function ouvrir_img(chem)
{
document.getElementById("img_ag").src=chem;
if (document.getElementById("img_ag").width > 350)
{document.getElementById("img_ag").width = 350;}
document.getElementById("cadre_img").style.top = document.body.scrollTop+10;
document.getElementById("cadre_img").style.left = 40;
document.getElementById("cadre_img").style.visibility = "visible";
deactiv_pop = setTimeout("fermer_menu()",30000)
}

function fermer_img()
{
document.getElementById("cadre_img").style.visibility = "hidden";
}