Marine Science 2016 Edition

Page 134 Chapter 6 Figure 134.2 A refractometer can also be used to measure salinity Photo Red Sea E stablishing tests for salinity U sing light or electrical conductivity Salinity is often measured by measuring how well electricity travels through the water. This property of water is called conductivity. Water that has dissolved salt in it will conduct electricity better than water with no dissolved salt. The more salt that is dissolved in the water, the better the water conducts electricity. The salt content of the water can be measured very precisely using the conductivity method (Figure 134.1). A conductivity / TDS / Salinity Tester is used to check salt content and comes in a kit with a probe, battery, electrode soaking solution and conductivity standard solution. The instrument gives a direct reading. U sing a refractometer Salinity can also be measured with a hand held refractometer (Figure 134.2) A refractometer measures the change of direction or bending of the light as it passes from air to water. Light moves slower in water than air. The more salt in the water, the slower the light moves A refractometer is the best choice for measuring salinity when only approximate values are needed. Refractometers are easy to use in the field and relatively inexpensive. The salinity is read from a scale in the viewfinder (Figure 134.3) Figure 134.1 A conductivity / TDS / Salinity Tester Image courtesy Select Scientific www.selectscientific.com.au Figure 134.3 Salinity readings Photo Red Sea