I have never heard that about saltpeter, Geez I hope not for I think its still an additive to food. Was used a lot in sausages as a preservative & to make the meat look red. I think any salt in excess can have ungood consequences.
In Victorian times Bromides were a favoured means of reducing the sexual desires of teenagers. I don't know what the chemical composition is - thou I assume they are a salt of bromine (I guess the info can be found via Google). They most probably have some adverse effect on people using them.
Actually on consideration, quantities of beer are very good for removing the ability even thou it increases the desire - thou I don't recommend this

But disphoric, the question that occurred to me is why do you want to keep from getting erections?