Da li postoje šibice koje gore, ako su mokre? Molim Vas, mogu li dobiti recept za izradu šibica. To mi je potrebno da bih mogla ići na takmičenje iz kemije.

Pitanje postavila: Ana Koračević: mkoracevic@hrvatska.com



Sto se tice sibica nasao sam jedan clanak u Enc. britannici. U njemu se ne govori nista o sibicama koje gore pod vodom, ali ima dosta o obicnim sibicama. Tekst je na engleskom, pa se nadam da to nece biti problem, dio koji se odnosi na kemijski sastav nalazi se na kraju, a ja sam ga podebljao. Sto se tice sibica koje gore pod vodom sad je to dosta aktualno, jer ce uskoro zapoceti olimpijske igre u Australiji, a u ceremoniji otvaranja je predvidjeno da se olimpijski plamen upali pod morem. Na mrezi ima dosta clanaka o tome (mozes ih naci preko nekog pretrazivaca uz kljucne rijeci magnesium torch (magnezijeva baklja)), a ja sam uvrstio jedan pod naslovom: "Olympic torch goes underwater". Glavni sastojak takvih podvodnih baklji je sitni magnezijev prah koji oksidacijom oslobadja vrlo veliku toplinu. Mg (s) + 1/2 O2 (g) -> MgO (s) entalpija reakcije = -602 kJ/mol Zbog intenzivne svjetlosti koja se oslobadja pri gornjoj reakciji, oksidacija magnezija se koristi kao izvor svjetlosti u fotografiji. Match splinter of wood, strip of cardboard, or other suitable flammable material tipped with a substance ignitable by friction. A match consists of three basic parts: a head, which initiates combustion; a tinder substance to pick up and transmit the flame; and a handle. There are two main types of modern friction matches: (1) strike-anywhere matches and (2) safety matches. The head of the strike-anywhere match contains all the chemicals necessary to obtain ignition from frictional heat, while the safety match has a head that ignites at a much higher temperature and must be struck on a specially prepared surface containing ingredients that pass ignition across to the head. The substance commonly used for obtaining combustion at the temperature of frictional heat is a compound of phosphorus. This substance is found in the head of strike-anywhere matches and in the striking surface of safety matches. In addition to the phosphoric igniting agent, three other main groups of chemicals are found in the match: (1) oxidizing agents, such as potassium chlorate, which supply oxygen to the igniting agent and the other combustible materials; (2) binders, such as animal glue, starches and gums, and synthetics, which bind the ingredients and are oxidized during combustion; post-combustion binders, such as ground glass, which fuse and hold the ash together, must also be used; and (3) inert materials, such as diatomaceous earth, which provide bulk and regulate the speed of reaction. Before the invention of matches, it was common to use specially made splinters tipped with some combustible substance, such as sulfur, to transfer a flame from one combustible source to another. An increased interest in chemistry led to experiments to produce fire by direct means on this splinter. Jean Chancel discovered in Paris in 1805 that splints tipped with potassium chlorate, sugar, and gum could be ignited by dipping them into sulfuric acid. Later workers refined this method, which culminated in the "promethean match" patented in 1828 by Samuel Jones of London. This consisted of a glass bead containing acid, the outside of which was coated with igniting composition. When the glass was broken by means of a small pair of pliers, or even with the user's teeth, the paper in which it was wrapped was set on fire. Other early matches, which could be both inconvenient and unsafe, involved bottles containing phosphorus and other substances. An example was François Derosne's briquet phosphorique (1816), which used a sulfur-tipped match to scrape inside a tube coated internally with phosphorus. These first matches were extremely difficult to ignite, and they frequently erupted in a shower of sparks. In addition, the smell was particularly offensive, and the warning printed on Jones's box ("Persons whose lungs are delicate should by no means use the Lucifers") seems well founded. Economic conditions between 1825 and 1835 seem to have favoured the manufacture of matches as an industrial proposition, although the first suppliers fell back on nonphosphoric formulas--i.e., those based mostly on potassium-chlorate mixtures. The first friction matches were invented by John Walker, an English chemist and apothecary, whose ledger of April 7, 1827, records the first sale of such matches. Walker's "Friction Lights" had tips coated with a potassium chloride-antimony sulfide paste, which ignited when scraped between a fold of sandpaper. He never patented them. Nonphosphoric friction matches were being made by G.-E. Merkel of Paris and J. Siegal of Austria, among others, by 1832, by which time the manufacture of friction matches was well established in Europe. In 1831 Charles Sauria of France incorporated white, or yellow, phosphorus in his formula, an innovation quickly and widely copied. In 1835 Janos Irinyi of Hungary replaced potassium chlorate with lead oxide and obtained matches that ignited quietly and smoothly. The discovery by the Austrian chemist Anton von Schrötter in 1845 of red phosphorus, which is nontoxic and is not subject to spontaneous combustion, led to the safety match, with its separation of the combustion ingredients between the match head and the special striking surface. J.E. Lundström of Sweden patented this method in 1855. Although safety matches became widely accepted, white phosphorus matches continued to be popular because of their keeping qualities and resistance to climatic conditions. However, at the end of the 19th century serious toxic effects of white phosphorus ("phossy jaw") were discovered in the factory workers who made such matches. Phosphorus sesquisulfide, much less toxic, was first prepared by the French chemist Georges Lemoine in 1864 but was not used in matches until E.-D. Cahen and H. Sevene of the French government match monopoly filed a patent in 1898; within a few years white phosphorus was outlawed nearly everywhere. Modern safety matches usually have antimony sulfide, oxidizing agents such as potassium chlorate, and sulfur or charcoal in the heads, and red phosphorus in the striking surface. Nonsafety matches usually have phosphorus sesquisulfide in the heads. Olympic torch goes underwater CAIRNS (AUSTRALIA): A team of experts took more than 25 attempts to devise the chemical formula that will power the Olympic torch during its first underwater journey on Tuesday. The inventors of the underwater flare have guaranteed the torch will stay alight when it is taken underwater for the first time in Olympic history on the Great Barrier Reef. The modified distress flare inserted into the Olympic torch housing will burn at more than 2,000 degrees celsius, producing 35,000 candlepower of light. A team of chemists and engineers at Melbourne pyrotechnics company Pains Wessex took nine months to perfect the flare. Pains Wessex managing director Charles Tegner said designing the torch was a challenge. "We had to produce a flare that would burn underwater at a depth of around about four metres and burn for a period of about three minutes, but it also had to look like the Olympic torch flame and it had to be clearly visible," he said. "Such flares don't normally exist." Olympic authorities also insisted that the torch did not give off any toxic by-products while it was in the world heritage-listed Great Barrier Reef marine park. The design team finally decided to use the highly combustible element magnesium in a finely powdered form to create the flame. (AFP)
Odgovorio: Goran Stefanic stefanic@rudjer.irb.hr



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