The board of trustees herein, in addition to other powers herein granted, shall have power to compel the attendance of witnesses to testify before it on all matters connected with the operation of this chapter, and its chair or any member of said board may administer oaths to such witnesses; to make all necessary rules and regulations for its guidance in conformity with the provisions of this chapter: PROVIDED, HOWEVER, That no compensation or emoluments shall be paid to any member of said board of trustees for any duties performed under this chapter as such trustees.