How did he know 1 unit is 1/12 of the weight of carbon atom.
In: 62
When carbon combines with oxygen in complete combustion, producing what we nowadays call carbon dioxide, the proportion, by mass, is always 8:3 — at least within the measurement precision available back then. Oxygen and hydrogen to make water? 8:1. Sulfur and oxygen to make sulfuric acid? I’d have to look it up, but it’s a whole-number ratio like the others. That kind of pattern strongly suggests that elements are made up of a whole number of unit masses.
And once you have that kind of data for a few dozen reactions, you can just try out hypotheses: *let’s suppose carbon has a mass of nine units: what does that mean for the other elements… okay, that would mean oxygen has twelve, and that nitrogen has, hmm, nine-and-two-thirds. Okay, so that doesn’t work, on to the next one*
And even if you only have pretty-reliable data for a few elements: hydrogen, carbon, nitrogen, oxygen, sulfur, phosphorus, and maybe sodium and potassium, there’s really only one solution that works out.
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