private void loadXML(ref TestGraph1 tg1)
        {
            XmlSerializationContext xmlsc = new XmlSerializationContext();

            xmlsc.Load(System.Environment.GetEnvironmentVariable("TEMP") + "\\TestGraphPersistence.xml");
            xmlsc.ContextEntities.Add("Model", new Model("Reconstituted Model"));
            tg1 = (TestGraph1)xmlsc.LoadObject("TG");
        }