Interesting question.
I’ll go with blue horseshoe crab blood. Makes a great cancer drug.
Or…
Shimmer. It’s a dessert topping. No, it’s a floor wax. It’s both!
Phenothaline:
Laxative (although they may have discontinued this application)
Used to test for blood (forensics)
acid/base indicator
Minor nitpick: It’s spelled phenolpthalein, I believe. One of them compounds to make HS chemists go nuts trying to pronounce it properly when they see it spelled out. 
Ah thanks. I’ve seen it spelled both ways but I imagine the spelling I used was devised to be more pronounceable.
But but but… it’s an old organic chemical. It’s not supposed to be easy to pronounce. Think of all the generations of chemists you’re letting down. 
potassium nitrate, a.k.a. saltpeter. A fertilizer and a component of gunpowder, it’s also the active ingredient in toothpaste for sensitive teeth. And if rumors at basic training were true, it’s also used as a libido suppressant in the food there :eek:
I’d heard that rumor, too, while I was at NTC Orlando’s bootcamp, back when it was the only Navy bootcamp with wimmens. According to Snopes, though, they were just talking through their hats at us.
I think a quicker question to answer would be which chemicals don’t have two or more uses. Here’s three from the top of my head:
Oxygen is also both a rocket fuel and used for respiration.
Chlorine has dozens (or hundreds) of uses including water purification and the manufacture of mustard gas.
Cyanide is used as a poison and also for gold mining.
Just for the record, the Master speaks on saltpeter.
Minor nitpick: Phenolphthalein.
Whose law is it that predicts that kind of thing? Gaudere’s?
It’s also used for baking
My nomination: Tritium.
Used as a fuel in thermonuclear weapons.
Also used to make glow-in-the-dark watches.
:smack: I’m a :wally
Teaches me to post after midnight.
(Wish it would… but I doubt it. :D)
That would be a long list too. As a general rule, the number of uses of a chemical is inversely proportional to the number of atoms in the chemical formula. Chemicals with only a few atoms (e.g. water and salt) have lots of uses; chemicals with dozens or hundreds of atoms frequently have none at all or just one which is usually medicinal. There’s exceptions to this rule, of course, but it’s a pretty good general rule.
BTW, I never believed the saltpeter rumor, not even the first time I heard it.
Fuller’s Earth.
Used in:
1)Making dyes fast.
2) Suspension agent for chemical & biological weapons.
As any home encyclopedia or online reference could tell you.
(last line for the benefit of any Official monitors.)
One that surprised me when I learned of it was using ammonia (regular housecleaning type) to make your lawn and houseplants greener. I really works well mixed with water and sprayed on the lawn.
Who knew?
Don’t forget fire extinguisher.
Does that really count as two separate uses, though? In both cases, it’s acting as a blood thinner. It’s just a question of how much thinner you want to make the blood. And in fact, medical use of warfarin does cause some side effects similar (though lesser in degree) to the effects which cause death in rats.
And isn’t saltpeter a not-uncommon food preservative? I thought that was why SPAM was pink, and why it has that flavor reminiscent of the smell of fireworks. There’s a lot of SPAM and similarly heavily-preserved foods in military diets, so it would stand to reason there’d be some saltpeter in there.
Chronos, I thought the mechanism for death by warfarin poisoning was basically the blood became so thin that it was pretty much uncontrolled haemophilia in the target organism - so the lethal mechanism is the same thing, taken to a much more extravagant level, as the therapeutic mechanism.
However, while the mechanism is the same - the intent, or use the compound is put to is diametrically opposed: On the one hand it is used to preserve life, and on the other to take life.
Now, what you seem to be looking for with your definition of use would be something similar to Viagara and the blood pressure medication it came from. One treats one symptom, and the other treats reptile dysfunction. But both are the same compound AIUI, just in different doses.
reptile dysfunction?
The lizard not working right?
Sorry, I was thinking of a bad joke, where that’s the punchline - The real reason the dinosaurs died out had been found, recently, you see. Sure mammals gave 'em problems. Sure there may have been an asteroid collision. But the real problem was that let something get the dinosaurs down, and nothing could get 'em back up again.
So, you see, they suffered from reptile dysfunction.