205 Liebig identified the blood as the site of the body's "chemical factory", where he believed processes of synthesis and degradation took place. He presented a view of disease in terms of chemical process, in which healthy blood could be attacked by external contagia; secreting organs sought to transform and excrete such substances; and failure to do so could lead to their elimination through the skin, lungs, and other organs, potentially spreading contagion. Again, although the world was much more complicated than his theory, and many of his individual ideas were later proved wrong, Liebig managed to synthesize existing knowledge in a way that had implications for doctors, sanitarians, and social reformers. The English medical journal The Lancet reviewed Liebig's work and translated his chemical lectures as part of its mission to establish a new era of medicine.^[8]: 207 Liebig's ideas stimulated medical research, led to the development of better techniques for testing experimental models of metabolism, and pointed to chemistry as fundamental to the understanding of health and disease.^[8]: 214

In 1850, Liebig investigated spontaneous human combustion, dismissing the simplistic explanations based on ethanol due to alcoholism.^[27]

Liebig and the chemistry of food

Liebig's Extract of Meat Company

Main article: Liebig's Extract of Meat Company

Building on his theories of the nutritional value of meat fluids, and seeking an inexpensive nutrition source for Europe's poor, Liebig developed a formula for producing beef extract. The details were published in 1847 so that "the benefit of it should ... be placed at the command of as large a number of persons as possible by the extension of the manufacture, and consequently a reduction in the cost".^[29]

Production was not economically feasible in Europe, where meat was expensive, but in Uruguay and New South Wales, meat was an inexpensive byproduct of the leather industry. In 1865, Liebig partnered with Belgian engineer George Christian Giebert,^[30] and was named scientific director of Liebig's Extract of Meat Company, located in Fray Bentos in Uruguay.^[7][31]

Other companies also attempted to market meat extracts under the name "Liebig's Extract of Meat". In Britain, a competitor's right to use the name was successfully defended on the grounds that the name had fallen into general use and become a generic term before the creation of any particular company.^[29] The judge asserted that "Purchasers must use their eyes", and considered the presentation of the products to be sufficiently different to enable the discriminating consumer to determine which of the products bore Liebig's signature and was supported by Liebig himself.^[32]

Liebig's company initially promoted their "meat tea" for its curative powers and nutritional value as a cheap, nutritious alternative to real meat. But such claims did not hold up to scrutiny. In 1868 the German physiologist Edward Kemmerich ran an experiment involving feeding the extract to dogs, every one of which died. After claims of its nutritional value were questioned, the company emphasized its convenience and flavor, marketing it as a comfort food.^[7]

The Liebig company worked with popular cookery writers in various countries to popularize their products. German cookery writer Henriette Davidis wrote recipes for Improved and Economic Cookery and other cookbooks. Katharina Prato wrote an Austro-Hungarian recipe book, Die Praktische Verwerthung Kochrecepte (1879). Hannah M. Young was commissioned in England to write Practical Cookery Book for the Liebig Company. In the United States, Maria Parloa extolled the benefits of Liebig's extract. Colorful calendars and trading cards were also marketed to popularize the product.^{[8]: 234–237}

The company also worked with British chemist Henry Enfield Roscoe to develop a related product, which it registered some years after Liebig's death, under the "Oxo" trademark. Oxo was trademarked worldwide in 1899 and in the United Kingdom in 1900. Originally a liquid, Oxo was released in cubed solid form in 1911.^[8]: 230

Posthumous honors

Liebig's portrait appeared on the 100 ℛ︁ℳ︁ banknote issued by the Reichsbank from 1935 until 1945.^[52] Printing ceased in 1945 but the note remained in circulation until the issue of the Deutsche Mark on 21 June 1948.

In 1946, after the end of World War II, the University of Giessen was officially renamed after him, "Justus-Liebig-Universität Giessen".^[11]

In 1953, the West German post office issued a stamp in his honor.^[53]

In 1953, the third General Assembly of the International Scientific Centre of Fertilizers (CIEC), founded in 1932, was organized in Darmstadt to honor Justus von Liebig on the 150th anniversary of his birth.^[54]

A portrait of Liebig hangs in the Burlington House headquarters of the Royal Society of Chemistry. It was presented to the society's forerunner, the Chemical Society, by his god-daughter, Mrs Alex Tweedie, née Harley, daughter of Emma Muspratt.^[55]

Liebig medals

Some organizations have granted medals in honor of Liebig. In 1871, the Versammlung deutscher Land- und Forstwirte (Assembly of German Farmers and Foresters) was first awarded a Liebig Gold Medal, given to Theodor Reuning. The image was struck from a portrait commissioned in 1869 from Friedrich Brehmer.^{[8]: 327–328 [56]}

For several years, the Liebig Trust Fund, established by Baron Liebig, was administered by the Royal Bavarian Academy of Sciences at Munich and members of the Liebig family. They were empowered to award gold and silver Liebig Medals to deserving German scientists "for the purpose of encouraging research in agricultural science". Silver medals could be awarded to scientists from other countries.^[57] Some of those who received medals include:

• 1893, silver, Sir John Lawes and Joseph Henry Gilbert, England^[58]
• 1894, silver, Professor Eugene Woldemar Hilgard, United States, "for meritorious work in the investigation of the physical and chemical properties of soils."^[57][59]
• 1896, gold, Professor Friedrich Stohmann, professor of agricultural chemistry in Leipzig University.^[60]
• 1899, gold, Albert Schultz-Lupitz, Germany^[61]
• 1908, gold, Max Rubner, Germany^[62]

In 1903, the Verein deutscher Chemiker (Association of German Chemists) also had a medal struck using Brehmer's portrait.^[8]: 329 Their Liebig Medal was first awarded in 1903 to Adolf von Baeyer, and in 1904 to Dr. Rudolf Knietsch of the Badische Anilin- und Soda-Fabrik.^[63] As of 2024^[update], it continues to be awarded.^[64]

At the third World Congress of CIEC, held at Heidelberg in 1957, the "Sprengel-Liebig Medal" was awarded to Dr. E. Feisst, president of CIEC, for outstanding contributions in agricultural chemistry.^[54]