Chromatography describes a series of techniques used for separating the components of a mixture of chemicals. The most common type of chromatography is column chromatography. This involves dissolving the mixture to be separated into a solution and flowing it over a column of stationary material that interacts to a different extent with each component of the mixture. As the liquid flows over the stationary phase, the components that interact most strongly will be held behind longer while those that interact weakly will be eluted from the column first. The liquid is collected into a series of small vials or test tubes, which will, hopefully, each only contain one component of the mixture. The solvent can then be evaporated from each vial to recover the individual components of the mixture. A wide variety of chromatographic techniques exist, and each generally follows the same basic principles as the column chromatography described here.