The board of library trustees shall file through the librarian on or before the last day in August of each year, a report with the State Librarian at Sacramento, giving the condition of its library and the number of volumes contained therein on the 30th day of June preceding. The report shall, in addition to other matters deemed expedient by the board of trustees or the district librarian, contain such statistical and other information as is deemed desirable by the State Librarian. For this purpose the State Librarian may send to the several district librarians instructions or question blanks so as to obtain the material for a comparative study of library conditions in the state.