Manganese is a chemical element with symbol Mn and atomic number 25. It is not found as a free element in nature. Manganese is a metal with important industrial metal alloy uses in stainless steels. Manganese is named for pyrolusite and other black minerals from the region of Magnesia in Greece, which gave its name to magnesium and the iron ore magnetite. By the mid-18th century, Swedish-German chemist Carl Wilhelm Scheele had used pyrolusite to produce chlorine. Scheele and others were aware that pyrolusite contained a new element, but they were unable to isolate it. Johan Gottlieb Gahn was the first to isolate an impure sample of manganese metal in 1774, which he did by reducing the dioxide with carbon. Manganese phosphating is used for corrosion prevention on steel. Ionized manganese is used industrially as pigments of various colors, which depend on the oxidation state of the ions; the permanganates of alkali and alkaline earth metals are powerful oxidizers. Manganese dioxide is used as the cathode material in alkaline batteries.
In biology, manganese ions function as cofactors for a large variety of enzymes with many functions. Manganese enzymes are essential in detoxification of superoxide free radicals in organisms that must deal with elemental oxygen. Manganese functions in the oxygen-evolving complex of photosynthetic plants. While the element is a required trace mineral for all known living organisms, it acts as a neurotoxin in larger amounts. Through inhalation, it can cause manganism, a condition in mammals leading to neurological damage, sometimes irreversible. Manganese is a silvery-gray metal, it is hard and brittle, difficult to fuse, but easy to oxidize. Manganese metal and its common ions are paramagnetic. Manganese tarnishes in air and oxidizes like iron in water containing dissolved oxygen. Occurring manganese is composed of one stable isotope, 55Mn. Eighteen radioisotopes have been isolated and described, ranging in atomic weight from 46 u to 65 u; the most stable are 53Mn with a half-life of 3.7 million years, 54Mn with a half-life of 312.3 days, 52Mn with a half-life of 5.591 days.
All of the remaining radioactive isotopes have half-lives of less than three hours, the majority of less than one minute. The primary decay mode before the most abundant stable isotope, 55Mn, is electron capture and the primary mode after is beta decay. Manganese has three meta states. Manganese is part of the iron group of elements, which are thought to be synthesized in large stars shortly before the supernova explosion. 53Mn decays to 53Cr with a half-life of 3.7 million years. Because of its short half-life, 53Mn is rare, produced by cosmic rays impact on iron. Manganese isotopic contents are combined with chromium isotopic contents and have found application in isotope geology and radiometric dating. Mn–Cr isotopic ratios reinforce the evidence from 26Al and 107Pd for the early history of the solar system. Variations in 53Cr/52Cr and Mn/Cr ratios from several meteorites suggest an initial 53Mn/55Mn ratio, which indicates that Mn–Cr isotopic composition must result from in situ decay of 53Mn in differentiated planetary bodies.
Hence, 53Mn provides additional evidence for nucleosynthetic processes before coalescence of the solar system. The most common oxidation states of manganese are +2, +3, +4, +6, +7, though all oxidation states from −3 to +7 have been observed. Mn2+ competes with Mg2+ in biological systems. Manganese compounds where manganese is in oxidation state +7, which are restricted to the unstable oxide Mn2O7, compounds of the intensely purple permanganate anion MnO4−, a few oxyhalides, are powerful oxidizing agents. Compounds with oxidation states +5 and +6 are strong oxidizing agents and are vulnerable to disproportionation; the most stable oxidation state for manganese is +2, which has a pale pink color, many manganese compounds are known, such as manganese sulfate and manganese chloride. This oxidation state is seen in the mineral rhodochrosite. Manganese most exists with a high spin, S = 5/2 ground state because of the high pairing energy for manganese. However, there are a few examples of S = 1/2 manganese.
There are no spin-allowed d–d transitions in manganese, explaining why manganese compounds are pale to colorless. The +3 oxidation state is known in compounds like manganese acetate, but these are quite powerful oxidizing agents and prone to disproportionation in solution, forming manganese and manganese. Solid compounds of manganese are characterized by its strong purple-red color and a preference for distorted octahedral coordination resulting from the Jahn-Teller effect; the oxidation state +5 can be produced by dissolving manganese dioxide in molten sodium nitrite. Manganate salts can be produced by dissolving Mn compounds, such as manganese dioxide, in molten alkali while exposed to air. Permanganate compounds are purple, can give glass a violet color. Potassium permanganate, sodium permanganate, barium permanganate are all potent oxidizers. Potassium permanganate called Condy's crystals, is a used laboratory reagent because of its oxidizing properties. Solutions of potassium permanganate were among the first stains and fixatives to be used in the preparation of biological cells and tissues for electron microscopy
Sugar is the generic name for sweet-tasting, soluble carbohydrates, many of which are used in food. The various types of sugar are derived from different sources. Simple sugars are called monosaccharides and include glucose and galactose. "Table sugar" or "granulated sugar" refers to a disaccharide of glucose and fructose. In the body, sucrose is hydrolysed into glucose. Sugars are found in the tissues of most plants, but sucrose is concentrated in sugarcane and sugar beet, making them ideal for efficient commercial extraction to make refined sugar. Sugarcane originated in tropical Indian subcontinent and Southeast Asia, is known of from before 6,000 BP, sugar beet was first described in writing by Olivier de Serres and originated in southwestern and Southeast Europe along the Atlantic coasts and the Mediterranean Sea, in North Africa, Macaronesia, to Western Asia. In 2016, the combined world production of those two crops was about two billion tonnes. Other disaccharides include lactose. Longer chains of sugar molecules are called polysaccharides.
Some other chemical substances, such as glycerol and sugar alcohols, may have a sweet taste, but are not classified as sugar. Sucrose is used in prepared foods, is sometimes added to commercially available beverages, may be used by people as a sweetener for foods and beverages; the average person consumes about 24 kilograms of sugar each year, or 33.1 kilograms in developed countries, equivalent to over 260 food calories per day. As sugar consumption grew in the latter part of the 20th century, researchers began to examine whether a diet high in sugar refined sugar, was damaging to human health. Excessive consumption of sugar has been implicated in the onset of obesity, cardiovascular disease and tooth decay. Numerous studies have tried to clarify those implications, but with varying results because of the difficulty of finding populations for use as controls that consume little or no sugar. In 2015, the World Health Organization recommended that adults and children reduce their intake of free sugars to less than 10%, encouraged a reduction to below 5%, of their total energy intake.
The etymology reflects the spread of the commodity. From Sanskrit शर्करा, meaning "ground or candied sugar," "grit, gravel", came Persian shakar, whence Arabic سكر, whence Medieval Latin succarum, whence 12th-century French sucre, whence the English word sugar. Italian zucchero, Spanish azúcar, Portuguese açúcar came directly from Arabic, the Spanish and Portuguese words retaining the Arabic definite article; the earliest Greek word attested is σάκχαρις. The English word jaggery, a coarse brown sugar made from date palm sap or sugarcane juice, has a similar etymological origin: Portuguese jágara from the Malayalam ചക്കരാ, itself from the Sanskrit शर्करा. Sugar has been produced in the Indian subcontinent since ancient times and its cultivation spread from there into modern-day Afghanistan through the Khyber Pass, it was not plentiful or cheap in early times, in most parts of the world, honey was more used for sweetening. People chewed raw sugarcane to extract its sweetness. Sugarcane was a native of Southeast Asia.
Different species seem to have originated from different locations with Saccharum barberi originating in India and S. edule and S. officinarum coming from New Guinea. One of the earliest historical references to sugarcane is in Chinese manuscripts dating to 8th century BCE, which state that the use of sugarcane originated in India. In the tradition of Indian medicine, the sugarcane is known by the name Ikṣu and the sugarcane juice is known as Phāṇita, its varieties and characterics are defined in nighaṇṭus such as the Bhāvaprakāśa. Sugar remained unimportant until the Indians discovered methods of turning sugarcane juice into granulated crystals that were easier to store and to transport. Crystallized sugar was discovered by the time of the Imperial Guptas, around the 5th century CE. In the local Indian language, these crystals were called khanda, the source of the word candy. Indian sailors, who carried clarified butter and sugar as supplies, introduced knowledge of sugar along the various trade routes they travelled.
Traveling Buddhist monks took sugar crystallization methods to China. During the reign of Harsha in North India, Indian envoys in Tang China taught methods of cultivating sugarcane after Emperor Taizong of Tang made known his interest in sugar. China established its first sugarcane plantations in the seventh century. Chinese documents confirm at least two missions to India, initiated in 647 CE, to obtain technology for sugar refining. In the Indian subcontinent, the Middle East and China, sugar became a staple of cooking and desserts. Nearchus, admiral of Alexander of Macedonia, knew of sugar during the year 325 B. C. because of his participation in the campaign of India led by Alexander. The Greek physician Pedanius Dioscorides in the 1st century CE described sugar in his medical treatise De Materia Medica, Pliny the Elder, a 1st-century CE Roman, described sugar in his Natural History: "Sugar is made in Arabia as well, but Indian sugar is better, it is a kind of honey found in cane, white as gum, it crunches between the teeth.
It comes in lumps the size of a hazelnut. Sugar is used only for medical purposes." Crusaders brought sugar back to Europe after their campaigns in the Hol
Magnesium in biology
Magnesium is an essential element in biological systems. Magnesium occurs as the Mg2+ ion, it is present in every cell type in every organism. For example, ATP, the main source of energy in cells, must bind to a magnesium ion in order to be biologically active. What is called ATP is actually Mg-ATP; as such, magnesium plays a role in the stability of all polyphosphate compounds in the cells, including those associated with the synthesis of DNA and RNA. Over 300 enzymes require the presence of magnesium ions for their catalytic action, including all enzymes utilizing or synthesizing ATP, or those that use other nucleotides to synthesize DNA and RNA. In plants, magnesium is necessary for synthesis of photosynthesis. A balance of magnesium is vital to the well-being of all organisms. Magnesium is a abundant ion in Earth's crust and mantle and is bioavailable in the hydrosphere; this availability, in combination with a useful and unusual chemistry, may have led to its utilization in evolution as an ion for signaling, enzyme activation, catalysis.
However, the unusual nature of ionic magnesium has led to a major challenge in the use of the ion in biological systems. Biological membranes are impermeable to magnesium, so transport proteins must facilitate the flow of magnesium, both into and out of cells and intracellular compartments. Chlorophyll in plants converts water to oxygen as O2. Hemoglobin in vertebrate animals transports oxygen as O2 in the blood. Chlorophyll is similar to hemoglobin, except magnesium is at the center of the chlorophyll molecule and iron is at the center of the hemoglobin molecule, with other variations; this process keeps living cells on earth alive and maintains baseline levels of CO2 and O2 in the atmosphere. Inadequate magnesium intake causes muscle spasms, has been associated with cardiovascular disease, high blood pressure, anxiety disorders, migraines and cerebral infarction. Acute deficiency is rare, is more common as a drug side-effect than from low food intake per se, but it can occur in people fed intravenously for extended periods of time.
The most common symptom of excess oral magnesium intake is diarrhea. Supplements based on amino acid chelates are much better-tolerated by the digestive system and do not have the side-effects of the older compounds used, while sustained-release dietary supplements prevent the occurrence of diarrhea. Since the kidneys of adult humans excrete excess magnesium efficiently, oral magnesium poisoning in adults with normal renal function is rare. Infants, which have less ability to excrete excess magnesium when healthy, should not be given magnesium supplements, except under a physician's care. Pharmaceutical preparations with magnesium are used to treat conditions including magnesium deficiency and hypomagnesemia, as well as eclampsia; such preparations are in the form of magnesium sulfate or chloride when given parenterally. Magnesium is absorbed with reasonable efficiency by the body from any soluble magnesium salt, such as the chloride or citrate. Magnesium is absorbed from Epsom salts, although the sulfate in these salts adds to their laxative effect at higher doses.
Magnesium absorption from the insoluble oxide and hydroxide salts is erratic and of poorer efficiency, since it depends on the neutralization and solution of the salt by the acid of the stomach, which may not be complete. Magnesium orotate may be used as adjuvant therapy in patients on optimal treatment for severe congestive heart failure, increasing survival rate and improving clinical symptoms and patient's quality of life. Magnesium can affect muscle relaxation through direct action on cell membranes. Mg2+ ions close certain types of calcium channels, which conduct positively charged calcium ions into neurons. With an excess of magnesium, more channels will be blocked and nerve cells activity will decrease. Intravenous magnesium sulphate is used in treating pre-eclampsia. For other than pregnancy-related hypertension, a meta-analysis of 22 clinical trials with dose ranges of 120 to 973 mg/day and a mean dose of 410 mg, concluded that magnesium supplementation had a small but statistically significant effect, lowering systolic blood pressure by 3–4 mm Hg and diastolic blood pressure by 2–3 mm Hg.
The effect was larger. Higher dietary intakes of magnesium correspond to lower diabetes incidence. For people with diabetes or at high risk of diabetes, magnesium supplementation lowers fasting glucose; the U. S. Institute of Medicine updated Estimated Average Requirements and Recommended Dietary Allowances for magnesium in 1997. If there is not sufficient information to establish EARs and RDAs, an estimate designated Adequate Intake is used instead; the current EARs for magnesium for women and men ages 31 and up are 265 mg/day and 350 mg/day, respectively. The RDAs are 420 mg/day. RDAs are higher than EARs so as to identify amounts that will cover people with higher than average requirements. RDA for pregnancy is 350 to 400 mg/day depending on age of the woman. RDA for lactation ranges 310 to 360 mg/day for same reason. For children ages 1–13 years the RDA increases with age from 65 to 200 mg/day; as for safety, the IOM sets Tolerable upper intake levels for vitamins and minerals when evidence is sufficient.
In the case of magnesium the UL is set at 350 mg/day. The UL is specific to magnesium consumed as a dietary supplement, the reason being that too much magnesium consumed at one time can caus
Human iron metabolism
Human iron metabolism is the set of chemical reactions that maintain human homeostasis of iron at the systemic and cellular level. Iron is both necessary to the body and toxic. Controlling iron levels in the body is a critically important part of many aspects of human health and disease. Hematologists have been interested in systemic iron metabolism because iron is essential for red blood cells, where most of the human body's iron is contained. Understanding iron metabolism is important for understanding diseases of iron overload, such as hereditary hemochromatosis, iron deficiency, such as iron deficiency anemia. Iron is an essential bioelement for most forms of life, from bacteria to mammals, its importance lies in its ability to mediate electron transfer. In the ferrous state, iron acts as an electron donor, while in the ferric state it acts as an acceptor. Thus, iron plays a vital role in the catalysis of enzymatic reactions that involve electron transfer. Proteins can contain iron as part of different cofactors, such as iron-sulfur clusters and heme groups, both of which are assembled in mitochondria.
Human cells require iron in order to obtain energy as ATP from a multi-step process known as cellular respiration, more from oxidative phosphorylation at the mitochondrial cristae. Iron is present in the iron-sulfur clusters and heme groups of the electron transport chain proteins that generate a proton gradient that allows ATP synthase to synthesize ATP. Heme groups are part of hemoglobin, a protein found in red blood cells that serves to transport oxygen from the lungs to the tissues. Heme groups are present in myoglobin to store and diffuse oxygen in muscle cells; the human body needs iron for oxygen transport. Oxygen is required for the survival of nearly all cell types. Oxygen is transported from the lungs to the rest of the body bound to the heme group of hemoglobin in erythrocytes. In muscles cells, iron binds myoglobin. Iron is potentially toxic, its ability to donate and accept electrons means that it can catalyze the conversion of hydrogen peroxide into free radicals. Free radicals can cause damage to a wide variety of cellular structures, kill the cell.
Iron bound to proteins or cofactors such as heme is safe. There are no free iron ions in the cell, since they form complexes with organic molecules. However, some of the intracellular iron is bound to low-affinity complexes, is termed labile iron or "free" iron. Iron in such complexes can cause damage. To prevent that kind of damage, all life forms; this binding allows cells to benefit from iron while limiting its ability to do harm. Typical intracellular labile iron concentrations in bacteria are 10-20 micromolar, though they can be 10-fold higher in anaerobic environment, where free radicals and reactive oxygen species are scarcer. In mammalian cells, intracellular labile iron concentrations are smaller than 1 micromolar, less than 5 percent of total cellular iron. In response to a systemic bacterial infection, the immune system initiates a process known as iron withholding. If bacteria are to survive they must obtain iron from their environment. Disease-causing bacteria do this in many ways, including releasing iron-binding molecules called siderophores and reabsorbing them to recover iron, or scavenging iron from hemoglobin and transferrin.
The harder they have to work to get iron, the greater a metabolic price they must pay. That means. So our control of iron levels appears to be an important defense against most bacterial infections. TB causing bacterium can reside within macrophages which are an iron rich environment and Borrelia burgdorferi utilises manganese in place of iron. People with increased amounts of iron, like people with hemochromatosis, are more susceptible to some bacterial infection. Although this mechanism is an elegant response to short-term bacterial infection, it can cause problems when inflammation goes on for longer. Since the liver produces hepcidin in response to inflammatory cytokines, hepcidin levels can increase as the result of non-bacterial sources of inflammation, like viral infection, auto-immune diseases or other chronic diseases; when this occurs, the sequestration of iron appears to be the major cause of the syndrome of anemia of chronic disease, in which not enough iron is available to produce enough hemoglobin-containing red blood cells.
Most well-nourished people in industrialized countries have 4 to 5 grams of iron in their bodies. Of this, about 2.5 g is contained in the hemoglobin needed to carry oxygen through the blood, most of the rest is contained in ferritin complexes that are present in all cells, but most common in bone marrow and spleen. The liver's stores of ferritin are the primary physiologic source of reserve iron in the body; the reserves of iron in industrialized countries tend to be lower in children and women of child-bearing age than in men and in the elderly. Women who must use their stores to compensate for iron lost through menstruation, pregnancy or lactation have lower non-hemoglobin body stores, which may consist of 500 mg, or less. Of the body's total iron content, about 400 mg is devoted to cellular proteins that use iron for important cellular processes like storing oxygen or performing energy-producing redox reactions. A small amount circulates through th
Proteins are essential nutrients for the human body. They are one of the building blocks of body tissue and can serve as a fuel source; as a fuel, proteins provide as much energy density as carbohydrates: 4 kcal per gram. The most important aspect and defining characteristic of protein from a nutritional standpoint is its amino acid composition. Proteins are polymer chains made of amino acids linked together by peptide bonds. During human digestion, proteins are broken down in the stomach to smaller polypeptide chains via hydrochloric acid and protease actions; this is crucial for the absorption of the essential amino acids that cannot be biosynthesized by the body. There are nine essential amino acids which humans must obtain from their diet in order to prevent protein-energy malnutrition and resulting death, they are phenylalanine, threonine, methionine, isoleucine and histidine. There has been debate as to whether there are 9 essential amino acids; the consensus seems to lean towards 9. There are five amino acids.
These five are alanine, aspartic acid, glutamic acid and serine. There are six conditionally essential amino acids whose synthesis can be limited under special pathophysiological conditions, such as prematurity in the infant or individuals in severe catabolic distress; these six are arginine, glycine, glutamine and tyrosine. Dietary sources of protein include both animals and plants: meats, dairy products and eggs, as well as grains and nuts. Vegans can get enough essential amino acids by eating plant proteins. Protein is a nutrient needed by the human body for maintenance. Aside from water, proteins are the most abundant kind of molecules in the body. Protein can be found in all cells of the body and is the major structural component of all cells in the body muscle; this includes body organs and skin. Proteins are used in membranes, such as glycoproteins; when broken down into amino acids, they are used as precursors to nucleic acid, co-enzymes, immune response, cellular repair, other molecules essential for life.
Additionally, protein is needed to form blood cells. Protein can be found in a wide range of food; the best combination of protein sources depends on the region of the world, cost, amino acid types and nutrition balance, as well as acquired tastes. Some foods are high in certain amino acids, but their digestibility and the anti-nutritional factors present in these foods make them of limited value in human nutrition. Therefore, one must consider digestibility and secondary nutrition profile such as calories, cholesterol and essential mineral density of the protein source. On a worldwide basis, plant protein foods contribute over 60 percent of the per capita supply of protein, on average. In North America, animal-derived foods contribute about 70 percent of protein sources. Meat, products from milk, eggs and fish are sources of complete protein. Whole grains and cereals are another source of proteins. However, these tend to be limiting in the amino acid lysine or threonine, which are available in other vegetarian sources and meats.
Examples of food staples and cereal sources of protein, each with a concentration greater than 7.0%, are buckwheat, rye, maize, wheat, sorghum and quinoa. Vegetarian sources of proteins include legumes, nuts and fruits. Legumes, some of which are called pulses in certain parts of the world, have higher concentrations of amino acids and are more complete sources of protein than whole grains and cereals. Examples of vegetarian foods with protein concentrations greater than 7 percent include soybeans, kidney beans, white beans, mung beans, cowpeas, lima beans, pigeon peas, wing beans, Brazil nuts, pecans, cotton seeds, pumpkin seeds, hemp seeds, sesame seeds, sunflower seeds. Food staples that are poor sources of protein include roots and tubers such as yams and sweet potato. Plantains, another major staple, are a poor source of essential amino acids. Fruits, while rich in other essential nutrients, are another poor source of amino acids; the protein content in roots and fruits is between 0 and 2 percent.
Food staples with low protein content must be complemented with foods with complete, quality protein content for a healthy life in children for proper development. A good source of protein is a combination of various foods, because different foods are rich in different amino acids. A good source of dietary protein meets two requirements: The requirement for the nutritionally indispensable amino acids under all conditions and for conditionally indispensable amino acids under specific physiological and pathological conditions The requirement for nonspecific nitrogen for the synthesis of the nutritionally dispensable amino acids and other physiologically important nitrogen-containing compounds such as nucleic acids and porphyrins. Healthy people eating a balanced diet need protein supplements; the table below presents the most important food groups as protein sources, from a worldwide perspective. It lists their respective performance as source of the limiting amino acids, in milligrams of limiting amino acid per gram of total protein in the food source.
The table reiterates the need for a balanced mix of
Zinc is a chemical element with symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. In some respects zinc is chemically similar to magnesium: both elements exhibit only one normal oxidation state, the Zn2+ and Mg2+ ions are of similar size. Zinc has five stable isotopes; the most common zinc ore is sphalerite, a zinc sulfide mineral. The largest workable lodes are in Australia and the United States. Zinc is refined by froth flotation of the ore and final extraction using electricity. Brass, an alloy of copper and zinc in various proportions, was used as early as the third millennium BC in the Aegean, the United Arab Emirates, Kalmykia and Georgia, the second millennium BC in West India, Iran, Syria and Israel/Palestine. Zinc metal was not produced on a large scale until the 12th century in India, though it was known to the ancient Romans and Greeks; the mines of Rajasthan have given definite evidence of zinc production going back to the 6th century BC. To date, the oldest evidence of pure zinc comes from Zawar, in Rajasthan, as early as the 9th century AD when a distillation process was employed to make pure zinc.
Alchemists burned zinc in air to form what they called "philosopher's wool" or "white snow". The element was named by the alchemist Paracelsus after the German word Zinke. German chemist Andreas Sigismund Marggraf is credited with discovering pure metallic zinc in 1746. Work by Luigi Galvani and Alessandro Volta uncovered the electrochemical properties of zinc by 1800. Corrosion-resistant zinc plating of iron is the major application for zinc. Other applications are in electrical batteries, small non-structural castings, alloys such as brass. A variety of zinc compounds are used, such as zinc carbonate and zinc gluconate, zinc chloride, zinc pyrithione, zinc sulfide, dimethylzinc or diethylzinc in the organic laboratory. Zinc is an essential mineral, including to postnatal development. Zinc deficiency affects about two billion people in the developing world and is associated with many diseases. In children, deficiency causes growth retardation, delayed sexual maturation, infection susceptibility, diarrhea.
Enzymes with a zinc atom in the reactive center are widespread in biochemistry, such as alcohol dehydrogenase in humans. Consumption of excess zinc may cause ataxia and copper deficiency. Zinc is a bluish-white, diamagnetic metal, though most common commercial grades of the metal have a dull finish, it is somewhat less dense than iron and has a hexagonal crystal structure, with a distorted form of hexagonal close packing, in which each atom has six nearest neighbors in its own plane and six others at a greater distance of 290.6 pm. The metal is hard and brittle at most temperatures but becomes malleable between 100 and 150 °C. Above 210 °C, the metal can be pulverized by beating. Zinc is a fair conductor of electricity. For a metal, zinc has low melting and boiling points; the melting point is the lowest of all the d-block metals aside from cadmium. Many alloys contain zinc, including brass. Other metals long known to form binary alloys with zinc are aluminium, bismuth, iron, mercury, tin, cobalt, nickel and sodium.
Although neither zinc nor zirconium are ferromagnetic, their alloy ZrZn2 exhibits ferromagnetism below 35 K. A bar of zinc generates a characteristic sound when bent, similar to tin cry. Zinc makes up about 75 ppm of Earth's crust. Soil contains zinc in 5–770 ppm with an average 64 ppm. Seawater has only 30 ppb and the atmosphere, 0.1–4 µg/m3. The element is found in association with other base metals such as copper and lead in ores. Zinc is a chalcophile, meaning the element is more to be found in minerals together with sulfur and other heavy chalcogens, rather than with the light chalcogen oxygen or with non-chalcogen electronegative elements such as the halogens. Sulfides formed as the crust solidified under the reducing conditions of the early Earth's atmosphere. Sphalerite, a form of zinc sulfide, is the most mined zinc-containing ore because its concentrate contains 60–62% zinc. Other source minerals for zinc include smithsonite, hemimorphite and sometimes hydrozincite. With the exception of wurtzite, all these other minerals were formed by weathering of the primordial zinc sulfides.
Identified world zinc resources total about 1.9–2.8 billion tonnes. Large deposits are in Australia and the United States, with the largest reserves in Iran; the most recent estimate of reserve base for zinc was made in 2009 and calculated to be 480 Mt. Zinc reserves, on the other hand, are geologically identified ore bodies whose suitability for recovery is economically based at the time of determination. Since exploration and mine development is an ongoing process, the amount of zinc reserves is not a fixed number and sustainability of zinc ore supplies cannot be judged by extrapolating the combined mine life of today's zinc mines; this concept is well supported by data from the United States Geol
The gram is a metric system unit of mass. Defined as "the absolute weight of a volume of pure water equal to the cube of the hundredth part of a metre, at the temperature of melting ice". However, in a reversal of reference and defined units, a gram is now defined as one thousandth of the SI base unit, the kilogram, or 1×10−3 kg, which itself is now defined by the International Bureau of Weights and Measures, not in terms of grams, but by "the amount of electricity needed to counteract its force" The only unit symbol for gram, recognised by the International System of Units is "g" following the numeric value with a space, as in "640 g" to stand for "640 grams" in the English language; the SI does not support the use of abbreviations such as "gr", "gm" or "Gm". The word gramme was adopted by the French National Convention in its 1795 decree revising the metric system as replacing the gravet introduced in 1793, its definition remained that of the weight of a cubic centimetre of water. French gramme was taken from the Late Latin term gramma.
This word—ultimately from Greek γράμμα, "letter"—had adopted a specialised meaning in Late Antiquity of "one twenty-fourth part of an ounce", corresponding to about 1.14 modern grams. This use of the term is found in the carmen de ponderibus et mensuris composed around 400 AD. There is evidence that the Greek γράμμα was used in the same sense at around the same time, in the 4th century, survived in this sense into Medieval Greek, while the Latin term did not remain current in Medieval Latin and was recovered in Renaissance scholarship; the gram was the fundamental unit of mass in the 19th-century centimetre–gram–second system of units. The CGS system co-existed with the MKS system of units, first proposed in 1901, during much of the 20th century, but the gram has been displaced by the kilogram as the fundamental unit for mass when the MKS system was chosen for the SI base units in 1960; the gram is today the most used unit of measurement for non-liquid ingredients in cooking and grocery shopping worldwide.
Most standards and legal requirements for nutrition labels on food products require relative contents to be stated per 100 g of the product, such that the resulting figure can be read as a percentage by weight. 1 gram = 15.4323583529 grains 1 grain = 0.06479891 grams 1 avoirdupois ounce = 28.349523125 grams 1 troy ounce = 31.1034768 grams 100 grams = 3.527396195 ounces 1 gram = 5 carats 1 gram = 8.98755179×1013 joules 1 undecimogramme = 1 "eleventh-gram" = 10−11 grams in the historic quadrant–eleventh-gram–second system a.k.a. hebdometre–undecimogramme–second system 500 grams = 1 Jin in the Chinese units of measurement. 1 gram is equal to 1 small paper clip or pen cap. The Japanese 1 yen coin has a mass of one gram, lighter than the British penny, the United States cent, the Euro cent, the 5 cent Australian coins. Conversion of units Duella Gold gram Orders of magnitude Gram at Encyclopædia Britannica