The general assembly shall annually appropriate such a sum as it may deem necessary, out of any money in the treasury not otherwise appropriated, to be expended by the state librarian for the purpose of caring for, preserving, and cataloguing the property of the state in the keeping of the Rhode Island Black Heritage Society, and for the purchase and binding of books relating to the history of the state, and for copying and preserving the records of the several towns of the state, and the state librarian, with the approval of the secretary of state, may pay this sum to the Rhode Island Black Heritage Society for this purpose.