Section 57. Each member of the board shall serve without compensation, but shall be paid by the commonwealth the expenses necessarily incurred by him in the discharge of his official duties. The board may, subject to chapter thirty-one, employ a secretary and such other clerical and technical assistants as may be necessary to discharge its official duties, shall establish their duties, and, subject to the provisions of sections forty-five to fifty, inclusive, of chapter thirty, shall fix their compensation which shall be paid by the commonwealth. The commonwealth shall provide the board with adequate office space and shall pay the expenses of the board incurred in the performance of its duties.