The span of time from about the beginning of the 1st century AD to about the 17th century is considered the period of alchemy. The alchemists believed that metals could be converted into gold with the aid of a marvelous mineral called the philosopher's stone, which they never succeeded in finding or making. They did discover new elements, and they invented basic laboratory equipment and techniques that are still used by chemists. However, the alchemists learned very little that was worthwhile concerning the fundamental nature of matter or of chemical behavior. They failed because their basic theories had almost nothing to do with what actually happens in chemical reactions.
In the 13th century such men as Roger Bacon, Albertus Magnus, and Raymond Lully began to realize how futile it was to search for the philosopher's stone. They suggested that alchemists might rather seek to help the world with useful new products and methods.
In the 16th century, another important leader in the new trend was Theophrastus Bombastus von Hohenheim, an aggressive, talented Swiss who used the Latin name Paracelsus. He insisted that the object of alchemy should be the cure of the sick. The elements, he said, were salt, sulfur, and mercury (long connected with the “elixir of life,” another nonexistent alchemical substance), and they would give health if present in the body in the proper proportions. On this basis he practiced medicine and attracted many followers. Thus began iatrochemistry, or chemistry applied to the study of medicine and the treatment of disease.
One of the first scientific chemists was Robert Boyle. In 1660 he helped found one of the first scientific organizations in Europe, the Royal Society of London. In a book called The Sceptical Chymist (1661) he rejected previous theories of the composition of matter and compiled the first list of the elements that are recognized today. He also discovered the relationship between the volume and the pressure of a gas.