§ 8. Additional officers and employees. The chairman shall have power to employ such officers, clerks, inspectors, experts and employees, and to make such contracts for special services as he may deem to be necessary to carry out this chapter, or to perform the duties and exercise the powers conferred by law upon the commission. The chairman, by certificate filed in the office of the commission may from time to time, specially authorize any officer or employee of the commission to conduct any investigation or hearing, which the commission is authorized to conduct, to take testimony in respect of the subject or matter under investigation, and report the testimony to the commission, and in the conduct of such investigation or hearing such officer or employee shall have all the powers of a commissioner.