Since the time man tamed fire, he has been using it to shed light onto the materials around him by burning and thus break them up into their components.
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When wood was burned, the ash in water broke up fats and curdled them into slippery blobs of soaps. Man discovered methods and techniques to make his fires burn hotter.
One method was to blow a stream of air into them using a bellow. Another was to use charcoal made from wood that had been very slowly burned under piles of earth and thus purified and concentrated. By placing fires in the closure of a furnace, he was able to make fire hot enough to burn and break apart rocks and crystals until they sweated out their metals.
Sand melted into glass. Colorful crystals broke apart in fires and released metals they contained. The minerals were first roasted in air, and then burnt using charcoal to obtain the pure metals left behind. The following metals were available to man - gold, silver, copper, lead, tin, iron, mercury and antimony.
Gold, Silver and Copper
Because gold, silver and copper were found in their native form on the surface of the earth, they were the very first metal to have been used by man. Gold and silver are very soft and could be only used as decoration and as a form of money.
Copper was commonly encountered as copper salts, and gave minerals such as azurite, malachite and turquoise their blue or green colors which were widely used as pigments. Copper was the first metal to be smelted from its ore at around 5000BC.
By 4000BC, it was cast into a shape in a mold and various tools and weapons were made from it.
Gold, silver and copper are one of the best conductors of electricity. They are one of the most ductile and malleable of metals.
Gold can be hammered into transparent sheets which are 0.0025mm thick. The amount of gold in an alloy is expressed in carats with pure gold referred to as having 24 carats. An alloy that contains 20 parts gold to 4 parts of another metal is referred to as having 20 carats.
It is estimated that only 121,000 tons of gold had been mined throughout history, making a cube about 20m high, 20m wide, and 20m long.
- About 18,000 tons (15%) have been used for industry and have never been recovered and reused.
- Of the remaining 103,000 tons of gold (85%), about a third has been made into gold bars held by national banks.
- The remaining 68,000 tons of gold (60%) are owned by private individuals as jewelry, coins, or bars.
Adding gold to glass gives it a beautiful ruby-red color. Adding silver behind a sheet of glass turns it into a mirror. Coating a silver ion solution on a film of paper allows light to change the silver ions to silver atoms which are black, thus etching a picture on it as in a photograph.
Lead
Lead is a heavy, soft, gray solid which is ductile, malleable and very easy to smelt.
A chief ore is galena (PbS) which was used in Ancient Egypt as a make-up around the eyes to reduce the glare of the desert sun and to repel flies, a potential source of disease.
Throughout history, lead has been used to make pots and pans, and water and sewer pipes and in paints. It is also used as roofing material and as ammunition. More recently it has been used as cable covering, as electrodes of car batteries, in solder, as an additive in gasoline and as shielding from radiation in x-ray rooms and nuclear reactors. Lead is a member of the carbon family and just like carbon hardens iron, lead hardens glass.
Tin
Tin, which rarely occurs free in nature, is a silvery-white, soft, malleable metal that can be highly polished. It has a highly crystalline structure and when a tin bar is bent, a ‘tin cry’ is heard, due to the breaking of these crystals.
Tin is used as a sheet for roofs and as a coating on the surface of other metals to prevent corrosion. ‘Tin’ cans, for example, are made of tin-coated steel.
A chief tin ore is cassiterite (SnO2). Tin is a member of the carbon family and just like carbon hardens iron, tin hardens copper.
Alloying copper with 10% tin makes bronze which is harder than copper and much easier to cast. The Bronze Age between 3500BC-1000BC marked a significant advance in human civilization with great improvement in transportation, food preparation, and quality of life making durable wheels and containers to store, transport and cook foods.
Iron
Meteorites frequently contain large quantities of iron, and the first iron used by ancient man was from these “stones from heaven”. The first iron extracted from the naturally occurring iron oxide deposits resulted from building a fire on ground rich in iron oxides. The ash left behind contained a small amount of iron sponge which when hammered into wrought iron was relatively ductile but lacking in hardness and strength.
Spears, arrow tips, daggers, and other tools and weapons were fabricated from it.
When iron ores were smelted with charcoal, carbon was absorbed into the iron lattice turning it into hard and strong steel. When the percent- age of carbon in the iron lattice was greater than 2%, pig iron was produced which could be cast, but was too brittle to be worked. When the iron ores had too many impurities, limestone was used to remove them.
Some chief ores of iron are pyrite (FeS2) and hematite (Fe2O3). Striking a pyrite nodule with a sharp piece of chert, or another pyrite nodule causes hot flecks of the pyrite to be struck off as sparks. The reddish color of hematite lends itself to use as a pigment. The red chalk writing of this mineral was one of the earliest in the history of humans.
Iron is far more abundant than bronze. Steel is stronger and holds an edge longer than bronze allowing the development of steel tools, weapons and wheels which were greatly superior to those made from bronze. This ushered in the Iron Age at about 1000BC. With the discovery of chromium in 1800AD and its addition to steel, the alloy stainless steel was made that did not rust.
Mercury
Mercury is the only liquid metal.
The chief ore of mercury is cinnabar (HgS) and when it is heated or rubbed with vinegar, mercury is released.
Metals easily dissolve in mercury to form alloys called amalgams much like salts dissolve in water. This technique is used to extract other metals from their ores.
Antimony
Antimony is a hard and brittle silvery-white shiny crystalline solid which is easily pulverized.
The chief ore of antimony is stibnite (Sb2S3), a black powder with a shiny shimmer used in Egyptian cosmetics 4000 years ago as a black eyeliner. Antimony was also used in making colored glazes for beads and glassware. In glass and ceramics, a small amount of it insures that the glass is clear and colorless.
In modern times, it is used in the manufacture of flame-retardant materials. Antimony has the unusual property that it expands as it freezes, like water does. Alloys made with antimony expand on cooling, retaining the finer details of molds.
Antimony alloys are therefore used in making typefaces for clear, sharp printing.
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