As we saw in the last section, the modern understanding of chemistry began in the second half of the eighteenth century with the advances of Antoine Lavoisier and others, and further contributions from John Dalton and Jöns Jacob Berzelius in the early 1800s. This period saw the emergence of organic chemistry, which, with the help of new conceptual and experimental tools, established itself as a discipline separate from inorganic chemistry over the next half century (Scholz 1987). The researchers of this period encountered considerable confusion due to the complexities and behavior of organic structures. Aided by increasingly accurate elementary analysis, they nevertheless made significant advances based on the empirical studies of structure chemistry. While these developments, along with other factors, helped the chemical and dye industries make large strides in chemical synthesis, the conceptual and experimental tools did not supply sufficient understanding of chemical systems to enable ammonia synthesis from the elements. Here we will focus on two developments that illustrate the experimentally-based approach to organic chemistry in the 1800s in order to frame the conceptual leap in physical chemistry toward the end of the century that led to Fritz Haber’s breakthrough.

The first was the formulation by Eilhard Mitscherlich in 1834, after studying the production of ether from ethanol and sulfuric acid (Fig. 3.1), that catalysis represented a specific kind of chemical phenomenon (Mitscherlich 1834b). With this assertion, many scattered observations were brought together under one classification.

Fig. 3.1
figure 1

Eilhard Mitscherlich’s apparatus for the synthesis of ether from ethanol and sulfuric acid. The ether was produced in the heated flask (a) on the right which contained sulfuric acid, water, and a thermometer (b). The alcohol was contained in the flask (d) and could be continuously supplied. The long pipe joining the left section to the right section of the apparatus served to collect the volatile ether. After the ether was cooled with water from the tank (m) and deposited in the long tube below, it could be removed (Mitscherlich 1834b)

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The reaction producing ether was well known long before Mitscherlich gave it theoretical underpinning. The first explanation came in 1797 and while different theories emerged over the next 35 years, they often ascribed a chemically active role to the sulfuric acid or suffered other drawbacks. Mitscherlich’s experimental setup was not new; he dripped ethanol into a mixture of boiling dilute sulfuric acid and alcohol to produce ether. It was, rather, his novel interpretation of the results which represented the advancement (Gräbe 1920, pp. 94–96), (Mittasch 1939, pp. 30–36), (Schütt 1992, pp. 121–127). “Therefore,” wrote Mitscherlich in consideration of his results,

it follows from the stated facts that alcohol dissociates into ether and water in contact with sulfuric acid at a temperature of about 140∘. Decomposition and formation occur very often in this way; we will call them decomposition and formation through contact. The best example is oxidized water; the smallest trace of fmanganese superoxide, of gold, of silver, or of other substances causes a dissociation into water and oxygen gas…without themselves sustaining the slightest alteration. The dissociation of [different] types of sugar in alcohol and carbonic acid, the oxidation of alcohol when it is transformed into acetic acid and the dissociation of urea and water into carbonic acid and ammonia also belong to this type of reaction. Initially, the substances are not changed. However, through the addition of a very slight quantity of ferment, which in this case is the contact substance, at a specific temperature, the change takes place rapidly. The transformation of starch into starch sugar, when it is boiled in water with sulfuric acid is very similar to the production of ether…Footnote 1

Mitscherlich, for the first time, collected many seemingly different chemical reactions, all of which were promoted by the presence of a substance that remained unchanged during the reaction, under a single expression: decomposition or formation through contact.

The importance of Mitscherlich’s idea was seized upon by Berzelius who wrote the following year (Berzelius 1835),Footnote 2

It is then shown that several simple and compound bodies, soluble and insoluble, have the property of exercising on other bodies an action very different from chemical affinity. The body effecting the changes does not take part in the reaction and remains unaltered through the reaction. This unknown body acts by means of an internal force, whose nature is unknown to us. This new force, up till now unknown, is common to organic and inorganic nature. I do not believe that this force is independent of the electrochemical affinities of matter; I believe on the contrary, that it is a new manifestation of the same, but, since we cannot see their connection and independence, it will be more convenient to designate the force by a new name. I will therefore call it the “Catalytic Force” and I will call “Catalysis” the decomposition of bodies by this force, in the same way that we call by “Analysis” the decomposition of bodies by chemical affinity.

Berzelius also recognized that catalysis was an important factor in living organisms and introduced contact processes into plant and animal chemistry.

Neither Berzelius nor Mitscherlich were the first to recognize the inimitability of catalytic processes (Mittasch 1939, pp. 1–36). Catalytic investigations in the era after Lavoisier began in 1781 with the transformation of potato starch into dextrin (a form of sugar) after the addition of tartaric acid or acetic acid. In 1811, Johann Wolfgang Döbereiner noticed the speed of the reaction depended on the concentration of the acid and postulated the reaction would eventually take place even if no acid were present. The boiling water changed the starch into dextrin and the acid only expedited the conversion. Soon after, it was noted that the facilitating substance was itself not changed during the reaction, but it remained unclear whether this behavior was altogether a new type of chemical phenomenon and there was little discussion. These and similar experiments investigated what is now called homogeneous catalysis, where the reacting substances and the catalyst are in the same material phase. Gaining detailed insight was difficult. In contrast, when observing substances in different phases, now called heterogeneous catalysis, the separate components of the reaction were more easily recognized. For example, in 1783, Jospeh Priestly allowed alcohol vapor to flow through a heated tobacco pipe and obtained ethylene.

Experiments on ammonia are also encountered in early catalysis research. One of the first was in 1788 when William Austin found tiny amounts of ammonia (“volatile alkali”) when nitrogen (“phlogisticated air”) was combined in a glass tube with water and iron filings. The iron in contact with water evolved hydrogen (“light inflammable air”), which, if it met the nitrogen “at the instant of its extrication,” combined to form ammonia (Austin 1788), (Thomson 1802, pp. 313–314), (Leigh 2004, p. 104). At the turn of the century, Humphrey Davy dissociated ammonia in a heated glass tube using a copper wire. His experiments were extended by Louis Jacques Thénard in 1813 using a variety of metals: Fe, Cu, Ag, Au, and Pt. Thénard noticed by testing an increased number of metals that there was a wide range of catalytic ability and attributed it to the large heat capacity and heat transfer through some metals. In the case of ammonia, Fe was the most effective catalyst but only the dissociation reaction seemed to proceed spontaneously. Ammonia was found ubiquitously in nature, so why was it, in contrast to water, so difficult to generate catalytically? The similarity in chemical formulae, NH3 and H2O, provided no clarification: the mystery of ammonia synthesis had begun.

Also of note in connection with the later success of ammonia synthesis and its role in fertilizer is Davy’s realization in 1812 that the presence of NO/NO2 in the lead chamber process increased the likelihood that sulfur dioxide (SO2) would be oxidized to sulfuric acid (H2SO4) with nitrosylsulfuric acid (NOHSO4) as an intermediate step. It was reasoned that the NO/NO2 took the place of platinum in heterogeneous reactions and led to the same dissociation and generation through contact. Ammonia could then be reacted with H2SO4 to make ammonium sulfate ((NH4)2SO4), a form of fixed nitrogen plants can assimilate (fertilizer).

In 1816, Davy performed important experiments on platinum, a metal which soon came to be considered the ultimate catalyst. He burned methane and other gases in air in the presence of a platinum wire below its annealing temperature (the wire was heated in the process and strengthened the theory of the heat capacity). The use of potash as an impurity and a finer, extended distribution of platinum were found to be advantageous, but no explanation could be found. Around this time, Döbereiner described catalytic activity as similar to ice crystal seeding, while Thénard suspected there was an electrical component to the mysterious phenomenon. He ventured the statement that all of the new observations may be due to the same “force” and began to consolidate them under a single description. In the 1820s, Döbereiner continued experiments with platinum and platinum sponges as contact materials. When the metal was in the presence of hydrogen, the gas began to combine with oxygen to form water; if oxygen concentrations were too low, the hydrogen combined with nitrogen to form small amounts of ammonia. The result was again puzzling because the large quantities of nitrogen in air did not lead to an appreciable ammonia yield–nitrogen was obstinate in its refusal to react with hydrogen. Despite the unanswered questions, Döbereiner’s experiments on platinum contributed greatly to the understanding of catalysis and unleashed a wave of research lasting into the 1840s that charted the temperature dependence of an increasing number of metals.

During his experiments, Döbereiner, too, began to consider many of the new observations to be consequences of the same behavior. The reactions were influenced “via mere contact and without participation by outside powers.”Footnote 3 However, he and other scientists did not understand the link between dissociation and association; they are competing and dynamic components of any chemical reaction. Not surprisingly, differing and widespread explanations of catalytic phenomena abounded in the 1820s, although it was clear that they were not “classical” chemical reactions. Rather than the results of catalytic reactions, the nature of catalytic action was becoming the focus of research, as exemplified in Mitscherlich’s work. Despite his and Berzelius’ unifying nomenclature, the terms catalysis and contact were not introduced without friction. Mitscherlich, Berzelius, Liebig, and others had (strongly) differing opinions on catalytic action, and for years the nature of the mechanism underlying the process was contested. Their efforts were, however, strongly influenced by empirical organic chemistry and did not lead to an understanding of the underlying role of a catalyst. With regard to ammonia synthesis in particular, Alwin Mittasch wrote (Mittasch 1951, p. 61),Footnote 4

Although the number of ammonia catalysts and the conceivable synthesis methods that were investigated were continuously expanded by the efforts of the most diverse investigators during the course of a century, the results would inevitably remain negative as long as the tools of the newer chemical research [physical chemistry] could not be applied to their fullest extent. Empirical research and technology could only reach the ambitious goal [of ammonia synthesis] after the establishment of a strict scientific definition of what was theoretically achievable in this henceforth highly focused field.Footnote 5

While it suffices here to state that catalytic or contact processes were defined as their own class of chemical phenomena in the nineteenth century and that the development of physical chemistry allowed for a deeper understanding of the role they play in chemical reactions (raising both forward and backward reaction rates), the mechanism behind catalytic activity has never shed its air of mystery. Somehow, the contact material creates a physical relationship between substances that is otherwise absent. The individual steps of the ammonia synthesis and other catalytic reactions are well-understood on a physicochemical basis for model catalysts such as iron single crystals. However, there is a material gap between model systems and the performance systems used in industry. No consensus exists on the exact nature of the active centers on performance catalyst surfaces and for this reason, complete catalyst engineering is not yet possible (Campbell 1994; Ertl 1980, 1990, 2008; Ertl et al. 1978, 1981, 1983; Schlögl 2003, 2015b, 2020; Somorjai and Park 2009; Spencer et al. 1981, 1982; Stoltze and Nørskov 1985, 1988). Catalysis research remains an evolving field.

Again using ammonia as an example, it was thought for most of the twentieth century that the catalytic ammonia synthesis reaction was completely dependent on the behavior of N2. Specifically, its dissociation (breaking the triple bond between the two N atoms) and its ability to adsorb onto the catalyst surface were seen as hurdles. Adsorbed single nitrogen atoms blocked active sites and impeded further N2 molecules from dissociation; they were the limiting factor for the reaction (Emmett and Brunauer 1933; Ertl et al. 1981). In the past two decades, however, it has emerged that the reaction is much more complex and dependent on microkinetics at the catalyst surface. In addition to the potential energy barrier for N2 dissociation, a different potential barrier can inhibit the hydrogenation of N to NH, NH2, and finally NH3; in general the process grows more difficult over the six hydrogenation steps of two nitrogen atoms and the generation of two molecules of ammonia. Under certain conditions, this barrier may be more limiting than the dissociation of N2. Furthermore, the ability of NH, NH2, and NH3 to adhere to the catalyst surface is of the same order of magnitude as the N atoms and contributes to the satiation of active sites in what is termed autopoisoning. These two important characteristics of a catalyst, the ability to dissociate N2 and to release N, NH, NH2, and NH3 from the surface to free active sites, are linked in a specific and, in conventional catalysts, non-ideal way (scaling relations) that limits the efficacy of today’s materials (Abild-Pedersen et al. 2007; Dahl et al. 2001; Geng et al. 2018; Honkala et al. 2007; Jacobsen et al. 2001; McKay et al. 2015; Poobalasuntharam et al. 2011; Vojvodic and Nørskov 2015; Vojvodic et al. 2014; Wang et al. 2011).

An overview and modern discussion of catalytic phenomena can be found in Schlögl (2015b).

Returning to organic chemistry, the second development we will discuss is the initial isolation (1825) and production (1834) of benzene—a hydrocarbon (its aromatic (ring) structure was proposed later, in 1865, by August Kekulé). The experimental investigation of benzene provides an example of the empirical approach in the nineteenth century and is also the basis for the aniline molecule in which one hydrogen atom from the benzene ring is replaced by an amino group (-NH2). Aniline was the first synthetic dyestuff and played a central role in the rise of the German dyestuff industry (Travis 1993a, pp. 166–178).

Dalton had already recognized the individual hydrocarbon compounds carburetted hydrogen (methane, CH4) and olefiant gas (ethylene, C2H4) at the beginning of the nineteenth century. In 1825, Michael Faraday isolated benzene, which he called bi-carburetted hydrogen (Faraday 1825), (Rocke 1984, pp. 29–40), (Ihde 1964, pp. 101–109). However, lack of knowledge about the structure of hydrocarbons prevented an exact stoichiometric identification. It was Mitscherlich who, in 1834, first synthesized benzene from benzoic acid heated over calcium hydroxide and proposed that it was composed of three proportions of carbon and three proportions of hydrogen (Mitscherlich 1834a), (Gräbe 1920, pp. 59–65), (Ihde 1964, pp. 184–190), (Rocke 1984, pp. 174–175), (Schütt 1992, pp. 114–120). Describing his method of examination, Mitscherich wrote,

If the benzoic acid is brought together with a strong base…and the mixture submitted to distillation, initially water will separate before a thin, oily fluid, develops which floats on top of the water. If the mixture is very slowly warmed, the residue in the retort is completely colorless and leaves no trace if dissolved with acid, [a reaction which] evolves carbonic acid; the solution in the acid is colorless and no gas is evolved during distillation. The benzoic acid disaggregates, therefore, into carbonic acid and an oily liquid [which turned out to be benzene] […] Because this liquid can be obtained from benzoic acid and is likely related to the benzoyl compound, it should preferably be named benzol [benzene]…Footnote 6

Distillation and combustion were two important methods of elementary analysis used in the nineteenth century to asses the makeup of organic matter (for example, of leaves) (Ihde 1964, pp. 173–179). For contrast, these empirical tools may be compared to the approaches of Haber and Nernst between 1903 and 1908 in the context of physicochemical experiments. Combined with catalysis, the conceptual tools of the empirical period of organic analysis made important contributions to the development of the chemical industry–even if they could not be used to determine a method for ammonia synthesis from the elements. Though it was not the first interaction between chemistry and industry (Scholz 1987), the dyes derived from aniline and other aromatic molecules after about 1860 were crucial in allowing the chemical industry to amass the capital and infrastructure that later allowed for a generous investment in ammonia synthesis research.

Aniline was identified in 1826 and had been isolated several times before August Wilhelm von Hofmann, a student of the Liebig School, clarified its constitution (C6H7N) in 1843 (Hofmann 1843; Perkin 1862; Zinin 1842), (Gräbe 1920, pp. 139–147, 213–219). It was during his research into the makeup of coal tar, which was considered a useless and even bothersome byproduct of the coking industry, that he improved the distillation process used to obtain aniline and realized it was available in larger quantities than originally thought. The discovery was important: the economic potential of aniline had already been identified for the production of synthetic (or coal tar) dyes. If aniline could be obtained cheaply it would facilitate the manufacture of these materials: they could replace the often costly biological sources of colorant and transform the growing international textile industry (Travis 1993a, pp. 31–33).

The first aniline-based dyestuff was aniline purple (also called tyrian purple or mauve), produced in 1856 by William Henry Perkin, a student of Hofmann’s. At the time, the British Empire was fighting the Crimean War and needed quinine to combat malaria. During his attempts to produce quinine, Perkin employed a simpler reaction involving aniline sulfate and potassium bichromate, which resulted in “a very unpromising black precipitate.” The substance, however, contained aniline purple and Perkin was able to isolate it (Perkin 1862). Helped by the Béchamp process for the large scale reduction of nitrobenzene to aniline (Béchamp 1854), it became the first commercially produced dyestuff made from coal tar and essentially started the modern organic chemical industry. In the same year, Perkin patented the production process. Later, he noted the role of pure science in his discovery, a quotation one could easily apply to ammonia synthesis (Perkin 1862).

…the process which is now employed for [the preparation of aniline] is a remarkable instance of the manner in which abstract scientific research becomes in the course of time of the most important practical service.

Perkin’s undertaking resulted not only in the development of new technology for chemical treatment and textile printing, but his success led others, including August Wilhelm von Hofmann himself, to enter the coal tar dye industry and draw on Perkin’s patented process. While the new dyes were not as durable as the original, they were more brilliant and more popular with the public. Soon, the competition, especially the aniline dye fuchsine, drove mauve from the market, and the new products secured the future of the industry (Edelstein 1961, pp. 759–765), (Travis 1993a, pp. 31–64).

The emergence of the coal tar dye industry brought together men of different backgrounds. Expertise in chemistry, catalysis, the printing trade, and engineering as well as access to capital all shared in making the new industry lucrative. The company BASF, which will appear again during Fritz Haber’s work on ammonia, illustrates the successful synthesis of these fields as well as the growth and hybridization of chemistry and industry (Abelshauser et al. 2004, pp. 1–27).

A forerunner company to BASF was founded in Mannheim in 1861 by Friedrich Engelhorn, the son of a brewmaster. Born in Mannheim in 1821, he left his hometown for nine years as a young man to travel Europe and further his education in the jewelry trade. In 1846, he returned as the small city of Mannheim began to feel the effects of the industrial revolution. Engelhorn’s experiences during his travels had brought him to European centers transformed by industrialization and, once back in Mannheim, he decided to pursue a career in industry rather than jewelry. In 1848, he founded a company that produced bottled gas for lighting–a mark of modern, industrialized cities. By 1851, his business had expanded and taken over the lease of the Mannheim gas works. Engelhorn himself directed the company both commercially and technically. In 1865, he sold his share in the company to concentrate on the aniline and dyestuff factory he had built next to the gas works several years earlier. Engelhorn had immediate access to a supply of coal tar from the neighboring gas production facility and benefited from the growing chemical infrastructure in Mannheim from which he obtained important precursor chemicals. Engelhorn chose Carl Clemm as technical director of the new company, a chemist who had experience with aniline dyes. Clemm had been recommended by his uncle Carl Clemm-Lennig, the director of the Mannheim Fertilizer Factory and former student of the Liebig School.

While other chemical companies began producing coal tar dyes in addition to their usual commercial products, Engelhorn focused on large-scale dye production from the beginning. Throughout the first half of the 1860s, his company continued to expand its infrastructure and hired Carl Clemm’s younger brother August as second technical director. The growth was so swift that Engelhorn soon wondered whether it would not be more profitable to produce the needed inorganic chemical precursors himself rather than continuing to purchase them from Mannheim’s established chemical provider, the Association of Chemical Factories.Footnote 7 Engelhorn approached the association in 1864 in an attempt to negotiate a better deal for his company, but when the agreement failed he decided to enter into direct competition and manufacture his own chemicals. At this time, the venture was risky because the establishment of other dye companies had made the future profitability of Engelhorn’s company, now called Sonntag, Engelhorn & Clemm, anything but certain. The breadth of the undertaking was too cost intensive for the company to spearhead on its own so Engelhorn turned to the Mannheim bank W.H. Ladenburg & Sons for assistance. Engelhorn’s standing in the industrial community of Mannheim, along with the reputations of the Clemms and fellow founder Friedrich August Sonntag, helped the partners secure the necessary funds from the bank and other investors to establish the first largely self-sufficient coal tar dye company. In 1865 the Badische Anilin- & Soda-Fabrik (BASF) was born.

Engelhorn had originally wished to keep the company in Mannheim but difficulties in negotiating the purchase of a suitable building site caused the company to look elsewhere. Eventually, he found a site across the Rhine River in Ludswigshafen. The smaller town was excited by the chance to catch up to its larger neighbor on the eastern bank and quickly authorized the purchase of the necessary land. The official seat of BASF remained, however, in Mannheim until 1919. Almost immediately, plans were finalized for new buildings and modern lighting. Rail links were proposed to connect the site to western destinations and the construction of a new bridge over the river connected rail lines to the east. The location also offered water, waste removal, and shipping opportunities from the Rhine. The Ludwigshafen site was ideal (Fig. 3.2).

Fig. 3.2
figure 2figure 2

The development of the BASF site at Ludwigshafen (1866–1901). This page, top: a photograph of a painting by Otto Bollhagen completed circa 1922, showing the site as it was circa 1866; bottom: 1873, drawing by W. Menges; 1881; Opposite page, top: painting by Robert Stieler; 1901; bottom: lithograph by Christoph Seitz. Source: BASF SE, Corporate History, Ludwigshafen

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Engelhorn lost no time initiating his plans of comprehensive dyestuff production on an unprecedented level. The company had been structured to allow access to new capital in the event of expansion, which, combined with the wealth of chemical and commercial experience, the internal production of precursor chemicals, and geographical advantages, launched BASF into the position of industry leader for decades. During this time, in 1865, it entered into agreements with partner companies and divided the dyestuff market to limit competition and increase efficiency—a practice that became common in the industry. BASF produced only red aniline dyes (fuchsine), which allowed it to invest resources in its inorganic chemistry department and expand the related infrastructure and expertise. At the end of the 1860s, a theoretical basis, in particular structural formulae, began to strengthen the empirical approach to organic molecule synthesis. Kekulé’s 1865 description of benzene as a ring of six carbon atoms was used to describe more complicated molecules and aided in the production of new synthetic dyestuffs. This is exemplified by alizarin, a synthetic replacement of the dye produced from the madder root. In 1868, in Adolf Baeyer’s laboratories at the Gewerbe Institute in Berlin, Carl Graebe and Carl Liebermann successfully synthesized alizarin from anthracene and anthraquinone, aided by the new theoretical considerations: all three molecules are fusions of three aromatic carbon rings (with appropriate substitutions of the hydrogen atoms). It was an important step in the synthesis of naturally occurring materials. Alizarin would be important for BASF’s continued success and the company obtained the patent rights soon after Graebe and Liebermann’s initial achievement, partly due to the efforts of Heinrich Caro. Caro had come to BASF in 1868 and, beyond his connections to W.H. Perkin and others in the English and German chemical industries, had developed organic synthesis methods with a science-based approach that proved valuable to his employer. He was joined in 1869 by Carl Glaser as part of a Friedrich Engelhorn’s continued effort to secure scientifically skilled employees. Graebe, Liebermann, Caro and Glaser later improved and upscaled the production of alizarin; the process remained central to BASF’s dyestuff activities until the end of the nineteenth century. It was not until Heinrich Brunck emerged as Engelhorn’s successor in the mid-1880s, however, that BASF’s era of “scientific competence, applications-oriented pragmatism, and longer-term planning” began in earnest and led to the inorganic chemical expertise key to the industrial upscaling of ammonia synthesis (Travis 1993a, pp. 163–178), (Abelshauser et al. 2004, pp. 23–37).

Originally, the inorganic department had served as BASF’s own source of starting materials for the dye department to produce chlorine, anthranilic acid, and other chemicals for the lucrative indigo. However, helped by the pervasive spirit of innovation at the company, the inorganic department gained autonomy by the turn of the twentieth century through the advances and experience gained under the leadership of Rudolf Knietsch. The implementation of his contact process for the production of sulfuric acid, a precursor chemical for indigo, was so successful that BASF went from a consumer to net industry supplier. BASF’s initial, failed attempts to synthesize ammonia from the elements with Wilhelm Ostwald in 1900 also took place in Knietsch’s laboratories, as did research on the electric arc and cyanamide processes. During this time, the effect of pressure and different catalysts on chemical yields were examined and the influence of additives on catalytic materials became evident. These and other ventures helped BASF diversify beyond dyestuffs and were important for the later expansion of the inorganic chemical industry (Mittasch 1951, pp. 87–88), (von Nagel 1991, pp. 13–15), (Reinhardt 1997, p. 240), (Abelshauser et al. 2004, pp. 30–57, 70–72).

Other chemical companies were also founded in the 1860s, including Hoechst, Bayer, and Agfa. Coal tar dyes grew beyond their original fashionable niche into one of the most important products of the industry. The change was aided by a prominent showcase of the newly available dyestuffs at the 1862 International Exhibition in London. From humble beginnings with aniline, to the replacement of organic dyes with azo and synthetic alizarin dyes, to synthetic indigo, dyestuffs had developed significantly. By 1900, the sale of these products helped the chemical industry gain the financial means to fund ammonia synthesis research (Haber 1958, pp. 80–91), (Travis 1993a, pp. 214–228, 237–239), (Abelshauser et al. 2004, pp. 57–70).Footnote 8

As the nineteenth century drew to a close, the growth of the dye industry led to a more intertwined relationship with scientific chemical research (Basalla 1988, p. 28). The recognition of science as a profession had gained traction throughout the century and the increased involvement of academics as employees in the dye companies fostered a closer alliance. Whereas in 1800 there were about 1000 professional scientists in the world, that number grew to about 10,000 by 1850 and 100,000 by 1900 (Greenaway 1966, pp. 33–34). The occupation of the chemist was also effected by this trend. Whereas in 1800 there had been approximately 200 professional working chemists, the number increased to about 6000 by 1895 (Scholz 1987, p. 166). BASF itself had 78 chemists in 1892, 65 holding a PhD (Travis 1993a, p. 220). They were not only researchers; chemists were often in the highest positions in the industry and made crucial strategies and economic decisions.

Thus, at the beginning of the twentieth century, there was a strong tradition of science in Prussia awaiting Fritz Haber and Walther Nernst (Kennedy 1987, p. 209–211), (Schütt 1992, pp. 152–165), (Travis 1993a, pp. 62–64), (Leigh 2004, p. 113), (Harwood 2005, pp. 77–91), (Klein 2015a, pp. 17–20, 273–278). Through them “an old Berliner tradition of the ‘relationships between chemistry and physics’ found its continuation and consolidation in a distinguished way (Bartel 1989, p. 69).”Footnote 9 Or, if we turn to the words of Wilhelm Ostwald from 1903 (Ostwald 1903),

If one asks about the means through which this state is reached, a decisive factor can be identified in the systematic exploitation of scientifically trained workers. No other nation has access to the human resources provided to German industry by our universities and trade schools. As long as this relationship is maintained any foreign competition may be discounted.Footnote 10

At the end of the nineteenth century, the knowledge, infrastructure, and financial assets were largely in place to tackle the more challenging problem of ammonia synthesis from the elements (Szöllösi-Janze 1998b, pp. 161–162). As we have seen, other factors revealing the need for a synthesis process had been understood for some time. The integral role of ammonia and fixed nitrogen in agriculture had been accepted for decades, its importance underscored by the growing world population. The main source of this nitrogen, imports from the saltpeter mines in Chile, were a limited natural resource and subject to import blockades; they had also been the focus of the five year War of the Pacific. Global stability and national safety were in question. However, despite this context and decades of attempts to synthesize ammonia, a solution had not been found.

Here again we consider Alwin Mittasch’s sentiments. The empirically based approach to chemical synthesis and catalysis in the nineteenth century made large contributions to the chemical industry, but they were not adequate to offer a solution to ammonia synthesis from the elements. There was still a missing component that would be found in a conceptual expansion within the scientific community itself. It allowed a holistic (or global) view and control of chemical reactions to alleviate the pressing problems of large scale, diverse industrial chemical production. This knowledge was gained during an intellectual transformation, during which scientists learned to view chemical processes as a problem at the intersection, or perhaps defining the intersection between chemistry and physics. Only with new theoretical tools was it possible to understand the fundamental concept of equilibrium in a chemical reaction and the exact role of a catalyst. The recognition, missed by the pioneers of catalysis, was that the dissociation and generation of a substance were linked and that the reaction was, therefore, reversible.