Robert Boyle (1627-1691), Anglo-Irish chemist who established chemistry as a separate science. His work stressed the need for experiment, precision and accurate observation. Boyle rejected the theory that four elements (fire, air, water and earth) were the basic constituents of the Universe. Boyle postulated that there were a large number of 'elements' which could not be broken down into simpler chemicals. He formulated Boyle's law, which states that for a gas at a constant temperature the product of its pressure and volume is a constant. He devised analytical tests including the use of vegetable dyes as acid-base indicators and flame tests to detect metals.