; payment in advance when authorized by the treasurer of the Gallery for membership in library, museum, and art associations or societies whose publications or services are available to members only, or to members at a price lower than to the general public; purchase, repair, and cleaning of uniforms for guards, and uniforms, or allowances therefor, for other employees as authorized by law (5 U.S.C. 5901–5902); purchase or rental of devices and services for protecting buildings and contents thereof, and maintenance, alteration, improvement, and repair of buildings, approaches, and grounds