Any person being held in the county jail in default of bail to await trial, except those held for treason, murder, arson, or rape, and except such as the sheriff may deem it improper to let out, may on application to the sheriff of the county, be allowed to work on the county farm or on the public roads or other county public works as other convicts are worked and at the same wage. The board of supervisors shall settle with prisoners so working at their regular meetings monthly. But if it appears that it is not to the best interest of the county to work such prisoners, the board may decline at any time to employ them.