One of the most revolutionary scientific works ever written, and also one of the most accessible, Lavoisier¿s Elementary Treatise on Chemistry established the constancy of weight in chemical reactions, revealed the composition of water, and set forth a clear concept of the nature of gases. The Treatise cemented a new, rational nomenclature that accurately expressed the nature of materials. Lavoisier presents experimental facts in expressions that are vivid, exact, and often poetical. As a result, the Treatise is still, after more than 200 years, a model of clarity and scientific reasoning. Lavoisier¿s magnificent work, last translated into English in 1790, is now presented in a rendition that preserves the natural and unadorned liveliness of Lavoisier¿s narrative prose. Howard Fisher¿s extensive commentary furnishes a gentle guiding hand through unfamiliar terms and experimental procedures.