<P> Jain philosophy, a non-creationist philosophy based on the teachings of Mahavira (6th century BC), states that the universe and its constituents such as matter cannot be destroyed or created . The Jain text Tattvarthasutra (2nd century CE) states that a substance is permanent, but its modes are characterised by creation and destruction . A principle of the conservation of matter was also stated by Nasīr al - Dīn al - Tūsī (around 13th century CE). He wrote that "A body of matter cannot disappear completely . It only changes its form, condition, composition, color and other properties and turns into a different complex or elementary matter". </P> <P> By the 18th century the principle of conservation of mass during chemical reactions was widely used and was an important assumption during experiments, even before a definition was formally established, as can be seen in the works of Joseph Black, Henry Cavendish, and Jean Rey . The first to outline the principle was given by Mikhail Lomonosov in 1756 . He demonstrated it by experiments and had discussed the principle before in 1774 in correspondence with Leonhard Euler, though his claim on the subject is sometimes challenged . A more refined series of experiments were later carried out by Antoine Lavoisier who expressed his conclusion in 1773 and popularized the principle of conservation of mass . The demonstrations of the principle led alternatives theories obsolete, like the phlogiston theory that claimed that mass could be gained or lost in combustion and heat processes . </P> <P> The conservation of mass was obscure for millennia because of the buoyancy effect of the Earth's atmosphere on the weight of gases . For example, a piece of wood weighs less after burning; this seemed to suggest that some of its mass disappears, or is transformed or lost . This was not disproved until careful experiments were performed in which chemical reactions such as rusting were allowed to take place in sealed glass ampoules; it was found that the chemical reaction did not change the weight of the sealed container and its contents . Weighing of gases using scales was not possible until the invention of the vacuum pump in 17th century . </P> <P> Once understood, the conservation of mass was of great importance in progressing from alchemy to modern chemistry . Once early chemists realized that chemical substances never disappeared but were only transformed into other substances with the same weight, these scientists could for the first time embark on quantitative studies of the transformations of substances . The idea of mass conservation plus a surmise that certain "elemental substances" also could not be transformed into others by chemical reactions, in turn led to an understanding of chemical elements, as well as the idea that all chemical processes and transformations (such as burning and metabolic reactions) are reactions between invariant amounts or weights of these chemical elements . </P>

Who discovered the law of conservation of mass