Ivory soap is 99 44/100% pure. Pure what? And what is the other 56/100%?

It all started in 1881 when Harley Procter, son of Procter & Gamble co-founder William Procter and a legendary soap salesman in his own right, decided he needed a new angle to hawk Ivory soap. Then as now people were impressed by scientific testimonials, and Harley decided if he could come up with a lab test showing Ivory was "purer" than other soaps, he�d win sales.

Trouble was, there wasn't a standard for purity in soap, so Harley hired an independent scientific consultant in New York to concoct one. The consultant concluded that a 100% pure soap would consist of nothing but fatty acids and alkali, the somewhat yukky sounding substances that nonetheless are the chief ingredients of most soap. Comparison tests were made with castile soaps � the standard of excellence at that time. One chemist's analysis was in table form with the ingredients listed by percentage. Harley Procter totaled the ingredients which did not fall into the category of pure soap (The impurities consisted of uncombined alkali, 0.11%; carbonates, 0.28%; and mineral matter, 0.17%) they equaled 56/100%. He subtracted from 100, and wrote the slogan "99-44/100% Pure�: It Floats." This became a pledge of quality to Ivory consumers. This phrase is so identified with Ivory, it's registered as a trademark with the United States Trademark office.

Reference Links:

http://www.snopes.com/business/origins/ivory.asp#add

http://www.straightdope.com/classics/a930820.html