Sec. 2. In making the annual per capita apportionment to the schools of the Counties having a population of not less than 100,000 and not more than 150,000 the County School Trustees shall also make an annual allowance out of the State and County Available Funds for the payment of the salary of the Superintendent of Public Instruction not less than $2,800.00 nor more than $3,800.00 and the Commissioner's Courts of the Counties having a population of not less than 100,000 nor more than 150,000 may expend out of the general fund of said counties any sums not exceeding the sum of $1200 per annum, to defray the expenses incurred by said County Superintendent which said sum or any part thereof shall be paid by said Commissioners upon certificate of said Superintendent that the expenses have been incurred in the discharge of his duties as such superintendent.