public static DatumTransformation CreateFromJson( 
   string json
)

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();
CompositeHVDatumTransformation xml_compositehv = CompositeHVDatumTransformation.CreateFromXML(xml);

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

// 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;