Full Idea
The alchemists sought the separation of the 'pure essences' of substances from unwanted impurities. This last goal was of great importance for the development of modern chemistry at the hands of Boyle and his successors.
Gist of Idea
Alchemists tried to separate out essences, which influenced later chemistry
Source
Peter Alexander (Ideas, Qualities and Corpuscles [1985], 01.1)
Book Reference
Alexander,Peter: 'Ideas, Qualities and Corpuscles' [CUP 1985], p.16
A Reaction
In a nutshell this gives us the reason why essences are so important, and also why they became discredited. Time for a clear modern rethink.