§ 136. Detention of wreck. All sheriffs, and all persons employed by them, and all other persons aiding and assisting in the recovery and preservation of wrecked property, shall be entitled to a reasonable allowance as salvage for their services, and to all expenses incurred by them in the performance of such services, out of the property saved, and the officer having the custody of such property shall detain the same until such salvage and expenses shall be paid and the salvage claimed in any case shall not exceed one-half of the value of the property or proceeds, and every agreement, order or adjustment allowing a greater salvage shall be void.