ยง 258. Closing of museum; admission fee during certain hours. The trustees of any institution supported under this chapter by public money, in whole or in part, may, so far as consistent with free use by the public at reasonable or specified hours, close any of its museum collections at certain other hours, for study, to meet the demands of special students or for exhibition purposes, and may charge an admission fee at such hours, provided that all receipts from such fees shall be paid into the treasury and be used for the maintenance or enlargement of the institution.