Section 52. Supervisors and instructors to instruct the prisoners in industries determined upon in accordance with section fifty-one of chapter one hundred and twenty-seven in the correctional institutions of the commonwealth shall be appointed by the commissioner, and in jails and houses of correction by the superintendents and keepers thereof, with the approval of the commissioner. Such supervisors and instructors shall have the same authority relative to the prisoners as the subordinate officers of the institution where they are employed. In the correctional institutions of the commonwealth they may be removed by the commissioner, and in jails and houses of correction by the superintendent or keeper thereof.