Field Method for Determining the Saltiness of Brackish Water

Abstract

For the purpose of measuring the salt content of the waters of Back Bay, Virginia, and Currituck Sound, North Carolina, as related to the distribution of different kinds of water plants commonly used for food by ducks and geese, a quick and convenient method for determining the salt content of the water was needed. Since the area to be examined was large, approximately 30 miles long and IO miles wide, a method that could be adapted to use in a motor boat, even while the motor boat was in motion, was wanted. This requirement made it impossible to use a hydrometer since with this instrumiient absence of any jarring motion is necessary. An important requirement for preliminary survey work of this kind is that a determination be made at the time the water sample is taken. Results thus obtained can be used to find out whether the saltiness is increasing or decreasing from place to place, and where the next sample should be taken. This advantage is lost if samples must be collected and transported to a laboratory for testing, and in addition, a duplication of time and effort is caused. It was found that Mohr's method for total chlorides by titration with silver nitrate was suitable; the use of a small graduated pipette for measuring the standard solution, and of ordinary test tubes for holding the samples of water, reduced the amount of needed apparatus to such an extent that the required glassware for a day's trip could be placed in a small basket. This paper describes the method that was found satisfactory, gives directions for making up the solutions needed in making the tests, and shows the results obtained by this method with different samples of water.