accessing to custom config file

Hi, 
I created config/facebook.php config file and put facebook configs in it. I have an library for facebook api in libraries/facebook.php

My question is how I can access configs from config/facebook.php in libraries/facebook.php. I mean how does CI system libraries do it. 

currently I am doing it in following way:

PHP Code:

   public function __construct()
    {
        $CI =& get_instance();
        $CI->load->config('facebook', TRUE);
        $this->appId = $CI->config->item('appId', 'facebook');
        $this->secret = $CI->config->item('secret', 'facebook');
        $this->cookie = $CI->config->item('cookie', 'facebook');
        $this->scope = $CI->config->item('scope', 'facebook');
    } 


when I searched for  'load->config(' in CI system directory it didnot find any result. So is this means CI system libs access to config files in different way?