John Dalton was able to supply experimental results to forcefully revive the idea of the atom.
He was influenced by the experiments of two Frenchmen, Antoine Lavoisier and Joseph Louis Proust.
Antoine Lavoisier (1743-1794) - Formulated the Law of Conservation of Matter: "Matter is neither gained nor lost during a chemical reaction." He did this by weighing materials before and after reactions. For example, the weights of the mercury and oxygen formed by decomposition of mercuric oxide were compared with the initial weight of the mercuric oxide.
Joseph Louis Proust (1754-1826) - Formulated the Law of Constant Porportions: "In a compound, the contsitutne elements are always present in a definite proportion by weight." Like Lavoisier, Proust also conducted quantitative experiments. He showed that regardless of how copper carbonate was prepared in the laboratory, or how it was isolated from nature, it always contained the same proportions of copper, oxygen and carbon - 5:4:1 parts by weight.
Read about Proust's research on copper in his own words.
Not all his contemporaries agreed with Proust's conclusions. Berthollet was able to combine different quantities of copper and tin to produce what seemed to him to be compounds of varying composition. What is the difference between the combination of carbon and oxygen in carbon dioxide, and the combination of copper and tin when they are heated together?
John Dalton (1766-1844)- Formulated the Law of Multiple Proportions : "In the formation of two or more compounds from the same elements, the weights of one element that combine with a fixed weight of a second element are in a ratio of small whole numbers (integers) such as 2 to 1, 3 to 1, 3 to 2, or 4 to 3." He had made a quantitative study of different compounds made from the same elements, such as carbon monoxide and carbon dioxide. He found that the weight ratio of carbon to oxygen in carbon monoxide was 3:4, and the weight ratio of carbon to oxygen in carbon dioxide was 3:8.
Read a short article about the 'Chemical atom in early 19th century chemistry' which describes the period including the work of the three scientists mentioned above.
Read John Dalton's own words as he discusses the opinions of some of his contemporaries and gives his own ideas about how elements combine to form compounds.