Powering a Negative ion generator

hi, i'm a bit of a noob when it comes to electricity and i have a question involving this negative ion generator i recently got. It runs off ac so i was going to just plug it into an outlet. I was wondering which wire to plug into which hole. There is black and white wire is im pretty sure is black is negative and white is positive. theres this funny plastic cap on the black wire though. any idea on what it is? Thanks!

Oh, my, I hate to give you any information because a little knowledge is a dangerous thing. But, anyway, AC does not have a defined Positive and Negative, the black wire is the "hot" one, to be connected to another black wire. The white wire is "neutral" and is to be connected to another white wire. Most AC recepticals have two slots and one round hole. The round hole is "ground" and is connected to the frame for safety. The wider slot is "neutral", the narrower slot is the "hot" one.

wow great, that makes things a bit clearer. so the black wire is the one with all the juice running through it? then what does this neutral white wire do? I guess theres more to this than i thought.

The current has to flow thru both wires, the Black wire is at high voltage relative to earth ground, the white wire is nominally at zero volts relative to earth ground.

so any safety tips i should be especially careful of before plugging this baby in?

One word of warning! - mains wire colours vary from country to country, presumably CrayonNinja is in the USA?- as is Russlk who replied, so is presumably correct for the States.

In the UK, mains wires used to be (many years ago), Red for Live, Black for Neutral, and Green for Earth (these colours are still used in housewiring cables - although the Earth wire is normally a bare copper wire, which you slide sleeving over).

Mains leads though, changed to Brown for Live, Blue for Neutral, and Green/Yellow for Earth - the change was made to improve visibility for colour blind people.