(1)Barbed wire, first patented in the United States in 1867, played an important part in the (2)development of American farming, as it enabled the settlers to make effective fencing to enclose (3)their land and keep cattle away from their crops. This had aconsiderable effect on cattle ranching, (4)since the herds no longer had unrestricted use ofthe plains for grazing, and the fencing led to (5)conflict between the farmers and the cattle ranchers.
(6) Before barbed wire came into general use, fencing was often made from serrated wire, which (7)was unsatisfactory because it broke easily when under strain, and could snap in cold weather due(8) to contraction. The first practical machine for producingbarbed wire was invented in 1874 by an (9)Illinois farmer, and between then and the end of the century about 400 types of barbed wire were (10)devised, of which only about a dozen were ever put to practical use.
(11)Modern barbed wire is made from mild steel, high-tensile steel, or aluminum. Mildsteel and (12)aluminum barbed wire have two strands twisted together to form a cablewhich is stronger than (13)single-strand wire and less affected by temperature changes. Single-strand wire, round or oval, is (14)made from high-tensile steel with the barbs crimped or welded on. The steel wires used are (15)galvanized ― coated with zinc to makethem rustproof. The two wires that make up the line wire or (16)cable are fed separately into a machine at one end. They leave it at the other end twisted together (17)and barbed. The wire to make the barbs is fed into the machine from the sides and cut to length by (18)knives that cut diagonally through the wire to produce a sharp point. This process continues (19)automatically, and the finished barbed wire is wound onto reels, usually made of wire, in lengths of (20)400 meters or in weights of up to 50 kilograms.
(21)A variation of barbed wire is also used for military purposes. It is formed into longcoils or (22)entanglements called concertina wire.
According to the author, the steel wires used to make barbed wire are specially processed to ...