The sheriff of the City of St. Louis may employ an attorney at law to aid and advise him in the discharge of his duties and to represent him in court, which said attorney shall be known as “sheriff’s attorney”, and who shall receive as compensation for his services as such sheriff’s attorney a sum of not less than three thousand dollars and not more than fifteen thousand dollars per annum, payable in semimonthly installments out of the same funds and revenue as the sheriff of such city is paid.