Extraction is a separation process in which one or more components are extracted from a mixture of substances - the extraction material - by means of an extracting agent. The extracted substance is called an extract, even if it is still in a dissolved form. The extraction is a physical process if the substance is not changed (but, e.g., only dissolved or adsorbed). However, there is a chemical process if the substance undergoes a chemical reaction. If a solvent is used as the extraction agent, the substances to be extracted dissolve better in the pure solvent than in the substance mixture. The solvent extracts the substance from the mixture, which dissolves more easily in it. Water or steam, acids, bases and liquefied carbon dioxide are examples of inorganic solvents. Alcohols, terpenes, diethyl ethers, vegetable oils, chlorinated hydrocarbons or n-hexane are used as organic solvents. As the pressure or temperature increases, the solubility of the substances tends to increase considerably. For this reason, some extractions are performed with hot solvents and/or under pressure.