function validate()
            {
                var doc = document.contact_form;
                if(doc.name.value == '')
                {
                    alert("Vul uw naam in aub.");
                    doc.name.focus();
                    return false;
                }
                if(doc.email.value == '')
                {
                    alert("Vul uw email in aub.");
                    doc.name.focus();
                    return false;
                }
                if(doc.message.value == '')
                {
                    alert("Vul uw vraag in aub.");
                    doc.message.focus();
                    return false;
                }
                return  true;
            }