1. Central Research and Development, DuPont Company, Experimental Station, P.O. Box 80228, Wilmington, Delaware 19880-0228, Little Falls Analytical DivisionNewport, Hewlett-Packard Company, 538 First State Boulevard, Newport, Delaware 19804, and Marshall Laboratory, DuPont Automative Products, 3401 Grays Ferry Avenue, Philadelphia, Pennsylvania 19146