Proposed the Law of Multiple Proportions which led to the Atomic Theory. The theory contained five principles:
1) all matter is composed of atoms
2)atoms of given element are identical in properties
3)atoms of different elements differ in properties
4)atoms of different elements combine in a simple, whole number ratio to form compounds
5)in chemical reactions, atoms are combined, separated, rearranged, but never created, changed, or destroyed.
He did many experiments with gases which was measure the amount of water vapor that air could absorb at different temperatures.