In the history of chemistry, the chemical revolution, also called the first chemical revolution, was the reformulation of chemistry during the seventeenth and eighteenth centuries, which culminated in the law of conservation of mass and the oxygen theory of combustion. During the 19th and 20th century, this transformation was credited to the work of the French chemist Antoine Lavoisier (the "father of modern chemistry"). However, recent work on the history of early modern chemistry considers the chemical revolution to consist of gradual changes in chemical theory and practice that emerged over a period of two centuries. The so-called scientific revolution took place during the sixteenth and seventeenth centuries whereas the chemical revolution took place during the seventeenth and eighteenth centuries. Several factors led to the first chemical revolution. First, there were the forms of gravimetric analysis that emerged from alchemy and new kinds of instruments that were developed in medical and industrial contexts. In these settings, chemists increasingly challenged hypotheses that had already been presented by the ancient Greeks. For example, chemists began to assert that all structures were composed of more than the four elements of the Greeks or the eight elements of the medieval alchemists. The Irish alchemist, Robert Boyle, laid the foundations for the Chemical Revolution, with his mechanical corpuscular philosophy, which in turn relied heavily on the alchemical corpuscular theory and experimental method dating back to pseudo-Geber. Earlier works by chemists such as Jan Baptist van Helmont helped to shift the belief in theory that air existed as a single element to that of one in which air existed as a composition of a mixture of distinct kinds of gasses. Van Helmont's data analysis also suggests that he had a general understanding of the law of conservation of mass in the 17th century. Furthermore, work by Jean Rey in the early 17th century with metals like tin and lead and their oxidation in the presence of air and water helped pinpoint the contribution and existence of oxygen in the oxidation process.