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.
Therefore, we can broadly categorize matter into two categories as pure substances and mixtures. Mixtures can be mainly divided into two, as homogeneous mixtures and heterogeneous mixtures. Pure Substance. Pure substance cannot be separated into two or more substances by any mechanical or physical method. Therefore, pure substance is homogenous. It has a uniform composition throughout the sample. Further, the properties of it are also uniform throughout the sample. Elements are pure substances. An element is a chemical substance, which consists of only a single type of atoms; hence, they are pure. There are about 118 elements given in the periodic table according to their atomic number. For example, the smallest element is the hydrogen.