Radioactivity Hall of Fame-Part I

Michael F. L'Annunziata , in Radioactivity, 2007

DEMOCRITUS (c.460–c.370 B.C.)

Democritus was a Greek philosopher born in Abdera in the north of Greece. Democritus was a student of Leucippus, who proposed the atomic theory of matter. There is little documentation on the philosophy of Leucippus; however, it was Democritus, who elaborated extensive works on his theories on the atomic structure of the physical world, of the universe, and the void of space. Although Democritus was a philosopher, he is included here among the list of great pioneers of physics and chemistry of the 19th and 20th centuries, because many of his teachings on the structure of matter were demonstrated finally by scientists over 2000 years after his death.

Democritus taught the theory of atomism, which held the belief that indivisible and indestructible atoms are the basic components of all matter in the universe. Thus the word atom is derived from the Greek atomos meaning indivisible. It was not until 20 centuries after Democritus did Rutherford, Bohr, Soddy, and others demonstrate the atom to be the smallest unit of an element consisting of a positively charged nucleus surrounded by electrons equal to the number of protons in the nucleus. Modern science has demonstrated that atoms remain undivided in matter (in accord with the early philosophical teachings of Democritus) or in chemical reactions with the exception of a limited removal, exchange, or transfer of electrons. The atom is also the basic unit of elements and is the source of nuclear energy. The postage stamp illustrated here was issued by Greece in 1961 to commemorate Democritus' teachings of atomism and the development of peaceful applications of atomic energy in the world.

Democritus was not alone in the teaching of atomism, but his writings on this philosophy were most extensive. He held that atoms were the tiniest of particles, too small to be perceived by the senses, of which all matter was composed, and that the atoms differed in size, shape, and mass. He also argued that atoms were in constant motion and could coalesce to form the larger bodies of matter that we can see, feel, and taste. The properties of matter that we can perceive with the senses such as color, taste, and hardness were the result of the interactions of atoms that constituted a given substance and the interactions of atoms with our body. For example, the taste of a substance would be the result of the interactions of atoms with the atoms of our tongue. Democritus also held to the belief of the existence of the "void" or empty space to which atoms or matter can move into. He argued that the lights of the Milky Way were the lights of distant stars, and that there existed other worlds, some with suns and moons, and others without. Likewise there would be other worlds with animal life, plants, and water and others without.

Much of Democritus' philosophy of atomism was demonstrated by modern science to be true. In honor of Democritus the national institution dedicated to research on peaceful applications of atomic energy for development in Greece is named the Democritus Nuclear Research Center. For additional reading on one of the greatest philosopher–scientists from antiquity see Taylor's book The Atomists (1999).

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Accommodation of the Rare Earths in the Periodic Table

Pieter Thyssen , Koen Binnemans , in Handbook on the Physics and Chemistry of Rare Earths, 2011

6 Seaborg's Actinide Concept

Although Bohr considered thorium, protactinium, and uranium as members of a second series of rare earths, the majority of chemists remained convinced that these elements were homologues of hafnium, tantalum and tungsten, for a time after Bohr had formulated his atomic theory. The reason for the delay of acceptance of a second rare-earth series was mainly due the fact that the highest valence states of thorium (+  IV), protactinium (+   V) and uranium (+   VI) suggested that these elements were transition metals. Moreover, with the exception of thorium and cerium, there are, besides the similarities in electronic configuration, only few similarities in chemical properties between the early actinide elements and the lanthanides. The chemical properties of uranium seem to differ very much from those of neodymium, whereas on the other hand there are striking similarities between uranium and the elements of group 5 (Cr, Mo, W). For instance, uranium and tungsten both form hexachlorides (UCl6 and WCl6). Uranium forms the ion U2O7 2− and the compound UO2Cl2, while chromium forms Cr2O7 2− and CrO2Cl2. However, one should note that the dissimilarities between uranium and neodymium are only evident when hexavalent uranium (the most common oxidation state for uranium) and trivalent neodymium (the most common oxidation state for neodymium) are compared. Uranium(III) on one hand, shows many similarities with neodymium(III), whereas on the other hand, uranium(IV) resembles thorium(IV) and cerium(IV). Another point of confusion was the very small energy differences between the 5f- and 6d-shell, even in the range of the chemical binding energy, so that it was difficult to predict when the 5f-shell started to be filled. It was assumed that in thorium, protactinium, and uranium the 6d-shell was being filled. Goldschmidt (1924) predicted that the transuranium elements up to element 96 would be platinum group elements. Nevertheless, several researchers believed in the existence of a second series of rare earths, even before the introduction of Bohr's atomic theory in 1922. As early as 1892, Bassett considered thorium and uranium to be analogous to cerium and praseodymium, respectively (Bassett, 1892). It should be noted that he preferred the order {Ce, Nd, Pr} rather than {Ce, Pr, Nd} for the lanthanides. Werner considered thorium as an analogue of cerium and uranium as an analogue of europium. Both authors reserved open spaces in their periodic tables for other members of the second rare earths series that were still undiscovered at that time.

In 1926, Goldschmidt demonstrated the analogies between the elements {Th, Pa, U} and the lanthanides on the basis of the observation that the volumes of Th4+ and U4+ showed the same contractions as the ions of the lanthanide series. Striking early examples of periodic tables in which actinium, thorium, protactinium, and uranium are considered as homologues of the rare earths lanthanum, cerium, praseodymium, and neodymium are the circular system and left-step table of Charles Janet (Janet, 1929).

Seaborg (1944, 1945) noticed that whereas thorium, protactinium, and uranium showed similarities in chemical behavior with zirconium, tantalum, and tungsten, respectively, neptunium and plutonium did not show such similarities with rhenium and osmium, or with technetium and ruthenium. For instance, in contrast to the volatiles osmium tetroxide and ruthenium tetroxide, there exists no volatile plutonium tetroxide. On the other hand, the chemical properties of neptunium and plutonium are very similar to those of thorium and uranium. These four elements have a stable +   IV oxidation state. ThO2, UO2, NpO2, and PuO2 are isomorphous and there is a steady decrease of the metallic ion radius when going from Th4+ to Pu4+. Other evidence was based on magnetic susceptibility data, on the absorption spectra of the ions in aqueous solution and in crystals, on the spectra of the gaseous atoms, and on additional crystallographic and chemical data. These observations made Seaborg propose the existence of a second rare-earth series that begins with actinium, in the same sense as that the lanthanide series begins with lanthanum. He termed this second rare-earth series the "actinide series.≥ The actinide elements do not tend to occupy the 6d orbital, but there is a gradual filling of the 5f shell over the actinide series. Although Seaborg assumed that thorium would be the first element at which the 5f orbital becomes occupied, he also considered the possibility that thorium and protactinium do not have 5f electrons, and that uranium has three 5f electrons. The actinide concept has as a consequence that +   III is a characteristic oxidation state for the actinides. However, a striking difference between the lanthanide and actinide series is the existence of oxidation states higher than +   IV in the actinide series (+   V and +   VI). This is an indication that the 5f electrons are less tightly bonded than the 4f electrons. Seaborg (1949) introduced the form of the periodic table with which so many chemists are familiar with: one that considers the lanthanides and actinides as footnotes of the main body of the periodic table. A detailed account of the development of the actinide concept can be found in Chapter 118 in this Handbook (Seaborg, 1994).

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František Wald (1861–1930)

Klaus Ruthenberg , in Philosophy of Chemistry, 2012

Publisher Summary

The Czech chemist František Wald (1861–1930) was professor of physicochemistry and metallurgy in the Czech Technical University of Prague from 1908 until the year of his death. He developed a theory of substances based on the concept of phase in response to his critique of atomic theories inspired in large part by Ernst Mach. Although František Wald left out of account topics which would, perhaps, be appropriate for a "complete" theory and philosophy of chemistry (such as an account of the character of processes, the relation between time and potentiality, the predictive power of certain, even "metaphysical" theoretical concepts, the periodicity of elements, and so on), his approach is original and highly suggestive. He gave intriguing and substantial pointers to how the theoretical gap between the existing, positive knowledge about stuff and the phenomenalist, operational description of the path leading to that knowledge might be closed.

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Prehistory of the Philosophy of Chemistry

Jaap van Brakel , in Philosophy of Chemistry, 2012

5 Ostwald, Cassirer, Paneth

In his anti-atomism, philosopher-chemist Ostwald aimed, first, to distinguish between what is given in experience and what is postulated by the mind: nothing compels us to affirm that mercury oxide "contains" mercury and oxygen. Second, he aimed to show that energy is the most general concept of the physical sciences. 23

In his Faraday lecture of 1904 he still argued vehemently against the atomic theory and, acknowledging his debt to Franz Wald, 24 stressed that the deduction of the laws governing the nature of substances must start from the conception of "phase," a concept far more general than that of substance. Ostwald was one of the first physical chemists to give reasonably precise empirical (macroscopic, thermodynamic) definitions of chemical substances. In his terminology, if the properties of two coexisting phases remain invariant during a phase change, the system is called hylotropic. If it is hylotropic over a range of temperatures as the pressure varies, it is a pure chemical substance. If it is not, it is a mixture. If it is hylotropic over all pressures and temperatures except the most extreme ones, it is a simple substance.

In 1907, while addressing metamerism, polymerism, and the role of valence in structure theory, 25 he acknowledges that when compared with "structure theory," his account in terms of differences in energy content "predicts, however, nothing whatever about the chemical reactions which are to be expected." He further acknowledges "the spatial arrangement of elements" to be "a very important aid." When the results of the experiments of Thomson on ions in the gas phase and Perrin on Brownian motion became available Ostwald finally surrendered in November 1908: 26

I have convinced myself that a short while ago we arrived at the possession of experimental proof for the discrete or particulate [körnige] nature of substances [Stoffe], which the atomic hypothesis has vainly sought for a hundred years, even a thousand years.

Referring to publications by Duhem, Ostwald, and Meyer, the neo-Kantian Ernst Cassirer included 17 pages of his Substanzbegriff und Funktionsbegrif (1910) on chemical concepts. Cassirer associated the progress of science with the change from "purely empirical" descriptions of their subject matter, toward the rational stage of "constructive concepts" and wrote: "The conceptual construction of exact natural science is incomplete on the logical side as long as it does not take into consideration the fundamental concepts of chemistry" (203). Constructive concepts (which lend themselves to mathematical treatment) were realised in theoretical physics from the very beginning (Galileo, Newton), but were only slowly developed in chemistry, the first examples being Richter's law of definite proportions, Dalton's law of multiple proportions, Gibbs's phase rule, the chemical atom characterised by atomic number, and the theory of composite radicals. Like many before him Cassirer stressed the relational aspect of chemical concepts and argued that the concept of a (chemical) atom is (since Dalton's law of multiple proportions) a relational, regulative ideal concept, "a mere relative resting point." The concept of the atom is (merely) a mediator; therefore, "we may abstract from all metaphysical assertions regarding the existence of atoms" (208).

The chemist Paneth, already cited twice, is of importance for the philosophy of chemistry because of his engagement in the debate with Fajans and von Hevesy concerning chemical identity in view of the discovery of isotopes [van der Vet, 1979] and because of a thoroughly researched lecture he gave in 1931. 27 It addresses the familiar question how "elements" persist in compounds. According to Paneth the apparent contradictions which arise can be dissolved by distinguishing clearly the double meaning or different aspects of the chemical concept of element, which are defined referring to one another. The Grundstoff or basic substance is "the indestructible stuff present in compounds and simple substances"; the einfacher Stoff or simple substance is "that form of occurrence in which an isolated basic substance uncombined with any other appears to our senses" (129-30, emphasis original). The latter is a chemical substance like others, except that it cannot be decomposed (further) by chemical means. 28 The former provides the basis for the systematic ordering of the elements in the periodic system. Although the atomic theory contributes enormously to our understanding, "the concept of basic substance as such does not in itself contain any idea of atomism", as Lavoisier acknowledged (133). Paneth extended his distinction to the radicals of organic chemistry (usually unobservable), compounds of higher order (such as SO3.H2O), as well as (forms of occurrence of) simple substances (because of different phases, allotropy, etc.). 29

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Atmospheric Thermodynamics

John M. Wallace , Peter V. Hobbs , in Atmospheric Science (Second Edition), 2006

The kinetic theory of gases pictures a gas as an assemblage of numerous identical particles (atoms or molecules) 3 4 5 6 that move in random directions with a variety of speeds. The particles are assumed to be very small compared to their average separation and are perfectly elastic (i.e., if one of the particles hits another, or a fixed wall, it rebounds, on average, with the same speed that it possessed just prior to the collision). It is shown in the kinetic theory of gases that the mean kinetic energy of the particles is proportional to the temperature in degrees kelvin of the gas.

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Nuclear Physics

Christopher R. Gould , ... Philip J. Siemens , in Encyclopedia of Physical Science and Technology (Third Edition), 2003

I Twentieth-Century History

The foundations of both modern nuclear physics and modern atomic physics were established by Ernest (Lord) Rutherford through a series of celebrated experiments first published in 1911. He used alpha particles from naturally radioactive emitters as projectiles to bombard a variety of targets, and he detected the scattered alpha particles by visually observing scintillations on a phosphorescent screen. From the distribution of scattered particles, he was able to demonstrate that the interaction of alpha particles with atoms obeyed Coulomb's inverse-square law down to distances on the order of 10−13  m   =   100 fm (1 fm   =   10−15  m).

The picture that emerged from Rutherford's experiments was that of an atom consisting of a massive core—the nucleus—of positive electric charge Ze, where –e is the charge on the electron and Z is the atomic number. The nucleus is surrounded by a negatively charged electron gas. Earlier atomic theories fell, most notably J. J. Thomson's model of electrons embedded in a positively charged "jelly." In 1913, Niels Bohr announced his atomic theory of electrons circling the nucleus in quantized planetary orbits. Further studies in atomic physics led to the discovery (invention) of quantum mechanics by Werner Heisenberg (1925) and Erwin Schrödinger (1926).

The discovery of the neutron by James Chadwick in 1932 clarified both the problem of isotopic composition and the connection between atomic weight A and nuclear spin. With protons and neutrons now known to be the building blocks of nuclei, the study of nuclear structure was launched.

In 1935, Hideki Yukawa postulated the existence of a new, intermediate-weight elementary particle, which he called the mesotron, to act as the agent to bind neutrons and protons together in the nucleus. Some confusion ensued when Carl Anderson and Seth Neddermeyer discovered a candidate particle in 1938 that did not seem to interact strongly with nuclei. The problem was resolved in 1947 by Cecil Powell and collaborators who identified two particles, the mu and the pi mesons, the latter being the Yukawa mesotron (now called the pion); the mu meson, or muon, is the Anderson–Neddermeyer particle. This was a remarkable triumph of speculative theoretical induction. It also completed the first phase in the microscopic description of nuclear structure. Subsequently, a host of elementary particles has been found, many of which play important roles in nuclear physics. (See Section VII.B.)

The discovery of fission by Otto Hahn and Fritz Strassmann in 1939 led to the development of the atomic (more properly nuclear) bomb during World War II and the attendant development of fission reactors for electrical power generation. The fusion process, which is the mechanism by which the sun and stars generate their energy, was the basis for development of the hydrogen bomb in the 1950s, and there has been intense research during the subsequent decades to harness thermonuclear fusion as a power source. At the same time, nuclear physics and chemistry have provided radioactive isotopes, radioactive and stable isotope identification techniques, nuclear magnetic resonance, etc. for medical diagnosis and treatment, geological and archaeological dating, tracing of water and atmospheric flow patterns, planetary and solar system histories, and numerous other applications.

At present, much interest is being concentrated on nuclear substructure, namely, the constituents of the protons, neutrons, and other particles previously considered to be elementary. The subparticles are called quarks; the proton and the neutron each contain three quarks.

Figure 1 summarizes, from top to bottom, the historical evolution of nuclear physics and nuclear phenomena studied with particle accelerations. At the lowest energies (longest length scales), the collective modes of nuclei—rotations and vibrations—are evident. As the energy increases (shorter length scales) the presence of individual nucleons in shell model orbits is revealed, the nucleons themselves interacting via the exchange of mesons. At the highest energies (shortest length scales), the quark and gluon structure of the nucleons is observed. The theory of nucleons interacting via the exchange of mesons is called quantum hadrodynamics (QHD). The theory of quark–gluon interactions is called quantum chromodynamics (QCD). Linking these descriptions of nuclear phenomena is a major challenge for theoretical physics.

FIGURE 1. Structure of nuclei revealed by projectiles of low to high energy (from top to bottom), probing shorter length scales as the energy increases.

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The First Law of Thermodynamics

In Practical Chemical Thermodynamics for Geoscientists, 2013

C Joule's experiments on the mechanical equivalent of heat

James Joule was one of the most remarkable amateur scientists of the 19th century (see sidebar). Starting about 1840, Joule began a series of ingenious experiments in which different types of work were converted into heat and the proportionality between the two was measured. In other words, Joule measured the mechanical equivalent of heat given by the ratio of work done to the heat produced. These experiments included the electrical heating of a wire coil immersed in water, the heating produced by compressing air into a cylinder that was immersed in water, and the heating produced by

JAMES PRESCOTT JOULE (1818–1889)

Joule was possibly the greatest amateur scientist of the 19th century. He was the son of a wealthy Manchester, England, brewer and conducted his experiments in the family brewery. John Dalton, who developed the atomic theory and Dalton's law, educated Joule and his brother. Joule published his first scientific paper about electric motors at the age of 19. His research on electricity led to Joule's law ( q

=

I 2 Rt), which gives the amount of heat generated by a current I flowing through a wire with resistance R for time t.

His electrical research led Joule to study the transformation of work into heat. He found that a given amount of work generates the same amount of heat, regardless of how the work is done. Joule measured the mechanical equivalent of heat to be 0.241 cal/J, which is quite close to the modern accepted value of 0.239 cal/J. His experimental work established the first law of thermodynamics. Joule's free expansion experiment and his later work on gas expansion with William Thomson (Kelvin), known as the Joule–Thomson (Kelvin) effect, laid the foundation for much of modern refrigeration technology. Joule's scientific papers on these and other topics are remarkable for their insights into the basic laws of nature. They are also entertaining reading.

Perhaps the most remarkable thing about Joule was his talent for making very precise measurements with rudimentary equipment. His experimental accuracy is legendary. His colleague, Kelvin, said of him, "His boldness in making such large conclusions from such very small observational effects is almost as noteworthy and admirable as his skill in extorting accuracy from them."

paddle wheels stirring water, sperm whale oil, or mercury. A summary of Joule's results is given in Table 3-1; you can see that some of the experiments Joule did were more accurate than others. All these data, however, led Joule to conclude that the amount of heat produced in his experiments depended only on the amount of work done—not on how the work was done or on the type of work.

Table 3-1. Joule's Determinations of the Mechanical Equivalent of Heat

Type of Work Work (ft-lb.) a
Turning paddle wheels in water (1849) 772.7
Turning paddle wheels in mercury (1849) 774.1
Rubbing together two iron blocks immersed in mercury (1849) 775
Turning paddle wheels in water (1845, 1847) 781.5
Turning paddle wheels in sperm whale oil (1845, 1847) 782.1
Turning paddle wheels in mercury (1845, 1847) 787.6
Compressing gas into a cylinder immersed in water (1843) 798
Electrical current through a wire coil immersed in water (1843) 838
Mean value (±1 sigma) for the amount of work done 789±22
The modern experimental value is equal to 777.72
The defined thermochemical calorie gives 777.65
a
From Joule (1850), "On the Mechanical Equivalent of Heat," Phil. Trans. Roy. Soc. London 140, 61, and references therein. The amount of work done is the number of foot pounds needed to raise the temperature of one pound of water by 1°F—in other words, foot pounds per BTU.

Joule's most famous and probably most accurate experiments were his paddle wheel experiments done in 1849. Figure 3-2 is a schematic diagram of these experiments in which falling weights were used to turn paddle wheels inside a tank of water. The tank contained stationary metal vanes to prevent rotation of water in the tank and to increase the frictional heating. The paddle wheels were positioned between the vanes; for example, from bottom to top the arrangement would be vane, paddle wheel, vane, paddle wheel, and so on. This entire apparatus was inside an insulated wood container (not shown) to prevent heat exchange with the surroundings. A system such as Joule's water tank, which is thermally insulated from the surroundings, is called an adiabatic system. The word adiabatic is derived from the Greek word adiabatos, which means impassable. Thus, an adiabatic wall is impassable to heat, an adiabatic system is perfectly thermally insulated from its surroundings, and an adiabatic process has no heat flow between the system and its surroundings.

FIGURE 3-2. A schematic diagram of Joule's paddle wheel experiment. When the handle was released, the weights fell, unwinding the cord and turning the paddles. This process was repeated several times and the resulting temperature increase of the water was measured.

The work done in Joule's experiments was calculated by multiplying the mass of the weights by the local acceleration of gravity and by the total distance they fell. The heat produced was calculated by measuring the temperature increase of the known mass of water contained in the insulated tank. Based on his paddle wheel experiments with water, Joule concluded that "the quantity of heat capable of increasing the temperature of a pound of water (weighed in vacuo, and taken at between 55° and 60°) by 1°Fahr. requires for its evolution the expenditure of a mechanical force represented by the fall of 772 lb. through the space of one foot." As shown in Table 3-1, Joule computed similar values for the amount of work needed to heat one pound of water from his other experiments.

Example 3-2. Using the energy conversion factors given in Table 3-2, we can convert Joule's results into more convenient units. Joule measured the work done in foot pounds (ft-lb) and gives the mechanical equivalent of heat in terms of British thermal units (BTU), which is the amount of heat needed to increase the temperature of one pound of water by 1°F. He found that one BTU was equivalent to 772 ft-lb. From Table 3-2, we see that 1 BTU   =   252.0 cal and that 772 ft-lb = (1.356)(772)   =   1046.8 J. Equating the two expressions we find that

Table 3-2. Energy Conversion Factors a

J cal erg eV liter-bar
1 J   = 1 0.239006 107 1.0364269   ×   10−5 10−2
1 cal = 4.184 1 4.184   ×   107 4.336410   ×   10−5 4.184   ×   10−2
1 erg = 10−7 2.390057   ×   10−8 1 1.0364269   ×   10−12 10−9
1 eV = 96,485.3415 23,060.5501 9.648534   ×   1011 1 964.853415
1 L bar = 100.000 23.90057 109 1.0364269   ×   10−3 1
1 L atm = 101.325 24.2173 1.01325   ×   109 1.0501595   ×   10−3 1.01325
1 BTU = 1,054.35 251.9957 1.05435   ×   1010 1.0927567   ×   10−2 10.5435
1 KWH a = 3.600   ×   106 860,420.65 3.600   ×   1013 37.311367 3.600   ×   104
1 ft-lb = 1.355818 0.324048 1.355818   ×   107 1.4052062   ×   10−5 1.355818   ×   10−2
1 cm−1 = 11.96266 2.85914 1.196266   ×   108 1.2398422   ×   10−4 0.1196266
liter-atm BTU KWH ft-lb cm−1
1 J = 9.8692327   ×   10−3 9.484517   ×   10−4 2.77778   ×   10−7 0.737562 8.359345   ×   10−2
1 cal = 4.1292795   ×   10−2 3.968322   ×   10−3 1.162222   ×   10−6 3.085960 0.349756
1 erg = 9.869232   ×   10−10 9.48452   ×   10−11 2.77778   ×   10−14 7.375621   ×   10−8 8.359345   ×   10−9
1 eV = 952.23628 91.511682 2.680148   ×   10−2 71,163.9331 8,065.5424
1 L bar = 0.986923 9.484517   ×   10−2 2.77778   ×   10−5 73.75621 8.359345
1 L atm = 1 9.610186   ×   10−2 2.814586   ×   10−5 74.73348 8.470106
1 BTU = 10.405625 1 2.928750   ×   10−4 777.6486 88.136752
1 KWH = 35,529.2376 3,414.426 1 2.655224   ×   106 3.009364   ×   105
1 ft-lb = 1.338088   ×   10−2 1.285928   ×   10−3 3.766161   ×   10−7 1 0.113338
1 cm−1 = 0.1180623 1.134595   ×   10−2 3.322961   ×   10−6 8.823205 1
a
eV   =   electron volts per mole; KWH   =   kilowatt hour; cm−1  =   cm−1 per mole

(3-8) 1 BTU = 252.0 cal = 1046.8 J = 772 ft-lb

In other words, Joule's result for the mechanical equivalent of heat is equal to 252.0 cal/1046.8 J   =   0.241 cal J−1, which is within 1% of the modern value of 0.239 cal J−1.

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Friedrich Wilhelm Ostwald (1853–1932)

Robert J. Deltete , in Philosophy of Chemistry, 2012

2 Intellectual Odyssey

Ostwald's general philosophical development may be divided into four overlapping, but reasonably distinct, periods. During the first of these, which lasted until around 1890, he was an articulate, if increasingly cautious, defender of much that was basic to the mechanical world-view. Ostwald was not always an opponent of the atomic theory in chemistry, or of kinetic and molecular theories generally. On the contrary, he enthusiastically endorsed such views, in works through the early 1880's, and remained a qualified supporter of them until he began seriously to write on energetics almost ten years later (see [Görs, 1999; Deltete, 2007a]). This is clearly visible in his development — rather naive at first, but later more circumspect — of atomic and kinetic theories in a variety of essays and textbooks. And it is evident, as well, in his defense of, and contributions to, the theories of Arrhenius and van 't Hoff, both of which developed particulate views of substances in solution. With certain exceptions, Ostwald no longer offered realistic interpretations of such theories after about 1885, but he defended their heuristic value until the end of the decade.

At the same time, though, Ostwald also began to appreciate more than he had previously the heuristic advantages of phenomenological thermodynamics — its great success in deriving old results clearly and concisely, and in predicting new ones, without the complications and uncertainties associated with molecular and mechanical detours [1887a; 1887b; 1891; 1892]. This was initially evident to him in areas of physical chemistry to which he had himself already made important contributions, but he soon recognized the power of thermodynamic reasoning in other areas as well. The key to that power, he thought, was the attention given in thermodynamics to energy and its transformations. Ostwald gradually came to believe that while theories based on micro-mechanical hypotheses had made little progress with many problems, non-mechanistic, energy-based approaches had been dramatically successful. Those successes encouraged him to study the various forms of energy more carefully for himself (see Deltete 1995b and 2007a).

The second period, which partially overlaps the first, extends from the late 1880's until just after the turn of the century. It is marked by Ostwald's rejection of atomism and mechanism — in any of their forms — and by his efforts to provide a comprehensive energetic alternative. In the early years of this period, Ostwald began to doubt even the heuristic value of molecular and mechanical theories. He questioned the complexity of their mathematical development and their reliance on, as he saw it, arbitrary and unjustifiable hypotheses. Increasingly, he viewed many such theories as irresponsibly speculative and unscientific. After the mid-1890's, in fact, Ostwald's attitude toward even well-established mechanical theories was so hostile that he sometimes denied that they had ever been of any value at all. Several general works from those years consist of little more than sweeping condemnations of the mechanical world-view (e.g., [1895b]).

Ostwald's views on energy during this period develop in two fairly distinct stages. In writings from 1887 to 1890, he was concerned primarily to establish the importance of energy alongside matter as central to a progressive natural science [1887a; 1887b; Deltete, 2007a]. There he insisted on the importance of energy considerations, not only for chemistry, but for other sciences as well. The emphasis in these works gradually shifts from chemical energy and its transformations to the creation of a general theory of energy. Increasingly, he saw any success of studies deploying quantities of energy as reason for thinking that a theory of energy could unify natural science. Ostwald's first efforts at constructing such a theory were tentative and incomplete (e.g., [1889]), but he became bolder as he gained confidence in his approach and its apparent results.

In 1891, Ostwald began to assert first the priority, and then the absolute supremacy of energy — conceptually, methodologically and ontologically. Though he had claimed reality and substantiality for energy as early as 1887, his ambitions for it grew as his thought progressed, and by mid-decade he was prepared to assert, unequivocally, that energy was the only reality. The same years witnessed Ostwald's most persistent attempts to construct a consistent and coherent science of energetics. A variety of factors influenced those efforts: discussions with colleagues and students; continued reflection on the conceptual structure of thermodynamics; study of earlier energetic writings, especially Georg Helm's; encouragement from Helm, Boltzmann and others to express his thoughts on energy in a systematic form; and a decisive encounter with the thermodynamic writings of Willard Gibbs (see [Deltete, 1995a; 1995b]). In a series of works, published between 1891 and 1895, Ostwald sought to show how the basic results of mechanics, thermodynamics and chemistry could all be derived from energetic first principles [1891; 1892; 1893a; 1893b; 1895a]. His early declarations of success were generally tentative and carefully worded, but those of the late l890's became increasingly emphatic. By the end of the decade, he was convinced that while individual problems still remained, the basic theoretical framework for their solution had been firmly established. But by then such residual problems were also of less interest to Ostwald than another ambitious project which had captured his attention.

In what follows, I will focus on these two periods in Ostwald's development, during which his efforts in behalf of energetics had its basis in physical science. A third period, which lasted from around the turn of the century until the beginning of the First World War, had as its center a more broadly philosophical project. Those years — most of them after he had resigned his chair at Leipzig — were characterized by his attempt to show that the sciences of life and the mind, such as biology and psychology, were also embraced by energetics. At the same time, however, the character and not just the content of his writings changed. Ostwald had been interested in philosophical issues (in scientific methodology, for example) from his student days, but beginning in the late 1890's such issues began to dominate his thoughts. Increasingly, he relied on general philosophical arguments to defend energetics, and global references to "Monismus" and "Weltanschauung" replaced detailed discussions of chemical affinity and the forms of energy (e.g., [1902; 1908]). Most witnesses thought that the first decade of this century marked the demise of energetics as a serious scientific proposal and its continuation only as a rather vague philosophical movement (e.g., [Arrhenius, 1923; Nernst, 1932]).

No attempt will be made here to discuss the works of a fourth period (which includes the development of his novel theory of colors) that completes Ostwald's intellectual odyssey, except to say that from just before the beginning of the WWI until the end of his life, Ostwald tried to formulate global social and political theories based on the principles of energetics (e.g. [1911; 1912; Deltete, 2008a]). There is much to admire in his efforts (Ostwald was internationalist, anti-war, and pro-environment), but they have at best only a vague connection to the energetic theory he had proposed two decades earlier.

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Solar Radiation, Black Bodies, Heat Budget, and Radiation Balance

M.B. Kirkham , in Principles of Soil and Plant Water Relations (Second Edition), 2014

25.15 Appendix: Biography of Ludwig Boltzmann

Ludwig Boltzmann (1844–1906), Austrian physicist, made important contributions to many branches of physics. His greatest achievements were the development of statistical mechanics and the statistical explanation of the second law of thermodynamics. He was born in Vienna on February 20, 1844, and studied at the university there, receiving his doctorate in 1866. He held professorships in mathematics (Vienna, 1873–1876), experimental physics (Graz, 1876–1889), and theoretical physics (Graz, 1869–1873; Munich, 1889–1893; Vienna, 1894–1900; Leipzig, 1900–1902; Vienna, 1902–1906). Despite his several professorships, theoretical physics was his real vocation (Klein, 1971).

In 1905, when he was professor of theoretical physics at the University of Vienna, Boltzmann was invited to give a course of lectures in the summer session at the University of California in Berkeley. His recollections of that summer survive in his popular essay, "Reise eines deutschen Professors ins Eldorado." An abridged translation is presented in Physics Today (Boltzmann, 1905). Boltzmann's great sense of humor is evident in this writing.

When Boltzmann began his scientific work, he attacked the problem, until then unconsidered, of explaining the second law of thermodynamics on the basis of the atomic theory of matter. In a series of papers published during the 1870s, Boltzmann showed that the second law could be understood by combining the laws of mechanics, applied to the motions of the atoms, with the theory of probability. In this way, he made clear that the second law is an essentially statistical law and that a system will approach a state of thermodynamic equilibrium, because the equilibrium state is overwhelmingly the most probable state. The entropy function of thermodynamics, whose behavior shows the trend to equilibrium and whose maximum value characterizes the equilibrium state, is itself a measure of the probability of the macroscopic state. (The equation relating entropy and probability is engraved on the monument at Boltzmann's grave in Vienna.) He built much of the structure of statistical mechanics, a structure later elaborated by the U.S. mathematical physicist Josiah Willard Gibbs (1839–1903) ( Klein, 1971).

Apart from Boltzmann's work on statistical mechanics, he made extensive calculations in the kinetic theory of gases. He was also one of the first Europeans to recognize and to expound on the importance of James Clerk Maxwell's (1831–1879; Scottish physicist) theory of electromagnetism, a subject on which he published a two-volume treatise. Boltzmann also derived, using thermodynamics, Stefan's law for black-body radiation, a derivation that Hendrik Antoon Lorentz (1853–1928, Dutch physicist who got the Nobel Prize in physics in 1902) called "a true pearl of theoretical physics" (Klein, 1971).

Boltzmann's work in statistical mechanics was strongly attacked by Wilhelm Ostwald (1853–1932; German chemist who received the Nobel Prize in chemistry in 1909) and the energeticists who did not believe in atoms and wanted to base all of physical science on energy considerations only. Boltzmann also suffered from misunderstandings, on the part of others, about his ideas on the nature of irreversibility. They did not fully grasp the statistical nature of his reasoning. He was fully justified against both sets of opponents by the discoveries in atomic physics, which began shortly before 1900 and by the fluctuation phenomena, such as Brownian motion, which could be understood only by statistical mechanics (Klein, 1971). In 1905, Einstein explained Brownian motion (Isaacson, 2009; pp. 25, 27) by means of Boltzmann's ideas (Cercignani, 1998; p. 102), but Boltzmann died apparently before he knew about Einstein's confirmation of his work. Cercignani (1998) gives an in-depth discussion of the scientific world in which Boltzmann lived.

Depressed by the criticism of his work, Boltzmann took his own life by hanging on September 5, 1906, at Duino, near Trieste, Italy (Klein, 1971).

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Evolution, Theory of

Gregory C. Mayer , Catherine L. Craig , in Encyclopedia of Biodiversity (Second Edition), 2013

Introduction

What a Theory is

Before embarking on an exposition of the theory of evolution, it is necessary to clear up a common misunderstanding that arises from a confusion of the vernacular and technical meanings of the word "theory." In everyday speech, "theory" is often taken to mean a guess, an hypothesis, or a speculation – something opposed to the more surely known "facts." In the context in which the word is used in the phrase "evolutionary theory," however, and indeed in much of science, it signifies a series of interconnected high-level generalizations based on a large body of evidence. Thus, one speaks of "atomic theory," "quantum theory," or the "germ theory of disease." Far from indicating that these sets of connected propositions are mere speculations, it indicates that they are well supported by a considerable corpus of data.

All scientific theories, of course, are provisional (as indeed are all scientific "facts") and subject to revision in the light of further data. It is always salutary to bear this in mind, and also that some of the ideas and findings are more likely to be subject to revision than others. But it is important to know that the word "theory" does not partition scientific propositions into those more or less likely to be revised. Rather, it attaches to some of the most well-supported propositions, as in the examples just discussed. It is in this sense that this article refers to the "theory of evolution."

What Evolution is

If "evolution" means "change over time," there are many things that evolve. Solar systems, for example, evolve. Stars condense, planets form, comets come and go, and stars age in predictable sequences. Languages also evolve. Within historical times, Latin has given rise to French, Spanish, Italian, and the other Romance languages, while contributing much vocabulary to the development of English. But the biological theory of evolution does not encompass cosmology or historical linguistics; rather it is restricted to organic evolution, that is, changes in living beings over time. This formulation is still too broad, since individual organisms grow and develop over time (i.e., have an ontogeny), but this is not evolution in the modern sense. The changes in life over time that concern humans are those that persist beyond the lifetime of a single individual and are transmissible to offspring (i.e., are heritable). So organic evolution consists of changes in living beings that transcend a single generation, and which, in principle, can be transmitted through an indefinite number of generations.

The theory of evolution, as considered here, is primarily concerned with the mechanisms of evolutionary change. The study of evolutionary mechanisms, or the causes of evolution, however, is but one of the two great branches of evolutionary biology (Futuyma, 1998). The other is the study of the history of life – phylogeny in the broad sense. The biodiversity observed today, and in the fossil record of past times, is the product of evolutionary mechanisms in tandem with changes in environment and geography acting on organic beings over long periods of time. This history of life and its present condition and causes, of both particular branches of the phylogenetic tree and biodiversity in general, are the subject of the greater part of this Encyclopedia.

Genetics, ecology, and developmental biology are among the disciplines that contribute largely to the study of evolutionary processes, whereas systematics and paleontology are among those that contribute to evolutionary history and the estimation of the evolutionary chronicle (O'Hara, 1988). All these disciplines, however, interact in ways that do not allow a neat separation of their contributions to the two sides of evolutionary biology. As Dobzhansky (1973) noted, nothing in biology makes sense unless it is studied in an evolutionary context, and all fields of biology provide insight into the processes of evolution and the history of life.

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