In all counties having a population of not less than thirteen thousand, four hundred (13,400) and not more than thirteen thousand, five hundred (13,500), and in all counties having a population of not less than five thousand, one hundred and eighty (5,180) and not more than five thousand, one hundred and ninety (5,190), according to the last preceding Federal Census, the County Board of School Trustees may make provisions for the traveling and office expenses of the County Superintendent of Public Instruction, and may make an allowance for such traveling and office expenses not exceeding the sum of Six Hundred Dollars ($600) per annum. The amount allowed herein shall be paid in twelve (12) monthly installments and in the same manner as the salary and maintenance of the office of County Superintendents are now paid.