Recent work on modification of the molybdenum-blue method for determination of dissolved inorganic phosphate in sea water (Wooster and Rakestraw, 1951) showed the need for a simple rugged device sui table for rapid and precise delivery of small quantities of reagents at sea. The two reagents used for phosphat e determination impose addit ional requirements on this device. Molybdic acid solution must be protected from the light and must not be allowed to come in contact with rubber;·stannous chloride solution must be protected from contact with the atmosphere.