Question

who said that each element was composed of extremely small particles

democritus
lavoisier
proust
dalton

Answer 1

I'm not the greatest on the history of chemistry but I think the answer is Democritus. His thoughts were strictly philosophical and there was no evidence to support his philosophy. Dalton's atomic theory, which came many years later, were based on experimental results and contained a similar statement (among others). Both Democritus and Dalton said it but Democritus seems to have said it first.