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A Matter of Life and Death
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17195 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
12 / 1990 |
2,894 Words |
| Author
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Harold Goldwhite
Harold Goldwhite is professor of chemistry at California
State University, Los Angeles. |
On September 15, 1677, the distinguished scientist Robert Boyle attended in London a meeting of the Royal Society, one of the earliest scientific societies and one that has endured to the present. A German scientist, Johan Daniel Krafft, was to make a demonstration of a remarkable new material. Boyle has left us a detailed account of the marvels shown that day. After the shutters of the room had been closed, Krafft showed the assembled group a small piece of material, about the size of a small marble, that glowed a vivid yellowish-green in the dark. "Mr. Krafft also calling for a sheet of paper and taking some of his stuff upon the tip of his finger, writ in large characters … DOMINI … which … shone so briskly, and lookt so oddly, that the sight was extremely pleasing." This wondrous material, which possessed the power to glow vividly in complete darkness, was the first sample of the element phosphorus (from the Greek phosphoros, meaning "light bringer") to be seen in England. The new element had been first isolated by an alchemist, Hennig Brand of Hamburg, around 1670. Brand's process was initially kept secret, but it was soon shared with Johann Kunckel, a German chemist, and Krafft, who carried the element to Holland, England, and even North America. Following some hints from Krafft, Robert Boyle and his assistant Robert Hooke worked out the preparation of phosphorus in September 1680, and Boyle's posthumous publication of the method, in 1691, was the first public scientific description of how the element was isolated. In brief, human urine was boiled down to a small volume and then placed in a retort with its outlet under water. When the retort was made red-hot in a furnace, phosphorus distilled out into the water, where it was collected.
The element - and where it's found
Phosphorus is the twelfth most abundant element in the earth's crust, which contains about 0.1 percent of it by weight; because of the great reactivity of the element, it is always found in combined form, usually as phosphates - salts of phosphoric acid, H3PO4. Phosphorus is element number 15 in the Periodic Table and is the second element in Group V. The most common valences of phosphorus are 3 and 5, as is indicated by the existence of two commercially available chlorides - the liquid phosphorus trichloride, PCl3, and the solid phosphorus pentachloride, PCl5. Only one isotope of phosphorus, of mass 31, occurs in the natural world. The radioactive isotope phosphorus-32 is made in reactors and is widely used as a tracer in chemistry and biochemistry of follow the reactions of phosphorus compounds.
As the original preparation procedure reveals,
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