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| == '''[[Alcmaeon of Croton]]''' == | | == '''[[Volatility (chemistry)]]''' == |
| ''by [[User:Anthony.Sebastian|Anthony.Sebastian]] | | ''by [[User:Anthony.Sebastian|Anthony.Sebastian]] and [[User:Milton Beychok|Milton Beychok]] |
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| '''Alcmaeon''', also '''Alcmaeon of Croton''', was an ancient Greek early-vintage [[natural philosopher]].<ref><font face="Gill Sans MT"><u>Note:</u>
| | {{Image|Vapor Pressure Chart2.png|right|350px|Example vapor pressure graphs of various liquids.}} |
| *Today scholars recognize 'natural philosophers' as early scientists, seeking rational explanations of phenomena observable on Earth and in the sky, often confining their explanations to hypothetical (theoretical) constructs, over time developing sophisticated and methodical observations, initiating experimental techniques, and engaging in commentary and criticism of each others' works. Scholars consider [[Thales|Thales of Miletus]], who flourished in the 6th century BCE, as the progenitor of natural philosophy, postulating water as the 'elementary' substance underlying all matter. [[Isaac Newton]] (1643-1727), whom we call today a mathematician and physicist, published his signal work in physics as <i>The Mathematical Principles of Natural Philosophy</i>.</font></ref> Alcmaeon had a wide spectrum of interests in natural phenomena (astronomical, anatomical, biological, cognitive, medical, ''inter alia''), offering explanations of them in rational mechanistic terms as opposed to the prevailing explanations in terms of supernatural forces, and he had a particular interest in medicine and physiology.<ref name=huffmansep2008>Huffman, Carl, "Alcmaeon", The Stanford Encyclopedia of Philosophy (Winter 2008 Edition), Edward N. Zalta (ed.), [http://plato.stanford.edu/archives/win2008/entries/alcmaeon/ Full-Text of Article.]
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| *<font face="Gill Sans MT">An extensive treatment of Almaeon's thinking and relationship to ancient Greek natural philosophy.</font></ref>
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| Longrigg states that of the medical theories of those natural philosophers in the era before [[Hippocrates|Hippocrates of Kos]] (who, with his disciples, left an extensive body of writings known as the Hippocratic treatises), only those of Alcmaeon have survived to any significant extent.<ref name=longrigg1993/>
| | In [[chemistry]] and [[physics]], '''volatility''' is a term used to characterize the tendency of a substance to vaporize.<ref>'''Note:''' To vaporize means to become a [[vapor]], the gaseous state of the substance.</ref> It is directly related to a substance' s [[vapor pressure]]. At a given [[temperature]], a substance with a higher vapor pressure will vaporize more readily than a substance with a lower vapor pressure.<ref>[http://www.bae.uky.edu/~snokes/BAE549thermo/gasesvapor.htm Gases and Vapor] ([[University of Kentucky]] website)</ref><ref>{{cite book|author=James G. Speight|title=The Chemistry and Technology of Petroleum|edition=4th Edition|publisher=CRC Press|date=2006|isbn=0-8493-9067-2}}</ref><ref name=Kister>{{cite book|author=Kister, Henry Z.|title=[[Distillation Design]]|edition=1st Edition|publisher=McGraw-Hill|year=1992|isbn=0-07-034909-6}}</ref> In other words, at a given temperature, the more volatile the substance the higher will be the pressure of the vapor in dynamic equilibrium with its vaporizing substance—i.e., when the rates at which molecules escape from and return into the vaporizing substance are equal. |
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| Ancient and modern scholars generally hold Alcmaeon in high esteem as an innovative thinker, as the originator or early proponent of the rationalistic explanation of health and disease, as an experimentalist, and as having a major influence on the development of Western medicine, in part through his influence on [[Hippocrates]] and his disciples.<ref name=longrigg1993/> "''[Alcmaeon's] anatomical researches, particularly into the structure of the eye, and his connecting the senses with the brain...mark him as a pioneer in pure medical science.''"<ref name=jonesphilmed>Jones WHS. (1979) [http://books.google.com/books?id=vaNMb8UssUgC&dq=Alcmaeon&source=gbs_navlinks_s Philosophy and medicine in ancient Greece: with an edition of Peri archaiēs iētrikēs]. Volume 8 of Johns Hopkins University Press reprints. Issue 8 of Bulletin of the History of Medicine. Supplements. Issue 8 of Henry E. Sigerist supplements to the Bulletin of the History of Medicine. Ayer Publishing. ISBN 9780405106064.</ref> Scholars have credited Alcmaeon as the first person to recognize the brain as the organ of sense perception, of intelligence, and as the seat of the mind.<ref name=doty2007>Doty RW. (2007) [http://dx.doi.org/10.1016/j.neuroscience.2007.02.046 Alkmaion's discovery that brain creates mind: a revolution in human knowledge comparable to that of Copernicus and of Darwin]. ''Neuroscience'' 147:561-8.
| | In common usage, the term applies primarily to [[liquid]]s. However, it may also be used to characterize the process of [[Sublimation (chemistry)|sublimation]] by which certain [[solid]] substances such as [[ammonium chloride]] (NH<sub>4</sub>Cl) and [[dry ice]], which is solid [[carbon dioxide]] (CO<sub>2</sub>), change directly from their solid form to a vapor without becoming a liquid. |
| *<font face="Gill Sans MT"><u>Abstract:</u> Without special examination the brain offers no clue that it is the organ of the mind. From the dawn of time man thus either ignored the problem as to the source of thought, or attributed it to a variety of anatomical structures, usually the heart. The brain held no place in such intuitions, and in most languages it is analogized to bone marrow. Furthermore, nothing in early medical systems claimed any intellectual capacity for the brain; the Egyptians, so fastidious in care for their afterlife, heedlessly discarded the brain in funerary practice. It was thus a unique event in world history when Alkmaion of Kroton (Alcmaeon, ca. 500 bc), based on anatomical evidence, proposed that the brain was essential for perception. Although no writings of Alkmaion survived, it was probably via a fortuitous linkage that his idea of the mental primacy of the brain was transmitted to, and preserved within, the teachings of the Hippocratic school. Nothing, of course, was secure as to mechanism, two millennia unfolding until the search for mind passed from the ventricles to the cerebral cortex. Nonetheless, Alkmaion was the beginning, and the ensuing understanding that he initiated is still transforming humanity's perception of the natural world, and their place within it.</font></ref> <ref name=debernardi>Debernardi A, Sala E, D'Aliberti G, Talamonti G, Franchini AF, Collice M. (2010) [http://www.ncbi.nlm.nih.gov/pubmed/20087125 Alcmaeon of Croton]. ''Neurosurgery'' 66:247-52 | [http://journals.lww.com/neurosurgery/Fulltext/2010/02000/Alcmaeon_of_Croton.11.aspx Free Full-Text].
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| *<font face="Gill Sans MT"><u>Abstract:</u> IN THE LATTER half of the sixth century BC, Croton was the site of the most famous medical school in Magna Graecia, where diseases of the human body were examined in a scientific and experimental manner instead of by using the contemporary supernatural, nearly magical concepts. Alcmaeon was one of the most active physicians interested in human physiology in the medical tradition of Croton. Although Alcmaeon was devoted to science and was a skillful experimentalist, little is known about his life and his exact birth date. The relative isolation of Alcmaeon from the great philosophical currents of his time probably facilitated his unprejudiced methodology and may have prevented him from disclosing his theories and demonstrating their value. He pioneered the concept of the relationship between the brain and the mind and was the first to identify the brain as the center of understanding and the essential organ for perceptions, sensations, and thoughts. Through systematic observations, Alcmaeon brought many things to light about the characteristics of the eye and the presence of channels connecting head sensory organs to the brain. He stated that the soul was immortal and introduced the tekmairesthai doctrine, through which the ideas of anamnesis and prognosis gave birth. We highlight his contributions to medical thought, and especially to neuroscience, which reveal Alcmaeon to be a thinker of considerable originality and one of the greatest philosophers, naturalists, and neuroscientists of all time.</font></ref>
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| Alcmaeon was born in about 515 BCE and lived sometime in the 500s BCE in the Greek city of Croton in Italy. Alcmaeon lived during and near the times of [[Pythagorus]] (ca. 570 – 490 BCE), also in Croton, and before [[Hippocrates|Hippocrates of Kos]] (460 – ca. 370 BCE).<ref name=nuttonancientmed>Nutton V. (2004) [http://www.questia.com/read/107508313 Ancient Medicine.] New York: Routledge
| | Any substance with a significant vapor pressure at temperatures of about 20 to 25 °[[Celsius (unit)|C]] (68 to 77 °[[Fahrenheit (unit)|F]]) is very often referred to as being ''volatile''. |
| *<u>Nutton states:</u> <font face="Gill Sans MT">Whether he [Alcmaeon] flourished in the late sixth century BC [close to 500 BC] or a generation or so later, in the second quarter of the fifth [475-450 BC], is disputed. Tradition claimed him as a pupil of Pythagoras [c.582–c.507 BC] 'in his old age', but the textual and historical basis for this assertion is far from sound, and Alcmaeon's interests and the sophistication of some of his methods are better suited to the later date.</font></ref> <ref name=longrigg1993>Longrigg J. (1993) [http://www.questia.com/read/103416571 Greek Rational Medicine: Philosophy and Medicine from Alcmaeon to the Alexandrians.] New York: Routledge.
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| *<u>Longrigg states:</u> <font face="Gill Sans MT">while a precise dating is impossible upon the available evidence, a period of activity around the second quarter of the fifth century BC would pose no insurmountable chronological problem with regard to the theories and views attributed to Alcmaeon.
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| *Longrigg gives a detail examination of the evidence for the dating of Alcmaeon’s life.</font></ref> <ref name=huffmansep2008/> <ref>[http://www.britannica.com/EBchecked/topic/13331/Alcmaeon Alcmaeon (2009) In Encyclopædia Britannica.] Retrieved November 07, 2009, from Encyclopædia Britannica Online.</font></ref>
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| ===Contributions of Alcmaeon=== | | === Vapor pressure, temperature and boiling point === |
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| [[Vesalius|Andreas Vesalius’s]] biographer, C. D. O’Malley, credits Alcmaeon as the earliest known “genuine student of anatomy”:
| | The vapor pressure of a substance is the pressure at which its gaseous (vapor) phase is in equilibrium with its liquid or solid phase. It is a measure of the tendency of [[molecule]]s and [[atom]]s to escape from a liquid or solid. |
| <blockquote>The earliest known genuine student of anatomy appears to have been Alcmaeon of Crotona, who lived in southern Italy, c. 500 B.C. Only the slightest fragments of his writing remain, but from these it does appear that he was the first to make dissections of animals, probably goats, and although almost nothing is known of the results, he did make the very important declaration that the brain is the central organ of intelligence.<ref name=omalley1964>O'Malley CD. (1964) Andreas Vesalius of Brussels, 1514-1564. Berkeley: University of California Press.
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| *<u>Note:</u> <font face="Gill Sans MT">Considered the definitive biography. Renown historian of medicine, F. N. L. Poynter, stated of Dr. O'Malley's book: "What strikes me immediately on reading Professor O'Malley's monumental work is the coolness of its judgment, the absence of any kind of special pleading or even of that warmth of expression which comes from the biographer's identification with his subject. This almost Olympian detachment is rare indeed and not to be found in any of the outstanding examples of the biographer's art which readily spring to mind." (See F. N. L. POYNTER. 1964. [http://dx.doi.org/10.1093/jhmas/XIX.4.321 Andreas Vesalius of Brussels — 1514-1564: A Brief Survey of Recent Work.] Journal of the History of Medicine and Allied Sciences 1964 XIX(4):321-326. PMID 14215447</font></ref></blockquote>
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| J. B. Wilbur and H. J. Allen give this introduction to Alcmaeon:
| | At [[atmospheric pressure]]s, when a liquid's vapor pressure increases with increasing temperatures to the point at which it equals the atmospheric pressure, the liquid has reached its [[boiling point]], namely, the temperature at which the liquid changes its state from a liquid to a gas throughout its bulk. That temperature is very commonly referred to as the liquid's ''normal boiling point''. |
| <blockquote>Physiology and medicine were Alcmaeon's prime interest, which accounts for his concern with cognition and the nature of the soul. Because medicine had not yet emerged as a distinct discipline, however, Alcmaeon also expressed opinions on the immortality of the soul as well as on astronomy and cosmology--thus going beyond the limitations of his own medical empiricism. There are no fragments and little other information concerning his views on these last two subjects, but in any case it would seem that Alcmaeon's contributions are his ideas concerning knowledge and the soul.<ref name=wilburallen>Wilbur JB, Allen HJ. (1979) [http://www.questia.com/read/82239065 The Worlds of the Early Greek Philosophers.] Prometheus Books: Buffalo, NY.
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| *<u>About this book, from its Preface:</u> <font face="Gill Sans MT">The authors of this book have tried to do two things in presenting the written materials ascribed to the early Greek philosophers (c. 585 B.C.-400 B.C.) and the historical context in which those writings occurred. The first was to present a more fully fleshed out picture of the ideas of these men than has been given in the past. Perhaps under the influence of a narrow empiricism there has been a preference for letting the fragments speak for themselves. The trouble with this approach is that, even where there is a goodly number of fragments left, as, for instance, by Heraclitus, an adequate context for interpretation is not always evident from the fragments alone. And in the case of a thinker such as Anaximander, on the other hand, where there is so little firsthand evidence, what does remain is obscure taken solely on its own terms. Opposed to this Scylla of parsimony, there is, of course, the Charybdis of prodigal speculation. But we did not wish to hew a predetermined course equidistant from these two extremes. Rather the goal was to suit our passage to the winds and waters, sometimes nearer one than the other, as seemed best....The second aim, also in the nature of a mean between extremes, was to find a happy balance between overwhelming the reader with all the scholarly paraphernalia of etymology and philology, and presenting a stripped-down version of the ideas that conveys no sense of the condition and source of our knowledge about them. While, for all but the specialist, the former detracts from the ideas presented, the latter fails to give a proper appreciation of the subject. In practice, this means that we<tried to indicate, whenever possible, who attributed an idea to a given philosopher while at the same time providing the student with the relevant passage so he can read for himself what, for instance, Heraclitus said about Pythagoras. For this reason, the fragments themselves as well as essential interpretive passages are included in the text. Testimonials by other thinkers, which are of great importance to our knowledge of the earliest of these Greek philosophers, are either included in the body of the text or referred to at the bottom of the page, depending upon their relevance. A guide to these testimonial sources appears at the end of the book, along with a selected bibliography for the period as well as for the thinkers.</font></ref></blockquote>
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| ''[[Alcmaeon of Croton|.... (read more)]]'' | | Not surprisingly, a liquid's normal boiling point will be at a lower temperature the greater is the tendency of its molecules to escape from the liquid, namely, the higher is its vapor pressure. In other words, the higher is the vapor pressure of a liquid, the higher is the volatility and the lower is the normal boiling point of the liquid. The adjacent vapor pressure chart graphs the dependency of vapor pressure upon temperature for a variety of liquids<ref name=Perry>{{cite book|author=R.H. Perry and D.W. Green (Editors)|title=Perry's Chemical Engineers' Handbook | edition=7th Edition|publisher=McGraw-Hill|year=1997|id=ISBN 0-07-049842-5}}</ref> and also confirms that liquids with higher vapor pressures have lower normal boiling points. |
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| | ''[[Volatility (chemistry)|.... (read more)]]'' |
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by Anthony.Sebastian and Milton Beychok
(PD) Image: Milton Beychok Example vapor pressure graphs of various liquids.
In chemistry and physics, volatility is a term used to characterize the tendency of a substance to vaporize.[1] It is directly related to a substance' s vapor pressure. At a given temperature, a substance with a higher vapor pressure will vaporize more readily than a substance with a lower vapor pressure.[2][3][4] In other words, at a given temperature, the more volatile the substance the higher will be the pressure of the vapor in dynamic equilibrium with its vaporizing substance—i.e., when the rates at which molecules escape from and return into the vaporizing substance are equal.
In common usage, the term applies primarily to liquids. However, it may also be used to characterize the process of sublimation by which certain solid substances such as ammonium chloride (NH4Cl) and dry ice, which is solid carbon dioxide (CO2), change directly from their solid form to a vapor without becoming a liquid.
Any substance with a significant vapor pressure at temperatures of about 20 to 25 °C (68 to 77 °F) is very often referred to as being volatile.
Vapor pressure, temperature and boiling point
The vapor pressure of a substance is the pressure at which its gaseous (vapor) phase is in equilibrium with its liquid or solid phase. It is a measure of the tendency of molecules and atoms to escape from a liquid or solid.
At atmospheric pressures, when a liquid's vapor pressure increases with increasing temperatures to the point at which it equals the atmospheric pressure, the liquid has reached its boiling point, namely, the temperature at which the liquid changes its state from a liquid to a gas throughout its bulk. That temperature is very commonly referred to as the liquid's normal boiling point.
Not surprisingly, a liquid's normal boiling point will be at a lower temperature the greater is the tendency of its molecules to escape from the liquid, namely, the higher is its vapor pressure. In other words, the higher is the vapor pressure of a liquid, the higher is the volatility and the lower is the normal boiling point of the liquid. The adjacent vapor pressure chart graphs the dependency of vapor pressure upon temperature for a variety of liquids[5] and also confirms that liquids with higher vapor pressures have lower normal boiling points.
.... (read more)
