[Use] : In organic chemical reactions, there is never a single reaction, in the reaction in addition to the main substance generation, there are other by-products and impurities. Therefore, in the organic chemistry test, to obtain more pure substances must pay attention to the refining work. Z The common and commonly used refining method is crystallization. With a suitable solvent, the substance to be purified is dissolved and crystallized to remove impurities and a pure single crystal is obtained.