"Traité élémentaire de chimie, tomes 1 & 2" by Antoine Laurent Lavoisier is a textbook published in 1789. Considered the first modern chemistry textbook, it redefines what an element is and catalogs thirty-three substances—though only twenty-three qualify by today's standards. Lavoisier presents groundbreaking ideas about chemical reactions, introduces the first chemical equation, and articulates a principle that would become known as the law of conservation of mass, fundamentally transforming how scientists understand matter.