When the board is ready for the transaction of business, it shall select one of its number to act as secretary, whose duty it shall be, when ordered by the board, to give at least two days’ notice in writing to the parties to the dispute of the time and place of hearing the same, which notice may be served personally on the parties or by fixing the same to the principal outer door or gate of the establishment of the employer. Where for any reason, service cannot be so made the notice may be served as the board shall direct.