soxhlet extraction 問題

you've to first understand the principle of soxhlet extraction.

solvent at the bottom flask is heated and vaporizes and go up to the condenser. after condensation, the liquid solvent drops into a smaller flask, which contains your solid sample.

the analyte in the sample is extracted by the solvent. after accumulating certain volume of solvent, the siphon 虹吸管 draws all the extracting solvent back to the bottom flask. the analyte is left in the bottom flask, while solvent keeps in the cycle and extract more and more analyte from the sample.

thus, to be exact, repeated cycles do not make the compound purer -- they increase the extraction efficiency, such that larger portion of the compound is extracted from the sample.