A Soxhlet extractor is a piece of laboratory apparatus invented in 1879 by Franz von Soxhlet.  It was originally designed for the extraction of a lipid from a solid  material. Typically, Soxhlet extraction is used when the desired compound has a limited solubility in a solvent, and the impurity is insoluble in that solvent. It allows for unmonitored and unmanaged operation while efficiently recycling a small amount of solvent to dissolve a larger amount of material.