Neidan Dictionary
erba 二八
two eights; two times 8
The symbolic weight of the two ingredients of the Elixir. Refers to the equal parts of Mercury (True Yin) and Lead (True Yang) required to compound the Elixir. Each ingredient weighs eight ounces (liang 兩), and together they amount to one pound (jin 斤). (In the traditional Chinese weight system, where one pound is divided into sixteen ounces, “eight ounces” is equivalent to “half pound”.)
⊛ Two times 8 corresponds to one pound: the Way of the Changes is correct and unbiased. 二八應一斤，易道正不傾。 (The Seal of the Unity of the Three, sec. 29)
⊛ For the Medicine to weigh one pound, the Two Eights are needed. 藥重一斤須二八。 Comm. Weng Baoguang: Eight ounces of Crow’s liver and half pound of Hare’s marrow together make one pound. 烏肝八兩，兔髓半斤，合成一斤。 (Awakening to Reality, "Regulated Verses", poem 7)
⊛ When Yin and Yang are of one kind, they conjoin; when the Two Eights match one another, they merge. 陰陽得類俱交感，二八相當自合親。 (Awakening to Reality, "Regulated Verses", poem 8)
⊛ What are the Two Eights? They are the numbers that make one pound: half pound of Lead, eight ounces of Mercury. It is not that there are truly pounds and ounces. It is only important that the two things are balanced. 或問何謂二八？曰：一斤之數也。半斤鉛，八兩汞。非真有斤兩。只要二物平勻。 (Li Daochun, The Harmony of the Center: An Anthology, chap. 3)
