MATERIALS

 

Arsenic is extremely poisonous semimetallic element. The atomic number of arsenic is 33. Arsenic is in group 15 (or Va) of the periodic table.

 

Chemically, arsenic is intermediate between metals and nonmetals. Its properties lie, in general, in the middle of the series formed by the family of the elements nitrogen, phosphorus, arsenic, antimony, and bismuth. Arsenic ranks about 52^nd in natural abundance among the elements in crustal rocks. When arsenic is heated, it sublimes, passing directly from solid to gaseous form at 613° C. A common form of arsenic is grey, metallic in appearance, and has a relative density of 5.7. A yellow, nonmetallic form also exists and has a relative density of 2.0. The atomic weight of arsenic is 74.92.

 

Arsenic has been known since ancient times. The pure element can be easily prepared by heating a common ore called arsenopyrite (FeAsS). Other common minerals are realgar (As₂S₂); orpiment (As₂S₃); and arsenic trioxide (As₂O₃); occasionally the pure element is found in nature. Arsenic occurs frequently in place of some of the sulphur in the sulphides that are the principal ores of many of the heavy metals. When these ores are roasted, the arsenic sublimes and can be collected from the dust in the flues as a by-product.

 

Arsenic is used in large quantities in the manufacture of glass to eliminate a green color caused by impurities of iron compounds. A typical charge in a glass furnace contains 0.5% of arsenic trioxide. Arsenic is sometimes added to lead to harden it and is also used in the manufacture of such military poison gases as lewisite and adamsite. Until the introduction of penicillin, arsenic was of great importance in the treatment of syphilis. In other medicinal uses, it has been displaced by sulpha drugs or antibiotics. It is also used in dentistry in endodontiy.  Lead arsenate, calcium arsenate and Paris green are used extensively as insecticides. Certain arsenic compounds, such as gallium arsenide (GaAs), are used as semiconductors. GaAs is also used as a laser material. Arsenic disulphide (As₂S₂), also known as red orpiment and ruby arsenic, is used as a pigment in the manufacture of fireworks and paints.

 

Arsenic is poisonous in doses significantly larger than 65 mg (1 grain), and the poisoning can arise from a single large dose or from repeated small doses, as, for example, inhalation of arsenical gases or dust. On the other hand, some persons, notably the so-called arsenic eaters of the mountains of southern Austria, have found that arsenic has a tonic effect and have built up a tolerance for it, so that they can ingest each day an amount that would normally be a fatal dose. This tolerance, however, does not protect them against the same amount of arsenic administered hypodermically.

 

A reliable test that can detect the presence of minute amounts of arsenic is often important, because arsenic is a violent poison, yet it is widely used and therefore is a frequent contaminant. The Marsh test, named after its inventor, the English chemist James Marsh, supplies a simple method for detecting traces of arsenic so minute that they would escape discovery in ordinary analysis. The substance to be tested is placed in a hydrogen generator and any arsenic present is converted to arsine (AsH3), which mixes with the evolved hydrogen. If the stream of hydrogen is heated as it passes through a glass tube, the arsine decomposes, and metallic arsenic is deposited in the tube. Minute amounts cause an appreciable stain; as little as 0.1 of arsenic or antimony can be detected by using the Marsh test.

 

Copper is brownish-red metallic element that is one of the most widely used of metals. Copper is one of the transition elements of the periodic table. The atomic number of copper is 29.

 

Copper was known to prehistoric people and was probably the first metal from which useful articles were made. Copper objects have been found among the remains of many ancient civilizations, including those of Egypt, Asia Minor, China, south-eastern Europe, Cyprus (from which the word copper is derived) and Crete. It was known to Native Americans, and American ores were found by the European explorers. It is also found in the pure state.

 

Copper melts at about 1083° C, boils at about 2567° C and has a relative density of 8.9. The atomic weight of copper is 63.846. Because of its many desirable properties, such as its conductivity of electricity and heat, its resistance to corrosion, its malleability and ductility, and its beauty, copper has long been used in a wide variety of applications. The principal uses are electrical, because of copper's extremely high conductivity, which is second only to that of silver. Because copper is very ductile, it can be drawn into wires of any diameter from about 0.025 mm upwards. The tensile strength of drawn copper wire is about 4200 kg/sq; it can be used in outdoor power lines and cables, as well as in house wiring, lamp cords, and electrical machinery such as generators, motors, controllers, signaling devices, electromagnets, and communications equipment.

 

Copper has been used for coins throughout recorded history and has also been fashioned into cooking utensils, vats, and ornamental objects. Copper was at one time used extensively for sheathing the bottom of wooden ships to prevent fouling. Copper can easily be electroplated, alone or as a base for other metals. Large amounts are used for this purpose, particularly in making electrotypes, reproductions of type for printing.

 

The metallurgy of copper varies with the composition of the ore. Native copper is crushed, washed, and cast in bars. Oxides and carbonates are reduced with carbon. The most important ores, the sulphides, contain not more than 12%, sometimes as little as 1% of copper; they must first be crushed and concentrated by flotation. The concentrates are smelted in a reverberatory furnace, which yields crude metallic copper, approximately 98% pure. Crude copper is further purified by electrolysis, yielding bars exceeding 99.9% purity.

Pure copper is soft but can be hardened somewhat by being worked. Alloys of copper, which are far harder and stronger than the pure metal, have higher resistance and so it is used for crown materials or fillings in dentistry. They do, however, have corrosion resistance almost as good as that of pure copper and are very easily worked in machine shops. The two most important alloys are brass, a zinc alloy, and bronze, a tin alloy. Both tin and zinc are sometimes added to the same alloy, and no sharp dividing line can be drawn between brass and bronze. Both are used in enormous quantities. Copper is also alloyed with gold, silver, and nickel, and is an important constituent of such alloys as Monel metal, gunmetal, and German silver.

 

Copper forms two series of chemical compounds: cuprous, in which the copper has a valence of 1, and cupric, in which the copper has a valence of 2. Cuprous compounds are easily oxidized to cupric, in many cases by mere exposure to air, and are of little industrial importance; cupric compounds are stable. Certain copper solutions have the power of dissolving cellulose, and large quantities of copper are for this reason used in the manufacture of rayon. Copper is also used in many pigments and in such insecticides as Paris green and such fungicides as Bordeaux mixture, although it is being largely replaced by synthetic organic chemicals for these purposes.

 

  

COTTON

 

   

Crom is used by for orthodontic apparatus, by crowns and by partial prosthesis in dentistry. 

 

Diamond is mineral form of carbon, valued as a precious stone, and also used for various industrial purposes. Diamonds occur in various forms, including the diamond proper (a crystalline gemstone), bort, ballas, and carbonado. Bort is an imperfectly crystallized type of diamond, extremely hard, and dark in color. The term bort sometimes is applied also to minute fragments of gem diamonds. Ballas is a compact, spherical mass of tiny diamond crystals of great hardness and toughness. Carbonado, sometimes called black diamond or carbon, is an opaque greyish or black form of diamond with no cleavage. Carbonado, ballas, and bort are all used industrially in lapidary (cutting and polishing) work and for the cutting edges of drills and other cutting tools. Diamond is used in dentistry for cutting teeth.

 

The name diamond is derived from the Greek word adamas (“invincible”), which was probably applied by the Greeks to any hard stone, such as corundum. The first distinct and undoubted reference to diamonds occurs in Roman literature of the 1^st century AD. The diamonds known to the Romans undoubtedly came from India, which, until the 18^th century, was the only known source of the stones. They were believed to be found only in the fabled mines of Golconda, the market city of the diamond trade; gems sold there came from a number of mines. In 1726 diamonds were discovered in Brazil, and in 1866 in South Africa, which is now the chief source of gem diamonds.

 

Famous Diamonds

A number of individual diamonds have become historic, primarily because of their size. The largest of all known diamonds is the Cullinan, which was discovered in the Premier mine in South Africa in 1905 and was presented to Edward VII by the government of the Transvaal. The Cullinan weighed 3,106 carats before cutting and was pronounced by crystallographers to be a cleavage fragment of a considerably larger stone. When the stone was cut, a total of 105 gems were produced, weighing 1,063 carats in all. The largest of these was a drop-shaped stone called the Star of Africa, 530.2 carats, the largest cut diamond in existence, and now set in the royal sceptre.

The Vargas diamond, found in Brazil in 1938, weighed 726.6 carats in its uncut state. When cut in 1945, it yielded 29 stones with a total weight of 411 carats. In 1934 a diamond of almost precisely the same weight, the Jonker diamond, was discovered in an alluvial deposit near the Premier mine and is the finest large diamond ever found; it was cut into 12 gems ranging from 125.35 to 5.3 carats in weight. In 1967 the Lesotho diamond was discovered. It weighed 601.25 carats uncut.

 

The Great Mogul diamond, reputed to have weighed 240 carats when cut, has disappeared since it was described by the French traveller Jean-Baptiste Tavernier in India in 1665. Some authorities believe that the Koh-i-noor diamond, which now weighs 106.1 carats and is one of the crown jewels, is a part of the Great Mogul.

 

Fluorite is mineral composed of calcium fluoride CaF₂, the principal fluorine-bearing mineral. It occurs as cubic, isometric crystals and cleavable masses with a hardness of 4 and sp. gr. of 3-3.3. When pure, fluorite is colorless and transparent, or translucent with a glassy lustre. It often occurs with impurities that make it yellow, blue, purple, green, rose, or brown. Several varieties exhibit fluorescence.

 

The mineral is usually found either in pure veins or associated with lead, silver, or zinc ores. It is common in limestone and dolomites, and is occasionally found as an accessory mineral in pegmatites and other igneous rocks. Exceptionally clear crystalline fluorite is mined in Cumbria and Derbyshire, England. Commercially important deposits in the United States occur in a region on the Ohio River that includes parts of Illinois and Kentucky.

Crystalline varieties, such as the fine-colored Derbyshire spar or Blue John, are often carved into vases and other similar ornaments and the variety chlorophane is used as a gem. The principal use of fluorite has been for the production of hydrofluoric acid, an essential raw material in the manufacture of synthetic cryolite and aluminium fluoride for the aluminium industry, and in many other applications in the chemical industry. Fluorite is also a standard flux used in the making of steel. Large quantities of fluorite are used in the production of enamel and opal glass, and perfect crystals are used for the manufacture of apochromatic lenses. Fluorite is also used in toothpastes and for fluoridation of children’s teeth. Fluorite helps to harden of enamel.

 

Gold symbol is Au (from Latin aurum, “gold”), soft, dense, bright yellow metallic element. Gold is one of the transition elements of the periodic table; its atomic number is 79. Pure gold is the most malleable and ductile of all the metals. It can easily be beaten or hammered to a thickness of 0.000013 cm, and 29 g could be drawn into a wire 100 km long. It is one of the softest metals (hardness, 2.5 to 3) and is a good conductor of heat and electricity. Gold is bright yellow and has a high lustre. Finely divided gold, like other metallic powders, is black; colloidally suspended gold ranges in color from ruby red to purple.

Gold is extremely inactive. It is unaffected by air, heat, moisture, and most solvents. It will, however, dissolve in mixtures containing chlorides, bromides, or some iodides. It will also dissolve in many oxidizing mixtures, in alkali cyanides, and in aqua regia, a mixture of hydrochloric and nitric acids. The chlorides and cyanides are important compounds of gold. Gold melts at about 1,064° C, boils at about 2,808° C and has a relative density of 19.3; its atomic weight is 196.967.

 

Gold is found in nature in quartz veins and secondary alluvial deposits as a free metal or in a combined state. It is widely distributed although it is rare, being 75^th in order of abundance of the elements in the crust of the earth. It is almost always associated with varying amounts of silver; the naturally occurring gold-silver alloy is called electrum. Gold occurs, in chemical combination with tellurium, in the minerals calaverite and sylvanite along with silver, and in the mineral nagyagite along with lead, antimony, and sulphur. It occurs with mercury as gold amalgam. It is generally present to a small extent in iron pyrites; galena, the lead sulphide ore that usually contains silver, sometimes also contains appreciable amounts of gold. Gold also occurs in sea water to the extent of 5 to 250 parts by weight to 100 million parts of water. Although the quantity of gold present in sea water is more than 9 billion metric tons, the cost of recovering the gold would be far greater than the value of the gold that could thus be recovered.

 

The metal has been known and highly valued from earliest times, not only because of its beauty and resistance to corrosion, but also because gold is easier to work than all other metals. In addition, gold was easier to obtain in pure form than the other metals. Because of its relative rarity, gold became used as currency and as a basis for international monetary transactions (Gold Standard). The unit used in weighing gold is the troy ounce; 1 troy ounce is equivalent to 31.1 grams.

 

The major portion of the gold produced is used in coinage and jewellery . For these purposes it is alloyed with other metals to give it the necessary hardness. The gold content in alloys is expressed in carats. Coinage gold is composed of 90 parts gold to 10 parts silver. Green gold used in jewellery contains copper and silver; white gold contains zinc and nickel, or platinum metals.

Gold is also used in the form of gold leaf in the arts of gilding and lettering. Purple of Cassius, a precipitate of finely divided gold and stannic hydroxide formed by the interaction of auric chloride and stannous chloride, is used in colouring ruby glass. Chlorauric acid is used in photography for toning silver images. Potassium gold cyanide is used in electrogilding. Gold is also used in dentistry. Radioisotopes of gold are used in biological research and in the treatment of cancer.

 

Gold production dates from the Etruscan, Minoan, Assyrian, and Egyptian civilizations, when placer gold was derived from alluvial sands and gravels by simple processes of washing or panning. Gold was produced in this manner at an early period in India, central Asia, the southern Ural Mountains and in the regions bordering the eastern Mediterranean. With progress in mining technique, primary auriferous (gold-bearing) veins were exploited; this type of gold mining attained some importance before the Christian era. During the Middle Ages little progress was made in gold production and mining.

 

At the time of the discovery of the Americas the value of the total gold stock of Europe was probably less than $225 million. During the succeeding 350 years, from the end of the 15^th century to about 1850, the world gold output totalled about 4,665,000 kg. South America and Mexico became large producers of gold during this period. Spain's domination in South America resulted, in the 16^th century, in a large increase in gold produced in the New World; some resulted from simple seizure of gold from the Native Americans, who had long mined the metal. In the same century Mexico contributed about 9% of the total world production. Gold was discovered in Australia in February 1851, and rich fields were found there.

 

South Africa is the world's leading supplier of gold, producing about 600 metric tons annually; its most important gold mines are in the Witwatersrand region. Some 70 other countries produce gold in commercial quantities, but about 80% of the total worldwide production now comes from South Africa, the United States, the former Soviet republics, Australia, Canada, China, and Brazil.

 

Gypsum is common mineral consisting of hydrated calcium sulphate (CaSO₄·2H₂O). It is a widely distributed form of sedimentary rock, formed by the precipitation of calcium sulphate from seawater, and is frequently associated with other saline deposits, such as halite and anhydrite, as well as with limestone and shale. Gypsum is produced in volcanic regions by the action of sulphuric acid on calcium-containing minerals; it is also found in most clays as a product of the action of sulphuric acid on limestone. It occurs in all parts of the world; some of the best workable deposits are in France, Switzerland, the United States, and Mexico. Alabaster, selenite, and satin spar are varieties of gypsum.

 

Artificial gypsum is obtained as a by-product in an old method for the manufacture of phosphoric acid. Rock phosphate, the essential constituent of which is tricalcium phosphate, is treated with sulphuric acid, producing phosphoric acid and gypsum. The gypsum is compacted into blocks and used for the construction of non-supporting walls in buildings. By properly controlling the concentration and temperature of sulphuric acid added to phosphate rock, a mixture of monocalcium phosphate, dicalcium phosphate, and gypsum may be obtained. This mixture is a valuable fertilizer, known as superphosphate.

Gypsum crystallizes in the monoclinic system in white or colorless crystals, which are massive or foliated in formation. Many specimens are colored green, yellow, or black by impurities. With a hardness ranging from 1.5 to 2, it is soft enough to scratch with a fingernail and has a relative density of 2.3. When heated to 128° C, it loses part of its water of crystallization and is converted into plaster of Paris, CaSO₄ · 1H₂O. Finely ground plaster of Paris, when mixed to a paste with water, sets in a short time into a hard mass of gypsum, the rehydrated crystals forming and interlocking in such a way as to cause expansion in volume.

 

Because of its property of swelling and filling all small spaces on drying, plaster of Paris is used extensively in making casts for statuary, ceramics, dental plates, fine metal parts for precision instruments, and surgical splints. Uncalcined gypsum is used as a fertilizer for dry, alkaline soil. It is also used as a bed for polishing plate glass and as a basis for paint pigments. Large amounts of gypsum are used as a retarder in portland cement.

 

 

 

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