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Upon oxygen depletion, a suite of alternate oxidants supports microbial respiration and inhibits the onset of sulfate (SO₄ ²) reduction. Waters in this intermediate state are referred to as ‘oxygen deficient’ or ‘suboxic’. This chapter discusses types of suboxic water column respiration, their occurrence, variability, and significance. Methodological problems are also discussed. Nitrate (NO₃ ^-) is the most abundant suboxic electron acceptor in oceanic water, but the suite of alternate oxidants includes nitrite (NO₂ ^-), nitric oxide (NO), nitrous oxide (N₂O), iodate (IO₃ ^-), manganese (Mn III and IV), iron (Fe III), and several other oxidants present at low concentrations. Although canonical denitrification, which involves reduction of nitrate to N₂O and N₂ is probably the single most important suboxic respiratory pathway in the water column, important additional respiratory pathways for dinitrogen (N₂) and N₂O production are also considered.

This chapter describes efforts to improve the fertility of California's soils. During the late nineteenth and early twentieth centuries, nitrogen depletion in California's soils was a major concern. Farmers relied on two imports from Chile—nitrogen-rich Chilean alfalfa (Medicago sativa) and Chilean sodium nitrate (NaNO₃)—to meet the nutrient demands of a continuously expanding agricultural system. Chilean alfalfa was indispensable to the emergence of Northern California's profitable dairy businesses, which made California into the nation's top milk butter, ice cream, and yogurt-producing state by the end of the twentieth century. Chilean sodium nitrate was essential to Southern California's prosperous citrus-fruit industry, which served as that region's primary engine of economic growth from the 1880s through World War II.

I shall now introduce you to one of the simplest kinds of chemical reaction: precipitation, the falling out from solution of newly formed solid, powdery matter when two solutions are mixed together. The process is really very simple and, I have to admit, not very interesting. However, I am treating it as your first encounter with creating a different form of matter from two starting materials, so please be patient as there are much more interesting processes to come. I would like you to regard it as a warming-up exercise for thinking about and visualizing chemical reactions at a molecular level. Not much is going on, so the steps of the reaction are reasonably easy to follow. There isn’t much to do to bring about a precipitation reaction. Two soluble substances are dissolved in water, one solution is poured into the other, and—providing the starting materials are well chosen—an insoluble powdery solid immediately forms and makes the solution cloudy. For instance, a white precipitate of insoluble silver chloride, looking a bit like curdled milk, is formed when a solution of sodium chloride (common salt) is poured into a solution of silver nitrate. Now, as we shall do many times in this book, let’s imagine shrinking to the size of a molecule and watch what happens when the sodium chloride solution is poured into the silver nitrate solution. As you saw in my Preliminary remark, when solid sodium chloride dissolves in water, Na+ ions and Cl– ions are seduced by water molecules into leaving the crystals of the original solid and spreading through the solution. Silver nitrate is AgNO3; Ag denotes a silver atom, which is present as the positive ion Ag+; NO3– is a negatively charged ‘nitrate ion’, 1. Silver nitrate is soluble because the negative charge of the nitrate ion is spread over its four atoms rather than concentrated on one, 2, as it is for the chloride ion, and as a result it has rather weak interactions with the neighbouring Ag+ ions in the solid.

Nitrate is the most common chemical contaminant in groundwater, affecting both human health and ecosystems. This chapter discusses how nitrate in groundwater has affected the health of the Chesapeake Bay and how it takes decades for changes in farming practices to reverse these trends. The chapter also examines the human health impacts of nitrate in groundwater within poor communities in California’s Central Valley. The chapter concludes with a discussion of source water protection by illustrating the comprehensive program for mapping groundwater protection zones in Denmark.

The problem of photochemically generated smog begins inside internal combustion engines, where at the high temperatures within the combustion cylinders and the hot exhaust manifold nitrogen molecules and oxygen molecule combine to form nitric oxide, NO. Almost as soon as it is formed, and when the exhaust gases mingle with the atmosphere, some NO is oxidized to the pungent and chemically pugnacious brown gas nitrogen dioxide, NO2, 1. We need to watch what happens when one of these NO2 molecules is exposed to the energetic ultraviolet photons in sunlight. We see a photon strike the molecule and cause a convulsive tremor of its electron cloud. In the brief instant that the electron cloud has swarmed away from one of the bonding regions, an O atom makes its escape, leaving behind an NO molecule. We now continue to watch the liberated O atom. We see it collide with an oxygen molecule, O2, and stick to it to form ozone, O3, 2. This ozone is formed near ground level and is an irritant; ozone at stratospheric levels is a benign ultraviolet shield. Now keep your eye on the ozone molecule. In one instance we see it collide with an NO molecule, which plucks off one of ozone’s O atoms, forming NO2 and letting O3 revert to O2. Another fate awaiting NO2 is for it to react with oxygen and any unburned hydrocarbon fuel and its fragments that have escaped into the atmosphere. We can watch that happening too where the air includes surviving fragments of hydrocarbon fuel molecules. A lot of little steps are involved, and they occur at a wide range of rates. Let’s suppose that some unburned fuel escapes as ethane molecules, CH3CH3, 3. Although ethane is not present in gasoline, a CH3CH2· radical (Reaction 12) would have been formed in its combustion and then combined with an H atom in the tumult of reactions going on there. You already know that vicious little O atoms are lurking in the sunlit NO2-ridden air. We catch sight of one of their venomous acts: in a collision with an H2O molecule they extract an H atom, so forming two ·OH radicals.

This penultimate chapter addresses the ecological consequences of the British "large planet" diet. The first part of the chapter examines the rise of mined, imported, or manufactured fertilizers: coprolites, superphosphates, Chilean nitrates, guano, and synthetic nitrates. It then explores the ecologies of vast frontier monocultures and mechanized agriculture. The chapter addresses the global agrarian crisis of the 1930s, particularly the phenomenon of the global dustbowl, which seemed to many contemporaries to be a portent that agricultural intensification was damaging planetary ecosystems. It also explores the rise of novel, intensified, systems of factory farming involving chicken and pigs. The final part of the chapter looks at the development of a backlash to the British world food system, in the form of vegetarianism and organic agriculture.

Photochemistry provides the important driving force that initiates chemistry in the atmosphere. We saw in Chapter II how light absorbed by ozone generates the important HO radical, and, in Chapter III, we reviewed how light absorption by NO2 leads to ozone formation. In this chapter, we discuss the photochemistry of the light-absorbing oxygenates: their photochemical lifetimes and the nature of the modes of photodecomposition they undergo. Of course, light of sufficient energy per quantum must be absorbed by a molecule if its photodecomposition is to occur. The hydrocarbons do not absorb tropospheric sunlight, as seen in Figure VIII-A-1. The light gray and dark gray lines, respectively, show the distribution of actinic flux present in the troposphere and upper stratosphere for overhead Sun. It can be seen that the larger alkanes, alkenes, and aromatic hydrocarbons absorb at somewhat longer wavelengths than the first member of the family, but none can be electronically excited by tropospheric radiation. Among the hydrocarbons, only the polycyclic aromatics absorb appreciable tropospheric sunlight, and their π → π* excitation does not result in decomposition but likely generates O2(1Δg) molecules by energy transfer; these molecules are usually quenched by collision to ground state O2(3Σg−) molecules (see Calvert et al., 2000). As atmospheric oxidation of the hydrocarbons occurs, initiated largely by HO radicals, a multitude of oxygenated organic species are generated. The absorption region for the oxygenates is generally shifted to longer wavelengths, although the alcohols, ethers, acids, and esters still show no overlap of the regions of tropospheric actinic flux. For the families of compounds shown, the only significant absorbers of tropospheric sunlight are the aldehydes (e.g., CH2O) and the ketones (e.g., CH3C(O)CH3). Formic acid and methyl formate, as well as the larger members of the acid and ester families, absorb sunlight available only at the higher altitudes of the stratosphere, where they are expected to photodecompose. However, these species are not expected to be present in the stratosphere because they are removed in the troposphere largely via HO reactions. In this chapter, we focus on the rates and pathways for photodecomposition of the aldehydes and ketones with less detailed considerations of the other less prevalent light-absorbing trace compounds.

The many different nitrogen-containing oxygenated volatile organic compounds that are present in the troposphere play important roles in the chemistry of our atmosphere. They can be emitted directly into the atmosphere, such as in the case of amides that are widely used as organic solvents, starting materials, or intermediates in different industries (e.g., synthetic polymers, manufacture of dyes, and synthesis of pesticides). Amides are formed in situ as intermediate products in the degradation of amines (e.g., see Tuazon et al., 1994; Finlayson-Pitts and Pitts, 2000). Nitrogen-containing oxygenated organic compounds are formed in the atmosphere also via reactions of alkoxy (RO) and alkyl peroxy radicals (RO2) with NO or NO2 leading to alkyl nitrates, alkyl nitrites, and peroxy acetyl nitrates. However, primary sources of these organic species have also been suggested such as diesel and other engines and biomass burning (e.g., see Simpson et al., 2002). Alkyl nitrates (RONO2) have been detected in both the urban and the remote troposphere (e.g., see Roberts, 1990; Walega et al., 1992; Atlas et al., 1992; Ridley et al., 1997; and Stroud et al., 2001; see also section I-D). Nitrates are formed as minor products in the reaction of peroxy radicals with NO. The nitrate yield increases with the size of peroxy radicals and can be as high as 20–30% for large (>C6) radicals (Calvert et al., 2008). Peroxyacyl nitrates (RC(O)O2NO2) are important constituents of urban air pollution. They have been identified in ambient air (e.g., see Bertman and Roberts, 1991; Williams et al., 1997, 2000; Nouaime et al., 1998; Hansel and Wisthaler, 2000; also see section I-D). They are formed from photochemical reactions via RC(O)O2 + NO2. A major role of these compounds is their capacity to act as a reservoir for NOx that can be transported from polluted urban to remote regions that are poor NOx regions and where their presence can increase NOx levels (Roberts, 1990). As with other volatile organic compounds (VOCs), once released to the atmosphere, nitrogen-containing organic compounds are expected to undergo degradation primarily via reaction with hydroxyl and nitrate radicals, reaction with ozone, and photolysis. Thermal decomposition is an important loss process for the peroxyacyl nitrates.

This chapter examines the abiotic environment of giant kelp. Macrocystis requires a hard substratum for settlement and attachment, water temperatures between about 4°C and 20°C, sea-bottom light intensities equivalent to 1% or greater than sea-surface irradiance, nitrate concentrations, oceanic salinities, and protection from extreme water motion. Macrocystis occupies much of the Pacific coast of California and Baja California, Mexico. It may be restricted by waters that are too warm or too low in nutrients, or severe water motion. Giant kelp forests flourish and are particularly well developed on outer coasts between depths of around 5 m and 20 m, beyond which sea-bottom light is often decreased for effective recruitment and growth. Macrocystis is usually absent from estuaries and far inside of protected bays because of a shortage of rocky substrata, increased sedimentation, and reduced light. Reduced salinity can also restrict Macrocystis in bays and other areas with large freshwater inputs.

When it became clear that nutrients cause the rise of dead zones, scientists next examined the possible sources of the nutrients. This chapter argues the biggest source today is agriculture. The expansion of the Gulf of Mexico dead zone directly follows the huge increase in agricultural productivity, especially for corn. Yields increased over six times since 1930 in part because farmers used more fertilizer, “to give the land a kick.” As the chapter explains, Nancy Rabalais and Gene Turner found a direct link between fertilizer use and nutrient levels in the Mississippi River. In spite of opposition from agribusinesses, their work led to the formation of a White House committee and passage of legislation to support work on the hypoxia problem. Agriculture is also the main source of nutrients feeding dead zones in other regions of the world. The chapter later points out that the biggest user of fertilizer is now China, where excessive nutrients have caused massive harmful algal blooms and other environmental problems.

June, when the snows come hurrying from the hills and the bridges often go, in the words of Emily Dickinson. In the beaver meadow, the snows are indeed hurrying from the surrounding hills. Every one of the 32 square miles of terrain upslope from the beaver meadow received many inches of snow over the course of the winter. Some of the snow sublimated back into the atmosphere. Some melted and infiltrated into the soil and fractured bedrock, recharging the groundwater that moves slowly downslope and into the meadow. A lot of the snow sat on the slopes, compacted by the weight of overlying snow into a dense, water-rich mass that now melts rapidly and hurries down to the valley bottoms. North St. Vrain Creek overflows into the beaver meadow, the water spilling over the banks and into the willow thickets in a rush. I can hear the roar of water in the main channel well before I can see it through the partially emerged leaves of the willows. Overhead is the cloudless sky of a summer morning. A bit of snow lingers at the top of the moraines. Grass nearly to my knees hides the treacherous footing of this quivering world that is terra non-firma. I am surrounded by the new growth of early summer, yet the rich scents of decay rise every time I sink into the muck. I walk with care, staggering occasionally, in this patchy, complex world that the beavers have created. I abruptly sink to mid-thigh in a muck-bottomed hole, releasing the scent of rotten eggs, but less than a yard away a small pocket of upland plants is establishing a roothold in a drier patch. A seedling spruce rises above ground junipers shedding yellow pollen dust and the meticulously sorted, tiny pebbles of a harvester ant mound. I extract my leg with difficulty and continue walking. As I walk around the margin of another small pond, the water shakes. Sometimes the bottom is firm in these little ponds, sometimes it’s mucky–I can’t tell simply by looking through the water.

Gibbs’ work was disseminated along two different paths. Path 1: Gibbs -> Maxwell -> Pupin -> Helmholtz -> van’t Hoff -> community. Path 2: Gibbs -> van der Waals -> Roozeboom -> community. This dissemination provided the means for Francis Arthur Freeth to employ the Gibbs phase rule in practice. Concluding discussion concerns the translation of Gibbs work.

Cheap meat, dairy, and eggs are an illusion—we pay for each with depleted forests, polluted freshwater, soil degradation, and climate change. Diet is the most critical decision we make with regard to our environmental footprint—and what we eat is a choice that most of us make every day, several times a day. Dietary choice contributes powerfully to greenhouse gas emissions (GHGE) and water pollution. Animal agriculture is responsible for an unnerving quantity of greenhouse gas emissions. Eating animal products—yogurt, ice cream, bacon, chicken salad, beef stroganoff, or cheese omelets—greatly increases an individual’s contribution to carbon dioxide, methane, and nitrous oxide emissions. Collectively, dietary choice contributes to a classic “tragedy of the commons.” Much of the atmosphere’s carbon dioxide (CO2) is absorbed by the earth’s oceans and plants, but a large proportion lingers in the atmosphere—unable to be absorbed by plants or oceans (“Effects”). Plants are not harmed by this process, but the current overabundance of carbon dioxide in the atmosphere causes acidification of the earth’s oceans. As a result of anthropogenic carbon dioxide emissions, the “acidity of the world’s ocean may increase by around 170% by the end of the century,” altering ocean ecosystems, and likely creating an ocean environment that is inhospitable for many life forms (“Expert Assessment”). Burning petroleum also leads to wars that devastate human communities and annihilate landscapes and wildlife—including endangered species and their vital habitats. Additionally, our consumption of petroleum is linked with oil spills that ravage landscapes, shorelines, and ocean habitat. Oil pipelines run through remote, fragile areas—every oil tanker represents not just the possibility but the probability of an oil spill. As reserves diminish, our quest for fossil fuels is increasingly environmentally devastating: Canada’s vast reserves of tar sands oil—though extracted, transported, and burned only with enormous costs to the environment—are next in line for extraction. Consuming animal products creates ten times more fossil fuel emission per calorie than does consuming plant foods directly (Oppenlander 18). (This is the most remarkable given that plant foods are not generally as calorically dense as animal foods.) Ranching is the greatest GHGE offender.

Humans have long recognized the hazards of microbial contamination of drinking water. Only since the 1960s, however, have epidemiologic studies systematically examined whether naturally occurring and/or manmade pollutants in drinking water affect cancer risk. Ironically, some of the measures taken to reduce microbial hazards have increased exposure to other contaminants. This chapter begins by discussing three waterborne exposures that affect large numbers of people and have been studied most extensively: inorganic arsenic, disinfection byproducts, and nitrate. Of these, only arsenic and its compounds are currently designated as carcinogenic to humans. It then discusses the evidence concerning two emerging issues: the carcinogenicity of toxins from cyanobacteria, an ancient and ubiquitous family of prokaryotic organisms formerly known as blue-green algae, now affected by climate change, and the methods of studying cancer in local communities where the water supply has been contaminated by industrial chemicals. Methodologic challenges complicate studies of these issues.

A wide range of trace gases, including dimethyl sulphide (DMS) and organohalogens, are formed in the surface oceans via biological and/or photochemical processes. Consequently, these gases become supersaturated in seawater relative to the overlying marine air, leading to a net flux to the atmosphere. Upon entering the atmosphere, they are subject to rapid oxidation or radical attack to produce highly reactive radical species which are involved in a number of important atmospheric and climatic processes. Organohalogens can affect the oxidizing capacity of the atmosphere by interacting with ozone, with implications for air quality, stratospheric ozone levels, and global radiative forcing. DMS and iodine-containing organohalogens (iodocarbons) can both contribute to direct and indirect impacts of aerosols on climate through the production of new particles and cloud condensation nuclei (CCN) in the clean marine atmosphere. Therefore, marine trace gases are considered a vital component of the earth’s climate system, and changes in the net production rate and subsequent sea-to-air flux could have an impact on globally important processes. In recent years, attention has turned to the impact that future ocean acidification may have on the production of such gases, with the greatest focus on DMS and organohalogens. In this chapter, the current state-of-the-art in this growing area of research is outlined. The oceans are a major source of sulphur (S), an element essential to all life, and marine emissions of the gas DMS (chemical formula (CH3)2S) represent a key pathway in the global biogeochemical sulphur cycle. The surface oceans are supersaturated with DMS relative to the atmosphere, resulting in a oneway flux from sea to air (Lovelock et al. 1972; Watson and Liss 1998). DMS is a breakdown product of the biogenically produced dimethyl sulphoniopropionate (DMSP): . . . (CH3)2S+CH2CH2COO- → (CH3)2S + CH2CHCOOH (acrylic acid) (11.1) . . . Single-celled marine phytoplankton are the chief producers of DMSP, and this reaction is catalysed intra- and extracellularly by the enzyme DMSP-lyase (Malin et al. 1992; Liss et al. 1997). The capacity of phytoplankton to produce DMSP varies between species, with prymnesiophytes considered to be the most prolific (Malin et al. 1992 ; Liss et al. 1997 ; Watson and Liss 1998).

Hydrological processes exert strong control over biological and climatic processes in every ecosystem. They are particularly important in the boreal zone, where the average annual temperatures of the air and soil are relatively near the phase-change temperature of water (Chapter 4). Boreal hydrology is strongly controlled by processes related to freezing and thawing, particularly the presence or absence of permafrost. Flow in watersheds underlain by extensive permafrost is limited to the near-surface active layer and to small springs that connect the surface with the subpermafrost groundwater. Ice-rich permafrost, near the soil surface, impedes infiltration, resulting in soils that vary in moisture content from wet to saturated. Interior Alaska has a continental climate with relatively low precipitation (Chapter 4). Soils are typically aeolian or alluvial (Chapter 3). Consequently, in the absence of permafrost, infiltration is relatively high, yielding dry surface soils. In this way, discontinuous permafrost distribution magnifies the differences in soil moisture that might normally occur along topographic gradients. Hydrological processes in the boreal forest are unique due to highly organic soils with a porous organic mat on the surface, short thaw season, and warm summer and cold winter temperatures. The surface organic layer tends to be much thicker on north-facing slopes and in valley bottoms than on south-facing slopes and ridges, reflecting primarily the distribution of permafrost. Soils are cooler and wetter above permafrost, which retards decomposition, resulting in organic matter accumulation (Chapter 15). The markedly different material properties of the soil layers also influence hydrology. The highly porous near-surface soils allow rapid infiltration and, on hillsides, downslope drainage. The organic layer also has a relatively low thermal conductivity, resulting in slow thaw below thick organic layers. The thick organic layer limits the depth of thaw each summer to about 50–100 cm above permafrost (i.e., the active layer). As the active layer thaws, the hydraulic properties change. For example, the moisture-holding capacity increases, and additional subsurface layers become available for lateral flow. The mosaic of Alaskan vegetation depends not only on disturbance history (Chapter 7) but also on hydrology (Chapter 6).

Stories of people doing their jobs well, treating each other with respect, and trying to make the world a better place are all examples of “good news.” Such stories don’t generate many website hits, nor do they bring people into the theaters. Instead, it seems readers and movie viewers would rather have the double pleasure of learning about bad behavior and its comeuppance. Five movies in this chapter overcome this problem; they are based on true stories. The advantage of such stories is the sympathy viewers feel as they appreciate the adversities the chemist has overcome to make their celebrated findings. For instance, in the documentary Me & Isaac Newton, which explores the motivations of seven scientists, pharmaceutical chemist Gertrude Elion is warm and charming as she describes why she decided to become a chemist. When she later describes her struggles to enter graduate school and then get a job as a chemist, the viewer is struck by her matter-of-fact, water-under-the-bridge tone. This all happened before she understood there was a climate of active discrimination against women that had nothing to do with their drive or abilities. Still later, she says the ultimate reward for all her work comes when someone thanks her for having developed the drug that cured a loved one. The disadvantage of using true stories is the need to create dramatic tension. The important moments in people’s lives rarely coincide with obvious indications that “this is the moment when everything fell into place,” whereas a movie’s linear narrative has to make that point clear to the audience. Another problem for moviemakers is that most people just aren’t very curious about the origins of everyday things. This is a challenge because very few chemicals cause the imagination to soar (unless you are a chemist), which may explain why all five movies based on true stories are about medicinal chemistry, which can be seen as the external evidence of the chemist’s desire to do good things for other people. Fictional movie chemists are less likely to develop medicines. Like the chemistry professors in chapter 8, they tend to develop chemical products for more selfish reasons.

At the time of publishing, it is exactly 50 years since Bob Dylan answered a number of enigmatic questions with the ambiguous line ‘the answer is blowin’ in the wind’ on the A-side of the record The Freewheelin’ Bob Dylan. But one of these, ‘How many years can a mountain exist before it’s washed to the sea?’ we can at least try to answer, as part of the solution lies in one of the more famous rules of thumb one learns as a novice chemist: positively charged metal ions combined with oxides (O2−), sulphides (S2−), phosphates (PO43− ), silicates (SiO42−), and carbonates (CO32−), are insoluble in water, whereas similar nitrates (NO3− ), chlorides (Cl−), and bromides (Br−), are soluble. In terms of stuff you’ve got in your kitchen, this means that when you put a spoon of table salt (NaCl) into water it will ‘disappear’, faster if you stir or heat, and the water will look exactly the same as before. For the insoluble stuff, we move to the more expensive regions of the cupboards and investigate the state of our silver and copperware. When things like these were to be on display, my mother used to have me clean them with silver or copper polish, as the oxides and sulphides tarnishing the metal surfaces did not go away in a normal wash with water—they are completely insoluble. A suitable but boring exercise, and as close to a chemistry set as I ever came as a child. What they normally don’t tell you in chemistry textbooks however, are the enormous consequences of these rules, visible all over the world. Why are mountains made of rocks from oxides, sulphides, phosphates, silicates, and carbonates? Because they are insoluble! Any mountains made from sodium chloride would indeed have been ‘washed to the sea’ thousands of years ago, and where NaCl can be mined it is also known as rock salt, and found either underground or in regions with a very dry climate. Which brings us to the hero and heroine if this chapter.

This is the first extensive interview with the “Orpheus of nitrate,” Bill Morrison, whose forte is finding interesting imagery, often imagery with obvious film decay, in celluloid film archives, then fashioning this material into works of his own. Morrison has explored American archives—most often, the paper print collection in the Library of Congress and the Moving Image Research Collections housed at the University of South Carolina, which archive the outtakes of the newsreels Fox Movietone produced for theatrical exhibition between 1928 and 1963; and recently, a collection of early silent films unearthed in the permafrost in Dawson City, Canada. Morrison is particularly drawn to moments when obvious film decay seems related to the content or implications of the imagery that remains uncorrupted. Morrison’s breakthrough feature, Decasia (2002), like nearly all his subsequent works, was produced in collaboration with accomplished composer/musicians from around the world. Morrison’s films are to be understood as image-music experiences.

In 1905, Sir William Crookes published a book entitled The Wheat Problem in which he reiterated what he had said in his British Association address of 1898. The content and tone are familiar: “The fixation of nitrogen is vital to the progress of civilized humanity, and unless we can class it among the certainties to come, the great Caucasian race will cease to be foremost in the world, and will be squeezed out of existence by races to whom wheaten bread is not the staff of life.” A whole gamut of processes for fixing nitrogen was described in a book published in 1914, and in 1919 an eminent U.S. electrochemist, H. J. M. Creighton, published a series of three papers entitled “How the Nitrogen Fixation Problem Has Been Solved.” However, the broader story was only just beginning to unfold. In about 1925, J. W. Mellor, in a justly celebrated sixteen-volume compendium, simply took Creighton at his word and stated quite baldly: “The problem has since [Crookes’ lecture] been solved.” Mellor describes not one but six processes that he believed were of industrial significance. These were: (1) the direct oxidation of dinitrogen by dioxygen to yield, initially, nitrogen oxides, as was undertaken in the Norwegian arc process; (2) the absorption of dinitrogen by metal carbides, subsequently developed as the cyanamide process; (3) the reaction of dinitrogen and dihydrogen by what has become known as the Haber process, or, more justifiably, the Haber–Bosch process; (4) the reaction of dinitrogen with metals, followed by treatment of the resultant nitrides with water; (5) the reaction of dinitrogen with carbon to form cyanides; and (6) the oxidation of dinitrogen during the combustion of coal or natural gas. Of these, only the first three really reached the stage of industrial exploitation, and only the Haber–Bosch process has been applied to any degree of significance since about 1950. The history of these three major developments is traced below. One of the first industrially significant reactions to be developed at the beginning of the twentieth century had already been known for more than 100 years.