private string Serialize(Rates dollarKurs)
 {
     return JsonConvert.SerializeObject(
         dollarKurs
     );
 }
 public void Publish(Rates rates)
 {
     webClient.Headers[HttpRequestHeader.ContentType] = "application/json";
     webClient.UploadString(MONEY_CHANGER_ENDPOINT, Serialize(rates));
 }