That in each county of this State with a population of not less than thirteen thousand, six hundred (13,600) and not more than thirteen thousand, six hundred fifty (13,650) and in all counties containing a population of not less than fifteen thousand, two hundred (15,200) and not more than fifteen thousand, seven hundred (15,700), as shown by the Federal Census last preceding such action, the county board of trustees is hereby authorized to set aside from the Available School Fund of the county, in accordance with the provisions of the General Law governing the assessment for the support of the county superintendent’s office, an amount not to exceed Six Hundred Dollars ($600) to defray the expenses of the county superintendent and the county board of trustees in the administration of the scholastic affairs of the county.