Possible Clues:

• Chemist's thick mixture extremely unpopular
• Pioneer in vaccination
• He was famous as a chemist over half Europe
• First rabies vaccine creator
• Scientist found over half the continent ...
• French chemist late on his way up
• Purest article devised by a scientist
• Chemist's gone halfway through Europe
• Former old city with housing for English chemist
• A purest sort of chemist