The ideas of lead and mercury use the ideas of lead, which is heavy and dense and lasts a long time without disintegrating, and mercury which is lively, active, and doesnt last a long time, to refer to states of mind. What is called lead in the alchemical texts is not ordinary material lead but the deep rich sense of true knowledge. This true knowledge is solid, deep, long-lasting and unbending like the sense one gets from lead. What is called mercury in the alchemical texts refers not to actual material mercury, but to the yin aspects of realitys nature; the side which is pliant, effervescent, spontaneous, unfathomable, and metaphysical. Because it is difficult to pin down and is formless and elusive this aspect of reality and consciousness is likened to mercury.
The Tiger and the Dragon
Alchemical language, when speaking of the tiger and the dragon, in most cases refers to either of two basic considerations. It means either the tiger as the physical aspects of life and the dragon as the spiritual aspectsthese are sometimes called the ordinary tiger and ordinary dragon. However, the terms are also used to refer to the non-ordinary aspects, or the aspects such as those of the conditioned consciousness and the emotionally obsessed or illusioned consciousness in relation to the evolved consciousness which has learned to transcend the ordinary states of being conditioned or being emotionally obsessed. When, through the self-cultivation work, one refines away the conditioned temperament and the obsessing emotional habits and feelings, then the ordinary tiger and dragon are overcome, and the true tiger and true dragon of primordial essence arise. When this happens a clarity is awakened which is so clear and fundamentally beautiful that it seems like a bright light or a shining mystic pearl. When this clarity is firmly in place it pervades the universe without hindrance.
The Jade Furnace
The jade furnace is symbolic language for the container within which the work of self-cultivation and empowerment takes place. It is called jade because the mellow and beautiful tones of jade are like the calm serenity and steady going quality of the work. The term furnace is used because it evokes the idea of slow cooking or slow evolution, just as one slowly evolves and changes when one applies oneself diligently and perseveringly in self-cultivation practice. The jade furnace does not refer to some specific place in the body. It would be a mistake for people to conceive of it in such a manner. One must go deeper than such surfacy approaches.
The medicines of alchemical language dont refer to physical medicines one should take into ones physical body, but to the medicines of real inner knowledge and conscious and conscientious practice. Ideas of yin, yang, subtlety, sensitivity, quietude, tranquility, perseverance, balance, evenness, honesty, sincerity, patience, simplicity, objectivity, etc. are the real medicines. To think that the terms alchemical medicines or spiritual medicines refer to mundane physical substances is to fall way short of proper and deep understanding.