Elements, four modern

Figure 1. Four key elements of modern lead finding.

By 1960, the elements of modern membrane science had been developed, but membranes were used in only a few laboratory and small, specialized industrial applications. No significant membrane industry existed, and total annual sales of membranes for all applications probably did not exceed 10 million in 2000 dollars. Membranes suffered from four problems that prohibited their widespread use as a separation process they were too unreliable, too slow, too un-selective, and too expensive. Partial solutions to each of these problems have been developed since the 1960s, and now membrane-based separation processes are commonplace. 

The concept that all substances are composed of elements and atoms goes back at least 2000 years. Originally, only four elements were recognized air, earth, fire, and water. Each substance was thought to consist of very small particles, called atoms, that could not be subdivided any further. This early mental concept of the nature of matter was extremely prescient, considering there were no experimental results to indicate that matter should be so and none to verify that it was so. Modern atomic theory is much more rigorously based, and we even have the ability to see atoms with special tunneling microscopes. All of chemistry is based on how atoms react with each other. 

In the next breath you take, almost all the atoms you inhale will be of elements in the final four groups of the periodic table. Except for the gases containing carbon and hydrogen, air is made up almost entirely of elements from this part of the p block, some as elements and some as compounds. The p-block elements are present in most of the compounds necessary for life and are used to create fascinating and useful modern materials, such as superconductors, plasma screens, and high-performance nanodevices. 

The apphed pretreatment techniques were digestion with a combination of acids in the pressurized or atmospheric mode, programmed dry ashing, microwave digestion and irradiation with thermal neutrons. The analytical methods of final determination, at least four different for each element, covered all modern plasma techniques, various AAS modes, voltammetry, instrumental and radiochemical neutron activation analysis and isotope dilution MS. Each participating laboratory was requested to make a minimum of five independent rephcate determinations of each element on at least two different bottles on different days. Moreover, a series of different steps was undertaken in order to ensure that no substantial systematic errors were left undetected. 

Discovery of the Periodic Table was rendered possible only after four decisive prerequisites had been achieved. These were (i) the abandonment of the metaphysical and occult notions of elements that typified the alchemical era (ii) the adoption of a modern and workable definition of an element (iii) the development of analytical chemical techniques for the isolation of the elements and determination of their properties and (iv) the devising of a means of associating each element with a characteristic natural number. The Periodic Table made its appearance on cue almost as soon as these preconditions had been fulfilled... 

In the modern periodic table, each box contains four data, as shown in Figure 1-2. Besides the element name and symbol, the atomic weight is at the bottom, and the atomic number is at the top. The elements are arranged in order of increasing atomic number in horizontal rows called periods. 

The world is a living being To the Hermeticists, all of the world, including rocks and streams, is alive and possesses a soul. The physical world was believed to be made of four physical elements earth, air, fire, and water. The elements would scatter, however, and the entire world would fall apart if they were not held together by the mysterious fifth element, the world soul, or Anima Mundi. This is in contrast with the modern scientific, materialist philosophy, which views the world as composed of nonliving matter. 

At the beginning of the seventeenth century, 13 elements were known. Nine—carbon, sulfur, iron, copper, silver, gold, tin, lead, and mercury—had been discovered in ancient times. Four more—arsenic, antimony, bismuth, and zinc—were discovered between around 1250 and 1500. It is not by chance that 11 of the 13 are metals. Some of them have relatively low melting points and were undoubtedly first produced when fires were laid on surface ores. Fires built by preliterate peoples in modern times have often produced small quantities of metals. A rich vein of silver was discovered in this manner by an Indian sheepherder in seventeenth-century Peru who built a fire at nightfall and found the next morning that the stone under the ashes was covered with silver. 

Even allowing for the ancient and medieval obsession with correspondences among the characteristics and creations of nature, there is clearly something about the four Aristotelian elements that has deep roots in human experience. The Canadian writer Northrop Frye writes The four elements are not a conception of much use to modern chemistry - that is, they are not the elements of nature. But... earth, air, water and fire are still the four elements of imaginative experience, and always will be. ... 

Plato s elements can be interconverted because of the geometric commonalities of their atoms . For Anaxagoras, all material substances are mixtures of all four elements, so one substance changes to another by virtue of the growth in proportion of one or more elements and the corresponding diminution of the others. This view of matter as intimate blends of elements is central to the antiquated elementary theories, and is one of the stark contrasts with the modern notion of an element as a fundamental substance that can be isolated and purified. 

Two additional material principles were added to the tria prima in the seventeenth century to form the five-principle view that characterized the iatrochemistry until the middle of the eighteenth century, when the four Aristotelian elements returned largely through the influence of the French chemist Pierre-Joseph Macquer. Robert P. Multhauf has given a splendid account of these pre-modern years in The Origins of Chemistry. ... 

It was not until the mid-1600s that chemists began to reject the idea of the Greeks four basic elements. In 1661, Boyle suggested the definition of "element" as we know it—something that cannot be reduced to a simpler substance by normal chemical means—and suggested there were many more than four elements. He is considered the founder of the modern element and one of the first true chemists. 

The above is a typical illustration of many confused notions of the ancients due to the fact that they possessed no knowledge of the elementary constituents of substances. The criteria for classification and nomenclature were based upon superficial phenomena, or upon the sources or the applicability of the substances to particular purposes. So long as the. concept prevailed that all substances consisted of variable quantities of the four Aristotelian elements, and that their properties were determined by the proportion of these elements, it was not possible for them to conceive of the possibility of a method of analysis based upon elementary compositions of bodies as understood in modern times. 

The formulation of the theory of the four elements credited to Empedocles is however the first clear notion of elements in a modern significance of the term which is found in Greek or Western thought. It is namely a clearly ex-... 

The atom of Democritus presents in its relation to the four elements, a certain analogy to the modern concept of... 

The above is not a complete statement of the theory of matter of Aristotle, but will, it is hoped, give an idea of the elaborateness and complexity of the Aristotelian concept, and serve to illustrate how far removed was his method of developing the theory from the inductive methods of modern science. The concept of the four elements as qualitative factors in the constitution of other bodies, with their inherent forces of heat, cold, moist, dry, became accepted by later centuries as basic truth. His notion of a fifth element, variously interpreted, also held a place in the thought of later times, but his more complex notions of the nature of the elements and matter had little influence on the later development of natural philosophy. 

A modern formulation of psychiatric disorders involves the integration of at least four key elements (1) genetic vulnerability to the expression of a disease (2) life event stressors that come that individual s way (divorce, financial problems, etc.) (3) the individual s personality, coping skills, and social support available from others ... 

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