In the day to day life, there are times when one needs to separate a useful substance from a mixture. This is done by using various methods of separation of substance. Mixture: A substance which is composed of two or more substances; in which each component retains its unique property; is called mixture. Air is a mixture of gases. Water which we drink is a mixture of pure water and many other substances. Pure Substance: A substance is called pure when each particle of the substance has the same unique property. For example; distilled water is pure water as each drop of it contains nothing but water. Need for separation of substances: Taking out useful substances from a mixture is usually the main reason for separation of substances. Sometimes, we also need to separate substances when we need to use different components in different ways.