If we dissolve some sugar in water, the mass of the solution will be precisely equal to the sum of the masses of the sugar and the water.

This and an infinite number of similar experiments show that the mass of a body is an invariable property. No matter how the body is crushed or dissolved, its mass remains fixed.

The same also holds for arbitrary chemical transformations. Suppose that coal burns up. It is possible to establish by means of careful weighings that the mass of the coal and the oxygen from the air which was used up during the burning will be exactly equal to the mass of the end products of the combustion.

The law of conservation of mass was verified for the last time at the end of the 19th century, when the technique of fine weighing had already been highly developed. It turned out that mass does not even change by an insignificant fraction of its value during the course of any chemical transformation.

Mass was considered to be invariable as far back as Ancient Times. This law first underwent an actual experimental verification in 1756. This was done by Mikhail Lomonosov, who proved the conservation of mass during the sintering of metals by means of experiments in 1756, and demonstrated the scientific significance the law.

Mass is the most important invariable characteristic of a body. The majority of the properties of a body is, so to say, in the hands of human beings. An iron bar that can be easily bent by hand can be made hard and brittle by tempering it. With the aid of ultrasonic waves, one can make a turbid solution transparent. Mechanical, electrical and thermal properties can be changed by means of external actions. If no matter is added to a body and not a single particle is separated from it, it is impossible¹ to change its mass, regardless of what external actions we resort to.

Mikhail Lomonosov [1711–1765]—an outstanding Russian scientist, the initiator of science in Russia, a great educator. In the field of physics, Lomonosov struggled resolutely against the notions widespread in the 18th century of electrical and thermal “fluids”, upholding the molecular-kinetic theory of matter. Lomonosov was the first to experimentally prove the constancy of the mass of matter participating in chemical transformations. Lomonosov carried out extensive research in the field of atmospheric electricity and meteorology. He constructed a series of remarkable optical instruments and discovered the atmosphere on Venus. Lomonosov created the basis of scientific Russian; he succeeded in translating the basic physical and chemical terms from the Latin exceptionally well.