if (document.images)
    {
      preload_image_object = new Image();
      // set image url
      image_url = new Array();
      image_url[0] = "../images/pngs/moleculesHome.png";
      image_url[1] = "../images/pngs/moleculesServices.png";
      image_url[2] = "../images/pngs/moleculesLocations.png";
      image_url[3] = "../images/pngs/moleculesRecruitment.png";
      image_url[4] = "../images/pngs/moleculesContacts.png";

       var i = 0;
       for(i=0; i<=4; i++) 
         preload_image_object.src = image_url[i];
    }