You may improve this article, discuss the issue on the talk page, or create a new article, as appropriate. (January 2015) The history of economic thought deals with different thinkers and theories in the subject that became political economy and economics, from the ancient world to the present day. It encompasses many disparate schools of economic thought.
A pure substance is a substance that cannot be separated by physical means. eg. filtration, evaporation, distillation or chromatography. Examples of pure substances include water, gold, glucose, carbon dioxide, oxygen and hydrogen. A pure substance is made up of one type of particle. The particle that makes up water is H 2 O. The particle that makes up carbon dioxide is CO 2.
A substance that has the same composition throughout. Pure substances are either elements or compounds, and should not be confused with mixtures. A homogeneous mixture is not the same as a pure substance, because although it has an unvarying composition, it cannot be reduced to a single type of atom or molecule.