atomic theory

In time, the article on chemistry links to Atomic Theory, and there we start to get answers to our question, in the ideal form: the history of our knowledge of the subject.

As I suspected, a real sense of atomic mass began to emerge from Lavoisier's experiments. Let's see, in the show on PBS, he ran water, or steam, through a heated iron gun barrel, and collected a gas on the other end. Since the iron combined with the oxygen in the steam, the gas that emerged was hydrogen. He then weighed the gun barrel, and found its weight to have increased. He weighed the hydrogen, and found that its weight, combined with the weight added to the barrel, equalled the weight of the water that had passed through the barrel.

Where it went from there, exactly, I'm not sure, but Lavoisier and those who proceeded from his work could tell that substances were being divided and recombined in certain proportions, which gave them evidence about the composition of the substances.

I must read further. Absolutely do link to these articles, as they are enthralling. (Note: they could use a bit of proof-reading.)