Alchemy may best be viewed as the eccentric, but brilliant relative, of the science family. Encompassing disciplines like physics, chemistry, medicine, and astrology, it also has roots in metallurgy, mysticism and spiritualism. Not surprisingly, there's been confusion and misunderstanding about what alchemy really is, or was. But it's clear that without alchemy, disciplines like chemistry and physics may not have advanced as they did.
The popular understanding of alchemy is that it's about transmutation, or changing common metals into gold or silver. Given its mystical roots, many have thought of alchemy as a sort of magic' science, but the truth is that medieval alchemists didn't have wands or spells. Rather, they worked with instruments and chemicals that today's modern scientists still use, with the only difference being that the instruments, chemicals and working conditions are much better now than they were back then. Not surprisingly, today's scientists get much better results.
Alchemy, in its simplest form, had three main goals. The first was indeed to find a way to transform common metals into precious gold or silver. But this was done through studying the make-up of those metals and trying to alter them at their most basic level. This is essentially what chemists, and to an extent, nuclear physicists try to do today.
The second goal of alchemy was to develop a panacea, or a cure-all, for diseases and to prolong life. Finally, alchemists also wanted to find, or develop, a universal solvent and this tied in closely with their pursuit of what was known as the philosopher's stone' which they believed would mystically imbue its owner with the knowledge of alchemy, and thus, make the attainment of all the goals possible. In other words, the philosopher's stone would make the person who had it into a super alchemist.'
Despite its mystical and spiritual ties, alchemy was a serious science, studied by the likes of Isaac Newton and St. Thomas Aquinas, during the Middle Ages. Alchemists were held in high esteem during this period and it is through their work that things like dyes, inks, paints, cosmetics and gunpowder were discovered and developed.
Today, the discovery and documentation (many hundreds of books and papers by alchemists from the 16th through 18th centuries still survive today) of the works performed by alchemists have helped to shape and develop the fields of chemistry, physics, medicine and astrology.
Alchemy can also be seen as a philosophical discipline, where the goals were really a metaphor or symbol of inner change. For instance, the pursuit of a panacea wasn't so much a chase for the true cure-all, but to transform from diseased and broken self' into a cured, and perfect being.
In short, alchemy can be seen as the grandfather (or perhaps great-grandfather) to many of today's science disciplines and theories. It is arguable that without the efforts of alchemists, chemistry, physics, and medicine wouldn't have been able to advance and develop as they did.