Prescott was one of the founders of the American Chemical Society...also reputed to have been the analyst who arrived at the figure of 99.44% for the purity of a common brand of soap.

In 1959 my organic chemistry professor Louis Feiser made that same claim for himself, right after describing his synthesis of Chlorophyll and invention of napalm (which he then gave to the Isrealis in 1948). He said the soap manufacturer had asked him for an analysis of their product, but because of rounding errors the results totaled only 99.44%, not 100%. Making a virtue of a necessity Madison Avenue did its thing, and the rest (as they say)...

Professor Feiser concluded his comments with the observation "99.44% what? 99 and 44/100ths percent matter, that's what...! So what's the other 0.56% ?"

I have no corroboration of either chemist's claim.

Anybody know when the slogan was popularized? Prescott must have died in the early Twentieth Century. Maybe that would distinguish.