Issues Setting Style.float = 'none'

I'm trying to change a div (#box) from being floated left to not being floated (i.e. being a normal block-level element) when a link (#move) is clicked. I'm doing this:

window.onload = function() {
var z = document.getElementById('move');
z.onclick = function() {
document.getElementById('box').style.float = 'none'
document.getElementById('box').style.width = ��px'
}
}

However, the div remains floated (confirmed by the handy FF web developer extension). The width does change, so it seems my problem is with the style.float bit. What am I doing wrong?