[konsumer]

I thought it was potassium chloride (salt Peter)

[CamperBob2]

Saltpeter is potassium nitrate. It's a diuretic, not sure why it would have any particular effect on libido.

[tacon]

http://www.snopes.com/military/saltpeter.asp

[pkroll]

This is specifically about the military, but searching for "saltpeter prisons" gets similar results:

http://www.snopes.com/military/saltpeter.asp

[konsumer]

Ah, salt Peter has potassium chloride AND sulfur.

[CamperBob2]

I think you're confusing it with some kind of extremely low-quality gunpowder.

[madengr]

Yep, that was it. Or maybe just salt on your peter.