In China, "alchemy" was originally a search for immortality through various drugs, herbs, and chemicals. This is known as wai-tan, external alchemy, and was developed probably around the 4th century b.c.e., half a millenium before the earliest reference to alchemy in the West.
Alongside this, and perhaps a little later, there developed nei-tan, internal alchemy, which was actually a sort of yoga or meditation-practice, not unlike Indian Tantra, which resembled external alchemy only in its terminology (the alchemical terms having a symbolic rather than a literal meaning). Internal alchemy had as its aim the cultivation of the life-force, and the consequent attainment of immortality of the personality.
The basic premise of the the esoteric or nei-tan Taoists is that man has only a limited store of vital-force (ch'i). This leaks away through day-to-day activities, and when it's all gone, that's it, the person's dead. But it is possible to make the ch'i go back inside, rather than outwards, and then up the spine to the crown. This obviously is very like the Tantric Kundalini. In ascending, the ch'i progresses through various stations, which are given exotic names like the Elixer-field, the Yellow Hall, the Heaven. Now comes the difference with Shakta based tantra. Reaching the top of the head, the ch'i then descends down the front of the body, down to the navel, and then around again, forming a complete circuit. This circut is known as "The Circulation of the Light", or "The Microcosmic Orbit".
There are so much contents in this field that to elaborate it in one chapter or volume remains impossible. So, here, by the separate topics, people can view it from different points. So, please come and choose the following links to read.