Justus von Liebig
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| Justus von Liebig |
Justus von Liebig was born in Darmstadt into the middle-class family of Johann Georg Liebig and Maria Caroline Möser in early May 1803.:1–3 His father was a drysalter and hardware merchant who compounded and sold paints, varnishes and pigments, which he developed in his own workshop.:1 From childhood Justus was fascinated with chemistry. At the age of 13, Liebig lived through the year without a summer, when the majority of food-crops in the northern hemisphere were destroyed by a volcanic winter.Germany was among the hardest-hit in the global famine that ensued, and the experience is said to have shaped Liebig's later work. Thanks in part to Liebig's innovations in fertilizers and agriculture, the 1816 famine became known as "the last great subsistence crisis in the Western world".
Liebig attended grammar school at the Ludwig-Georgs-Gymnasium in Darmstadt, from the age of 8 to Leaving without a certificate of completion, he was apprenticed for several months to the apothecary Gottfried Pirsch (1792–1870) in Heppenheim before returning home, possibly because his father could not afford to pay his indentures. He worked with his father for the next two years,then attended the University of Bonn, studying under Karl Wilhelm Gottlob Kastner, a business associate of his father. When Kastner moved to the University of Erlangen, Liebig followed him.
Liebig left Erlangen in March 1822, in part because of his involvement with the radical Korps Rhenania (a nationalist student organization) but also because of his hopes for more advanced chemical studies. The circumstances are clouded by possible scandal.In late 1822 Liebig went to study in Paris on a grant obtained for him by Kastner from the Hessian government. He worked in the private laboratory of Joseph Louis Gay-Lussac, and was also befriended by Alexander von Humboldt and Georges Cuvier (1769–1832). Liebig's doctorate from Erlangen was conferred on 23 June 1823, a considerable time after he left, as a result of Kastner's intervention on his behalf. Kastner pleaded that the requirement of a dissertation be waived, and the degree granted in absentia.
Research and development
Liebig left Paris to return to Darmstadt in April 1824. On 26 May 1824 at the age of 21 and with Humboldt's recommendation, Liebig became a professor extraordinarius at the University of Giessen.Liebig's appointment was part of an attempt to modernize the University of Giessen and attract more students. He received a small stipend, without laboratory funding or access to facilities.
His situation was complicated by the presence of existing faculty: Professor Wilhelm Zimmermann (1780–1825) taught general chemistry as part of the philosophy faculty, leaving medical chemistry and pharmacy to Professor Philipp Vogt in the medical faculty. Vogt was happy to support a reorganization in which pharmacy was taught by Liebig and became the responsibility of the faculty of arts, rather than the faculty of medicine. Zimmermann found himself competing unsuccessfully with Liebig for students and their lecture fees. He refused to allow Liebig to use existing space and equipment, and finally committed suicide on 19 July 1825. The deaths of Zimmermann and a Professor Blumhof who taught technology and mining opened the way for Liebig to apply for a full professorship. Liebig was appointed to the ordentlicher chair in chemistry on 7 December 1825, receiving a considerably increased salary and a laboratory allowance.
Liebig married Henriette "Jettchen" Moldenhauer (1807–1881), the daughter of a state official, in May 1826. They had five children, Georg (1827–1903), Agnes (1828–1862), Hermann (1831–1894), Johanna (1836–1925) and Marie (1845–1920). Although Liebig was Lutheran and Jettchen Catholic, their differences in religion appear to have been resolved amicably by bringing their sons up in the Lutheran religion and their daughters as Catholics.
Transforming chemical education
Liebig and several associates proposed to create an institute for pharmacy and manufacturing within the university.The Senate, however, uncompromisingly rejected their idea, stating that it was not the university's task to train "apothecaries, soapmakers, beer-brewers, dyers and vinegar-distillers."As of 17 December 1825, they ruled that any such institution would have to be a private venture. This decision actually worked to Liebig's advantage. As an independent venture, he could ignore university rules and accept both matriculated and non-matriculated students.Liebig's institute was widely advertised in pharmaceutical journals, and opened in 1826.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 square metres, including 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 8 or 9 students at a time. He lived in a cramped apartment on the floor above with his wife and children.
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.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, and they helped create an international reputation for their Doktorvater. His laboratory became renowned as a model institution for the teaching of practical chemistry.It was also significant for its emphasis on applying discoveries in fundamental research to the development of specific chemical processes and products.
In 1833, Liebig was able to convince chancellor Justin von Linde to include the institute within the university.In 1839, he obtained government funds to build a lecture theatre and 2 separate laboratories, designed by architect Paul Hofmann. The new chemistry laboratory featured innovative glass-fronted fume cupboards and venting chimneys.By 1852, when he left Giessen for Munich, more than 700 students of chemistry and pharmacy had studied with Liebig.
Instrumentation
A significant challenge facing nineteenth 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 ingenious array of five glass bulbs, called a Kaliapparat to trap oxidation products. Water was absorbed in a bulb of hygroscopic calcium chloride which was weighed to measure hydrogen. Carbon dioxide was absorbed in a potassium hydroxide solution in the three lower bulbs and used to measure carbon. Oxygen was calculated from the difference. A coal fire was used for combustion.Weighing carbon and hydrogen directly, rather than estimating them volumetrically, greatly increased the method's accuracy of measurement.Liebig's assistant Carl Ettling perfected glass-blowing techniques for producing the kaliapparat, and demonstrated them to visitors.Liebig's kaliapparat simplified the technique of quantitative organic analysis and rendered it routine.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.His method of combustion analysis was used pharmaceutically, and certainly made possible many contributions to organic, agricultural and biological chemistry.
Liebig also popularized use of a counter-current water-cooling system for distillation, still referred to as a Liebig condenser.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.
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 was able to develop 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.
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.
Liebig's book discussed chemical transformations within living systems, both plant and animal, outlining a theoretical approach to agricultural chemistry. The first part of the book focused on plant nutrition, the second on chemical mechanisms of putrefaction and decay.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.
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.
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.: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, and 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.
Liebig reaffirmed the importance of De Saussures' 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.By the late 1830s, researchers like Karl Sprengel were using Liebig's methods of combustion analysis to assess manures, concluding that their value could be attributed to their constituent minerals.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.
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). As well as 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.
Liebig's Barrel
Liebig also popularized Carl Sprengel's "Theorem of minimum" (known as 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.
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 there was not sufficient nitrogen in the atmosphere, and argued that nitrogen-based fertilizer was needed to grow the healthiest possible crops.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 testing in actual agricultural conditions, and to lack of nitrogen in the mixtures.
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.Nitrogen fertilizers are now widely used throughout the world, and their production is a substantial segment of the chemical industry.
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.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.
French researchers such as Jean-Baptiste Dumas and Jean-Baptiste Boussingault believed that animals assimilated sugars, proteins, and fats from plant materials and lacked the ability to synthesize them. 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 starch.Other researchers built upon his work, confirming the abilities of animals to synthesize sugar and build fat.
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.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.This proposed model was justifiably criticized. Berzelius stingingly stated that "this facile kind of physiological chemistry is created at the writing table".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.
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.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 significant 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.Liebig's ideas stimulated significant 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.
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