The navy standard water testing outfit has been indispensable, yet if an electric indicator could be sufficiently developed to do the work of the former, there would be considerable saving in: (a) Chemicals; and (b) the time necessary for making the tests. There are now on the market accurate and elaborate water testers, but none seem to be practical for use aboard ship.
To obtain accurate data for developing a suitable electric indicator for the chlorine in water, it was necessary to run several tests. These tests gave the most promising results, as shown in Figs. 2 and 3. The complete apparatus is shown in Fig. 1. In a glass tube, 1½ inches in diameter, were fitted terminals of ?-inch brass wire, 1 inch apart, and 8 inches long. Two 60-watt Mazda lights connected in parallel were used as the pilot lights in the actual tests, but one light of the proper size would be preferable.
Water containing varying amounts of chlorine was poured into the tube till the pilot lights showed a faint glow, then the height of the water in tube and the ammeter readings were taken. These readings were taken only as a check, for the amperage for each test was approximately .12 amperes. With the height of the water in the tube, or with what is the same thing, with the immersion of the terminals as the ordinates, and with the number of grains of chlorine per gallon as the abscissæ, a curve was plotted. Since the conductivity of water varies with different temperatures, tests were made with the water at different temperatures. These results are shown in Fig. 3. Curves were also plotted (Fig. 2) with the immersion of the terminals as ordinates and with the temperature of the water as abscissæ. Water containing different amounts of chlorine was tested, giving the different curves, as shown in Fig. 2. This curve gives the better results when the temperature of the water and immersion of the terminals are known and it is desired to measure the chlorinity.
To obtain the amount of chlorine in water where it is unknown, fill the tube till the pilot lights glow faintly, read the amount the terminals are submerged, then, knowing the temperature of the water, pick off on the curves (Fig. 2) the number of grains of chlorine per gallon.
The electric chlorine indicator does not, of course, discriminate between one kind of substance and another; analysis alone can do that. But in most instances in which water testing is carried out for marine engineering purposes, the substance present in the water is chlorine. Such tests are not made for purposes of analysis, but usually to find out the amount of chlorine that is present in the water; and in this case the electric chlorine indicator gives the required information with a rapidity and simplicity unapproached by any chemical test.