For the extra, new and additional duties imposed upon the Alabama Public Service Commission and the members thereof by this article and for the performance of duties which are and will be hereafter required of said commission and the members thereof under this article, each member of the commission, in addition to the compensation otherwise provided by law to be paid to him for his service as a member of the commission, shall receive $1,800.00 annually, which shall be paid semimonthly, as the salaries of other state officers are paid, out of the appropriation provided by law for payment of salaries and expenses of the commission and its employees.