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BIG ENCYCLOPEDIA FOR CHILDREN AND ADULTS
When did civilization appear? Detailed answer
Directory / Big encyclopedia. Questions for quiz and self-education Did you know? When did civilization appear? Much time has passed since man has reached what we call a civilized society. At first, man, like animals, was in a wild state. He did not speak and ate only what he could find. Later, people began to live in groups, learned how to make fire, and even later they learned how to make tools and hunt. Man learned to make pottery for cooking, began to live in tribes, could move from one area to another. The next stage of human development, which was called the era of barbarism, showed that man had learned to grow food from seeds and tame animals. Then he began to smelt such metals as copper and iron, which made it possible to produce more advanced tools and build his own dwelling. The appearance of rock paintings can be considered the end of the era of barbarism and the beginning of the era of civilization. The invention of writing is considered the beginning of the era of civilization, as it allowed a person to record the events of the past. Thus, people could study the experience of their ancestors. This happened about 5-6 thousand years ago. By the time man has reached this stage of development, he too has improved in many ways. He developed agriculture and industry to the point where people could live in villages and even cities. There was management, trade, laws, there was also the migration of people. The earliest civilizations known to us from the history of civilization are Egyptian and Babylonian. The Egyptians invented writing 4500 years ago. They had an elaborate management system; they used mathematical calculations in the construction of the pyramids; they had a calendar; skillful architects appeared; various mechanisms have been used. About 4000 years ago, civilization developed on the island of Crete, and about 4500 years ago, the Sumerian civilization developed on the banks of the Tigris and Euphrates rivers. Author: Likum A.
What is made from celluloid? Ping-pong balls and collar stiffeners. Celluloid film has not been made for a long time. The main ingredient of celluloid is cellulose nitrate, while modern film is made from cellulose acetate. Celluloid is considered to be the first plastic. In strictly technical terms, it is a thermoplastic, which means that every time it is reheated, it can be given almost any shape. Celluloid is composed of cellulose nitrate and camphor. Cellulose occurs naturally in the cell walls of plants. Camphor is obtained from camphor laurel, it can be distinguished by the characteristic smell of naphthalene, the balls of which, by the way, are made from it. For the first time in history, celluloid was obtained in the English city of Birmingham by Alexander Parkes, who patented it for use in the manufacture of waterproof clothing. And celluloid became a cheap substitute for ivory: billiard balls and artificial teeth began to be made from it. Because of its malleability, celluloid made cinema possible because rigid glass plates cannot pass through a projector. True, on the other hand, celluloid is not only terribly combustible, but also rapidly decomposing, which greatly complicates storage. Therefore, the use of celluloid has been greatly reduced these days. Celluloid has been replaced by more stable plastics: cellulose acetate (derived from wood pulp) and polyethylene (a byproduct of gasoline production). Cellulose nitrate (or nitrocellulose) was invented by accident in 1846 by Christian Schönbein, the man who had discovered ozone six years earlier. While experimenting in the kitchen with nitric and sulfuric acid, Shenbein accidentally broke the bottle, wiped all this mess from the table with his wife's cotton apron, and hung it up to dry on the stove. But the fabric immediately burned out with an explosion - this is how the first new explosive was discovered (the very first, gunpowder, was invented in ancient China). The new material was called "gun cotton" (guncotton). It was smokeless and four times more powerful than regular gunpowder. Schönbein immediately patented the discovery and sold the exclusive rights to manufacture it to John Hall and Sons. The following year, their factory in Faversham, Kent, exploded, burying twenty-one workers in the rubble. Numerous fatal explosions also took place in France, Russia and Germany. A stable product was obtained only forty years later, in 1889, when the English chemists James Dewar and Frederick Abel developed cordite based on nitrocellulose and nitroglycerin. Seven years earlier, Dewar had invented the thermos.
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