Today there is a matter related to petroleum ether and ethyl acetate. The use of the two is quite important. Petroleum ether has a clear and sparse nature, and is often used as an aid for extraction and separation. Ethyl acetate has a good aroma and solubility. The two cooperate, and in many alchemy techniques, each can develop its own capabilities. Either they are combined to improve the essence, or they are combined to adjust the properties of matter. Its method is exquisite, and those who are not well versed in this way cannot understand it. When operating, observe its proportions, observe its changes, and act according to reason. The wonders of these two have great power in all matters, and they should be studied carefully and used well.