Detect when scrollbar reaches top of div?

Question

I'm trying to animate a boxShadow on the scroll event of my #container div. Everything works except I can't figure out a good way to detect the scrollbar reaching the top so that the boxShadows can animate out. This is my code so far

   $('#container').scroll(
        function()
        {
            $('#white').animate(
            {
                boxShadow: "0 8px 8px -7px #696868"
            },
            "fast"); 
            if ($('#container').scrollTop() == 0)
            {
                $('#white').animate(
                {
                    boxShadow: "0 0 0 0 #696868"
                },
                "fast");
            }
        }
    );

I've added a demo. The initial on scroll animate works perfectly, but when the bar returns to top their is a rather long delay before the second animation kicks in. http://jsfiddle.net/JYqC3/14/

Solution

Hope this helps

Used .scrollTop

$('#my_div').scroll(function() {
    var pos = $('#my_div').scrollTop();
    if (pos == 0) {
        alert('top of the div');
    }
});

DEMO

EDIT: better animation added to demo