Preindustrial workers built huge industries based on the liquid's cleaning power and corrosiveness--and the staler the pee, the better
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The cleansing power of pee: If you’ve investigated the ingredients in your household cleaners, you may have noticed a prevalent ingredient: ammonia. As a base, ammonia is a useful cleanser because dirt and grease–which are
slightly acidic–get neutralized by the ammonia. Even though
early Europeans knew about soap, many launderers preferred to use urine for its ammonia to get tough stains out of cloth. In fact, in ancient Rome, vessels for collecting urine were commonplace on streets–passers-by would relieve themselves into them and when the vats were full their contents were taken to a
fullonica (a laundry), diluted with water and poured over dirty clothes. A worker would stand in the tub of urine and
stomp on the clothes, similar to modern washing machine’s agitator.
Even after making soap became more prevalent, urine–known as
chamber lye for the chamber pots it was collected in–was often used as a soaking treatment for tough stains "