Sec. 6. COUNTIES OF 30,275 TO 30,300. From and after the passage of this Act in all counties of the State of Texas having a population of not more than thirty thousand, three hundred (30,300) nor less than thirty thousand, two hundred and seventy-five (30,275), according to the last preceding Federal Census, shall be not less than the sum of Two Thousand, Four Hundred Dollars ($2,400) per annum nor more than the sum of Three Thousand, Two Hundred Dollars ($3,200) per annum to be fixed by the county board of education of each of such counties, and in making the annual per capita apportionment to the schools of such counties, the county board of education of such counties shall make an annual allowance out of the State and county available school funds for the payment of the salary of the superintendent of public instruction for such counties payable in twelve equal payments out of the State and county available school fund of such counties.