The Twentieth Century

The present book is an attempt to rectify this omission. Ideally, as we have just argued, we should present a coherent account of the whole field of chemistry in which the results of structural studies appeared in their rightful place among those of the many other means of determining chemical constitution. This, however, would be a formidable task, and, indeed, an unnecessary one when there already exist so many works on chemistry, valency theory and other aspects of the solid state. We shall therefore presuppose the reader to have some knowledge of general chemical principles, and we shall confine ourselves to a discussion of those properties of solids, directly related to crystal structure, which are not normally considered in detail in chemical works. 

The development of X-ray crystal structure analysis immediately threw valuable new light on the question of the nature of interatomic forces, for it provided the first means of determining experimentally the 

This identification of the chemical and the physical bond at once led to the association with the chemist s ionic and covalent bonds of two other types of binding force not previously regarded as chemical in nature at all, namely, the metallic bond responsible for the cohesion of a metal, and the very much weaker van der Waals or residual bond responsible for the crystallization of the inert gases at very low temperatures. These metallic and van der Waals forces, however, did not lend themselves as readily as did the ionic and covalent to any simple explanation in terms of the Bohr theory, and it is only in recent years that the development of quantum mechanics has enabled a qualitative and even quantitative description of these bonds to be given. At the same time quantum theory has furnished a more exact description of the properties of the ionic and covalent bonds, which were previously so successfully described qualitatively in terms of older ideas, so that it is now possible to give a satisfactory theoretical explanation of many of the physical and chemical properties of simple structures. 

We may summarize the above discussion by saying that a review of the crystal structures of different types of solid emphasizes the dominating role of the interatomic forces in determining the structural arrangement, and that these forces may be conveniently divided into four distinct types  

Let it be said at once that it is now clear that the distinction between these four bond types is by no means absolute, and that in many crystals the bonds possess an intermediate character, displaying something of the properties of two or more types. We shall return to this point at length later, but initially we shall find it convenient to discuss these bond types in isolation and to illustrate their properties by considering some simple structures in which only bonds possessing little or no intermediate character are found. 

The principal technological changes in the engineering control of air pollution were the perfection of the motor-driven fan, which allowed large-scale gas-treating systems to be built the invention of the electrostatic precipitator, which made particulate control in many processes feasible and the development of a chemical engineering capability for the design of process equipment, which made the control of gas and vapor effluents feasible. 

During this period, no significant national air pollution legislation or regulations were adopted anywhere in the world. However, the first state air pollution law in the United States was adopted by California in 1947. 

During these two decades, almost every country in Europe, as well as Japan, Australia, and New Zealand, experienced serious air pollution in its larger cities. As a result, these countries were the first to enact national air pollution control legislation. By 1980, major national air pollution research centers had been set up at the Warren Springs Laboratory, Stevenage, England the Institut National de la Sante et de las Recherche Medicale at 

As in Europe, air pollution research activity expanded tremendously in the United States during these three decades. The headquarters of federal research activity was at the Robert A. Taft Sanitary Engineering Center of the PHS in Cincinnati, Ohio, during the early years of the period and at the National Environmental Research Center in Triangle Park, North Carolina, at the end of the period. 

An International Air Pollution Congress was held in New York City in 1955 (16). Three National Air Pollution Conferences were held in Washington, D.C., in 1958 (17), 1962 (18), and 1%6 (19). In 1959, an International Clean Air Conference was held in London (20). 

The turn of century was not marked by any important progress in the knowledge of the micas, based on Niggli s text (see above). 

Indeed, what was needed was a new technique. This breakthrough was provided by X-ray diffraction which, by a strange coincidence, was developed on the eve of the First World War, i.e., at the conventional end of the belle epoque. 

Obviously some time had to pass, a little more than a decade, before X-ray diffraction had a practical application to micas, but the path had been opened to a new science, structural crystallography, which was immediately incorporated into the older science of mineralogy. 

The repeated angular measurements on crystals of various forms had filled volumes. However, contrary to the views of Haiy concerning a close correspondence between crystalline form and chemical composition, these measurements brought no useful contribution to systematic mineralogy except for the possibility of verifying the existence of polymorphs and the presence of isomorphic series. 

The improved analytical techniques had led, by the end of the 19 century, to the correct establishment of atomic ratios occurring in the various micas. However, the obsolete view of the silicates as salts of different silicic acids hindered the understanding of the true nature of a group of minerals having homogeneous physical characteristics, but with notable and inexplicable chemical differences. X-ray diffraction would solve this problem. 

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One of the most significant achievements of the twentieth century is the description of the quantum mechanical laws that govern the properties of matter. It is relatively easy to write down the Hamiltonian for interacting fennions. Obtaining a solution to the problem that is sufficient to make predictions is another matter. 

Cobalt compounds have been in use for centuries, notably as pigments ( cobalt blue ) in glass and porcelain (a double silicate of cobalt and potassium) the metal itself has been produced on an industrial scale only during the twentieth century. Cobalt is relatively uncommon but widely distributed it occurs biologically in vitamin B12 (a complex of cobalt(III) in which the cobalt is bonded octahedrally to nitrogen atoms and the carbon atom of a CN group). In its ores, it is usually in combination with sulphur or arsenic, and other metals, notably copper and silver, are often present. Extraction is carried out by a process essentially similar to that used for iron, but is complicate because of the need to remove arsenic and other metals. 

John von Neuman, one of the greatest mathematicians of the twentieth century, believed that the sciences, in essence, do not try to explain, they hardly even try to interpret they mainly make models. By a model he meant a mathematical construct that, with the addition of certain verbal interpretations, describes observed phenomena. The justification of such a mathematical construct is solely and precisely that it is expected to work. Stephen Hawking also believes that physical theories are just mathematical models we construct and that it is meaningless to ask whether they correspond to reality, just as it is to ask whether they predict observations. 

When considering how the evolution of life could have come about, the seeding of terrestrial life by extraterrestrial bacterial spores traveling through space (panspermia) deserves mention. Much is said about the possibility of some form of life on other planets, including Mars or more distant celestial bodies. Is it possible for some remnants of bacterial life, enclosed in a protective coat of rock dust, to have traveled enormous distances, staying dormant at the extremely low temperature of space and even surviving deadly radiation The spore may be neither alive nor completely dead, and even after billions of years it could have an infinitesimal chance to reach a planet where liquid water could restart its life. Is this science fiction or a real possibility We don t know. Around the turn of the twentieth century Svante Arrhenius (Nobel Prize in chemistry 1903) developed this theory in more detail. There was much recent excitement about claimed fossil bacterial remains in a Martian meteorite recovered from Antarctica (not since... 

Ethylene (as well as propylene) produced from carbon dioxide subsequently allows ready preparation of the whole array of hydrocarbons, as well as their derivatives and products that have become essential to our everyday life. Whereas the nineteenth century relied mostly on coal for energy as well as derived chemical products, the twentieth century greatly supplemented this with petroleum and nat-... 

Beginning in the middle of the twentieth century alternative methods of acetylene production became practical One of these is based on the dehydrogenation of ethylene... 

Our experience conditions us to focus on the organic components of the reaction—l arginine and l citrul line—and to give less attention to the inorganic one—nitric oxide (nitrogen monoxide NO) To do so however would lead us to overlook one of the most important discoveries in biology in the last quarter of the twentieth century... 

Watson and Crick published their work in a pa per entitled A Structure for Deoxyribose Nucleic Acid in the British journal A/ature on April 25 1953 In addition to being one of the most important pa pers of the twentieth century it is also remembered for one brief sentence appearing near the end... 

Attributed to C. N. Reilley (1925-1981) on receipt of the 1965 Fisher Award in Analytical Chemistry. ReiUey, who was a professor of chemistry at the University of North Carolina at Chapel HiU, was one of the most influential analytical chemists of the last half of the twentieth century. 

Colorimetry, in which a sample absorbs visible light, is one example of a spectroscopic method of analysis. At the end of the nineteenth century, spectroscopy was limited to the absorption, emission, and scattering of visible, ultraviolet, and infrared electromagnetic radiation. During the twentieth century, spectroscopy has been extended to include other forms of electromagnetic radiation (photon spectroscopy), such as X-rays, microwaves, and radio waves, as well as energetic particles (particle spectroscopy), such as electrons and ions. ... 

The earliest examples of analytical methods based on chemical kinetics, which date from the late nineteenth century, took advantage of the catalytic activity of enzymes. Typically, the enzyme was added to a solution containing a suitable substrate, and the reaction between the two was monitored for a fixed time. The enzyme s activity was determined by measuring the amount of substrate that had reacted. Enzymes also were used in procedures for the quantitative analysis of hydrogen peroxide and carbohydrates. The application of catalytic reactions continued in the first half of the twentieth century, and developments included the use of nonenzymatic catalysts, noncatalytic reactions, and differences in reaction rates when analyzing samples with several analytes. 

It was not until the twentieth century that furfural became important commercially. The Quaker Oats Company, in the process of looking for new and better uses for oat hulls found that acid hydrolysis resulted in the formation of furfural, and was able to develop an economical process for isolation and purification. In 1922 Quaker announced the availability of several tons per month. The first large-scale appHcation was as a solvent for the purification of wood rosin. Since then, a number of furfural plants have been built world-wide for the production of furfural and downstream products. Some plants produce as Httie as a few metric tons per year, the larger ones manufacture in excess of 20,000 metric tons. 

Classical and Quantum Mechanics. At the beginning of the twentieth century, a revolution was brewing in the world of physics. For hundreds of years, the Newtonian laws of mechanics had satisfactorily provided explanations and supported experimental observations in the physical sciences. However, the experimentaUsts of the nineteenth century had begun delving into the world of matter at an atomic level. This led to unsatisfactory explanations of the observed patterns of behavior of electricity, light, and matter, and it was these inconsistencies which led Bohr, Compton, deBroghe, Einstein, Planck, and Schrn dinger to seek a new order, another level of theory, ie, quantum theory. 

Although the use of simple diluents and adulterants almost certainly predates recorded history, the use of fillers to modify the properties of a composition can be traced as far back as eady Roman times, when artisans used ground marble in lime plaster, frescoes, and po22olanic mortar. The use of fillers in paper and paper coatings made its appearance in the mid-nineteenth century. Functional fillers, which introduce new properties into a composition rather than modify pre-existing properties, were commercially developed eady in the twentieth century when Goodrich added carbon black to mbber and Baekeland formulated phenol— formaldehyde plastics with wood dour. 

Fibers (see Fibers, survey) used in textile production can have a wide variety of origins plants, ie, ceUulosic fibers (see Fibers, cellulose esters) animals, ie, protein fibers (see Wool) and, in the twentieth century, synthetic polymers. Depending on the part of the plant, the ceUulosic fibers can be classified as seed fibers, eg, cotton (qv), kapok bast fibers, eg, linen from flax, hemp, jute and leaf fibers, eg, agave. Protein fibers include wool and hair fibers from a large variety of mammals, eg, sheep, goats, camels, rabbits, etc, and the cocoon material of insect larvae (sUk). Real sUk is derived from the cocoon of the silkworm, Bombjx mori and for a long time was only produced in China, from which it was traded widely as a highly valuable material. 

Aryl Phosphates. Aryl phosphates were introduced into commercial use early in the twentieth century for flammable plastics such as cellulose nitrate and later for cellulose acetate. CeUulosics are a significant area of use but are exceeded now by plastici2ed vinyls (93—95). Principal appHcations are in wire and cable insulation, coimectors, automotive interiors, vinyl moisture barriers, plastic greenhouses (Japan), furniture upholstery, conveyer belts (especially in mining), and vinyl foams. 

Fomialdehyde [50-00-0] H2C=0, is the first of the series of aUphatic aldehydes. It was discovered by Buderov ia 1859 and has been manufactured siace the beginning of the twentieth century. Annual woddwide production capacity now exceeds 15 x 10 t (calculated as 37% solution). Because of its relatively low cost, high purity, and variety of chemical reactions, formaldehyde has become one of the wodd s most important iadustrial and research chemicals (1). 

Early in the twentieth century, the first attempts to manufacture formamide directiy from ammonia and carbon monoxide under high temperature and pressure encountered difficult technical problems and low yields (23). Only the introduction of alkaU alkoxides in alcohoHc solution, ie, the presence of alcoholate as a catalyst, led to the development of satisfactory large-scale formamide processes (24). 

The development of the principles of nucleation and growth eady in the twentieth century (2) ultimately led to the discovery that certain nucleating agents can induce a glass to crystallize with a fine-grained, highly uniform microstmcture that offers unique physical properties (3). The first commercial glass-ceramic products were missile nose cones and cookware. 

The term Grignard reaction refers to both the preparation of a class of organomagnesium haUde compounds and their subsequent reaction with a wide variety of organic and inorganic substrates. As such it has had a wide and profound influence on synthetic chemistry since its first elucidation by Victor Grignard at the beginning of the twentieth century. 

Reciprocating Compressors. Prior to 1895, when Linde developed his air Hquefaction apparatus, none of the chemical processes used industrially required pressures much in excess of I MPa (145 psi) and the need for a continuous supply of air at 20 MPa provided the impetus for the development of reciprocating compressors. The introduction of ammonia, methanol, and urea processes in the early part of the twentieth century, and the need to take advantage of the economy of scale in ammonia plants, led to a threefold increase in the power required for compression from 1920 to 1940. The development of reciprocating compressors was not easy Htfle was known about the effects of cycles of fluctuating pressure on the behavior of the... 

Although a few simple hydrides were known before the twentieth century, the field of hydride chemistry did not become active until around the time of World War II. Commerce in hydrides began in 1937 when Metal Hydrides Inc. used calcium hydride [7789-78-8J, CaH2, to produce transition-metal powders. After World War II, lithium aluminum hydride [16853-85-3] LiAlH, and sodium borohydride [16940-66-2] NaBH, gained rapid acceptance in organic synthesis. Commercial appHcations of hydrides have continued to grow, such that hydrides have become important industrial chemicals manufactured and used on a large scale. 

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