Failure adding a hash literal to an array in Ruby on Rails

Question

Within a controller, I have this code:

@placements = []

    empty_placement = {
      'placement' => { 
        'competition_id'  => '', 
        'division_id'     => '', 
        'dancetype_id'    => '', 
        'leader_id'       => '', 
        'leader_name'     => '', 
        'follower_id'     => '', 
        'follower_name'   => '', 
        'rank'            => '', 
        'result'          => '', 
        'leader_points'   => '', 
        'follower_points' => '' 
      } 
    }
@placements << empty_placement

@placements << empty_placement

@placements << empty_placement

respond_to do |format|
  format.json{ render :json => @placements }
end

The problem: It returns an array like this

[{},{},{}]

I'm obviously doing something wrong, but just can't spot it.

Thanks for any light you're able to shed on this.