A demon salesman, the flamboyant builder who put up this building was surely aware of the sales value of saying, “The Fred F. French Building, Five-fifty-one Fifth Avenue, at Fortyfifth Street.” But his creation had more to recommend it than euphony. Built in 1927 on a tight corner plot, the long, thin building proved that a slab rising from a series of setbacks could turn a profit despite the overpriced land available in midtown. The very narrowness of the building meant that most of the office space it enclosed was within reach of natural light and thus rentable at prime rates, and the elevators at the end of long central corridors gave the remainder of each floor the flexibility to be designed for a variety of uses. French’s thirtyeight-story building was the first skyscraper on this part of Fifth Avenue, and he tricked it out sumptuously, from the bronze in its lobby to the multicolored faience decorations on top — among them heads of Mercury, the messenger, “spreading the message of the French plan.”