沉淀、結晶与萃取都是分离提純过程中的重要方法。这三种方法在理論上有密切的关系,在試剂发展上也有相互的影响。萃取是后来居上的方法,也是理論联系实际的学科。既要求現象及数据的累积,又要求理論的多方发展。是深入細致与广泛联系的结合。 Precipitation, crystallization and extraction are important methods in the separation and purification process. The three methods in theory are closely related, in the development of reagents also have mutual influence. Extraction is the method that comes from behind, but also the theory with the practice of the subject. Requires the accumulation of phenomena and data, but also requires the theory of multi-development. It is a combination of in-depth and extensive contact.