Except as in this act otherwise provided, all original appointments to and promotions within the classified service shall be for a probationary period, the length of which for the several classes in the classified service shall be determined by the board, but dismissals or demotions may be made by the sheriff at any time during such period, but in no event shall such probationary period be less than one (1) year nor more than eighteen (18) months. At the end of the probationary period the sheriff shall notify the civil service board in writing whether or not the probationer is a satisfactory employee and may receive the status of a permanent appointee.