What does the "furnace" in the novel Xian Ni mean?

Double cultivation term: generally refers to female cultivators who are used by powerful male cultivators to absorb yin and replenish yang. Such female cultivators have a low status and their existence is only used by male cultivators to absorb yin and improve their skills. This term is often mentioned in cultivation novels. Source: For furnace cauldron, you can choose Yin people who are fifteen or sixteen years old and above, with beautiful eyebrows, white teeth, red lips, smooth face, delicate skin, clear voice, and smooth speech. This is a good weapon. It should not be used if the vitality is weak, yellow and thin, the menstrual water is irregular, and the person is around forty years old. Whenever you interact with someone, choose a time when the wind and sun are calm, calm down and mediate, and fight with a method that does not let out. When the person is in a state of agitation and confusion, there will be fluid under the tongue but it is cold, and the Yin fluid will flow smoothly. At this time, The great medicine for women is out. Then smack his tongue tightly, and use his left hand to prick the lower part of his right side, and then the spirit energy will be released. Inhale the breath and liquid, and then the jade stem can also absorb the vaginal essence into the palace, like water flowing straight up, and then use the sword. , then it is wonderful. If the tongue is picked from the top, it is called the water of Tianchi; if the milk is picked from the middle, it is called the innate wine; if the yin is picked from the bottom, it is called the heavenly wine of the future. Cui Gongyun: The weather comes first, and the weather comes later. Those who get it are often like being drunk. Is this a joke? Pick it three times according to the law. If the yin essence is not strong enough, wait for it to be very emotional, smack its tongue quickly, withdraw the turtle with less time, like holding back a stool, then the yin essence will be released by itself. This method is ingenious and extremely effective. It should not be taught lightly to reveal secrets. Be careful! Be careful.