Bones (or osseous material) serve a number of diverse purposes in the human anatomy. In addition to providing structure, protection, and support for the organs of the body, bones also house marrow, which produces blood cells. Within the bones are also stored the calcium deposits which the body may access, via resorption, when needed. Additionally, bones detoxify the system, by removing heavy metals, such as lead and arsenic, as well as other toxins, from the bloodstream. Osseous tissue itself is made of water (about 1/4 of the bone weight), organic material (about 1/3 of the bone weight, most of which is the protein, ossein) and inorganic minerals (calcium, phosphorus, and magnesium predominate, though iron, sodium, potassium, chlorine, and fluorine are also present in small amounts). Most bones (with the exception of those of the skull) are initially pre-formed in cartilage and are then ossified as the newborn develops.
Two basic classification methods exist to categorize the bones of the body. These two classification systems are based upon anatomical location (axial or appendicular), and shape (long, short, flat, and irregular). Axial bones are the eighty bones which lie along the central, vertical axis of the body and support and protect the head and torso and include the skull and the spinal column.
Appendicular bones include the one hundred twenty-six bones which comprise the appendages, including the shoulders and hips, arms and legs, hands and feet, and fingers and toes. The shape classifications include long bones (such as the radius, humerus, and femur), the short bones (such as the carpals, tarsals, and manual and pedal phalanges), flat bones (such as the sternum, cranium bones, and scapulae), and irregular
bones (such as the vertebrae). Research Bone
Chemical dating is an absolute dating technique that depends on measuring the chemical composition of a specimen. Chemical dating can be used when the specimen is known to undergo slow chemical change at a known rate. For instance, phosphate in buried bones is slowly replaced by fluoride ions from the ground water. Measurement of the proportion of fluorinepresent gives a rough estimate of the time that the bones have been in the ground. Another, more accurate, method depends on the fact that amino acids in living organisms are L- optical isomers. After death, these racemize and the age of bones can be estimated by measuring the relative amounts of D- and L- amino acids present. Research Chemical dating
Fluorine is a very poisonous greenish-yellow gaseous element with the symbol F belonging to the group known as the halogens. It is the most chemically reactive element (many substances ignite spontaneously in it), and for this reason it is never found uncombined. Fluorine was isolated in 1886 by Moissan by the electrolysis of a solution of potassic fluoride in hydrofluoric acid. Fluorine has also been detected in the bones, teeth, blood, milk, and urine; in plants; in volcanic sublimates;
in rocks; in coprolites and mineral phosphates and in a variety of minerals. Research Fluorine
Van der Waals' forces are a type of weak intermolecular force that exists between all pairs of atoms and molecules that are not chemically bonded; they give rise to the existence of solids and liquids, affect the surface tension and viscosities of liquids, and cause gases to cool when they expand suddenly. Although the exact nature of van der Waals' forces varies from case to case, the most general cause is the correlation of the motions of the electrons in two adjacent molecules, producing an attractive force. The motion of the electrons in one molecule only affects the electrons in another when the molecules are very close, and
van der Waals' forces operate only over short distances. The forces increase as the number of electrons in a molecule increases, so the boiling-points of the halogens increase from fluorine to iodine and those of the alkanes increase as the carbonchain lengthens. These forces are named after their discoverer Johannes van der Waals. Research Van der Waals' forces
Xenon is a rare, gaseous element discovered in July 1898. It's symbol is Xe.
Xenon is a heavy (4.5 times heavier than air), unreactive stable gas occurring in air in trace percentages. It is one of the noble gases. Today, xenon is recovered on a commercial scale by the fractional distillation of liquid air. Natural xenon is a mixture of nine stable isotopes in the following percentages; xenon-124 (0.096); xenon-126 (0.090); xenon-128 (1.92); xenon-129 (26.44); xenon-130 (4.08); xenon-131 (21.18); xenon-132 (26.89) ; xenon-134 (10.44); and
xenon-136 (8.87).
The xenon found in some stony meteorites shows a large proportion of xenon-129, believed to be a product of radioactive decay of iodine-129, whose half-life is 17,000,000 years. Study of the xenon- 129 content of meteorites casts light on the history of the solar system. More than a dozen radioactive xenon isotopes produced by fission of uranium and other nuclear reactions are known. For example, xenon-135 (9.2-hour half-life) is produced by uraniumfission in nuclear reactors, where it is troublesome because it absorbs fission-producing neutrons. In 1962, a sample of xenon combined with an ion of platinum and fluorine to produce the first noble gas compound, previously the noble gases were thought to be inert. Now, xenon is known to combine with fluorine, oxygen, cesium, and alkali metals to form the corresponding fluorides, oxides and salts. All xenon compounds are toxic, although the gas itself is not.
Xenon has been used as an aesthetic, and is used as a tracer to measure lung capacity. It is the most popular gas used in strobe lamps and in high speed electronic flash bulbs used in photography. Electrical excitation of xenon atoms produces a brilliant white light. Some of its compounds have limited application as oxidizing agents. Xenon gas also has applications in modern nuclear power reactors. Research Xenon
Humite, named after the English mineralogist Sir Abraham Hume, is a fairly rare mineral of a transparentvitreous brown colour, found in the ejected masses of Vesuvius and in hydrothermal veins. It is a silicate of iron and magnesia, containing fluorine. Humite was confirmed as a distinct species of mineral in 1813. Research Humite
The Probert Encyclopaedia was designed, edited and programed by
Matt and Leela Probert
Abbreviations
Research Bone
