Alchemy is best described as a form of 'proto-science' rather than a distinct science in its own right. This is because, although many observations and theories made by alchemists were based on scientific fact, they often explained these in terms of 'magic' or divine intervention.
The most well-known of alchemical pursuits was the practically futile quest to turn base metals into precious ones, especially lead into gold. However, there is little evidence to suggest that the majority of alchemists had an interest in this, and may not have believed it possible. Their lack of interest may have been because, in the plague-ridden times of medieval Europe, medical uses of alchemy would prove to be a much more reliable source of gold.
Another popular view is that of alchemists as accident-prone bumblers, gleefully participating in trial and error experiments like an unwatched GCSE chemistry student, and regularly causing fires and explosions. In contrast, the writings of many alchemists which survive today show a good understanding of several branches of chemistry, though some details often escaped their attention.
Practitioners of alchemy were often categorised with astrologers, conjurors and other 'magicians,' even when their popularity was at its height. This led to many being classed as witches or sorcerers, a fate which also befell many of the earliest 'true' scientists.
Alchemy still exists today, a preserve of the paranormal, and many alchemical theories have made the transition from science to spiritualism.