Sentence:  The [Isaac] Newton that emerges from the [unpublished] manuscripts is far from the popular image of a rational practitioner of cold and pure reason. The architect of modern science was himself not very modern. He was obsessed with <WSD>alchemy</WSD>. 
Meaning of the word marked with <WSD> tags:  The ancient search for a universal panacea, and of the philosopher's stone, that eventually developed into chemistry.