Homogeneous and heterogeneous mixtures mixture is air. In physical chemistry and materials science this refers to substances and mixtures which are in a single phase. This is in contrast to a substance that is heterogeneous. A solution has been a special type of homogeneous mixture. Solutions are homogeneous because the ratio of solute to solvent remains the same throughout the solution even if homogenized with multiple sources, and stable because the solute will not settle out after any period of time, and it cannot be removed by a filter or by centrifuge. This type of mixture is very stable, i.e., its particles do not
Amount of substance especially the early metallurgists, probably had some notion of amount of substance, but there are no surviving records of any generalization of the idea beyond a set of recipes. In 1758, Mikhail Lomonosov questioned the idea that mass was the only measure of the quantity of matter, but he did so only in relation to his theories on gravitation. The development of the concept of amount of substance was coincidental with, and vital to, the birth of modern chemistry. Amount of substance Amount of substance is a standard-defined quantity that measures the size of an ensemble of particles, such as