When a motion for a new trial shall be granted or refused, either party may reduce to writing the reasons offered for said new trial, together with the substance of the evidence in the case, and also the decision of the court on said motion, and tender the same as a bill of exceptions; and it shall be the duty of the judge to allow and sign the same. Such bill of exceptions shall be a part of the record in the cause, and it may embrace the motion, the judgment, or other matters of record. The appellant may assign for error that the court below improperly granted or refused a new trial.