The supervising officer in cooperation with the superintendent, prior to July first in each year, shall fix the annual or monthly salaries of all of the officers, exclusive of the superintendent, and all of the employees in each of the several institutions mentioned in this chapter. It shall classify such officers and employees into grades, and the salaries paid to those in each grade, all other factors being equal, must be uniform in the several institutions. The schedule of salaries fixed by the supervising officer shall become operative on July first in the year in which the same are fixed. The supervising officer in cooperation with the superintendent may fix the salaries of additional employees hired after July first and may increase the salary of any employee deemed worthy of such increase. Such salaries must be paid in the same manner as other expenses of the several institutions are paid. All of the salaries in each institution, however, must be within the limits fixed by the appropriations made by the legislative assembly for salaries in such institution.