These days, mankind doesn’t do a whole lot with urine. We excrete it, then we flush it. Maybe we hand it to a doctor first. But as an excellent post on Smithsonian.com points out, ancient human ingenuity discovered many (scientifically valid) uses for the substance most of us view as waste.
The bulk of them stemmed from urine’s compound urea, which decays to become ammonia. Ammonia is handy for all sorts of things, from tanning leather to making gunpowder (and in gunpowder’s case, human excrement was another ingredient). But the most nauseatingly brilliant of these uses might have been in ancient Rome, when urine served as a tooth-whitener. In this case, the ammonia functioned as a bleaching agent.
Now, while I shudder to think how this seemingly magical property of urine was first discovered, it’s a testament to the human tendency to repurpose the resources around us as tools, discovering the most specific of solutions out of the most plentiful of products. It’s design at the anthropological level.
Interestingly enough–as long as we’re on the topic of tooth-whitening accidents–in the 1800s, peroxide was used as an oral antiseptic to treat gums. Shortly thereafter, no doubt after spilling onto enough teeth, it was discovered that that peroxide could become the mojo behind all sorts of viable tooth-whitening products.
Luckily, our own aged urine never made it to mass market.