Pseudoscientific forerunner of chemistry (7)
I believe the answer is:
alchemy
'pseudoscientific forerunner of chemistry' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for alchemy that I've seen before include "process of going for gold" , "Search for gold and philosopher's stone" , "Chemistry's forerunner" , "Black art" , "Old form of chemistry" .)