Chemistry is the science of the composition and structure of materials and of the changes that materials undergo. It is also used in improving standards of living, making it possible for such substances as rubber, nylon, and plastics to be made from completely different materials. New materials and new properties of old materials are always being discovered. Some earlier products discovered from chemical reactions are ceramics, glass, and metals. Dyes and medicines were other early products obtained from natural substances. Some practical applications that chemistry is used for are to make stronger metals, improve soil, and the developments of live-saving drugs. Modern technology depends highly on these advancements; chemistry is a way of explaining our material world. Many people can't understand the importance of chemistry if they aren't planning on being a chemist. What many people don't realize is that chemistry provides employment to people in laboratories, universities, schools, and businesses. A knowledge of chemistry is also needed in fields such as medicine, agriculture, and engineering. Modern chemistry is only about two centuries old. Earlier history of chemistry can be divided into three periods: "black magic," alchemy, and "primitive modern." Black magic was from prehistoric times to the beginning of the Christian Era. People believed that spirits controlled natural occurrences and they used magic to persuade these spirits to help in operations. During this period only some practical knowledge was gathered. Some elements such as iron, gold, and copper were recognized. There was also some progress in glass making, metalworking, and alloying. Thales and Aristotle contemplated the nature of matter, and they believed that earth, air, fire and water composed all matter. They thought that they could remove certain qualities like hardness or temperature from common materials to make rarer substances. They did know that iron...
