jQuery, find if element has any text

$("span.col").each(function(){
    if (!$(this).text().trim().length) {
        $(this).addClass("foo");
    }
});

http://jsfiddle.net/cfgr9/1/

Obviously instead of adding a class you can do as you like, return the object etc

UPDATE: Removed strange hidden character after final semicolon that caused js error.