public static DatumTransformation CreateFromJson( 
   string jsonString
)

{
  // Create singleton from wkid
  CompositeGeographicTransformation cgt =
      ArcGIS.Core.Geometry.CompositeGeographicTransformation.Create(108272);
  int count = cgt.Count;    // count = 1

  IList<GeographicTransformation> gts = cgt.Transformations
                                  as IList<GeographicTransformation>;
  gts.Add(ArcGIS.Core.Geometry.GeographicTransformation.Create(1437, false));
  count = cgt.Count;        // count = 2

  // create from an enumeration
  CompositeGeographicTransformation another_cgt =
                ArcGIS.Core.Geometry.CompositeGeographicTransformation.Create(gts);
  GeographicTransformation gt0 = another_cgt[0];
  GeographicTransformation gt1 = another_cgt[1];

  // get the inverse
  CompositeGeographicTransformation inversed_cgt = another_cgt.GetInverse() as CompositeGeographicTransformation;
  // inversed_cgt[0] is same as gt1
  // inversed_cgt[1] is same as gt0

  var wkt = gt0.Wkt;
  // create from string 
  CompositeGeographicTransformation third_cgt =
     ArcGIS.Core.Geometry.CompositeGeographicTransformation.Create(wkt, gt0.IsForward);
  count = third_cgt.Count;        // count = 1

  // create from josn
  string json = cgt.ToJson();
  CompositeGeographicTransformation joson_cgt =
    DatumTransformation.CreateFromJson(json) as CompositeGeographicTransformation;
}

{
  HVDatumTransformation hv1 = HVDatumTransformation.Create(108034);
  HVDatumTransformation hv2 = HVDatumTransformation.Create(108033, false);
  List<HVDatumTransformation> hvs = new List<HVDatumTransformation>() { hv1, hv2 };

  // create from enumeration
  CompositeHVDatumTransformation compositehv =
                  CompositeHVDatumTransformation.Create(hvs);
  int count = compositehv.Count;      // count = 2

  List<HVDatumTransformation> transforms =
                 compositehv.Transformations as List<HVDatumTransformation>;
  HVDatumTransformation tranform = transforms[0];
  // transform.Wkid = 108034

  // get inverse
  CompositeHVDatumTransformation inverse_compositehv =
         compositehv.GetInverse() as CompositeHVDatumTransformation;

  // create from xml
  string xml = compositehv.ToXml();

  var xml_compositehv = CompositeHVDatumTransformation.CreateFromXml(xml);

  // create from json
  string json = compositehv.ToJson();
  CompositeHVDatumTransformation json_compositehv =
      DatumTransformation.CreateFromJson(json) as CompositeHVDatumTransformation;
}