If the compensation claimed or offered in any case shall exceed fifty pounds, and if the party claiming such compensation desire to have the same settled by arbitration, and signify such desire to the promoters of the undertaking before they have presented their petition to the sheriff to summon a jury in respect of such lands, under the provisions herein-after contained, by a notice in writing, stating in such notice the nature of the interest in such lands in respect of which he claims compensation, and the amount of the compensation so claimed, and unless the promoters of the undertaking be willing to pay the amount of compensation so claimed, and shall enter into a written agreement for that purpose, then, within twenty-one days after the receipt of any such notice from any party so entitled, the same shall be settled by arbitration in the manner herein-after provided.