Alchemy is a Science of Soul that results from an understanding of God, Nature, and Man. A perfect knowledge of any of one them cannot be obtained without the knowledge of the other two, for these three are one and inseparable. Alchemy is not merely an intellectual but a spiritual science, because that which belongs to the spirit can only be spiritually known. Nevertheless, it is also a science dealing with material things, for spirit and matter are only two opposite manifestations or poles of the eternal One.
Alchemy in its more material aspect teaches how minerals, metals, plants, animals, and men may be generated or made to grow from their "seeds." In other words, how that generation, which is accomplished during long periods of time in the due course of the action of evolution and natural law, may be accomplished in a comparatively short time, if these natural laws are guided and supplied with the proper material by the spiritual knowledge of man. There is no doubt that gold can be made to grow by alchemical means, though it requires an alchemist to make the experiment succeed, and he who is attracted by the material power of gold will not obtain possession of the spiritual power necessary to practice the art.
It is therefore a grave mistake to confuse alchemy with chemistry. Modern chemistry is an artificial science that deals only with the external forms in which the elements of matter are manifesting themselves. It never produces anything truly new to creation; it can only recombine atoms and molecules into different substances. We may mix and compound and decompose chemical bodies an unlimited number of times and cause them to appear in various different forms, but at the end, we will have no augmentation of the underlying substances nor anything more than the recombinations of the substances that have been employed at the beginning. Alchemy does not mix or compound anything; it causes that which already pre-exists in a latent state to become active and grow. Alchemy is, therefore, more comparable to biology than to chemistry; and, in fact, the growth of a plant, a tree , or an animal or the evolution of whole species are alchemical processes going on in the laboratory of nature, and performed by the Great Alchemist -- the power of the divine Mind acting in nature.
Alchemy Is an Art (from Alchemy by Franz Hartmann)Alchemy is also an art, and as every art requires an artist to exercise it, likewise this divine science and art can be practiced only by those who are in possession of the divine power necessary for that purpose. It is true that the external manipulations required for the production of certain alchemical preparations may, like an ordinary chemical process, be taught to anybody capable of reasoning. However, the results that such a person would accomplish would be without life, for only he in whom the true life has awakened can awaken it from its sleep in matter and cause visible forms to grow from the primordial Chaos of nature.
Alchemy in its highest aspect deals with the spiritual regeneration of man and teaches how a god may be made out of a human being or, to express it more correctly, how to establish the conditions necessary for the development of divine powers in man, so that a human being may became a god by the power of God in the same sense that a seed becomes a plant by the aid of the Four Elements and the action of the invisible Fifth Element (the Quintessence or Life Force).
(source: http://www.alchemylab.com/what_is_alchemy.htm)