Page 4 - Principles of Applied Engineering
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1.2  ThE hisToriCal DEvElopmEnT of EnginEEring      9

                                   Bronze age
            Bronze Age             During the Bronze Age, which lasted from about 3000 b.c. to about 1200 b.c., people
                                   began to craft tools and weapons from bronze rather than from stone. The Bronze Age
                                   actually began with the discovery of copper. Copper is a soft metal, so it was not prac-
                                   tical for tools. During the Bronze Age, however, people learned that copper ore could
                                   be heated using charcoal to yield pure copper. They discovered that by melting other
                                   ores with copper, they could produce a stronger metal. Bronze is a mixture of the met-
            alloy                  als copper and tin. A mixture of two or more metals is called an alloy.
                                      Bronze is lighter than stone, and bronze tools and weapons can be made sharper
                                   than those made of stone. Using bronze, early humans created new tools such as knives,
                                   hooks, and pins. They could also craft large urns and vessels to hold water and food
                                   (Figure 1-1).

                                                figure 1-1  Because bronze is lighter than stone, it was used to
                                                make urns, pots, and tools.

                                   iron age
            Iron Age               The Iron Age, the era when iron came into common use, followed the Bronze Age at
                                   different times around the world. It began around 1200 b.c. in the Middle East and
                                   about 450 b.c. in Great Britain. It was shorter than either of the two previous periods,
                                   lasting only about 1,000 years.
            smelting                  Iron was made from iron ore through a process called smelting, in which the ore
                                   was melted to take out the impurities. The early iron-smelting furnace was a clay-lined
                                   hole in the ground. Iron ore and charcoal were placed in the hole, and then air was
                                   pumped in with a bellows. Air from the  bellows made the charcoal burn hot enough to
                                   soften the ore into a mass of iron. This mass was hammered into the desired shape
                                   while it was still red hot (Figure 1-2).

   Ch01_p007-046.indd   9                                                                                  2/9/16   3:27 PM
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