When the sale is for cash, if, after satisfying the mortgage debt, with costs and expenses, there is a surplus, it shall be brought into court for the benefit of the mortgagor or the person entitled thereto, subject to the order of the court. If such surplus remains in court for three months without being applied for, the judge may direct it to be put out at interest, subject to the order of the court, for the benefit of the persons entitled thereto, to be paid to them upon order of the court.