n the 13th century such alchemists as Roger Bacon, Albertus Magnus, and Raymond Lully began to realize that the search for the philosopher's stone was quite useless. They began to feel that alchemists might better search for ways and means to help the world's work with useful new products and new methods. In the 16th century, another important leader in the new trend appeared in Theophrastus Bombastus von Hohenheim, an aggressive, talented Swiss. Like many learned men of his day, he adopted a Latin name, using Paracelsus ("superior to Celsus," Celsus being a distinguished Roman physician of the 1st century AD).

Paracelsus insisted that the object of alchemy should be the cure of the sick rather than the fruitless search for gold. The elements, he said, were salt, sulfur, and mercury (long connected with the "elixir"), and they would give health if present in the body in the proper proportions. On this basis he practiced medicine and attracted many followers. This was the period of iatrochemistry, or chemistry applied to the study of medicine (see Medicine).

One of the first really scientific chemists was Robert Boyle. In a book called 'The Sceptical Chymist' he rejected the elements of the iatrochemists and started the list of elements which are recognized today. His name is also associated with a law concerning the volume and pressure of gases. In 1661, he helped found a scientific society which later became the Royal Society of England.