Chemist and physicist. Born 1627; died 1691. First to distinguish correctly the difference between a mixture and a compound. Systematized wet analysis. Demonstrated the value of Bacon's system. Inaugurated the employment of vegetable color tests to ascertain acidity and alkalinity. Compiled the earliest table of specific gravity for various waters. Improved the air pump. Experimented in pneumatics. Formulated the law of gases which bears his name.