Two methods were used to determine the chloride content in water from cores taken in southwestern Nassau County, Long Island, New York, during tests to find the salt-water front. The centrifuge-extraction method successfully yielded water samples from sands, clayey sands, and silts for chloride determinations as low as 200 p. p. m. A dilution method was devised for clays and silty clays, and is based on the assumption that all salts in the formation fluid are precipitated during drying and redissolved when an excess of distilled water is added to the dried sample. During coring operations, the addition of fluorescein dye to the drilling fluid makes it possible to separate by inspection the contaminated portions of the cores before making determinations.

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