serge said:
and I think someone says a natural base is in bird poo?
I was that person.
Bird poo, or the fancy-pants term - guano, contains ammonia, which is a base. I think this one's kind of dodgy though.
Acids: Ethanoic - vinegar, methanoic - ants, hydrochloric - stomach, citric - fruits, sulfuric, nitric and carbonic - acid rain.
Bases: Sodium hydrogen carbonate - baking soda, ammonia - guano. I can't think of many bases.
Anyway, follow Serge's link. I was probably less sleepy when I answered that one.