could be made from certain rock and that bronze was a mixture of copper and tin. From the beginning of the Christian Era to the 17th and 18th centuries was the period of chemistry known as alchemy. Alchemists believed that metals could be changed into gold with the help of a mystical stone which was never found. They did, however, discover many new elements and compounds. Paracelsus, a talented Swiss alchemist, decided that alchemy should be for helping to cure the sick instead of searching for gold. The main elements that he used were salt, sulfur, and mercury, all which are connected to "elixir." This period of practicing medicine was known as iatrochemistry, which is the study of medicine with chemistry applied. One of the first real scientific chemist was Robert Boyle. In 1661, he helped to find the Royal Society of England, a scientific society. For about two centuries after Boyle, scientists started making useful discoveries, even though, they were far from understanding the true nature of matter or knowing what happens in chemical reactions. One of the most confusing events of this time period was the theory of burning, or combustion, called the phlogiston theory. According to this theory, a yellowness or hardness was supposed to escape from substances during the burning process. By now, chemists were starting to learn that they must test these theories with experiments. In 1774, Joseph Priestley discovered that a certain gas, now known as oxygen, was required in the burning process. A few years earlier, Henry Cavendish had discovered hydrogen and Antoine Lavoisier used the findings to formulate the presently accepted theory of combustion. This is often said to have marked the beginning of modern chemistry. In chemistry experiments must be run to prove hypothesizes that a chemist has stated. In an experiment you must make observations under circumstances in which variables can be controlled in a way that the results can ...
