There was a Swiss doctor who called himself Paracelsus. He was an alchemist but not an ordinary one. He didn't think it was at all important to find methods for making gold. He thought that alchemist should search for medicine to cure sickness. He was not a great scientist and some of his idea were entirely wrong. But he wanted to put an end to ancient beliefs and start over. There he was right. He was also right in wanting to test ideas by experiments.
  In the beginning of 1580's an Italian scientist named Galileo showed that it was very important to make accurate measurements. More could be learned in this way than in any other. His work in physics and astronomy helped to establish modern science. Lavoisier, a French chemist, explained that a candle didn't really disappear if it burned. The carbon and hydrogen it in combined with the oxygen of the air. They formed carbon dioxyde gas and water vapour. If the candle burned in a clossed vessel, the weight of the candle and vessel did not change.
  Chemists tried to arrange the elements in the order of their atomic weights. The most successful arranger was a Russian chemist, Dmitri Mendeleev. In 1869 he arranged the elements in rows and columns. He published the first periodic table, which became the basis of theoritical chemistry. The periodic table provides an easy way to show the dividion of the elements into two : acid and base.