accessing iframe elements from rails 3 partial

I am trying to access iframe dom elements from rails 3 partial but its not as expected.

I am trying to access the iframe like this

$j("#batch_grid_frame").contents().find('#ship_box_id').html("HTML")

When i access the page from application it does not update the DOM. But when i run the same below code in browser console this works.

$j("#batch_grid_frame").contents().find('#ship_box_id').html("HTML")

Any help will be appreciated. Thanks.