That is the Law of Mass Conservation in chemical reaction, which is well-known today as "in a chemical reaction, the mass of reactants is equal to the mass of the products." Lomonosov, together with Lavoisier, is regarded as the one who discovered the law of mass conservation.[22]
He stated that all matter is composed of corpuscles – molecules that are "collections" of elements – atoms. In his dissertation "Elements of Mathematical Chemistry" (1741, unfinished), the scientist gives the following definition: "An element is a part of a body that does not consist of any other smaller and different bodies ... corpuscle is a collection of elements forming one small mass."[23] In a later study (1748), he uses the term "atom" instead of "element", and "particula" (particle) or "molecule" instead of "corpuscle".
He regarded heat as a form of motion, suggested the wave theory of light, contributed to the formulation of the kinetic theory of gases, and stated the idea of conservation of matter in the following words: "All changes in nature are such that inasmuch is taken from one object insomuch is added to another. So, if the amount of matter decreases in one place, it increases elsewhere. This universal law of nature embraces laws of motion as well, for an object moving others by its own force in fact imparts to another object the force it loses" (first articulated in a letter to Leonhard Euler dated 5 July 1748, rephrased and published in Lomonosov's dissertation "Reflexion on the solidity and fluidity of bodies", 1760).[24]