function _useOraclize() internal {
    require(!pendingOraclize);
    pendingOraclize = true;    
    determiningWinner = true;
    DeterminingWinner(currentRoundNumber, block.timestamp);
    oraclize_query("WolframAlpha", "random number between 1 and 25", oraclizeCallbackGas);
    OraclizeQuerySent(currentRoundNumber, block.timestamp);
  }