Got it.

In ‘The Mannichon Solution,’ a nebbish chemist working in the detergents department while dreaming of the Nobel Prize accidently discovers a solution that might make him rich and famous but that kills any organism with yellow pigment, and for which the only likely buyer is the C.I.A. (to drop into the Yangtze to solve the ‘yellow peril’ problem).

Many thanks to reader Sergey, who found that for me, and also to the several readers who pointed me to Heinlein’s “Sixth Column,” which, though not the story I remembered, looks to be worth reading.